A tea biochar-supported manganese oxide composite material, its preparation method and application

Abstract

The present invention discloses a tea biochar-supported manganese oxide composite material, its preparation method and application. This composite material is obtained by fully mixing manganese dioxide nanoparticles and tea powder in a mass ratio of 1:(1-7) and then calcining. The present invention utilizes the reducing substances contained in tea leaves to reduce manganese dioxide to MnO, Mn3O4 and Mn2O3 during the process of loading manganese oxides, thereby improving the catalytic performance of the composite material. The waste tea-derived biochar-supported manganese oxide composite material prepared by the present invention contains uniformly distributed calcium carbonate nanoparticles; the calcium carbonate nanoparticles can serve as alkali active sites to improve the degradation efficiency of ozone on organic matter. In addition, the manganese oxides in the composite material provided by the present invention are uniformly dispersed on the waste tea-derived biochar, and the manganese oxides are not easily agglomerated during the catalytic ozone process, effectively increasing the active sites of the catalyst and being beneficial to improving the degradation efficiency of refractory organic matter.

Description

Technical Field

[0001] The present invention relates to the technical fields of nanomaterials and water purification environment, and particularly relates to a tea biochar-supported manganese oxide composite material, a preparation method thereof, and an application thereof. Background Art

[0002] Pyrazine compounds are usually used as pharmaceutical intermediates, flavorings for foods, beverages and perfumes, and are widely present in the environment, which can cause odor problems in drinking water. At present, only a few methods for biodegradation of pyrazine have been recorded, but biodegradation has problems such as a long period, harsh survival conditions for microorganisms, and low degradation efficiency. Therefore, it is urgent to find a method for efficiently degrading pyrazine compounds.

[0003] Heterogeneous catalytic ozonation technology is a convenient and effective advanced oxidation technology. By using a catalyst to catalyze ozone to generate a large number of reactive oxygen species such as hydroxyl radicals, organic pollutants in water can be degraded non-selectively, and it has been widely used in drinking water and wastewater treatment.

[0004] Metal oxides are widely used as catalysts in heterogeneous catalytic ozonation technology, but metal oxides usually have disadvantages such as a large amount of metal used, easy aggregation in water, and a large amount of dissolution resulting in secondary pollution. In recent years, metal-free carbon-based materials have also been widely used as catalysts and catalytic carrier materials for heterogeneous catalytic ozonation technology because of their rich functional groups and defect structures on the surface. However, single carbon-based materials have disadvantages such as instability of some active groups, easy consumption, and good biocompatibility of carbon-based materials, which are easily covered by biofilms or natural organic matter and inactivated. In recent years, a large number of studies have also reported composites of metal oxides and carbon-based materials, which can not only play the advantages of metal oxides and carbon-based materials, but also improve and avoid the problems existing in metal oxides and carbon-based materials. However, most of the composite materials reported at present have cumbersome preparation procedures and are not economical enough. Therefore, it is necessary to seek a catalyst with a simple preparation method, low cost and good catalytic ozonation for efficiently degrading pyrazine compounds. Summary of the Invention

[0005] The purpose of the present invention is to provide a preparation method of a waste tea-derived biochar-supported manganese oxide composite material (Mn-nWT, where n represents the mass ratio of manganese dioxide nanoparticles to tea powder) and its application in efficiently catalytic ozonation degradation of organic pollutants. The preparation method has simple process, low cost, non-toxic and harmless, and manganese oxides are uniformly dispersed on the waste tea-derived biochar; at the same time, the obtained composite material contains uniformly distributed calcium carbonate nanoparticles. The composite material can be applied to efficiently catalytic ozonation degradation of organic pollutants in tap water or urban sewage.

[0006] In a first aspect, the present invention provides a tea biochar-supported manganese oxide composite material, which is obtained by fully mixing manganese dioxide nanoparticles and tea powder in a mass ratio of 1:(1-7) and then calcining.

