CN112138700A - Bismuth phosphate-based heterojunction photocatalyst and preparation method thereof - Google Patents
Bismuth phosphate-based heterojunction photocatalyst and preparation method thereof Download PDFInfo
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- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J27/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
- B01J27/24—Nitrogen compounds
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- B01J35/39—
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Abstract
The invention discloses a bismuth phosphate-based heterojunction photocatalyst and a preparation method thereof, wherein the photocatalyst is a heterojunction photocatalyst constructed by bismuth phosphate and graphite-phase carbon nitride, and the preparation method comprises the following steps: preparation of nanorod BiPO by microwave method4Preparation of light and thin g-C by calcination3N4G to C3N4And BiPO4Grinding and compounding by a ball milling method to obtain the heterojunction photocatalytic material g-C3N4/BiPO4(ii) a The prepared heterojunction photocatalyst has high activity, high light utilization rate, good stability and reusability, simple preparation process, economy and high efficiency, and has good application prospect.
Description
Technical Field
The invention belongs to the technical field of photocatalysis, and particularly relates to a bismuth phosphate-based heterojunction photocatalyst and a preparation method thereof.
Background
The photocatalysis technology is a green advanced oxidation technology with good application prospect, and is widely applied to the aspect of treating emerging pollutants. The traditional photocatalyst is limited by the defects of narrow spectral response range, high recombination rate of photo-generated electron hole pairs and the like. Although bismuth-based semiconductor photocatalysts have attracted attention as photocatalysts having good application values in recent years, single bismuth-based photocatalysts have been difficult to meet practical needs although the separation efficiency of photogenerated electron-hole pairs is improved compared with that of conventional photocatalysts, and the single bismuth-based photocatalysts still need to be improved through modification progress.
BiPO4As is more common in bismuth systemsThe semiconductor has good removal capability for organic pollutants, and also has good performance for removing antibiotics. The pollutants in antibiotic sewage are of various complex types, and BiPO is used in the existing research4The degraded antibiotic has single type and low degradation efficiency under visible light conditions, thereby improving BiPO4The effective separation efficiency of photo-generated electrons and holes of the material and the utilization rate of visible light are particularly important for improving the photocatalytic activity. g-C as non-metallic catalyst3N4Has good conductive property, but has higher recombination efficiency of photogenerated electron-hole pairs, so that the pure g-C3N4The visible light catalytic activity of the photocatalyst needs to be improved, and g-C needs to be added3N4And BiPO4The semiconductor material is combined with a heterojunction composite material to improve the photocatalytic activity. The method for constructing the heterojunction between the semiconductor and the semiconductor is a common composite modification method at present, two or more semiconductor materials are compounded through a certain experimental method, and a space potential difference is formed after the compounding, so that the aim of improving the separation efficiency of electron-hole pairs is fulfilled, the utilization rate of visible light is increased, and the photocatalytic performance is improved.
At present, BiPO4The preparation of the nano structure adopts a chemical vapor deposition method, a sonochemical method, a hydrothermal method and the like, and BiPO4The composite material is prepared by a hydrothermal method, a solvothermal method, a high-temperature solid phase method and the like. The methods need to carry out reaction synthesis at extremely high temperature, rapid heating speed or long reaction time, and the preparation process has the defects of large power consumption, long time and the like.
Disclosure of Invention
In order to solve the problems, the invention discloses a bismuth phosphate-based heterojunction photocatalyst and a preparation method thereof, and BiPO prepared by a microwave method4Mainly adopts a high-energy ball milling method and graphite phase carbon nitride g-C3N4Constructs a heterojunction photocatalytic material g-C3N4/ BiPO4The simple mechanical grinding method can be used as a general way for improving the activity of the photocatalyst, and the preparation method is simple, economic and efficient.
In order to achieve the purpose, the invention provides the following technical scheme:
a preparation method of a bismuth phosphate-based heterojunction photocatalyst comprises the following steps:
Further, g-C in the step 33N4And BiPO4The mass ratio of the solid powder is 1: 10-100.
Further, BiPO in the step 34The mass ratio of the solid powder to the agate beads is 1: 10-15.
Further, BiPO in the step 34The mass ratio of the solid powder to the water is 10-15: 1.
