A nano Co / Mg(OH)2 catalyst and its preparation method and application

Abstract

The present invention provides a nano-Co / Mg(OH)₂ catalyst. CoCl₂ and sodium dodecyl sulfate (SDS) solution are added to the MgCl₂ solution, and at the same time, NaOH solution is added dropwise. After stirring at room temperature, a white suspension is obtained; then it is quickly transferred to a high-temperature and high-pressure hydrothermal reaction kettle, nitrogen is introduced for 10 min, and then it is sealed for hydrothermal reaction. Then, centrifugal separation is carried out, and after vacuum drying and grinding, the nano-Co / Mg(OH)₂ catalyst is obtained, which is nano hexagonal magnesium hydroxide with a high specific surface area. The preparation method is simple and easy to operate, and the formed catalytic material has stable properties, high purity, high catalytic activity and high selectivity.

Description

Technical Field

[0001] The invention relates to the field of catalysts for controlling ammonia nitrogen concentration in wastewater for environmental protection, and in particular to a nano Co / Mg(OH)2 catalyst and a preparation method thereof. The nano magnesium hydroxide catalyst is used for catalyzing ozone oxidation of ammonia nitrogen. Background Art

[0002] With the development of chemical industry, electroplating and other industries, more and more ammonia nitrogen is discharged into rivers and lakes, causing eutrophication of water bodies, promoting the proliferation of algae, leading to the death of fish and other aquatic organisms due to lack of oxygen, reducing water quality and destroying biodiversity. High-concentration ammonia nitrogen wastewater has poor biodegradability, low carbon and nitrogen values, and is difficult to treat. At the same time, the proliferation of algae may threaten human health.

[0003] At present, the ammonia nitrogen wastewater treatment methods widely reported in the literature mainly include physicochemical treatment technology (breakpoint chlorination method, ion exchange method, electrochemical oxidation method, etc.) and biological treatment technology (complete nitrification and denitrification, nitrite denitrification and anaerobic ammonia oxidation, etc.). The breakpoint chlorination method requires the addition of a large amount of chlorine, which produces by-products of chloramine and chlorinated organic matter, which can easily cause secondary pollution. The ion exchange method generally uses zeolite as an ion exchange resin. Long-term use can easily cause suspended matter to block the zeolite pores and reduce the exchange efficiency. The chemical precipitation method uses the addition of phosphoric acid or hydrogen phosphate to generate ammonium magnesium phosphate precipitation to achieve the purpose of reducing ammonia nitrogen. Its disadvantage is that it introduces new impurity phosphates, which can also cause secondary pollution.

[0004] Biochemical treatment is the main link in reducing pollutants in urban sewage at present, and it is also the final destination for improving the quality and efficiency of sewage treatment. Its operation will directly affect the urban water environment and the quality of life of the people. Among them, the control of nitrogen pollution indicators has always been the focus and difficulty of urban sewage pollution control. However, my country's sewage treatment plants currently generally have the characteristics of low influent concentration, low carbon-nitrogen ratio, and high inorganic suspended solids concentration. Adding carbon sources and increasing aeration are often used to improve denitrification efficiency. Therefore, the use of traditional complete nitrification and denitrification processes to treat urban sewage has problems such as high treatment difficulty, high operating costs, and high sludge production. With the increasingly stringent emission standards, traditional wastewater treatment technology can no longer meet the requirements. One of the key measures to solve the problem is to carry out deep treatment after the biochemical treatment unit. The catalytic ozone oxidation process has the advantages of high decomposition efficiency, thorough oxidation of pollutants, less secondary pollution, and simple operation, which has attracted widespread attention. Its basic principle is to use solid metals, metal oxides, or metals or metal oxides loaded on carriers to initiate ozone decomposition in the reaction system to produce highly oxidizing superoxide radicals (·O 2- ), hydroxyl radicals (·OH) and other active species, thereby degrading pollutants in wastewater. The current catalyst preparation process is cumbersome, costly and has the problem of over-oxidation, which limits the further development of this method.

