CN108786895B - BiOCOOH/g-C3N4 composite photocatalyst and its preparation method and application - Google Patents

Abstract

The invention discloses a BiOCOOH/g-C ₃ N ₄ composite photocatalyst, a preparation method and application thereof, and relates to the technical field of photocatalysis. In the BiOCOOH/g‑C ₃ N ₄ composite photocatalyst, BiOCOOH is embedded in the g‑C ₃ N ₄ lamella structure; the molar ratio of BiOCOOH and g‑C ₃ N ₄ is (0.15～4.75):1. The composite photocatalyst has strong visible light response capability, high photo-generated electron-hole pair separation efficiency, high catalytic activity, and high visible light catalytic degradation efficiency for wastewater containing organic dyes. The preparation method includes the following steps: synthesizing a composite photocatalyst with g-C ₃ N ₄ , a soluble bismuth salt and a solvent by a hydrothermal method; the molar ratio of the soluble bismuth salt and g-C ₃ N ₄ is (0.15-4.75):1 . The preparation method has the advantages of cheap and readily available raw materials, simple process, simple operation, and no secondary pollution.

Description

BiOCOOH/g-C3N4 composite photocatalyst and its preparation method and application

technical field

The invention relates to the technical field of preparation of nanometer functional materials and photocatalysis, in particular to a BiOCOOH/gC ₃ N ₄ composite photocatalyst and a preparation method and application thereof.

Background technique

With the rapid development of modern society and economy, the problems of environmental pollution and energy crisis have become more and more serious, which have seriously threatened human health and social development. Semiconductor photocatalysis technology has shown superior performance in _solving environmental pollution and energy crisis. and CO ₂ , both show very good application prospects.

Some traditional semiconductor photocatalysts, such as the well-studied _TiO2 photocatalysts, have the advantages of low price, high chemical stability, and non-toxicity, but their low chemical energy level positions, large band gaps, and low quantum efficiency limit their practical applications. application. Cadmium sulfide (CdS) and zinc oxide (ZnO) have certain advantages as traditional semiconductor photocatalysts, but the chemical properties of these two are unstable, and photodissolution occurs at the same time as photocatalysis, and the dissolution of harmful metal ions has certain effects. biological toxicity. Moreover, the photocatalytic activity of traditional semiconductor photocatalysts is greatly limited due to the narrow photoresponse range and high photogenerated electron-hole recombination probability.

Traditional single gC ₃ N ₄ photocatalysts have the disadvantages of small specific surface area and high recombination probability of photogenerated electron-hole pairs, which limit their photocatalytic activity. Its catalytic activity can be improved by compounding with some semiconductor materials. However, most of the semiconductor materials currently used for compounding with gC ₃ N ₄ are the semiconductor materials with high price or complicated synthesis process, which reduces the advantage of gC ₃ N ₄ as a low-cost catalyst, thus affecting its practical application. .

In view of this, the present invention is proposed.

SUMMARY OF THE INVENTION

The first object of the present invention is to provide a BiOCOOH/gC ₃ N ₄ composite photocatalyst, which is formed by embedding BiOCOOH in the lamellar structure of gC ₃ N ₄ , wherein the molar ratio of BiOCOOH and gC ₃ N ₄ is (0.15 ~4.75): 1. The composite photocatalyst has strong visible light response ability, high photo-generated electron-hole pair separation efficiency, high catalytic activity, and high visible light catalytic degradation efficiency for wastewater containing organic dyes.

The second object of the present invention is to provide a preparation method of BiOCOOH/gC ₃ N ₄ composite photocatalyst, which has the advantages of cheap and readily available raw materials, simple process, simple operation and no secondary pollution.

The third object of the present invention is to provide the application of BiOCOOH/gC ₃ N ₄ composite photocatalyst in photocatalytic degradation of dye wastewater.

In order to realize the above-mentioned purpose of the present invention, the following technical solutions are specially adopted:

In a first aspect, the present invention provides a BiOCOOH/gC ₃ N ₄ composite photocatalyst, wherein the BiOCOOH is embedded in the gC ₃ N ₄ sheet structure;

The molar ratio of the BiOCOOH to the gC ₃ N ₄ is (0.15-4.75):1.

Preferably, based on the technical solution provided by the present invention, the molar ratio of the BiOCOOH to the gC ₃ N ₄ is (0.5-3):1, preferably (0.8-1.5):1.

Preferably, on the basis of the technical solution provided by the present invention, the microstructure of the BiOCOOH is flower shape, white fungus shape, sponge shape or spherical shape;

Preferably, the microstructure of the BiOCOOH is flower-like.

Preferably, based on the technical solutions provided by the present invention, the particle size of the BiOCOOH/gC ₃ N ₄ composite photocatalyst is 300-1200 nm, preferably 400-1100 nm, more preferably 500-1000 nm.

In the second aspect, the present invention provides a preparation method of BiOCOOH/gC ₃ N ₄ composite photocatalyst, comprising the following steps:

The BiOCOOH/gC ₃ N ₄ composite photocatalyst was synthesized by hydrothermal method with gC ₃ N ₄ , soluble bismuth salt and solvent; the molar ratio of soluble bismuth salt and gC ₃ N ₄ was (0.15～4.75):1;

Preferably, the soluble bismuth salt includes one of bismuth nitrate pentahydrate, bismuth chloride or bismuth bromide, preferably bismuth nitrate pentahydrate;

Preferably, the solvent comprises one of N,N-dimethylformamide, mannitol, ethylene glycol, diethylene glycol or triethylene glycol, preferably N,N-dimethylformamide;

Preferably, the molar ratio of the soluble bismuth salt to gC ₃ N ₄ is (0.5-3):1, more preferably (0.8-1.5):1.

Preferably, on the basis of the technical solution provided by the present invention, the preparation method of BiOCOOH/gC ₃ N ₄ composite photocatalyst includes the following steps:

The soluble bismuth salt is added to the solvent, mixed uniformly until transparent, water and gC ₃ N ₄ are added, and the mixture is uniformly mixed and then heat-treated to obtain a BiOCOOH/gC ₃ N ₄ composite photocatalyst.

Preferably, on the basis of the technical solution provided by the present invention, the heat treatment conditions include: a heating temperature of 110-130° C. and a heating time of 11-14 h.

Preferably, on the basis of the technical solution provided by the present invention, the preparation method of the BiOCOOH/gC ₃ N ₄ composite photocatalyst further comprises purifying, drying and grinding after heat treatment to obtain the BiOCOOH/gC ₃ N ₄ composite photocatalyst. step;

Preferably, the purification method includes solid-liquid separation, water washing or alcohol washing;

Preferably, the drying conditions include: a drying temperature of 50-70° C., preferably 55-65° C.; and a drying time of 7-14 hours, preferably 8-12 hours.