Further, the ball milling speed in the step 3 is 260-280 rpm.
Further, the ball milling time in the step 3 is 0-24 h.
Further, the molar ratio of the bismuth nitrate to the disodium hydrogen phosphate in the step 1 is 1: 1-1.5.
Further, the mass ratio of the bismuth nitrate to the water in the step 1 is 1: 80-85.
Further, the power of the microwave device in the step 1 is set to be 800-900W, and the stirring reaction time is 15-20 min.
Further, in the step 2, the calcining temperature is 550-600 ℃, the heating rate is 5-10 ℃/min, and the calcining time is 4-8 h; the drying temperature in the step 1 is 60-65 ℃, and the drying time is 12-16 h; and in the step 3, the drying temperature is 60-65 ℃, and the drying time is 12-16 h.
Compared with the prior art, the invention has the following advantages and beneficial effects:
（1）BiPO4the preparation method adopts a microwave method, the microwave method provides a good environment for uniform nucleation for the material, can generate more photoproduction electrons and holes which are effectively separated, improves the catalytic efficiency, brings potential progress in the aspect of large-scale synthesis of the nano material, is a simple, efficient and economic process method which is easier to solve practical problems and has practical application benefits.
(2) The heterojunction visible light composite photocatalyst g-C prepared by the invention3N4/BiPO4The composite material prepared by the ball milling method not only successfully constructs a heterojunction structure, but also reduces the particle size of the material, increases the specific surface area and provides more active sites, thereby improving the photocatalytic activity. Compared with the traditional photocatalysis, the composite photocatalytic material has the advantages that the utilization rate of visible light is improved; and BiPO alone4Comparative example g-C3N4The addition of (2) greatly improves the lifetime of the photogenerated electron holes. The composite catalyst system is applied to an experiment for degrading organic pollutants by photocatalysis, shows excellent photocatalysis capability under the condition of visible light, and has good chemical stability.
Drawings
FIG. 1, BiPO4、g-C3N4And different proportions of g-C3N4/BiPO4XRD pattern of (a);
FIG. 2 BiPO4、g-C3N4And different proportions of g-C3N4/BiPO4Ultraviolet-visible absorption spectrum of (a);
FIG. 3 BiPO4、g-C3N4And different proportions of g-C3N4/BiPO4A photocurrent graph of (a);
FIG. 4, g-C3N4/BiPO4XPS spectra of (a): (a) total map, (b) Bi 4f, (C) C1 s, (d) P3 d, (e) N1s, (f) O1 s;
FIG. 5, sample TEM image (a-b) BiPO4/C3N, HR-TEM image of the sample (c-d) BiPO4/C3N4；
FIG. 6, N of sample2Adsorption-desorption isotherms: (a) g-C3N4，（b）BiPO4，（c）g-C3N4/BiPO4；
FIG. 7, BiPO4And g-C3N4/BiPO4A photoluminescence spectrum of (a);
FIG. 8, BiPO4And g-C3N4/BiPO4Electrochemical impedance spectroscopy of (a);
fig. 9, scanning electron micrograph of sample: (a) non-ball milled BiPO4(b) unground g-C3N4(C) ball milling 8h g-C3N4/BiPO4(d) ball milling 18h g-C3N4/BiPO4(e) ball milling of 24h g-C3N4/BiPO4And (f) g-C3N4/BiPO4EDS energy spectrum of (a).
Detailed Description
The technical solutions provided by the present invention will be described in detail below with reference to specific examples, and it should be understood that the following specific embodiments are only illustrative of the present invention and are not intended to limit the scope of the present invention.
Example 1
The bismuth phosphate-based heterojunction photocatalyst prepared in the embodiment comprises the following steps:
Example 2
The other conditions were the same as in example 1 except that 0.1g, 0.3g and 1g g-C were added3N4Checking to add different amounts of g-C3N4For g to C3N4/BiPO4The impact of performance.
Example 3
XRD, ultraviolet-visible diffuse reflection and photocurrent characterization are carried out on the samples of the example 1 and the example 2, and the characterization results are shown in figure 1, figure 2 and figure 3, wherein the percentage content in the figure is g-C3N4The addition amount of BiPO4The mass percentage of the added amount.
