Cordierite / Ag / AgCl visible light photocatalyst, preparation method and application thereof

Abstract

The application belongs to the field of photocatalysis, and particularly relates to a coptite / Ag / AgCl visible light photocatalyst, a preparation method and application thereof; the application utilizes the coptite, a waste automobile exhaust catalyst carrier extracted by a noble metal, for secondary use, filters and washes the coptite to obtain coptite particles free of impurity ions, and then prepares the coptite / Ag / AgCl photocatalytic material through a two-step method of co-precipitation and photoreduction; the method has the advantages of short reaction time, simple operation, low cost, no other organic reagents involved, and green environmental protection; the coptite / Ag / AgCl photocatalytic material obtained has a small band gap, a higher separation efficiency of electron holes, a high visible light catalytic effect on organic pollutants tetracycline in water, and a catalytic performance greatly higher than that of single-phase Ag / AgCl material.

Description

Technical Field

[0001] This invention belongs to the field of photocatalysis technology, specifically, it relates to a cordierite / Ag / AgCl visible light photocatalyst, its preparation method, and its application. Background Technology

[0002] With societal progress and development, water pollution problems and incidents have frequently occurred, seriously impacting the ecosystem, human health, and the sustainable development of human society. Common methods for treating pollutants in water include physical and chemical methods. Traditional physical adsorption is ineffective in treating organic pollutants in water, while chemical treatment easily causes secondary pollution. Photocatalysis technology utilizes light irradiation to degrade organic pollutants in water, offering advantages such as low cost, ease of operation, and no secondary pollution, making it one of the effective methods for solving water pollution problems. However, most photocatalysts only respond to ultraviolet light, exhibiting low utilization of sunlight, severely limiting their application in practical industrial and daily life. Therefore, there is a need to find photocatalysts that respond to visible light.

[0003] Silver halide photocatalysts (Ag / AgCl, Ag / AgBr, Ag / AgI) are highly favored in photocatalysis research due to their good activity, high crystallinity, and ease of preparation. Their excellent photocatalytic degradation activity is mainly attributed to the plasmon resonance effect of Ag, exhibiting strong spectral absorption in the ultraviolet-visible light band. However, inherent limitations of the material itself restrict the application of Ag / AgCl in photocatalysis. Firstly, AgCl is photosensitized and easily photocorrodes under light irradiation, leading to unstable cycling performance and hindering its practical recyclability, thus increasing application costs. Secondly, photogenerated electrons and holes generated under light readily recombine, resulting in low quantum efficiency and limited degradation activity for organic matter.

[0004] Cordierite (2MgO·2Al2O3·5SiO2) is a silicate mineral widely used in metallurgy, electronics, and automotive industries. It can be used as a high-quality refractory material, electronic packaging material, and catalyst support. Patent CN 108772056 A uses cordierite as a support to prepare M... x (Bi,Zr)Ti 1-x O2 / Mn-Ce-O / cordierite catalyst for VOCs treatment; patent CN117181282A prepared Pt-M@molecular sieve / cordierite catalyst for the hydrogenation of nitrobenzene to p-aminophenol, but there is currently no research on photocatalytic degradation of organic pollutants in water, especially tetracycline, using cordierite as a support. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention proposes a simple and rapid method for preparing cordierite / Ag / AgCl photocatalytic materials, using cordierite carriers obtained from the recovery of precious metals (platinum group elements) from cordierite-type waste automotive exhaust catalysts as raw materials. This method further utilizes waste automotive exhaust catalysts and solves the problems of complex preparation processes, poor photocatalytic performance, and instability of existing Ag / AgCl materials. It features a short reaction time, simple operation, low cost, and does not involve other organic reagents, making it environmentally friendly. The cordierite / Ag / AgCl photocatalytic material obtained by this invention has a small band gap and higher electron-hole separation efficiency, exhibiting a high visible light photocatalytic effect on organic pollutants in water, with catalytic performance significantly higher than that of single-phase Ag / AgCl materials.

[0006] This invention utilizes cordierite, a catalyst carrier for waste automotive exhaust gas, extracted with precious metals. First, the cordierite is filtered and washed to obtain cordierite powder free of impurities. Then, a two-step process of co-precipitation and photoreduction is used to prepare cordierite / Ag / AgCl photocatalytic material. The specific scheme is as follows.

