Floating-type silver phosphate / zinc ferrite / floating bead composite photocatalyst, and preparation method therefor and use thereof, and organic wastewater treatment method

Abstract

A floating-type silver phosphate / zinc ferrite / floating bead composite photocatalyst, and a preparation method therefor and the use thereof, and a wastewater treatment method. The floating-type silver phosphate / zinc ferrite / floating bead composite photocatalyst comprises floating beads, a zinc ferrite thin film coating the floating beads, and silver phosphate deposited on the zinc ferrite thin film, wherein zinc ferrite in the zinc ferrite thin film and the silver phosphate form a heterojunction. In the catalyst, floating beads serve as a carrier, such that the catalyst can float on the surface of an aqueous solution during use, thereby facilitating recycling; in addition, silver phosphate is deposited after the surface of the carrier is coated with the zinc ferrite thin film, thereby improving the photocatalytic activity of the catalyst under visible light. The preparation method for the catalyst is simple to operate and easy to industrialize.

Description

A floating silver phosphate / zinc ferrite / floating bead composite photocatalyst, its preparation method and application, and organic wastewater treatment method Technical Field

[0001] The present application relates to the field of catalyst technology, and in particular to a floating silver phosphate / zinc ferrite / floating bead composite photocatalyst, a preparation method and application thereof, and an organic wastewater treatment method. Background Art

[0002] Since its discovery in 2010, silver phosphate (Ag3PO4) has attracted widespread attention for its strong oxidizing ability under visible light and excellent photocatalytic effect. However, silver phosphate has a relatively high solubility in water and will undergo photocorrosion during the photocatalytic process, resulting in the disadvantages of silver phosphate photocatalysts such as difficulty in recycling, low stability, and easy deactivation, which greatly limits its practical application. To solve this problem, researchers have modified silver phosphate by using precious metals, carbon nanomaterials, etc., or by compounding materials such as oxide semiconductors, silver halides, and clay with Ag3PO4 to improve the stability and photocatalytic activity of Ag3PO4. However, these methods are limited to the preparation of powder photocatalysts, which are not easy to recycle and reuse, which to a certain extent increases the cost of photodegradation in practical applications.

[0003] Summary of the Invention

[0004] In view of this, the purpose of this application is to provide a floating silver phosphate / zinc ferrite / floating bead composite photocatalyst, its preparation method and application, and a wastewater treatment method. The floating silver phosphate / zinc ferrite / floating bead composite photocatalyst provided in this application is easy to recycle and reuse, and has excellent photocatalytic activity.

[0005] In order to achieve the above application objectives, this application provides the following technical solutions:

[0006] The present application provides a floating silver phosphate / zinc ferrite / floating bead composite photocatalyst, comprising floating beads, a zinc ferrite film coated on the floating beads, and silver phosphate deposited on the zinc ferrite film;

[0007] The zinc ferrite and silver phosphate in the zinc ferrite film form a heterojunction.

[0008] The present application also provides a method for preparing the floating silver phosphate / zinc ferrite / floating bead composite photocatalyst described in the above technical solution, comprising the following steps:

[0009] The trivalent iron salt, zinc salt and complexing agent are dissolved and mixed, and sol reaction and aging are carried out in sequence to obtain a sol system;

[0010] After immersing the floating beads in the sol system, the sol system is roasted to obtain a zinc ferrite / floating bead composite material;

[0011] After the zinc ferrite / floating bead composite material is immersed in a silver salt solution, phosphate is added, and composite reaction and calcination are carried out in sequence to obtain the floating silver phosphate / zinc ferrite / floating bead composite photocatalyst.

[0012] Preferably, the molar ratio of the ferric ions in the ferric salt to the zinc ions in the zinc salt is 2:1; the molar ratio of the total molar ratio of the ferric ions in the ferric salt and the zinc ions in the zinc salt to the molar ratio of the complexing agent is 1:1.

[0013] Preferably, the ferric salt includes one or more of ferric nitrate, ferric chloride and ferric sulfate.

[0014] Preferably, the zinc salt comprises one or more of zinc nitrate, zinc chloride and zinc sulfate.

[0015] Preferably, the complexing agent comprises one or more of citric acid, ammonium citrate, sodium citrate and potassium citrate.

[0016] Preferably, the dissolving and mixing of the ferric salt, zinc salt and complexing agent comprises: dissolving the ferric salt and zinc salt in a first solvent to obtain a metal salt solution, dissolving the complexing agent in a second solvent to obtain a complexing agent solution; and mixing the metal salt solution and the complexing agent solution.

