Floatable catalyst and preparation method thereof

Abstract

The invention discloses a floatable catalyst and a preparation method thereof.The catalyst is obtained by generating resorcinol-formaldehyde resin on the surface of a protonated tungsten oxide-carbon nitride heterojunction in situ and can float on the water surface, and the preparation method of the catalyst comprises the steps that after carbon nitride is treated with concentrated sulfuric acid, the carbon nitride is added into the concentrated sulfuric acid; the preparation method comprises the following steps: preparing a heterostructure composite material with tungsten oxide, adding the composite material into an alcohol solution containing resorcinol and formaldehyde for dipping and loading, and calcining at 100-300 DEG C to obtain the catalyst capable of floating on the water surface. According to the preparation principle, the surface confinement effect is applied, resorcinol-formaldehyde resin is promoted to generate an unconventional structure on the surface of tungsten oxide-carbon nitride, and the density of the catalyst is reduced, so that the catalyst can float on the surface of water. The catalyst does not adopt an inert carrier or an adhesive, is simple to prepare and firm in structure, and has a very good application prospect.

Description

Technical Field

[0001] This invention belongs to the field of catalytic materials technology, specifically relating to a floatable catalyst and its preparation method. Background Technology

[0002] Currently, with the increasing prominence of energy crises and environmental pollution, solar energy utilization has become a hot research area, and photocatalysis technology is considered one of the effective ways to solve these problems. Besides photocatalytic water splitting to produce hydrogen, oxygen, and hydrogen peroxide, or synthesizing ammonia from atmospheric nitrogen, photocatalysis technology can also drive redox reactions under sunlight at room temperature to degrade pollutants and achieve deep mineralization, which is of great significance for clean energy production and environmental pollution control. Graphitic carbon nitride (g-C3N4) has advantages such as visible light responsiveness, low cost and availability, and good chemical stability, but it also has disadvantages such as small specific surface area, high photogenerated charge recombination rate, and low light utilization efficiency. Among the continuously improving methods, loading noble metal nanoparticles or clusters onto protonated modified carbon nitride to enhance catalyst performance (Patent 202110712289.X) is a feasible approach. Additionally, preparing phosphorus-doped carbon nitride nanosheets modified with sulfonic acid functional groups can also improve the photocatalytic hydrogen production performance of carbon nitride materials (Xue Mengqi, Master's Thesis, Anhui University, 2022). Alternatively, preparing gold / acid-modified carbon nitride (AW / CN-H) nanomaterials using nitric acid-modified dicyandiamine and chloroauric acid as raw materials also effectively improves the photocatalytic performance of the catalyst (Peng Qiong, Master's Thesis, Nanjing University of Science and Technology, 2018). Furthermore, synthesizing sulfonic acid-functionalized g-C3N4 nanosheets (SACN) through a simple solid-phase thermal reaction between g-C3N4 and aminosulfonic acid is beneficial for improving light utilization efficiency (Zhang Min, Journal of Catalysis, 2022, 43: 526-535).

[0003] Conventional carbon nitride catalysts, improved using conventional methods, have a density greater than water. During use, rapid mechanical stirring or gas agitation is required to suspend the catalyst. However, under natural conditions, sunlight always shines on the water surface. As water depth increases, the light absorption capacity of the catalyst below the surface decreases significantly, greatly affecting photocatalytic efficiency. Therefore, catalysts floating on the surface have a greater advantage in light utilization. Furthermore, catalysts at the water surface are more likely to contact gas molecules, making them particularly suitable for gas-based photocatalytic reactions. In addition, floating catalysts are easier to recover, thus avoiding water pollution, and therefore hold great promise for environmental remediation. For these reasons, floatable catalysts have attracted widespread attention.