[0007] A method for preparing a cordierite / Ag / AgCl visible light photocatalyst includes the following steps:

[0008] Step 1: Thoroughly clean the collected waste automotive exhaust catalyst carrier cordierite to remove excess impurities from the surface, dry it, and obtain clean cordierite powder; disperse the cordierite powder in deionized water to obtain cordierite suspension.

[0009] Step 2: Weigh an appropriate amount of silver nitrate granules and disperse them in deionized water to prepare a silver nitrate solution; weigh an appropriate amount of potassium chloride powder and disperse it in deionized water to prepare a potassium chloride solution.

[0010] Step 3: After the cordierite suspension is wrapped in a light-proof container, it is transferred to a constant temperature water bath stirring device. Silver nitrate solution and potassium chloride solution are added dropwise in sequence to carry out the reaction. After the reaction is completed, it is allowed to cool naturally to room temperature.

[0011] Step 4: After the reaction in step (3), use a xenon lamp as the light source to carry out a photoreduction reaction until the system changes from grayish-white to dark gray. Then, filter, wash and dry the system to obtain cordierite / Ag / AgCl photocatalytic material.

[0012] In this invention, in step (1), the cordierite carrier of the waste automobile exhaust catalyst is derived from the cordierite-type waste automobile exhaust catalyst after the recovery of precious metals; before cleaning, the cordierite carrier of the waste automobile exhaust catalyst is first ground and finely processed.

[0013] In this invention, in step (1), the cleaning method of the waste automobile exhaust catalyst carrier cordierite is vacuum filtration washing. The waste cordierite catalyst is placed on the filter membrane and washed with anhydrous ethanol 2-4 times, and then washed with deionized water more than 5 times. The drying temperature is 50-70℃ and the drying time is 4-12h. The concentration of the cordierite powder suspension is between 10-50mg / mL.

[0014] In this invention, in step (2), the concentration of silver nitrate solution is between 0.005-0.1 mol / L, and the concentration of potassium chloride solution is between 0.005-0.1 mol / L.

[0015] In this invention, in step (3), the temperature of the constant temperature water bath is controlled between 25-35℃. After adding the silver nitrate solution, the reaction is carried out for 40-80 minutes. Then, the potassium chloride solution is added dropwise. After adding the potassium chloride solution, the reaction is continued for 100-150 minutes. The molar ratio of silver nitrate to potassium chloride is 1:1. The mass ratio of cordierite to silver nitrate is between 7:1 and 14:1.

[0016] In this invention, in step (4), the photoreduction reaction time is 10-30 min; the product is washed with anhydrous ethanol and deionized water in sequence; the drying temperature is 50-70℃ and the drying time is 4-12 h.

[0017] The present invention also provides a cordierite / Ag / AgCl visible light photocatalyst prepared by the above-described method. Preferably, Ag / AgCl accounts for 6-10 wt% of the total mass of the visible light photocatalyst.

[0018] Furthermore, this invention provides an application of the above-mentioned cordierite / Ag / AgCl visible light photocatalyst in the degradation of organic pollutants in wastewater under visible light conditions. Preferably, the organic pollutant is tetracycline.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] 1. This invention not only makes resource-efficient use of the carrier in waste automobile exhaust catalysts, but also improves the inherent defects of Ag / AgCl materials, enabling efficient degradation of organic pollutants in wastewater under visible light conditions, thus improving the feasibility of photocatalysis in practical water treatment applications.

[0021] 2. The photocatalytic effect of the cordierite / Ag / AgCl photocatalytic material prepared by this invention is much higher than that of single-phase Ag / AgCl, and it has high stability, is easy to recycle, and has high recycling value.

[0022] 3. This invention makes resource-efficient use of cordierite, a material used in waste automotive exhaust catalysts, thereby reducing the subsequent processing pressure on waste catalyst carriers.

[0023] 4. The preparation process of the cordierite / Ag / AgCl photocatalytic material of the present invention is green and environmentally friendly, simple to operate, and has high practical application value. Attached Figure Description

[0024] Figure 1 This is a schematic diagram illustrating the synthesis of cordierite / Ag / AgCl composite photocatalytic materials.

[0025] Figure 2 XRD patterns of cordierite, Ag / AgCl, cordierite / Ag / AgCl-4, cordierite / Ag / AgCl-6, cordierite / Ag / AgCl-8, and cordierite / Ag / AgCl-10.