[0017] Preferably, the first solvent and the second solvent both include one or more of ethanol, water and ethylene glycol.

[0018] Preferably, the temperature of the sol reaction is 60-80° C., the time is 0.5-1 hour, and the sol reaction is carried out under stirring.

[0019] Preferably, the aging temperature is room temperature and the aging time is 48 to 72 hours.

[0020] Preferably, the particle size of the floating beads is 40 to 60 meshes.

[0021] Preferably, before the floating beads are immersed in the sol system, the process further comprises: screening, acid washing, washing and drying the floating beads in sequence.

[0022] Preferably, the volume ratio of the floating beads to the sol system is 1:3 to 1:2.

[0023] Preferably, the immersion time of the floating beads is 20 to 40 minutes; and the immersion of the floating beads is carried out under stirring conditions.

[0024] Preferably, after the floating beads are soaked and before being roasted, the process further comprises: filtering out excess sol system and drying; the drying temperature is 70-90°C.

[0025] Preferably, the calcination temperature is 450-600° C., the holding time is 1.5-3 h, and the heating rate to the calcination temperature is 2-4° C. / min.

[0026] Preferably, the silver salt in the silver salt solution includes silver nitrate; and the phosphate includes one or more of disodium hydrogen phosphate, sodium dihydrogen phosphate and sodium phosphate.

[0027] Preferably, the molar ratio of silver ions in the silver salt solution to phosphate radicals in the phosphate is 3:1 to 2:1.

[0028] Preferably, the temperature of the composite reaction is room temperature, and the time is 1 to 2 hours.

[0029] Preferably, after the composite reaction and before calcination, the excess liquid is filtered out and the process is dried.

[0030] Preferably, the calcination temperature is 150-250° C., the holding time is 30-60 minutes, and the heating rate to the calcination temperature is 2-4° C. / min.

[0031] The present application also provides the use of the floating silver phosphate / zinc ferrite / floating bead composite photocatalyst described in the above technical solution or the floating silver phosphate / zinc ferrite / floating bead composite photocatalyst prepared by the preparation method described in the above technical solution in wastewater treatment.

[0032] The present application also provides a method for treating organic wastewater, comprising the following steps:

[0033] Mixing the catalyst and organic wastewater, and photocatalytically degrading organic matter in the organic wastewater under visible light irradiation;

[0034] The organic matter includes one or more of methylene blue, methyl orange, phenol and rhodamine B;

[0035] The catalyst is the floating silver phosphate / zinc ferrite / floating bead composite photocatalyst described in the above technical solution or the floating silver phosphate / zinc ferrite / floating bead composite photocatalyst prepared by the preparation method described in the above technical solution.

[0036] Preferably, the usage ratio of the catalyst to wastewater is 5-10 g:1 L.

[0037] The present application provides a floating silver phosphate / zinc ferrite / floating bead composite photocatalyst, comprising floating beads, a zinc ferrite film coated on the floating beads, and silver phosphate deposited on the zinc ferrite film; the zinc ferrite and silver phosphate in the zinc ferrite film form a heterojunction. The catalyst provided by the present application uses floating beads as a carrier, which enables the catalyst to float on the surface of an aqueous solution during application, making it easy to recover; at the same time, silver phosphate is deposited after the zinc ferrite film is coated on the surface of the carrier, thereby improving the photocatalytic activity of the catalyst under visible light. At the same time, floating beads (FACs) are a waste product of fly ash, and using them as a carrier is a waste utilization, which has great economic benefits and reduces the cost of catalyst preparation.

[0038] This application also provides a method for preparing the floating silver phosphate / zinc ferrite / bead composite photocatalyst described in the above technical solution. This method first prepares a ZnFe2O4 sol system, immerses beads in the ZnFe2O4 sol system, and coats the beads with a layer of ZnFe2O4 to form a zinc ferrite / bead composite material. The zinc ferrite / bead composite material is then immersed in a silver salt solution to allow the silver salt to adhere fully to the bead surface. Phosphate is then added to form silver phosphate in situ on the bead surface, thereby obtaining the floating silver phosphate / zinc ferrite / bead composite photocatalyst. The preparation method provided by this application is simple to operate and readily industrializable. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 shows the XRD spectra of ZnFe2O4, Ag3PO4 / ZnFe2O4 and Ag3PO4;