[0004] Patent CN117623238A discloses a DA-type carbon nitride, its chitosan composite microspheres, and its application in aflatoxin degradation. This involves fixing carbon nitride within chitosan spheres to achieve its buoyancy. Patent CN117225477A discloses a self-floating bismuth oxybromide / carbon nitride aerogel sphere, which is obtained by hydrothermal reaction of bismuth nitrate pentahydrate, carbon nitride, and sodium alginate, followed by cross-linking and curing in a CaCl2 solution, and then freeze-drying to obtain a porous spherical structure. Patent CN116651490A discloses a multi-level radial microspherical basic phosphate-carbon nitride composite material and its preparation method and application. This involves dispersing carbon nitride in deionized water to obtain a suspension, then adding phosphate and spraying it into a metal acetate solution to generate flocculent insoluble matter. The resulting multi-level radial microspherical basic phosphate-carbon nitride composite material is then separated, washed, and dried.Patent CN115254149A discloses a floatable carbon nitride-based piezoelectric photocatalyst, its preparation method, and its application. This photocatalyst is obtained by surface-mounting fish-scale tubular carbon nitride and vanadium-doped bismuth iodate with melamine sponge as a framework, resulting in a photocatalytic material that can float on the surface of organic pollutant solutions. Patent CN114570404A discloses a floating photocatalytic material for water remediation and its preparation method. This involves preparing defective carbon nitride nanosheets through a secondary calcination method, then depositing silver carbonate nanoparticles in situ and adhering them to a perlite surface using ethyl polystyrene adhesive, thus obtaining a floatable carbon nitride-based piezoelectric photocatalyst. Floating photocatalytic materials; Patent CN109908955B discloses a method for preparing a self-floating carbon nitride / cellulose acetate flexible photocatalytic porous film, which uses graphitic carbon nitride treated with strong oxidizing acid as raw material, and then forms a uniform mixed solution with cellulose acetate before coating to obtain a self-floating film; Li Jia et al. (dissertation, Guangdong University of Technology, 2022) carried out the preparation of floating modified graphitic carbon nitride photocatalytic films and their inhibition and algal toxin degradation mechanism against Microcystis aeruginosa, using pyromellitic anhydride-modified graphitic carbon nitride to prepare a stable floating film. Photocatalytic films floating on water surface; Patent CN202410125874.3 discloses a floating catalyst and its application in the synthesis of p-hydroxyphenylhydantoin, which is a floating catalyst obtained by loading copper and manganese co-doped nano-TiO2 hydrosol onto fly ash cenospheres to form a gel and then sintering it at 600-700℃; Patent CN202311852533.8 discloses a floating aerogel algae removal catalyst, which is a material obtained by loading single metal atoms onto guar gum as a carrier and then carbonizing it at 700-720℃; Patent CN202311865950. 6. A method for preparing M-SA / TiO2-g-C3N4 metal nanocomposite materials was reported. The method involved freeze-drying a colloidal solution containing Pt and TiO2 nanoparticles to obtain Pt / TiO2 aerogel. This aerogel, along with tetrabutyl titanate, ethanol, and acetonitrile, was then added to an acetonitrile and ammonia dispersion containing SiO2 nanoparticles. The addition of copper salt yielded a precipitate. This precipitate underwent stepwise reactions with tetraethyl orthosilicate, an alkaline solution, chloroplatinic acid, and g-C3N4. Finally, cross-linking with acrylamide, bisacrylamide, and an initiator resulted in the metal nanocomposite material. While these studies have shown significant improvement and achieved catalyst floatability, most employ inert supports or binders, which can mask or encapsulate the active components of the catalyst, reducing the number of active sites per unit surface area. Furthermore, the use of supports or binders presents challenges such as complex preparation processes and the susceptibility of the supports or binders to degradation.

[0005] This invention first combines protonated carbon nitride with tungsten oxide to obtain a Z-shaped heterostructure carbon nitride-tungsten oxide catalytic material, which promotes the separation of photogenerated charges. Based on this, in-situ polymerization of photoactive resorcinol-formaldehyde resin on the surface of nano-carbon nitride-tungsten oxide is achieved through a simple adsorption-loading and calcination method, resulting in a composite photocatalytic material with reduced density that can float on the water surface. This material can be used as a photocatalyst, such as for the photocatalytic conversion to synthesize hydrogen peroxide or for the photocatalytic degradation of pollutants in water. Summary of the Invention

[0006] The purpose of this invention is to provide a floatable catalyst and its preparation method. Specifically, it is a catalyst that can float on water by in-situ generating resorcinol-formaldehyde resin on the surface of protonated tungsten oxide-carbon nitride. The catalyst has a self-floating function on the water surface and can be used in the field of photocatalysis, especially suitable for photocatalytic scenarios in natural environments.