[0005] Based on this, achieving one-step denitrification of low-concentration ammonia nitrogen wastewater through optimization and regulation of catalyst structure is a hot topic and difficulty in current research. Summary of the invention

[0006] In view of the problems of complex preparation and high cost of ozone catalysts, secondary pollution, low efficiency of ozone denitrification and over-oxidation, the present invention provides a nano Co / Mg(OH)2 catalyst, which uses magnesium chloride as a magnesium source and sodium hydroxide as a precipitant, and undergoes a hydrothermal reaction with a cobalt metal solution to obtain nano hexagonal magnesium hydroxide with a high specific surface area. The preparation method is simple and easy to control, and the formed catalytic material has stable properties, high purity, high catalytic activity and high selectivity.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] A nano Co / Mg(OH)2 catalyst is prepared by the following method, the steps are:

[0009] Step 1: Add CoCl2 and sodium dodecyl sulfate (SDS) solution to MgCl2 solution, and add NaOH solution dropwise at the same time, and stir at room temperature to obtain a white suspension A;

[0010] Step 2: quickly transfer the suspension A to a high temperature and high pressure hydrothermal reactor and pass nitrogen for 10 min, then seal and perform hydrothermal reaction to obtain suspension B;

[0011] Step 3: Centrifuge the suspension B, vacuum dry it, and grind it to obtain a nano Co / Mg(OH)2 catalyst.

[0012] As a more optimal technical solution of the present invention, the concentration of the MgCl2 solution in step 1 is 10-50 g / ml.

[0013] As a more optimal technical solution of the present invention, the concentration of the NaOH solution in step 1 is 1 mol / L.

[0014] As a more optimal technical solution of the present invention, the concentration of the SDS solution in step 1 is 1 g / L.

[0015] As a more optimal technical solution of the present invention, the doping ratio of CoCl2 and MgCl2 in step 1 is 2-20%.

[0016] As a more optimal technical solution of the present invention, the doping ratio of CoCl2 and MgCl2 in step 1 is 1-5%.

[0017] As a more optimal technical solution of the present invention, the stirring speed in step 1 is 500-700 r / min.

[0018] As a more optimal technical solution of the present invention, the stirring time in step 1 is 60 to 80 minutes.

[0019] As a more optimal technical solution of the present invention, the hydrothermal temperature in step 2 is 120-200°C.

[0020] As a more optimal technical solution of the present invention, the hydrothermal temperature in step 2 is 160°C.

[0021] As a more optimal technical solution of the present invention, the hydrothermal reaction time in step 2 is 2-8h.

[0022] As a more optimal technical solution of the present invention, the hydrothermal reaction time in step 2 is 4 hours.

[0023] As a more optimal technical solution of the present invention, the drying temperature in step three is 50° C. and the drying time is 4 hours.

[0024] Another object of the present invention is to provide the use of the above-mentioned nano Co / Mg(OH)2 catalyst in the treatment of ammonia nitrogen wastewater, so as to realize the rapid conversion of ammonia nitrogen in water into nitrogen gas, thereby reducing the total nitrogen in water.

[0025] The nano Co / Mg(OH)2 catalyst of the present invention adopts a hydrothermal oxidation method, is easy to prepare, and has a wide source of raw materials, thus solving the problems of complex catalyst preparation, high cost, secondary pollution, low ozone denitrification efficiency alone, and over-oxidation.

[0026] The nano Co / Mg(OH)2 catalyst of the present invention has an average particle size of 50-150 nm, presents a regular hexagonal plate shape, and has a specific surface area of ​​300-380 m 2 / g. During use, ammonia nitrogen is first adsorbed on the surface of nano Co / Mg (OH) 2 catalyst, and then excited by ozone to trigger the production of a series of active species, so that the ammonia nitrogen removal rate reaches 90.1%, and 61.6% of ammonia nitrogen is converted into gaseous nitrogen, realizing one-step denitrification.

