Photocatalyst for degrading formaldehyde and preparation method thereof

Abstract

The invention relates to the technical field of formaldehyde pollution treatment materials, and discloses a photocatalyst for degrading formaldehyde and a preparation method thereof, and the photocatalyst contains an activated carbon substrate, anatase TiO2 and modified nitrogen-sulfur co-doped carbon quantum dots. Wherein the carbon quantum dots are prepared from a hydroxyl-containing aromatic dianhydride compound, a carbon source compound and an amino-containing nitrogen-sulfur donor compound through a hydrothermal reaction, and can enhance formaldehyde adsorption and broaden light response to a visible light region; the crystal form and the hydroxyl content of TiO2 are regulated and controlled through ammonium fluoride; after being pretreated by nitric acid, the activated carbon and other components form a chemical cross-linked network, and the photocatalyst solves the problems that a traditional photocatalyst material is prone to adsorption saturation and low in light utilization rate.

Description

Technical Field

[0001] This application belongs to the field of formaldehyde pollution control technology, specifically relating to a photocatalyst for degrading formaldehyde and its preparation method. Background Technology

[0002] Formaldehyde, as one of the main pollutants in indoor air, is characterized by high toxicity and a long release period of 3-15 years. Long-term exposure can harm the human respiratory and nervous systems and even induce cancer. Therefore, the research and development of indoor formaldehyde purification technology is of great practical significance.

[0003] Existing formaldehyde treatment technologies are mainly divided into two categories: physical adsorption and photocatalytic degradation. Physical adsorption methods often use activated carbon as the adsorbent material. Although it can quickly capture formaldehyde, activated carbon has a limited adsorption capacity and is prone to saturation. After saturation, it needs to be frequently replaced or regenerated, otherwise it may lead to formaldehyde desorption and secondary pollution. Photocatalytic degradation uses anatase TiO2 as the core catalyst, which can completely oxidize formaldehyde into harmless CO2 and H2O without secondary pollution. However, pure anatase TiO2 can only respond to ultraviolet light, which accounts for less than 5% of indoor light, resulting in extremely low light utilization. Moreover, photogenerated electron-hole pairs are prone to recombination, which limits catalytic efficiency and makes it difficult to meet the high-efficiency degradation requirements of low-concentration formaldehyde in indoor environments. Traditional composite materials are mostly physically mixed. The interfacial bonding between activated carbon and TiO2 is weak, and particle agglomeration is prone to occur, resulting in low efficiency of formaldehyde transfer from adsorption sites to catalytic sites. At the same time, there is a lack of effective means to broaden the light response range of TiO2, and it is still impossible to overcome the technical bottleneck of low visible light utilization, making it difficult to balance formaldehyde degradation efficiency, long-term stability, and indoor applicability.

[0004] Therefore, developing a formaldehyde degradation material that can achieve efficient adsorption, broad spectral response, and low carrier recombination rate has become a key requirement in the current field of indoor air purification. Summary of the Invention

[0005] The purpose of this application is to overcome the shortcomings of existing formaldehyde treatment technologies. In the case of physical adsorption methods, activated carbon is easily saturated and causes secondary pollution, while in traditional photocatalysis methods, anatase TiO2 has a narrow light response range, high photogenerated electron-hole recombination rate, and low catalytic efficiency. The application provides a carbon quantum dot modified activated carbon-based photocatalyst that has the advantages of high efficiency in adsorption and enrichment, broad spectral response, high catalytic activity, and long-term cycle stability.

[0006] To achieve the above objectives, this application adopts the following technical solution:

[0007] In a first aspect, this application provides a photocatalyst for degrading formaldehyde, comprising the following components: an activated carbon substrate, anatase TiO2, and modified nitrogen-sulfur co-doped carbon quantum dots;

[0008] The preparation steps of modified nitrogen-sulfur co-doped carbon quantum dots include:

[0009] Aromatic dianhydride compounds containing hydroxyl groups were dissolved in deionized water and stirred at 70-80℃ for 10-15 min until completely dissolved. Then, a carbon source compound was added, and the temperature was raised to 80-90℃ and stirred for 25-35 min. Next, an amino-containing nitrogen-sulfur donor compound was added to the resulting reaction solution, which was then transferred to a hydrothermal reactor and hydrothermally reacted at 150-200℃ for 4-5 h. The resulting product was purified by dialysis and then freeze-dried to obtain modified nitrogen-sulfur co-doped carbon quantum dots.

