CN109261189B

CN109261189B - TiO22-CuO/g-C3N4Synthesis method of composite nano material and CO2Application in photocatalytic reduction

Info

Publication number: CN109261189B
Application number: CN201811292433.3A
Authority: CN
Inventors: 谭正德; 赵娅俐; 曹洁; 李敏; 刘军
Original assignee: Hunan Institute of Engineering
Current assignee: Hunan Institute of Engineering
Priority date: 2018-10-31
Filing date: 2018-10-31
Publication date: 2021-10-01
Anticipated expiration: 2038-10-31
Also published as: CN109261189A

Abstract

The invention discloses a TiO2₂‑CuO/g‑C₃N₄Synthesis method of composite nano material and CO₂Application in photocatalytic reduction. The invention adopts a sol-gel method to synthesize TiO in different dispersion media₂‑CuO/g‑C₃N₄A composite nanomaterial. The light absorption boundary of the material obtained by the invention is red-shifted, and CO is reduced by photocatalysis₂The efficiency is improved, and due to the irregular accumulation structure, the surface light reaction active sites of the catalyst are increased, so that the CO is reduced by photocatalysis₂The efficiency is enhanced. The obtained material is used as a photocatalyst for CO application₂In the photocatalytic reduction, the highest yield of the reduction product methanol can reach 0.702 mg/g-cat/min. Meanwhile, the invention discusses the reduction of CO by the photocatalyst through a control experiment and the addition of different trapping agents₂Mechanism and reduction route of (1), to give h⁺、e^‑And free radicals reduce CO for the catalyst₂The active factor of (1).

Description

TiO22-CuO/g-C3N4Synthesis method of composite nano material and CO2Application in photocatalytic reduction

Technical Field

The invention relates to a photocatalytic material, in particular to a TiO₂-CuO/g-C₃N₄Synthesis method of composite nano material and CO₂Application in photocatalytic reduction.

Background

CO in the atmosphere₂The increase in content is mainly due to the use of fossil fuels for energy and transportation combustion. The growing shortage of natural fuels, the green color of chemical productionThe demand for colorization is increasing, and our natural resources treasury will decrease if the consumption of fossil fuels continues to proceed at the same rate or higher. In order to meet the green requirement of chemical production, CO is used₂Effective solutions for emission development are urgently needed. Conversion of CO at present₂The novel method comprises chemical lung conversion, electrochemical reduction, novel hydrogen storage material conversion, biological utilization and photocatalytic reduction. In which CO is photocatalytically converted₂The conversion into usable resources is a milder process, and the process consumes less energy, and the required energy is photon energy of light. Since the discovery by Fujishima and Honda in 1972 that water can be photoelectrically decomposed to produce hydrogen and oxygen by using a Ti-based electrode, research on photoelectrocatalysis has been receiving extensive attention. To realize CO₂The practical application of the photocatalytic reduction meets the requirement of green chemistry, and CO is used₂Technologies for converting feedstock into hydrocarbon fuels are attracting attention. But due to CO₂Is a thermodynamically very stable compound, and high energy, i.e., thermal energy, electric energy, solar energy, etc., is consumed to break the C ═ O bond during the conversion process. Solar energy is applied to the field of photocatalysis due to the advantages of universality, harmlessness, huge size, long time and the like. Thus, photocatalytic reduction of CO₂CO reduction for hydrocarbon fuels₂Venting while achieving one of the effective methods of carbon recycling.

In the photocatalytic process, titanium dioxide (TiO)₂) Due to its excellent properties, it is considered to be the best catalyst in photocatalytic processes. But TiO2₂The photocatalytic performance is reduced and practical application is limited due to the inherent defects of wide forbidden band width, easy generation of charge carriers and rapid recombination. In order to improve the photocatalytic efficiency, a plurality of methods are adopted to compound the semiconductor and other materials so as to improve the photocatalytic activity. But at present, CO cannot be fundamentally solved₂Low conversion efficiency. Therefore, the technology needs to be applied in practice, and the whole catalytic system needs to be improved to improve the catalytic activity and the product selectivity, so as to realize CO₂High efficiency transformation of (1). CuO is a p-type semiconductor having a narrow forbidden band width,it is considered to be a good connecting material because of its simple electron trapping effect, and TiO is used as a binder₂Recombination with it can form a p-n junction, facilitating charge separation between electrons and holes. However, CuO has only the potential of its Conduction Band (CB) to generate superoxide radicals, and the potential of its Valence Band (VB) may not be sufficient to oxidize to generate hydroxyl radicals, thus limiting its application.