Preferably, on the basis of the technical solution provided by the present invention, the gC ₃ N ₄ is prepared by a polycondensation method;

Preferably, the preparation method of gC ₃ N ₄ includes the following steps: heat-treating the carbon-nitrogen precursor, heating from normal temperature to 530-570° C. at a constant rate, holding for 3-5 hours, cooling and grinding to obtain gC ₃ N ₄ ;

Preferably, the carbon-nitrogen precursor includes one of dicyandiamide, melamine or aminodicyandiamide;

Preferably, the heating rate is 10-20°C/min.

In a third aspect, the present invention provides the application of the BiOCOOH/gC ₃ N ₄ composite photocatalyst in photocatalytic degradation of dye wastewater.

Compared with the prior art, the beneficial effects of the present invention are:

(1) The BiOCOOH/gC ₃ N ₄ composite photocatalyst provided by the present invention is composited by embedding BiOCOOH in the lamellar structure of gC ₃ N ₄ . The conduction band and valence band positions of BiOCOOH are more correct than gC ₃ N _4. After the recombination of BiOCOOH and gC ₃ N ₄ , an interfacial heterojunction will be formed at the junction of the two semiconductors, which makes the photogenerated electrons and holes play a role in the heterojunction. Under rapid migration and separation, each undergoes a redox reaction. The composite photocatalyst has strong visible light response capability, high photo-generated electron-hole pair separation efficiency, high catalytic activity, and high visible light catalytic degradation efficiency for wastewater containing organic dyes.

(2) The preparation method of the BiOCOOH/gC ₃ N ₄ composite photocatalyst provided by the present invention has the advantages of cheap and readily available raw materials, simple process, simple operation and no secondary pollution.

(3) The degradation efficiency of the BiOCOOH/gC ₃ N ₄ composite photocatalyst provided by the present invention to amino black 10B dye is 1.42 times and 2.69 times that of pure gC ₃ N ₄ and pure BiOCOOH, respectively, and the degradation rate of amino black 10B can reach 89.16%.

Description of drawings

Fig. 1 is the transmission electron microscope picture of BiOCOOH/gC ₃ N ₄ composite photocatalyst prepared in Example 4 of the present invention;

2 is a photocurrent response diagram of the pure gC ₃ N ₄ prepared in Comparative Example 1 of the present invention, the pure BiOCOOH prepared in Comparative Example 2 and the BiOCOOH/gC ₃ N ₄ composite photocatalyst prepared in Example 4;

3 is a graph showing the visible light catalytic effect of pure gC ₃ N ₄ prepared in Comparative Example 1, pure BiOCOOH prepared in Comparative Example 2 and BiOCOOH/gC ₃ N ₄ composite photocatalyst prepared in Example 4 on amino black 10B aqueous solution.

Detailed ways

The embodiments of the present invention will be described in detail below with reference to the examples, but those skilled in the art will understand that the following examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. If the specific conditions are not indicated in the examples, it is carried out according to the conventional conditions or the conditions suggested by the manufacturer. The reagents or instruments used without the manufacturer's indication are conventional products that can be purchased from the market.

According to the first aspect of the present invention, a BiOCOOH/gC ₃ N ₄ composite photocatalyst is provided, where BiOCOOH is embedded in the gC ₃ N ₄ lamella structure; the molar ratio of BiOCOOH and gC ₃ N ₄ is (0.15～4.75 ):1.

As a typical non-metallic semiconductor photocatalyst, graphitic carbon nitride (gC ₃ N ₄ ) has been widely used in the fields of photo-splitting water for hydrogen production, photo-degradation of organic pollutants and organic photosynthesis. The band gap of gC ₃ N ₄ is about 2.7 eV, which has a good response to visible light, and it also has good thermal and chemical stability; in addition, gC ₃ N ₄ has a two-dimensional planar conjugated structure (plane Two-dimensional sheet structure) can be used as a good substrate material for the construction of composite photocatalysts. However, traditional single gC ₃ N ₄ photocatalysts have the disadvantages of small specific surface area and high recombination probability of photogenerated electron-hole pairs, which limit their photocatalytic activity.

Bismuth oxyformate (BiOCOOH) is composed of layered [Bi ₂ O ₂ ] ²⁺ and zigzag COOH ^- structures, and the polydentate carboxylic acid groups are arranged into a chain polymer, which can improve its effective absorption of light, and BiOCOOH Compared with other bismuth-based semiconductors, it does not contain toxic elements such as halogen and sulfur, and does not bring secondary pollution to the environment. It is a promising photocatalyst. However, due to the wide band gap of BiOCOOH, it is not suitable for It is conducive to its absorption of visible light.

The _gC3N4 is compounded with _BiOCOOH to form a structure in which _BiOCOOH is embedded in the sheets of _gC3N4 , the molar ratio of _BiOCOOH : _gC3N4 in the _BiOCOOH / _gC3N4 composite photocatalyst is typical but non-limiting Examples are 0.15:1, 0.25:1, 0.3:1, 0.5:1, 0.8:1, 1:1, 1.2:1, 1.5:1, 1.8:1, 2:1, 2.5:1, 3:1 , 4:1 or 4.75:1.

Since both the conduction band and valence band of BiOCOOH are more correct than gC ₃ N ₄ , after the recombination of BiOCOOH and gC ₃ N ₄ , an interfacial heterojunction will be formed at the junction of the two semiconductors, so that the photogenerated electrons and holes are in the heterojunction. Under the action of rapid migration and separation, and their respective redox reactions occur. BiOCOOH/gC ₃ N ₄ composite photocatalyst improves the defects of narrow photoresponse range and low photocatalytic efficiency of single semiconductor photocatalyst, and improves its practical application value. The composite photocatalyst has strong visible light response capability, high photo-generated electron-hole pair separation efficiency, high catalytic activity, and high visible light catalytic degradation efficiency for wastewater containing organic dyes.

In a preferred embodiment, the molar ratio of BiOCOOH and gC ₃ N ₄ in the BiOCOOH/gC ₃ N ₄ composite photocatalyst is (0.5-3):1, preferably (0.8-1.5):1.

By further optimizing the molar ratio of BiOCOOH and gC ₃ N ₄ , the BiOCOOH/gC ₃ N ₄ composite photocatalyst can have a higher visible light catalytic degradation efficiency, and improve its visible light responsiveness and photogenerated electron-hole pair separation efficiency.