[0010] Furthermore, the activated carbon substrate includes any one of coconut shell activated carbon or bamboo charcoal; the anatase TiO2 has a particle size of 20-30 nm; and the modified nitrogen-sulfur co-doped carbon quantum dots have a particle size of 3-6 nm.

[0011] Furthermore, the hydroxyl-containing aromatic dianhydride compounds include one or more of 3-hydroxyphthalic anhydride or 6-hydroxynaphthalic anhydride; the carbon source compounds include one or more of glucose, fructose, lactose and maltose; and the amino-containing nitrogen and sulfur donor compounds include one or more of thiourea, aminothiourea and thioacetamide.

[0012] Furthermore, in the preparation steps of modified nitrogen-sulfur co-doped carbon quantum dots, the mass ratio of carbon source compound, amino-containing nitrogen-sulfur donor compound, hydroxyl-containing aromatic dianhydride compound and deionized water is (3-5):(2-3):(1-2):(90-94).

[0013] Furthermore, the mass ratio of activated carbon substrate, anatase TiO2 and modified nitrogen-sulfur co-doped carbon quantum dots is (55-70):(28-44):(1-2).

[0014] Adding ammonium fluoride to the titanium source solution generates anatase phase TiO2, which creates micro-defects on the TiO2 surface, increasing the number and distribution density of surface hydroxyl groups (-OH). The hydroxyl groups provide sufficient active sites for the esterification reaction with modified nitrogen and sulfur co-doped carbon quantum dots, and can also be converted into highly oxidizing hydroxyl radicals (·OH) under photoexcitation, thus achieving the oxidative decomposition of formaldehyde.

[0015] Modified nitrogen-sulfur co-doped carbon quantum dots achieve broad-spectrum response and efficient formaldehyde enrichment. The preparation process involves a stepwise chemical reaction of hydroxyl-containing aromatic dianhydrides with carbon source compounds and amino-containing nitrogen-sulfur donor compounds: first, the hydroxyl-containing aromatic dianhydrides are dissolved and activated at a suitable temperature; then, after adding the carbon source compound, stable COC bonds are formed through a dehydration condensation reaction; next, amino-containing nitrogen-sulfur donor compounds are added for a hydrothermal reaction, utilizing the ring-opening reaction between the amino groups of the amino-containing nitrogen-sulfur donor compound and the anhydride groups of the hydroxyl-containing aromatic dianhydrides. The directional introduction of carboxyl groups (-COOH) onto the surface of carbon quantum dots allows the oxygen atoms in the carboxyl groups to form stable hydrogen bonds with the hydrogen atoms in the aldehyde groups of formaldehyde molecules, significantly enhancing the adsorption affinity of carbon quantum dots for formaldehyde molecules. At the same time, the introduction of hydroxyl-containing aromatic dianhydride compounds and nitrogen and sulfur elements alters the electronic conjugation system of carbon quantum dots, narrowing their band gap and extending the photoresponse range from the ultraviolet region to the visible light region, making them suitable for indoor lighting environments. Furthermore, the surface defects formed by the hydroxyl-containing aromatic dianhydride compounds and carbon quantum dots can act as electron traps, capturing photogenerated electrons to reduce the recombination of photogenerated electron-hole pairs.

[0016] Activated carbon substrate serves as the adsorption framework and support. After nitric acid pretreatment, oxygen- and nitrogen-containing functional groups such as hydroxyl (-OH) and amino (-NH2) are introduced onto the surface, enhancing the adsorption capacity of activated carbon for formaldehyde molecules. The high specific surface area and microporous structure of activated carbon itself provide a large number of adsorption sites, while the surface functional groups further enhance the adsorption capacity by forming hydrogen bonds or electrostatic interactions with formaldehyde molecules. On the other hand, the hydroxyl and amino groups on the surface of activated carbon can undergo esterification or amidation reactions with the carboxyl groups on the surface of modified nitrogen-sulfur co-doped carbon quantum dots, and the carboxyl groups of modified nitrogen-sulfur co-doped carbon quantum dots can also undergo esterification reactions with the hydroxyl groups on the surface of TiO2, ultimately constructing a chemical cross-linked network.

[0017] Secondly, this application provides a method for preparing a photocatalyst for degrading formaldehyde, comprising the following steps:

[0018] S1. The activated carbon substrate is ultrasonically treated with 0.5 mol / L nitric acid solution for 30-45 min, washed, and then vacuum dried at 100-120℃ for 4-6 h to obtain a pretreated activated carbon substrate. The pretreated activated carbon substrate is dispersed in deionized water to form an activated carbon substrate aqueous dispersion with a concentration of 0.1-0.2 g / mL.