And the performances of the non-metal semiconductor and the metal oxide photocatalyst are equivalent, and the non-metal semiconductor and the metal oxide photocatalyst have obvious advantages in material cost and light adsorption range. And in all non-metallic semiconductors, graphite-like phase C₃N₄Has the advantages of low cost, simple preparation process, good stability, proper electronic structure, excellent photocatalytic performance and the like, and g-C₃N₄The material is a two-dimensional layered structure, and the layer structure of the material is provided with a C-N aromatic heterocyclic ring, so that the material can stably exist in the air at 600 ℃, and Van der Waals force is generated between layers, thereby being beneficial to electron transmission. But g-C₃N₄The photocatalytic capability is reduced due to the high combination rate of photogenerated electrons and holes under visible light, so that the defects of easy recombination of the holes and low catalytic efficiency are overcome, and the method has important significance. Furthermore, CO is produced by photocatalysis₂One key issue in the reduction to hydrocarbon fuels is the product formation mechanism. To date, photocatalytic reduction of CO has been carried out₂The mechanism of (A) has not been clearly studied. During the photocatalytic reaction, charge carrier formation is only caused when photons with energies greater than the band gap are absorbed, their oxidation and reduction potentials leading to a reaction. At the same time, the charge carriers must have good mobility to migrate to the surface of the material, so that the charge carriers can undergo various recombinations and traps, thereby initiating the photochemical reaction.

Disclosure of Invention

The invention aims to provide TiO₂-CuO/g-C₃N₄Synthesis method of composite nano material and CO₂Application in photocatalytic reduction.

The technical scheme of the invention is as follows:

TiO2₂-CuO/g-C₃N₄Composite nano materialThe synthesis method of the material comprises the following steps:

(1) putting melamine into a crucible with a cover, roasting in a muffle furnace at 450-650 ℃ for 3-6 h, cooling with the furnace, and obtaining g-C₃N₄Grinding into powder, pouring the powder into an open crucible, and roasting at 400-600 ℃ for 1-3 h to obtain g-C₃N₄Dispersing the nanosheets in an alcohol-water mixed solution, and performing ultrasonic treatment for 5-30 min to obtain g-C₃N₄A dispersion liquid;

(2) uniformly mixing butyl titanate and alcohol, dropwise adding alcohol-water mixed solution, stirring for 30-60 min, adding copper nitrate until blue sol is formed, drying to obtain a precursor, then placing the precursor in a muffle furnace, and roasting at 350-500 ℃ for 2-5 h to obtain the nano catalyst TiO₂-CuO, named TC;

(3) under stirring, adding g-C₃N₄Dropwise adding the dispersion liquid into the blue sol obtained in the step (2) to form gel, drying to obtain a precursor, placing the precursor in a muffle furnace, and roasting at 350-500 ℃ for 2-5 h to obtain the nano-catalyst TiO₂-CuO/g-C₃N₄Named TCC.

Further, g-C₃N₄The mass-volume ratio of the nanosheet to the alcohol-water mixed solution is 0.1-0.3: 4-15 g/ml.

Further, the volume ratio of the butyl titanate to the alcohol is 4-7: 15-35, wherein the alcohol is one or more than two of absolute ethyl alcohol, polyvinyl alcohol and polyethylene glycol.

Further, the alcohol in the alcohol-water mixed solution is one or more than two of absolute ethyl alcohol, polyvinyl alcohol and polyethylene glycol.

Further, in the alcohol-water mixed solution, the volume ratio of alcohol to water is 40-80: 1 to 4.

Further, the mass volume ratio of the copper nitrate to the butyl titanate is 0.1-0.3: 4-7 g/ml.

TiO obtained by the above synthesis method₂-CuO/g-C₃N₄Composite nano material in CO₂The application in photocatalytic reduction comprises the following steps:

with TiO₂-CuO/g-C₃N₄The composite nanometer material is used as photocatalyst in saturated NaHCO₃Introducing CO into the solution₂5-10 min, then sealing, reacting for 20-50 min under the irradiation of ultraviolet/visible light source, and reacting CO₂And reduced to methanol. Method for measuring photocatalytic activity:

the method adopts Phchem-III photocatalysis reaction instrument test of Beijing Newbit and uses saturated NaHCO₃Is a reaction medium.

