Coordinated Mn-NG catalyst for sewage treatment as well as preparation method and application thereof

Abstract

The invention discloses a coordination Mn-NG catalyst for sewage treatment as well as a preparation method and application of the coordination Mn-NG catalyst. The coordination Mn-NG catalyst comprises 0.05-5mM of MnCl2, 0.5-5g of melamine and 0.1-1mM of glucose. The preparation method comprises the following steps: firstly, mixing and dissolving a MnCl2 solution with melamine and glucose in proportion; then evaporating moisture to dryness by a water bath heating method, and freeze-drying the obtained solid material to obtain a precursor; and grinding the precursor, calcining at a high temperature, pickling, grinding, washing and drying to obtain the composite material. The coordination Mn-NG catalyst is used for removing p-HBA in water, and the method has the advantages that the method is easy to operate, the degradation efficiency is high, materials are convenient to recycle, and the influence of various inorganic anions, natural organic matter and other factors is small.

Description

Technical Field

[0001] The invention belongs to the technical field of heterogeneous catalysts, and specifically relates to a coordinated Mn-NG catalyst for sewage treatment, and a preparation method and application thereof. Background Art

[0002] p-HBA (para-hydroxybenzoic acid) is an important organic compound, and its sources mainly include chemical synthesis and natural existence. In industrial production, it is usually synthesized through the chemical reaction of phenol and propylene, and in nature, some plants also contain this compound. However, although p-HBA has a wide range of applications in food, medicine, and cosmetics, people who have long-term and large-scale contact or special physical conditions may have adverse reactions to it, such as skin irritation and allergies.

[0003] In the past decade, advanced oxidation technologies (AOPs) based on PMS (peroxymonosulfate) have received increasing attention in the degradation of refractory organic pollutants in water. The purpose of advanced oxidation technologies is to use different physical or chemical means and catalysts to activate or catalyze oxidants to produce highly oxidizing active species, thereby efficiently degrading or even completely mineralizing some refractory pollutants.

[0004] PMS has an asymmetric molecular structure containing peroxide bonds (OO), which can be activated by free radical and non-free radical pathways, accompanied by the generation of different active species, such as free radicals, namely sulfate radicals (SO4 - ·) and hydroxyl radicals (·OH), singlet oxygen ( 1 O2), high-valent metal species and metal-PMS complexes. Compared with other advanced oxidation technologies that produce hydroxyl radicals, advanced oxidation technologies based on PMS have been rapidly developed due to their stronger oxidation ability, wider pH application range and better selectivity. In addition, PMS has low storage requirements and low cost, and its operation process is simple and safe. It can exist for a long time and effectively oxidize organic pollutants, and has very good commercial value and application prospects.

[0005] Since PMS has limited ability to directly oxidize pollutants and cannot achieve rapid removal of many pollutants, a variety of methods for effectively activating PMS have been developed to improve its efficiency in oxidizing and degrading pollutants. These methods mainly include high-temperature thermal excitation, ultraviolet (UV) excitation, and transition metal activation. Transition metal ions (Mn +) has multiple valence states and can spontaneously activate PMS without the need for additional heat or light energy. This technology is similar to Fenton's reagent, with simple reaction equipment, mild reaction conditions, and low energy consumption, and has therefore attracted widespread attention from environmental workers. Although transition metal ions can effectively activate PMS, as a homogeneous ion activation method, this method still has the same disadvantages as the homogeneous Fenton system: (1) Metal ions are not easy to recover and are likely to cause secondary environmental pollution; (2) Fe 2+ Activated PMS has high requirements on system pH, which increases the operating cost in disguise; (3) Co 2+ , Cu 2+ 、Ag + There are problems such as high toxicity of metal ions or high prices. Therefore, researchers turned their research focus to the development of PMS heterogeneous activators. The characteristics of this type of catalyst are based on transition metal oxides (M x O y ) to develop and improve.

[0006] As a typical transition metal element, manganese has a special multiple valence state. Its oxidation state can be mutually converted during the catalytic process and is accompanied by the transfer of a single electron, which makes manganese oxides applicable to AOPs as active sites for activating PMS. In addition, compared with many metal oxides, manganese oxides have large reserves in nature and are less harmful to the environment, which has attracted more and more attention in the field of heterogeneous catalysis. In order to make manganese oxide catalysts more suitable for the reaction of activating PMS to degrade organic pollutants, researchers have developed supported manganese oxide catalysts, that is, manganese oxide is loaded onto a carrier material to ensure the dispersibility of the active component manganese oxide, while also forming coordination with non-metallic elements. The controllable carrier size can effectively improve the sedimentation of the catalyst. In addition, manganese oxide anchored on the surface of the carrier has higher stability than single manganese oxide particles, which can significantly reduce the dissolution of manganese ions.

