CN114011452A

CN114011452A - Phosphorus-doped graphite-phase carbon nitride/bismuth vanadate heterojunction and application thereof

Info

Publication number: CN114011452A
Application number: CN202111485053.3A
Authority: CN
Inventors: 殷旭东; 李德豪; 谢文玉; 毛玉凤; 刘正辉; 王儒珍; 朱越平; 刘志森
Original assignee: Guangdong University of Petrochemical Technology
Current assignee: Guangdong University of Petrochemical Technology
Priority date: 2021-12-07
Filing date: 2021-12-07
Publication date: 2022-02-08

Abstract

The invention belongs to the field of new materials, and discloses a phosphorus-doped graphite-phase carbon nitride/bismuth vanadate heterojunction and application thereof. Phosphorus doped g-C₃N₄/BiVO₄The heterojunction is obtained by uniformly mixing a PCN salt solution, a Bi salt solution and a vanadium salt solution and performing hydrothermal synthesis. Phosphorus doped g-C of some embodiments of the invention₃N₄/BiVO₄The heterojunction is mainly in a thin rod shape, tiny PCN particles are attached to the thin rod, the layered size is about 150-300 nm, micropores exist on the rod-shaped main body, the PCN and the BVO are in close contact, and the rod-shaped particles are uniformly dispersed in the composite catalyst, so that the heterojunction has good performance of degrading organic matters through photocatalysis.

Description

Phosphorus-doped graphite-phase carbon nitride/bismuth vanadate heterojunction and application thereof

Technical Field

The invention relates to a material with photocatalytic activity and application thereof.

Background

Organic pollutants have serious influence on the water quality of water bodies, and antibiotic residues are important to remove among a plurality of organic pollutants.

Visible light driven photocatalysis can exploit the vast amount of available solar energy to degrade organic pollutants, including Eps. The photocatalytic activity under visible light irradiation is affected by various factors, of which the visible light absorption edge and the transport characteristics of photo-induced carriers are two key factors. Therefore, several effective methods for synthesizing the separation carrier have been proposed in order to improve the photocatalytic performance. The photodegradation means becomes one of the most important methods for treating and controlling the antibiotic pollution, in the future research, the photodegradation technology is more and more important in the treatment process of the antibiotic wastewater pollution, and more people select the method which can play an important role in the treatment of the antibiotic-polluted wastewater.

A large number of researches show that the photocatalytic activity is mostly influenced by factors such as an energy band structure, a phase structure, an exposed crystal face, morphology, particle size and the like. The influence of the crystal structure of the semiconductor photocatalyst on the photocatalytic activity is mainly reflected in the influence of crystal forms, crystal faces, lattice spacing, crystallinity and the like, and certain catalysts can generate certain lattice defects possibly due to the properties of the crystals, wherein the lattice defects can capture holes or photon-generated electrons and can also serve as a recombination center of current carriers, so that the influence on the semiconductor photocatalytic material is in two aspects. In addition, the same catalyst has different crystal forms and different photocatalytic activities. For example, TiO₂There are three crystal types of rutile type, anatase type and flat type. Wherein the anatase form of TiO₂Has relatively stable chemical properties and large specific surface area. More readily adsorb organic phase and O₂ ^-And thus its photocatalytic activity is higher.

Bismuth vanadate (BiVO)₄) Has good physical and chemical stability, and can be used for treating diabetesHas strong photocatalytic activity under the irradiation of light, and is a promising photocatalytic material. BiVO₄Mainly divided into three crystal forms according to the structure: tetragonal zircon type, monoclinic scheelite type, and tetragonal scheelite type. The three crystal forms are respectively abbreviated as BiVO₄(z-t)、BiVO₄(s-m) and BiVO₄(s-t). In the three crystal forms, BiVO is adopted₄(s-m) highest activity, although BiVO₄The crystal structure of (z-t) is relatively close to that of (z-t), but the photocatalytic activities of the (z-t) and the (z-t) are greatly different. The main reason is BiVO₄The forbidden band width of (z-t) is 2.9eV, and the response range is mainly in the ultraviolet region (300 nm)<λ<380 nm); and BiVO₄The forbidden band width of (s-m) is only 2.4eV, and the response range can be extended to the visible light region (lambda)>420 nm). Single BiVO₄(s-m) has the defects of high photoinduction carrier recombination rate, low quantum yield, low visible light response and the like, and limits practical application. Some increase of BiVO₄Methods for photocatalytic activity have been developed, such as noble metal deposition, element doping, and heterojunction formation. In previous studies, the two most common types of heterojunctions were the p-n heterojunction and the Z-type heterojunction. The conventional p-n heterojunction system improves the carrier separation efficiency and visible light response, but reduces the redox capacity due to the reduction of the conduction band and the increase of the valence band. Compared with the traditional heterojunction, the Z-type heterojunction is beneficial to the separation of current carriers and can optimize the oxidation reduction capacity at the same time. Adopts Z-shaped heterojunction to build novel BiVO₄Based on a catalyst to improve the photocatalytic performance. The heterostructure has good prospect for degrading organic compounds. Typical semiconductors g-C₃N₄Has the advantages of large specific surface area, proper energy band structure, good chemical stability and the like. Considering g-C in general₃N₄And BiVO₄、Bi₂WO₆、SnS₂The Z-type heterojunction is constructed through coupling, and the heterojunction can provide a better way for promoting the separation and transfer of photogenerated electron-hole pairs.