[0027] The ammonia nitrogen wastewater treatment method using the nano Co / Mg(OH)2 catalyst prepared by the present invention can be used alone or in combination with other water treatment processes. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a SEM image of the nano Co / Mg(OH)2 catalyst prepared in Example 2 of the present invention;

[0029] Figure 2 This is the Fourier infrared spectrum of the nano Co / Mg(OH)2 catalyst prepared in Example 2 of the present invention;

[0030] Figure 3 This is a nitrogen adsorption / desorption curve diagram of the nano Co / Mg(OH)2 catalyst prepared in Example 2 of the present invention;

[0031] Figure 4 This is a comparison chart of the conversion products after removing ammonia nitrogen from nano-Mg(OH)2 catalyst under different hydrothermal temperature conditions.

[0032] Figure 5 This is a comparison of the conversion products after removing ammonia nitrogen from nano-Co / Mg(OH)2 catalyst under different cobalt doping ratios. DETAILED DESCRIPTION

[0033] The present invention is further defined in the following examples. Based on the following description and these examples, those skilled in the art can ascertain the essential characteristics of the present invention and, without departing from the essence and scope of the present invention, can make various changes and modifications to the present invention to adapt it to various uses and conditions.

[0034] Embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. The reagents or instruments used are conventional products that can be obtained commercially without specifying the manufacturer. The quantitative tests in the following embodiments were repeated three times, and the results were averaged.

[0035] Example 1

[0036] A method for preparing a nano Mg(OH)2 catalyst comprises the following steps:

[0037] (1) Weigh 20.23 g of MgCl2·6H2O and add it to 100 mL of distilled water to prepare MgCl2 solution;

[0038] (2) Weigh 4 g of NaOH and add it to 100 mL of distilled water to prepare a 1 mol / L sodium hydroxide solution;

[0039] (3) Weigh 0.02 g / L of SDS solution and add it to 20 mL of distilled water to prepare a 1 g / L SDS solution;

[0040] (4) Add SDS solution to the MgCl2 solution, and at the same time, add NaOH solution dropwise, and fully react for 70 minutes at room temperature and a stirring speed of 600 r / min to obtain a suspension;

[0041] (5) Transfer the suspension in (4) to a high-temperature and high-pressure hydrothermal reactor, and introduce nitrogen to remove the air in the reactor for 10 minutes, and then seal it. Set the stirrer speed to 200 r / min. The hydrothermal temperature is 160°C. After the hydrothermal reaction for 4 hours, the autoclave is naturally cooled for 12 hours.

[0042] (6) After the autoclave is cooled to room temperature, the product obtained by the reaction is centrifuged and filtered, and washed several times with methanol, anhydrous ethanol and distilled water in sequence. The washed precipitate is placed in an electric heated air drying oven, set at 50°C, and dried for 24 hours to obtain a nano-Mg(OH)2 catalyst.

[0043] Example 2

[0044] A method for preparing a nano Co / Mg(OH)2 catalyst comprises the following steps:

[0045] (1) Weigh 19.83 g MgCl2·6H2O and 0.41 g CoCl2 and add them to 100 mL distilled water to prepare a 2% CoCl2 / MgCl2 solution;

[0046] (2) Weigh 4 g of NaOH and add it to 100 mL of distilled water to prepare a 1 mol / L sodium hydroxide solution;

[0047] (3) Add 0.02 g / L sodium dodecyl sulfate (SDS) into 20 mL of distilled water to prepare a 1 g / L SDS solution;

[0048] (4) adding solution (3) to solution (1), and at the same time adding dropwise the solution in solution (2), and reacting the mixture for 70 min at room temperature and stirring at 600 r / min to obtain a suspension;

[0049] (5) Transfer the suspension in (4) to a high-temperature and high-pressure hydrothermal reactor, and introduce nitrogen to remove the air in the reactor for 10 minutes, and then seal it. Set the stirrer speed to 200 r / min. The hydrothermal temperature is 160°C. After the hydrothermal reaction for 4 hours, the autoclave is naturally cooled for 12 hours.

[0050] (6) After the autoclave is cooled to room temperature, the product obtained by the reaction is centrifuged and filtered, and washed several times with methanol, anhydrous ethanol and distilled water in sequence. The washed precipitate is placed in an electric heated air drying oven, set at 50°C, and dried for 24 hours to obtain a nano Co / Mg(OH)2 catalyst.