3Bi-C, 2Bi-C, 1Bi-C, 0.5Bi-C, 0.3Bi-C and 0.25Bi-C shown in Figure 3 represent the BiOCOOH/gC ₃ N ₄ composite photocatalysts, BiOCOOH and gC ₃ The molar ratios of _N4 were 3:1, 2:1, 1:1, 0.5:1, 0.3:1 and 0.25:1.

In a preferred embodiment, the microstructure of BiOCOOH is flower-like, tremella-like, sponge-like or spherical;

Preferably, the microstructure of BiOCOOH is flower-like.

BiOCOOH with different morphologies can be prepared by solvothermal method, and spherical, sponge-like, tremella-like and flower-shaped BiOCOOH can be prepared by using mannitol, ethylene glycol, diethylene glycol and triethylene glycol as solvents, respectively. The microscopic morphology of BiOCOOH is closely related to the catalytic activity.

BiOCOOH with flower-like microstructure is preferred because of its larger specific surface area and higher degradation catalytic activity, and the BiOCOOH/gC ₃ N ₄ composite photocatalyst obtained by compounding with gC ₃ N ₄ also has higher activity.

In a preferred embodiment, the particle size of the BiOCOOH/gC ₃ N ₄ composite photocatalyst is 300-1200 nm, preferably 400-1100 nm, more preferably 500-1000 nm.

The typical but non-limiting particle size of the BiOCOOH/gC ₃ N ₄ composite photocatalyst is, for example, 300 nm, 500 nm, 700 nm, 900 nm, 1000 nm, 1100 nm or 1200 nm.

The catalyst with small particle size is beneficial to improve the catalytic performance. The photogenerated carriers can migrate from the interior of the catalyst particle to the surface of the particle by diffusion. The probability of recombination with holes will be smaller, and the photocatalytic activity will be higher. In addition, the smaller the particle size of the catalyst, the more particles per unit mass are dispersed in the same solution, so the efficiency of light absorption is higher.

Preferably, the particle size of the BiOCOOH/gC ₃ N ₄ composite photocatalyst is nanoscale, the catalyst particle size is small, and it has strong visible light response capability, high photogenerated electron-hole pair separation efficiency, and high catalytic activity.

According to the second aspect of the present invention, a preparation method of BiOCOOH/gC ₃ N ₄ composite photocatalyst is provided, comprising the following steps:

The BiOCOOH/gC ₃ N ₄ composite photocatalyst was synthesized by hydrothermal method with gC ₃ N ₄ , soluble bismuth salt and solvent; the molar ratio of soluble bismuth salt and gC ₃ N ₄ was (0.15-4.75):1.

Typical but non _- limiting molar ratios of soluble bismuth salt to _gC3N4 are, for example, 0.15:1, 0.25:1, 0.3:1, 0.5:1, 0.8:1, 1:1, 1.2:1, 1.5:1 , 1.8:1, 2:1, 2.5:1, 3:1, 4:1, or 4.75:1.

The hydrothermal synthesis refers to the synthesis that utilizes the chemical reaction of substances in an aqueous solution under the conditions of a temperature of 100-1000°C and a pressure of 1MPa-1GPa. Under hydrothermal conditions, because the reaction is at the molecular level, the reactivity increases, so the hydrothermal reaction can replace some high-temperature solid-phase reactions. In the present invention, the catalytic degradation efficiency of the BiOCOOH/gC ₃ N ₄ composite photocatalyst synthesized by the hydrothermal method is higher.

The preparation method of the BiOCOOH/gC ₃ N ₄ composite photocatalyst provided by the invention has the advantages of cheap and readily available raw materials, simple process, simple operation and no secondary pollution.

Soluble bismuth salts include, but are not limited to, bismuth nitrate pentahydrate, bismuth chloride, or bismuth bromide, preferably bismuth nitrate pentahydrate.

Solvents include, but are not limited to, N,N-dimethylformamide, mannitol, ethylene glycol, diethylene glycol or triethylene glycol, preferably N,N-dimethylformamide.

Preferably, the molar ratio of the soluble bismuth salt to gC ₃ N ₄ is (0.5-3):1, more preferably (0.8-1.5):1.

In a preferred embodiment, the preparation method of BiOCOOH/gC ₃ N ₄ composite photocatalyst comprises the following steps:

The soluble bismuth salt is added to the solvent, mixed uniformly until transparent, water and gC ₃ N ₄ are added, and the mixture is uniformly mixed and then heat-treated to obtain a BiOCOOH/gC ₃ N ₄ composite photocatalyst.

Preferably, the volume of the added water is 40-60 mL; the reference volume of the added water is: for every 1 mL of solvent added, add 8-10 mL of water at the same time;

Typical but non-limiting volumes of water added are, for example, 40 mL, 45 mL, 50 mL, 55 mL, or 60 mL.

Preferably, the heat treatment is carried out in a 100 mL stainless steel autoclave containing a Teflon liner.

Adding an appropriate amount of water to dilute the reaction raw materials can improve the efficiency of hydrothermal synthesis. A stainless steel high-pressure reactor containing a polytetrafluoroethylene lining is preferred as the hydrothermal reactor, because it has the effects of corrosion resistance, anti-sticking, high temperature and high pressure, and can improve the efficiency of hydrothermal synthesis.

In a preferred embodiment, the heat treatment conditions include: the heating temperature is 110-130° C., and the heating time is 11-14 h.

Typical but non-limiting heating temperatures are, for example, 110°C, 115°C, 120°C, 125°C or 130°C.

Typical but non-limiting heating times are eg 11h, 12h, 12.5h, 13h, 13.5h or 14h.

In this preferred embodiment, by controlling the heat treatment temperature and time, the prepared BiOCOOH/gC ₃ N ₄ composite photocatalyst can have better performance and higher catalytic activity.

In a preferred embodiment, the preparation method of the BiOCOOH/gC ₃ N ₄ composite photocatalyst further comprises the steps of purifying, drying and grinding after heat treatment to obtain the BiOCOOH/gC ₃ N ₄ composite photocatalyst;

Preferably, the purification method includes solid-liquid separation, water washing or alcohol washing;

Preferably, the drying conditions include: a drying temperature of 50-70° C., preferably 55-65° C.; and a drying time of 7-14 hours, preferably 8-12 hours.

The solid-liquid separation can be carried out by means of centrifugation, filtration or pressure filtration. The purpose of solid-liquid separation is to obtain the prepared initial product quickly.

The number of times of water washing or alcohol washing is preferably 3 to 5 times, preferably deionized water for water washing, and absolute ethanol, ethylene glycol, isopropanol or diethylene glycol for alcohol washing, preferably absolute ethanol . The purpose of washing with water or alcohol is to remove impurities and improve the purity of the prepared BiOCOOH/gC ₃ N ₄ composite photocatalyst.