g-C₃N₄The relatively wide base band gap (2.71eV) essentially limits its potential for use in the visible light regime. For a single g-C₃N₄The material(s) of the material(s),none of the techniques can maintain its high photocatalytic efficiency while extending its activity to the longer wavelength end of the solar spectrum, e.g., 700 nm. Thus, g-C₃N₄Matrix composites or hybrid materials are an alternative material. Doping of non-metal elements, such as boron, carbon, sulfur, selenium, phosphorus and the like, is an effective way for reducing the reserve volume of the coal bed gas. These elements are rich in physical substances, free of metals and less toxic. In addition, the crystal structure of the photocatalyst is greatly different from that of the well-known ionic crystal photocatalyst, so that the photocatalyst has a special electronic structure and can be researched as an unrivaled elementary photocatalyst to find that g-C₃N₄Can be kept stable at 600 ℃ and can be completely decomposed at 750 ℃, and has better thermal stability. In addition, g-C₃N₄The polymer is cheap and nontoxic, can be easily prepared from ready-made precursors, and the polymer structure of the polymer is easy to improve the optical and electrical properties of the polymer by various modification means.

BiVO of great elegance₄/g-C₃N₄Preparation of nano heterojunction photocatalytic material and its performance research [ D]Zhejiang university adopts in-situ growth method to control BiVO₄At g-C _₃N_₄The growth is carried out in the gaps of the nano particles, and the combination between two phases is further enhanced through calcination to prepare the g-C₃N₄/BiVO₄A composite photocatalytic material. The amount of cetyltrimethylammonium bromide (CTAB), H, was studied₂BiVO (bismuth oxide) under O dosage and hydrothermal reaction condition₄The structural appearance and the influence rule of the performance change.

CN106492871A discloses a bismuth vanadate-loaded composite photocatalyst prepared by hybridizing g-C with phosphorus, and a preparation method thereof₃N₄Nanosheet as a carrier, and phosphorus hybridized g-C₃N₄The nano-chip is decorated with BiVO₄And (3) granules. The preparation method is to hybridize phosphorus to g-C₃N₄Mixing the nanosheets with a nitric acid solution containing ammonium vanadate and bismuth nitrate, ultrasonically dispersing, stirring, mixing with urea, and heating in a water bath to obtain the nano-particles. The difference of the invention is that BiVO₄BiVO with particles as carriers₄On the granulePhosphorus hybridized g-C3N4 nanosheets are modified. The composite photocatalyst has the advantages of high photocatalytic activity, good stability and the like, and the preparation method has the advantages of simplicity, simplicity and convenience in operation, low cost, low energy consumption and the like.

BiVO prepared by existing method₄The heterojunction still has certain defects, and the catalytic performance needs to be further improved. However, how to prepare BiVO with excellent performance₄Heterojunctions remain a challenging task.

Disclosure of Invention

The invention aims to overcome at least one defect of the prior art and provide phosphorus-doped g-C with more excellent photocatalytic performance₃N₄/BiVO₄A heterojunction and its applications.

The technical scheme adopted by the invention is as follows:

in a first aspect of the present invention, there is provided:

phosphorus-doped g-C₃N₄/BiVO₄The preparation method of the heterojunction comprises the following steps:

preparation to give phosphorus-doped g-C₃N₄Marked as PCN;

dissolving a Bi salt in a solvent to be marked as solution A, and dissolving a vanadium salt in the solvent to be marked as solution B;

adding PCN into the solution A and/or the solution B, and uniformly mixing to obtain solution C;

adjusting the pH value of the solution C to be not less than 9.5, adding EDTA-2Na, and continuously stirring for reaction;

transferring the emulsion obtained by the reaction into a high-pressure kettle to carry out hydrothermal synthesis reaction;

after the hydrothermal synthesis reaction is finished, taking the precipitate, cleaning, drying and grinding to obtain phosphorus-doped g-C₃N₄/BiVO₄A heterojunction.