[0007] Preferably, the mass ratio of the manganese dioxide nanoparticles to the tea powder is 1:5.

[0008] Preferably, the calcination temperature after mixing the manganese dioxide nanoparticles and the tea powder is 400-500 °C.

[0009] In a second aspect, the present invention provides a method for preparing a tea biochar-supported manganese oxide composite material, which comprises the following steps:

[0010] Step 1: Dry the tea and then grind it to obtain tea powder.

[0011] Step 2: Mix the manganese dioxide nanoparticles and the tea powder in a mass ratio of 1:5, add deionized water, mix evenly under ultrasonic conditions, and then dry.

[0012] Step 3: Grind the solid product obtained in Step 2 and then calcine it to obtain the tea biochar-supported manganese oxide composite material.

[0013] Preferably, the tea in Step 1 is waste Longjing green tea.

[0014] Preferably, the tea in Step 1 is brewed and washed several times with water before grinding. The brewing is specifically carried out by brewing the tea with 80 °C deionized water, and the amount of deionized water used is 50 times the mass of the tea; the drying conditions are overnight drying at 60 °C in a vacuum drying oven and sieving through a 70-mesh sieve.

[0015] Preferably, the preparation process of the manganese dioxide nanoparticles in Step 2 is as follows:

[0016] a. Dissolve sodium thiosulfate and potassium permanganate in deionized water respectively. After heating the two solutions in a 60 °C ultrasonic cleaning bath, drop the sodium thiosulfate solution into the potassium permanganate solution under magnetic stirring in a 60 °C water bath until the dropping is complete, and then age for 2 h in a 60 °C water bath.

[0017] b. Take out the suspension after the water bath aging and let it cool naturally to room temperature, and carry out solid-liquid separation by centrifugation or filtration.

[0018] c. Dry the separated solid component and then send it to a tube furnace for calcination.

[0019] Preferably, in step a, the concentrations of the sodium thiosulfate solution and the potassium permanganate solution are 0.376 mol / L and 0.2 mol / L respectively; the volume ratio of the sodium thiosulfate solution to the potassium permanganate solution is 1:5.

[0020] Preferably, in step b, the conditions for centrifugal separation are 10,000 revolutions per minute for 3 minutes, with multiple water washes; the conditions for filtration separation are vacuum filtration using a 0.45 μm filter membrane, with multiple water washes.

[0021] Preferably, in step c, the drying conditions are: drying in an oven at 110 °C for 12 h. The calcination conditions are: adding to a tubular furnace and heating to 400 °C at a rate of 5 °C per minute under high-purity nitrogen protection, calcining for 4 hours, and then naturally cooling.

[0022] Preferably, in step two, drying is carried out under the conditions of an 80 °C water bath or an 80 °C oven.

[0023] Preferably, in step two, the amount of deionized water used is 10 times the total mass of the manganese dioxide nanoparticles and the tea powder.

[0024] Preferably, in step three, the calcination conditions are: adding the solid product obtained in step two to a tubular furnace and heating to 450 °C at a rate of 3 °C per minute under high-purity argon protection, calcining for 3 hours, and then naturally cooling.

[0025] In a third aspect, the present invention provides an application of a tea biochar-supported manganese oxide composite material as a catalyst in the ozonation degradation of organic pollutants.

[0026] Preferably, the organic pollutant to be treated is a pyrazine compound.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] 1. The present invention utilizes the reducing substances contained in tea leaves. During the process of loading manganese oxides, manganese dioxide is reduced to MnO and Mn3O4. The low-valent manganese (Mn 2+ , Mn 3+ ) enhances the ability of Mn atoms to transfer electrons to ozone, thereby improving the catalytic performance of the obtained composite material.

[0029] 2. The present invention utilizes the characteristic that tea leaves are rich in calcium, so that the prepared waste tea-derived biochar-supported manganese oxide composite material contains uniformly distributed calcium carbonate nanoparticles; these calcium carbonate nanoparticles can serve as basic active sites to improve the degradation efficiency of organic matter by catalytic ozone.