XRD is used for determining the crystalline phase structure of the prepared sample, and XRD patterns of photocatalytic materials with different proportions prepared in the experimental process are shown in figure 1. In the figure, for BiPO prepared by microwave method419.0 °, 21.3 °, 25.3 °, 27.2 °, 29.1 °, 31.2 °, 34.5 ° and 36.9 ° respectively correspond to BiPO4The (011), (-111), (200), 120), (012), (-202) and (-212) crystal planes of (E), which are also consistent with the results in the standard spectrogram library (JCPDS 15-0767). The sharp and intense diffraction peaks of the sample indicate pure BiPO4Has high crystallinity. Pure g-C prepared by experiment3N4At the bits of 2 theta =13.0 ° and 2 theta =27.4 °Characteristic peaks are generated, which correspond to a repeating structure (100) crystal face in the same plane of graphite phase carbon nitride and a (002) crystal face stacked between layers respectively, and the result is consistent with that in a standard spectrogram library (JCPDS-50-0367). However, for g-C3N4/BiPO4g-C could not be determined from XRD patterns3N4A diffraction peak of (A), which indicates g-C3N4Highly dispersed in the bulk phase of the sample. Thus, ball milling is an effective method for efficiently milling samples with high dispersion, with pure g-C3N4Diffraction peak ratio of (g-C)3N4/BiPO4g-C is detected in the sample3N4Typical peak of (a). In addition, no other crystalline phases were detected, so that it was concluded that in g-C3N4And BiPO4Does not form new substances in the high-energy ball milling process, proves that g-C3N4/BiPO4The high purity sample of (2).
The optical properties of the photocatalytic material are characterized and researched by utilizing ultraviolet-visible diffuse reflection, the result is shown in figure 2, and the result shows that the prepared heterojunction g-C3N4/BiPO4Has absorption in the visible absorption region, g-C3N4/BiPO4The absorption edge band is about 470nm, and obvious absorption peaks appear between 350-450nm, compared with BiPO before compounding4A red shift appeared indicating g-C3N4/BiPO4The composite catalyst can more effectively utilize sunlight. In addition, 5wt% g-C can be seen in the figure3N4/BiPO4The optical absorption intensity of the photocatalyst is better than that of the photocatalyst compounded in other proportions.
The photocurrent test is an experimental method for representing the photoelectric response capability of a material, electrons generated by the photocatalyst under the excitation of simulated sunlight are transferred to form photocurrent, and the size of the photocurrent reflects the separation and migration of photo-generated charges in the photocatalyst. In general, the stronger photocurrent generated by the sample under illumination indicates that the material has stronger photoresponse capability and relatively lower carrier recombination efficiency. The photocurrent response of the sample is shown in FIG. 3, with 5wt% photocatalytic material g-C3N4/BiPO4The photocurrent intensity of the light source is obviously larger than that of single BiPO4And other proportions of materials, from which we can speculate that 5wt% g-C3N4/BiPO4Compared with pure bismuth phosphate, carbon nitride and other composite samples with different proportions, the composite sample can generate more photo-generated electrons and holes which are effectively separated under illumination, and the photo-response capability is stronger.
To investigate g-C further3N4/BiPO4The samples of example 1 were further characterized by XPS, TEM and HR-TEM, BET, PL, EIS and the results are shown in FIGS. 4 to 9.
To further prove BiPO4And g-C3N4The mutual action between the nano-sheets is characterized and analyzed by XPS characterization means to determine the surface composition and chemical valence state of the catalyst, so as to determine BiPO4And g-C3N4The chemical combination valence state of each element in the photocatalyst is subjected to peak separation treatment by using XPSpeak software. The analysis results are shown in FIG. 4, where in FIG. 4 (a) is 5wt% g-C3N4/BiPO4The full spectrum of the photocatalyst, the chemical binding energies of 284.8, 158.5, 132.4, 397.4 and 530.2eV correspond to the peaks of C1 s, Bi 4f, P2P, N1s and O1 s, respectively, and the analysis result shows that the sample contains Bi, N, P, O and C elements. 5wt% g-C3N4/BiPO4Peak intensity ratio of C1 s to N1s in (1) g-C3N4Weak, probably due to g-C3N4Lower levels resulted in the result. These results demonstrate BiPO4/C3N4And (4) forming a complex.