In some examples, the molar mixing ratio of the Bi salt to the vanadium salt, calculated as Bi and V, is 1: (0.95-1.05).

In some examples, the pH of the solution C is adjusted to 9.5-11.

In some examples, the ratio of the addition amount of EDTA-2Na to the amount of Bi is (100-150) g of EDTA-2 Na: 1mol of Bi.

In some examples, the temperature of the hydrothermal synthesis is 160-200 ℃.

In some examples, the hydrothermal synthesis time is 8-20 h.

In some examples, the ratio of PCN to Bi is (0.04 to 5) g PCN: 1mol of Bi.

In some examples, the Bi salt is selected from bismuth nitrate.

In some examples, the vanadium salt is selected from NH₄VO₃。

In some examples, the phosphorus is doped with g-C₃N₄The preparation method of the powder comprises the following steps: urea and melamine were dissolved in water in a mass ratio of 1:1 and (NH) was added₄)₂HPO₄Uniformly dispersing, drying, fully grinding, transferring into a crucible, heating to 500-600 ℃, completely calcining, cooling, and grinding for the second time to obtain phosphorus-doped g-C₃N₄Powder of, wherein (NH)₄)₂HPO₄The addition amount of (B) is 0.04% of the total mass of urea and melamine.

In a second aspect of the present invention, there is provided:

a method for treating organic waste water comprising using the phosphorus-doped g-C of the first aspect of the present invention₃N₄/BiVO₄The heterojunction is subjected to photocatalytic degradation.

The invention has the beneficial effects that:

phosphorus doped g-C of some embodiments of the invention₃N₄/BiVO₄The heterojunction is mainly in a thin rod shape, tiny PCN particles are attached to the thin rod, the layered size is about 150-300 nm, micropores exist on a rod-shaped main body, the PCN and the BVO are in close contact, and the rod-shaped particles are uniformly dispersed in the composite catalyst. This structure allows the phosphorus to be doped with g-C₃N₄/BiVO₄The heterojunction has a plurality of catalytic sites, and the photocatalytic capacity of the heterojunction can be remarkably improved.

Phosphorus doped g-C of some embodiments of the invention₃N₄/BiVO₄The heterojunction has good performance of photocatalytic degradation of organic matters.

Drawings

FIG. 1 is an SEM image of various samples;

FIG. 2 is a TEM image of sample 1-PCN/BVO;

FIG. 3 is a HRTEM image of sample 1-PCN/BVO;

FIG. 4 is a mapping chart of the sample;

FIG. 5 is an XRD pattern of different samples;

FIG. 6 is a graph of infrared spectra of different samples;

FIG. 7 is an XPS plot of sample 1-PCN/BVO;

FIG. 8 is a graph of light absorption characteristics of different samples;

FIG. 9 is a graph showing the variation of the TC peak observed when the 1-PCN/BVO composite catalyst degrades a TC solution;

FIG. 10 is fluorescence spectra of different samples;

FIG. 11 is the transient photocurrent response results for different samples;

FIG. 12 is a graph of the effect of catalyst concentration on photocatalytic performance;

FIG. 13 is the effect of different initial concentrations of TC solution on degradation efficiency;

FIG. 14 is a graph of the photocatalytic degradation of TC over different catalysts;

FIG. 15 is a graph of the effect of different water sources on photocatalytic performance;

FIG. 16 is a graph of the effect of different active oxidant quenchers on photocatalytic efficiency;

FIG. 17 shows ESR test results;

FIG. 18 is the cycle efficiency of the catalyst;

FIG. 19 shows XRD spectrum and XPS spectrum of recovered 1-PCN/BVO.

Detailed Description

The technical scheme of the invention is further illustrated by combining examples and experiments.

g-C₃N₄Doping with phosphorus g-C₃N₄Preparation of

For convenience of comparison, g-C₃N₄The preparation method comprises the following steps:

urea and melamine were mixed in a mass ratio of 1:1 and then ground into powder with an agate mortar. Then thePlacing the powder in a ceramic crucible, and heating at 550 deg.C in a muffle furnace for 5 deg.C for min^-1The temperature rising rate of (2) was calcined at room temperature of 25 ℃ for 4 hours. After the reaction is finished, naturally cooling the obtained sample to room temperature, putting the sample into agate mortar, and grinding the mixture into powder to obtain g-C₃N₄(referred to as CN).

Phosphorus doped g-C₃N₄The preparation method comprises the following steps:

urea and melamine in a mass ratio of 1:1 and 0.01 g (NH)₄)₂HPO₄Grinding into powder, transferring the mixture into crucible, heating at 550 deg.C for 4 hr at a heating rate of 5 deg.C for min^-1. Calcining, grinding to obtain yellow powder to obtain phosphorus-doped g-C₃N₄(denoted as PCN).