[0040] Figure 2 shows the XRD spectra of FACs, ZnFe2O4 / FACs, Ag3PO4 / FACs and Ag3PO4 / ZnFe2O4 / FACs;

[0041] Figure 3 shows the UV-vis spectra of different photocatalysts;

[0042] Figure 4 shows the effects of floating beads (a) and Ag3PO4 / ZnFe2O4 / FACs (b) in aqueous solution;

[0043] Figure 5 shows the SEM images of FACs (a), ZnFe2O4 / FACs (b and c), Ag3PO4 / FACs (d) and Ag3PO4 / ZnFe2O4 / FACs (e and f);

[0044] Figure 6 shows the degradation rates of MB by ZnFe2O4, Ag3PO4, and Ag3PO4 / ZnFe2O4 under visible light;

[0045] Figure 7 shows the degradation rate of MB by ZnFe2O4 / FACs, Ag3PO4 / FACs and Ag3PO4 / ZnFe2O4 / FACs under visible light;

[0046] Figure 8 shows the photocatalytic degradation of Ag3PO4 / FACs and Ag3PO4 / ZnFe2O4 / FACs after five cycles of use. DETAILED DESCRIPTION

[0047] The present application provides a floating silver phosphate / zinc ferrite / floating bead composite photocatalyst, comprising floating beads, a zinc ferrite film coated on the floating beads, and silver phosphate deposited on the zinc ferrite film;

[0048] The zinc ferrite and silver phosphate in the zinc ferrite film form a heterojunction.

[0049] The floating silver phosphate / zinc ferrite / floating bead composite photocatalyst provided herein includes floating beads. In this application, the floating beads are hollow microspheres extracted from fly ash waste and characterized by light weight, fine particle size, thin walls, and hollow interior. Their chemical composition is primarily SiO2 and Al2O3, with a glassy phase content of 80% to 85%. The composite photocatalyst prepared using the floating beads as a carrier not only floats on the water surface for extended periods, fully absorbing light energy, but also exhibits excellent adsorption properties that enhance the catalyst's photodegradation performance, facilitating its recovery and repeated reuse.

[0050] The floating silver phosphate / zinc ferrite / floating bead composite photocatalyst provided in the present application includes a zinc ferrite film coated on the floating beads.

[0051] The floating silver phosphate / zinc ferrite / floating bead composite photocatalyst provided in the present application includes silver phosphate deposited on the zinc ferrite film.

[0052] In the present application, zinc ferrite and silver phosphate in the zinc ferrite film form a heterojunction.

[0053] The present application also provides a method for preparing the floating silver phosphate / zinc ferrite / floating bead composite photocatalyst described in the above technical solution, comprising the following steps:

[0054] The trivalent iron salt, zinc salt and complexing agent are dissolved and mixed, and sol reaction and aging are carried out in sequence to obtain a sol system;

[0055] After immersing the floating beads in the sol system, the sol system is roasted to obtain a zinc ferrite / floating bead composite material;

[0056] After the zinc ferrite / floating bead composite material is immersed in a silver salt solution, phosphate is added, and composite reaction and calcination are carried out in sequence to obtain the floating silver phosphate / zinc ferrite / floating bead composite photocatalyst.

[0057] In this application, unless otherwise specified, the raw materials used in this application are preferably commercially available products.

[0058] The present invention dissolves and mixes a trivalent iron salt, a zinc salt and a complexing agent, and sequentially performs a sol reaction and aging to obtain a sol system.

[0059] In the present application, the ferric iron salt preferably includes one or more of ferric nitrate, ferric chloride, and ferric sulfate, more preferably ferric nitrate, and even more preferably Fe(NO3)3·9H2O. In the present application, the zinc salt preferably includes one or more of zinc nitrate, zinc chloride, and zinc sulfate, more preferably zinc nitrate, and even more preferably Zn(NO3)2·6H2O. In the present application, the complexing agent preferably includes one or more of citric acid, ammonium citrate, sodium citrate, and potassium citrate, and even more preferably citric acid.

[0060] In the present application, the ratio of the amount of ferric ions in the ferric salt to the amount of zinc ions in the zinc salt is preferably 2: 1. In the present application, the ratio of the total amount of ferric ions in the ferric salt and the amount of zinc ions in the zinc salt to the amount of the complexing agent is preferably 1: 1.