[0019] S2. Add ammonium fluoride powder to the titanium source solution and stir to dissolve. Stir and perform hydrothermal reaction. Wash, filter, dry and calcine the product to obtain anatase TiO2. Disperse the anatase TiO2 in anhydrous ethanol to form a TiO2 ethanol dispersion. Add modified nitrogen-sulfur co-doped carbon quantum dots and stir at 60-70℃ for 5-6 hours. After centrifugation, wash the precipitate with anhydrous ethanol and dry at 80-90℃ for 2-3 hours to obtain TiO2-modified nitrogen-sulfur co-doped carbon quantum dot composite.

[0020] S3. Add the above-mentioned TiO2-modified nitrogen-sulfur co-doped carbon quantum dot composite to the activated carbon substrate aqueous dispersion, stir at a constant temperature of 50-60℃ for 7-8h, filter the product, wash with deionized water until the filtrate is colorless, and vacuum dry at 90-100℃ and vacuum degree of -0.08~-0.1MPa for 3-4h to obtain the photocatalyst for degrading formaldehyde.

[0021] Furthermore, in S1, the mass ratio of activated carbon substrate to nitric acid solution is 1:(10-15).

[0022] Furthermore, in S2, the preparation steps of the titanium source solution include: taking tetrabutyl titanate, anhydrous ethanol and deionized water, first placing the anhydrous ethanol under stirring at 300-500 rpm, then adding tetrabutyl titanate dropwise into the ethanol at a rate of 1-2 drops / second, and continuing to stir for 10-15 minutes to form a pre-dispersion; then adding deionized water at the same dropping rate, and continuing to stir for 20-30 minutes to obtain the titanium source solution.

[0023] Furthermore, the volume ratio of tetrabutyl titanate, anhydrous ethanol, and deionized water in the titanium source solution is 1:5:1.

[0024] Furthermore, in S2, the mass ratio of ammonium fluoride powder to titanium source solution is 1:(16-32), the stirring time is 15-20 min, the hydrothermal reaction temperature is 160-180℃, and the time is 4-6 h; the product is washed until the pH is 7-8; the calcination temperature is 400-450℃, and the time is 1-2 h; the concentration of the TiO2 ethanol dispersion is 0.05-0.1 g / mL.

[0025] In the preparation of TiO2, ammonium fluoride is produced by F... - By controlling the TiO2 crystal form to the anatase phase and creating micro-defects on the TiO2 surface, these defects can enhance the interfacial bonding force with nitrogen-sulfur co-doped carbon quantum dots, reduce electron transport resistance, and further improve the utilization efficiency of photogenerated carriers.

[0026] Beneficial technical effects:

[0027] This application provides a photocatalyst for formaldehyde degradation and its preparation method. During the preparation of anatase TiO2, ammonium fluoride is added to induce micro-defects on its surface, increasing the surface hydroxyl content. Under photoexcitation, the hydroxyl groups are converted into highly oxidizing hydroxyl radicals (·OH), which are used to oxidize and decompose formaldehyde molecules. Modified nitrogen-sulfur co-doped carbon quantum dots introduce carboxyl groups, achieving adsorption of formaldehyde molecules through hydrogen bonding, thus realizing the efficient enrichment of low-concentration formaldehyde. Simultaneously, the introduction of hydroxyl-containing aromatic dianhydrides and nitrogen-sulfur elements alters the carbon quantum dots... The electron conjugation system of the dots narrows the band gap and extends the photoresponse range of TiO2 from only responding to the ultraviolet light region to the visible light region, making it suitable for indoor lighting environments. Activated carbon can physically adsorb a large amount of formaldehyde due to its high specific surface area and microporous structure. After pretreatment, the hydroxyl and amino groups on the surface of activated carbon can undergo esterification or amidation reactions with the carboxyl groups on the surface of modified nitrogen-sulfur co-doped carbon quantum dots. Combined with the esterification reaction of the carboxyl groups of modified nitrogen-sulfur co-doped carbon quantum dots and the hydroxyl groups on the surface of TiO2, a chemical cross-linking network is constructed, avoiding the component loss problem caused by traditional physical mixing. Attached Figure Description

[0028] Figure 1 A flowchart illustrating a method for preparing a photocatalyst for degrading formaldehyde, as provided in this application. Detailed Implementation

[0029] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, a detailed description of specific embodiments of this application will be provided below.

