Composite material NaFeS2 / ZnO for efficient degradation of formaldehyde under visible light catalysis and preparation method thereof

Abstract

The present invention provides a composite material NaFeS2 / ZnO for efficient formaldehyde degradation under visible light catalysis and a preparation method thereof, belonging to the field of air purification, and aims to solve the problem of low catalytic performance resulting from low sunlight utilization rate and wide band gap of current photocatalysts. The method comprises: step 1, using Fe(NO3)3·9H2O and Na2S·9H2O as reactants, and preparing NaFeS2 by a hydrothermal synthesis method; step 2, mixing a ZnSO4·7H2O solution and a Na2CO3 solution in a molar ratio of 1-3:1, stirring and mixing at room temperature to obtain a precipitate, washing, separating, and drying the precipitate to obtain a precursor Zn5(OH)6(CO3)2; and calcining the precursor Zn5(OH)6(CO3)2 and the NaFeS2 in a molar ratio of 1:100 at 300°C for 2h to obtain the NaFeS2 / ZnO.

Description

Technical Field

[0001] The present invention relates to the technical field of photocatalytic oxidation, and in particular to a composite material NaFeS2 / ZnO for efficiently degrading formaldehyde under visible light catalysis and a preparation method thereof. Background Art

[0002] The ecological environment encompasses both indoor and outdoor environments. Currently, concern about the ecological environment has entered the third generation of pollution: "indoor decoration pollution." Among the various indoor air pollutants originating from various interior decoration materials, formaldehyde is a major pollutant and a major source of volatile organic compounds (VOCs). Formaldehyde in air primarily originates from decoration materials, furniture, incomplete combustion of traditional fuels, smoke, and cosmetics. Short-term exposure to formaldehyde can irritate organs and cause adverse symptoms. Long-term exposure to indoor air pollutants is detrimental to health and may lead to sick building syndrome, building-related illnesses, and, in extreme cases, cancer. Therefore, effective formaldehyde removal is crucial for improving air quality and protecting human health. Formaldehyde (HCHO) has been designated a carcinogen by the International Agency for Research on Cancer (IARC), an agency of the World Health Organization (WHO).

[0003] Generally speaking, HCHO has the characteristics of long release period, even at low concentrations (as low as 0.10 mg / m 3 ) can also cause great harm to the human body. Since most residents spend more than 80% of their time indoors every day, it is necessary to pay more attention to solving the problem of indoor formaldehyde pollution.

[0004] In view of this major problem, people have tried various strategies to remove indoor HCHO, such as ventilation, adsorption, thermal / ozone catalytic oxidation, plasma degradation and photocatalytic oxidation. Among them, the adsorption method uses the strong adsorption capacity of adsorbents such as activated carbon, molecular sieves, silica gel, etc. to remove formaldehyde, including physical adsorption and chemical adsorption. However, this method has limited adsorption capacity and cumbersome processing. Plasma degradation produces a large number of active species through gas discharge to react with formaldehyde to achieve the purpose of formaldehyde removal. This method is highly efficient, but the energy consumption is also high. Photocatalytic oxidation, due to the advantages of controllability, renewability, sustainability and no secondary pollution, is a promising green technology for gaseous HCHO purification.

[0005] However, the effectiveness of photocatalytic oxidation technology in removing pollutants depends on the performance of the photocatalyst. Currently, photocatalysts have the problems of a wide band gap and low utilization rate of sunlight, which leads to low catalytic performance and limited catalytic effect. Therefore, the development of a photocatalyst with a wide band gap, high utilization rate of sunlight and good catalytic effect is the focus of current research. Summary of the Invention

[0006] In view of this, the present invention aims to propose a composite material NaFeS2 / ZnO for efficient visible light catalytic degradation of formaldehyde and a preparation method thereof, so as to solve the problem that the current photocatalyst has a wide band gap and low utilization rate of sunlight, resulting in limited catalytic effect.

[0007] The first aspect of the present invention provides a method for preparing a composite material NaFeS2 / ZnO for efficient visible light photocatalytic degradation of formaldehyde, the method comprising:

[0008] Step 1, using Fe(NO3)3·9H2O and Na2S·9H2O as reactants, NaFeS2 is prepared by a hydrothermal synthesis method;

[0009] Step 2: Mixing a ZnSO4·7H2O solution and a Na2CO3 solution at a molar ratio of 1-3:1, stirring the mixture at room temperature to obtain a precipitate, washing, separating, and drying the precipitate to obtain a precursor Zn5(OH)6(CO3)2;

[0010] The precursor Zn5(OH)6(CO3)2 and the NaFeS2 with a molar ratio of 1:100 are calcined at 300°C for 2h to obtain the NaFeS2 / ZnO.