[0007] Studies have found that in PMS activation technology, activation technology based on carbon materials has obvious advantages because it can effectively degrade organic pollutants, and is efficient, economical, environmentally friendly and easy to prepare. Therefore, in the study of PMS activation, the synthesis and modification of new carbon materials will become a new research hotspot. The excellent properties of graphene make it a base material for single-atom catalysts. Doping heteroatoms such as N, S, and P on graphene can increase defect sites, increase electron transfer, and form coordination to prepare for the next step of doping metal atoms. Traditional transition metal single atoms such as Co, Fe, and Ni can be anchored on nitrogen-doped carbon-based materials, greatly increasing the reaction activity, but different metals will cause different reaction mechanisms in the system of activating PMS, and the reaction activities of different metals are different. Therefore, it is urgent to develop a catalyst with high activity and high stability so that it can effectively activate PMS and efficiently remove organic pollutants in water. Summary of the invention

[0008] In view of the deficiencies in the prior art, the present invention provides a coordinated Mn-NG catalyst for sewage treatment and a preparation method and application thereof, which can effectively activate PMS and efficiently remove p-HBA in water.

[0009] The present invention is achieved through the following technical solutions:

[0010] A method for preparing a coordinated Mn-NG catalyst for sewage treatment comprises the following steps:

[0011] Step 1) dissolving 0.05-5 mM MnCl2, 0.5-5 g melamine and 0.1-1 mM glucose in ultrapure water, stirring continuously until they are completely dissolved; then heating in a water bath to evaporate the water, and then freeze-drying to obtain a precursor;

[0012] Step 2) Grind the precursor obtained in step 1), then place it in a tube furnace for calcination under a nitrogen atmosphere, and then acid-wash, water-wash and dry to obtain the product.

[0013] Preferably, the calcination parameters in step 2) are as follows: initial temperature is 25°C, heating rate is 5°C / min, heating to 400°C and maintaining for 1 hour, then continuing to heat to 800°C and maintaining for 2 hours, and then naturally cooling to room temperature.

[0014] Preferably, the specific steps of the acid washing, water washing and drying in step 2) are as follows: the sample obtained after calcination is soaked in 3M HCl solution at 80°C for 10 hours, then rinsed with deionized water until the filtrate is neutral, and dried in an oven at 60°C for 12 hours.

[0015] The coordinated Mn-NG catalyst prepared by the above preparation method.

[0016] The above-mentioned coordinated Mn-NG catalyst is used in sewage treatment, wherein the sewage treatment is to remove p-hydroxybenzoic acid in water.

[0017] Preferably, peroxymonosulfate is added to wastewater containing p-hydroxybenzoic acid, and then the coordinated Mn-NG catalyst is added to initiate the degradation reaction, and stirring is continued.

[0018] Preferably, the peroxymonosulfate is KHSO5, and the dosage is 0.2-2.0 mM; the dosage of the coordinated Mn-NG catalyst is 0.1-0.5 g / L.

[0019] Preferably, the concentration of p-hydroxybenzoic acid in the sewage is 50 μM.

[0020] Preferably, the concentration of inorganic anions in the sewage is 10 mM, and the concentration of natural organic matter is 1-10 mg / L.

[0021] Preferably, the pH value of the sewage is 3-11.

[0022] The beneficial effects of the present invention are as follows:

[0023] (1) The coordinated Mn-NG catalyst of the present invention can be used to remove p-HBA in water with high removal efficiency and short removal time.

[0024] (2) The coordinated Mn-NG catalyst of the present invention has a simple synthesis process, is safe to operate, and has low requirements on preparation conditions and equipment.

[0025] (3) The coordinated Mn-NG catalyst of the present invention is applied to the removal of p-HBA in water, and its removal effect is little affected by factors such as pH value, various inorganic anions and natural organic matter (NOM).

[0026] (4) The present invention selects a manganese oxide catalyst with excellent performance and adjusts the coordination configuration of the catalyst and the electronic structure in the metal by heteroatom doping, thereby obtaining a nitrogen-doped carbon-based manganese oxide catalyst with low coordination configuration and good electronic structure.