[0007] The present invention discloses a floatable catalyst and its preparation method. The preparation method involves adding carbon nitride to 98.3% concentrated sulfuric acid and heating it to 80-100°C to promote its dissolution, obtaining a protonated carbon nitride solution. Then, 5%-30% of tungsten oxide (WO3) equivalent to the mass of carbon nitride is added and stirred continuously until it dissolves into a transparent brown solution. The solution is then ultrasonically mixed for 20 minutes. The transparent brown solution is then slowly added dropwise to a low-temperature solvent while stirring continuously until a solid precipitates. The solution is then filtered, dried, and ground to obtain tungsten oxide-supported carbon nitride (denoted as WCN), i.e., tungsten oxide-carbon nitride (WCN) with a Z-shaped heterostructure. The tungsten oxide-supported carbon nitride is then added to an alcohol solution containing resorcinol and formaldehyde. A small amount of ammonia is added dropwise and mixed evenly. The solvent is removed by rotary evaporation, and the solution is dried and ground. The resulting solid is then calcined at 100-300°C for 1-5 hours to obtain a catalyst that can float on water.

[0008] The above-described floatable catalyst and its preparation method, wherein the low-temperature solvent is an ice-water mixture or one of methanol, ethanol, or propanol frozen below room temperature; the alcohol is one of methanol, ethanol, or propanol; the amount of resorcinol is 5% to 50% of the mass of tungsten oxide-carbon nitride; the amount of formaldehyde is 2 to 4 times the amount of resorcinol used; the addition of a small amount of ammonia water is the amount of ammonia water added in the catalyst-grade mixture, that is, 1 to 2 drops of ammonia water are added to every 20 mL of the mixture, one drop is about 0.02 mL, and the concentration of the ammonia water used is 25% to 28%, which plays a role in promoting the polymerization of resorcinol and formaldehyde.

[0009] The above-described floatable catalyst and its preparation method are described above. The catalyst possesses self-floating properties, allowing it to float on the water surface for photocatalytic conversion or photocatalytic degradation reactions under natural light. Because the catalyst can fully contact O2 in the air, it does not require low concentrations of dissolved oxygen in the water, thus increasing O2 utilization and enhancing the oxygen reduction reaction. Similarly, when used for direct photocatalytic degradation of pollutants, the high surface O2 concentration promotes the generation of various oxygen free radicals, thereby increasing the oxidative degradation rate of pollutants.

[0010] The above-described floatable catalyst and its preparation method are based on the principle that tungsten oxide and carbon nitride both possess visible light activity, and their combination yields a Z-type heterojunction that has been documented in the literature (ACS Appl. Nano Mater. 2020, 3, 2, 1298-1306; J Alloy). Compd (2022, 896, 162931) is a highly effective method to improve the photocatalytic performance of catalysts. Our improvement lies in dissolving carbon nitride in concentrated sulfuric acid, which not only achieves the protonation of carbon nitride but also ensures molecular-level contact with the dissolved tungsten oxide, thereby achieving uniform loading and ensuring the homogeneous structure of tungsten oxide-carbon nitride (WCN). This results in a highly uniform Z-shaped heterojunction, which is more conducive to the transfer and separation of photogenerated charges. In addition, the treatment with concentrated sulfuric acid also leaves a small portion of sulfonic acid groups, i.e., aminosulfonic acid structures, on the surface of WCN, which is the result of the interaction between concentrated sulfuric acid and the amino groups in carbon nitride. Based on WCN, by impregnating resorcinol and formaldehyde solutions and adding ammonia, the reactive monomers resorcinol, formaldehyde, and catalyst ammonia are loaded together on the surface of tungsten oxide-carbon nitride. Under a certain calcination temperature in the later stage, in-situ polymerization is carried out to form a resorcinol-formaldehyde resin with photocatalytic activity. Due to the spatial confinement effect of the tungsten oxide-carbon nitride surface and the influence of surrounding carbon nitride groups such as amino groups, resorcinol and formaldehyde cannot freely polymerize into conventional spheres. Instead, they form hollow, elongated ellipsoidal shapes, thus reducing the density of the material. Furthermore, during the forming process, due to the influence of surrounding WCN surface groups such as amino and aminosulfonic acid groups, as well as the participation of amino groups in the resin polymerization reaction, the shape will grow directly on the carbon nitride surface and have a very stable structure. This is something that cannot be achieved by conventional loading methods, such as directly impregnating the resin solution and then calcining.