[0030] 3. In the manganese oxide-loaded composite material (Mn-nWT) derived from waste tea prepared by the present invention, manganese oxides are uniformly dispersed on the waste tea-derived biochar, and the manganese oxides are not easily agglomerated during the catalytic ozone process, effectively increasing the active sites of the catalyst and facilitating the improvement of the degradation efficiency of refractory organic compounds.

[0031] 4. In the manganese oxide-loaded composite material (Mn-nWT) derived from waste tea prepared by the present invention, manganese oxides and biochar are closely combined and promote each other in the catalytic ozone degradation of organic pollutants; biochar can accelerate electron transfer and transmission, enabling the valence state of manganese to smoothly convert among +2, +3, and +4 valence states, and the structure of biochar is more stable under the loading of manganese oxides.

[0032] 5. The manganese oxide-loaded composite material (Mn-nWT) derived from waste tea prepared by the present invention has stable properties in the oxidation system and good repeatability. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a high-resolution transmission electron microscopy (HRTEM) image of the Mn-5WT composite material prepared in Example 1 of the present invention;

[0034] Figure 2 It is a comparison graph of the ozone catalytic degradation efficiency of the composite materials prepared in Examples 1-4 and Comparative Example 1 of the present invention for the pyrazine compound 2,3,5-trimethylpyrazine (TrMP).

[0035] Figure 3 It is a comparison graph of the outlet ozone concentration of the ozone catalytic degradation of TrMP by the composite materials prepared in Examples 1-4 and Comparative Example 1 of the present invention.

[0036] Figure 4 It is a graph of the cyclic repeated degradation efficiency of the ozone catalytic degradation of TrMP by the Mn-5WT composite material prepared in Example 1 of the present invention.

[0037] Figure 5 It is a comparison graph of X-ray diffraction (XRD) before and after the reaction of the Mn-5WT composite material prepared in Example 1 of the present invention as a catalyst for the catalytic ozone degradation of TrMP. DETAILED DESCRIPTION OF THE INVENTION

[0038] The content of the present invention will be further described below with reference to the accompanying drawings and specific embodiments, but it should not be construed as a limitation to the present invention. Without departing from the spirit and essence of the present invention, simple modifications or substitutions made to the methods, steps, or conditions of the present invention all fall within the scope of the present invention. If not specifically specified, the technical means used in the embodiments are conventional means well known to those skilled in the art. The materials, reagents, etc. used in the following embodiments can be obtained from commercial sources without special instructions.

[0039] Example 1

[0040] A preparation method of Mn-5WT composite catalytic material, comprising the following steps:

[0041] (1) Dissolve 9.332 g of anhydrous sodium thiosulfate in 100 mL of deionized water, and dissolve 15.803 g of potassium permanganate in 500 mL of deionized water. Put them into an ultrasonic cleaning bath (working power: 40 kHz, 200 W) and keep it at a constant temperature of 60 °C for a period of time. Then transfer the potassium permanganate solution into a magnetic stirring water bath at 60 °C and continuously stir at a speed of 120 revolutions per minute until the sodium thiosulfate solution is completely dropped. Stop stirring and age in a water bath at 60 °C for 2 h. After the reaction is completed, solid-liquid separation is carried out by centrifugation (centrifugation conditions: 10,000 r / min, 3 min). The solid component is washed with water multiple times until the filtrate is neutral in pH. Then the solid component is sent into an oven and dried at 110 °C for 12 h. The dried solid is sent into a tube furnace and calcined at 400 °C for 4 h under the protection of high-purity nitrogen with a heating rate of 5 °C / min, and then naturally cooled to room temperature to obtain manganese dioxide nanoparticles.