[0030] Many specific details are set forth in the following description in order to provide a full understanding of this application. However, this application may also be implemented in other ways different from those described herein. Those skilled in the art can make similar extensions without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0031] Example 1

[0032] like Figure 1 As shown, this embodiment provides a method for preparing a photocatalyst for degrading formaldehyde, comprising the following steps:

[0033] S1. Mix coconut shell activated carbon with 0.5 mol / L nitric acid solution at a mass ratio of 1:10, and sonicate for 45 min. After washing with deionized water, dry under vacuum at 100℃ for 6 h to obtain pretreated coconut shell activated carbon. Disperse the pretreated coconut shell activated carbon in deionized water to form a coconut shell activated carbon base aqueous dispersion with a concentration of 0.2 g / mL.

[0034] S2. Add ammonium fluoride powder to the titanium source solution, wherein the mass ratio of ammonium fluoride powder to titanium source solution is 1:16. Stir for 20 min until completely dissolved, transfer to a hydrothermal reactor, and react hydrothermally at 160℃ for 6 h. Wash the product until pH 7.2, filter, dry, and calcine at 400℃ for 2 h to obtain anatase TiO2 with a particle size of 20 nm. Disperse the anatase TiO2 in anhydrous ethanol to form a TiO2 ethanol dispersion with a concentration of 0.05 g / mL. Add modified nitrogen-sulfur co-doped carbon quantum dots, stir at 60℃ for 6 h, centrifuge at 3000 rpm for 15 min, wash the precipitate three times with anhydrous ethanol, and dry at 80℃ for 3 h to obtain the TiO2-modified nitrogen-sulfur co-doped carbon quantum dot composite.

[0035] The titanium source solution is prepared as follows: tetrabutyl titanate, anhydrous ethanol, and deionized water are taken in a volume ratio of 1:5:1. The anhydrous ethanol is first stirred at 300 rpm. Then, tetrabutyl titanate is added dropwise to the ethanol at a rate of 1 drop / second, and the mixture is stirred continuously for 15 minutes until a transparent pale yellow pre-dispersion is formed. Subsequently, deionized water is added at the same dropping rate, and the mixture is stirred for another 30 minutes to obtain the titanium source solution.

[0036] The method for preparing the modified nitrogen-sulfur co-doped carbon quantum dots is as follows: glucose, thiourea, 3-hydroxyphthalic anhydride and deionized water are taken in a mass ratio of 3:2:1:94. First, the 3-hydroxyphthalic anhydride is dissolved in deionized water and stirred at 70°C for 15 min until completely dissolved. Then, glucose is added, and the temperature is raised to 80°C and stirred for 35 min. Next, thiourea is added, and the mixture is transferred to a hydrothermal reactor and hydrothermally reacted at 150°C for 5 h. The reaction product is purified by dialysis and then freeze-dried to obtain modified nitrogen-sulfur co-doped carbon quantum dots with a particle size of 3 nm.

[0037] S3. Add TiO2-modified nitrogen-sulfur co-doped carbon quantum dot composite to the coconut shell activated carbon substrate aqueous dispersion, stir at 50℃ for 8h; filter, wash with deionized water until the filtrate is colorless, and vacuum dry at 90℃ and vacuum degree -0.08MPa for 4h to obtain the photocatalyst for degrading formaldehyde.

[0038] In the photocatalyst, the mass ratio of coconut shell activated carbon substrate, anatase TiO2, and modified nitrogen-sulfur co-doped carbon quantum dots is 70:28:2.

[0039] Example 2

[0040] like Figure 1 As shown, this embodiment provides a method for preparing a photocatalyst for degrading formaldehyde, comprising the following steps:

[0041] S1. Mix bamboo charcoal with 0.5 mol / L nitric acid solution at a mass ratio of 1:15, and sonicate for 45 min. After washing with deionized water, vacuum dry at 120℃ for 6 h to obtain pretreated bamboo charcoal. Disperse the pretreated bamboo charcoal in deionized water to form a bamboo charcoal base aqueous dispersion with a concentration of 0.2 g / mL.

