CN115770564A

CN115770564A - Photocatalyst and preparation method thereof

Info

Publication number: CN115770564A
Application number: CN202211577524.8A
Authority: CN
Inventors: 刘金坤; 王宝清; 高帅; 李新新
Original assignee: Shandong Anran Nanometre Ind Development Co ltd
Current assignee: Shandong Anran Nanometre Ind Development Co ltd
Priority date: 2022-12-09
Filing date: 2022-12-09
Publication date: 2023-03-10

Abstract

The invention belongs to the technical field of photocatalysts and discloses a photocatalyst and a preparation method of the photocatalyst. The photocatalyst comprises the composite fiber at least comprising three n-type crystalline semiconductor materials, wherein the n-type crystalline semiconductor materials of bismuth oxide, titanium dioxide and zinc oxide form heterojunction in the composite fiber, and the movement of electrons and holes is promoted, so that the band gap is reduced, the response capability of the photocatalyst to visible light is improved, and the catalytic efficiency of the photocatalyst under the condition of the visible light is further improved.

Description

Photocatalyst and preparation method thereof

Technical Field

The invention belongs to the technical field of photocatalysts, and particularly relates to a photocatalyst and a preparation method of the photocatalyst.

Background

In recent years, policies of energy conservation and emission reduction are gradually implemented, and efficient photocatalysts capable of reducing pollution and energy consumption are always the directions of efforts in academia and industry. Titanium dioxide is the most studied photocatalyst at present, but the band gap of the photocatalyst is large, ultraviolet light is often needed to achieve effective activation, and solar radiation consists of about 5% of ultraviolet light, 43% of visible light and 52% of near infrared light, so that the solar responsivity of titanium dioxide is low, and the use of titanium dioxide in wide industrial application is limited. Therefore, efforts are made to modify titanium dioxide to improve its catalytic efficiency.

It is generally believed that a larger surface area to volume ratio will improve the catalytic performance of the catalyst and therefore commercial titanium dioxide on the market is often marketed in the form of nanoparticles for the purpose of having a larger surface area to volume ratio. However, due to the small size of the nanoparticles, they may easily detach from the carrier and be inhaled into the human body by a user passing nearby. Especially when located near an air or liquid flow, the nanoparticles detached from the support may be dispersed into the environment with the air or liquid flow, possibly having an influence on the ecological environment. At the same time, the inhalation of nanoparticles into the human body may also cause health problems. Therefore, only titanium dioxide or other substances capable of acting as a photocatalyst are made into nanoparticles, and although the catalytic activity can be improved to some extent, the application range thereof is limited due to the above problems.

In view of the above, the present invention is particularly proposed.

Disclosure of Invention

The technical problem to be solved by the present invention is to overcome the defects of the prior art, and to provide a photocatalyst and a method for preparing the photocatalyst, wherein a heterojunction is formed by a plurality of n-type crystalline semiconductor materials, so that the band gap can be reduced, and the response capability of the photocatalyst to visible light can be improved, thereby improving the catalytic efficiency of the photocatalyst under the condition of visible light.

In order to solve the technical problems, the invention adopts the technical scheme that:

a photocatalyst comprising a composite fiber comprising an n-type crystalline semiconductor material comprising bismuth oxide, titanium dioxide and zinc oxide, forming a heterojunction in the composite fiber.

In the scheme, the heterojunction is provided in the composite fiber through different kinds of crystalline semiconductor materials, and the formation of the heterojunction can promote the movement of electrons and holes, so that the band gap can be reduced, and the response capability of the photocatalyst to visible light can be improved. The separation efficiency of photoinduced electrons/holes and the photocatalytic performance of the photocatalyst are improved through a heterojunction structure in the composite fiber, and the interface charge transfer can be promoted and the catalytic efficiency can be improved because the transfer of vector charges from one semiconductor to another semiconductor has proper thermodynamic band edge positions. Particularly, the catalytic efficiency of the photocatalyst under the visible light condition is improved by the scheme, and the application field of the photocatalyst under the visible light condition is widened.

Further, in the composite fiber, the mass ratio of bismuth oxide is 0.1wt% to 0.4wt%, preferably 0.1wt% to 0.2wt%, and more preferably 0.2wt%;

preferably, the mass ratio of bismuth oxide to zinc oxide to titanium dioxide is 1.5 to 2:1 to 20, preferably 1.

In the above solution, the three different crystalline semiconductor materials have different thermal expansion coefficients, wherein TiO ₂ ZnO and Bi ₂ O ₃ Respectively has a thermal expansion coefficient of 9x10 ^-6 K ^-1 、4.75×10 ^-6 K ^-1 And 18x10 ^-6 K ^-1 . The composite fiber of the present invention is prepared by using a precursor containing three elements of bismuth, titanium and zincThe spinning solution is obtained after electrostatic spinning, and Bi in the composite fiber ₂ O ₃ When the ratio of (1) to (2) is controlled to be 0.1 to 0.2 percent, the composite fiber is smooth and uniform in shape; when Bi is present ₂ O ₃ When the ratio of (a) to (b) is further increased to 0.3% to 0.4%, some branched nanofibers are formed. If Bi is further increased ₂ O ₃ Due to severe thermal shock and shrinkage aging occurring at the initial stage of the formation of the composite fiber, the composite fiber is easily broken into short rods, resulting in a decrease in impedance.

The test shows that when Bi is used ₂ O ₃ At 0.2%, the composite fiber maintains the largest heterojunction for charge transport, and thus the band gap energy is the lowest, with optimal catalytic efficiency.

Further, the crystal form of the titanium dioxide comprises an anatase phase and a rutile phase;

preferably, the mass ratio of the rutile phase to the anatase phase is 1.05-20, preferably 1:5-20, more preferably 1:5-10.

In the above scheme, tiO ₂ /ZnO/Bi ₂ O ₃ The reduction in band gap energy of The (TZB) composite fiber can be attributed to anatase TiO ₂ Rutile type TiO ₂ ZnO and Bi ₂ O ₃ Synergistic effect between them. Due to the synergy between the conduction bands of these composites, in TiO ₂ Some sub-bands are formed in the forbidden bands, impurities and defects are introduced, and therefore band gap energy is reduced.

In TZB composite fiber, the band position alignment is beneficial to the movement of electrons and holes, and leads to a lower band gap, and the large charge separation caused by different energy positions also reduces the recombination rate of photo-generated electron/hole pairs. Therefore, the photocatalyst containing the TZB composite fiber can effectively promote water vapor in air or water molecules in liquid to generate free radicals and simultaneously generate oxygen radicals and hydroxyl radicals. The generated radicals may react with the target compound (e.g., any contaminants in the air or liquid) to degrade or convert the target compound into harmless substances.

Further, the composite fiber further comprises a p-type crystalline semiconductor material selected from cuprous oxide, copper oxide, cadmium telluride, and combinations thereof.

In the scheme, the composite fiber comprises a combination of an n-type crystal semiconductor and a p-type crystal semiconductor, so that a p-n heterojunction can be formed, the response wavelength range of the semiconductor can be expanded through a sensitization effect, and the recombination of charge carriers can be inhibited through a built-in electric field effect, so that the photocatalytic performance of the photocatalyst is further improved.

Further, the composite fiber has a one-dimensional nanostructure;

preferably, the composite fiber is selected from the group consisting of nanofibers, truncated nanofibers, nanowires, nanorods, and combinations thereof;

preferably, the composite fiber is a nanofiber and has nanocrystals dispersed on the surface of the nanofiber;

more preferably, the diameter of the nanofibers is 50 to 1000nm, preferably 80 to 100nm, more preferably 90nm; the diameter of the nanocrystal is 5-150 nm, preferably 10nm.

In the above scheme, when the photocatalyst is used to realize a photocatalytic effect, the nanocrystals provide a considerable surface-to-volume ratio for the adhesion of the target compound, while promoting the photocatalytic process. The nanocrystals include n-type crystalline semiconductor materials bismuth oxide, titanium dioxide, and zinc oxide, which allow for vector displacement of charges (e.g., electrons and holes). By close packing of the nanocrystals and providing a heterojunction structure, the photocatalytic performance is improved. Meanwhile, the nano-fiber with the nano-crystal adhered on the surface has larger photocatalytic reaction surface area, and the nano-fiber has larger length-diameter ratio, so the risk of absorbing the nano-material into the body is reduced.

Further, the composite fiber further comprises a polymer coating layer;

preferably, the polymer coating has a porous structure, and/or is light transmissive, and/or is gas permeable.