[0042] (2) Take 10 g of waste Longjing green tea leaves, add 500 mL of 80 °C deionized water and steep for 2 h. Wash the tea leaves three times with deionized water, drain the water, put them into a vacuum drying oven and dry overnight at 60 °C. Then grind them into powder with a mortar and sieve them through a 70-mesh sieve to obtain waste tea powder.

[0043] (3) Prepare a mixture of 0.1 g of manganese dioxide nanoparticles and 0.5 g of waste tea powder in 6 mL of deionized water (i.e., the mass ratio of manganese dioxide nanoparticles to waste tea powder is 1:5). After ultrasonic treatment for 60 minutes (working power: 40 kHz, 200 W), place it in a water bath at 80 °C and evaporate to dryness, then send it into a tube furnace for calcination. The calcination conditions are to heat to 450 °C at a rate of 3 °C / min under the protection of high-purity argon, and calcine for 3 h and then naturally cool to room temperature to obtain the Mn-5WT composite material, in which the manganese oxides include MnO and Mn3O4.

[0044] The HRTEM image of the Mn-5WT composite material obtained in this example is as Figure 1 shown; it can be seen from Figure 1 that in the Mn-5WT composite material prepared in this example, the manganese oxide particles are evenly dispersed on the biochar material and have obvious crystal lattices, indicating that its crystallinity is relatively high.

[0045] Example 2

[0046] A preparation method of an Mn-1WT composite catalytic material. The difference between this example and Example 1 is that: in step (3), the mass ratio of manganese dioxide nanoparticles to waste tea powder is 1:1, and 0.1 g of manganese dioxide nanoparticles and 0.1 g of waste tea powder are mixed into 2 mL of deionized water. The obtained Mn-1WT composite catalytic material, wherein the manganese oxides include MnO2 and Mn2O3.

[0047] Example 3

[0048] A preparation method of an Mn-3WT composite catalytic material. The difference between this example and Example 1 is that: in step (3), the mass ratio of manganese dioxide nanoparticles to waste tea powder is 1:3, and 0.1 g of manganese dioxide nanoparticles and 0.3 g of waste tea powder are mixed into 4 mL of deionized water. The obtained Mn-3WT composite catalytic material, wherein the manganese oxides include MnO, Mn3O4 and Mn2O3.

[0049] Example 4

[0050] A preparation method of an Mn-7WT composite catalytic material. The difference between this example and Example 1 is that: in step (3), the mass ratio of manganese dioxide nanoparticles to waste tea powder is 1:7, and 0.1 g of manganese dioxide nanoparticles and 0.7 g of waste tea powder are mixed into 8 mL of deionized water. The obtained Mn-7WT composite catalytic material, wherein the manganese oxide is MnO.

[0051] Comparative Example 1

[0052] A preparation method of a wood chip-derived biochar supported manganese oxide composite material (Mn-5WW) composite catalytic material. The difference between this example and Example 1 is that: in step (2), the waste Longjing green tea leaves are replaced with commercially purchased wood chip powder, and 10 g of wood chip powder is mixed with manganese dioxide nanoparticles in a mass ratio of 1:5 through the same treatment steps as the waste Longjing green tea leaves in step (2) of Example 1. 0.1 g of manganese dioxide nanoparticles and 0.5 g of wood chip powder are mixed into 6 mL of deionized water, and the subsequent treatment steps are the same as those in step (3) of Example 1. The obtained Mn-5WW composite catalytic material, wherein the manganese oxide is MnO2.

[0053] To compare the catalytic effects of the composite catalytic materials provided in Examples 1-4 and Comparative Example 1 in the process of ozone catalytic advanced oxidation of organic pollutants, the following comparative tests were carried out. The organic pollutant to be degraded is the odor organic pollutant 2,3,5-trimethylpyrazine (TrMP). The specific test process is as follows:

[0054] (1) Dissolve TrMP in 1 L of deionized water to obtain a simulated wastewater with a TrMP concentration of 5 μm / L.