[0061] In the present application, dissolving and mixing the ferric iron salt, zinc salt, and complexing agent comprises: dissolving the ferric iron salt and zinc salt in a first solvent to obtain a metal salt solution, dissolving the complexing agent in a second solvent to obtain a complexing agent solution; and mixing the metal salt solution and the complexing agent solution. In the present application, the first solvent and the second solvent preferably comprise one or more of ethanol, water, and ethylene glycol, more preferably ethanol, and even more preferably anhydrous ethanol.

[0062] In the present application, the temperature of the sol reaction is preferably 60 to 80° C., and the time is preferably 0.5 to 1 hour. In the present application, the sol reaction is preferably carried out under stirring.

[0063] In the present application, the aging temperature is preferably room temperature, and the aging time is preferably 48 to 72 hours; and the aging is preferably carried out under the condition of a sealed system.

[0064] After obtaining the sol system, the present application immerses the floating beads in the sol system and then calcines the sol system to obtain a zinc ferrite / floating bead composite material.

[0065] In the present application, the particle size of the floating beads is preferably 40 to 60 meshes.

[0066] In the present application, before the floating beads are immersed in the sol system, the process also includes: screening, pickling, washing and drying the floating beads in sequence. In the present application, the screening preferably includes: rinsing and sorting the floating beads with distilled water, and taking the floating beads particles that can completely float on the water surface and have complete morphology as carriers. In the present application, the pickling reagent is preferably a nitric acid solution, and the mass concentration of the nitric acid solution is preferably 12%; the pickling method is preferably immersion, and the immersion time is preferably 12 hours. In the present application, the pickling can remove the fine dust deposited on the surface of the floating beads, making the surface clean and facilitating the subsequent loading of the zinc ferrite film layer. In the present application, the washing reagent is preferably water, and the water is preferably pure water. The present application does not specifically limit the number of washing times and the amount of the washing reagent, until the pH value of the washing solution obtained by washing is neutral. In the present application, the drying temperature is preferably 90°C.

[0067] In the present application, the volume ratio of the floating beads to the sol system is preferably 1:3 to 1:2.

[0068] In the present application, the immersion time of the floating beads is preferably 20 to 40 minutes; the immersion of the floating beads is carried out under stirring conditions.

[0069] After the immersion of the beads and before the calcination, the present application preferably further comprises: filtering out excess sol system and drying. In the present application, the drying temperature is preferably 70-90°C.

[0070] In the present application, the calcination temperature is preferably 450-600°C, the holding time is preferably 1.5-3 hours, and the heating rate to the calcination temperature is preferably 2-4°C / min. In the present application, the calcination is preferably carried out in a muffle furnace.

[0071] After the calcination, the present application preferably further comprises: cooling to room temperature with the furnace, washing with water, and drying the intact granular material floating on the water surface.

[0072] In the present application, the calcination can convert the zinc ferrite from a precursor formed during sol-gel into a zinc ferrite product, and the zinc ferrite is more tightly bound to the surface of the floating beads.

[0073] After obtaining the zinc ferrite / floating bead composite material, the present application immerses the zinc ferrite / floating bead composite material in a silver salt solution, adds phosphate, and sequentially performs composite reaction and calcination to obtain the floating silver phosphate / zinc ferrite / floating bead composite photocatalyst.

[0074] In the present application, the silver salt in the silver salt solution preferably includes silver nitrate, and the solvent of the silver salt solution is preferably water and / or ethanol, more preferably ethanol, and even more preferably anhydrous ethanol.

[0075] In the present application, the phosphate preferably includes one or more of disodium hydrogen phosphate (Na2HPO4), sodium dihydrogen phosphate, and sodium phosphate. The phosphate is preferably used in the form of a phosphate solution. The solvent of the phosphate solution is preferably the same as the solvent in the silver salt solution, which is not described in detail here. In the present application, the phosphate solution is preferably added dropwise to the silver salt solution.

[0076] In the present application, the zinc ferrite / floating bead composite material is preferably impregnated for 20 to 40 minutes; the zinc ferrite / floating bead composite material is preferably impregnated under stirring and in the dark. In the present application, the dark environment can prevent the silver ions from reacting under light and converting into elemental silver.

[0077] In the present application, the molar ratio of silver ions in the silver salt solution to phosphate ions in the phosphate is preferably 3:1.