[0011] The beneficial effects of this invention are as follows:

[0012] 1) The catalyst is prepared by directly dissolving carbon nitride in sulfuric acid. It can not only complete the protonation reaction to guide the polymerization of hydroquinone-formaldehyde resin in the later stage, but also achieve molecular-level contact and doping with tungsten oxide dissolved in the later step, thereby ensuring that tungsten oxide-carbon nitride has a homogeneous heterojunction structure.

[0013] 2) Visible light-active resorcinol-formaldehyde resin is obtained through in-situ polymerization under the spatial confinement effect of tungsten oxide-carbon nitride surface. The resulting material is a spherical shape with reduced density, which enables the catalyst to float on the water surface. This not only facilitates light absorption in the natural environment but also eliminates the need for stirring, thus providing energy-saving advantages.

[0014] 3) Combining resorcinol-formaldehyde resin, which has high visible light activity, with Z-type heterojunction tungsten oxide-carbon nitride further improves the visible light absorption performance of the catalyst, and enhances charge transfer and separation efficiency through the built-in electric field of the heterojunction.

[0015] 4) Under the spatial confinement effect of tungsten oxide-carbon nitride surface, resorcinol-formaldehyde resin is generated in situ. The groups in carbon nitride participate in the structure of the resin, ensuring the stability of the catalyst structure.

[0016] 5) The catalyst obtained by this method can float on the water surface without the need for a low-density support, and the separation of the main catalyst component from the support during use will not occur, thus ensuring the stability of the catalyst structure. Attached Figure Description

[0017] Figure 1 Comparison of infrared spectra of tungsten oxide-carbon nitride-resorcinol formaldehyde resin (WCN-PF-1) and raw materials at each stage. In this diagram, CN represents carbon nitride, CNS represents carbon nitride precipitated after dissolution with sulfuric acid (i.e., protonated carbon nitride), WCN represents tungsten oxide-carbon nitride heterojunction catalyst, and WCN-PF-1 is the floatable catalyst obtained in Example 1, and the same applies below.

[0018] Figure 2 Comparison of X-ray crystallography (XRD) images of carbon nitride (CN), protonated carbon nitride (CNS), tungsten oxide (WO3), and tungsten oxide-carbon nitride (WCN).

[0019] Figure 3 X-ray diffraction (XRD) pattern of resorcinol-formaldehyde resin modified tungsten oxide-carbon nitride (WCN-PF-1) prepared in Example 1.

[0020] Figure 4 Scanning electron microscope (SEM) image of tungsten oxide-carbon nitride (WCN) prepared in Example 1.

[0021] Figure 5 Scanning electron microscope (SEM) image of the resorcinol-formaldehyde resin modified tungsten oxide-carbon nitride (WCN-PF-1) prepared in Example 1.

[0022] Figure 6 X-ray photoelectron spectrum of tungsten oxide-carbon nitride (WCN) prepared in Example 1.

[0023] Figure 7 X-ray photoelectron spectrum of the resorcinol-formaldehyde resin modified tungsten oxide-carbon nitride (WCN-PF-1) prepared in Example 1.

[0024] Figure 8 Photograph of the resorcinol-formaldehyde resin modified tungsten oxide-carbon nitride (WCN-PF-1) prepared in Example 1 floating on the water surface.

[0025] Figure 9 Comparison of photocurrent densities between catalysts WCN-PF-1 and WCN.

[0026] Figure 10 Comparison of infrared spectra of the WCN-PF catalysts prepared in each embodiment. The numbers following WCN-PF correspond one-to-one with the serial numbers of each embodiment, representing the catalyst obtained in that embodiment.

[0027] Figure 11 Comparison of X-ray diffraction (XRD) spectra of the WCN-PF catalysts prepared in each embodiment. The numbers following WCN-PF correspond one-to-one with the serial numbers of each embodiment, indicating the catalyst obtained in that embodiment.

[0028] Figure 12 Comparison of UV-Vis diffuse reflectance spectra of the WCN-PF catalysts prepared in each embodiment (including WCN). The numbers following WCN-PF correspond one-to-one with the serial numbers of each embodiment, representing the catalysts obtained in that embodiment. Detailed Implementation

[0029] The present invention will be further described below with reference to the accompanying drawings and embodiments. It should be noted that the following embodiments are merely illustrative of the invention and should not be construed as limiting the scope of protection of the invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the invention are within the scope of protection of the invention. The specific process parameters in the following embodiments are also merely examples of preferred conditions and are not intended to limit the specific values ​​in the embodiments.