[0027] (5) In the coordinated Mn-NG catalyst of the present invention, the Mn-N site and the manganese oxide are the catalytic active centers. The low coordination configuration increases the electron density of the Mn atomic center, and N-doped C further optimizes the electronic structure of the active center. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a scanning electron microscope photograph of the coordinated Mn-NG catalyst synthesized in Example 1;

[0029] Figure 2is a transmission electron microscope photograph of the coordinated Mn-NG catalyst synthesized in Example 1;

[0030] Figure 3 is the removal rate of p-HBA in water in different systems in Example 2;

[0031] Figure 4 is the removal rate of p-HBA in water at different dosages of the coordinated Mn-NG catalyst in Example 3;

[0032] Figure 5 is the removal rate of p-HBA in water at different PMS dosages in Example 4;

[0033] Figure 6 is the removal rate of p-HBA in water in the presence of different anions in Example 5;

[0034] Figure 7 is the removal rate of p-HBA in water in the presence of different concentrations of NOM in Example 6;

[0035] Figure 8 is the removal rate of p-HBA in water under different pH conditions in Example 7. DETAILED DESCRIPTION

[0036] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0037] Unless otherwise specified, the technical means used in the following examples are all conventional means well known to those skilled in the art, and the experimental methods without specifying the specific conditions are all conventional methods in the art.

[0038] Example 1 Preparation and characterization of coordinated Mn-NG catalyst

[0039] 1. Preparation of coordinated Mn-NG catalyst

[0040] (1) Weigh 5 mmol of manganese chloride, 2 g of melamine, and 3 mmol of glucose into a 50 mL beaker, add 30 mL of ultrapure water, and dissolve them all at a stirring speed of 600 rpm. Then, evaporate all the water at 90° C. using a water bath heating method to obtain a solid product. The solid product is then freeze-dried for 12 hours to obtain a precursor.

[0041] (2) The precursor was then placed in a tubular furnace under a nitrogen atmosphere with an initial temperature of 25°C, and the temperature was raised to 400°C at a heating rate of 5°C / min, then heat treated for 1 hour, and then continued to be heated to 800°C and maintained for 2 hours. The sample was taken out after naturally cooling to room temperature.

[0042] (3) The calcined sample was soaked in a 3M HCl solution at 80° C. for 10 h, then rinsed with deionized water until the filtrate was neutral, and dried in an oven at 60° C. for 12 h to obtain the coordinated Mn-NG catalyst.

[0043] 2. Sample test characterization

[0044] Scanning electron microscopy images of the coordinated Mn-NG catalyst are shown in Figure 2. Figure 1 The transmission electron microscope photo is shown in Figure 2 As shown in the figure, it can be seen that the coordinated Mn-NG catalyst prepared in this embodiment has a rough surface and an amorphous carbon structure with a large number of Mn3O4 nanoparticles distributed on it.

[0045] Example 2 Comparison of p-HBA removal from water by different systems

[0046] 1. Experimental steps

[0047] Three different systems were set up to remove p-HBA from water, and the removal rate of p-HBA in water was tested within 20 minutes. The details are as follows:

[0048] (1) System 1: The coordinated Mn-NG catalyst prepared in Example 1 was added to a solution containing 50 μM p-HBA at a dosage of 0.5 g / L. The pH of the solution was then adjusted to 3 and the stirring speed was maintained at 600 rpm.

[0049] (2) System 2: PMS was added to a solution containing 50 μM p-HBA at a dosage of 1 mM, and the pH of the solution was adjusted to 3. The stirring speed was maintained at 600 rpm.

[0050] (3) System 3: PMS was first added to a solution containing 50 μM p-HBA as the treatment object, and then the pH of the solution was adjusted to 3. The coordinated Mn-NG catalyst prepared in Example 1 was then added at a dosage of 0.5 g / L, and the stirring speed was maintained at 600 rpm.

[0051] 2. Experimental results

[0052] The results are as follows Figure 3 As shown, within 20 minutes, the removal rate of p-HBA in water was only 3.03% when the coordinated Mn-NG was added alone, and the removal rate of p-HBA in water was only 0.14% when PMS was added alone. However, the removal rate of p-HBA in water could reach 98.21% when PMS and coordinated Mn-NG catalyst were added.