Typical but non-limiting drying temperatures are eg 50°C, 52°C, 54°C, 56°C, 58°C, 60°C, 62°C, 64°C, 66°C, 68°C or 70°C.

Typical but non-limiting drying times are eg 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h or 18h.

The drying temperature and time are limited and optimized, so that moisture or other solvents contained in the BiOCOOH/gC ₃ N ₄ composite photocatalyst can be rapidly volatilized to obtain a dry BiOCOOH/gC ₃ N ₄ composite photocatalyst.

In a preferred embodiment, gC ₃ N ₄ is prepared by polycondensation;

Using the polycondensation method to prepare gC ₃ N ₄ has the advantages of simple preparation process, short time consumption, and high photocatalytic activity of the prepared gC ₃ N ₄ .

Preferably, the preparation method of gC ₃ N ₄ comprises the following steps:

The carbon-nitrogen precursor is heat-treated, heated from room temperature to 530-570° C. at a constant rate, kept for 3-5 hours, cooled and ground to obtain gC ₃ N ₄ .

Normal temperature refers to the normal room temperature under experimental conditions or the temperature of the reaction raw materials at room temperature.

Typical but non-limiting temperatures are, for example, 530°C, 540°C, 550°C, 560°C or 570°C;

The incubation time is typically but not limited to, for example, 3h, 3.5h, 4h, 4.5h or 5h;

Carbon and nitrogen precursors include but are not limited to one of dicyandiamide, melamine or aminodicyandiamide;

Dicyandiamide, melamine or aminodicyandiamide are preferred as carbon-nitrogen precursors, gC ₃ N ₄ with good structure and performance can be prepared, and the prepared gC ₃ N ₄ has high catalytic activity.

Preferably, the heating rate is 10-20°C/min.

Typical but non-limiting heating rates are, for example, 10°C/min, 12°C/min, 14°C/min, 16°C/min, 18°C/min or 20°C/min.

A typical preparation method of BiOCOOH/gC ₃ N ₄ composite photocatalyst, comprising the following steps:

(a) 1～2mmol of bismuth nitrate pentahydrate is added to 5～6mL of N,N-dimethylformamide, and mixed at room temperature until transparent;

(b) adding 40-60 mL of deionized water, and ultrasonically mixing for 5-7 minutes;

(c) adding 0.031g～0.368g gC ₃ N ₄ powder, and ultrasonically mixing for 5～7min;

(d) transferring the suspension obtained in step (c) into a 100 mL stainless steel autoclave containing a polytetrafluoroethylene lining, and keeping the temperature at 110-130° C. for 11-14 hours;

(e) centrifuging the product obtained in step (d), washing with deionized water and absolute ethanol for 3 to 5 times, drying at 50 to 70° C. for 10 to 14 h, and grinding to obtain BiOCOOH/gC ₃ N ₄ composite photocatalyst.

The typical preparation method of BiOCOOH/gC ₃ N ₄ composite photocatalyst adopts bismuth nitrate pentahydrate, N,N-dimethylformamide and gC ₃ N ₄ as reaction raw materials to prepare BiOCOOH/gC ₃ N ₄ composite photocatalyst. The raw material used in the preparation method has low price, simple process, and the prepared composite photocatalyst has high visible light catalytic activity.

According to the third aspect of the present invention, the application of BiOCOOH/gC ₃ N ₄ composite photocatalyst in photocatalytic degradation of dye wastewater is provided;

Preferably, the dye in the dye wastewater includes one or more of amino black 10B, methylene blue, rhodamine B or methyl orange, preferably amino black 10B;

Preferably, the application includes the following steps: mixing the BiOCOOH/gC ₃ N ₄ composite photocatalyst and the dye wastewater in a dark environment, and performing a photocatalytic reaction under simulated sunlight for 30-120 minutes after mixing uniformly.

Typical but non-limiting photocatalytic reaction times are, for example, 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 80 min, 90 min, 100 min, 110 min or 120 min.

The BiOCOOH/gC ₃ N ₄ composite photocatalyst provided by the invention has high visible light catalytic degradation efficiency to wastewater containing organic dyes, can be used in photocatalytic degradation of dye wastewater, and has good application prospects. The BiOCOOH/gC ₃ N ₄ composite photocatalyst provided by the invention has a degradation efficiency of 1.42 times and 2.69 times that of pure gC ₃ N ₄ and pure BiOCOOH for amino black 10B dye, respectively, and the degradation rate of amino black 10B can reach 89.16%.

In order to further understand the present invention, the method and effect of the present invention will be further described in detail below with reference to specific embodiments. Each raw material involved in the present invention can be obtained commercially.

Example 1

A BiOCOOH/gC ₃ N ₄ composite photocatalyst, the flower-like BiOCOOH is embedded in the gC ₃ N ₄ sheet structure; the molar ratio of BiOCOOH and gC ₃ N ₄ is 3:1;

The preferred preparation method of the above-mentioned BiOCOOH/gC ₃ N ₄ composite photocatalyst includes the following steps:

(1) 1mmol of bismuth nitrate pentahydrate was added to 5mL of N,N-dimethylformamide, and mixed at room temperature until transparent;

(2) Add 40 mL of deionized water, and ultrasonically mix for 5 min;

( ₃ ) add 0.031g _gC3N4 powder, ultrasonically mix for 5min;

(4) transferring the suspension obtained in step (3) into a 100 mL stainless steel autoclave containing a polytetrafluoroethylene lining, and keeping the temperature at 130° C. for 11 h;

(5) centrifuging the product obtained in step (4), washing with deionized water and absolute ethanol for 3 times, drying at 70° C. for 10 h, and grinding to obtain BiOCOOH/gC ₃ N ₄ with a particle size of about 1200 nm composite photocatalyst.

Example 2

A BiOCOOH/gC ₃ N ₄ composite photocatalyst, the flower-like BiOCOOH is embedded in the gC ₃ N ₄ sheet structure; the molar ratio of BiOCOOH and gC ₃ N ₄ is 0.25:1;

The preferred preparation method of the above-mentioned BiOCOOH/gC ₃ N ₄ composite photocatalyst includes the following steps:

(1) 1mmol of bismuth nitrate pentahydrate was added to 5mL of N,N-dimethylformamide, and mixed at room temperature until transparent;

(2) Add 40 mL of deionized water, and ultrasonically mix for 5 min;

(3) add 0.368g gC ₃ N ₄ powder, and ultrasonically mix for 5min;

(4) transferring the suspension obtained in step (3) into a 100 mL stainless steel autoclave containing a polytetrafluoroethylene lining, and keeping the temperature at 130° C. for 11 h;

(5) centrifuging the product obtained in step (4), washing with deionized water and absolute ethanol for 5 times, drying at 50° C. for 14 h, and grinding to obtain BiOCOOH/gC ₃ N ₄ with a particle size of about 300 nm composite photocatalyst.

