Metal composite fenton-like solid catalyst, preparation thereof and application thereof to removal of malachite green and cr(vi) in wastewater

Abstract

The application discloses a metal composite Fenton-like solid catalyst and preparation and application of the metal composite Fenton-like solid catalyst in removal of malachite green and Cr(VI) in wastewater, and belongs to the technical field of degradation and removal of cationic dyes and chromium by adsorption. 2+ -Silica. Compared with liquid chelating agents involved in the existing research, EDDS in the catalyst structure can provide six coordination atoms due to the structure of four carboxyl and diimino groups, and can form a stable metal complex with Co 2+ by virtue of the superior metal chelating characteristics of the hexadentate ligand EDDS. The metal composite solid catalyst prepared by grafting the spacer arm on the silica gel matrix can be separated by filtration and the like, and the subsequent regeneration operation can be performed by selecting a suitable eluent, so that the metal composite solid catalyst has the characteristics of easy separation, regeneration and reusability.

Description

Technical Field

[0001] The invention belongs to the technical field of degrading and removing cationic dyes and chromium by an adsorption method, and particularly relates to a metal composite Fenton-like solid catalyst and its preparation and application in removing malachite green and Cr(VI) from wastewater. Background Art

[0002] Malachite green (MG) is a cationic triphenylmethane basic dye widely used in the textile, acrylic, aquaculture, and medical disinfection industries. However, MG is considered a potential teratogen and carcinogen, inhibiting growth, fertility, and food intake; it can also damage the skin, kidneys, heart, and bones. Furthermore, various chemical products are currently being introduced into the manufacturing processes of metallurgy, leather manufacturing, electroplating, and dyeing. Hexavalent chromium (Cr(VI)) compounds, in particular, are commonly used in the textile and leather industries as mordants to enhance dye fixation. This results in the coexistence of heavy metal ions (Cr(VI)) in MG wastewater. Cr(VI) is not only a highly toxic carcinogen but also a major cause of nephritis and gastrointestinal ulcers. Furthermore, even after separation from wastewater, Cr(VI) can migrate within the food chain, leading to secondary environmental pollution. Previous research has explored various methods for removing MG and Cr(VI) from wastewater, including adsorption, microbial, photocatalytic, and electrocatalytic methods. Among them, advanced oxidation processes (AOPs) based on the generation of free radical species with high oxidative capacity are a promising solution for the tertiary treatment of urban water and wastewater. Fenton reaction is the most widely used method in AOPs. Its reaction principle is to generate free radical species with high oxidative capacity in the presence of Fe 2+ In the presence of ions, H2O2 is decomposed into hydroxyl radicals and hydrogen peroxide free radicals. However, the successful implementation of traditional FENTON is limited to acidic wastewater, which greatly limits the promotion and application of this method. At the same time, a large amount of iron sludge is produced after the reaction, causing secondary pollution to the environment.

[0003] Aminopolycarboxylic acid (APCA) ligands can form stable complexes with metal ions, thus overcoming the defects and shortcomings of traditional FENTON. In recent years, the application of such ligands in homogeneous Fenton and Fenton-like processes has increased. Hu Y et al. added the chelating agent ethylenediaminetetraacetic acid (EDTA) to the classic FENTON reaction system. Because the EDTA used is liquid and the ligand has low biodegradability, it persists in the homogeneous FENTON reaction system, causing secondary pollution problems. As a green chelating ligand that is biodegradable and non-toxic, ethylenediamine disuccinic acid (EDDS) is considered to be a suitable alternative to EDTA.

[0004] Currently, researchers are adding other transition metal elements to the traditional FENTON to improve the efficiency of FENTON, and cobalt is one of the efficient catalysts. 2+ It is the active center for catalytic activation of H2O2, and Co 3+ / Co 2+ The redox couple can transfer electrons and thus improve the catalytic activity of the entire system. Although cobalt is an excellent peroxide catalyst, it is highly toxic. 2+ It will cause great harm to the environment, which greatly affects the application of cobalt-based materials as Fenton-like catalysts. EDDS can provide 6 coordination atoms due to its tetracarboxyl & diimino structure. The superior metal chelating properties of the hexadentate ligand EDDS can be used with Co 2+ Forming a stable metal complex, and then participating in the Fenton-like reaction in the form of a Fenton-like catalyst. However, the application of the above homogeneous Fenton still has the problem of liquid catalyst EDDS-Co 2+ Difficulties in recovery, as well as subsequent separation, regeneration and recycling of catalysts. Summary of the Invention