Phosphorus doped g-C₃N₄/BiVO₄And BiVO₄Preparation of

Phosphorus doped g-C₃N₄/BiVO₄The preparation of (1):

0.005mol of Bi (NO)₃)₃·5H₂O and 0.005mol NH₄VO₃Dissolving in 15mL of ethylene glycol respectively, and marking as a solution A and a solution B respectively;

then adding a certain amount of PCN into the solution A, magnetically stirring and mixing the two solutions to obtain a solution C, adjusting the pH value of the solution C to about 10 by using ammonia water, and then adding 0.600g of EDTA-2 Na;

after stirring for 20 minutes, the synthesized yellow emulsion was transferred to a 50 ml stainless steel autoclave, heated to 180 ℃ and kept at 180 ℃ for 10 hours;

the yellow precipitate obtained finally is washed by deionized water and ethanol for six times alternately, and then is collected and ground into powder after being kept in an oven at 80 ℃ for 12 hours.

The amounts of PCN added to solution a were 0.0002, 0.001, 0.005, 0.025, and 0.5g, respectively, and the heterojunction photocatalysts were named x-PCN/BVO (x ═ 0.2, 1, 5, 25, and 500), respectively.

Preparation of simple BiVO₄(BVO) for comparison, the preparation method is the same as that of phosphorus-doped g-C₃N₄/BiVO₄Preparation ofAdditionally, no PCN was added to the solution A.

Performance detection

Fig. 1 is an SEM image of different samples, wherein (a) pure CN; (b) pure PCN; (c) pure BVO; (d) 1-PCN/BVO. As can be seen, the pure CN samples exist mainly in the form of microporous blocks and layers, the pure PCN samples mainly have porous sheets, and the pure BVO has a butterfly shape and a size of about 200 nm. The 1-PCN/BVO form is mainly a fine rod, and fine particles are attached to the fine rod, because the composite catalyst takes bismuth vanadate as a substrate, the fine particles attached to the fine rod are PCN, and the layer size is about 200 nm. Not only the fine particles are attached to the surface of the 1-PCN/BVO composite catalyst, but also micropores exist on the rod shape. The PCN and the BVO are closely contacted and uniformly dispersed in the composite catalyst as rod-shaped particles. Compared with pure PCN and pure BVO catalysts, the 1-PCN/BVO composite catalyst not only has a micropore structure, but also has a combined rod-shaped and block-shaped structure. After the PCN is added, the composite catalyst keeps close contact and uniform dispersion, and the photocatalytic efficiency of the material is improved.

To further confirm the formation of the 1-PCN/BVO photocatalyst, TEM, High Resolution Transmission Electron Microscope (HRTEM) images and mapping patterns of the samples were taken.

FIG. 2 is a TEM image of sample 1-PCN/BVO showing a mixture of small particles attached to the rod, forming a 1-PCN/BVO photocatalyst with an average size of 100 to 200nm, and observing the presence of some micropores on the catalyst.

FIG. 3 is an HRTEM image of sample 1-PCN/BVO. As can be seen, the 1-PCN/BVO photocatalyst has a small crystallite size relative to the particle size (10-100 nm). The smaller grain size indicates that the BVO microplates used in this study consist of many crystalline or polycrystalline structures observed in SAED mode (c). The PCN was successfully deposited as platelets on the BVO microplate surface (d), corresponding to a lattice of 0.491 nm. The lattice spacing of the surface of the 1-PCN/BVO photocatalyst composite material is 0.462nm, and can be directed to the (002) plane of PCN (JCPDS 87-526).

FIG. 4 is a mapping chart of the sample in which (a) is a 1-PCN/BVO mapping chart; (b) the elements of (a) to (g) correspond to elements of C, N, Bi, O, P and V, respectively. The uniform distribution of C, N, Bi, O, P and V elements can be clearly seen, which indicates that the composite catalyst is successfully prepared. The mapping element ratio is shown in Table 3-1, and it can be seen that the P ratio is only 0.04% less and the N ratio is 3.41% less, which also explains why the XPS P, N peak has no peak, and the 1-PCN/BVO catalyst recombination is successful, as can be seen from the element composition.