[0026] Figure 3 Scanning electron micrographs of waste cordierite carrier and cordierite / Ag / AgCl-8.

[0027] Figure 4 Diagrams showing the degradation of tetracycline (TC) catalyzed by Ag / AgCl, cordierite / Ag / AgCl-4, cordierite / Ag / AgCl-6, cordierite / Ag / AgCl-8, and cordierite / Ag / AgCl-10 under visible light. Detailed Implementation

[0028] The present invention will now be clearly and completely described in conjunction with embodiments, so that those skilled in the art can have a more comprehensive understanding of the present invention.

[0029] The main raw materials used in the synthetic material of this invention are: cordierite-type waste automobile exhaust catalyst carrier (obtained by recovering platinum group elements from cordierite-type waste automobile exhaust catalyst through wet or pyrometallurgical processes), deionized water (laboratory-made), silver nitrate (AgNO3, analytical grade), potassium chloride (KCl, analytical grade), and ethanol (C2H6O, analytical grade).

[0030] In this embodiment, the recovered cordierite-type waste automotive exhaust catalyst carrier was cleaned by a vacuum filtration and washing method: the cordierite-type waste automotive exhaust catalyst carrier was collected in a mortar and ground thoroughly, rinsed three times with anhydrous ethanol, then rinsed five times with deionized water, and then the sample was transferred to a 60°C electric thermostatic blower dryer and dried for 6 hours to obtain clean cordierite powder.

[0031] Example 1

[0032] Weigh 0.92g of cordierite powder and place it in a beaker. Add 50ml of deionized water and sonicate for 30min to disperse it evenly. Then weigh 0.094g of silver nitrate powder and 0.04g of potassium chloride powder and add them to beakers containing 30ml of deionized water respectively. Sonicate for 10min to disperse them evenly to obtain silver nitrate solution and potassium chloride solution.

[0033] Wrap the beaker containing cordierite powder in aluminum foil to protect it from light, then transfer it to a constant-temperature water bath with a stirrer. Set the temperature to 30°C, and first add silver nitrate solution dropwise using a separatory funnel at a rate of approximately 1 drop per second, reacting for 1 hour. Then, continue adding potassium chloride solution dropwise using a separatory funnel at a rate of 1 drop per 2 seconds, reacting for 2 hours. Reduce the reaction product with a 300W xenon lamp for 10-30 minutes. Then filter, wash three times with anhydrous ethanol, then three times with deionized water, and transfer to an electrically heated constant-temperature dryer to dry at 60°C for 8 hours. The prepared sample is labeled cordierite / Ag / AgCl-n (AAC-n), where "n" represents the mass percentage of Ag / AgCl in cordierite / Ag / AgCl, which are 4%, 6%, 8%, and 10%, respectively. The sample prepared in this example is cordierite / Ag / AgCl-8.

[0034] The above describes the preparation process of the cordierite / Ag / AgCl photocatalytic material in Example 1. The prepared material was characterized in a series of ways, and the results are as follows.

[0035] Figure 2 XRD patterns of clean cordierite powder, Ag / AgCl, cordierite / Ag / AgCl-4, cordierite / Ag / AgCl-6, cordierite / Ag / AgCl-8, and cordierite / Ag / AgCl-10. For AgCl, all diffraction peaks are in agreement with the standard card (PDF#31-1238). 0 The characteristic peak at 38.1° corresponds to the (111) crystal plane of Ag (PDF#04-0783). This proves the successful composite of cordierite and Ag / AgCl.

[0036] Figure 3 The images show scanning electron micrographs of clean cordierite powder and cordierite / Ag / AgCl-8. As can be seen from the images, the clean cordierite powder particles are relatively large, approximately 2–8 μm in size, and exhibit a rough surface structure. Ag / AgCl nanoparticles are relatively uniformly loaded on the cordierite support surface with only slight agglomeration. This demonstrates that combining Ag / AgCl nanoparticles with a cordierite support can solve the problem of AgCl's tendency to agglomerate and achieve a high composite rate.

[0037] Example 2

[0038] Weigh 0.96g of cordierite powder and place it in a beaker. Add 50ml of deionized water and sonicate for 30min to disperse it evenly. Then weigh 0.047g of silver nitrate powder and 0.021g of potassium chloride powder and add them to beakers containing 30ml of deionized water respectively. Sonicate for 10min to disperse them evenly to obtain silver nitrate solution and potassium chloride solution.