[0055] (2) Load the simulated wastewater into the ozone catalytic reaction device as the experimental group and the control group; a total of five experimental groups and one control group are set up; add the composite catalytic materials prepared in Examples 1 to 4 and Comparative Example 1 into the ozone catalytic reaction devices of Experimental Groups 1-5 respectively; the catalyst dosage in each experimental group is 50 mg, so that the catalyst concentration in the simulated wastewater is 0.05 g / L.

[0056] (3) Continuously aerate ozone into the reactors of all experimental groups and the control group, and detect the ozone concentration at the reactor outlet. Sample and monitor the concentration of TrMP in the simulated wastewater at regular intervals.

[0057] The results of the comparative experiment are as Figure 2 and 3 shown. In Figure 2 , ● represents the remaining concentration of TrMP in the control group without adding a catalyst; ▲ represents the remaining concentration of TrMP in Experimental Group 1 (adding the catalyst prepared in Example 1); ▼ represents the remaining concentration of TrMP in Experimental Group 2 (adding the catalyst prepared in Example 2); represents the remaining concentration of TrMP in Experimental Group 3 (adding the catalyst prepared in Example 3); represents the remaining concentration of TrMP in Experimental Group 4 (adding the catalyst prepared in Example 4); ■ represents the remaining concentration of TrMP in Experimental Group 5 (adding the catalyst prepared in Comparative Example 1).

[0058] Figure 2 The results show that ozone alone degrades 53.8% of TrMP after 20 minutes of reaction without adding a catalyst; adding the Mn-5WT composite material prepared in Example 1 catalytically degrades 84.7% of TrMP within 1 minute and can reach 97.8% after 20 minutes; adding the Mn-1WT composite material prepared in Example 2 degrades 91.2% of TrMP after 20 minutes of reaction; adding the Mn-3WT composite material prepared in Example 3 degrades 88.3% of TrMP after 20 minutes of reaction; adding the Mn-7WT composite material prepared in Example 4 degrades 86.8% of TrMP after 20 minutes of reaction; adding the Mn-5WW composite material prepared in Comparative Example 1 degrades 58.6% of TrMP after 20 minutes of reaction. A series of Mn-nWT all show the performance of efficiently degrading pollutants, but the composite material of manganese oxide loaded on biochar derived from sawdust powder (Mn-5WW) cannot promote the degradation of pollutants, indicating that using waste tea as the biochar source can effectively improve the catalytic performance of the obtained catalyst, that is, the composite material of manganese oxide loaded on biochar with waste tea as the raw material (Mn-nWT) of the present invention has excellent performance.

[0059] In Figure 3Among them, ● represents the ozone outlet concentration of the control group without catalyst; ▲ represents the ozone outlet concentration of experimental group 1 (adding the catalyst prepared in Example 1); ▼ represents the ozone outlet concentration of experimental group 2 (adding the catalyst prepared in Example 2); represents the ozone outlet concentration of experimental group 3 (adding the catalyst prepared in Example 3); represents the ozone outlet concentration of experimental group 4 (adding the catalyst prepared in Example 4); ■ represents the ozone outlet concentration of experimental group 5 (adding the catalyst prepared in Comparative Example 1).

[0060] Figure 3 The results show that the Mn-5WT, Mn-1WT, Mn-3WT and Mn-7WT composite materials prepared in Examples 1-4 can catalyze the decomposition of ozone to generate free radicals. The ability of the Mn-5WW prepared in Comparative Example 1 to catalytically decompose ozone is poor, which is consistent with Figure 2 the results in

[0061] Through ICP-OES testing, the dissolution amount of manganese ions in the simulated wastewater after the reaction of experimental group 1 is only 0.024 mg / L, and the dissolution amount is extremely low, indicating that the Mn-5WT composite catalytic material has high stability. Figure 4 It shows that after four cyclic experiments, the Mn-5WT composite material can still efficiently catalyze the degradation of organic pollutant TrMP by ozone. Figure 5 It shows that the X-ray diffraction patterns before and after the reaction of the Mn-5WT composite material catalyzing the degradation of organic pollutant TrMP by ozone are basically the same. The original diffraction peaks of MnO, Mn3O4 and CaCO3 all exist, and no new diffraction peaks are generated, indicating that the Mn-5WT composite material has high stability and the valence state of manganese remains basically stable before and after the reaction.