[0051] The SEM test results of nano Co / Mg(OH)2 catalyst are as follows Figure 1As shown, it can be observed that the catalyst obtained after adding the structure directing agent is a nanoscale regular hexagonal plate, which is consistent with the morphology of nano Co / Mg(OH)2. Figure 1 It shows that the diameter of the nano Co / Mg(OH)2 catalyst is about 50~150nm and the thickness is about 10~20nm. It can be seen that the nano Co / Mg(OH)2 prepared by high temperature and high pressure hydrothermal method forms a regular layered structure. Figure 2 The results show that the main surface functional groups of nano Co / Mg (OH) 2 are hydroxyl groups and OH groups. The BET test of nano Co / Mg (OH) 2 shows that the specific surface area of ​​nano Co / Mg (OH) 2 is 333.66 m 2 / g, the average pore size of the prepared nano Co / Mg(OH)2 catalyst is 7.22nm, which belongs to the microporous structure.

[0052] Example 3

[0053] The application of a nano Co / Mg(OH)2 catalyst prepared in Example 2 is as follows:

[0054] (1) Using 41.42 mg / L NH4Cl solution to simulate secondary effluent, adding it into the reactor, and then adding the nano Co / Mg(OH)2 catalyst in Example 1 into the reactor, the pH value of the solution was 9, and the temperature was room temperature;

[0055] (2) 1.2 mg / L ozone was introduced into the reactor for catalytic oxidation reaction to complete the deep treatment of low-concentration ammonia nitrogen wastewater.

[0056] According to the experimental results, NH4 + The -N removal rate can reach 90.19%, the TN removal rate is 61.43%, and the gaseous nitrogen production is calculated to be 61.43% through the formula.

[0057]

[0058] Example 4

[0059] The preparation and application of a nano Mg(OH)2 catalyst are as follows:

[0060] The material synthesis method was carried out according to Example 1, but the hydrothermal temperature was adjusted to 100° C. Thus, a 100° C. nano-Mg(OH)2 catalyst was obtained.

[0061] The material is used to catalyze 10 mg / L NH4 + -N aqueous solution, the process is carried out according to Example 3. NH4 + The -N removal efficiency was 29.97% and the gaseous nitrogen yield was 14.88%.

[0062] Embodiment 5,

[0063] The preparation and application of a nano Mg(OH)2 catalyst are as follows:

[0064] The material synthesis method is compared with Example 1. The hydrothermal temperature is adjusted to 120°C. Thus, a 120°C nano-Mg(OH)2 catalyst is obtained.

[0065] The material is used to catalyze 10 mg / L NH4 + -N aqueous solution, the process is carried out according to Example 3. NH4 + The -N removal efficiency was 38.15% and the gaseous nitrogen yield was 5.68%.

[0066] Example 6

[0067] A nano Mg(OH)2 catalyst and its application are as follows:

[0068] The material synthesis method was carried out according to Example 1, but the hydrothermal temperature was adjusted to 140° C. Thus, a 140° C. nano Co / Mg(OH)2 catalyst was obtained.

[0069] The material is used to catalyze 10 mg / L NH4 + -N aqueous solution, the process is carried out according to Example 3. NH4 + The -N removal efficiency was 51.77% and the gaseous nitrogen yield was 2.80%.

[0070] Example 7

[0071] The preparation and application of a nano Mg(OH)2 catalyst are as follows:

[0072] The material synthesis method was carried out according to Example 1, but the hydrothermal temperature was adjusted to 160° C. Thus, a 160° C. nano-Mg(OH)2 catalyst was obtained.

[0073] The material is used to catalyze 10 mg / L NH4 + -N aqueous solution, the process is carried out according to Example 3. NH4 + The -N removal efficiency was 57.22% and the gaseous nitrogen yield was 4.07%.

[0074] Example 8

[0075] The preparation and application of a nano Mg(OH)2 catalyst are as follows:

[0076] The material synthesis method was carried out according to Example 1, but the hydrothermal temperature was adjusted to 180° C. Thus, a 180° C. nano-Mg(OH)2 catalyst was obtained.