[0011] Furthermore, in step 1, Fe(NO3)3·9H2O and Na2S·9H2O are used as reactants to prepare NaFeS2 by a hydrothermal synthesis method, comprising:

[0012] Step 1-1, adding the Fe(NO3)3·9H2O and the Na2S·9H2O in a mass ratio of 1:3 to distilled water, stirring at 100°C for 10 minutes, then reducing the stirring temperature to 60°C and continuing stirring for 30 minutes, and adding sodium hydroxide to the stirred solution to obtain a mixed solution;

[0013] Step 1-2, transferring the mixed solution obtained in step 1-1 to a hydrothermal reactor and performing a hydrothermal reaction at 180° C. for 24 hours;

[0014] Step 1-3: After the result of step 1-2 is cooled to room temperature, it is washed and dried to obtain the NaFeS2.

[0015] Furthermore, in step 2, the concentration of the ZnSO4·7H2O solution is 0.5 mol / L; the concentration of the Na2CO3 solution is 0.5 mol / L.

[0016] Furthermore, in step 2, the washing includes:

[0017] The precipitate was washed alternately with deionized water and ethanol for 6-10 times and then separated.

[0018] Furthermore, the dosage of the sodium hydroxide is 0.5 mol / L.

[0019] Furthermore, in the steps 1-3, the washing comprises:

[0020] Wash alternately with acetone and ethanol 6-10 times.

[0021] The second aspect of the present invention provides a composite material NaFeS2 / ZnO prepared by the preparation method described in the first aspect above;

[0022] Furthermore, in the composite material NaFeS2 / ZnO, the mass ratio of NaFeS2 to ZnO is 8:1.

[0023] The third aspect of the present invention provides an application of a composite material NaFeS2 / ZnO prepared by the preparation method described in the first aspect above, wherein the composite material NaFeS2 / ZnO is applied to remove formaldehyde in the air.

[0024] The preparation method of the composite material NaFeS2 / ZnO for efficient visible light photocatalytic degradation of formaldehyde provided by the present invention has the following advantages over the prior art:

[0025] The present invention provides a method for preparing a composite material NaFeS2 / ZnO for efficient formaldehyde degradation under visible light catalysis, comprising: step 1, using Fe(NO3)3·9H2O and Na2S·9H2O as reactants to prepare NaFeS2 by a hydrothermal synthesis method; step 2, mixing a ZnSO4·7H2O solution and a Na2CO3 solution in a molar ratio of 1-3:1, stirring and mixing at room temperature to obtain a precipitate, washing, separating, and drying the precipitate to obtain a precursor Zn5(OH)6(CO3)2; and calcining the precursor Zn5(OH)6(CO3)2 and the NaFeS2 in a molar ratio of 1:100 at 300°C for 2h to obtain the NaFeS2 / ZnO.

[0026] Therefore, the present invention prepares the composite material NaFeS2 / ZnO by compounding NaFeS2 and ZnO, and adopts NaFeS2 to broaden the light absorption range of ZnO, so that the prepared composite material NaFeS2 / ZnO has a wider light absorption range, can cover the entire visible spectrum, and improves the utilization rate of the composite material NaFeS2 / ZnO for sunlight; at the same time, since NaFeS2 and ZnO form a heterojunction during the compounding process, it is helpful to separate photogenerated carriers in the photocatalytic process, thereby avoiding the problem of too fast recombination of photogenerated electron-hole pairs, and thus the composite material NaFeS2 / ZnO has higher photocatalytic performance; the composite material NaFeS2 / ZnO prepared by the present invention is used as a photocatalyst to remove formaldehyde, which has good application prospects; at the same time, since in the preparation process, NaFeS2 is first prepared, and then NaFeS2 is added during the preparation of ZnO to directly prepare the composite material NaFeS2 / ZnO, the preparation method is simple and easy, and can be applied to large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings, which constitute part of the present invention, are provided to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are provided to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0028] Figure 1 A flow chart showing the steps of preparing a composite material NaFeS2 / ZnO for efficient degradation of formaldehyde under visible light catalysis provided by an embodiment of the present invention;

[0029] Figure 2 This is a SEM image of the composite material NaFeS2 / ZnO prepared in Example 1;

[0030] Figure 3 Ultraviolet diffuse reflectance spectra of the composite material NaFeS2 / ZnO prepared in Example 1, NaFeS2 prepared in Comparative Example 1, and ZnO prepared in Comparative Example 2;

[0031] Figure 4 This is a N2 adsorption-desorption isotherm of the composite material NaFeS2 / ZnO prepared in Example 1;

[0032] Figure 5 This is a Fourier transform infrared spectrum of the composite material NaFeS2 / ZnO prepared in Example 1;

[0033] Figure 6 This is a comparison chart of the performance of the composite material NaFeS2 / ZnO prepared in Example 1, NaFeS2 prepared in Comparative Example 1, and ZnO prepared in Comparative Example 2 in degrading formaldehyde as photocatalysts;

[0034] Figure 7This is a bar chart of the removal efficiency of three consecutive formaldehyde removal experiments conducted on the composite material NaFeS2 / ZnO prepared in Example 1. DETAILED DESCRIPTION

[0035] In order to make the above-mentioned purpose, feature and a little bit of the present invention more obvious and easy to understand, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. Below is a detailed description of the embodiment of the present invention. This embodiment is implemented under the premise of the technical solution of the present invention, and provides detailed implementation methods and specific operating procedures, but the protection scope of the present invention is not limited to the following examples. If specific experimental steps or conditions are not specified in the embodiment, the operation or conditions of the conventional experimental steps described in the prior art in this area can be carried out. If the manufacturer of the reagents and other instruments is not specified, they are all conventional reagent products that can be obtained by commercial purchase.