[0039] A beaker containing cordierite powder was wrapped in aluminum foil to protect it from light. It was then transferred to a constant-temperature water bath with a stirrer, set at 30°C. Silver nitrate solution was first added dropwise using a separatory funnel at a rate of approximately one drop per second, and the reaction was allowed to proceed for 1 hour. Subsequently, potassium chloride solution was added dropwise using a separatory funnel at a rate of one drop per 2 seconds, and the reaction was allowed to proceed for 2 hours. The resulting product was then reduced using a 300W xenon lamp for 10–30 minutes. After filtration, the product was washed three times with anhydrous ethanol, then three times with deionized water, and finally dried in an electrically heated constant-temperature dryer at 60°C for 8 hours. Cordierite / Ag / AgCl-4 was thus prepared.

[0040] Example 3

[0041] Weigh 0.94g of cordierite powder and place it in a beaker. Add 50ml of deionized water and sonicate for 30min to disperse it evenly. Then weigh 0.07g of silver nitrate powder and 0.03g of potassium chloride powder and add them to beakers containing 30ml of deionized water respectively. Sonicate for 10min to disperse them evenly to obtain silver nitrate solution and potassium chloride solution.

[0042] A beaker containing cordierite powder was wrapped in aluminum foil to protect it from light. It was then transferred to a constant-temperature water bath with a stirrer, set at 30°C. Silver nitrate solution was first added dropwise using a separatory funnel at a rate of approximately one drop per second, and the reaction was allowed to proceed for 1 hour. Subsequently, potassium chloride solution was added dropwise using the separatory funnel at a rate of one drop per 2 seconds, and the reaction was allowed to proceed for 2 hours. The resulting product was then reduced using a 300W xenon lamp for 10–30 minutes. After filtration, the product was washed three times with anhydrous ethanol, then three times with deionized water, and finally dried in an electrically heated constant-temperature dryer at 60°C for 8 hours. Cordierite / Ag / AgCl-6 was thus prepared.

[0043] Example 4

[0044] Weigh 0.9g of cordierite powder and place it in a beaker. Add 50ml of deionized water and sonicate for 30min to disperse it evenly. Then weigh 0.108g of silver nitrate powder and 0.052g of potassium chloride powder and add them to beakers containing 30ml of deionized water respectively. Sonicate for 10min to disperse them evenly to obtain silver nitrate solution and potassium chloride solution.

[0045] A beaker containing cordierite powder was wrapped in aluminum foil to protect it from light. It was then transferred to a constant-temperature water bath with a stirrer, set at 30°C. Silver nitrate solution was first added dropwise using a separatory funnel at a rate of approximately one drop per second, and the reaction was allowed to proceed for 1 hour. Subsequently, potassium chloride solution was added dropwise using a separatory funnel at a rate of one drop per 2 seconds, and the reaction was allowed to proceed for 2 hours. The resulting product was then reduced using a 300W xenon lamp for 10–30 minutes. After filtration, the product was washed three times with anhydrous ethanol, then three times with deionized water, and finally dried in an electrically heated constant-temperature dryer at 60°C for 8 hours. Cordierite / Ag / AgCl-10 was thus prepared.

[0046] Visible photocatalytic performance test

[0047] The visible light photocatalytic performance of this material was studied using tetracycline as the target degradation product. In the photocatalytic experiment, 50 mg of cordierite / Ag / AgCl was used as the photocatalyst, and 50 mL of a 10 mg / L tetracycline solution was used as the target degradation product. A 300W xenon lamp with a 420 nm filter was used as the light source, and the photocatalytic experiment was conducted at room temperature. First, the reaction system was placed in the dark and stirred for 30 minutes to reach adsorption equilibrium. Then, the light source was turned on to initiate the photocatalytic reaction. During the reaction, 1 mL of the mixture was taken from the system every 5 minutes, centrifuged, and the concentration of tetracycline was detected by high-performance liquid chromatography (HPLC) to analyze its degradation.

[0048] The results of implementation of Examples 1-4 are shown in Table 1 and Figure 4 .