[0077] The material is used to catalyze 10 mg / L NH4 + -N aqueous solution, the process is carried out according to Example 3. NH4 + The -N removal efficiency was 38.15% and the gaseous nitrogen yield was 5.68%.

[0078] Example 9

[0079] The preparation and application of a nano Mg(OH)2 catalyst are as follows:

[0080] The material synthesis method was carried out according to Example 1, but the hydrothermal temperature was adjusted to 200° C. Thus, a 200° C. nano-Mg(OH)2 catalyst was obtained.

[0081] The material is used to catalyze 10 mg / L NH4 + -N aqueous solution, the process is carried out according to Example 3. NH4 + The -N removal efficiency was 16.35% and the gaseous nitrogen yield was 2.62%.

[0082] Compared with Example 1, the hydrothermal time of Examples 4-9 remains unchanged, and the variable factor is the hydrothermal temperature. Figure 4 The results show that Mg(OH)2NH4 at 200℃ + -N removal efficiency is 16.35%, gaseous nitrogen production is 2.62%; 180℃ Mg(OH)2 NH4 + -N removal efficiency is 38.15%, gaseous nitrogen production is 5.68%; 160℃ Mg(OH)2 NH4 + -N removal efficiency is 57.22%, gaseous nitrogen production is 4.07%; 140℃ Mg(OH)2 NH4 + -N removal efficiency is 51.77%, gaseous nitrogen production is 2.80%; 120℃ Mg(OH)2 NH4 + -N removal efficiency is 38.15%, gaseous nitrogen production is 5.68%; 100℃ Mg(OH)2 NH4 + The -N removal efficiency was 29.97% and the gaseous nitrogen production was 14.88%.

[0083] Therefore, the hydrothermal temperature will affect the crystallinity of the nano-Mg(OH)2 catalyst, and then affect its catalytic effect. The ozone catalytic oxidation effect of Mg(OH)2 prepared at 160°C is the best.

[0084] Example 10

[0085] The preparation and application of a nano Co / Mg(OH)2 catalyst are as follows:

[0086] The material synthesis method was carried out according to Example 2, but the addition amounts of MgCl2·6H2O and CoCl2 were adjusted to 19.31 g and 1.02 g, respectively. Thus, a nano 5% Co / Mg(OH)2 catalyst was obtained.

[0087] The material is used to catalyze 10 mg / L NH4 + -N aqueous solution, the process is carried out according to Example 3. NH4 + The -N removal efficiency was 66.31% and the gaseous nitrogen yield was 46.42%.

[0088] Embodiment 11

[0089] The preparation and application of a nano Mg(OH)2 catalyst are as follows:

[0090] Material Synthesis Method Compared with Example 2, the addition amounts of MgCl2·6H2O and CoCl2 were adjusted to 18.30 g and 2.03 g, respectively, and the other preparation conditions remained unchanged. Thus, a nano 10% Co / Mg(OH)2 catalyst was obtained.

[0091] The material is used to catalyze 10 mg / L NH4 + -N aqueous solution, the process is carried out according to Example 3. NH4 + The -N removal efficiency was 58.35% and the gaseous nitrogen yield was 44.23%.

[0092] Example 12

[0093] The preparation and application of a nano Mg(OH)2 catalyst are as follows:

[0094] The material synthesis method was carried out according to Example 2, but the addition amounts of MgCl2·6H2O and CoCl2 were adjusted to 16.26 g and 4.07 g, respectively. Thus, a nano 20% Co / Mg(OH)2 catalyst was obtained.

[0095] The material is used to catalyze 10 mg / L NH4 + -N aqueous solution, the process is carried out according to Example 3. NH4 + The -N removal efficiency was 50.40% and the gaseous nitrogen yield was 35.26%.