[0036] Formaldehyde is a major indoor air pollutant and a major volatile organic compound (VOC). Formaldehyde in the air primarily comes from decoration materials, furniture, incomplete combustion of traditional fuels, smoke, and cosmetics. Short-term exposure to formaldehyde can irritate organs and cause adverse symptoms. Long-term exposure to indoor air pollutants is detrimental to health and may lead to sick building syndrome, building-related illnesses, and, in extreme cases, cancer. Therefore, effective formaldehyde removal is crucial for improving air quality and protecting human health.

[0037] At present, a variety of methods have been developed for the removal of indoor formaldehyde, such as ventilation, adsorption, thermal / ozone catalytic oxidation, plasma degradation and photocatalytic oxidation. 3 ) will also cause great harm to the human body, so ventilation takes a long time and needs to be diffused to 0.10mg / m 3 The following are: Adsorption is the use of the strong adsorption capacity of activated carbon, molecular sieves, silica gel, etc. to remove formaldehyde through physical adsorption or chemical adsorption, but this method has limited adsorption capacity and cumbersome processing; plasma degradation is the use of gas discharge to produce a large number of active species, which react with formaldehyde to achieve the purpose of formaldehyde removal. This method is highly efficient but requires high energy consumption; and photocatalytic oxidation technology, due to its strong controllability, good regeneration, and good sustainability, has become the key research direction of gaseous formaldehyde purification.

[0038] However, the effectiveness of formaldehyde removal using photocatalytic oxidation technology depends on the performance of the photocatalyst. Among the numerous semiconductor photocatalysts, zinc oxide (ZnO) has been widely used in the photocatalytic industry due to its unique electronic structure, diverse morphologies, and ease of fabrication. However, ZnO has a wide band gap (3.2-3.4 eV) and only absorbs ultraviolet light, resulting in low utilization of sunlight. Furthermore, since electrons and holes excited by ultraviolet light easily recombine with each other, that is, photogenerated carriers directly and rapidly recombine upon excitation, its photocatalytic activity, especially visible light photocatalytic performance, is severely inhibited, resulting in limited effectiveness of ZnO on formaldehyde removal.

[0039] In view of this, the present invention provides a composite material NaFeS2 / ZnO for efficient visible light catalytic degradation of formaldehyde and a preparation method thereof. By adding NaFeS2 to ZnO, since NaFeS2 is a narrow-bandgap magnetic semiconductor material whose light absorption range covers the entire visible spectrum, the composite material NaFeS2 and ZnO can be composited to broaden the light absorption range of ZnO, thereby improving the composite material's utilization of sunlight. At the same time, since NaFeS2 and ZnO form a heterojunction in the prepared composite material NaFeS2 / ZnO, the separation efficiency of photogenerated carriers is improved and the rapid recombination of photogenerated electron-hole pairs is avoided. Thus, a composite material NaFeS2 / ZnO with good photocatalytic performance is prepared. The composite material NaFeS2 / ZnO prepared by the present invention is used as a photocatalyst for removing formaldehyde from the air. Since the composite material NaFeS2 / ZnO has adsorption properties and good photocatalytic properties, it has a good removal effect on formaldehyde from the air through the synergistic effect of photocatalysis and adsorption.

[0040] The composite material NaFeS2 / ZnO for efficient degradation of formaldehyde under visible light catalysis and its preparation method provided by the present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments.

[0041] A first aspect of an embodiment of the present invention provides a method for preparing a composite material NaFeS2 / ZnO for efficient visible light photocatalytic degradation of formaldehyde.

[0042] Reference Figure 1 , Figure 1 The following is a flow chart showing the steps of preparing a composite material NaFeS2 / ZnO for efficient degradation of formaldehyde under visible light catalysis provided by an embodiment of the present invention. Figure 1 Shown, including:

[0043] S1, NaFeS2 was prepared by hydrothermal synthesis using Fe(NO3)3·9H2O and Na2S·9H2O as reactants.

[0044] The specific steps for preparing NaFeS2 include:

[0045] Step 1-1, adding Fe(NO3)3·9H2O and Na2S·9H2O in a molar ratio of 1:3 to distilled water, stirring at 100°C for 10 minutes, then reducing the stirring temperature to 60°C and continuing stirring for 30 minutes, and adding sodium hydroxide to the stirred solution to obtain a mixed solution;

[0046] Step 1-2, transferring the mixed solution obtained in step 1-1 to a hydrothermal reactor and performing a hydrothermal reaction at 180° C. for 24 hours;

[0047] Step 1-3: After the result of step 1-2 is cooled to room temperature, it is washed and dried to obtain the NaFeS2.

[0048] The washing process is performed by alternating acetone and deionized water for 6-10 times. The purpose of washing with acetone is to remove the by-product NaNO3 in the reaction process. The drying step is as follows: the washed product is placed in an oven and vacuum-dried at 60-80°C for 12-24 hours.