Example 3

A BiOCOOH/gC ₃ N ₄ composite photocatalyst, the flower-like BiOCOOH is embedded in the gC ₃ N ₄ sheet structure; the molar ratio of BiOCOOH and gC ₃ N ₄ is 2:1;

The preferred preparation method of the above-mentioned BiOCOOH/gC ₃ N ₄ composite photocatalyst includes the following steps:

(1) 1mmol of bismuth nitrate pentahydrate was added to 5mL of N,N-dimethylformamide, and mixed at room temperature until transparent;

(2) Add 40 mL of deionized water, and ultrasonically mix for 5 min;

( ₃ ) add 0.046g _gC3N4 powder, ultrasonically mix for 5min;

(4) transferring the suspension obtained in step (3) into a 100 mL stainless steel autoclave containing a polytetrafluoroethylene lining, and keeping the temperature at 120° C. for 12 h;

(5) The product obtained in step (4) was centrifuged, washed three times with deionized water and absolute ethanol, dried at 60° C. for 12 h, and ground to obtain BiOCOOH/gC ₃ N ₄ with a particle size of about 800 nm. composite photocatalyst.

Example 4

A BiOCOOH/gC ₃ N ₄ composite photocatalyst, the flower-like BiOCOOH is embedded in the gC ₃ N ₄ sheet structure; the molar ratio of BiOCOOH and gC ₃ N ₄ is 1:1;

The preferred preparation method of the above-mentioned BiOCOOH/gC ₃ N ₄ composite photocatalyst includes the following steps:

(1) 1mmol of bismuth nitrate pentahydrate was added to 5mL of N,N-dimethylformamide, and mixed at room temperature until transparent;

(2) Add 40 mL of deionized water, and ultrasonically mix for 5 min;

( ₃ ) add 0.092g _gC3N4 powder, ultrasonically mix for 5min;

(4) transferring the suspension obtained in step (3) into a 100 mL stainless steel autoclave containing a polytetrafluoroethylene lining, and keeping the temperature at 120° C. for 12 h;

(5) The product obtained in step (4) was centrifuged, washed three times with deionized water and absolute ethanol, dried at 60° C. for 12 h, and ground to obtain BiOCOOH/gC ₃ N ₄ with a particle size of about 600 nm. composite photocatalyst.

Example 5

A BiOCOOH/gC ₃ N ₄ composite photocatalyst, the flower-like BiOCOOH is embedded in the gC ₃ N ₄ sheet structure; the molar ratio of BiOCOOH and gC ₃ N ₄ is 0.5:1;

The difference between the preferred preparation method of the above BiOCOOH/gC ₃ N ₄ composite photocatalyst and the preparation method of Example 4 is that 0.184g of gC ₃ N ₄ powder is added.

Example 6

A BiOCOOH/gC ₃ N ₄ composite photocatalyst, the flower-like BiOCOOH is embedded in the gC ₃ N ₄ sheet structure; the molar ratio of BiOCOOH and gC ₃ N ₄ is 0.3:1;

The difference between the preferred preparation method of the above BiOCOOH/gC ₃ N ₄ composite photocatalyst and the preparation method of Example 4 is that 0.276g of gC ₃ N ₄ powder is added.

Example 7

A BiOCOOH/gC ₃ N ₄ composite photocatalyst, the flower-like BiOCOOH is embedded in the gC ₃ N ₄ sheet structure; the molar ratio of BiOCOOH and gC ₃ N ₄ is 1:1;

The difference between the preferred preparation method of the above BiOCOOH/gC ₃ N ₄ composite photocatalyst and the preparation method of Example 4 is that bismuth chloride replaces bismuth nitrate pentahydrate.

Example 8

A BiOCOOH/gC ₃ N ₄ composite photocatalyst, spherical BiOCOOH is embedded in a gC ₃ N ₄ sheet structure; the molar ratio of BiOCOOH and gC ₃ N ₄ is 1:1;

The difference between the preferred preparation method of the above-mentioned BiOCOOH/gC ₃ N ₄ composite photocatalyst and the preparation method of Example 4 is that mannitol replaces N,N-dimethylformamide.

Example 9

A BiOCOOH/gC ₃ N ₄ composite photocatalyst, BiOCOOH is embedded in a gC ₃ N ₄ sheet structure; the molar ratio of BiOCOOH and gC ₃ N ₄ is 0.15:1;

The difference between the preferred preparation method of the above-mentioned BiOCOOH/gC ₃ N ₄ composite photocatalyst and the preparation method of Example 4 is that 0.613 g of gC ₃ N ₄ powder is added.

Example 10

A BiOCOOH/gC ₃ N ₄ composite photocatalyst, BiOCOOH is embedded in a gC ₃ N ₄ sheet structure; the molar ratio of BiOCOOH and gC ₃ N ₄ is 4.75:1;

The difference between the preferred preparation method of the above-mentioned BiOCOOH/gC ₃ N ₄ composite photocatalyst and the preparation method of Example 4 is that 0.019 g of gC ₃ N ₄ powder is added.

Comparative Example 1

A preparation method of gC ₃ N ₄ photocatalyst, comprising the following steps:

(1) take 3g of dicyandiamide and put it into the alumina crucible with lid;

(2) Move it into a muffle furnace, set the heating rate to 10°C/min, heat it to 550°C and keep it for 4h;

(3) Naturally cooled to room temperature, and ground to obtain a yellow gC ₃ N ₄ photocatalyst with a particle size of about 600 nm.

Comparative Example 2

A preferred preparation method of BiOCOOH photocatalyst, comprising the following steps:

(1) 1mmol of bismuth nitrate pentahydrate is first dissolved in 5mL of N,N-dimethylformamide solvent, and mixed to transparent at room temperature;

(2) Add 40 mL of deionized water, and ultrasonically mix for 10 min;

(3) transferring the mixed solution obtained in step (2) into a 100 mL stainless steel autoclave containing a polytetrafluoroethylene lining, and keeping the temperature at 120° C. for 12 h;

(4) The product obtained in step (3) was centrifuged, washed three times with deionized water and absolute ethanol, dried at 60 °C for 12 h, and ground to obtain a white BiOCOOH photocatalyst with a particle size of about 600 nm.

Comparative Example 3

A BiOCOOH/gC ₃ N ₄ composite photocatalyst, BiOCOOH is embedded in a gC ₃ N ₄ sheet structure; the molar ratio of BiOCOOH and gC ₃ N ₄ is 0.05:1;

The difference between the preferred preparation method of the above BiOCOOH/gC ₃ N ₄ composite photocatalyst and the preparation method of Example 4 is that 1.84g of gC ₃ N ₄ powder is added.