[0062] Example 6

[0063] A method for degrading organic pollutants in tap water or urban sewage by ozone advanced oxidation technology, and the specific process is as follows: after adding the composite material prepared in any one of Examples 1-4 to the water body to be treated, ozone is introduced into the water body to be treated.

Claims

1. Application of a tea biochar-supported manganese oxide composite material as a catalyst in the ozonation degradation of organic pollutants; characterized in that: The preparation process of the tea biochar-supported manganese oxide composite material includes the following steps: Step 1: Dry the tea leaves and then grind them to obtain tea powder; Step 2: Mix manganese dioxide nanoparticles and tea powder in a mass ratio of 1:5, add deionized water, mix evenly under ultrasonic conditions, and then dry; Step 3: Grind the solid product obtained in Step 2 and then calcine it at 450 °C to obtain the tea biochar-supported manganese oxide composite material; the calcium in the tea powder makes the composite material contain calcium carbonate nanoparticles as alkali active sites.

2. The application according to claim 1, characterized in that: In Step 1 of the preparation process of the tea biochar-supported manganese oxide composite material, the tea leaves are brewed and washed several times with water before grinding; the brewing is specifically carried out by brewing the tea leaves with deionized water at 80 °C, and the amount of deionized water used is 50 times the mass of the tea leaves; the drying conditions are overnight drying at 60 °C in a vacuum drying oven and sieving with a 70-mesh sieve.

3. The application according to claim 1, wherein: The preparation process of the manganese dioxide nanoparticles described in Step 2 of the preparation process of the tea biochar-supported manganese oxide composite material is as follows: a. Dissolve sodium thiosulfate and potassium permanganate in deionized water respectively to obtain their solutions. After heating both solutions in a 60 °C ultrasonic cleaning bath, drop the sodium thiosulfate solution into the potassium permanganate solution under magnetic stirring in a 60 °C water bath until the dropping is complete, and then age for 2 h in a 60 °C water bath; b. Take out the suspension after the water bath aging and let it cool naturally to room temperature, and perform solid-liquid separation by centrifugation or filtration; c. Dry the separated solid component and then send it to a tube furnace for calcination.

4. The application according to claim 3, characterized in that: In Step a of the preparation process of the manganese dioxide nanoparticles, the concentrations of the sodium thiosulfate solution and the potassium permanganate solution are 0.376 mol / L and 0.2 mol / L respectively; the volume ratio of the sodium thiosulfate solution to the potassium permanganate solution is 1:5; In Step b, the centrifugation separation conditions are 10,000 revolutions per minute for 3 minutes, and wash with water multiple times; The filtration separation conditions are vacuum filtration using a 0.45 μm filter membrane and wash with water multiple times; In Step c, the drying conditions are: drying at 110 °C in an oven for 12 h; the calcination conditions are: adding to the tube furnace and heating to 400 °C at a rate of 5 °C per minute under high-purity nitrogen protection, calcining for 4 hours, and then naturally cooling.

5. The application according to claim 1, wherein: In Step 2 of the preparation process of the tea biochar-supported manganese oxide composite material, the amount of deionized water used is 10 times the total mass of the manganese dioxide nanoparticles and the tea powder.

6. The application according to claim 1, wherein: In Step 3 of the preparation process of the tea biochar-supported manganese oxide composite material, the calcination conditions are: adding the solid product obtained in Step 2 to the tube furnace and heating to 450 °C at a rate of 3 °C per minute under high-purity argon protection, calcining for 3 hours, and then naturally cooling.

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