[0030] Example 1

[0031] A floatable catalyst and its preparation method are disclosed, which is a composite catalyst for in-situ generation of resorcinol-formaldehyde resin on the surface of protonated carbon nitride-tungsten oxide and its preparation method. Further, the following embodiment is provided:

[0032] Step 1: Preparation of carbon nitride. Based on the method described in the literature (Chemical Engineering Journal, 2022, 427: 131710), equal masses of nitrogen-rich precursors, namely melamine (ML), cyanuric acid (CY), and thiourea (TU) (e.g., 3:3:3, 1 g each), were transferred to boiling water. The water volume was adjusted according to their solubility to obtain a solution. The three solutions were mixed and stirred for 30 min, then transferred to a Teflon-lined reactor and kept in an oven at 100 °C for 4 h. After natural cooling, the mixture was centrifuged, washed, dried in an oven at 80 °C, and ground to obtain carbon nitride (CN) prepolymer. A certain mass of CN prepolymer was placed in a crucible and subjected to gradient calcination in a muffle furnace: first calcined at 520 °C for 100 min, then heated to 550 °C for 2 h. After natural cooling, pale yellow carbon nitride, denoted as CN, was obtained.

[0033] Step 2: Preparation of Tungsten Oxide-Carbon Nitride Heterojunction (WCN) Take 5 mL of concentrated sulfuric acid in a beaker, add 1 g of the carbon nitride prepared in Step 1, and heat on a 100°C heating stage to promote its dissolution. After obtaining a solution, add 0.15 g of WO3. After it dissolves into a transparent brown solution, sonicate for 20 min. While stirring, slowly add the sonicated solution dropwise to 25 mL of ice-cold methanol. After the addition is complete, continue stirring for 30 min, then let stand to allow the solid to settle completely. Filter, wash the filter cake three times with a small amount of methanol, dry at 80°C for 5 h, and grind to obtain the composite catalyst tungsten oxide-carbon nitride (WCN).

[0034] Step 3: Prepare a floatable composite catalyst based on WCN. Dissolve 0.05g of resorcinol in 40mL of ethanol, add 0.12g of 37% formaldehyde, and sonicate for 5min. Then add 1g of WCN and continue sonicating for 20min. Add 2 drops of ammonia and stir for 1min. Immediately remove the solvent by rotary evaporation at 50℃. Then dry the resulting solid at 80℃ for 12h. After grinding, transfer it to a tube furnace (natural air atmosphere) for gradient calcination: increase the temperature to 100℃ at 5℃ / min and hold for 0.5h, then continue to increase the temperature to 150℃ at 5℃ / min and hold for 0.5h, then continue to increase the temperature to 200℃ at 5℃ / min and hold for 1h. After calcination, the solid sample was taken out after cooling to room temperature and then ground slightly in a mortar to obtain a resorcinol-formaldehyde resin modified WCN catalyst, labeled as WCN-PF-1, where WCN represents tungsten oxide-carbon nitride heterojunction, PF represents toluene-formaldehyde resin, and 1 corresponds to Example 1.