[0049] In the embodiment of the present invention, sodium hydroxide is added to provide an alkaline environment to generate NaFeS2. Therefore, the amount of sodium hydroxide added does not need to be too much, as long as it can produce NaFeS2. In the embodiment of the present invention, the amount of sodium hydroxide added is 0.5 mol / L.

[0050] In some embodiments, since there are many methods for preparing NaFeS2, the reactants or preparation methods used can be adjusted as needed. For example, iron oxide and sodium thiosulfate can be used as reactants to prepare NaFeS2 by a hydrothermal method, or by a calcination method. The present invention does not impose any specific restrictions.

[0051] S2, after mixing the ZnSO4·7H2O solution and the Na2CO3 solution in a molar ratio of 1-3:1, stirring and mixing at room temperature to obtain a precipitate, washing, separating and drying the precipitate to obtain a precursor Zn5(OH)6(CO3)2; calcining the precursor Zn5(OH)6(CO3)2 and the NaFeS2 in a molar ratio of 1:100 at 300°C for 2h to obtain the NaFeS2 / ZnO.

[0052] The concentrations of the ZnSO4·7H2O solution and the Na2CO3 solution are not specifically limited in the present invention, as long as the molar ratio of ZnSO4·7H2O to Na2CO3 is 1-3:1; for example, 0.5 mol / L ZnSO4·7H2O solution and 0.5 mol / L Na2CO3 solution are mixed.

[0053] For example, a ZnSO4·7H2O solution and a Na2CO3 solution are mixed at a molar ratio of 1:1;

[0054] Mix ZnSO4·7H2O solution and Na2CO3 solution in a molar ratio of 2:1;

[0055] Mix ZnSO4·7H2O solution and Na2CO3 solution in a molar ratio of 3:1.

[0056] Preferably, considering that the precursor is Zn5(OH)6(CO3)2, in order to obtain as much Zn5(OH)6(CO3)2 as possible and reduce impurities, a ZnSO4·7H2O solution and a Na2CO3 solution with a molar ratio of 3:1 are mixed to generate a precursor Zn5(OH)6(CO3)2.

[0057] The specific washing method is: washing the precipitate with deionized water and ethanol alternately for 6-10 times.

[0058] The specific drying method is: after separating the washed precipitated impurities, place it in an oven and vacuum dry it at 60-80° C. for 12-24 hours.

[0059] In some embodiments, to achieve uniform compounding of NaFeS2 and ZnO, after preparing NaFeS2, a ZnSO4·7H2O solution and a Na2CO3 solution can be mixed to obtain a precursor, Zn5(OH)6(CO3)2. Zn5(OH)6(CO3)2 can then be calcined at a certain temperature to obtain pure ZnO. Subsequently, NaFeS2 and ZnO are mixed and compounded using ultrasound or other methods to obtain the composite material NaFeS2 / ZnO.

[0060] ZnO has been widely used in the photocatalytic industry due to its unique electronic structure, diverse morphologies, and ease of fabrication. However, ZnO has a wide band gap (3.2-3.4 eV) and only absorbs ultraviolet light, resulting in low sunlight utilization. Furthermore, because electrons and holes excited by ultraviolet light easily recombine with each other, photogenerated carriers directly and rapidly recombine upon excitation, its photocatalytic activity, particularly visible light photocatalytic performance, is severely inhibited.

[0061] NaFeS2 is a ternary alkali metal-based chalcogenide, a mixed-valence material whose chemical and physical properties depend on the oxidation state of iron. NaFeS2 possesses inherent magnetic and photoelectric properties and has been used as glassy carbon powder and cathode materials, but its material properties and applications are rarely explored. Its deep valence band position and broad light absorption range make it promising for application in photocatalysis.

[0062] Therefore, by compounding NaFeS2 and ZnO, the wider light absorption range of NaFeS2 can be used to make up for the deficiency of ZnO that only absorbs ultraviolet light. Moreover, since both are semiconductor materials, they can form a heterojunction, thereby improving the separation efficiency of photogenerated carriers and thus improving the photocatalytic performance. In this way, a photocatalyst with a wide optical absorption range, covering the entire visible spectrum and high photogenerated carrier separation efficiency can be prepared, and the catalyst has high catalytic performance.

[0063] A second aspect of an embodiment of the present invention provides a composite material NaFeS2 / ZnO prepared by the preparation method described in the first aspect above.

[0064] In the composite material NaFeS2 / ZnO obtained in the embodiment of the present invention, the mass ratio of NaFeS2 to ZnO is 8:1; the composite material NaFeS2 / ZnO is observed by scanning electron microscopy and the following is obtained: Figure 2 The SEM image shown in the figure shows that the composite material NaFeS2 / ZnO is a nanosheet structure.