[0078] In the present application, the temperature of the composite reaction is preferably room temperature, and the time is preferably 1 to 2 hours; the time of the composite reaction is preferably counted from the time the phosphate solution is added. In the present application, the composite reaction is preferably carried out under stirring.

[0079] In the present application, disodium hydrogen phosphate is used as phosphate and silver nitrate is used as silver salt, and the chemical reaction formula of the composite reaction includes: Na2HPO4+3AgNO3=Ag3PO4.

[0080] After the composite reaction and before calcination, the present application preferably further comprises filtering out excess liquid and drying. In the present application, the drying temperature is preferably 80° C. and the drying time is preferably 24 hours.

[0081] In the present application, the calcination temperature is preferably 150-250° C., the holding time is preferably 30-60 minutes, and the heating rate to the calcination temperature is 2-4° C. / min.

[0082] After the calcination, the present application preferably further comprises cooling the furnace temperature to room temperature, washing with water, and taking the floating silver phosphate / zinc ferrite / floating bead composite photocatalyst with intact particles floating on the water surface.

[0083] The present application also provides the use of the floating silver phosphate / zinc ferrite / floating bead composite photocatalyst described in the above technical solution or the floating silver phosphate / zinc ferrite / floating bead composite photocatalyst prepared by the preparation method described in the above technical solution in wastewater treatment.

[0084] The present application also provides a method for treating organic wastewater, comprising the following steps:

[0085] Mixing the catalyst and organic wastewater, and photocatalytically degrading organic matter in the organic wastewater under visible light irradiation;

[0086] The catalyst is the floating silver phosphate / zinc ferrite / floating bead composite photocatalyst described in the above technical solution or the floating silver phosphate / zinc ferrite / floating bead composite photocatalyst prepared by the preparation method described in the above technical solution.

[0087] In the present application, the organic matter includes one or more of methylene blue, methyl orange, phenol and rhodamine B.

[0088] In the present application, the usage ratio of the catalyst to wastewater is preferably 5-10 g:1 L.

[0089] In the present application, the degradation temperature is preferably room temperature.

[0090] The floating silver phosphate / zinc ferrite / floating bead composite photocatalyst provided by the present application, its preparation method and application, and wastewater treatment method are described in detail below in conjunction with the examples, but they should not be understood as limiting the scope of protection of the present application.

[0091] Pretreatment of floating beads

[0092] Floating beads with a mesh size of 40-60 are screened, rinsed with distilled water, and sorted. The beads that float completely on the water surface and have intact morphology are selected as the carrier for the photocatalytic material. The screened beads are soaked in a 10% dilute HNO3 solution for 12 hours to remove fine dust deposited on the beads' surface and clean the surface for subsequent zinc ferrite coating. The acidified beads are then repeatedly washed with pure water until the pH of the rinse solution is neutral. Finally, the beads are dehydrated and dried in a 90°C drying oven for later use.

[0093] Example 1

[0094] 1.49g Zn(NO₃)₂·6H₂O and 4.04g Fe(NO₃)₃·9H₂O solids were weighed and dissolved in 40mL of anhydrous ethanol in a molar ratio of 1:2. 3.15g of citric acid solids (equimolar to the metal ions) were weighed and dissolved in 20mL of anhydrous ethanol. The two solutions were mixed thoroughly and heated with a constant-temperature magnetic stirrer at 70°C for half an hour. The mixture was sealed and aged at room temperature for 48 hours to obtain a sol system. A certain amount of pretreated FACs beads were immersed in the prepared sol system and stirred thoroughly to thoroughly mix the beads and sol system. The solution was then poured through a sieve to filter out excess sol system. The solution was then dried in an 80°C oven for 24 hours. The solution was then heated to 500°C in a muffle furnace at a heating rate of 3°C / min for 2 hours and then cooled as the temperature of the furnace decreased. The obtained product is rinsed with deionized water, and the complete loaded floating beads floating on the water surface are taken out and dried to obtain the zinc ferrite / floating beads composite material ZnFe2O4 / FACs for use.

[0095] 1g of silver nitrate was dissolved in 20mL of ethylene glycol. 1g of the prepared ZnFe2O4 / FACs was then immersed in the solution and stirred on a magnetic stirrer in the dark for half an hour. 10mL of ethanol containing 0.3g of sodium dihydrogen phosphate (NaH2PO4) was then slowly added to the clear solution and stirred for 1 hour. The solution was then poured onto a sieve to remove excess liquid. The solid was then dried in an 80°C oven for 24 hours and then heated to 200°C in a muffle furnace at a heating rate of 3°C / min for 30 minutes. After cooling, the solution was rinsed with deionized water. The intact supported photocatalyst that floated on the surface was removed and dried to produce the Ag3PO4 / ZnFe2O4 / FACs composite catalyst.