[0053] Example 3 Comparison of p-HBA removal from water under different dosage conditions of coordinated Mn-NG catalyst

[0054] 1. Experimental steps

[0055] First, PMS (1 mM) was added to the solution with 50 μM p-HBA as the treatment object, and then the pH of the solution was adjusted to 3. Then, different amounts (0.1 g / L, 0.2 g / L, 0 / 3 g / L, 0.4 g / L, 0.5 g / L) of the coordinated Mn-NG catalyst prepared in Example 1 were added to each reaction system, and the stirring speed was maintained at 600 rpm.

[0056] 2. Experimental results

[0057] The removal rate of p-HBA in water at different dosages of coordinated Mn-NG catalyst is as follows: Figure 4 As shown, it can be seen that when the dosage of the coordinated Mn-NG catalyst is 0.1g / L, the removal rate of p-HBA within 20min is only 62.93%; when the dosage of the coordinated Mn-NG catalyst is 0.2g / L, the removal rate of p-HBA within 20min is 83.51%; when the dosage of the coordinated Mn-NG catalyst is 0.3g / L, the removal rate of p-HBA within 20min can reach 97.61%; when the dosage of the coordinated Mn-NG catalyst is 0.4g / L, the removal rate of p-HBA within 20min can reach 98.21%; when the dosage of the coordinated Mn-NG catalyst is 0.5g / L, the removal rate of p-HBA within 20min tends to be stable, which is also 98.21%.

[0058] Example 4 Comparison of p-HBA removal from water using PMS in combination with coordinated Mn-NG catalyst under different dosage conditions

[0059] 1. Experimental steps

[0060] First, different amounts (0.2mM, 0.5mM, 1mM, 1.5mM, 2.0mM) of PMS were added to the solution with 50μM p-HBA as the treatment object, and then the pH of the solution was adjusted to 3, and then the coordinated Mn-NG catalyst (0.5g / L) prepared in Example 1 was added to each reaction system. The stirring speed was maintained at 600rpm.

[0061] 2. Experimental results

[0062] The removal rate of p-HBA in water at different PMS dosages is as follows Figure 5As shown, it can be seen that when the PMS dosage is 0.2mM, the removal rate of p-HBA within 20min is only 11.24%; when the PMS dosage is 0.5mM, the removal rate of p-HBA within 20min is only 28.29%; when the PMS dosage is 1.0mM, the removal rate of p-HBA within 20min rises to 98.08%; when the PMS dosage is 1.5mM, the removal rate of p-HBA within 20min can reach 99.73%; when the PMS dosage is 2.0mM, the removal rate of p-HBA within 20min tends to be stable at 99.75%.

[0063] Example 5 Effect of the Presence of Different Anions on the Removal of p-HBA from Water by Coordinated Mn-NG Catalyst

[0064] 1. Experimental steps

[0065] First, PMS (1 mM) was added to a solution containing 50 μM p-HBA as the treatment object, and different anions (Cl - 、NO3 - 、SO4 2- 、HPO4 2- ), and the anion concentration is 10mM (the corresponding cation is Na + ), then the solution pH was adjusted to 3, and then the coordinated Mn-NG catalyst (0.5 g / L) prepared in Example 1 was added to each reaction system. The stirring speed was maintained at 600 rpm.

[0066] 2. Experimental results

[0067] The removal rate of p-HBA in water in the presence of anions is as follows: Figure 6 As shown, it can be seen that Cl - When the concentration is 10mM, the removal rate of p-HBA can reach 96.67% within 20min; NO3 - When the concentration is 10mM, the removal rate of p-HBA can reach 97.36% within 20min; SO4 2- When the concentration is 10mM, the removal rate of p-HBA can reach 81.90% within 20min; HPO4 2- When the concentration was 10 mM, the removal rate of p-HBA could reach 78.54% within 20 min.

[0068] The experimental results of this example show that in the presence of high concentrations of different anions, although there are differences in the removal rates of p-HBA, the differences are not large, indicating that the system has a strong ability to resist interference from inorganic anions.

[0069] Example 7 Effect of different concentrations of natural organic matter (NOM) on the removal of p-HBA from water by coordinated Mn-NG catalyst

[0070] 1. Experimental steps

[0071] First, PMS (1 mM) was added to the solution with 50 μM p-HBA as the treatment object, and the NOM concentration was 1 mg / L, 2 mg / L, 5 mg / L, and 10 mg / L, and then the solution pH was adjusted to 3, and then the coordinated Mn-NG catalyst (0.5 g / L) prepared in Example 1 was added to each reaction system. The stirring speed was maintained at 600 rpm.