[0065] In the embodiment of the present invention, NaFeS2 and ZnO in the composite material are both semiconductors, and a heterojunction is formed during the composite process, wherein the heterojunction is the interface region formed by the contact between two different semiconductors. Under the condition of light excitation, the interface transfer and spatial separation of electron holes are realized through the heterojunction, which can avoid the problem of low photocatalytic performance caused by rapid recombination of photoinduced carriers; thus, by combining NaFeS2 with ZnO, the separation efficiency of photogenerated carriers is improved, thereby improving the catalytic performance of the photocatalyst.

[0066] The third aspect of the embodiments of the present invention provides an application of a composite material NaFeS2 / ZnO prepared by the preparation method described in the first aspect above, wherein the composite material NaFeS2 / ZnO is applied to the removal of formaldehyde in the air.

[0067] In an embodiment of the present invention, the composite material NaFeS2 / ZnO can be applied to formaldehyde, SO2, ammonia, nitrogen oxides, etc. in the air. Preferably, the modified nanocomposite material for high-efficiency visible light catalytic formaldehyde removal prepared in an embodiment of the present invention is used as a photocatalyst to remove formaldehyde.

[0068] The composite material NaFeS2 / ZnO prepared in an embodiment of the present invention is used as a photocatalyst and applied to the removal of formaldehyde. Under the irradiation of visible light (λ>400nm) with an intensity of 2 standard suns, the catalyst dosage is 0.1g, the initial formaldehyde concentration is 100ppm, and the initial temperature is room temperature, its formaldehyde degradation efficiency can reach as high as 99.5% after 140 minutes; therefore, the composite material NaFeS2 / ZnO in an embodiment of the present invention is applied to the removal of formaldehyde and has good application prospects.

[0069] The embodiment of the present invention provides a method for preparing a composite material NaFeS2 / ZnO for efficient formaldehyde degradation under visible light catalysis. The method comprises the following steps: first preparing NaFeS2, and then adding the prepared NaFeS2 during the process of preparing ZnO to obtain the composite material NaFeS2 / ZnO; thereby, by compounding NaFeS2 and ZnO, NaFeS2 is used to broaden the light absorption range of ZnO, so that the prepared composite material NaFeS2 / ZnO has a wider light absorption range, can cover the entire visible spectrum, and improves the utilization rate of sunlight by the composite material NaFeS2 / ZnO; at the same time, since both NaFeS2 and ZnO are semiconductor materials, a heterojunction is formed during the compounding process, which can enable photogenerated carriers to achieve interfacial transfer, thereby improving the separation efficiency of photogenerated carriers and avoiding the problem of too rapid recombination of photogenerated electron-hole pairs, so that the prepared composite material NaFeS2 / ZnO has better photocatalytic performance.

[0070] The composite material NaFeS2 / ZnO prepared in an embodiment of the present invention is applied to the removal of formaldehyde in the air. Under the irradiation of visible light (λ>400nm) with an intensity of 2 standard suns, the catalyst dosage is 0.1g, the initial formaldehyde concentration is 100ppm, and the initial temperature is room temperature, the degradation efficiency of formaldehyde can reach as high as 99.5% after 140 minutes. Therefore, the composite material NaFeS2 / ZnO prepared in an embodiment of the present invention has good application prospects in the removal of formaldehyde in the air.

[0071] In addition, since NaFeS2 is prepared first and then added during the preparation of ZnO to directly prepare the composite material NaFeS2 / ZnO, the preparation method is simple and easy and can be applied to large-scale production.

[0072] In order to enable those skilled in the art to better understand the present invention, the following describes the composite material NaFeS2 / ZnO for efficient degradation of formaldehyde under visible light catalysis and its preparation method through multiple specific embodiments.

[0073] Ferric nitrate nonahydrate (Fe(NO₃)₃·9H₂O), sodium sulfide nonahydrate (Na₂S·9H₂O), zinc sulfate heptahydrate (ZnSO₄·7H₂O), sodium carbonate (Na₂CO₃), and sodium hydroxide (NaOH) were purchased from Aladdin (Shanghai, China). All reagents were used without further purification. Deionized water was used in all experiments.

[0074] Example 1

[0075] Dissolve 40 mM Fe(NO₃)₃·9H₂O and 120 mM Na₂S·9H₂O in distilled water to prepare a 100 mL solution. Stir at 100°C for 10 minutes, then reduce the temperature to 60°C and continue stirring for 30 minutes. Add 0.05 mol NaOH to the stirred solution.

[0076] The solution after adding sodium hydroxide was transferred to a hydrothermal reactor and hydrothermally reacted at 180°C for 24 hours; the result of the hydrothermal reaction was cooled to room temperature, washed several times with ethanol and acetone, and dried at 80°C to obtain solid NaFeS2.

[0077] 40 mL of 0.5 mol / L ZnSO4·7H2O and 40 mL of 0.5 mol / L Na2CO3 solution were stirred and mixed at room temperature to obtain a precipitate. The precipitate was washed, separated, and dried to obtain the precursor Zn5(OH)6(CO3)2.

[0078] 0.02 mol of precursor Zn5(OH)6(CO3)2 was mixed with 2 mol of NaFeS2 and calcined at 300°C for 2 h to obtain the composite material NaFeS2 / ZnO.