[0096] Comparative Example

[0097] Take 1g of silver nitrate and dissolve it in 20mL of ethylene glycol. Stir it on a magnetic stirrer in the dark for half an hour. Then, slowly add 10mL of ethanol solution containing 0.3g of disodium hydrogen phosphate (Na2HPO4) to the above silver nitrate solution and stir it for 1h. After washing and drying, Ag3PO4 powder is prepared.

[0098] ZnFe2O4 powder was prepared in the manner of Example 1.

[0099] ZnFe2O4 powder, Ag3PO4 / ZnFe2O4 powder, and Ag3PO4 / FACs were prepared using the method and parameters of Example 1. ZnFe2O4 / FACs and FACs were also used as comparative examples.

[0100] Figure 1 is the XRD spectra of ZnFe2O4, Ag3PO4 / ZnFe2O4 and Ag3PO4, and Figure 2 is the XRD spectra of FACs, ZnFe2O4 / FACs, Ag3PO4 / FACs and Ag3PO4 / ZnFe2O4 / FACs. It can be seen from Figure 1 that the XRD curves of ZnFe2O4 and Ag3PO4 are consistent with the ZnFe2O4 standard card (JCPDS82-1042) and Ag3PO4 standard card (JCPDS 06-0505), respectively. The diffraction peaks of the prepared materials are relatively sharp and there are no obvious impurity peaks, indicating that the prepared catalysts have high crystallinity. All diffraction peaks on the XRD curve of ZnFe2O4 / Ag3PO4 can be found on both Ag3PO4 and ZnFe2O4 standard cards, indicating that the prepared composite photocatalyst does not contain other substances and that the recombination between ZnFe2O4 and Ag3PO4 is a physical effect rather than a chemical reaction. Figure 2 clearly shows that the fly ash FACs exhibit sharp, characteristic diffraction peaks for Al2O3, in addition to characteristic diffraction peaks for silicon oxide and iron oxide. This demonstrates that the high-temperature-formed fly ash FACs possess a complete crystal structure and are a type of aluminosilicate ceramic composed of multiple oxides. Their physicochemical properties are very stable, making them suitable as catalyst supports. At the same time, it was found that in addition to the unique diffraction peaks of FACs, the other diffraction peaks of the XRD curves of ZnFe2O4 / FACs, Ag3PO4 / FACs, and Ag3PO4 / ZnFe2O4 / FACs corresponded to the ZnFe2O4 and Ag3PO4 standard cards, respectively, indicating that ZnFe2O4, Ag3PO4, and Ag3PO4 / ZnFe2O4 / FACs have the same structure as the FACs. e2 O4 was successfully loaded on the surface of FACs.

[0101] Figure 3 shows the UV-vis spectra of different photocatalysts. As shown in Figure 3, the absorption wavelength of ZnFe2O4 / FACs is around 750nm, the absorption wavelength of Ag3PO4 / FACs is around 600nm, and the absorption wavelength of Ag3PO4 / ZnFe2O4 / FACs is around 650nm. The absorption band edge of the bead catalyst shows a certain degree of red shift relative to the powder catalyst, which is mainly related to the composition of the carrier beads. The absorption band edge of Ag3PO4 / ZnFe2O4 / FACs also shows a red shift relative to Ag3PO4 / FACs, indicating that the absorption range of Ag3PO4 / ZnFe2O4 for visible light has increased, which helps to improve the utilization rate of visible light by the composite and promote the progress of the photocatalytic reaction.

[0102] Figure 4 shows the effects of floating beads (a) and Ag3PO4 / ZnFe2O4 / FACs (b) in aqueous solution. It can be seen from Figure 4 that the prepared Ag3PO4 / ZnFe2O4 / FACs can float or suspend in the water body, which is convenient for recovery; whether it is the unloaded floating beads (a) or the loaded Ag3PO4 / ZnFe2O4 / FACs (b), their particles float on the surface of the aqueous solution.