Comparative Example 4

A BiOCOOH/gC ₃ N ₄ composite photocatalyst, BiOCOOH is embedded in a gC ₃ N ₄ sheet structure; the molar ratio of BiOCOOH and gC ₃ N ₄ is 6:1;

The difference between the preferred preparation method of the above BiOCOOH/gC ₃ N ₄ composite photocatalyst and the preparation method of Example 4 is that 0.015g of gC ₃ N ₄ powder is added.

Comparative Example 5

Embodiment 1 of patent CN201710027325.2 specifically includes the following steps:

(1) Preparation of gC ₃ N ₄ : Weigh 30g of urea in a covered ceramic crucible, place it in a muffle furnace, heat from room temperature 25°C to 400°C in an air atmosphere, keep the temperature at 400°C for 2 hours, and continue heating to 550°C, constant temperature at 550°C for 2h, naturally cooled to room temperature 25°C, ground the sample to obtain gC ₃ N ₄ as a pale yellow powder;

(2) Preparation of gC ₃ N ₄ /Ag: Dissolve 4.0 mmol of silver nitrate in 50 mL of deionized water, ultrasonically dissolve for 5 min, and stir in a dark room protected from light for 10 min; weigh 40 mg of gC ₃ N ₄ obtained in step (1) and add silver nitrate solution Disperse uniformly by ultrasonic for 10 min, continue stirring at 600 rpm in the dark for 1 h; configure 180 g/L glucose solution, add 10 mL of gC ₃ N ₄ and silver nitrate mixed solution, and stir in a water bath at 60 °C for 2 h in the dark; stop stirring for static After standing for 0.5 h, centrifugation, washing (5 times of water, 1 time of absolute ethanol) and drying at 55°C to obtain gC ₃ N ₄ /Ag composite material;

(3) Preparation of gC ₃ N ₄ /Ag/Ag ₃ PO ₄ : Weigh 1.326 mg of ferric nitrate nonahydrate and 0.512 mg of sodium dihydrogen phosphate, put them in 100 mL of deionized water, and mix them uniformly by ultrasonication for 10 min. Add 40 mg of gC ₃ N ₄ /Ag composite material, mix uniformly by ultrasonic for 10 min, stir the reaction at 600 rpm in the dark at 28°C for 2 h, let stand for 0.5 h, centrifuge the obtained product, wash (5 times of water, 1 time of absolute ethanol), After drying at 55°C, a Z-type gC ₃ N ₄ /Ag/Ag ₃ PO ₄ composite photocatalyst with a particle size of about 600 nm was obtained after grinding.

Comparative Example 6

Patent CN201410082715.6 Embodiments 1, 2 and 6 specifically include the following steps:

(1) Weigh 10g of melamine, put it into the corundum ark, place it in the middle of the tube furnace, heat it to 550°C at a heating rate of 2°C/min, and keep it at 550°C for 4 hours. After cooling, it was taken out and ground with a mortar to obtain a yellow powder gC ₃ N ₄ sample;

(2) Weigh 0.4 g of the sample in step (1) and put it into a wide-mouthed bottle, add 80 mL of isopropyl alcohol, tighten the bottle cap, ultrasonicate for 10 h to form a suspension, and then centrifuge the suspension at 3000 rpm/min Remove the precipitate for 10 min, and then centrifuge the upper layer suspension at 12,000 rpm/min at a high speed to obtain a pale yellow gC ₃ N ₄ solid sample;

(3) Weigh 0.072 g of the sample obtained in step (2) and add it to 50 mL of absolute ethanol in which 1.333 g (5 mmol) of CdS was dissolved. After ultrasonication for 30 min, stir for 5 h to fully mix, and then add 0.376 g (5 mmol) Thioacetamide was stirred for 1 h to dissolve and mix, and the mass ratio of two-dimensional ultrathin gC ₃ N ₄ to CdS was 1:10. After that, it was put into a reaction kettle, placed in an oven at 180°C for 12 hours, and then cooled to room temperature naturally. The obtained precipitate was washed three times with deionized water and twice with absolute ethanol, and the obtained precipitate was vacuumed at 100°C. After drying in an oven for 12 hours, the gC ₃ N ₄ /CdS composite photocatalyst with a particle size of about 600 nm was obtained after grinding.

Experimental Example 1 Transmission Electron Microscope Experiment

The composite photocatalysts prepared in Examples 1-10 and Comparative Examples 1-6 were subjected to transmission electron microscopy detection experiments. The microscopic morphology of the composite photocatalysts is shown in Table 1.

Table 1 Micromorphology of composite photocatalysts

It can be seen from the TEM results in Table 1 that the microscopic morphology of the BiOCOOH/gC ₃ N ₄ composite photocatalysts prepared in Examples 1-7 and Examples 9 and 10 all show flower-like BiOCOOH embedded in gC ₃ N ₄ sheets In the layer structure, the microscopic morphology of the BiOCOOH/gC ₃ N ₄ composite photocatalyst prepared in Example 8 shows that spherical BiOCOOH is embedded in the lamellar structure of gC ₃ N ₄ . Figure 1 is a transmission electron microscope image of the BiOCOOH/gC ₃ N ₄ composite photocatalyst sample prepared in Example 4 of the present invention. It can be seen from the figure that the flower-shaped BiOCOOH is successfully embedded in the gC ₃ N ₄ lamellar structure.

Compared with the gC ₃ N ₄ prepared in Example 1, TEM results show that its microstructure is a lamellar structure, which can be used as a good base material for constructing composite photocatalysts. Compared with the _BiOCOOH prepared in Example ₂ , the results of transmission electron microscopy show that its microstructure is flower _- like, with a large specific surface area and high catalytic activity _. high. The microscopic morphology of the BiOCOOH/gC ₃ N ₄ composite photocatalysts prepared in Comparative Examples 3 and 4 shows that the flower-like BiOCOOH is embedded in the lamellar structure of gC ₃ N ₄ , but the flower-like BiOCOOH in Comparative Example 3 is less than that in Comparative Example 4. There are more BiOCOOH in the flower shape. Comparative Examples 5 and 6 are the disclosed preparation methods of composite photocatalysts. The microstructures of the prepared composite photocatalysts are shown in Table 1. The specific surface areas of the composite photocatalysts prepared in Comparative Examples 5 and 6 are significantly smaller than those prepared in Examples 1-10. composite photocatalyst.

Experimental Example 2 Photocurrent Response Detection

The photocurrent response changes of the composite photocatalysts prepared in Examples 1-10 and Comparative Examples 1-6 were detected under simulated sunlight irradiation conditions, and the results are shown in Table 2.