[0079] Example 2

[0080] Dissolve 40 mM Fe(NO₃)₃·9H₂O and 120 mM Na₂S·9H₂O in distilled water to prepare a 100 mL solution. Stir at 100°C for 10 minutes, then reduce the temperature to 60°C and continue stirring for 30 minutes. Add 0.05 mol NaOH to the stirred solution.

[0081] The solution after adding sodium hydroxide was transferred to a hydrothermal reactor and hydrothermally reacted at 180°C for 24 hours; the result of the hydrothermal reaction was cooled to room temperature, washed several times with ethanol and acetone, and dried at 80°C to obtain solid NaFeS2.

[0082] 80 mL of 0.5 mol / L ZnSO4·7H2O and 40 mL of 0.5 mol / L Na2CO3 solution were stirred and mixed at room temperature to obtain a precipitate. The precipitate was washed, separated, and dried to obtain the precursor Zn5(OH)6(CO3)2.

[0083] 0.02 mol of precursor Zn5(OH)6(CO3)2 was mixed with 2 mol of NaFeS2 and calcined at 300°C for 2 h to obtain the composite material NaFeS2 / ZnO.

[0084] Example 3

[0085] Dissolve 40 mM Fe(NO₃)₃·9H₂O and 120 mM Na₂S·9H₂O in distilled water to prepare a 100 mL solution. Stir at 100°C for 10 minutes, then reduce the temperature to 60°C and continue stirring for 30 minutes. Add 0.05 mol NaOH to the stirred solution.

[0086] The solution after adding sodium hydroxide was transferred to a hydrothermal reactor and hydrothermally reacted at 180°C for 24 hours; the result of the hydrothermal reaction was cooled to room temperature, washed several times with ethanol and acetone, and dried at 80°C to obtain solid NaFeS2.

[0087] 120 mL of 0.5 mol / L ZnSO4·7H2O and 40 mL of 0.5 mol / L Na2CO3 solution were stirred and mixed at room temperature to obtain a precipitate. The precipitate was washed, separated, and dried to obtain the precursor Zn5(OH)6(CO3)2.

[0088] 0.02 mol of precursor Zn5(OH)6(CO3)2 was mixed with 2 mol of NaFeS2 and calcined at 300°C for 2 h to obtain the composite material NaFeS2 / ZnO.

[0089] Comparative Example 1

[0090] Dissolve 40 mM Fe(NO₃)₃·9H₂O and 120 mM Na₂S·9H₂O in distilled water to prepare a 100 mL solution. Stir at 100°C for 10 minutes, then reduce the temperature to 60°C and continue stirring for 30 minutes. Add 0.05 mol NaOH to the stirred solution.

[0091] The solution after adding sodium hydroxide was transferred to a hydrothermal reactor and hydrothermally reacted at 180°C for 24 hours; the result of the hydrothermal reaction was cooled to room temperature, washed several times with ethanol and acetone, and dried at 80°C to obtain solid NaFeS2.

[0092] Comparative Example 2

[0093] 40 mL of 0.5 mol / L ZnSO4·7H2O and 40 mL of 0.5 mol / L Na2CO3 solution were stirred and mixed at room temperature to obtain a precipitate. The precipitate was washed, separated, and dried to obtain the precursor Zn5(OH)6(CO3)2.

[0094] The precursor Zn5(OH)6(CO3)2 was calcined at 300℃ for 2h to obtain ZnO powder.

[0095] Figure 2 The SEM image of the composite material NaFeS2 / ZnO prepared in Example 1 of the present invention is shown in FIG. Figure 2 It can be seen that the composite material NaFeS2 / ZnO is a nanosheet structure.

[0096] The NaFeS2 / ZnO prepared in Example 1, the NaFeS2 prepared in Comparative Example 1 and the ZnO prepared in Comparative Example 2 were analyzed by UV spectrometer to obtain the following: Figure 3 The UV diffuse reflectance spectrum shown is based on Figure 3 It can be seen that the light absorption edge of ZnO prepared in Comparative Example 2 is around 390nm, while the optical absorption of NaFeS2 prepared in Comparative Example 1 covers the entire visible spectrum; and in the NaFeS2 / ZnO prepared in Example 1 of the present invention, the addition of NaFeS2 causes the ultraviolet spectrum to red-shift, and the optical absorption range of ZnO is expanded by NaFeS2; although the visible light absorption intensity is slightly weakened compared to NaFeS2, the absorption range still covers the entire visible spectrum, and a large absorption tail peak appears, indicating that it can utilize sufficient visible light; therefore, it can be concluded that the composite material NaFeS2 / ZnO was successfully synthesized.

[0097] The adsorption-desorption experiment was carried out on the composite material NaFeS2 / ZnO prepared in Example 1. The experimental results are as follows: Figure 4 As shown, from the N2 adsorption-desorption isotherm diagram of the composite material NaFeS2 / ZnO prepared in Example 1, it can be seen that the composite material NaFeS2 / ZnO prepared in the embodiment of the present invention not only has photocatalytic ability, but also has strong adsorption capacity for adsorbates and can also remove organic pollutants by adsorption; therefore, the composite material NaFeS2 / ZnO prepared in the embodiment of the present invention can synergistically remove formaldehyde through photocatalysis and adsorption.