[0042] S2. Add ammonium fluoride powder to the titanium source solution, wherein the mass ratio of ammonium fluoride powder to titanium source solution is 1:32. Stir for 20 min until completely dissolved, transfer to a hydrothermal reactor, and react hydrothermally at 180℃ for 6 h. Wash the product until pH 8, dry it, and calcine at 450℃ for 2 h to obtain anatase TiO2 with a particle size of 30 nm. Disperse the anatase TiO2 in anhydrous ethanol to form a TiO2 ethanol dispersion with a concentration of 0.1 g / mL. Add modified nitrogen-sulfur co-doped carbon quantum dots, stir at 70℃ for 6 h, centrifuge at 2500 rpm for 15 min, wash the precipitate three times with anhydrous ethanol, and dry at 90℃ for 3 h to obtain the TiO2-modified nitrogen-sulfur co-doped carbon quantum dot composite.

[0043] The titanium source solution is prepared as follows: tetrabutyl titanate, anhydrous ethanol and deionized water are taken in a volume ratio of 1:5:1. First, the anhydrous ethanol is stirred at 500 rpm. Then, tetrabutyl titanate is added dropwise to the ethanol at a rate of 2 drops / second and stirred continuously for 15 minutes to form a pre-dispersion. Subsequently, deionized water is added at the same dropping rate and stirred for another 30 minutes to obtain the titanium source solution.

[0044] The modified nitrogen-sulfur co-doped carbon quantum dots are prepared as follows: fructose, aminothiourea, 6-hydroxynaphthalenedicarboxylic anhydride and deionized water are taken in a mass ratio of 5:3:2:90. First, 6-hydroxynaphthalenedicarboxylic anhydride is dissolved in deionized water and stirred at 80°C for 15 min until completely dissolved. Fructose is added, and the temperature is raised to 90°C and stirred for 35 min. Then, aminothiourea is added, and the mixture is transferred to a hydrothermal reactor and hydrothermally reacted at 200°C for 5 h. The reaction product is purified by dialysis and then freeze-dried to obtain modified nitrogen-sulfur co-doped carbon quantum dots with a particle size of 6 nm.

[0045] S3. Add TiO2-modified nitrogen-sulfur co-doped carbon quantum dot composite to the bamboo charcoal substrate aqueous dispersion, stir at 60℃ for 8 hours; filter, wash with deionized water until the filtrate is colorless, and vacuum dry at 100℃ and vacuum degree -0.1MPa for 4 hours to obtain the photocatalyst for degrading formaldehyde.

[0046] In the photocatalyst, the mass ratio of bamboo charcoal activated carbon substrate, anatase TiO2, and modified nitrogen-sulfur co-doped carbon quantum dots is 55:44:1.

[0047] Example 3

[0048] like Figure 1As shown, this embodiment provides a method for preparing a photocatalyst for degrading formaldehyde, comprising the following steps:

[0049] S1. Mix coconut shell activated carbon with 0.5 mol / L nitric acid solution at a mass ratio of 1:12.5, and sonicate for 37.5 min. After washing with deionized water, dry under vacuum at 110℃ for 5 h to obtain pretreated coconut shell activated carbon. Disperse the pretreated coconut shell activated carbon in deionized water to form a coconut shell activated carbon base aqueous dispersion with a concentration of 0.15 g / mL.

[0050] S2. Add ammonium fluoride powder to the titanium source solution, wherein the mass ratio of ammonium fluoride powder to titanium source solution is 1:24. Stir for 17.5 min until completely dissolved, transfer to a hydrothermal reactor, and react hydrothermally at 170℃ for 5 h. Wash the product until pH is 7.5, dry it, and calcine it at 425℃ for 1.5 h to obtain anatase TiO2 with a particle size of 25 nm. Disperse the anatase TiO2 in anhydrous ethanol to form a TiO2 ethanol dispersion with a concentration of 0.075 g / mL. Add modified nitrogen-sulfur co-doped carbon quantum dots, stir at 65℃ for 5.5 h, centrifuge at 3000 rpm for 20 min, wash the precipitate three times with anhydrous ethanol, and dry at 85℃ for 2.5 h to obtain the TiO2-modified nitrogen-sulfur co-doped carbon quantum dot composite.

[0051] The titanium source solution was prepared as follows: tetrabutyl titanate, anhydrous ethanol, and deionized water were taken in a volume ratio of 1:5:1. The anhydrous ethanol was first stirred at 400 rpm, and then tetrabutyl titanate was added dropwise to the ethanol at a rate of 1.5 drops / second. The mixture was stirred continuously for 12.5 min to form a pre-dispersion. Subsequently, deionized water was added at the same dropping rate, and the mixture was stirred for another 25 min to obtain the titanium source solution.