3.5mg of photocatalyst and 15mL of saturated NaHCO were weighed₃The solution was placed in a 25mL round bottom flask and charged with CO₂Sealing the round-bottom flask after 5min, reacting under irradiation of ultraviolet/visible light source for 25min, collecting 5mL sample solution, measuring absorbance A at maximum absorption wavelength (λ ═ 570nm) with 722S visible spectrophotometer by chromic acid method_iThe data was recorded and the methanol yield was calculated.

In the formula: a. the_iRepresents the absorbance of the sample to be tested;

m_crepresents the amount of catalyst used;

t- - -represents the photocatalytic reduction of CO₂And (4) reaction time.

In the invention, g-C₃N₄With TiO₂After the CuO is compounded, the defects that a single catalyst is easy to compound photo-generated electrons and holes and low in catalytic efficiency can be improved, and the ternary composite nano material with red shift in a response interval and large specific surface area is prepared; the invention has the beneficial effects that:

(1)TiO₂-CuO/g-C₃N₄the light absorption boundary of the composite nano material is red-shifted, and CO is reduced by photocatalysis₂The efficiency is improved;

(2)TiO₂-CuO/g-C₃N₄the irregular accumulation structure of the composite nano material increases the surface photoreactive active sites of the catalyst, so that the CO is reduced by photocatalysis₂Enhancing the efficiency;

(3)TiO₂-CuO/g-C₃N₄photocatalytic reduction of CO by composite nano material₂The reaction for generating the methanol is cooperatively controlled by electron-hole and free radicals, the main active factor in the reaction is a hole, the electron is the next time, and the influence of the free radicals is weak;

(4)TiO₂-CuO/g-C₃N₄photocatalytic reduction of CO by composite nano material₂The reaction to produce methanol as a single product is routed to CO₂Directly getting electrons on the surface of the catalyst to generate methanol.

Drawings

FIG. 1 is a standard graph of methanol.

FIG. 2 shows TiO obtained in example 3₂-CuO/g-C₃N₄XRD spectrum of (1).

FIGS. 3 to 5 show TiO obtained in example 3₂-CuO/g-C₃N₄SEM image of the nanocomposite.

FIG. 6 shows TiO obtained in example 3₂-CuO/g-C₃N₄EDS profile of nanocomposite.

FIG. 7 shows TiO obtained in example 3₂-CuO/g-C₃N₄TEM images of the nanocomposites.

FIG. 8 shows TiO obtained in example 3₂-CuO/g-C₃N₄Adsorption-desorption isotherms of the nanocomposite.

FIG. 9 shows TiO obtained in example 3₂-CuO/g-C₃N₄Pore size distribution curve of the nanocomposite.

FIG. 10 shows TiO obtained in example 3₂-CuO/g-C₃N₄UV-Vis spectra of nanocomposites.

FIG. 11 shows TiO obtained in example 3₂-CuO/g-C₃N₄XPS spectra of (A).

FIGS. 12 to 16 show TiO obtained in example 3₂-CuO/g-C₃N₄High resolution XPS spectra.

FIG. 17 shows the photocatalytic reduction of CO with different catalyst dosages₂Influence graph of (c).

FIG. 18 shows different compositionsPhotocatalytic CO reduction₂Influence graph of (c).

FIG. 19 shows the photocatalytic reduction of CO at different calcination temperatures₂Influence graph of (c).

FIG. 20 is a graph of the effect of different dispersants on photocatalytic reduction of CO 2.

FIG. 21 shows different pairs of inhibitors vs. TiO₂-CuO/g-C₃N₄Graph of the effect of the photocatalytic reduction performance of the nanocomposite.

FIG. 22 shows the control of different photoreaction conditions on TiO₂-CuO/g-C₃N₄Graph of the effect of the photocatalytic reduction performance of the nanocomposite.

Detailed Description

The present invention will be described in further detail with reference to specific examples, but the present invention is not limited thereto.

Example 1 g-C₃N₄Preparation of the Dispersion

Weighing a certain amount of melamine, putting the melamine into a crucible with a cover, placing the crucible in a muffle furnace to be roasted for 4 hours at 550 ℃, cooling the crucible along with the furnace, and obtaining g-C₃N₄Grinding into powder. Pouring the powder into an open crucible, and roasting at 500 ℃ for 2h to obtain g-C₃N₄Nanosheets; weighing 0.2g g-C₃N₄Dispersing in 5mL of absolute ethyl alcohol and 0.2mL of deionized water (polyvinyl alcohol, polyethylene glycol) mixed solution, and performing ultrasonic treatment for 10min to obtain g-C₃N₄And (3) dispersing the mixture.