TABLE 3-11 elemental content scale of-PCN/BVO

Pure CN, pure PCN, pure BiVO₄And XRD patterns of PCN/BVO composite photocatalysts with different mass ratios are shown in figure 5. For pure CN and PCN, a diffraction peak at 27.40 degrees can be clearly seen, and a less obvious diffraction peak at 13.04 degrees is also clearly seen, which respectively corresponds to a (002) diffraction crystal face and a (100) diffraction crystal face of CN (JCPDS-87-1526), and the synthesized CN has good crystallinity, and the diffraction peak of the PCN is basically the same as that of the CN, except that after the PCN is added with phosphorus, the diffraction peak at 27.40 degrees is changed into small and large, but has the good performance of the CN, and even the photocatalysis performance is improved. Pure BVO showed a series of narrow and sharp diffraction peaks, and all characteristic peaks of the prepared pure BVO were observed to be in full agreement with the standard monoclinic phase (PDF #14-0688) of BVO, indicating that the preparation of BVO was successful. For a series of PCN/BVO composite photocatalysts, the characteristic peak of PCN is observed to gradually appear as the content of PCN is increased. The peak of P doping at 28.2 ℃ is significantly higher for 1-CN/BVO compared to 1-PCN/BVO. An XRD pattern of the PCN/BVO sample shows that a characteristic diffraction peak is composed of two phases of PCN and BVO, and the PCN/BVO composite photocatalyst is successfully prepared.

The infrared spectrums of the CN, PCN, BVO and 1-PCN/BVO composite catalyst are shown in FIG. 6. For CN, PCN, from 3000 to 3300cm^-1The wide absorption band of (a) can be attributed to the N-H tensile vibration mode; 1300-1700 cm^-1Dense bands within the range are typical tensile vibrational modes for C-N and C ═ N heterocycles; while the PCN is located at 785cm^-1The reduction of the peak may be due to the addition of a phosphorus source to CNInfluence. In BVO, at 760cm^-1Can be attributed to the VO₄Antisymmetric stretching vibration mode of V-O bond in tetrahedron. The main characteristic peak of PCN at 785cm can be observed in the FTIR spectrum of the 1-PCN/BVO composite catalyst^-1With a depression therein, compared to the characteristic peak of BVO, indicating the presence of PCN material, 1300-^-1In the dense band in the range, it was observed that BVO and PCN phases coexisted in the 1-PCN/BVO composite catalyst, in accordance with XRD analysis.

The XPS was used to examine the elemental chemical composition and state of the 1-PCN/BVO sample, and the results are shown in FIG. 7, in which (a) the 1-PCN/BVOXPS full spectrum; (b) c_1s，(c)V_2p，(d)O_1s，(e)Bi_4f(ii) high-resolution XPS spectra of (f) BVO and PCN. The results show that P, C, N, Bi, V and O exist in the composite material. Since the PCN was added in a small amount, the P, N characteristic peak appeared not to be significant, and a corresponding single graph was not given, although the presence of P, N could be seen from the full spectrum. As can be seen from the XPS spectrum (b) of C1s, the two peaks at 284.88 and 289.43eV are respectively assigned to sp²C-C bonds and sp²Bond carbons, these two peaks are considered to be the predominant carbon species in CN. (e) Is Bi_4fXPS spectra. The two single peaks at 159.28eV and 164.58eV in the figure can be assigned to Bi 4f_7/2And Bi 4f_5/2. The two most obvious single peaks appearing at 516.73eV and 529.98eV respectively correspond to V2 p_3/2And V2 p_1/2The peak pattern is shown in FIG. 6-c. The O1s spectrum shown in FIG. 6-d has a distinct characteristic peak at 529.93 eV. The XPS results further confirmed that PCN was introduced into BiVO4a, consistent with XRD, FTIR, SEM and HRTEM characterization results. As the VB-XPS spectrum is plotted in FIG. 6-f, since the first half of the PCN has two slopes, the slope in the front part is smaller than that in the back part, so that the slope is larger when the slope is plotted, and the value intersected with the x axis is E_VBThus E of PCN_VB3.83eV, E of BVO_VB＝1.55eV。

The light absorption characteristics of CN, PCN, BVO and 1-PCN/BVO composite catalysts were measured by UV-visible DRS spectroscopy, and the test results of the four catalysts are shown in FIG. 8. When the particle diameter is reduced to a certain value, the energy gap is widened. The synthesized sample showed strong absorption in the visible range. The steep shape indicates that the strong absorption is due to band gap transitions and not from impurity levels. After the PCN is introduced, the absorption capacity of the composite sample is improved, and the photodegradation activity is improved. In addition, the absorbance margin of the 1-PCN/BVO composite catalyst is slightly blue-shifted compared with that of pure CN and PCN, which indirectly indicates that the redox ability of the 1-PCN/BVO composite catalyst has an important influence on the improvement of the activity. In addition, the forbidden bandwidth of BVO and PCN can be calculated according to the following formula:

αhν＝A(hν-E_g)^n/2 (3-1)

wherein α, v, a, h and Eg represent an absorption coefficient, an optical frequency, a constant, a planck constant and a band gap energy, respectively.