[0072] 2. Experimental results

[0073] The removal rate of p-HBA in water in the presence of NOM is as follows Figure 7 As shown, it can be seen that when the NOM concentration is 1 mg / L, the removal rate of p-HBA within 20 minutes can reach 96.01%; when the NOM concentration is 2 mg / L, the removal rate of p-HBA within 20 minutes can reach 93.06%; when the NOM concentration is 5 mg / L, the removal rate of p-HBA within 20 minutes is 73.15%; when the NOM concentration is 10 mg / L, the removal rate of p-HBA within 20 minutes is only 51.69%.

[0074] The experimental results of this example show that NOM is an active species in the competition reaction system between organic matter and p-HBA. However, even so, the removal rate of p-HBA is still above 50%, indicating that the system has strong oxidation selectivity.

[0075] Example 7 Effect of different pH conditions on the removal of p-HBA from water by coordinated Mn-NG catalyst

[0076] 1. Experimental steps

[0077] First, PMS (1 mM) was added to the solution containing 50 μM p-HBA, and then the pH of the solution was adjusted to 3, 5, 7, 9, and 11. Then, the coordinated Mn-NG catalyst (0.5 g / L) prepared in Example 1 was added to each reaction system. The stirring speed was maintained at 600 rpm.

[0078] 2. Experimental results

[0079] The removal rate of p-HBA in water under different pH conditions is as follows Figure 8As shown, it can be seen that when the pH is 3, the removal rate of p-HBA within 20 minutes can reach 98.25%; when the pH is 5, the removal rate of p-HBA within 20 minutes is 52.24%; when the pH is 7, the removal rate of p-HBA within 20 minutes is 42.37%; when the pH is 9, the removal rate of p-HBA within 20 minutes is only 33.78%; when the pH is 11, the removal rate of p-HBA within 20 minutes is only 16.18%.

[0080] The experimental results of this example show that the coordinated Mn-NG catalyst is more likely to activate PMS to degrade p-HBA under acidic conditions.

[0081] The embodiments described above are only some embodiments of the present invention, rather than all 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. The scope of protection of the present invention shall be subject to the scope required by the claims. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work shall fall within the scope of protection of the present invention.

Claims

1. A method for preparing a coordinated Mn-NG catalyst for sewage treatment, characterized in that: The following steps are involved: Step 1) dissolving 0.05-5 mM MnCl2, 0.5-5 g melamine and 0.1-1 mM glucose in ultrapure water, stirring continuously until they are completely dissolved; then heating in a water bath to evaporate the water, and then freeze-drying to obtain a precursor; Step 2) Grind the precursor obtained in step 1), then place it in a tube furnace for calcination under a nitrogen atmosphere, and then acid-wash, water-wash and dry to obtain the product.

2. The method for preparing a coordinated Mn-NG catalyst for sewage treatment according to claim 1, characterized in that: Step 2) The calcination parameters are as follows: initial temperature is 25°C, heating rate is 5°C / min, heating to 400°C and maintaining for 1 hour, then continuing to heat to 800°C and maintaining for 2 hours, and then naturally cooling to room temperature.

3. The method for preparing a coordinated Mn-NG catalyst for sewage treatment according to claim 1, characterized in that: Step 2) The specific steps of acid washing, water washing and drying are as follows: the sample obtained after calcination is soaked in 3M HCl solution at 80°C for 10 hours, then rinsed with deionized water until the filtrate is neutral, and dried in an oven at 60°C for 12 hours.

4. The coordinated Mn-NG catalyst prepared by the preparation method according to any one of claims 1 to 3.

5. The use of the coordinated Mn-NG catalyst in sewage treatment as claimed in claim 4, characterized in that: The sewage treatment is to remove p-hydroxybenzoic acid in water.

6. The use according to claim 5, characterized in that: The peroxymonosulfate is added to the wastewater containing p-hydroxybenzoic acid, and then the coordinated Mn-NG catalyst is added to initiate the degradation reaction, and the mixture is continuously stirred.

7. The use according to claim 6, characterized in that: The peroxymonosulfate is KHSO5, and the dosage is 0.2-2.0 mM; the dosage of the coordinated Mn-NG catalyst is 0.1-0.5 g / L.

8. The use according to claim 6, characterized in that: The concentration of p-hydroxybenzoic acid in the sewage is 50 μM.

9. The use according to claim 6, characterized in that: The concentration of inorganic anions in the sewage is 10 mM, and the concentration of natural organic matter is 1-10 mg / L.

10. The use according to claim 6, characterized in that: The pH value of the sewage is 3-11.

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