[0096] Compared with Example 1 and Example 2, the temperature and time of Example 10-11 remain unchanged, and the variable factor is the doping ratio of the cobalt element. Figure 5 The results show that the NH4 + -N removal efficiency is 57.22%, gaseous nitrogen production is 4.07%; NH4 +-N removal efficiency is 90.19%, gaseous nitrogen production is 61.43%; 5% Co / Mg(OH)2 NH4 + -N removal efficiency is 66.31%, gaseous nitrogen production is 46.42%; 10% Co / Mg (OH) 2 NH4 + -N removal efficiency is 58.35%, gaseous nitrogen production is 44.23%; 20% Co / Mg (OH) 2 NH4 + The -N removal efficiency was 50.40% and the gaseous nitrogen yield was 35.26%.

[0097] According to the experimental results, the cobalt doping ratio will affect the selectivity of ammonia nitrogen and gaseous products of nano-Co / Mg(OH)2 catalyst, and affect its catalytic effect. The nano-Co / Mg(OH)2 prepared with a cobalt doping ratio of 2% has the best ozone catalytic oxidation effect.

[0098] In other embodiments of the present invention, it is verified that the concentration of the MgCl2 solution is between 10-50g / ml and other values ​​other than the above embodiment 2, the concentration of the NaOH solution is between 0.1-10mol / L and other values ​​other than the above embodiment 2, the concentration of the SDS solution is between 1.5-5g / L and other values ​​other than the above embodiment 2, the stirring speed is between 500-700r / min and other values ​​other than the above embodiment 2, and the stirring time is between 60-80min and other values ​​other than the above embodiment 2. + -N removal efficiency and gaseous nitrogen production were the same as those in Example 2 or within 0.5%.

[0099] The embodiments described above are part of the embodiments of the present invention, rather than all of the embodiments. The detailed description of the embodiments of the present invention is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

Claims

1. A method for preparing a nano Co / Mg(OH)2 catalyst for treating ammonia nitrogen wastewater, characterized in that: The steps include: CoCl2 and sodium dodecyl sulfate solution were added to MgCl2·6H2O solution, and NaOH solution was added dropwise at the same time, and a white suspension A was obtained after stirring at room temperature; the suspension A was quickly transferred to a high-temperature and high-pressure hydrothermal reactor and nitrogen was passed through for 10 minutes, and then the reactor was sealed for hydrothermal reaction to obtain suspension B; the suspension B was centrifuged, vacuum dried, and then ground to obtain a nano-Co / Mg(OH)2 catalyst; The doping ratio of CoCl2 and MgCl2·6H2O is 2-20%.

2. The method for preparing a nano Co / Mg(OH)2 catalyst for treating ammonia nitrogen wastewater according to claim 1, characterized in that: The concentration of the MgCl2·6H2O solution is 10-50 g / mL; the concentration of the NaOH solution is 0.1-10 mol / L; and the concentration of the sodium dodecyl sulfate solution is 0.5-5 g / L.

3. The method for preparing a nano Co / Mg(OH)2 catalyst for treating ammonia nitrogen wastewater according to claim 1, characterized in that: The doping ratio of CoCl2 and MgCl2·6H2O is 1-5%.

4. The method for preparing a nano Co / Mg(OH)2 catalyst for treating ammonia nitrogen wastewater according to claim 1, characterized in that: The stirring speed is 500-700 r / min; the stirring time is 60-80 min.

5. The method for preparing a nano Co / Mg(OH)2 catalyst for treating ammonia nitrogen wastewater according to claim 1, characterized in that: The hydrothermal reaction temperature is 120-200°C.

6. The method for preparing a nano Co / Mg(OH)2 catalyst for treating ammonia nitrogen wastewater according to claim 5, characterized in that: The hydrothermal reaction temperature is 160°C.

7. The method for preparing a nano Co / Mg(OH)2 catalyst for treating ammonia nitrogen wastewater according to claim 1, characterized in that: The hydrothermal reaction time is 2-8h.

8. A nano Co / Mg(OH)2 catalyst, characterized in that: Obtained according to any one of the preparation methods described in claims 1-7.

9. Use of the nano Co / Mg(OH)2 catalyst according to claim 8 in the treatment of ammonia nitrogen wastewater.

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