[0052] The modified nitrogen-sulfur co-doped carbon quantum dots are prepared as follows: lactose, thioacetamide, 3-hydroxyphthalic anhydride and deionized water are taken in a mass ratio of 4:2.5:1.5:92. First, the 3-hydroxyphthalic anhydride is dissolved in deionized water and stirred at 75°C for 12.5 min until completely dissolved. Then, lactose is added, and the temperature is raised to 85°C and stirred for 30 min. Next, thioacetamide is added, and the mixture is transferred to a hydrothermal reactor and hydrothermally reacted at 175°C for 4.5 h. The reaction product is purified by dialysis and then freeze-dried to obtain modified nitrogen-sulfur co-doped carbon quantum dots with a particle size of 4.5 nm.

[0053] S3. Add TiO2-modified nitrogen-sulfur co-doped carbon quantum dot composite to the coconut shell activated carbon substrate aqueous dispersion, stir at 55℃ for 7.5h; filter, wash with deionized water until the filtrate is colorless, and vacuum dry at 95℃ and vacuum degree -0.09MPa for 3.5h to obtain the photocatalyst for degrading formaldehyde.

[0054] In the photocatalyst, the mass ratio of coconut shell activated carbon substrate, anatase TiO2, and modified nitrogen-sulfur co-doped carbon quantum dots is 62:36:2.

[0055] Example 4

[0056] like Figure 1 As shown, this embodiment provides a method for preparing a photocatalyst for degrading formaldehyde, comprising the following steps:

[0057] S1. Mix bamboo charcoal with 0.5 mol / L nitric acid solution at a mass ratio of 1:13 and sonicate for 40 min. After washing with deionized water, vacuum dry at 105℃ for 4.5 h to obtain pretreated bamboo charcoal. Disperse the pretreated bamboo charcoal in deionized water to form a bamboo charcoal base aqueous dispersion with a concentration of 0.12 g / mL.

[0058] S2. Add ammonium fluoride powder to the titanium source solution, wherein the mass ratio of ammonium fluoride powder to titanium source solution is 1:28, stir for 16 min until completely dissolved, transfer to a hydrothermal reactor, and react hydrothermally at 165℃ for 4.8 h; wash the product until pH 7.3, dry it, and calcine at 430℃ for 1.2 h to obtain anatase TiO2 with a particle size of 23 nm; disperse the anatase TiO2 in anhydrous ethanol to form a TiO2 ethanol dispersion with a concentration of 0.06 g / mL; add modified nitrogen-sulfur co-doped carbon quantum dots, stir at 62℃ for 5.3 h; centrifuge at 3000 rpm for 15 min, wash the precipitate three times with anhydrous ethanol, and dry at 82℃ for 2.3 h to obtain the TiO2-modified nitrogen-sulfur co-doped carbon quantum dot composite;

[0059] The titanium source solution was prepared as follows: tetrabutyl titanate, anhydrous ethanol, and deionized water were taken in a volume ratio of 1:5:1. The anhydrous ethanol was first stirred at 350 rpm, and then tetrabutyl titanate was added dropwise to the ethanol at a rate of 1.3 drops / second. The mixture was stirred for 13 minutes to form a pre-dispersion. Then, deionized water was added at the same dropping rate, and the mixture was stirred for another 26 minutes to obtain the titanium source solution.

[0060] The modified nitrogen-sulfur co-doped carbon quantum dots are prepared as follows: maltose, aminothiourea, 6-hydroxynaphthalenedicarboxylic anhydride, and deionized water are taken in a mass ratio of 3.8:2.2:1.4:92.6. First, the 6-hydroxynaphthalenedicarboxylic anhydride is dissolved in deionized water and stirred at 73°C for 13 min until completely dissolved. Then, maltose is added, and the temperature is raised to 83°C and stirred for 31 min. Next, aminothiourea is added, and the mixture is transferred to a hydrothermal reactor and hydrothermally reacted at 185°C for 4.2 h. The reaction product is purified by dialysis and then freeze-dried to obtain modified nitrogen-sulfur co-doped carbon quantum dots with a particle size of 4 nm.

[0061] S3. Add TiO2-modified nitrogen-sulfur co-doped carbon quantum dot composite to the bamboo charcoal substrate aqueous dispersion, stir at 52℃ for 7.2h; filter, wash with deionized water until the filtrate is colorless, and vacuum dry at 93℃ and vacuum degree -0.085MPa for 3.2h to obtain the photocatalyst for degrading formaldehyde.

[0062] In the photocatalyst, the mass ratio of bamboo charcoal activated carbon substrate, anatase TiO2, and modified nitrogen-sulfur co-doped carbon quantum dots is 60:39:1.