EXAMPLE 2 photocatalyst TiO₂Preparation of-CuO

Weighing 5mL of butyl titanate and 20mL of absolute ethyl alcohol, uniformly mixing, dropwise adding a mixed solution of the absolute ethyl alcohol and deionized water, stirring for 40min, adding 0.20g of copper nitrate until blue sol is formed, and drying to obtain a precursor; placing the precursor in a muffle furnace, and roasting at 400 ℃ for 3h to obtain the nano-catalyst TiO₂-CuO, named TC.

Example 3 photocatalyst TiO₂-CuO/g-C₃N₄Preparation of

Measuring 5mL of butyl titanate and 20mL of absolute ethyl alcohol, uniformly mixing, and dropwise adding the mixed solution of the absolute ethyl alcohol and the deionized waterStirring for 40min, adding 0.20g of copper nitrate, and stirring for 30min to obtain blue sol; 5mL of g-C was added under rapid stirring₃N₄Dropwise adding the dispersion liquid into the blue sol to form gel, drying to obtain a precursor, placing the precursor in a muffle furnace, roasting at 400 ℃ for 3h to obtain the nano-catalyst TiO₂-CuO/g-C₃N₄Named TCC.

Example 4 determination of photocatalytic Activity

The test of the photocatalytic performance is carried out by adopting a Phchem-III photocatalytic reactor of Beijing Newbit and using saturated NaHCO₃Is a reaction medium.

In the formula: a. the_iRepresents the absorbance of the sample to be tested;

m_crepresents the amount of catalyst used;

t- - -represents the photocatalytic reduction of CO₂And (4) reaction time.

Example 5 Activity factor detection assay

In the presence of a catalyst TiO₂-CuO/g-C₃N₄-1% CO of polyvinyl alcohol₂Respectively adding tert-butyl alcohol, ammonium persulfate and KI as OH and photoproduction electron e in the photocatalytic reduction experiment^-And an electrically generated hole h + trapping agent.

As shown in FIG. 21, the yield of the reduced product without the addition of the inhibitor was 0.702mg/g cat/min, and was slightly decreased when t-butanol was added, indicating that OH is photocatalytic reduction of CO₂Active species in the process. When the ammonium persulfate is added, the reaction mixture is stirred,the degradation rate is obviously reduced, which indicates that the photo-generated electrons e^-Is the photocatalytic reduction of CO₂The major active species in the process. However, when potassium iodide was added, the degradation rate was significantly suppressed, indicating that the electron hole h was⁺In the process, CO is photo-catalytically reduced₂The most predominant active species. Thus, in the photocatalytic reduction of CO₂In the process, the predominant active species is the photogenerated hole h⁺Photo-generated electron e^-Second, photocatalytic reduction of CO by OH₂The inhibitory effect of (c) is the weakest. From the results of the experiment, TiO can be presumed₂-CuO/g-C₃N₄Composite catalyst for photocatalytic reduction of CO₂Is the result of electron-hole and radical synergy.

Example 6 reduction Path test

In the presence of a catalyst TiO₂-CuO/g-C₃N₄-1% CO of polyvinyl alcohol₂In the photocatalytic reduction experiment of (1), in a reactor in which 3.5mg of a catalyst and 15mL of saturated sodium bicarbonate were added, no substance was added, and CO was introduced₂Reacting for 2min under the irradiation of an ultraviolet light source and with the addition of a certain amount of formic acid and formaldehyde, sampling, and testing the content of the product by a spectrophotometry.

The test results are shown in FIG. 22, with CO being introduced₂The yield of the reduction product of the reaction system is 0.654mg/g cat/min at most, the blank reaction system has almost no photocatalytic reduction activity, and the reaction systems of formaldehyde and formic acid are respectively added, so that the photocatalytic reduction activity is extremely low, and the photocatalytic reduction path of the catalyst is presumed as follows:

2H₂O+4h⁺→O₂+4H⁺

CO₂+6H⁺+6e^-→CH₃OH+H₂O

the invention adopts a spectrophotometry method to measure the concentration of the methanol and draws a standard curve. Taking 6 25mL volumetric flasks, accurately transferring 0.01mg/mL methanol standard solution 0, 0.10, 0.20, 0.40, 0.60 and 0.80mL, testing according to a spectrophotometry method, and drawing a standard curve by taking the absorbance A as a vertical coordinate and the methanol mass m (mug) as a horizontal coordinate. The fitting standard curve equation is as follows: a is 0.0015+0.00639m,

regression coefficient R²＝0.99932，

The methanol content of the reduction product was then determined by means of this standard curve, which is shown in FIG. 1.