[0005] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a metal composite Fenton-like solid catalyst and its preparation and application in removing malachite green and Cr(VI) from wastewater, so as to solve the technical problems of environmental pollution, difficult recovery and difficult separation and regeneration existing in the existing liquid Fenton-like catalyst.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] The present invention discloses a metal composite Fenton-like solid catalyst, the structural formula of the metal composite Fenton-like solid catalyst is as follows:

[0008]

[0009] The present invention also discloses a method for preparing the metal composite Fenton-like solid catalyst, comprising the following steps: taking EDDS-Silica adsorbent, adsorbing CoCl2·6H2O solution for 2 hours, and preparing the metal composite Fenton-like solid catalyst EDDS-Co 2+ -Silica.

[0010] Preferably, the adsorption of the CoCl2·6H2O solution is carried out at 30°C and 200 r / min.

[0011] Preferably, the concentration of the CoCl2·6H2O solution is 1 mmol / L and the pH value is 4.64.

[0012] Preferably, the ratio of CoCl2·6H2O solution to EDDS-Silica adsorbent is 20 mL:1 g.

[0013] Further preferably, the preparation method of the EDDS-Silica adsorbent comprises:

[0014] 1) Synthesis of γ-GLDP-EDDS

[0015] Take EDDS and add it to water, adjust the pH value of the system to 10.0-11.0, add γ-GLDP dropwise under stirring, let it stand for 1 hour, and then stir and react at 65℃ for 12 hours;

[0016] 2) Preparation of EDDS-Silica Adsorbent

[0017] The upper layer solution after the γ-GLDP-EDDS reaction was taken and allowed to stand, the pH value was adjusted to 4.0, silica gel was added, ultrasonicated for 3-5 minutes, reacted at 90-95° C. for 2 hours, washed and dried to obtain EDDS-Silica adsorbent.

[0018] More preferably, in step 1), the ratio of EDDS to water is (3-6) g: (40-80) mL, and the ratio of added γ-GLDP to EDDS is (2-4) mL: (3-6) g.

[0019] More preferably, in step 2), the average particle size of the silica gel used is 7-15 μm.

[0020] More preferably, in step 2), the cleaning and drying are performed by rinsing with 10% HAc three times, then washing with water until neutral, and drying at 60° C. for 24 h.

[0021] The invention also discloses the application of the metal composite Fenton-like solid catalyst in removing malachite green and Cr(VI) from wastewater.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The metal composite Fenton-like solid catalyst EDDS-Co disclosed in the present invention 2+ -Silica, compared with the liquid chelating agents involved in existing research, the EDDS in the catalyst structure can provide 6 coordination atoms due to the structure of tetracarboxyl & diimino groups. The superior metal chelating properties of the hexadentate ligand EDDS can be used with Co 2+The metal complex is grafted onto a silica gel matrix using a spacer arm to form a stable metal complex. The resulting metal composite solid catalyst can be separated from the solid by simple methods such as filtration, and then regenerated by selecting a suitable eluent. This makes it easy to separate, regenerate, and reuse.

[0024] The metal composite Fenton-like catalyst EDDS-Co prepared by the present invention 2+ -Silica can expand the acidity range of Fenton degradation by chelating the iron ions in the Fenton reagent and can be used as a heterogeneous Fenton solid catalyst to improve the degradation efficiency of MG. Experimental verification shows that under the positive synergistic effect of MG and Cr(VI), EDDS-Co 2+ The Silica metal composite Fenton-like catalyst is suitable for the synergistic degradation and removal of Cr(VI) and MG in binary wastewater, effectively reducing the total chromium content in the wastewater, avoiding the shortcomings of previous studies that only degraded Cr(VI) without removing it. It also removes total iron to meet emission standards. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 For Silica, EDDS-Silica, EDDS-Co 2+ -Silica infrared spectrum; where a is Silica, EDDS-Silica, EDDS-Co 2+ -Infrared spectrum scanning results of Silica adsorbent; b is the wavelength range of Figure a is screened to 500-900 cm -1 The results between

[0026] Figure 2 EDDS-Silica adsorption material, EDDS-Co 2+ -Silica metal chelate adsorption material is used for the degradation and removal of MG-Cr(VI) binary simulated wastewater. (a) and (b) are the degradation and removal rates of MG and Cr(VI); (c) shows the effect of contact time on the removal rate of MG by the two materials; (d) shows the degradation and removal of residual total chromium and total iron in the solution by EDDS-Silica.