[0063] Comparative Example 1

[0064] Comparative Example 1 provides a method for preparing a photocatalyst for degrading formaldehyde. Compared with Example 1, no modified nitrogen-sulfur co-doped carbon quantum dots were added in S2, and other operation steps and process parameters were the same as in Example 1.

[0065] Comparative Example 2

[0066] Comparative Example 2 provides a method for preparing a photocatalyst for degrading formaldehyde. Compared with Example 1, S2 does not contain anatase TiO2, but other operating steps and process parameters are the same as in Example 1.

[0067] The performance of the photocatalysts for degrading formaldehyde prepared in the above embodiments and comparative examples was tested, and the results are shown in Table 1.

[0068] Table 1. Performance test results of photocatalysts for formaldehyde degradation prepared in each embodiment and comparative example.

[0069]

[0070] Examples 1-4 all utilize coconut shell activated carbon, anatase TiO2, and modified nitrogen-sulfur co-doped carbon quantum dots to prepare carbon quantum dot-modified activated carbon-based photocatalysts for formaldehyde degradation. Each photocatalyst exhibits excellent formaldehyde degradation performance and cycle stability. In principle, the modified nitrogen-sulfur co-doped carbon quantum dots directionally introduce carboxyl functional groups through a stepwise reaction between hydroxyl-containing aromatic dianhydride compounds, carbon source compounds, and amino-containing nitrogen-sulfur donor compounds. This enhances the adsorption and enrichment capacity for formaldehyde through hydrogen bonding, addressing the problem of insufficient substrate for low-concentration formaldehyde catalysis. Furthermore, by altering the electron conjugation system and narrowing the band gap, the photoresponse is extended from ultraviolet to the visible light region. Simultaneously, surface defects capture photogenerated electrons, reducing carrier recombination rate. Ammonium fluoride selectively inhibits the formation of the rutile phase in TiO2, ensuring… The presence of the purified anatase phase and the induction of micro-defects on the surface to increase the hydroxyl content create conditions for the generation of hydroxyl radicals (·OH), ensuring efficient catalytic reaction. Activated carbon, after nitric acid pretreatment, introduces hydroxyl and amino groups. On one hand, this enhances formaldehyde adsorption capacity due to its high specific surface area and functional groups; on the other hand, it forms amidation or esterification bonds with modified nitrogen-sulfur co-doped carbon quantum dots. Combined with the esterification of modified nitrogen-sulfur co-doped carbon quantum dots and TiO2, a stable chemical cross-linking network is constructed, completely avoiding the problem of traditional physical component detachment and achieving adsorption catalysis. Performance test results show that the formaldehyde degradation rate exceeds 94% under visible light for 6 hours and surpasses 97% under ultraviolet light, with a light response range fully covering the indoor visible light region (375-710nm). The formaldehyde degradation rate remains stable at 0.88-0.93 mg / (g·h), fully verifying the effectiveness of the technical solution in catalytic activity, light response capability, and long-term stability.

[0071] Comparative Example 1, lacking modified nitrogen-sulfur co-doped carbon quantum dots, had its photoresponse limited to the ultraviolet region, and its visible light degradation rate plummeted to 61.5%, resulting in a significant decline in cycle stability. This highlights the irreplaceable role of modified nitrogen-sulfur co-doped carbon quantum dots in photoresponse broadening and carrier regulation.

[0072] Comparative Example 2, lacking anatase TiO2, relied solely on physical adsorption by activated carbon, resulting in a degradation rate of less than 20% and no recycling value, demonstrating the crucial role of anatase TiO2 as a catalytic core.

[0073] It should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the spirit and scope of the technical solutions of this application, and all such modifications and substitutions should be covered within the scope of the claims of this application.

Claims

1. A photocatalyst for degrading formaldehyde, characterized in that, It includes the following components: activated carbon substrate, anatase TiO2, and modified nitrogen-sulfur co-doped carbon quantum dots; The preparation steps of modified nitrogen-sulfur co-doped carbon quantum dots include: Aromatic dianhydride compounds containing hydroxyl groups were dissolved in deionized water and stirred at 70-80℃ for 10-15 min until completely dissolved. Then, a carbon source compound was added, and the temperature was raised to 80-90℃ and stirred for 25-35 min. Next, an amino-containing nitrogen-sulfur donor compound was added to the resulting reaction solution, which was then transferred to a hydrothermal reactor and hydrothermally reacted at 150-200℃ for 4-5 h. The resulting product was purified by dialysis and then freeze-dried to obtain modified nitrogen-sulfur co-doped carbon quantum dots.