In the scheme, the polymer coating layer is used for increasing the elasticity of the composite fiber by utilizing the flexibility of the polymer, so that the situation that the composite fiber is broken in the use process of the photocatalyst is reduced, and the durability of the photocatalyst is improved. The polymer coating layer has a porous structure and is permeable, and light can be allowed to penetrate through the polymer coating layer and irradiate the surface of the semiconductor material inside the polymer coating layer, so that the photocatalytic effect of the photocatalyst is realized. The polymeric coating also needs to allow free permeation of gases from the environment to reach the interior so that contaminants in the ambient gas can be degraded or converted into harmless substances.

Further, the composite fiber is attached to a base material;

preferably, the substrate is a flexible substrate;

preferably, the substrate has light transmission and/or breathability;

preferably, the substrate has a network structure of nanometer size;

more preferably, the substrate is composed of polymer fibers, inorganic fibers or cellulose fibers, forming a network structure.

In the above scheme, the composite fiber has a nano size, and especially when it is completely composed of inorganic substances, it is very brittle and easily broken to affect the performance of the photocatalyst. The base material is used for firmly fixing the composite fibers, can avoid the loss of the composite fibers in the photocatalyst, can provide support for the composite fibers and reduce the breakage of the composite fibers.

The base material with the net-shaped structure is used for providing support for the composite fibers, so that the composite fibers can be accommodated in the net-shaped structure to be firmly fixed. The net structure comprises a porous structure, so that light can penetrate through the substrate to act on the composite fibers to perform a photocatalytic reaction. Meanwhile, gas can freely pass through the composite fibers and a base material directly exposed to the external environment, so that the composite fibers are ensured to generate a photocatalytic reaction to effectively degrade pollutants in the environment. The substrate has a degree of light transmission and air permeability, thereby achieving better retention of the position of the conjugate fibers without significantly affecting the photocatalytic performance.

Further preferably, the polymer fibers comprise dacron, and the average diameter of the dacron is preferably 90-220 nm.

Polyester is a suitable substrate material due to its water-insoluble and inert properties to solar radiation. The nano-network structure is formed by adopting the polyester nano-fibers with the average diameter of 90-220 nm, so that the nano-fibers, the truncated nano-fibers or the nano-rods can be firmly captured and adhered. Of course, the diameter of the polyester nanofiber can be adjusted according to the diameter of the composite fiber to adapt to actual needs.

Further, for the photocatalyst with composite fibers attached to the substrate, the packing density of the composite fibers at the area close to the surface of the photocatalyst is smaller than that of the composite fibers at the area close to the bottom of the photocatalyst; alternatively, the diameter of the composite fiber is smaller near the photocatalyst surface region than near the photocatalyst bottom region.

In the above solution, the photocatalyst surface area can directly receive light, and larger pores can be formed by using composite fibers with smaller packing density or smaller diameter, so that more light can penetrate and act on the composite fibers at the bottom. And the composite fiber with higher bulk density or larger diameter is concentrated at the bottom of the photocatalyst and used for reflecting or capturing light, thereby being capable of more fully utilizing illumination energy.

The preparation method of the photocatalyst is characterized by comprising the following steps:

(1) Preparing a precursor spinning solution containing bismuth, titanium and zinc;

(2) Carrying out electrostatic spinning by adopting the precursor spinning solution to obtain electrospun fibers;

(3) And collecting the electrospun fiber and calcining to obtain the photocatalyst.

In the scheme, the precursor spinning solution is a mixed solution simultaneously containing three elements of bismuth, titanium and zinc, and the TZB composite fiber simultaneously containing three n-type crystalline semiconductor materials of bismuth oxide, titanium dioxide and zinc oxide can be obtained by one-step spinning combined with subsequent calcination treatment. Different from the preparation method in the prior art that different types of semiconductor materials need to be formed layer by layer, the preparation method can obviously improve the preparation efficiency and shorten the process period.

Further, in the step (1), in the precursor spinning solution, the bismuth-containing compound accounts for 0.1 to 1% of the total mass of the precursor spinning solution in terms of bismuth oxide, the zinc-containing compound accounts for 0.1 to 1% of the total mass of the precursor spinning solution in terms of zinc oxide, and the titanium-containing compound accounts for 1 to 10% of the total mass of the precursor spinning solution in terms of titanium dioxide;

preferably, in the precursor spinning solution, the compound containing bismuth element accounts for 0.2 to 0.8 percent of the total mass of the precursor spinning solution in terms of bismuth oxide, the compound containing zinc element accounts for 0.1 to 0.4 percent of the total mass of the precursor spinning solution in terms of zinc oxide, and the compound containing titanium element accounts for 2 to 8 percent of the total mass of the precursor spinning solution in terms of titanium dioxide;

preferably, the step (1) specifically comprises: mixing 1-5% titanium tetraisopropoxide acetic acid solution and 2-6% polyvinylpyrrolidone (PVP) ethanol solution with the same mass concentration, carrying out ultrasonic treatment on the mixed solution, adding zinc acetate dihydrate accounting for 0.05-0.8% of the total mass of the mixed solution and bismuth nitrate pentahydrate accounting for 0.2-0.8% of the total mass of the mixed solution according to the set proportion of bismuth, zinc and titanium elements, and continuing ultrasonic treatment to obtain a precursor spinning solution for sol-gel spinning;

more preferably, in step (1), a 3% by volume solution of titanium tetraisopropoxide in acetic acid and an equivalent mass concentration of 4% by mass solution of polyvinylpyrrolidone (PVP) in ethanol are mixed.

In the scheme, the concentration of each element is adjusted by controlling the amount of the compound containing titanium, zinc and bismuth in each element in the precursor spinning solution, so that the Bi in the composite fiber can be adjusted ₂ O ₃ The content is adjusted, so that the prepared photocatalyst has higher photocatalytic activity.

Further, the precursor spinning solution which is fully and uniformly mixed and obtained in the step (1) is sent into a nozzle-free electrostatic spinning device for electrostatic spinning.

Specifically, the rotating electrode transports the thin film of solution out of the reservoir. Under the action of the electric field, an unstable jet is generated because the surface tension of the liquid surface is replaced by the electric field force between the positively charged rotating electrode and the grounded collector. The positive charges deposited on the fibers repel each other as the fibers are ejected into the air, and as they evaporate, they decrease in diameter as they fly freely from the rotating electrode to the grounded collector.

Further, in the step (3), the temperature is increased to 600-700 ℃ at the temperature rising rate of 0.5-2 ℃/min in the calcining process;

preferably, the heating rate is 1 ℃/min, and the target temperature of heating is 650 ℃.

Specifically, the collected electrospun fibers were calcined in an oven with a temperature that slowly rose to 650 ℃ at 1 ℃/min. In the calcining process, under the controllable evaporation condition of low-speed temperature rise, residual organic compounds (such as ethanol and PVP) and residual moisture in the composite fiber are slowly removed, and meanwhile, compounds containing bismuth, zinc and titanium in the electrospun fiber are calcined into corresponding oxides, and finally the photocatalyst is obtained.

Further, the composite fiber further comprises a polymer coating layer.

In order to prepare the composite fiber comprising the polymer coating layer, the preparation method comprises the steps of mixing the precursor spinning solution obtained in the step (1) with a polymer solution to obtain a composite solution; performing composite spinning by using the composite solution in the step (2), and forming inorganic fibers at least containing three elements of bismuth, titanium and zinc in the obtained electrospun fiber in the polymer coating layer; and (4) calcining the collected electrospun fibers in the step (3) to enable the polymer coating layer to have light transmittance.

Another method for preparing the composite fiber comprising the polymer coating layer is that the electrospun fiber is calcined in the step (3) to obtain the composite fiber, and the method further comprises a step (4) after the step (3): coating the composite fiber obtained in the step (3) to apply a polymer coating, and then calcining to form a polymer coating layer with a porous structure;

preferably, the manner of applying the polymer coating on the composite fiber includes a physical coating manner or a chemical coating manner; the chemical coating means may be a chemical vapor deposition method.

Further, step (5) is also included after step (3): and (4) combining the composite fiber obtained in the step (3) with a base material to obtain the photocatalyst with the composite fiber attached to the base material.

Further, the step (5) specifically comprises: mixing the composite fibers with a solvent to prepare a suspension, and applying the suspension to a base material to realize the combination of the composite fibers and the base material;

preferably, subjecting the composite fiber obtained in the step (3) to ultrasonic treatment to form a truncated composite fiber, wherein the truncated composite fiber comprises nanorods and/or truncated nanofibers; fully mixing the truncated composite fibers with ethanol to prepare a suspension, and introducing the truncated composite fibers in the suspension into a base material in a spraying, dip-coating or deep casting mode;

more preferably, the composite fiber is processed into small sections by ultrasonic treatment for 15-60 min.

Further, the spraying mode specifically comprises: the resulting suspension was transferred to a reservoir of a spraying device, and the suspension containing the chopped composite fibers was uniformly sprayed on the substrate by the spraying device.