[0103] Figure 5 shows SEM images of FACs (a), ZnFe2O4 / FACs (b and c), Ag3PO4 / FACs (d), and Ag3PO4 / ZnFe2O4 / FACs (e and f). Figure 5 (a) shows that the beads are regular spherical, with a particle size of approximately 200 μm and a relatively smooth surface. Figure 5 (b) shows that the surface of the beads becomes noticeably roughened after ZnFe2O4 is loaded onto them. Figure 5 (c) shows that the ZnFe2O4 is loaded onto the beads with irregular morphologies, with particle sizes ranging from 200 to 400 nm and relatively uniform dispersion. Figure 5 (d) shows that the Ag3PO4 particles are scattered and deposited on the surface of the beads, with a less uniform distribution. Figures 5 (e) and (f) show that Ag3PO4 and ZnFe2O4 form large heterojunction particles loaded onto the surface of the beads, and the particles are tightly bonded to the surface.

[0104] 0.05g of powdered catalyst and 0.5g of different catalysts supported by floating beads were placed in 100mL of methylene blue (MB) in organic wastewater with a concentration of 10mg / L. Degradation was performed under dark and light conditions. The results are shown in Figures 6 and 7. Figure 6 shows the degradation rates of MB by ZnFe2O4, Ag3PO4, and Ag3PO4 / ZnFe2O4 under visible light, while Figure 7 shows the degradation rates of MB by ZnFe2O4 / FACs, Ag3PO4 / FACs, and Ag3PO4 / ZnFe2O4 / FACs under visible light. Figures 6 and 7 show that the dark reaction and methylene blue photolysis blank experiments showed almost no adsorption or degradation of the dye. In Figure 6, the degradation rate of MB by ZnFe2O4 alone was only 30% within 30 minutes, while that of Ag3PO4 alone was 73%. The Ag3PO4 / ZnFe2O4 composite achieved an 86% degradation rate within 30 minutes, representing 56% and 13% increases over the two monomers, respectively. This indicates that the Ag3PO4 and ZnFe2O4 composite catalysts exhibited superior catalytic activity to the monomer catalysts. In Figure 7, the photocatalytic activity of the monomer catalysts combined with the floating beads was significantly enhanced. The degradation rates of methylene blue increased to 40% for ZnFe2O4 / FACs and 83% for Ag3PO4 / FACs. The Ag3PO4 / ZnFe2O4 / FACs composite photocatalyst achieved a 99% degradation rate within 30 minutes, approximately 13% higher than the Ag3PO4 / ZnFe2O4 powder photocatalyst. The photocatalytic degradation rate was also significantly increased.

[0105] Figure 8 shows the photocatalytic degradation of Ag3PO4 / FACs and Ag3PO4 / ZnFe2O4 / FACs after five cycles. It can be seen from Figure 8 that the photocatalytic efficiency of the Ag3PO4 / FACs catalyst is significantly reduced when it is used for the second time. On the one hand, the silver phosphate and the floating beads cannot be firmly combined and partially dissolved in water. On the other hand, the defects of Ag3PO4 itself cannot be overcome, that is, photocorrosion occurs, causing Ag3PO4 to be converted into Ag 0 , making this catalyst unsuitable for recycling. The Ag3PO4 / ZnFe2O4 / FACs solid catalyst is not only 99% recyclable, but after five cycles, the catalyst degradation rate drops only slightly from an initial 99% to 91%. Eliminating catalyst loss, the stability of Ag3PO4 / ZnFe2O4 / FACs remains excellent.

[0106] The above is only a preferred embodiment of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present application. These improvements and modifications should also be regarded as the scope of protection of the present application.

Claims

1. A floating silver phosphate / zinc ferrite / floating bead composite photocatalyst, characterized in that: It comprises floating beads, a zinc ferrite film coated on the floating beads, and silver phosphate deposited on the zinc ferrite film; The zinc ferrite and silver phosphate in the zinc ferrite film form a heterojunction.

2. The method for preparing the floating silver phosphate / zinc ferrite / floating bead composite photocatalyst according to claim 1, characterized in that: The following steps are involved: The trivalent iron salt, the zinc salt and the complexing agent are dissolved and mixed, and sol reaction and aging are carried out in sequence to obtain a sol system; After the floating beads are immersed in the sol system, they are roasted to obtain a zinc ferrite / floating bead composite material; After the zinc ferrite / floating bead composite material is immersed in a silver salt solution, phosphate is added, and a composite reaction and calcination are performed to obtain the floating silver phosphate / zinc ferrite / floating bead composite photocatalyst.