[0035] Figure 1 A comparison of the infrared spectra of catalyst WCN-PF-1 and the raw materials used is presented. It can be seen that the carbon nitride treated with sulfuric acid has a higher concentration at 1150 cm⁻¹. -1The catalyst exhibits S=O bond characteristics on both sides, and this structure was maintained during later modifications, indicating the presence of sulfur, which is beneficial for improving photocatalytic performance. After modification with tungsten oxide, the catalyst showed improved performance at 800 cm⁻¹. -1 The increased absorption is attributed to the W=O bond vibration in tungsten oxide. After modification with resorcinol-formaldehyde resin, the peak shape around 1400 cm⁻¹ shows a significant change, indicating the presence of this organic structure on the catalyst surface. (Appendix) Figure 2 XRD comparisons of raw materials at different stages are given. It can be seen that tungsten oxide has more characteristic peaks, while carbon nitride only shows its (002) diffraction peak around 2θ = 27°, and its (100) diffraction peak near 2θ = 13.1° is not obvious. CNS obtained after treatment with concentrated sulfuric acid and then precipitation shows a new diffraction peak between 2θ = 11 and 13°, possibly due to the intercalation of sulfuric acid molecules. When CNS is combined with tungsten oxide, the peak between 2θ = 11 and 13° in WCN changes, showing only a diffraction peak similar to that of carbon nitride (100), indicating that the structure of carbon nitride is partially restored after treatment with tungsten oxide. Except for the diffraction peak of carbon nitride (002) around 2θ = 27°, the XRD mainly shows the crystal characteristics of tungsten oxide. After further modification with resorcinol-formaldehyde resin, the XRD of the catalyst WCN-PF-1 is shown. Figure 3 The XRD pattern is similar to that of WCN, and no obvious resin characteristic peaks are observed. In fact, the characteristic peaks of this resin are around 2θ = 26°, which are easily masked by the characteristic peaks of tungsten oxide. Figure 4 and Figure 5 Scanning electron microscope (SEM) images of WCN and WCN-PF-1 are shown respectively. The morphology clearly shows... Figure 5 The resin is an in-situ generated elongated ellipsoidal resin that is very tightly bound to the substrate catalyst. In addition, the modification of WCN with this resin further adjusts the bulk structure and increases the specific surface area. Figure 6 and Figure 7 The X-ray photoelectron spectra of WCN and WCN-PF-1 are shown respectively. It can be seen that the catalyst contains five elements: C, O, N, S and W. After WCN is modified with PF, the C content in the catalyst increases significantly, indicating that there is a resin structure on the surface of WCN. Figure 8 The image shows that catalyst WCN-PF-1 can float on water without any stirring, which is beneficial for maximizing light absorption at the interface and facilitating the photocatalytic reaction involving gases. Additionally, the photocurrent responses of catalysts WCN-PF-1 and WCN under xenon lamp irradiation at wavelengths above 300 nm were measured; a comparison figure is shown below. Figure 9 WCN-PF-1 exhibits a higher photocurrent density than WCN, indicating that the former has better photogenerated charge separation performance.

[0036] The photocatalytic conversion of this catalyst to hydrogen peroxide was investigated: Under xenon lamp (300 W / m²) irradiation, 10 mg of catalyst WCN-PF-1 was added to 10 mL of neutral deionized water, ultrasonically dispersed for 1 min, and allowed to stand in the dark for 0.5 h. Air was then introduced and bubbled through the solution for 4 h of photocatalytic reaction (>300 nm). Afterwards, 2 mL of the solution was removed by high-speed centrifugation to remove the catalyst, and the hydrogen peroxide concentration was measured to be 1.12 mM. Under acidic conditions (pH = 3), the hydrogen peroxide yield per unit mass of catalyst reached as high as 19.4 mmol·g⁻¹. -1 ·h -1 A concentration of 1.12 mM hydrogen peroxide meets the requirements for preparing Fenton's reagent. If a small amount of ferrous chloride is added, it can become Fenton's reagent, which can be used to rapidly degrade organic pollutants in water.

[0037] Example 2

[0038] Steps 1 and 2 in this embodiment are the same as in Embodiment 1 described above. Step 3 in this embodiment is as follows: Dissolve 0.05g of resorcinol in 40mL of ethanol, add 0.12g of 37% formaldehyde, ultrasonically disperse for 5min, add 1g of WCN, continue ultrasonic mixing for 20min, add 2 drops of ammonia and stir for 1min, immediately remove the solvent by rotary evaporation at 50℃, then dry the resulting solid at 80℃ for 12h, grind it, and transfer it to a tube furnace (natural air atmosphere) for gradient calcination: increase the temperature to 100℃ at 5℃ / min, hold for 0.5h, then continue to increase the temperature to 150℃ at 5℃ / min, hold for 0.5h, then continue to increase the temperature to 250℃ at 5℃ / min, hold for 2h. After calcination, the solid sample was taken out after cooling to room temperature and then ground slightly in a mortar to obtain a resorcinol-formaldehyde resin modified WCN catalyst, labeled as WCN-PF-2, where WCN represents tungsten oxide-carbon nitride heterojunction, PF represents toluene-formaldehyde resin, and 2 corresponds to Example 2.

[0039] Figure 10 The infrared spectra of the catalysts obtained in each embodiment show that the peaks are similar in position and have similar structures. Figure 11 and Figure 12 The X-ray diffraction patterns and UV-Vis diffuse reflectance spectra of the catalysts obtained in different embodiments are compared. It can be seen that the crystal structures of the catalysts prepared in each embodiment are similar. Compared with WCN, the light absorption of the catalysts prepared in each embodiment is significantly enhanced at around 560 nm, indicating that toluene-formaldehyde resin is generated in situ on the surface of WCN.