From FIG. 8, it can be calculated that the band gap energies of BVO and PCN are 2.6eV and 2.3eV, respectively.

FIG. 9 shows the variation of TC peak studied when the 1-PCN/BVO composite catalyst degrades TC solution, and it can be seen that raw water TC has an obvious characteristic peak at 357nm, and with the addition of the catalyst, the characteristic peak at 357nm of TC becomes smaller or even disappears under the irradiation of visible light, and the secondary characteristic peak near 290nm shifts, which indicates that TC generates other products in the degradation process, and the 1-PCN/B VO composite catalyst can effectively photocatalytically degrade TC.

The fluorescence spectrum of the catalyst is shown in FIG. 10, and the emission intensity sequence of the four samples is CN>PCN>BVO is 1-PCN/BVO composite catalyst. The results show that the emission intensity of the 1-PCN/BVO composite catalyst heterostructure is obviously lower than that of pure CN and PCN, but is similar to that of the BVO sample, which is probably because the composite catalyst takes BVO as a substrate, and the PCN is added in a small amount, so the emission intensities of the two are similar, which means the excited state in the 1-PCN/BVO composite catalyst^-/h⁺The composite efficiency of the pair is higher. PL results demonstrate that the co-operation of heterostructures and P doping between two semiconductors promotes photogeneration e^-/h⁺And (4) separating the pairs.

The number of electron-hole pairs is revealed using the transient photocurrent response, and the results are shown in fig. 11. It can be seen from the figure that the original CN intensity is the lowest, while the PCN intensity is stronger because P is doped on the basis of CN, so that the photocurrent intensity of PCN is higher than that of pure CN. The photocurrent intensity of the pure BVO is lower than that of the 1-PCN/BVO composite catalyst, namely, the 1-PCN/BVO composite catalyst shows stronger transient photocurrent response, which can be attributed to the heterojunction effect of the phosphorus-doped carbon nitride and the bismuth vanadate. The 1-PCN/BVO composite catalyst in the figure has the best transient photocurrent response.

Evaluation of photocatalytic Activity and stability

Influence of different amounts of photocatalyst

The cost of the photocatalyst has a significant weight in commercial applications considering the practical application of the photocatalyst. Therefore, aiming at the problem, the experiment researches the influence of different dosage of the photocatalyst on the photodegradation TC of the 1-PCN/BVO composite material. The experiment designs the influence of the photocatalytic performance of the catalyst concentration in the range of 0.05-2.0 g/L as shown in FIG. 12, and when the dosage of the prepared photocatalyst is increased from 0.05g/L to 2.0g/L, the relative photocatalytic removal efficiency of TC is increased from 74.62% to 89.29%. In the process, the dosage of the photocatalyst is gradually increased, and the photocatalytic efficiency is reduced after the concentration of the catalyst reaches 2.0 g/L. This result demonstrates that proper photocatalyst dosage is critical to achieve optimal photocatalyst performance. The phenomenon of the above experiment can be explained from the following aspects:

the higher photocatalyst dosage can provide more active sites and active species in the photocatalytic degradation process, thereby improving the photocatalytic performance;

secondly, when the dosage of the photocatalyst exceeds the optimal value, the excessive photocatalyst can increase the turbidity of the reaction solution and reduce the transmittance of the irradiated light, thereby inhibiting the photocatalytic activity of the reaction system to a great extent.

In a laboratory, considering that the preparation of the catalyst is not easy, and the total volume of the degraded TC solution is 100mL, the dosage of the photocatalyst is finally determined to be 0.2g/L in all the degradation experiments.

Influence of different contaminant concentrations

Since the initial concentration of the target pollutant also affects the performance of the photocatalyst, the degradation efficiency of TC solution with different initial concentrations in the reaction system with the catalyst concentration of 1-PCN/BVO 20mg/L is shown in FIG. 13, and when the initial concentration of TC is increased from 10mg/L to 30mg/L, the degradation efficiency of TC is decreased from 80.63% to 59.62%. Experimental results have shown that higher initial contaminant concentrations can adversely affect the photocatalytic reaction process, possibly due to reduced transmission of visible light through the reaction solution due to reduced opportunity and path for transmission of photons. Thus, fewer photons are allowed to migrate to the surface and active sites of the photocatalyst. In addition, intermediates generated during photocatalytic degradation may occupy limited reaction centers, compete with TC molecules and as the initial concentration of TC increases, competition increases, resulting in relatively low removal efficiency. Therefore, to fully utilize the photocatalytic activity of the photocatalyst and reduce the effect of the TC concentration on the analysis in this study, the TC concentration was selected to be 10mg/L throughout the experiment.