The dip coating mode specifically includes: immersing the base material into the suspension containing the chopped composite fibers at a constant speed and staying for a period of time to make the chopped composite fibers adhere to the net-shaped structure of the base material; then the base material is pulled up, the cut composite fiber is captured/deposited on the base material, and the redundant solvent is discharged from the surface; the remaining solvent is subjected to an evaporation process, thereby forming a thin nanofiber mat in the substrate.

In the above-described solutions, when immersing the substrate in the suspension, care should be taken to avoid air ingress into the substrate. If air enters the interior of the substrate, the resulting air bubbles will block the pores of the network of the substrate, reducing the entrapment and adhesion rate of the chopped composite fibers in the substrate, and possibly resulting in an uneven distribution of the chopped composite fibers in the substrate. The substrate is immersed in the suspension containing the chopped composite fibers at a constant speed, so that air can be smoothly discharged out of the substrate, thereby preventing the above-mentioned problems.

The deep pouring mode specifically comprises the following steps: dropping the suspension onto the substrate with a dropper to allow the suspension to enter the pores of the network of the substrate, and then drying the substrate to remove the solvent; or, for the base material with large area, the dropper can be replaced by an automatic multi-dropper device, and the suspension is dripped in the area with large area of the base material simultaneously, so as to ensure the uniformity of the distribution of the composite fibers on the base material;

preferably, the above steps are repeated a plurality of times to increase the high bulk density of the composite fibers in the matrix.

In the above-described aspect, the steps of dropping the suspension and drying the base material may be repeatedly performed a plurality of times, the adjustment of the amount of the composite fiber load on the base material may be achieved by controlling the number of times of repeated execution, and may be easily controlled by a user according to personal practice.

After the technical scheme is adopted, compared with the prior art, the invention has the following beneficial effects.

1. The photocatalyst provided by the invention has composite fibers formed by at least three n-type crystalline semiconductor materials, heterojunction is formed in the composite fibers, and the heterojunction can be excited by light with longer wavelength in a band gap reduction mode, so that the response capability of the photocatalyst on visible light is improved, and the aim of improving the catalytic efficiency of the photocatalyst under the condition of visible light is fulfilled. The photocatalyst can be applied under the condition of natural illumination, and can realize more efficient degradation of pollutant in the environment. Meanwhile, the semiconductor material for realizing the photocatalysis exists in the composite fiber with the one-dimensional nano structure, so that the semiconductor material has a larger length-diameter ratio, the potential risk of secondary pollution caused by the separation of nano particles is avoided, and the harm of human body inhalation is reduced.

2. According to the invention, the precursor spinning solution contains bismuth, titanium and zinc at the same time, and the composite fiber containing bismuth oxide, titanium dioxide and zinc oxide can be obtained after electrostatic spinning and subsequent calcining treatment are directly carried out, and various semiconductor materials do not need to be prepared layer by layer, so that the preparation method is simpler and the efficiency is higher. The content of each element in the precursor spinning solution is controlled, so that the content of different semiconductors in the composite fiber can be adjusted, and the photocatalyst with higher photocatalytic activity can be obtained.

The following describes embodiments of the present invention in further detail with reference to the accompanying drawings.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention, are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention without limiting the invention to the right. It is obvious that the drawings in the following description are only some embodiments, and that for a person skilled in the art, other drawings can be derived from them without inventive effort. In the drawings:

FIG. 1 is a schematic diagram of the movement of electrons and holes in TZB-P1-P2 composite fibers of the present invention;

FIG. 2 is a Scanning Electron Microscope (SEM) image of TZB composite fibers of the present invention;

FIG. 3 is a TZB composite fiber of the present invention, as well as a TZ composite fiber, a TB composite fiber and a commercial TiO ₂ The absorption spectrogram of the nano particles (P25) is between 200 and 800 nm;

FIG. 4 is a schematic view (tangential to the flow direction) of a first arrangement of the photocatalyst in embodiment 7 of the present invention;

FIG. 5 is a schematic view (perpendicular to the flow direction) of a second arrangement of the photocatalyst in embodiment 7 of the present invention;

FIG. 6 is a schematic view of a third arrangement of the photocatalyst in embodiment 7 (forming an included angle with the flow direction);

FIG. 7 is a schematic view of a purification apparatus including a photocatalyst in example 8 of the present invention;

FIG. 8 is a schematic structural diagram of a purification apparatus including a photocatalyst in example 9 of the present invention;

FIG. 9 is a schematic view of a photocatalyst with a corrugated structure in example 10 of the present invention.

In the figure: 10. a housing; 11. a transparent window; 20. a filter; 30. a photocatalyst; 31. a first photocatalyst; 32. a second photocatalyst; 33. a third photocatalyst; 34. and (4) folding the photocatalyst.

It should be noted that the drawings and the description are not intended to limit the scope of the inventive concept in any way, but to illustrate it by a person skilled in the art with reference to specific embodiments.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and the following embodiments are used for illustrating the present invention and are not intended to limit the scope of the present invention.

In the description of the present invention, it should be noted that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "inner", "outer", etc., indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be construed as limiting the present invention.

In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; may be directly connected or indirectly connected through an intermediate. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.

The embodiment of the invention provides a photocatalyst, which comprises composite fibers. Wherein the composite fiber comprises an n-type crystalline semiconductor material comprising bismuth oxide (Bi) ₂ O ₃ ) Titanium dioxide (TiO) ₂ ) And zinc oxide (ZnO), forming a heterojunction in the composite fiber. The formation of heterojunctions, which may facilitate the transport of electrons and holes, is provided in the composite fiber by different kinds of crystalline semiconductor materialsThe band gap can be reduced, and the response capability of the photocatalyst to visible light can be improved.

In the present invention, the composite fiber includes TiO ₂ ZnO and Bi ₂ O ₃ The three semiconductors provide a number of heterojunctions that facilitate the movement of electrons and holes, thereby reducing the band gap. Alternatively, other combinations of semiconductors may be used to form the composite fiber, such as TiO ₂ Composite fiber of/ZnO (TZ) and TiO ₂ /Bi ₂ O ₃ (TB) conjugate fiber or ZnO/Bi ₂ O ₃ Composite fibers, other possible semiconductors that can reduce the band gap can also be used.

In a preferred embodiment of the present invention, the photocatalyst comprises a plurality of composite fibers. As shown in fig. 2, the composite fiber is a nanofiber and has nanocrystals dispersed on the surface of the nanofiber. Nanocrystals provide a substantial surface-to-volume ratio for the adhesion of target compounds and facilitate the photocatalytic process. And, these nanocrystals are semiconductors with appropriate band position alignment, i.e., bi ₂ O ₃ 、TiO ₂ And ZnO, which allows for vector displacement of charges such as electrons and holes.

These nanocrystalline semiconductors are tightly packed and provide a heterojunction structure in the composite fiber, which can improve the photo-induced electron/hole separation efficiency and photocatalytic performance. The vector charge transfer from one semiconductor to another semiconductor has appropriate thermodynamic band edge positions, which can promote interface charge transfer and improve the catalytic efficiency of the photocatalyst. It is understood that other semiconductor materials having suitable energy band positions may be used in the present invention.

In the composite fiber, the nano fiber structure with the nano crystals dispersed on the surface improves the surface area to volume ratio of the nano fiber, thereby providing a large surface area for the photocatalytic reaction of a photocatalyst.

In a further preferred embodiment of the present invention, the nanocrystals have a diameter of 5nm to 150nm, more preferably about 10nm. The large surface area allows the nanocrystals to act as efficient receivers of photons during illumination, increasing the efficiency of absorption of light energy, and the inside of the nanofibers have heterojunctions formed of different semiconductor materials, reducing the transition energy, facilitating the movement of electrons and holes, reducing the band gap, thus allowing efficient transport of charge in the holes inside the nanofibers, and thus the nanofibers can act as high-speed paths for transporting charge. In addition, compared with the nano particles, the nano fiber with the nano crystals has larger photocatalytic reaction surface area, and can obviously improve the photocatalytic efficiency of the photocatalyst. On the other hand, the nano-fibers have larger length-diameter ratio, so that the risk of the nano-materials in the photocatalyst being absorbed into the body is also reduced.

Further preferably, the nanofibers have a diameter of about 50nm to 1000nm and may extend to several meters long. More preferably, the composite nanofibers have a diameter of 80 to 100 nm. As a preferred embodiment of the present invention, the nanofibers 11 have a diameter of about 90 nm.