[0040] Using the same test conditions as in Example 1, the catalyst WCN-PF-2 obtained in Example 2 was used to conduct a photocatalytic synthesis of hydrogen peroxide in neutral water. After 4 hours of illumination, the hydrogen peroxide concentration reached 0.95 mM.

[0041] Example 3

[0042] Step 1 in this embodiment is the same as in Embodiment 1 described above.

[0043] Step 2: Preparation of Tungsten Oxide-Carbon Nitride Heterojunction (labeled: WCN) Take 5 mL of concentrated sulfuric acid in a beaker, add 1 g of the carbon nitride prepared in Step 1, and heat on an 80°C heating plate to promote its dissolution. After obtaining a solution, add 0.25 g of WO3. After it dissolves into a transparent brown solution, sonicate for 20 min. While stirring, add the sonicated solution dropwise to 30 mL of an ice-water mixture. After the addition is complete, continue stirring for 30 min, then let stand to allow the solid to settle completely. Filter, wash the filter cake three times with a small amount of methanol, dry at 80°C for 5 h, and grind to obtain the composite catalyst tungsten oxide-carbon nitride (WCN).

[0044] Step 3: Dissolve 0.1g of resorcinol in 40mL of ethanol, add 0.24g of 37% formaldehyde, and sonicate for 5min. Then add 1g of WCN and continue sonicating for 20min. Add 2 drops of ammonia and stir for 1min. Immediately remove the solvent by rotary evaporation at 50℃. Dry the resulting solid at 80℃ for 10h, grind it, and transfer it to a tube furnace (natural air atmosphere) for gradient calcination: increase the temperature to 100℃ at 5℃ / min, hold for 0.5h, then continue increasing the temperature to 150℃ at 5℃ / min, hold for 0.5h, and then continue increasing the temperature to 200℃ at 5℃ / min, hold for 2h. After calcination, cool to room temperature and remove the solid sample. Grind it slightly in a mortar to obtain a resorcinol-formaldehyde resin modified WCN catalyst, labeled WCN-PF-3, where WCN represents tungsten oxide-carbon nitride heterojunction, PF represents toluene-formaldehyde resin, and 3 represents Example 3.

[0045] The infrared spectrum, X-ray crystal diffraction pattern, and ultraviolet-visible diffuse reflectance spectrum of the catalyst WCN-PF-3 obtained in this embodiment are shown in the figures below. Figure 10 , Figure 11 and Figure 12 As can be seen from these figures, the catalyst prepared in this embodiment has a similar structure to the catalysts in the previous embodiments and belongs to the same type of catalyst.

[0046] Using the same test conditions as in Example 1, the catalyst WCN-PF-3 obtained in Example 3 was used to conduct a photocatalytic synthesis of hydrogen peroxide in neutral water. After 4 hours of illumination, the hydrogen peroxide concentration reached 1.04 mM.

[0047] Example 4

[0048] Steps 1 and 2 of this embodiment are the same as those in Embodiment 1 described above. Step 3 of this embodiment is as follows: Dissolve 0.1g of resorcinol in 40mL of ethanol, add 0.24g of 37% formaldehyde, sonicate for 5min, add 1g of WCN, continue sonication for 20min, add 2 drops of ammonia and stir for 1min, immediately remove the solvent by rotary evaporation at 50℃, then dry the resulting solid at 80℃ for 10h, grind it, and transfer it to a tube furnace (natural air atmosphere) for gradient calcination: increase the temperature to 100℃ at 5℃ / min, hold for 0.5h, then continue to increase the temperature to 150℃ at 5℃ / min, hold for 0.5h, then continue to increase the temperature to 300℃ at 5℃ / min, hold for 1h. After calcination, the solid sample was taken out after cooling to room temperature and then ground slightly in a mortar to obtain a resorcinol-formaldehyde resin modified WCN catalyst, labeled as WCN-PF-4, where WCN represents tungsten oxide-carbon nitride heterojunction, PF represents toluene-formaldehyde resin, and 4 corresponds to Example 4.