2. The photocatalyst for degrading formaldehyde according to claim 1, characterized in that, The activated carbon substrate includes either coconut shell activated carbon or bamboo charcoal. The anatase TiO2 has a particle size of 20-30 nm; The modified nitrogen-sulfur co-doped carbon quantum dots have a particle size of 3-6 nm.

3. The photocatalyst for degrading formaldehyde according to claim 1, characterized in that, The hydroxyl-containing aromatic dianhydride compounds include one or more of 3-hydroxyphthalic anhydride or 6-hydroxynaphthalic anhydride; The carbon source compound includes one or more of glucose, fructose, lactose, and maltose; The amino-containing nitrogen and sulfur donor compounds include one or more of thiourea, aminothiourea, and thioacetamide.

4. The photocatalyst for degrading formaldehyde according to claim 1, characterized in that, In the preparation steps of the modified nitrogen-sulfur co-doped carbon quantum dots, the mass ratio of carbon source compound, amino-containing nitrogen-sulfur donor compound, hydroxyl-containing aromatic dianhydride compound and deionized water is (3-5):(2-3):(1-2):(90-94).

5. A photocatalyst for degrading formaldehyde according to claim 1, characterized in that, The mass ratio of the activated carbon substrate, anatase TiO2, and modified nitrogen-sulfur co-doped carbon quantum dots is (55-70):(28-44):(1-2).

6. A method for preparing a photocatalyst for degrading formaldehyde according to any one of claims 1-5, characterized in that, Includes the following steps: S1. The activated carbon substrate is ultrasonically treated with 0.5 mol / L nitric acid solution for 30-45 min, washed, and then vacuum dried at 100-120℃ for 4-6 h to obtain a pretreated activated carbon substrate. The pretreated activated carbon substrate is dispersed in deionized water to form an activated carbon substrate aqueous dispersion with a concentration of 0.1-0.2 g / mL. S2. Add ammonium fluoride powder to the titanium source solution and stir to dissolve. Stir and perform hydrothermal reaction. Wash, filter, dry and calcine the product to obtain anatase TiO2. Disperse the anatase TiO2 in anhydrous ethanol to form a TiO2 ethanol dispersion. Add modified nitrogen-sulfur co-doped carbon quantum dots and stir at 60-70℃ for 5-6 hours. Centrifuge the product and wash the precipitate with anhydrous ethanol. Dry at 80-90℃ for 2-3 hours to obtain TiO2-modified nitrogen-sulfur co-doped carbon quantum dot composite. S3. Add the above-mentioned TiO2-modified nitrogen-sulfur co-doped carbon quantum dot composite to the activated carbon substrate aqueous dispersion, stir at a constant temperature of 50-60℃ for 7-8h, filter the product, wash with deionized water until the filtrate is colorless, and vacuum dry at 90-100℃ and vacuum degree of -0.08~-0.1MPa for 3-4h to obtain the photocatalyst for degrading formaldehyde.

7. The method for preparing a photocatalyst for degrading formaldehyde according to claim 6, characterized in that, In S1, the mass ratio of the activated carbon substrate to the nitric acid solution is 1:(10-15).

8. The method for preparing a photocatalyst for degrading formaldehyde according to claim 6, characterized in that, In S2, the preparation steps of the titanium source solution include: taking tetrabutyl titanate, anhydrous ethanol and deionized water, first placing the anhydrous ethanol in a stirring state of 300-500 rpm, then adding tetrabutyl titanate dropwise into the ethanol at a rate of 1-2 drops / second, and continuing to stir for 10-15 minutes to form a pre-dispersion; then adding deionized water at the same dropping rate, and continuing to stir for 20-30 minutes to obtain the titanium source solution.

9. A method for preparing a photocatalyst for degrading formaldehyde according to claim 8, characterized in that, The volume ratio of tetrabutyl titanate, anhydrous ethanol, and deionized water in the titanium source solution is 1:5:

1.

10. A method for preparing a photocatalyst for degrading formaldehyde according to claim 6, characterized in that, In S2, the mass ratio of ammonium fluoride powder to titanium source solution is 1:(16-32), the stirring time is 15-20 min, the hydrothermal reaction temperature is 160-180℃, and the time is 4-6 h; the product is washed until the pH is 7-8; the calcination temperature is 400-450℃, and the time is 1-2 h; the concentration of the TiO2 ethanol dispersion is 0.05-0.1 g / mL.

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