The photocatalyst in the embodiment of the invention is prepared by a sol-gel assisted electrostatic spinning method. Specifically, precursor spinning solution containing titanium, zinc and bismuth is prepared, and after uniform solution is obtained through ultrasonic full mixing treatment, the uniform solution is sent to a nozzle-free electrostatic spinning device. The rotating electrode conveys the solution film out of the liquid storage tank, and under the action of an electric field, because the surface tension of the liquid surface is replaced by the electric field force between the positively charged rotating electrode and the grounded collector, unstable jet flow is generated. The positive charges deposited on the fibers repel each other as the fibers are ejected into the air, and the diameter of the fibers continuously decreases as they are evaporated and fly freely from the rotating electrode to the ground collector. The collected electrospun fibers were then calcined in an oven, the temperature slowly increasing to 650 ℃ at 1 ℃/min. Under the controlled evaporation, the residual organic compounds and residual moisture in the fiber are slowly removed, and finally the photocatalyst is obtained. The composite fiber is filled with TiO ₂ ZnO and Bi ₂ O ₃ The nanocrystal of (1).

Similar methods can also be used to make other photocatalysts with similar composite fibers, such as TZ composite fibers and TB composite fibers, just by adjusting the composition of the precursor spinning solution.

For TiO in the photocatalyst of the invention ₂ /ZnO/Bi ₂ O ₃ The (TZB) composite fiber was analyzed for phase in the range of 20 ° to 80 ° (2 θ) by X-ray diffraction (XRD), and it was found that the TZB composite fiber contained anatase type titanium dioxide, rutile type titanium dioxide, zinc oxide and bismuth oxide.

As shown in FIG. 3, TZB composite fibers of the present invention, and TZ composite fibers, TB composite fibers and commercial TiO were measured by reflectance spectroscopy of U/V-Vis Diffuse Reflectance Spectroscopy (DRS) in the range of 200 to 800nm, respectively ₂ The absorption spectrum of the nano-particles (P25) between 200 and 800nm shows that the absorption edge of TZB composite fiber is transferred to the visible region, and TZB composite fiber is compared with commercial TiO ₂ The nanoparticles (P25) have a significantly increased absorbance in the ultraviolet range and can also absorb part of the visible range. Using the Kubelka-Munk equation, TZB composite fibers (where Bi is present) can be determined ₂ O ₃ /ZnO/TiO ₂ 1) and TiO, wherein the mass ratio of (1) ₂ The band gaps of the nanoparticles (P25) were 2.51eV and 3.12eV, respectively.

With TiO ₂ Compared with the nano particles, the band gap energy of the TZB composite fiber is obviously reduced, which can be attributed to anatase type TiO ₂ Rutile type TiO ₂ ZnO and Bi ₂ O ₃ Synergistic effect between them. In particular, in TiO, due to the synergy between the conduction bands of these semiconductor materials ₂ Some sub-bands are formed in the forbidden bands, impurities and defects are introduced, and therefore band gap energy is reduced.

The energy values for the TZB composite fiber are listed in table 1 below, with the band alignment facilitating electron and hole movement and resulting in a lower bandgap energy. The large charge separation caused by the different energy positions also reduces the recombination rate of the photo-generated electron/hole pairs. Furthermore, the photocatalyst containing TZB composite fibers has good photocatalytic activity, and can effectively promote water vapor in air or water molecules in liquid to generate free radicals and generate oxygen radicals and hydroxyl radicals.

TABLE 1 vacuum energy (eV) of TZB conjugate fiber

Semiconductor device and method for manufacturing the same	Bi ₂ O ₃	Anatase type TiO ₂	Rutile type TiO ₂	ZnO
					Conduction band	-4.83	-4.31	-4.21	-4.19
Valence band	-7.63	-7.31	-7.41	-7.39

The photocatalyst of the present invention is capable of removing contaminants, including chemical contaminants, from flowing gases or liquids by photocatalysis, and may be any substance that has an adverse effect when introduced into the environment, which may have an adverse health effect on animals and plants. The chemical contaminants may be, for example, nitrogen oxides, volatile organic compound contaminants, and organic dyes.

Specifically, in the photocatalytic process, photons from a light source are absorbed by the photocatalyst surface, thereby exciting electrons and subsequently generating free radicals within the material. The generated radicals may react with a target compound (e.g., any contaminant in air or liquid) to degrade or convert the compound into a harmless substance. In practical applications, the light source may be selected from ultraviolet light, visible light, or a combination thereof.

Tests show that the photocatalyst has remarkable photocatalytic activity on Rodamine B (RhB) in water, nitrogen Oxide (NO) in air and volatile organic compound pollutants (VOC) in air under the irradiation of sunlight. With commercial TiO having similar specific surface area ₂ Compared with nano particles (the particle size is about 100 nm), the photocatalyst prepared from the TZB composite fiber has a remarkable improvement on the photocatalytic degradation effect of NO and VOC.

In a further preferred embodiment of the invention, the composite fibre may comprise a combination of n-type and p-type crystalline semiconductor materials. The p-n heterojunction type photocatalyst can not only enlarge the response wavelength range of a semiconductor through a sensitization effect, but also inhibit the recombination of charge carriers through a built-in electric field effect, thereby further improving the photocatalytic performance of the photocatalyst with the composite fiber.

In particular, the p-type crystalline semiconductor material may be selected from cuprous oxide (Cu) ₂ O), copper oxide (CuO), cadmium telluride (CdTe), and combinations thereof. For example, the n-type crystalline semiconductor material TiO ₂ ZnO and Bi ₂ O ₃ And p-type crystalline semiconductor material Cu ₂ O (bandgap of 2.0 eV), cuO (bandgap of 1.2 eV), cdTe (bandgap of 1.4 eV), and the like are used together to form a composite fiber used in the photocatalyst of the present invention.

As shown in FIG. 1, a first P-type semiconductor material P1 having a higher energy level than ZnO may be used, which may trigger electron transfer to ZnO and then from ZnO to TiO ₂ From TiO 2 ₂ To Bi ₂ O ₃ . Vice versa, holes are easily transferred from the n-type semiconductor material ZnO to the first P-type semiconductor material P1, and thus a series of holes can be initiated from Bi ₂ O ₃ Transfer to TiO ₂ From TiO ₂ To ZnOAnd the transition from ZnO to P1.

Furthermore, a second P-type semiconductor material P2 with the energy level higher than that of the first P-type semiconductor material P1 can be selected and added into the composite fiber, and the P2 has a proper energy level, so that the transfer of electrons and holes between the P1 and the P2 can be realized, and the photocatalytic performance of the photocatalyst with the composite fiber can be further improved.

According to calculation, band gap energies of the TZ composite fiber, the TB composite fiber and the TZB composite fiber in the photocatalyst according to the embodiment of the present invention were determined to be 2.96eV, 2.62eV and 2.51eV, respectively. Compared with commercial TiO ₂ The band gap energy of the nano particles is 3.12eV, and the band gap energy of the TZ composite fiber and the TB composite fiber is reduced to a certain extent due to the synergistic effect generated by the alignment of the energy band positions. However, since the TZB composite fiber contains three different n-type crystalline semiconductor materials and thus has the most heterojunctions, a high-speed channel can be established for effective charge transfer by utilizing the heterojunctions between the nanocrystals, and therefore the band gap energy of the TZB composite fiber is the lowest.

As a further preferred embodiment of the present invention, the composite fiber in the photocatalyst further includes a polymer coating layer for increasing the elasticity of the composite fiber. Due to TiO ₂ ZnO and Bi ₂ O ₃ All inorganic materials are adopted, and the addition of the polymer coating layer can effectively prevent the composite fiber with the nano structure from breaking, so that the durability of the photocatalyst is improved.

Preferably, the polymer cladding layer is porous and permeable to allow light to penetrate the polymer cladding layer and interact with the semiconductor material therein. Preferably, the polymer cladding layer also allows gases from the environment to freely permeate through the polymer cladding layer to the semiconductor material inside and vice versa.

The photocatalyst of the composite fiber comprising the polymer coating layer is prepared by the following steps: and compounding polymer solutions with different viscosities with the precursor spinning solution, performing electrostatic spinning to obtain electrospun fibers with inorganic fibers (at least comprising three elements of bismuth, titanium and zinc) formed inside the polymer coating layer, and finally calcining to enable the polymer coating layer to have light transmittance.

The other preparation method comprises the following steps: the resulting TZB composite fiber is directly coated by a chemical or physical process (e.g., chemical vapor deposition) and then post-calcined to form the polymer coating with a porous structure.

In another preferred embodiment of the present invention, the photocatalyst further includes a substrate for firmly fixing the composite fibers, and the composite fibers are attached to the substrate, so as to prevent the composite fibers from running off during the use of the photocatalyst, and provide support for the composite fibers to reduce the breakage of the composite fibers.

In order to better maintain the position of the composite fibers without significantly affecting the photocatalytic performance, a substrate having a mesh structure may be used to provide support for the composite fibers, and the composite fibers may be received in the mesh structure to be firmly fixed. The substrate needs to provide at least some degree of optical and gas permeability for photocatalytic activity. Thus, preferably, the network comprises a porous structure such that it allows light to penetrate the substrate and interact with the composite fibers to perform a photocatalytic reaction. In addition, gas can freely pass through the substrate between the composite fiber and the environment.