In addition, taking the material obtained in example 3 as an example, the obtained material was subjected to various characterizations such as XRD, SEM, EDS, TEM, BET, Uv-Vis DRS, XPS, etc., and the details are as follows.

FIG. 2 is a graph showing that TiO2-CuO/g-C is present at a calcination temperature of 400 ℃ in example 3₃N₄XRD pattern of the sample. As can be seen from FIG. 2, the broad peak at 12.25 ° (100) is g-C₃N₄The ordered arrangement of triazine structures of (1), corresponding to characteristic X-ray diffraction peaks of anatase TiO2 at 25.43 ° (101), 37.8 ° (004), 48.28 ° (200), is comparable to the prior art (Muzakki A, Shabrany H, Saleh R. Synthesis of ZnO/CuO and TiO)₂/CuO nanocomposites for light and ultrasound assisted degradation of a textile dye in aqueous solution[J]2016,1725(1): 1797-1805) and the prior art (Tu Shenghui, Hu Yaping, Zhang Ting, et al Synthesis of graphene-CuO/TiO₂composite catalysts and photocatalytic hydrogen production activity[J]Pure TiO of Functional Materials,2016, 47(4):11-16.)₂、CuO-TiO₂Comparison, addition of g-C₃N₄After TiO2₂-CuO/g-C₃N₄The sample was not observed for g-C directly₃N₄Diffraction peak generated by stacking structure of conjugated aromatic ring at 27.07 deg., and g-C₃N₄、TiO₂Has a peak position shift, which may be g-C₃N₄Diffraction peak of and anatase type TiO₂Is caused by overlapping diffraction peaks. In addition, g-C₃N₄The diffraction peak at the (100) crystal face is relatively strong, indicating that the spacing between layers is reduced, TiO₂The CuO may be sandwiched between g and C₃N₄Between the layers.In addition, a CuO characteristic peak with weak intensity can be observed at 35 °, but a diffraction peak of CuO at 38 ° cannot be directly observed, possibly because the diffraction peaks of CuO and TiO2 overlap after the ternary complex is formed, and the instrument is difficult to accurately distinguish. In conclusion, the synthetic method of the invention successfully obtains TiO₂-CuO/g-C₃N₄A nanocomposite material.

FIGS. 3 to 5 are TiO, respectively₂-CuO/g-C₃N₄SEM image of the nano composite material, TiO can be clearly seen₂-CuO/g-C₃N₄Morphology and structure of the nanocomposite, irregular nanoparticles and lumps were observed. According to the literature (Kobayashi Y, Nozaki T, Kanasaki R, et al₂Loaded with Magnetite for Photocatalytic Degradation of Methylene Blue[J]The SEM image shows particles and lumps, presumably because the composition is not uniform, the lumps are stacked, and the portion with much composition is granular. FIG. 6 is TiO₂-CuO/g-C₃N₄EDS diagram of the nanocomposite, which further identifies TiO₂-CuO/g-C₃N₄Composition of the nanocomposite. According to the EDS test results (figure 6), Cu, Ti, C and N elements are found in the nano composite material and are deduced to be consistent with elements contained in the ternary composite material.

FIG. 7 is TiO₂-CuO/g-C₃N₄TEM images of the nanocomposites. TEM images at 100nm, 20nm and 5nm are shown in a, b and c of FIG. 7, respectively. FIG. 7b clearly shows TiO₂-CuO/g-C₃N₄The nanocomposite is composed of particles, and is presumed to have a black portion of CuO and a light black portion of g-C₃N₄Sheet structure, and particle size less than 20 nm. From this, nano CuO, g-C can be obtained₃N₄Found dispersed in TiO₂A surface.

FIG. 8 and FIG. 9 are TiO, respectively₂-CuO/g-C₃N₄The absorption-desorption isotherm and pore size distribution curve of the nanocomposite show thatThe specific surface area and pore size distribution of the composite catalyst. From FIGS. 8 and 9, it can be seen that TiO₂-CuO/g-C₃N₄The nano composite material has higher specific surface area and more uniform pore size distribution. As can be seen from FIG. 8, the isotherm curve is consistent with the V curve in IUPAC. With pure TiO₂In contrast, TiO₂-CuO/g-C₃N₄The crystal grain size of (A) becomes large and the specific surface area is reduced, which may be due to g-C₃N₄The dispersion is poor, so that the particles agglomerate, or a small amount of carbon atoms exist in the heat treatment process and are doped into TiO₂Thereby promoting grain growth.