Different proportions of photocatalyst degradation efficiency

The photocatalytic degradation curves of TC over different catalysts are shown in fig. 14. The blank experiment shows that, in the absence of a photocatalyst, TC is degraded by 1.01% under 60 minutes of irradiation, and is almost not degraded, and the result of the control experiment without a photocatalyst shows that the photolysis effect is negligible during the photocatalytic degradation. After the photocatalyst is added, the TC concentration is gradually reduced under the irradiation of visible light. As can be seen from fig. 14, the degradation efficiencies of pure CN, pure PCN and BVO were 23.75%, 52.02% and 49.54%, respectively, under 60 minutes of visible light irradiation. Compared with pure CN, pure PCN and BVO, the removal rate of the x-PCN/BVO nano composite material is gradually improved and then reduced along with the reduction of the content of PCN, the degradation effect reaches a peak value when the amount of PCN is 0.001g, and the photocatalytic activity of the x-PCN/BVO composite material is effectively improved. On the basis, in order to prove that P in PCN plays a role in comparison with the optimal addition amount of 0.001g of PCN, the 1-CN/BVO composite material is prepared by the same preparation method, 10mg/L of TC solution is degraded by comparing the 1-CN/BVO with the 1-PCN/BVO, the efficiencies are 65.36% and 77.33% respectively, and the P doping can be reacted to improve the photocatalytic activity of the composite material.

In order to compare the photocatalytic activities of different photocatalysts more intuitively, the dynamics of degrading TC by photocatalysis are also explored, and a first-level (3-2) model and a second-level (3-3) model are simulated, and are shown in a table 3-2.

-ln(C/C₀)＝k₁ t (3-2)

1/C-1/C₀＝k₂ t (3-3)

TABLE 3-2 first and second kinetics of TC degradation

Wherein k is₁、k₂(min^-1) Is the apparent rate constant simulating first and second order kinetics. C₀And C are the concentrations of the TC solution at the time of initial and light reaction t respectively.

And from Table 3-2 it can be seen that: quasi-second order kinetics of R²The two-stage model is selected because it is better than the first stage. And in secondary kinetics, where the reaction rate constants for pure PCN and BVO are 2.90X 10, respectively, as calculated by fitting^-3min^-1And 2.24X 10^-3min^-1. The reaction rate constant of the compounded photocatalyst 1-PCN/BVO was 3.16X 10^-2min^-1The reaction rate constant of the 1-PCN/BVO sample is 10.9 times that of PCN and 14.1 times that of BVO, and the sample has good photocatalytic performance. Therefore, the 1-PCN/BVO composite catalyst can remarkably improve the activity of the photocatalyst and accords with the secondary kinetics of TC degradation.

Influence of different Water sources

Since the initial state of the reaction substrate has a great influence on the photocatalytic performance in consideration of practical use, the experiment collected various water sources as the 1-PCN/BVO composite material for removing the TC solution. The water sources collected this time are respectively: deionized water in a laboratory, tap water in a tap, lake water in a ferry school area and water in a ferry bridge of the Xiaodongjiang officer, the water sources are taken as main solvents, tetracycline hydrochloride medicament is added to prepare 10mg/L TC solution, and whether different water sources influence the photocatalysis performance or not is analyzed. The degradation efficiency of TC in deionized water, tap water, lake water and Xiaodongjiang water is 80.63%, 81.06%, 66.22% and 65.24% respectively, as shown in FIG. 15. In these water sources, the efficiency of TC solution prepared from tap water is slightly higher than that of TC solution prepared from deionized water due to the existence of various competitive substances, the error source may be experimental operation error, or it may be that a substance existing in tap water can promote the activity of the catalyst, and the removal rate of other samples is lower than that of deionized water, but the effect is still good. The results show that the prepared 1-PCN/BVO composite material has the potential of treating practical antibiotic wastewater.

Influence of different active species

Generally, to verify the reaction process and electron transfer mechanism, three common active oxidants need to be examined: hydroxyl radical (. OH), hole (h)⁺) And superoxide radical (. O)₂ ^-) The function of (1). We performed quenching experiments on free radicals generated during the photocatalytic process under visible light in 1-PCN/BVO, and the experimental results are shown in FIG. 16. Disodium ethylenediaminetetraacetate (EDTA-2Na), ascorbic acid and Isopropanol (IPA) were used as h⁺、·O₂ ^-And OH in an amount of 0.1mM, 1mM, and 1mM, respectively. As can be seen from FIG. 16, the addition of ascorbic acid significantly inhibited the photodegradation of TC, and compared to the blank without the addition of the quencher, the addition of ascorbic acid inhibited the TC by 61.97% within 60min, indicating O₂ ^-Is the most important active substance in the TC photodegradation process. After EDTA-2Na is added, the degradation rate of TC in 60min is also greatly reduced by 39.73%, which indicates that O is removed₂ ^-Outer, h⁺Is another major active. When IPA was added, the degradation rate of TC was slightly reduced compared to the blank, and the inhibition rate was 0.81% in 60min, indicating that OH is a minor active species during the photocatalytic reaction.