[0098] The composite material NaFeS2 / ZnO prepared in Example 1 was analyzed by infrared spectrometer to study the composition and structure of the synthesized sample. Figure 5 The Fourier transform infrared spectrum shown is for NaFeS2, 1100 cm -1 is the characteristic peak of Fe-S; for ZnO, the peak is at 549cm -1and 621cm -1 and ZnO respectively correspond to the stretching and deformation of ZnO; for NaFeS2 / ZnO, the main typical absorption peaks of NaFeS2 and ZnO both exist in NaFeS2 / ZnO, further indicating the successful synthesis of the composite material NaFeS2 / ZnO.

[0099] Test Example 1

[0100] This test example is used to verify the degradation performance of the composite material NaFeS2 / ZnO prepared in Example 1, NaFeS2 prepared in Comparative Example 1, and ZnO prepared in Comparative Example 2 as photocatalysts for formaldehyde.

[0101] Photocatalytic activity evaluation:

[0102] In a 1.5L quartz photocatalytic reactor, at room temperature, under visible light irradiation, a 5W fan was used to photocatalytically remove formaldehyde. A 350W xenon lamp was placed vertically outside the photoreactor. A UV cutoff filter (420nm) was used to remove ultraviolet rays. The average light intensity at the surface of the reaction solution in the reaction solution was measured by a photon density meter to be 200mW / cm 2 , i.e., 2 standard solar intensities (AM3G), 0.1g of catalyst and 15ml of deionized water were ultrasonically mixed in a Petri dish (7.0cm diameter) for 25 minutes to form a suspension. The Petri dish was vacuum dried at 60°C for 1 hour, and a uniform photocatalyst film formed on the bottom of the dish. The dish was then placed in a photocatalytic reactor. A certain amount of 38% formaldehyde aqueous solution was injected into the photoreactor, and the initial concentration of evaporated HCHO after reaching adsorption-desorption equilibrium in the dark was 100ppm. During the irradiation process, the formaldehyde, CO2, and H2O concentrations in the reactor were monitored online using a photoacoustic infrared multi-gas monitor (INNOVA Air Tech 95 Instruments Model 1412). The formaldehyde removal rate (Y) was calculated as Y (%) = (1-C / C0) × 100%, where C and C0 are the formaldehyde concentrations at 0 and tmin, respectively.

[0103] The test results show that under the irradiation of visible light (λ>400nm) with 2 standard solar intensities, the catalyst dosage is 0.1g, the initial formaldehyde concentration is 100ppm, and the initial temperature is room temperature, the formaldehyde degradation efficiency of the composite material NaFeS2 / ZnO is as high as 99.5% after 140 minutes.

[0104] in, Figure 6 The performance comparison of NaFeS2 / ZnO prepared in Example 1, NaFeS2 prepared in Comparative Example 1, and ZnO prepared in Comparative Example 2 as photocatalysts for formaldehyde degradation is shown in FIG. Figure 6It can be seen that under the same conditions of illumination, after 140 minutes, ZnO alone has almost no formaldehyde degradation due to its non-absorption of visible light, and the degradation efficiency of pure NaFeS2 on formaldehyde is only 50%; while the degradation efficiency of NaFeS2 / ZnO on formaldehyde can reach 99.5%.

[0105] Test Example 2

[0106] Continuous degradation experiment:

[0107] After the first degradation reaction was completed, the culture dish containing the photocatalyst was dried at 60°C for 0.5 hours and then placed back into the reactor for the next formaldehyde removal reaction. Except for the materials, the other reaction conditions remained the same as the first time. After the second reaction was completed, the above steps were repeated for the third degradation experiment.

[0108] The test results are as follows Figure 7 As shown, Figure 7 The formaldehyde removal effect diagrams obtained from the first, second and third formaldehyde degradation experiments are shown. Figure 7 It can be seen that in three consecutive degradation tests, the degradation efficiency of the composite material NaFeS2 / ZnO prepared in Example 1 for formaldehyde is above 90%, and the catalytic activity of the surface composite material NaFeS2 / ZnO as a photocatalyst remains good after three cycles, and its catalytic performance has better stability.

[0109] According to the above experiments, the composite material NaFeS2 / ZnO prepared in the embodiment of the present invention is a nanosheet structure, and the ultraviolet diffuse reflectance spectrum shows that it has a wide visible light absorption range and can cover the entire visible spectrum. Therefore, it has a high utilization rate of sunlight. Since both NaFeS2 and ZnO are semiconductors, the composite formation of a heterojunction can improve the separation efficiency of photogenerated carriers, thereby obtaining a composite material with good photocatalytic performance. The composite material NaFeS2 / ZnO prepared in the embodiment of the present invention has certain adsorption properties; therefore, when the composite material NaFeS2 / ZnO prepared by the implementation of the present invention is used as a photocatalyst to remove formaldehyde, it can synergistically act through adsorption properties and photocatalytic properties.