FIG. 10 is TiO₂-CuO/g-C₃N₄Absorption spectrum of the nanocomposite. And the literature (Li Huiquan, Jin Feng, Chen Wei. Effect of Nd Doping and Artificial Zeolite on the Photolattic Activity of TiO₂[J]The Natural Science Edition of TiO in Journal of Fuyang Teachers College 2007,24(1):39-41₂Compared with g-C, CuO₃N₄Composite TiO₂-CuO/g-C₃N₄The absorption of the sample in a visible light area is enhanced, the strong absorption range is wide, and the absorption edge has an obvious red shift phenomenon. This phenomenon occurs because the composite photocatalyst incorporates TiO₂UV response Range of CuO and g-C₃N₄Visible light response range of, and g-C₃N₄Is less than TiO₂And the band gap of CuO enables photo-generated electrons generated by light excitation to migrate at a two-phase interface, so that the composite material generates red shift on light absorption, and further the photocatalytic activity is improved. These results show that TiO₂-CuO/g-C₃N₄Improvement of TiO by nano composite material₂The photocatalyst plays an effective role in light-capturing performance.

FIGS. 11-16 are TiO₂-CuO/g-C₃N₄X-ray photoelectron spectroscopy (XPS) of the nanocomposite. And the literature (Xu S, Du A J, Liu J, et al. high y effective CuO incorporated TiO)₂nanotube photocatalyst for hydrogen production from water[J].International Journal of Hydrogen Energy,2011,36(11) 6560 and 6568) medium-purity TiO₂Compared with the standard XPS, the elements Ti, O and C can be detected in the two materials, which indicates that Ti and O exist in TiO₂-CuO/g-C₃N₄In the nano composite material, a standard Ti 2p orbit in the literature has two broad peaks at 457.3 eV and 463.0eV, and the observation of a high-resolution XPS spectrogram 12 in the Ti 2p orbit shows that the Ti 2p orbit has two broad peaks at 458.3 eV and 463.8eV, which belong to TiO respectively₂Middle Ti⁴⁺2p_3/2And Ti⁴⁺2p_1/2The Ti-O bond of the spin photoelectron shows that the binding energy of the Ti 2p peak in the sample is shifted to the direction of high binding energy, and Ti is TiO₂Exist in the form of (1). This change is mainly due to the addition of CuO and g-C₃N₄After that cause Ti⁴⁺Change of the chemical environment of (a). In which C is also present in pure TiO₂The XPS spectrum of (A) is mainly due to the adsorption result during the experiment. And literature (Ran J, Jaroniec M, Qiao S Z. catalysts in Semiconductor-based Photocalatic CO₂Reduction:Achievements,Challenges,and Opportunities.[J]Pure g-C in Advanced Materials,2018,30(7):1704649.)₃N₄The XPS spectra of C, N, O are compared with those of the two materials, and according to the high resolution spectrum of C1 s in FIG. 13, the broad peak at 284.6eV is caused by the C-C coordination of the surface amorphous carbon, while the broad peak at 288.6eV is caused by sp²Bonded carbon, i.e., N-C-N. In the figure, the C1 s has a broad peak generation at 288.6eV, and the contrast pure g-C3N4 has a broad peak at 288.3eV, TiO₂-CuO/g-C₃N₄The nanocomposite was slightly higher than pure g-C₃N₄Mainly due to the presence of TiO₂And CuO₂The composite function. From the literature (Ran J, Jaronie M, Qiao S Z. catalysts in Semiconductor-based Photocalatic CO)₂ Reduction:Achievements,Challenges,and Opportunities.[J]Advanced Materials,2018,30(7):1704649.) pure g-C₃N₄The broad peaks of the middle N1 s at 398.5, 399.2 and 400.6eV are respectively derived from pyridine nitrogen, pyrrole nitrogen and graphitized nitrogen (Huang Z, Sun Q, Lv K, et al. Effect of contact interface between TiO)₂, and g-C₃N₄,on the photoreactivity of g-C₃N₄/TiO₂,photocatalyst:(001)vs,(101)facets of TiO₂[J]Applied Catalysis B Environmental 2015,164(2015): 420-427.). As can be seen from FIG. 14, TiO₂-CuO/g-C₃N₄The binding energy of pyridine N (398.6eV) in N1 s of the nanocomposite is increased by 0.1eV, and the binding energy of pyrrole N (399.6eV) is increased by 0.4eV, reflecting that g-C₃N₄CuO and TiO₂Interface forces therebetween. As can be seen from FIG. 15, two peaks exist in the O1 s region, the main peak binding energy is 529.4eV, and the two peaks are bonded with TiO₂O in crystal lattice₂ ^-The binding energy (528.8eV) is close, so that it is presumed to be TiO₂Neutralized Ti⁴⁺Bound oxygen [ O-Ti-O]. At the same time, a shoulder appeared at 531.4eV, probably because water molecules remained on the TiO₂Surface-formed oxyhydrogen [ -O-H ]]It presents active species that can capture the electron production, thereby accelerating the photocatalytic reduction process. TiO2₂-CuO/g-C₃N₄The characteristic 'vibration' peak of CuO can be obviously observed in the XPS spectrum diagram 16 of a Cu 2p orbit of the nano composite material, and the Cu 2p peaks at 933.8 and 953.9eV_3/2And Cu 2p_1/2Indicating that Cu is present in the form of CuO in the composite. The binding energy of each orbit in the spectrogram of each element under high resolution is not changed, and the g-C is proved₃N₄Combined with CuO in TiO₂A surface.