To further determine the role of free radicals in the photocatalytic degradation of organic processes on 1-PCN/BVO,the catalyst is sent out to make Electron Spin Resonance (ESR), which is a very important modern analytical technique for detecting uncoupled electrons in substances and their interactions with surrounding atoms, and which has the advantages of high sensitivity and resolution and no damage to the sample structure during the measurement. The experimental sample is mainly made of superoxide radical (. O)₂ ^-) And capture of hydroxyl radicals (. OH). ESR test results are shown in FIG. 17, and the test results were 5min, 15min and 30min under visible light irradiation, respectively, and DMPO/. O could be detected within 30min₂ ^-Four-wire ESR signal (a) of typical mode. And in DMPO/. O₂ ^-No characteristic signal appears in the dark, confirming that O is generated in the photocatalysis process₂ ^-A free radical. In addition, under the irradiation of visible light, 5min, 15min and 30min are respectively detected, and under the condition of irradiation of visible light, a characteristic signal (b) related to DMPO/. OH is detected, which indicates that OH free radicals are also formed in the photocatalysis process. ESR analysis and radical trapping experimental results show that O is generated in the photocatalysis process₂ ^-The component plays the most important role, OH is the secondary active component.

Reusability of photocatalyst

Considering the utility of the photocatalyst, its cycling efficiency as can be seen in FIG. 18, no significant deactivation was observed in the heterojunction photocatalyst after 3 consecutive cycles of the 1-PCN/BVO composite catalyst. Meanwhile, XRD spectrum and XPS spectrum of the 1-PCN/BVO after the first recovery and the second recovery are shown in figure 19. Similar to the previous samples. It can be shown that the prepared 1-PCN/BVO heterojunction photocatalyst shows excellent light stability in the photocatalytic degradation reaction.

The foregoing is a more detailed description of the invention and is not to be taken in a limiting sense. It will be apparent to those skilled in the art that simple deductions or substitutions without departing from the spirit of the invention are within the scope of the invention.

Claims

1. Phosphorus-doped g-C₃N₄/BiVO₄The preparation method of the heterojunction comprises the following steps:

preparation to give phosphorus-doped g-C₃N₄Marked as PCN;

2. Phosphorus doped g-C according to claim 1₃N₄/BiVO₄A heterojunction, characterized in that: calculated by Bi and V, the molar mixing ratio of the Bi salt to the vanadium salt is 1: (0.95-1.05).

3. Phosphorus doped g-C according to claim 1₃N₄/BiVO₄A heterojunction, characterized in that: and adjusting the pH value of the solution C to 9.5-11.

4. Phosphorus doped g-C according to claim 1₃N₄/BiVO₄A heterojunction, characterized in that: the ratio of the addition amount of EDTA-2Na to the amount of Bi is (100-150) g of EDTA-2 Na: 1mol of Bi.

5. Phosphorus doped g-C according to claim 1₃N₄/BiVO₄A heterojunction, characterized in that: the temperature of the hydrothermal synthesis is 160-200 ℃; and/or the hydrothermal synthesis time is 8-20 h.

6. Phosphorus doped g-C according to any of claims 1 to 5₃N₄/BiVO₄A heterojunction, characterized in that: the dosage ratio of PCN to Bi is (0.04 to E)5)g PCN：1 mol Bi。

7. Phosphorus doped g-C according to any of claims 1 to 5₃N₄/BiVO₄A heterojunction, characterized in that: the Bi salt is selected from bismuth nitrate.

8. Phosphorus doped g-C according to any of claims 1 to 5₃N₄/BiVO₄A heterojunction, characterized in that: the vanadium salt is selected from NH₄VO₃。

9. The method according to any one of claims 1 to 5, wherein: the phosphorus is doped with g-C₃N₄The preparation method of the powder comprises the following steps: urea and melamine were dissolved in water in a mass ratio of 1:1 and (NH) was added₄)₂HPO₄Uniformly dispersing, drying, fully grinding, transferring into a crucible, heating to 500-600 ℃, completely calcining, cooling, and grinding for the second time to obtain phosphorus-doped g-C₃N₄Powder of, wherein (NH)₄)₂HPO₄The addition amount of (B) is 0.04% of the total mass of urea and melamine.

10. A method for treating organic wastewater, comprising using the phosphorus-doped g-C of any one of claims 1 to 9₃N₄/BiVO₄The heterojunction is subjected to photocatalytic degradation.