Material of substrate, diameter of composite fiber, total thickness h of substrate and basis weight (g/m) of composite fiber ² Gsm) can be adjusted as desired. The weight distribution of the composite fibers need not be uniform throughout the thickness of the substrate, for example, they may be arranged such that fewer composite fibers are on the surface (e.g., loose packing or lower packing density) to allow for large pores to be formed for more light to penetrate, and more composite fibers are at the bottom (e.g., dense or higher packing density) for reflecting or capturing light. This effect can also be obtained by the composite fibres near the surface having a smaller diameter and the composite fibres near the bottom having a larger diameter.

In one embodiment of the invention, the substrate may be comprised of a polymer, inorganic fibers, or cellulose. Preferably, polymer fibers, such as polyester fibers, are used to form the network of the substrate. Polyester is a suitable substrate material due to its water-insoluble and inert properties to solar radiation.

Further, the base material is composed of a terylene nano fiber network with the average fiber diameter of 90-220 nm. Such a network having nanostructures can firmly capture and adhere composite fibers having one-dimensional nanostructures, such as nanofibers, truncated nanofibers, or nanorods. It can be understood that the diameter of the polyester nano-fiber can be adjusted according to the diameter of the composite fiber to adapt to the actual requirement.

In order to bond the TZB composite fiber of the present invention to the base material, the following preparation method was employed.

After TZB composite fiber is prepared, TZB composite fiber is processed into small segments through ultrasonic treatment for 15-60 min, and the truncated nano fiber or nano rod is obtained. The chopped nanofibers or nanorods are then suspended in the dispersion and mixed thoroughly. Ethanol is preferably used for the dispersion because it has good wetting properties and can easily penetrate the pores of the polyester. It will be appreciated that other solutions having good wetting properties may also be used as the dispersion. After mixing, the truncated nanofibers or nanorods can be introduced into the substrate by spraying, dipping, deep casting, or any common physical process.

In the present invention, at least the following three schemes can be adopted to prepare the photocatalyst having the substrate on which the uniformly distributed and highly-stacked truncated nanofibers are provided.

According to the first scheme, composite fibers are introduced in a spraying mode. Specifically, a suspension in which chopped composite fibers are dispersed is prepared, the suspension is transferred to a reservoir of a spraying device connected to pressurized nitrogen, and then the suspension is uniformly sprayed on a polyester substrate.

And in the second scheme, composite fibers are introduced by adopting a dip-coating mode. Specifically, a polyester substrate is immersed into suspension containing the chopped composite fibers at a constant speed, and the substrate stays in the suspension for a period of time, so that the chopped composite fibers are adhered to a net structure of the substrate; then the terylene substrate is pulled up, the truncated composite fiber is captured/deposited in the substrate, and redundant liquid is discharged from the surface; finally, a thin nanofiber mat is formed in the substrate by evaporating the remaining solvent.

In the above-described solutions, when immersing the substrate in the suspension, care should be taken to avoid air ingress into the substrate. If air enters the interior of the substrate, the resulting air bubbles can block the pores of the substrate, reducing the entrapment and adhesion rate of the chopped composite fibers in the substrate, and also resulting in uneven distribution of the chopped composite fibers in the substrate. Therefore, the substrate should be carefully immersed into the suspension at a constant speed to expel air from the substrate during the intake process.

And a third scheme is that the composite fiber is introduced in a deep pouring mode. Specifically, the suspension is dropped onto the substrate with a dropper, the suspension is allowed to enter the pores of the substrate, and then the substrate is dried. Or, an automatic multi-dropper device is adopted to be applied to the base material with a large area so as to ensure the distribution uniformity of the composite fibers on the whole area of the base material. Preferably, the above steps may be repeated to ensure a high bulk density of the composite fibers in the substrate.

In the above-described aspect, the amount of the composite fiber supported on the base material is adjustable as desired, and in the above-described manner, the amount of the supported composite fiber can be adjusted by the number of times the suspension is dropped, and can be easily controlled by a user according to personal practice.

The photocatalyst comprises a base material capable of fixing the composite fiber, so that the photocatalyst is more easily applied to various devices to play the photocatalytic effect. In particular, the photocatalyst having a substrate may be applied to a flexible surface, such as a mask for removing contaminants while breathing, or a wearable garment for removing harmful gases before they come into contact with the body. Meanwhile, the amount of the composite fiber supported on the substrate can be controlled, and for example, the amount of the final composite fiber can be adjusted by simply repeating the preparation process of spraying, dipping, or dropping the suspension, or by adjusting the concentration of the composite fiber in the suspension. Therefore, the application range of the photocatalyst is wider due to the use of the base material, and the photocatalytic performance of the composite fiber in the photocatalyst is not obviously influenced.

Example 1

This example prepares photocatalyst TZB composite fiber, where TZB composite fiber is Bi ₂ O ₃ 0.1% of nanofibres:

(1) Mixing an acetic acid solution of titanium tetraisopropoxide with the volume concentration of 3% and an ethanol solution of polyvinylpyrrolidone with the mass concentration of 4% in an equal manner, carrying out ultrasonic treatment on the mixed solution for 30min, then adding zinc acetate dihydrate accounting for 0.1% of the total mass of the mixed solution and bismuth nitrate pentahydrate accounting for 0.2% of the total mass of the mixed solution, and carrying out ultrasonic full mixing treatment for 6h to obtain a precursor spinning solution which is uniformly mixed;

(2) Sending the precursor spinning solution obtained in the step (1) into a nozzle-free electrostatic spinning device for electrostatic spinning to obtain electrospun fibers;

(3) Collecting the electrospun fiber obtained in the step (2), calcining in a furnace, slowly raising the temperature to 600 ℃ at 1.5 ℃/min in the calcining process, and slowly removing residual organic compounds (such as ethanol and PVP) and residual water in the composite fiber under the controlled evaporation, thereby finally obtaining the photocatalyst TZB composite fiber.

In this example, the TZB composite fiber prepared was a nanofiber having an average diameter of about 85 nm.

Example 2

This example prepares photocatalyst TZB composite fiber, where TZB composite fiber is Bi ₂ O ₃ 0.2% of nanofibres:

(1) Mixing an acetic acid solution of titanium tetraisopropoxide with the volume concentration of 3% and an ethanol solution of polyvinylpyrrolidone with the mass concentration of 4% in an equal mass manner, carrying out ultrasonic treatment on the mixed solution for 30min, then adding zinc acetate dihydrate accounting for 0.2% of the total mass of the mixed solution and bismuth nitrate pentahydrate accounting for 0.4% of the total mass of the mixed solution, and carrying out ultrasonic full mixing treatment for 6h to obtain a precursor spinning solution which is uniformly mixed;

(3) Collecting the electrospun fiber obtained in the step (2), calcining in a furnace, slowly raising the temperature to 650 ℃ at 1 ℃/min in the calcining process, and slowly removing residual organic compounds (such as ethanol and PVP) and residual water in the composite fiber under the controlled evaporation, thereby finally obtaining the photocatalyst TZB composite fiber.

In this example, the TZB composite fiber prepared was a nanofiber having an average diameter of about 90 nm.

Example 3

This example prepares photocatalyst TZB composite fiber, where TZB composite fiber is Bi ₂ O ₃ 0.3% of nanofibers:

(1) Mixing an acetic acid solution of titanium tetraisopropoxide with the volume concentration of 3% and an ethanol solution of polyvinylpyrrolidone with the mass concentration of 4% in an equal mass manner, carrying out ultrasonic treatment on the mixed solution for 30min, then adding zinc acetate dihydrate accounting for 0.3% of the total mass of the mixed solution and bismuth nitrate pentahydrate accounting for 0.6% of the total mass of the mixed solution, and carrying out ultrasonic full mixing treatment for 6h to obtain a precursor spinning solution which is uniformly mixed;

(3) Collecting the electrospun fiber obtained in the step (2), calcining in a furnace, slowly raising the temperature to 650 ℃ at 0.5 ℃/min in the calcining process, and slowly removing residual organic compounds (such as ethanol and PVP) and residual water in the composite fiber under the controlled evaporation, thus finally obtaining the photocatalyst TZB composite fiber.