[0110] When the composite material NaFeS2 / ZnO prepared by the embodiment of the present invention is used as a photocatalyst for the removal of formaldehyde in the air, under the conditions of visible light (λ>400nm) of 2 standard suns' intensity, a catalyst dosage of 0.1g, an initial formaldehyde concentration of 100ppm, and an initial temperature of room temperature, the composite material NaFeS2 / ZnO has a formaldehyde degradation efficiency of up to 99.5% after 140 minutes, while the formaldehyde removal rate of NaFeS2 alone is only about 50% after 140 minutes of illumination, and the formaldehyde degradation rate of ZnO alone is almost unaffected after 140 minutes of illumination. By comparison, it can be seen that the composite material NaFeS2 / ZnO prepared by the embodiment of the present invention has good photocatalytic performance as a photocatalyst. Through multiple continuous degradation tests, it can be seen that the composite material NaFeS2 / ZnO prepared by the embodiment of the present invention can still achieve a formaldehyde removal rate of more than 90% in three degradation tests, with good catalytic activity and stable catalytic performance, and has good application prospects in removing formaldehyde in the air.

[0111] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included in the scope of protection of the present invention.

[0112] For simplicity of description, the method embodiments are described as a series of actions. However, those skilled in the art should be aware that the present invention is not limited by the order of the actions described, as certain steps can be performed in other orders or simultaneously according to the present invention. Furthermore, those skilled in the art should also be aware that the embodiments described in this specification are preferred embodiments, and the actions and components involved are not necessarily required for the present invention.

[0113] The above is a detailed introduction to the composite material NaFeS2 / ZnO for efficient degradation of formaldehyde by visible light catalysis provided by the present invention and its preparation method. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for those skilled in the art, according to the ideas of the present invention, there will be changes in the specific implementation methods and application scopes. In summary, the content of this specification should not be understood as a limitation on the present invention.

Claims

1. Application of a composite material NaFeS2 / ZnO for efficient degradation of formaldehyde under visible light catalysis, characterized in that: The composite material NaFeS2 / ZnO is used as a photocatalyst to remove formaldehyde, SO2, ammonia or nitrogen oxides in the air; The preparation method of the composite material NaFeS2 / ZnO comprises: Step 1, using Fe(NO3)3·9H2O and Na2S·9H2O as reactants, NaFeS2 is prepared by a hydrothermal synthesis method; Step 2: Mixing a ZnSO4·7H2O solution and a Na2CO3 solution at a molar ratio of 1-3:1, stirring the mixture at room temperature to obtain a precipitate, washing, separating, and drying the precipitate to obtain a precursor Zn5(OH)6(CO3)2; The precursor Zn5(OH)6(CO3)2 and the NaFeS2 with a molar ratio of 1:100 are calcined at 300°C for 2h to obtain the NaFeS2 / ZnO.

2. The use of the composite material NaFeS2 / ZnO for efficient degradation of formaldehyde under visible light catalysis according to claim 1, characterized in that: In the step 1, Fe(NO3)3·9H2O and Na2S·9H2O are used as reactants to prepare NaFeS2 by a hydrothermal synthesis method, comprising: Step 1-1, adding the Fe(NO3)3·9H2O and the Na2S·9H2O in a mass ratio of 1:3 to distilled water, stirring at 100°C for 10 minutes, then reducing the stirring temperature to 60°C and continuing stirring for 30 minutes, and adding sodium hydroxide to the stirred solution to obtain a mixed solution; Step 1-2, transferring the mixed solution obtained in step 1-1 to a hydrothermal reactor and performing a hydrothermal reaction at 180° C. for 24 hours; Step 1-3: After the result of step 1-2 is cooled to room temperature, it is washed and dried to obtain the NaFeS2.

3. The use of the composite material NaFeS2 / ZnO for efficient degradation of formaldehyde under visible light catalysis according to claim 1, characterized in that: In step 2, the concentration of the ZnSO4·7H2O solution is 0.5 mol / L; the concentration of the Na2CO3 solution is 0.5 mol / L.

4. The use of the composite material NaFeS2 / ZnO for efficient degradation of formaldehyde under visible light catalysis according to claim 1, characterized in that: In the step 2, the molar ratio of the ZnSO4·7H2O to the Na2CO3 is 3:

1.

5. The use of the composite material NaFeS2 / ZnO for efficient degradation of formaldehyde under visible light catalysis according to claim 1, characterized in that: In the step 2, the washing comprises: The precipitate was washed alternately with deionized water and ethanol 6-10 times.

6. The use of the composite material NaFeS2 / ZnO for efficient degradation of formaldehyde under visible light catalysis according to claim 2, characterized in that: The dosage of the sodium hydroxide is 0.5 mol / L.

7. The use of the composite material NaFeS2 / ZnO for efficient degradation of formaldehyde under visible light catalysis according to claim 2, characterized in that: In the steps 1-3, the washing comprises: Wash alternately with acetone and ethanol 6-10 times.

8. The use of the composite material NaFeS2 / ZnO for efficient degradation of formaldehyde under visible light catalysis according to claim 1, characterized in that: The composite material NaFeS2 / ZnO is applied to remove formaldehyde in the air.

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