In addition, photocatalytic reduction of CO was also investigated₂Condition, composite ratio, calcination temperature and dispersant for photocatalytic reduction of CO₂The effect of the performance is as follows.

FIG. 17 shows photocatalyst TiO calcined at 400 deg.C₂-CuO/g-C₃N₄(1% polyvinyl alcohol) different dosage photocatalytic reduction CO₂Graph of the effect relationship. As can be seen from the figure, CO was introduced in the experiment₂The amount of (A) is a fixed value, and when no catalyst is added, CO₂Basically no reduction reaction occurs, and CO is subjected to photocatalytic reduction along with the increase of the using amount of the catalyst₂The yield of the catalyst is increased and then reduced, when the catalytic dosage is 3.5mg, the catalytic efficiency of the catalyst is optimal, and when the catalytic dosage is more than 3.5mg, the catalytic efficiency is obviously reduced, and the phenomenon appearsThis is because the amount of CO in the reactor is 3.5mg₂The content of (a) and the catalyst reach a saturation state, and the increase of the amount of the catalyst can cause the catalyst to generate light scattering and shielding effects, so that the catalytic efficiency is reduced, and therefore, the optimal dosage of the experimental catalyst is 3.5 mg.

FIG. 18 shows the g-C at a calcination temperature of 400 DEG C₃N₄With TiO₂Catalyst TiO with different composite ratios₂-CuO/g-C₃N₄Photocatalytic reduction of CO₂Influence of yield is shown. As can be seen from FIG. 18, g-C is not found₃N₄Composite catalyst TiO₂-CuO has extremely low photocatalytic reduction activity. And the content of the reduction product methanol is increased and then reduced along with the increase of the composite ratio to form an extreme value, namely when the composite ratio is 0.2, TiO₂-CuO/g-C₃N₄To CO₂The photoreduction efficiency of (2) is maximized, and the yield of the reduction product methanol is 0.571 mg/(g/cat. min). When the composite ratio is less than 0.2, the catalyst TiO₂-CuO/g-C₃N₄To CO₂The photoreduction efficiency of (2) is remarkably increased with the increase of the composite ratio. The photoreduction efficiency decreases after the recombination ratio exceeds 0.2. The reason for this is when g-C₃N₄When the recombination amount exceeds a threshold value, a photon-generated carrier recombination center may be formed, so that the recombination rate of photon-generated electrons and holes is enhanced, and the catalyst is used for photocatalytic reduction of CO₂The activity of (4) is decreased.

FIG. 19 shows the synthesis of TiO catalyst at different calcination temperatures₂-CuO、TiO₂-CuO/g-C₃N₄(composite ratio 0.2) photocatalytic reduction of CO₂Graph of the effect relationship. As can be seen from FIG. 19, with the continuous increase of the calcination temperature, the reduction efficiencies of the two catalysts are both increased and then decreased, and the peak appears at 400 ℃, and the yields of the reduction products methanol are 0.087mg/(g cat min) and 0.523mg/(g cat min), respectively. The reason may be that when the temperature is too low, g-C₃N₄With TiO₂The compounding efficiency is poor; high temperature easily causes powder sintering agglomeration, the specific surface area is reduced, and simultaneously, overhigh temperature can cause g-C₃N₄Thereby affecting the activity of the catalyst, so that the photocatalytic reduction efficiency of the catalyst is lowered. It is also possible, for example, to use the literature (Peng Fuchang, Chen Qiali, Wu Yuxi, et al₃N₄/TiO₂Composite and Its Visible Light Photocatalytic Performance[J]China Ceramics,2018(2) said catalyst prepared at a calcination temperature below 350 ℃ is mostly amorphous to CO₂The reduction activity of (a) is low; the proportion of the catalyst anatase phase is larger at about 400 ℃, and the catalyst anatase phase accounts for CO₂The reduction activity of (A) is higher; the catalyst particles grow rapidly with increasing calcination temperature and the rutile form grows more rapidly when calcined at the same temperature, whereas in TiO the rutile form grows more rapidly₂The photocatalytic activity of rutile in the three crystal forms of (A) is the lowest, and in addition, TiO₂The transition from anatase to rutile can provide heat for the phase transition to further accelerate grain growth, resulting in reduced catalytic performance.