Table 2 Photocurrent density

It can be seen from Table 2 that the photocurrent densities of the composite photocatalysts prepared in Examples 1-10 are all between 0.00038-0.00054 mA/m ² , and the photocurrent densities of the photocatalysts prepared in Comparative Examples 1-6 are all between 0.00015-0.00035 mA/ between ^m2 .

In Examples 1-10, the BiOCOOH/gC ₃ N ₄ composite photocatalyst prepared in Example 4 had the highest current density, and the BiOCOOH/gC ₃ N ₄ composite photocatalyst prepared in Example 9 had the lowest current density. The main difference between Examples 9 and ₄ is the molar ratio of BiOCOOH and _gC3N4 in the composite photocatalyst. This indicates that the molar ratio of _BiOCOOH and _gC3N4 affects the visible light responsiveness and photogenerated electron-hole pair separation efficiency of the _BiOCOOH / _gC3N4 composite photocatalyst. Embodiment 4 is a best preferred solution of the present invention.

The photocurrent densities of the composite photocatalysts prepared in Examples 1-10 are all greater than those of the photocatalysts prepared in Comparative Examples 1 and 2. FIG. 2 is a graph showing the photocurrent response change of the photocatalyst samples prepared in Example 4 of the present invention and Comparative Examples 1 and 2 under simulated sunlight irradiation conditions. It can be seen from the figure that under the same conditions, the three samples all generated fast and stable photocurrents, and the transient corresponding photocurrents of the BiOCOOH/gC ₃ N ₄ composite photocatalyst samples prepared in Example 4 were compared The pure gC ₃ N ₄ prepared in 1 and the pure BiOCOOH samples prepared in Comparative Example 2 were significantly improved, and their transient photocurrent density was 0.00054 mA/m ² , which were 2.16 times and 2.16 times higher than those of pure gC ₃ N ₄ and pure BiOCOOH, respectively. 3.6 times. This indicates that the formation of heterostructures between BiOCOOH and gC ₃ N ₄ in the BiOCOOH/gC ₃ N ₄ composite photocatalyst can effectively improve the separation efficiency of gC ₃ N ₄ photogenerated electrons and holes, thereby enhancing its photocatalytic activity.

The photocurrent densities of Comparative Examples 3 and 4 are significantly lower than those of the composite photocatalysts prepared in Examples 1-10, and the BiOCOOH/gC ₃ N ₄ composite photocatalysts prepared in Comparative Examples 3 and 4 in BiOCOOH and gC ₃ N A molar ratio of ₄ is not within the scope of the present invention. This shows that the BiOCOOH/gC ₃ N ₄ composite photocatalyst can only have a strong visible light response under the conditions specified in the present invention.

The photocurrent densities of Comparative Examples 5 and 6 are significantly lower than those of the composite photocatalysts prepared in Examples 1-10, which indicates that the BiOCOOH/gC ₃ N ₄ provided by the present invention has strong visible light responsiveness and higher The separation efficiency of photogenerated electron-hole pairs is better than that of the composite photocatalysts prepared in Comparative Examples 5 and 6.

Experimental Example 3 Photocatalytic Degradation Experiment

The photocatalysts prepared in Examples 1-10 and Comparative Examples 1-6 were used in the photocatalytic degradation experiment of organic dye amino black 10B, and the specific process and steps were as follows:

The photocatalysts prepared in Examples 1-10 and Comparative Examples 1-6 were each taken 20 mg and dispersed into an open quartz glass beaker containing 50 mL of 10 mg/L Amino Black 10B solution, and mixed for 30 min under dark conditions to achieve adsorption equilibrium. ; Take a 35W xenon lamp as the light source, and place it at a horizontal distance of 5cm from the quartz glass beaker; turn on the light source, take 7mL of solution from the reaction system to a centrifuge tube every 30min, put it into the centrifuge, set the rotating speed to 4000rmp, and the time to be 8min, After high-speed centrifugation, the supernatant was taken into a quartz cuvette, and the absorbance of the supernatant at a wavelength of 613 nm was measured under an ultraviolet-visible spectrophotometer to obtain the concentration change of amino black 10B in the solution. The test results at 120 min are shown in Table 3.

Table 3 Degradation rate of amino black 10B

It can be seen from Table 3 that the degradation rates of the composite photocatalysts prepared in Examples 1-10 to amino black 10B were all between 76.03% and 89.16%, and the degradation rates of the photocatalysts prepared in Comparative Examples 1-6 to amino black 10B were all in the range of 76.03%-89.16%. Between 34.65%-74.96%.

In Examples 1-10, the BiOCOOH/gC ₃ N ₄ composite photocatalyst prepared in Example 4 had the highest degradation rate, and the BiOCOOH/gC ₃ N ₄ composite photocatalyst prepared in Example 9 had the lowest degradation rate. The main difference between 9 and ₄ is the molar ratio of BiOCOOH and _gC3N4 in the composite photocatalyst. This indicates that the molar ratio of BiOCOOH and gC ₃ N ₄ affects the catalytic degradation rate of the BiOCOOH/gC ₃ N ₄ composite photocatalyst. Embodiment 4 is a best preferred solution of the present invention.

The degradation rates of the composite photocatalysts prepared in Examples 1-10 were all higher than those of pure gC ₃ N ₄ and pure BiOCOOH photocatalysts prepared in Comparative Examples 1 and 2. Figure 3 shows the change curve of photocatalytic degradation rate with time under the action of pure gC ₃ N ₄ , pure BiOCOOH and BiOCOOH/gC ₃ N ₄ composite photocatalysts of 50 mL of 10 mg/L amino black 10B solution, respectively. It can be seen from Figure 3 that after 35w xenon lamp irradiation for 120min, the photocatalytic degradation rate of the composite photocatalyst for amino black 10B is significantly higher than that of pure _gC3N4 and pure _BiOCOOH , among which the photocatalytic efficiency of the composite photocatalyst 1Bi-C The highest, the degradation rate of amino black 10B can reach 89.16% at 120min.

The degradation rates of Comparative Examples 3 and 4 are significantly lower than the photocurrent densities of the composite photocatalysts prepared in Examples 1-10, and the BiOCOOH/gC ₃ N ₄ composite photocatalysts prepared in Comparative Examples 3 and 4 have the same ratio of BiOCOOH and gC ₃ N ₄ The molar ratio of is not within the scope of protection of the present invention. This shows that the BiOCOOH/gC ₃ N ₄ composite photocatalyst can only have a strong visible light response under the conditions specified in the present invention.