[0049] Table 1. Implementation Results

[0050]

[0051] Figure 4 This diagram shows the degradation of tetracycline (TC) catalyzed by Ag / AgCl, cordierite / Ag / AgCl-4, cordierite / Ag / AgCl-6, cordierite / Ag / AgCl-8, and cordierite / Ag / AgCl-10 under visible light. Where C0 is the initial concentration of tetracycline, C... t It is the concentration of tetracycline after being exposed to visible light for a certain period of time;

[0052] When cordierite powder was used as a catalyst, the degradation rate of tetracycline was 20.1%. Ag / AgCl showed a degradation rate of 81% after 20 minutes. However, when cordierite / Ag / AgCl-8 was used as a catalyst, the degradation rate of tetracycline reached 100% after 20 minutes of visible light irradiation. This indicates that the photocatalytic activity of cordierite / Ag / AgCl is significantly higher than that of a single-phase catalyst, and cordierite / Ag / AgCl-8 exhibits the highest catalytic activity.

[0053] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and improvements made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing a cordierite / Ag / AgCl visible light photocatalyst, characterized in that, Includes the following steps: Step 1: Thoroughly clean the cordierite carrier of the waste automobile exhaust catalyst to remove excess impurities on the surface, dry it, and obtain clean cordierite powder; disperse the cordierite powder in deionized water to obtain cordierite suspension. Step 2: Weigh an appropriate amount of silver nitrate granules and disperse them in deionized water to prepare a silver nitrate solution; weigh an appropriate amount of potassium chloride powder and disperse it in deionized water to prepare a potassium chloride solution. Step 3: After the cordierite suspension is wrapped in a light-proof container, it is transferred to a constant temperature water bath stirring device. Silver nitrate solution and potassium chloride solution are added dropwise in sequence to carry out the reaction. After the reaction is completed, it is allowed to cool naturally to room temperature. Step 4: After the reaction in step (3), the system is subjected to a photoreduction reaction using a xenon lamp as the light source until the system changes from grayish-white to dark gray. The system is then filtered, washed, and dried sequentially to obtain the cordierite / Ag / AgCl photocatalytic material; Ag / AgCl accounts for 6-10 wt% of the total mass of the visible light photocatalyst; wherein: In step (1), the cordierite carrier of the waste automobile exhaust catalyst comes from the cordierite-type waste automobile exhaust catalyst after the recovery of precious metals; before cleaning, the cordierite carrier of the waste automobile exhaust catalyst is first ground and finely treated; the cleaning method of the cordierite carrier of the waste automobile exhaust catalyst is vacuum filtration washing, the cordierite waste catalyst is placed on the filter membrane and washed with anhydrous ethanol 2-4 times, and then washed with deionized water more than 5 times; In step (2), the concentration of silver nitrate solution is between 0.005 and 0.1 mol / L, and the concentration of potassium chloride solution is between 0.005 and 0.1 mol / L; In step (3), the temperature of the constant temperature water bath is controlled between 25-35℃. After adding the silver nitrate solution, the reaction is carried out for 40-80 minutes. Then, the potassium chloride solution is added dropwise. After adding the potassium chloride solution, the reaction is continued for 100-150 minutes. The molar ratio of silver nitrate to potassium chloride is 1:

1. The mass ratio of cordierite to silver nitrate is between 7:1 and 14:

1.

2. The preparation method of the cordierite / Ag / AgCl visible light photocatalyst according to claim 1, characterized in that, In step (1), the drying temperature is 50-70℃ and the drying time is 4-12h; the concentration of cordierite powder suspension is between 10-50mg / mL.

3. The preparation method of the cordierite / Ag / AgCl visible light photocatalyst according to claim 1, characterized in that, In step (4), the photoreduction reaction time is 10-30 min; the product is washed with anhydrous ethanol and deionized water in sequence; the drying temperature is 50-70℃ and the drying time is 4-12 h.

4. A cordierite / Ag / AgCl visible light photocatalyst prepared by the preparation method according to any one of claims 1-3.

5. The application of the cordierite / Ag / AgCl visible light photocatalyst according to claim 4 in the degradation of organic pollutants in wastewater under visible light conditions.

6. The application of the cordierite / Ag / AgCl visible light photocatalyst according to claim 5 in the degradation of organic pollutants in wastewater under visible light conditions, characterized in that, The organic pollutant is tetracycline.

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