FIG. 20 is g-C₃N₄The composite ratio is 0.2, the roasting temperature is 400 ℃, and the influence of different dispersants added into a catalyst system on the photocatalytic performance of the catalyst is shown in a relational graph. The dispersant added in the present invention is polyethylene glycol or polyvinyl alcohol, and as can be seen from fig. 20, the catalyst system to which polyethylene glycol or polyvinyl alcohol is added reduces CO by photocatalysis₂The optimal yield is 0.620mg/g cat/min and 0.681mg/g cat/min respectively, and compared with the yield of the catalyst in 3.2.2, the photocatalytic reduction efficiency of the catalyst system added with the dispersing agent is obviously improved. As shown in fig. 20, the two dispersing systems with two dispersants added have a tendency of increasing photocatalytic reduction efficiency with concentration and then decreasing photocatalytic reduction efficiency with concentration, and the concentrations of polyethylene glycol and polyvinyl alcohol are respectively 2% and 1% to achieve the best yield, because polyethylene glycol and polyvinyl alcohol are polymers with special physical and chemical properties, and have dispersing ability, so that the catalyst tends to be uniform in the compounding process among substances in the preparation process, and agglomeration is avoided, and when the dispersant exceeds the dispersantAt a certain concentration, the interface adsorption at the moment is saturated, and redundant dispersing agents can only form micelles in a phase system, so that the possibility of agglomeration is increased, and the photocatalytic reduction performance of the catalyst is reduced.

The invention synthesizes TiO with nano particles and sheet stacking structure in different mediums by adopting a sol-gel method₂-CuO/g-C₃N₄Composite nano material, discussing the photocatalytic reduction of CO by the ternary composite nano catalyst₂The efficiency and mechanism in (1) can be obtained as follows:

Claims

1. TiO2₂-CuO/g-C₃N₄Composite nano material in CO₂The application of the photocatalytic reduction is characterized by comprising the following steps:

with TiO₂-CuO/g-C₃N₄The composite nanometer material is used as photocatalyst in saturated NaHCO₃Introducing CO into the solution₂5-10 min, then sealing, reacting for 20-50 min under the irradiation of ultraviolet/visible light source, and reacting CO₂Reducing the methanol to methanol;

the TiO is₂-CuO/g-C₃N₄The synthesis method of the composite nano material comprises the following steps:

（1）g-C₃N₄preparation of the Dispersion

Weighing a certain amount of melamine, putting the melamine into a crucible with a cover, placing the crucible in a muffle furnace to be roasted for 4 hours at 550 ℃, cooling the crucible along with the furnace, and obtaining g-C₃N₄Grinding into powder, pouring the powder into an open crucible, and roasting at 500 deg.C for 2h to obtain g-C₃N₄Nanosheets; weighing 0.2g g-C₃N₄Dispersing in the mixed solution of 5mL of absolute ethyl alcohol and 0.2mL of deionized water, adding dispersant polyvinyl alcohol or polyethylene glycol, wherein the concentrations of the polyethylene glycol and the polyvinyl alcohol are respectively 2% and 1%, and performing ultrasonic treatment for 10min to obtain g-C₃N₄A dispersion liquid;

(2) weighing 5mL of butyl titanate and 20mL of absolute ethyl alcohol, uniformly mixing, dropwise adding a mixed solution of the absolute ethyl alcohol and deionized water, stirring for 40min, adding 0.20g of copper nitrate, and stirring for 30min to obtain blue sol; 5mL of g-C was added under rapid stirring₃N₄Dropwise adding the dispersion liquid into the blue sol to form gel, drying to obtain a precursor, placing the precursor in a muffle furnace, and roasting at 400 ℃ for 3h to obtain the composite nano material TiO₂-CuO/g-C₃N₄。