[0049] The infrared spectrum, X-ray crystal diffraction pattern, and ultraviolet-visible diffuse reflectance spectrum of the catalyst WCN-PF-4 obtained in this embodiment are shown in the figures below. Figure 10 , Figure 11 and Figure 12 As can be seen from these figures, the catalyst prepared in this embodiment has a similar structure to the catalysts in the previous embodiments and belongs to the same type of catalyst.

[0050] Using the same test conditions as in Example 1, the catalyst WCN-PF-4 obtained in Example 4 was used to conduct a photocatalytic synthesis of hydrogen peroxide in neutral water. After 4 hours of illumination, the hydrogen peroxide concentration reached 0.72 mM.

[0051] Example 5

[0052] Steps 1 and 2 of this embodiment are the same as those in Embodiment 1 described above. Step 3 of this embodiment is as follows: Dissolve 0.2g of resorcinol in 40mL of ethanol, add 0.48g of 37% formaldehyde, ultrasonically disperse for 5min, add 1g of WCN, continue ultrasonication for 20min, add 3 drops of ammonia water and stir for 1min, immediately remove the solvent by rotary evaporation at 50℃, then dry the resulting solid at 80℃ for 10h, grind it, and transfer it to a tube furnace (natural air atmosphere) for gradient calcination: increase the temperature to 100℃ at 5℃ / min, hold for 0.5h, then continue to increase the temperature to 150℃ at 5℃ / min, hold for 0.5h, and then continue to increase the temperature to 250℃ at 5℃ / min, hold for 1h. After calcination, the solid sample was taken out after cooling to room temperature and then ground slightly in a mortar to obtain a resorcinol-formaldehyde resin modified WCN catalyst, labeled as WCN-PF-5, where WCN represents tungsten oxide-carbon nitride heterojunction, PF represents toluene-formaldehyde resin, and 5 corresponds to Example 5.

[0053] The infrared spectrum, X-ray crystal diffraction pattern, and ultraviolet-visible diffuse reflectance spectrum of the catalyst WCN-PF-5 obtained in this embodiment are shown in the figures below. Figure 10 , Figure 11 and Figure 12 As can be seen from these figures, the catalyst prepared in this embodiment has a similar structure to the catalysts in the previous embodiments and belongs to the same type of catalyst.

[0054] Using the same test conditions as in Example 1, the catalyst WCN-PF-5 obtained in Example 5 was used to conduct a photocatalytic synthesis of hydrogen peroxide in neutral water. After 4 hours of illumination, the hydrogen peroxide concentration reached 0.78 mM.

Claims

1. A floatable catalyst and its preparation method, wherein the catalyst is a water-floating catalyst obtained by in-situ generation of resorcinol-formaldehyde resin on the surface of a protonated tungsten oxide-carbon nitride heterojunction. The preparation method of the catalyst is as follows: carbon nitride is added to concentrated sulfuric acid and heated to 80-100°C to promote its dissolution, resulting in a solution of protonated carbon nitride. Then, 5%-30% of tungsten oxide (WO3) equivalent to the mass of carbon nitride is added, and the solution is stirred to promote its dissolution into a transparent brown solution. The solution is then ultrasonically mixed for 20 min. Under stirring, the ultrasonically mixed solution is slowly added dropwise to a low-temperature solvent. The mixture is stirred continuously until a solid precipitates out. The solution is then filtered, dried, and ground to obtain tungsten oxide-loaded carbon nitride. The tungsten oxide-loaded carbon nitride is then added to an alcohol solution containing resorcinol and formaldehyde. A small amount of ammonia is added dropwise and mixed evenly. The alcohol solvent is removed by rotary evaporation, and the solution is dried and ground. The resulting solid is calcined at 100-300°C for 1-5 h to obtain a water-floating catalyst.

2. The floatable catalyst and its preparation method according to claim 1, wherein the low-temperature solvent is an ice-water mixture, or one of methanol, ethanol, or propanol that has been frozen at a temperature below room temperature.

3. The floatable catalyst and its preparation method according to claim 1, wherein the alcohol solution containing resorcinol and formaldehyde is one of ethanol, methanol, and propanol, the amount of resorcinol is 5% to 50% of the mass of tungsten oxide-carbon nitride, and the amount of formaldehyde is 2 to 4 times the amount of resorcinol used.

4. According to claim 1, the floating catalyst and its preparation method, the addition of a small amount of ammonia water means adding a catalytic amount of ammonia water to the mixture, that is, adding 1 to 2 drops of ammonia water to every 20 mL of the mixture.

Images