The degradation rates of Comparative Examples 5 and 6 are significantly lower than those of the composite photocatalysts prepared in Examples 1-10, which indicates that the BiOCOOH/gC ₃ N ₄ provided by the present invention has strong visible catalytic activity and high catalytic degradation efficiency, Better than the composite photocatalysts prepared in Comparative Examples 5 and 6.

Although specific embodiments of the present invention have been illustrated and described, it should be understood that various other changes and modifications can be made without departing from the spirit and scope of the invention. Therefore, it is intended that all such changes and modifications as fall within the scope of this invention be included in the appended claims.

Claims (21)

1. A BiOCOOH/gC ₃ N ₄ composite photocatalyst, wherein the BiOCOOH is embedded in the lamellar structure of the gC ₃ N ₄ ; The molar ratio of the BiOCOOH and the gC ₃ N ₄ is (0.15~4.75):1. 2 . The BiOCOOH/gC ₃ N ₄ composite photocatalyst according to claim 1 , wherein the molar ratio of the BiOCOOH to the gC ₃ N ₄ is (0.5˜3):1. 3 . 3. The BiOCOOH/gC ₃ N ₄ composite photocatalyst according to claim 1, wherein the molar ratio of the BiOCOOH to the gC ₃ N ₄ is (0.8-1.5):1. 4 . The BiOCOOH/gC ₃ N ₄ composite photocatalyst according to claim 1 , wherein the microstructure of the BiOCOOH is flower shape, white fungus shape, sponge shape or spherical shape. 5 . 5 . The BiOCOOH/gC ₃ N ₄ composite photocatalyst according to claim 1 , wherein the microstructure of the BiOCOOH is flower-shaped. 6 . 6 . The BiOCOOH/gC ₃ N ₄ composite photocatalyst according to claim 1 , wherein the BiOCOOH/gC ₃ N ₄ composite photocatalyst has a particle size of 300-1200 nm. 7 . 7 . The BiOCOOH/gC ₃ N ₄ composite photocatalyst according to claim 1 , wherein the BiOCOOH/gC ₃ N ₄ composite photocatalyst has a particle size of 400-1100 nm. 8 . 8 . The BiOCOOH/gC ₃ N ₄ composite photocatalyst according to claim 1 , wherein the BiOCOOH/gC ₃ N ₄ composite photocatalyst has a particle size of 500-1000 nm. 9 . 9. A preparation method of the BiOCOOH/gC ₃ N ₄ composite photocatalyst according to any one of claims 1-8, characterized in that, comprising the following steps: The BiOCOOH/gC ₃ N ₄ composite photocatalyst was synthesized by hydrothermal method with gC ₃ N ₄ , soluble bismuth salt, organic solvent and water; the molar ratio of soluble bismuth salt and gC ₃ N ₄ was (0.15~4.75):1; The soluble bismuth salt includes one of bismuth nitrate pentahydrate, bismuth chloride or bismuth bromide; the organic solvent includes N,N-dimethylformamide, mannitol, ethylene glycol, diethylene glycol or triethylene glycol one of ethylene glycol. 10 . The preparation method of BiOCOOH/gC ₃ N ₄ composite photocatalyst according to claim 9 , wherein the organic solvent is N,N-dimethylformamide. 11 . The preparation method of BiOCOOH/gC ₃ N ₄ composite photocatalyst according to claim 9, wherein the soluble bismuth salt is bismuth nitrate pentahydrate. 12. The preparation method of BiOCOOH/gC ₃ N ₄ composite photocatalyst according to claim 9, wherein the molar ratio of soluble bismuth salt and gC ₃ N ₄ is (0.5～3):1. 13. The preparation method of BiOCOOH/gC ₃ N ₄ composite photocatalyst according to claim 9, wherein the molar ratio of soluble bismuth salt and gC ₃ N ₄ is (0.8~1.5):1. 14. The preparation method of BiOCOOH/gC ₃ N ₄ composite photocatalyst according to any one of claims 9-13, characterized in that, comprising the following steps: The soluble bismuth salt is added into an organic solvent, mixed uniformly until transparent, water and gC ₃ N ₄ are added, and the mixture is uniformly mixed and then heat-treated to obtain a BiOCOOH/gC ₃ N ₄ composite photocatalyst. 15 . The preparation method of BiOCOOH/gC ₃ N ₄ composite photocatalyst according to claim 14 , wherein the heat treatment conditions comprise: a heating temperature of 110-130° C. and a heating time of 11-14 hours. 16 . 16. The preparation method of BiOCOOH/gC ₃ N ₄ composite photocatalyst according to claim 14, characterized in that, the preparation method of said BiOCOOH/gC ₃ N ₄ composite photocatalyst further comprises purifying, drying and grinding after heat treatment , the steps of obtaining BiOCOOH/gC ₃ N ₄ composite photocatalyst; The purification method includes solid-liquid separation, water washing or alcohol washing; The drying conditions include: a drying temperature of 50-70° C. and a drying time of 7-14 hours. 17 . The preparation method of BiOCOOH/gC ₃ N ₄ composite photocatalyst according to claim 16 , wherein the drying temperature is 55-65° C. 18 . 18. The preparation method of BiOCOOH/gC ₃ N ₄ composite photocatalyst according to claim 16, wherein the drying time is 8-12 h. 19. The preparation method of the BiOCOOH/gC ₃ N ₄ composite photocatalyst according to claim 9, wherein the gC ₃ N ₄ is prepared by a polycondensation method; The preparation method of the gC ₃ N ₄ comprises the following steps: The carbon-nitrogen precursor is heat-treated, heated from room temperature to 530-570° C. at a constant rate, kept for 3-5 hours, cooled and ground to obtain gC ₃ N ₄ ; the carbon-nitrogen precursor includes dicyandiamide, melamine or aminodicyandiamide. A kind of; the heating rate is 10~20℃/min. 20. A preparation method of the BiOCOOH/gC ₃ N ₄ composite photocatalyst according to any one of claims 1-8 or the BiOCOOH/gC ₃ N ₄ composite photocatalyst according to any one of claims 9-19, obtained by Application of BiOCOOH/gC ₃ N ₄ composite photocatalyst in photocatalytic degradation of dye wastewater; The dyes in the dye wastewater include one or more of amino black 10B, methylene blue, rhodamine B or methyl orange. The application includes the following steps: the BiOCOOH/gC ₃ N ₄ composite photocatalyst and the dye wastewater are protected from light. Mixing under simulated sunlight, the photocatalytic reaction is carried out for 30-120 min after mixing uniformly. 21. The application of the BiOCOOH/gC ₃ N ₄ composite photocatalyst in the photocatalytic degradation of dye wastewater according to claim 20, wherein the dye in the dye wastewater is amino black 10B.

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