Example 4

This example prepares photocatalyst TZB composite fiber, where TZB composite fiber is Bi ₂ O ₃ 0.4% of nanofibres:

(1) Mixing an acetic acid solution of titanium tetraisopropoxide with the volume concentration of 3% and an ethanol solution of polyvinylpyrrolidone with the mass concentration of 4% in an equal mass manner, carrying out ultrasonic treatment on the mixed solution for 30min, then adding zinc acetate dihydrate accounting for 0.4% of the total mass of the mixed solution and bismuth nitrate pentahydrate accounting for 0.8% of the total mass of the mixed solution, and carrying out ultrasonic full mixing treatment for 6h to obtain a precursor spinning solution which is uniformly mixed;

(3) Collecting the electrospun fiber obtained in the step (2), calcining in a furnace, slowly raising the temperature to 700 ℃ at 1 ℃/min in the calcining process, and slowly removing residual organic compounds (such as ethanol and PVP) and residual water in the composite fiber under the controllable evaporation, thereby finally obtaining the photocatalyst TZB composite fiber.

In this example, the TZB composite fiber prepared was a nanofiber having an average diameter of about 95 nm.

Example 5

This example prepares photocatalyst TZB composite fiber, where TZB composite fiber is Bi ₂ O ₃ 0.5% of nanorods:

(1) Mixing an acetic acid solution of titanium tetraisopropoxide with the volume concentration of 3% and an ethanol solution of polyvinylpyrrolidone with the mass concentration of 4% in an equal mass manner, carrying out ultrasonic treatment on the mixed solution for 30min, then adding zinc acetate dihydrate accounting for 0.5% of the total mass of the mixed solution and bismuth nitrate pentahydrate accounting for 1% of the total mass of the mixed solution, and carrying out ultrasonic full mixing treatment for 6h to obtain a precursor spinning solution which is uniformly mixed;

(3) Collecting the electrospun fiber obtained in the step (2), calcining in a furnace, slowly raising the temperature to 650 ℃ at 1 ℃/min in the calcining process, and slowly removing residual organic compounds (such as ethanol and PVP) and residual water in the composite fiber under the controlled evaporation, thus finally obtaining the photocatalyst TZB composite fiber.

In this example, the TZB composite fibers were prepared as nanorods of varying lengths with an average diameter of about 100 nm. This is thatSince Bi ₂ O ₃ The content of the composite nano-fiber is high, the thermal expansion coefficients of the three semiconductor materials are different, severe thermal shock and shrinkage aging occur in the early stage of the calcining process, and the composite nano-fiber is broken into short rods.

Example 6

In this example, TZB nanofibers prepared in example 2 were loaded on a substrate to prepare a photocatalyst, and the substrate was a non-woven fabric substrate made of a PET nanofiber network having an average fiber diameter of 90nm to 220nm. The method is realized by the following steps:

(1) The TZB nanofibers prepared in the above example 2 were sonicated for about 1 hour to be processed into chopped composite fibers, which were then suspended in ethanol and mixed thoroughly to prepare a suspension;

(2) Immersing a PET (polyethylene terephthalate) base material into the suspension obtained in the step (1) at a constant speed, and allowing the base material to stay in the suspension for a period of time to enable the cut composite fibers to be adhered to a base material network, wherein the speed needs to be slow and constant during immersion, so that the phenomenon that air enters the base material to form gaps to cause low or uneven load capacity is avoided;

(3) The PET substrate is pulled up, the chopped composite fibers are captured/deposited in the substrate, and the redundant solvent is discharged from the surface;

(4) And (3) placing the substrate in an oven, drying the substrate for 1h at 75 ℃, then heating the substrate to 100 ℃ for treatment for 0.5h, evaporating the solvent, and forming a thin nanofiber mat in the substrate to finish loading.

Comparative example 1

The photocatalyst TZ composite fiber is prepared according to the following steps:

(1) Mixing an acetic acid solution of titanium tetraisopropoxide with the volume concentration of 3% with an ethanol solution of polyvinylpyrrolidone with the mass concentration of 4% in an equal mass manner, carrying out ultrasonic treatment on the mixed solution for 30min, then adding zinc acetate dihydrate accounting for 0.1% of the total mass of the mixed solution, and carrying out ultrasonic full mixing treatment for 6h to obtain a precursor spinning solution which is uniformly mixed;

(3) And (3) collecting the electrospun fiber obtained in the step (2), calcining in a furnace, slowly raising the temperature to 650 ℃ at 1 ℃/min in the calcining process, and slowly removing residual organic compounds (such as ethanol and PVP) and residual water in the composite fiber under the controllable evaporation, thus finally obtaining the photocatalyst TZ composite fiber.

Comparative example 2

The comparative example prepares photocatalyst TB composite fiber according to the following steps:

(1) Mixing an acetic acid solution of titanium tetraisopropoxide with the volume concentration of 3% and an ethanol solution of polyvinylpyrrolidone with the mass concentration of 4% in an equal mass manner, carrying out ultrasonic treatment on the mixed solution for 30min, then adding bismuth nitrate pentahydrate accounting for 0.4% of the total mass of the mixed solution, and carrying out ultrasonic full mixing treatment for 6h to obtain a precursor spinning solution which is uniformly mixed;

(3) Collecting the electrospun fiber obtained in the step (2), calcining in a furnace, slowly raising the temperature to 650 ℃ at 1 ℃/min during the calcining process, and slowly removing residual organic compounds (such as ethanol and PVP) and residual moisture in the composite fiber under the controlled evaporation, thereby finally obtaining the photocatalyst with the TB composite fiber.

Comparative example 3

This comparative example is commercial TiO ₂ Nanoparticles from: germany winning, degussa titanium dioxide AEROXIDE P25 (P25).

Test example 1

This test example compares the photocatalytic performance of examples 1 to 4 and comparative examples 1 to 3 as photocatalysts. Specifically, under the illumination time of 30min, the degradation rate of NO by different photocatalysts was tested, and the results are shown in table 2 below.

TABLE 2 comparison of the degradation rates of different photocatalysts for NO

	Principal Components	Degradation Rate (%)
			Example 1	TZB composite fiber	36
Example 2	TZB composite fiber	67
			Example 3	TZB composite fiber	19
Example 4	TZB composite fiber	17
			Comparative example 1	TZ composite fiber	35
Comparative example 2	TB composite fiber	45
			Comparative example 3	Commercial TiO 2 ₂ Nanoparticles (P25)	5

As can be seen from the above test results, the composite fiber was comparable to TiO ₂ The nano-particles, the degradation rate of NO under the same illumination condition is obviously improved, which is mainly due to the lower band gap energy caused by the heterojunction in the composite fiber. Compared with the TZ composite fiber or the TB composite fiber, the TZB composite fiber has higher degradation rate of NO, so that the performance of the composite fiber in converting pollutants such as NO into harmless substances is more excellent, and the composite fiber has more excellent photocatalytic performance.

Test example 2

This test example compares Bi in TZB composite fiber ₂ O ₃ The influence of the content on the photocatalytic performance of the composite fiber as a photocatalyst is realized, the preparation method of the photocatalyst is the same as that in the embodiment 2, and the addition amount of the bismuth nitrate pentahydrate in the step (1) is only changed to prepare Bi in the TZB composite fiber ₂ O ₃ The contents of the photocatalysts are different. The prepared different photocatalysts and the commercialized TiO are respectively tested under the illumination time of 30min ₂ The degradation rate of nanoparticles (P25) to NO, the results are shown in table 3 below.

TABLE 3 Bi in TZB composite fibers ₂ O ₃ Influence of the amount

From the above test results, it can be seen that the TZB composite fiber of the present invention is used as a photocatalyst, compared with TiO ₂ The nano particles have obvious improvement on the degradation rate of NO. At the same time, when Bi ₂ O ₃ When the content is increased from 0.1% to 0.2%, the degradation rate of NO increases, and Bi further increases ₂ O ₃ The degradation rate of NO is reduced. When controlling Bi in TZB composite fiber ₂ O ₃ When the content of (b) is 0.2%, the degradation rate of NO is the best. This is because when Bi is present ₂ O ₃ When the content of (3) is 0.2%, the TZB composite fiber keeps the largest heterojunction for charge transmission, and the band gap energy is the lowest; when Bi is present ₂ O ₃ When the content of (B) exceeds 0.2%, the nanofiberThe reason is that some branches are formed, so that the impedance is reduced and the charge transfer efficiency is reduced.

Test example 3

This test example compares TZB composite fiber from example 2 with commercial TiO of comparative example 3 ₂ Photocatalytic effect of nanoparticles (P25) under full spectrum illumination.

Specifically, o-xylene was selected as a representative Volatile Organic Compound (VOCs) contaminant, and 50mg of the photocatalyst in example 2 and comparative example 3 was used, respectively, to examine the removal rate of o-xylene after 10min under full spectrum illumination.

The detection result shows that the commercial TiO ₂ The removal rate of the nano particles to the o-xylene is very low, and is only 5.25%, while the removal rate of the TZB composite fiber in the example 2 to the o-xylene is as high as 100%.