To further investigate the morphological and microstructural details of the samples, we observed the samples by TEM and HR-TEM. A part of the layers stacked g-C due to the effect of ball milling3N4Conversion to g-C with lamellar structure3N4And has obvious transparency. From FIGS. 5(a-b) it is clear that g-C in the layer is3N4Meso-dispersed BiPO4Presence of BiPO4And g-C3N4The interface blur between was observed, indicating that g-C was formed3N4/BiPO4The core-shell heterostructure is favorable for charge transfer. A clear interface is observed in the HR-TEM image of the sample of FIG. 5 (c), showing the two types of lattices in which BiPO can be clearly seen4And the areas without lattice stripes are amorphous g-C3N4. A smaller lattice, about 0.306 nm, can be observed in FIG. 5 (c), and BiPO can be seen in FIG. 5 (d)4Is a single crystal structure. Perfect crystal quality and BiPO4And C3N4The sharp interface between the two will promote the separation of photogenerated carriers.
The specific surface area of the sample was also analyzed as shown in fig. 6. C3N4、BiPO4And C3N4/BiPO4Have specific surface areas of 10.636, 14.36 and 20.865m, respectively2(ii) in terms of/g. When adding C3N4Then, the specific surface area of the sample is increased, and the higher specific surface area provides more adsorption sites and active sites, so that the adsorption and degradation efficiency of pollutants is improved, and the photocatalytic activity of the sample is improved.
To study g-C deeply3N4Introduction of (2) to BiPO4The separation of photo-generated electron-hole pairs was analyzed by PL spectroscopy, as shown in FIG. 7, where the emission spectrum was mainly at 450nm, the sample produced a strong fluorescence peak at 450nm, and 5wt% g-C3N4/BiPO4Peak intensity of (A) is higher than that of BiPO4A significant decrease, which indicates g-C3N4The introduction of (2) can effectively promote the separation of photon-generated carriers and reduce the g-C by 5wt%3N4/BiPO4The recombination rate of the photo-generated electron-hole pairs is improved, so that the photocatalytic activity of the photocatalyst is improved.
To better understand pure BiPO4And g-C3N4The typical Electrochemical Impedance Spectroscopy (EIS) response was performed for reasons of different photosensitivity of the/BiPO 4 composite. As shown in fig. 8, only one arc or half circle appears on the EIS image, which is the rate determining step in the photocatalytic process. The smaller the arc radius on the EIS Nyquist plot, the more efficient the separation of photogenerated electrons and holes, and vice versa. Display deviceWhile it is readily apparent that FIG. 8 shows an arc radius of 5wt% g-C3N4/BiPO4The composite photocatalyst is purer than BiPO4Small, this indicates 5wt% g-C3N4/BiPO4The composite photocatalyst is purer than BiPO4Has smaller resistance and higher charge transfer efficiency. As a result, g-C3N4And BiPO4Coupling is formed after ball milling and compounding, which is beneficial to the separation and migration of charges, thereby improving the photocatalytic activity.
Example 4
The other conditions were the same as example 1 except that the ball milling time was 8 hours and 24 hours, respectively, and the ball milling time was checked for g-C3N4/BiPO4The impact of performance.
The samples of example 1 and example 4 were subjected to SEM, EDS characterization and the results are shown in figure 9.
The SEM can visually observe the surface appearance of a sample, and the elemental composition of the surface of the material can be analyzed by utilizing the representation of the elemental energy spectrum, so as to confirm whether the compounding is successful or not. The appearance characterization result of the sample by the scanning electron microscope is shown in fig. 9. FIGS. 9a and 9b are respectively non-ball milled monomer BiPO4And ungelled monomers g-C3N4Scanning electron micrographs of the powder. As can be seen from FIG. 9(a), BiPO4Is a rod-shaped crystal with the diameter of about 100-200 nm and has certain regularity. As can be seen from FIG. 9(b), g-C3N4Presenting a stacked block structure. And FIGS. 9(C-e) show g-C ball milled for 8h, 18h, and 24h, respectively3N4/BiPO4The scanning electron microscope image of (a) shows that the size is obviously reduced compared with that of the sample which is not ball-milled, wherein the sample which is ball-milled for 18h has better dispersibility. However, the aggregation of the sample with the ball milling time of 24h is slightly higher than that of 18h, which indicates that when the ball milling time is longer than the optimum time, the high surface energy gradually coagulates the sample with the increase of the ball milling time, resulting in the decrease of the specific surface area of the sample.