3. The preparation method according to claim 2, characterized in that: The molar ratio of the trivalent iron ions in the trivalent iron salt to the zinc ions in the zinc salt is 2:1; the molar ratio of the total molar ratio of the trivalent iron ions in the trivalent iron salt and the zinc ions in the zinc salt to the molar ratio of the complexing agent is 1:

1.

4. The preparation method according to claim 2 or 3, characterized in that: The ferric iron salt includes one or more of ferric nitrate, ferric chloride and ferric sulfate.

5. The preparation method according to claim 2 or 3, characterized in that: The zinc salt includes one or more of zinc nitrate, zinc chloride and zinc sulfate.

6. The preparation method according to claim 2 or 3, characterized in that: The complexing agent includes one or more of citric acid, ammonium citrate, sodium citrate and potassium citrate.

7. The preparation method according to claim 2, characterized in that: The dissolving and mixing of the ferric iron salt, zinc salt and complexing agent comprises: dissolving the ferric iron salt and zinc salt in a first solvent to obtain a metal salt solution, dissolving the complexing agent in a second solvent to obtain a complexing agent solution; and mixing the metal salt solution and the complexing agent solution.

8. The preparation method according to claim 7, characterized in that: The first solvent and the second solvent both include one or more of ethanol, water and ethylene glycol.

9. The preparation method according to claim 2 or 7, characterized in that: The temperature of the sol reaction is 60-80° C., the time is 0.5-1 hour, and the sol reaction is carried out under stirring.

10. The preparation method according to claim 2 or 7, characterized in that: The aging temperature is room temperature and the aging time is 48 to 72 hours.

11. The preparation method according to claim 2, characterized in that: The particle size of the floating beads is 40 to 60 meshes.

12. The preparation method according to claim 2 or 11, characterized in that: Before the floating beads are immersed in the sol system, the method further includes: screening, acid washing, washing and drying the floating beads in sequence.

13. The preparation method according to claim 2, characterized in that: The volume ratio of the floating beads to the sol system is 1:3 to 1:

2.

14. The preparation method according to claim 2 or 13, characterized in that: The immersion time of the floating beads is 20 to 40 minutes; the immersion of the floating beads is carried out under stirring conditions.

15. The preparation method according to claim 2, characterized in that: After the floating beads are soaked and before being roasted, the method further includes: filtering out excess sol system and drying; the drying temperature is 70-90°C.

16. The preparation method according to claim 2, characterized in that: The calcination temperature is 450-600° C., the heat preservation time is 1.5-3 hours, and the heating rate to the calcination temperature is 2-4° C. / min.

17. The preparation method according to claim 2, characterized in that: The silver salt in the silver salt solution includes silver nitrate; the phosphate includes one or more of disodium hydrogen phosphate, sodium dihydrogen phosphate and sodium phosphate.

18. The preparation method according to claim 2 or 17, characterized in that: The molar ratio of the silver ions in the silver salt solution to the phosphate radicals in the phosphate is 3:1 to 2:

1.

19. The preparation method according to claim 2, characterized in that: The temperature of the composite reaction is room temperature and the time is 1 to 2 hours.

20. The preparation method according to claim 2, characterized in that: After the composite reaction and before calcination, the method further includes filtering out excess liquid and performing drying.

21. The preparation method according to claim 2, characterized in that: The calcination temperature is 150-250° C., the heat preservation time is 30-60 minutes, and the heating rate to the calcination temperature is 2-4° C. / min.

22. Use of the floating silver phosphate / zinc ferrite / floating bead composite photocatalyst according to claim 1 or the floating silver phosphate / zinc ferrite / floating bead composite photocatalyst prepared by the preparation method according to claims 2 to 21 in wastewater treatment.

23. A method for treating organic wastewater, characterized in that: The following steps are involved: The catalyst and the organic wastewater are mixed, and the organic matter in the organic wastewater is photocatalytically degraded under visible light irradiation; The organic matter includes one or more of methylene blue, methyl orange, phenol and rhodamine B; The catalyst is the floating silver phosphate / zinc ferrite / floating bead composite photocatalyst described in claim 1 or the floating silver phosphate / zinc ferrite / floating bead composite photocatalyst prepared by the preparation method described in claims 2 to 21.

24. The wastewater treatment method according to claim 23, characterized in that: The dosage ratio of the catalyst to wastewater is 5-10g:1L.

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