Test example 4

This test example compares the effect of the substrate in the photocatalyst on its photocatalytic performance. Specifically, the TZB nanorods 30mg prepared in example 5, the TZB nanofibers 30mg prepared in example 2, and the photocatalyst prepared in example 6 (30 mg of truncated TZB nanofibers supported on a substrate) were taken, and the removal rate of NO was respectively tested under 30min illumination, and the results are shown in table 4 below.

TABLE 4 comparison of the degradation rates of the substrates for NO

	Principal Components	Degradation Rate (%)
			Example 2	Individual TZB nanofibers	67
Example 5	Individual TZB nanorods	15
			Example 6	Base material loaded with TZB nano-fibers	70

From the above experimental results, it can be seen that the NO-substrate TZB nanorods are used as photocatalyst alone, compared with the NO-substrate TZB nanofibers as photocatalyst, the NO removal force is lower, mainly because the TZB nanorods have unsmooth surface morphology, form some branches, cause resistance to decrease, and the charge transfer efficiency is reduced, compared with the TZB nanofibers.

In contrast, in comparative examples 2 and 6, TZB nanofibers supported on a substrate can exhibit substantially the same photocatalytic activity as TZB nanofibers alone. The above results confirm that the use of the substrate does not significantly affect the photocatalytic performance of the composite fiber supported on the substrate. Therefore, the composite fiber can be loaded on the base material to prepare the photocatalyst, and the photocatalyst can be prepared into sheets with the length of several meters according to the size of the base material, so that different application scenes can be met. Meanwhile, the degradation rate of the photocatalyst obtained in the embodiment 6 to NO is slightly higher than that of the photocatalyst obtained in the embodiment 2, because after the TZB nano-fibers are subjected to ultrasonic treatment in the embodiment 6, the TZB nano-fibers are cut off, the surface area to volume ratio of the nano-fibers is improved, and further the photocatalytic activity is improved to a certain extent.

Example 7

The embodiment provides a purification device with the photocatalyst in the embodiment. Specifically, the photocatalyst is installed inside the purification device, and can be used for purifying air in an air channel or removing pollutants in liquid flowing through a pipeline.

As shown in fig. 4 to 6, the photocatalyst 30 of the present embodiment is disposed in a flow channel of the purification apparatus through which the polluted gas or liquid passes, and receives external light. The contaminated gas or liquid flows through the photocatalyst 30, and harmful contaminants therein react with free radicals generated around the photocatalyst 30 after being excited by light, and are degraded or converted into harmless substances, thereby obtaining clean gas or fluid.

Further, in the present embodiment, the photocatalyst 30 includes composite fibers and a substrate, and the photocatalyst 30 can be supported in a flow channel for gas or liquid to pass through by the substrate.

As shown in fig. 4, in the preferred embodiment, the photocatalyst 30 is arranged in a tangential direction with respect to the flow direction of the gas or liquid to ensure high photocatalytic activity for removing contaminants in the fluid.

Specifically, in the present embodiment, the purification efficiency of the photocatalyst 30 having different arrangement directions with respect to the flow direction of the gas or the liquid is compared, wherein the light irradiation direction is perpendicular to the flow direction to irradiate the photocatalyst 30 inside the flow channel.

As shown in fig. 4, the photocatalyst 30 is arranged in the channel in a direction tangential to the flow direction. As shown in fig. 5, the photocatalyst 30 is arranged in the channel in a direction perpendicular to the flow direction. As shown in fig. 6, the photocatalyst 30 is arranged in the channel at an angle α to the flow direction.

It was found from the NO removal efficiency test that only the arrangement of the photocatalyst 30 as shown in fig. 4 (i.e., tangential to the flow direction) achieved the same performance as the photocatalyst having loosely-combined nanorods (i.e., not including the substrate). In the case of the photocatalyst 30 vertically disposed as shown in fig. 5, the efficiency equivalent to the arrangement of the photocatalyst 30 shown in fig. 4 can be achieved only when the loading amount of the composite fibers on the substrate is increased.

Specifically, the test results show that the removal efficiency of NO gradually decreases as the angle between the photocatalyst 30 and the flow direction gradually increases from 0 ° to 90 °. In detail, at 30min, the removal rates of NO by the photocatalyst 30 placed at the included angles of 0 °,30 °, 45 ° and 90 ° are 42%, 32%, 23%, and 13%, respectively. This is probably because the amount of composite fibers on which light irradiation can be received is reduced as the photocatalyst 30 is gradually erected from a horizontal disposition. However, the reduction in NO removal rate can be compensated for by increasing the loading of the composite fibers on the substrate.

The present embodiments also provide a method of removing contaminants from a flowing gas or liquid, comprising: placing the photocatalyst 30 in the vicinity of a gas or liquid; a light source is provided to excite the photocatalyst 30 to perform a photocatalytic reaction.

Further, the light source is selected from ultraviolet light, visible light, or a combination thereof. For example, a light source may be artificially provided, or sunlight may be directly utilized. The photocatalyst 30 is activated to generate radicals, such as oxygen radicals and hydroxyl radicals, thereby converting pollutants in the fluid into harmless substances to be discharged.

Further, the gas or liquid flows through the photocatalyst 30 from the upstream end to the downstream end of the photocatalyst 30, thereby removing the pollutants in the gas or liquid.

In a preferred embodiment of this embodiment, the substrate of the photocatalyst 30 has a net structure, and the net structure substrate can perform a filtering function so as to capture particles existing in the fluid. Thus, the photocatalyst 30 can simultaneously remove particle impurities and purify chemical pollutants in the fluid, and the purification effect is better.

In this embodiment, the photocatalyst 30 can be applied to medical equipment, infrastructure, vehicles, pipes, buildings, appliances, and the like, and the purpose of cleaning air or liquid can be achieved by utilizing the photocatalytic performance thereof.

Example 8

As shown in fig. 7, this embodiment provides a specific structure of the purification apparatus described in embodiment 7 above.

In this embodiment, the purifying apparatus has a housing 10, and a flow passage for allowing the polluted gas or liquid to flow through for purification is formed inside the housing 10. The housing 10 is provided with a transparent window 11, and light can be irradiated to the photocatalyst through the transparent window 11.

Further, a first photocatalyst 31 is disposed in the flow channel in the housing 10, and the first photocatalyst 31 is disposed at an angle θ relative to the flow direction of the fluid. At least one transparent window 11 is disposed above the first photocatalyst 31, under the irradiation of light through the transparent window 11, the radicals generated by the first photocatalyst 31 realize the decomposition and purification of the pollutants, and capture the particles in the fluid while the polluted gas or liquid passes through.

In a further embodiment of the present invention, a second photocatalyst 32 is further disposed downstream of the first photocatalyst 31, and the second photocatalyst 32 is disposed in a tangential direction with respect to the flow direction of the gas or liquid. Preferably, the second photocatalyst 32 may be installed at another transparent window 11 located downstream of the first photocatalyst 31.

By providing the second photocatalyst 32, it is possible to ensure that most of the target pollutants in the fluid are sufficiently removed before being discharged from the flow channel of the purification apparatus.

In this embodiment, the first photocatalyst 31 and the second photocatalyst 32 are disposed in the purification device, so that the two-stage photocatalytic process can ensure that the clean gas or liquid is discharged, and the discharged fluid basically contains no pollutants.

Example 9

As shown in fig. 8, this embodiment is a further limitation of embodiment 8, and the photocatalyst is used in combination with a filter and disposed inside the housing 10.

Specifically, the purifying device of the present embodiment includes a third photocatalyst 33 disposed inside the housing 10 and below the transparent window 11, the third photocatalyst 33 is attached to the filter 20, and the filter 20 is disposed upstream of the third photocatalyst 33. The third photocatalyst 33 is disposed at an angle θ with respect to the flow direction of the fluid.

The purification device of the embodiment can realize the purification of the polluted gas or liquid by adopting a single-stage photocatalysis process in a horizontal or inclined state. When the polluted gas or liquid flows, the filter 20 filters out suspended particles upstream of the third photocatalyst 33, and the third photocatalyst 33 immediately following it can remove or convert harmful pollutants in the gas or liquid. When the contaminated gas or liquid flows from the upstream end of the filter 20 and the third photocatalyst 33 to the downstream end of the filter 20 and the third photocatalyst 33, the filter 20 and the third photocatalyst 33 are disposed at an angle with respect to the flow direction, so that the filtering efficiency of the filter 20 and the photocatalytic activity of the third photocatalyst 33 can be improved.

In the above scheme, the filter 20 is located inside the housing 10 upstream of the third photocatalyst 33, so that most of the suspended particles are removed before contacting the third photocatalyst 33. Thus, the risk of the third photocatalyst 33 being clogged by the suspended particles is reduced, thereby extending the life span of the third photocatalyst 33. Some fine particles may also flow through the third photocatalyst 33 if the suspended particles are not filtered out in advance. These fine particles may scatter the light irradiated through the transparent window 11, thereby reducing the intensity of light irradiated on the third photocatalyst 33, thereby reducing the efficiency of photocatalytic decomposition or conversion of contaminants. The present embodiment is advantageous to maintain high and constant photocatalytic efficiency of the third photocatalyst 33 by disposing the filter 20 upstream of the third photocatalyst 33.