FIG. 9(f) is the result of SEM-EDS analysis, visually expressing the corresponding element distribution in the catalyst, and EDS images verifying whether the sample is composed of C, N, P, O and Bi elements. The highest peak is obtained when preparing EDS samplesBackground peaks of carbon conductive tape used. g-C3N4/BiPO4Contains five elements of Bi, P, O, C and N, and is uniformly distributed in the composite catalyst, and further proves that BiPO4/C3N4The sample synthesis was successful.
The technical means disclosed in the invention scheme are not limited to the technical means disclosed in the above embodiments, but also include the technical scheme formed by any combination of the above technical features. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principle of the present invention, and such improvements and modifications are also considered to be within the scope of the present invention.
Claims (10)
1. The preparation method of the bismuth phosphate-based heterojunction photocatalyst is characterized by comprising the following steps of:
step 1, BiPO4The preparation of (1): adding bismuth nitrate into water for ultrasonic dissolution, then adding disodium hydrogen phosphate for stirring and dissolution to obtain a mixed solution, placing the mixed solution into a microwave device for stirring and reaction, centrifuging, drying a precipitate obtained by centrifuging in an oven to obtain BiPO4A solid powder;
step 2, g-C3N4The preparation of (1): weighing 5-10 g of melamine, placing the melamine in a crucible for calcining, naturally cooling to room temperature, and grinding into powder to obtain g-C3N4；
Step 3, g-C3N4/BiPO4The preparation of (1): weighing BiPO4Placing the solid powder in an agate jar, adding agate beads, mixing, and weighing g-C3N4Putting the mixture into an agate jar, adding water, ball-milling, and then putting the mixture into an oven for drying to obtain g-C3N4 /BiPO4A photocatalyst.
2. The method for preparing the bismuth phosphate-based heterojunction photocatalyst as claimed in claim 1, wherein g-C in the step 33N4And BiPO4The mass ratio of the solid powder is 1: 10-100.
3. The method for preparing a bismuth phosphate-based heterojunction photocatalyst as claimed in claim 1, wherein BiPO in the step 34The mass ratio of the solid powder to the agate beads is 1: 10-15.
4. The method for preparing a bismuth phosphate-based heterojunction photocatalyst as claimed in claim 1, wherein BiPO in the step 34The mass ratio of the solid powder to the water is 10-15: 1.
5. The method for preparing the bismuth phosphate-based heterojunction photocatalyst according to claim 1, wherein the ball milling rotation speed in the step 3 is 260-280 rpm.
6. The method for preparing a bismuth phosphate-based heterojunction photocatalyst according to claim 1, wherein the ball milling time in the step 3 is 0-24 h.
7. The method for preparing a bismuth phosphate-based heterojunction photocatalyst according to claim 1, wherein the molar ratio of bismuth nitrate to disodium hydrogen phosphate in the step 1 is 1: 1-1.5.
8. The preparation method of the bismuth phosphate-based heterojunction photocatalyst as claimed in claim 1, wherein the mass ratio of bismuth nitrate to water in the step 1 is 1: 80-85.
9. The method for preparing a bismuth phosphate-based heterojunction photocatalyst according to claim 1, wherein the power of a microwave device in the step 1 is 800-900W, and the stirring reaction time is 15-20 min.
10. The preparation method of the bismuth phosphate-based heterojunction photocatalyst according to claim 1, wherein in the step 2, the calcination temperature is 550-600 ℃, the temperature rise rate is 5-10 ℃/min, and the calcination time is 4-8 h; the drying temperature in the step 1 is 60-65 ℃, and the drying time is 12-16 h; and in the step 3, the drying temperature is 60-65 ℃, and the drying time is 12-16 h.
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| CN114534758A (en) * | 2022-01-07 | 2022-05-27 | 苏州科技大学 | Bismuth ferrite/graphite phase carbon nitride composite material and preparation method and application thereof |
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