Further, as for the purification apparatus for purifying the gas, the filter 20 therein may be made of microfibers having an average fiber diameter of 1 to 30 μm, or nanofibers having an average fiber diameter of 50 to 1000nm, or may be composed of a combination of microfibers and nanofibers. For purification devices for purifying liquids, the filter 20 therein may be made of any conventional filter material suitable for removing particles from liquids, such as foams and membranes.

In this embodiment, the angle θ between the combination of the filter 20 and the third photocatalyst 33 and the horizontal direction (i.e., the flow direction) may be any angle between 0 ° and 90 °. Preferably, the included angle θ is between 10 ° and 40 °. More preferably, the included angle θ is 20 ° to 30 °.

According to the embodiment 7, when the content of the composite fiber in the photocatalyst is constant, the smaller the included angle θ is, the higher the removal rate of the photocatalyst to the pollutants is. In practical applications, however, the smaller the angle θ, for example, less than 15 °, the longer the extension of the photocatalyst in the flow direction for the same area, and thus the larger the channel for the photocatalyst to extend through. The angle theta is most preferably 20 deg. to 30 deg. in consideration of the actual design and performance of the photocatalyst.

In the purification apparatus of the present embodiment, by disposing the filter 20 and the third photocatalyst 33 in combination and at an angle with respect to the horizontal plane, high filtering efficiency and high photocatalytic efficiency can be obtained.

In a further aspect of this embodiment, a second photocatalyst 32 disposed tangentially to the flow direction may also be disposed downstream of the third photocatalyst 33 to ensure that the final discharged fluid is substantially free of contaminants.

Example 10

As shown in fig. 9, the present embodiment is different from embodiment 8 described above in that: the photocatalyst disposed inside the housing 10 is a pleated photocatalyst 34 having a pleated structure.

Specifically, the pleated photocatalyst 34 in the present embodiment includes a flexible substrate that is pleated so that the pleated photocatalyst 34 is disposed in a V-shape or zigzag shape entirely inside the housing 10. With the above arrangement, the pleated photocatalyst 34 of the present embodiment can increase the surface area for realizing the photocatalytic reaction, and at the same time, can reduce the speed of the fluid flowing through the pleated photocatalyst 34 along the direction perpendicular to the surface of the photocatalyst.

Referring to fig. 9, the fluid flows through the pleated photocatalyst 34 at an original plane velocity a, and the geometry of the pleats of the pleated photocatalyst 34 can decompose the original plane velocity a into two components, namely an effective plane velocity A1 perpendicular to the surface of the pleated photocatalyst 34 and a velocity component A2 parallel to the surface of the pleated photocatalyst 34. It can be seen that the magnitude of the effective face velocity A1 is significantly less than the original face velocity a. Thus, the gas or liquid can be more fully contacted with the surface of the folded photocatalyst 34, which is beneficial to the photocatalyst to realize higher photocatalytic performance.

In the process of using the photocatalyst, the flow rate of gas or liquid can also influence the photocatalytic performance of the photocatalyst to a certain extent. The removal effect of the photocatalyst prepared from the TZ composite fibers on NO is tested at different flow rates, the photocatalyst with the same area and the same TZ composite fiber loading capacity is adopted, and when the fluid flow rates are respectively 0.5, 1.5, 2 and 3L/min, the removal rates of the photocatalyst on NO are respectively 82%, 64%, 58% and 52%. It can be seen that the NO removal rate increases with decreasing fluid flow rate. This is because the flow rate (or flow velocity) of NO in the fluid decreases with a decrease in the flow velocity, and the longer the contact time between NO and photogenerated hydroxyl radicals generated by the action of the photocatalyst is, the higher the NO removal efficiency is.

From the above test results, it can be seen that the relationship between the photocatalytic performance of the photocatalyst and the surface velocity of the fluid flowing through the photocatalyst is obtained, that is, the pleated photocatalyst 34 obtained by pleating the flexible substrate in this embodiment can improve the photocatalytic activity by reducing the effective surface velocity A2.

In a further aspect of this embodiment, the pleated photocatalyst 34 may also be used in combination with a filter. Specifically, the filter is configured with a pleated geometry that matches the pleated photocatalyst 34, thereby increasing the surface area of the filter and reducing the face velocity. Through all setting up filter and photocatalyst into the fold structure, can obtain the filtration efficiency of higher filtering particle impurity to and get rid of harmful contaminant's purification performance.

Example 11

As shown in fig. 7 to 9, the present embodiment is further defined by the above embodiment 8 or 9, and the second photocatalyst 32 has a corrugated structure of the corrugated photocatalyst 34 shown in fig. 7.

Specifically, the second photocatalyst 32 has a corrugated structure, thereby providing grooves at least on the lower surface thereof, and the extending direction of the grooves is parallel or nearly parallel to the flow direction of the fluid. The lower side surface of the second photocatalyst 32 is provided with a groove, so that the blockage of fluid is effectively avoided, meanwhile, the contact area between the fluid carrying pollutants and the second photocatalyst 32 is increased, and further, the photocatalysis efficiency can be further improved through the arrangement of the contact area maximization.

In a preferred embodiment of this embodiment, the second photocatalyst having a corrugated structure extends from the inner wall of the housing to the middle of the housing, so as to extend into the gas or liquid flowing through, thereby contacting with the contaminants in the gas or liquid to the maximum extent, and further increasing the photocatalytic activity.

Although the present invention has been described with reference to a preferred embodiment, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

1. A photocatalyst comprising a composite fibre, characterised in that the composite fibre comprises an n-type crystalline semiconductor material comprising bismuth oxide, titanium dioxide and zinc oxide, forming a heterojunction in the composite fibre.

2. The photocatalyst as claimed in claim 1, wherein the composite fiber contains bismuth oxide in an amount of 0.1 to 0.4wt%, preferably 0.1 to 0.2wt%, and more preferably 0.2wt%;

3. The photocatalyst as set forth in claim 1 or 2, wherein the crystal form of titanium dioxide comprises an anatase phase and a rutile phase;

4. The photocatalyst of any one of claims 1 to 3, wherein the composite fiber further comprises a p-type crystalline semiconductor material selected from the group consisting of cuprous oxide, copper oxide, cadmium telluride, and combinations thereof.

5. The photocatalyst as set forth in any one of claims 1 to 4, wherein the composite fiber has a one-dimensional nanostructure;

6. The photocatalyst as set forth in any one of claims 1 to 5, wherein the composite fiber further comprises a polymer coating layer;

7. The photocatalyst as set forth in any one of claims 1 to 6, further comprising a substrate to which the composite fiber is attached;

preferably, the substrate is a flexible substrate;

preferably, the substrate has light transmission and/or breathability;

preferably, the substrate has a network structure of nanometer size;

more preferably, the base material is composed of polymer fibers, inorganic fibers or cellulose fibers, forming a network structure;

8. The preparation method of the photocatalyst is characterized by comprising the following steps:

(3) And collecting the electrospun fibers and calcining to obtain the photocatalyst.

9. The method of preparing a photocatalyst according to claim 8, wherein in the step (1), the compound containing bismuth element accounts for 0.1 to 1% of the total mass of the precursor spinning solution in terms of bismuth oxide, the compound containing zinc element accounts for 0.1 to 1% of the total mass of the precursor spinning solution in terms of zinc oxide, and the compound containing titanium element accounts for 1 to 10% of the total mass of the precursor spinning solution in terms of titanium oxide in the precursor spinning solution;

preferably, in the precursor spinning solution, the bismuth-containing compound accounts for 0.2 to 0.8 percent of the total mass of the precursor spinning solution in terms of bismuth oxide, the zinc-containing compound accounts for 0.1 to 0.4 percent of the total mass of the precursor spinning solution in terms of zinc oxide, and the titanium-containing compound accounts for 2 to 8 percent of the total mass of the precursor spinning solution in terms of titanium dioxide;

preferably, the step (1) specifically comprises: mixing 1-5% titanium tetraisopropoxide acetic acid solution and 2-6% polyvinylpyrrolidone ethanol solution in equal amount, carrying out ultrasonic treatment on the mixed solution, adding zinc acetate dihydrate accounting for 0.05-0.8% of the total mass of the mixed solution and bismuth nitrate pentahydrate accounting for 0.2-0.8% of the total mass of the mixed solution, and continuing ultrasonic treatment to obtain a precursor spinning solution.

10. The method of claim 8 or 9, wherein in the step (3), the temperature is raised to 600-700 ℃ at a rate of 0.5-2 ℃/min during the calcination process;