[0027] Figure 3 This is the mechanism of synergistic degradation and removal of MG-Cr(VI) by adsorption materials. DETAILED DESCRIPTION

[0028] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0029] It should be noted that the terms "first", "second", etc. in the description and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that the numbers used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0030] The present invention is described in further detail below with reference to the accompanying drawings:

[0031] The main raw materials used in the present invention are EDDS-Silica and EDDS-Co 2+ -Silica adsorption materials were all homemade in the laboratory; the MG-Cr(VI) binary wastewater simulation solution was prepared in the laboratory; and all chemical reagents used were commercially available analytical grade products.

[0032] Example 1: EDDS-Co 2+ Degradation and removal of MG and chromium (VI) in binary simulated wastewater using a Fenton-like Silica composite catalyst

[0033] (1) Preparation of MG-Cr(VI)-containing binary wastewater simulation solution

[0034] (i) Preparation of binary simulated wastewater stock solution

[0035] Accurately weigh 0.2829 g K2Cr2O7 and 0.1 g MG, dissolve them separately and dilute to 100 mL to obtain a 1 g / L Cr(VI) stock solution and a 1 g / L MG stock solution.

[0036] (ii) Preparation of binary simulated wastewater

[0037] Take 10 mL of each MG and Cr(VI) stock solution, mix and dilute to 1000.0 mL to obtain a binary simulated wastewater solution containing 10 mg / L Cr(VI) and 10 mg / L MG. Adjust the pH with hydrochloric acid or sodium hydroxide solution.

[0038] (2) EDDS-Silica was prepared by referring to the existing synthesis method. 1.0000 g of EDDS-Silica was weighed and adsorbed with 20.00 mL of 1 mmol / L CoCl2·6H2O solution (pH 4.64) at 30°C and 200 r / min for 2 h to obtain EDDS-Co 2+ -Silica.

[0039] The preparation method of the EDDS-Silica adsorbent comprises:

[0040] 1) Synthesis of γ-GLDP-EDDS

[0041] Take EDDS and add it to water, adjust the pH value of the system to 10.0-11.0, add γ-GLDP dropwise under stirring, let it stand for 1 hour, and then stir and react at 65℃ for 12 hours;

[0042] The ratio of EDDS to water was 6 g:80 mL, and the ratio of γ-GLDP to EDDS was 4 mL:6 g.

[0043] 2) Preparation of EDDS-Silica Adsorbent

[0044] Take the upper layer solution after the γ-GLDP-EDDS reaction, adjust the pH value to 4.0, add silica gel (average particle size of 8 μm), ultrasonicate for 3-5 minutes, react at 90-95°C for 2 hours, rinse three times with 10% HAc, then wash with water until neutral, and dry at 60°C for 24 hours to obtain EDDS-Silica adsorbent.

[0045] The prepared materials were characterized by infrared spectroscopy. Figure 1 a is Silica, EDDS-Silica, EDDS-Co 2+ -Silica adsorbent infrared spectrum scanning results, compared with silica gel, EDDS-Silica and EDDS-Co 2+ -Infrared spectrum of Silica adsorbent shows:

[0046] 2885 and 2823cm -1 The small peaks at and near the center are caused by the stretching vibrations of CH3 and CH2 introduced by the spacer arm γ-GLDP and EDDS in the compound; the stretching vibrations of the carbonyl (C=O) in the carboxyl group on EDDS produce peaks at 1733 and 1649 cm-1 Corresponding peaks: 1400 and 1218 cm -1 The peaks at 1095 cm are caused by the bending vibration of CH and the stretching vibration of CN introduced by γ-GLDP and EDDS, respectively; -1 The peak at 808 cm corresponds to the stretching vibration of Si-O-Si at the junction of silica gel matrix and γ-GLDP; -1 The peak at is attributed to the stretching vibration of Si-C introduced by γ-GLDP; Figure 1 In a, it can be clearly observed that at wavelengths of 2823, 1095 and 808 cm -1 The absorption peaks near the EDDS-Silica structure belong to the structure of EDDS-Silica itself, which also shows that EDDS-Silica has 2+ After modification, its structural characteristics remain stable; Figure 1 The wavelength range in a is screened to 500-900cm -1 (like Figure 1 As shown in b), it is not difficult to see that the metal Co 2+ After modification, at a wavelength of 650cm -1 A new absorption peak appears near the surface, which is caused by the stretching vibration of Co-O bond, indicating that the metal Co 2+ The above analysis shows that EDD-Silica, EDDS-Co 2+ -Silica adsorbent has been successfully synthesized.

[0047] Subsequently, inductively coupled plasma atomic emission spectrometry (ICP-AES) was used to determine the metal Co in the solution before and after adsorption using deionized water as the blank solution. 2+ The concentration of metal Co on EDDS-Silica was calculated according to the following formula. 2+ The bonding amount q e .

[0048]

[0049] Where: C0—initial concentration, mg / L; C e —Concentration at equilibrium, mg / L; m—grams of EDDS-Silia, mg / g.

[0050] Table 1 EDDS-Co 2+ -Silica Co 2+ The bonding amount

[0051]

[0052] The test results were tested three times and the average value was obtained to obtain EDDS-Co 2+-Silica material Co 2+ The bonding amount is 1.063 mg / g.

[0053] From the above, it can be seen that the Fenton-like catalyst EDDS-Co 2+ -Silica has been successfully prepared.

[0054] Accurately weigh two 3.0 mg portions of EDDS-Silica and EDDS-Co 2+ Silica adsorption material was used. 50.00 mL of binary wastewater simulants at pH 3.0 and 7.0 were pipetted, and FENTON reagent containing 100 μmmol / L FeSO4·7H2O and 20 mmol / L H2O2 was added. The tubes were sealed and placed in a constant temperature shaker at 200 rpm and 25°C for 1 hour. Afterwards, the supernatant was filtered and assayed.

[0055] (3) Using visible spectrophotometry with deionized water as the blank solution, linear standard curves were obtained between the absorbance and concentration of MG and between the absorbance and concentration of Cr(VI). Based on the standard curves, the initial and equilibrium concentrations of MG and Cr(VI) in the wastewater were measured, and the removal rates of MG and Cr(VI) were calculated according to the following formulas.

[0056]

[0057] Where: C0—initial concentration, mg / L; C e —Concentration at equilibrium, mg / L.

[0058] Figure 2 EDDS-Silica, EDDS-Co 2+ -Silica adsorption material is used for the removal of MG-Cr(VI) binary simulated wastewater. Figures (a) and (b) show the removal rates of MG and Cr(VI) by the adsorption material, respectively. Figure 2 The EDDS-Silica adsorbent achieved a removal rate of over 85% for MG and Cr(VI), demonstrating excellent removal efficiency. This is attributed to the superior metal chelation properties of the hexadentate EDDS ligand. Furthermore, pH had little effect on the removal rates of MG and Cr(VI), indicating that the use of this type of adsorbent can effectively expand the pH range of wastewater research.

[0059] Depend on Figure 2 From (a) and (c), we can see that EDDS-Co 2+-Silica composite Fenton-like catalyst can achieve a degradation removal rate of MG and Cr(VI) of more than 93%, and also shows a positive effect in treating simulated wastewater containing MG-Cr(VI). It has a better removal effect than EDDS-Silica material and a significantly improved degradation rate. The time to achieve the same removal effect can be shortened from 1 hour to 30 minutes. This is attributed to the Co 3+ / Co 2+ The redox couple improves the catalytic activity of the entire system through electron transfer, and the synergistic effect of Co-Fe can promote the rapid progress of the entire FENTON reaction.

[0060] Studies have shown that: although EDDS-Silica, EDDS-Co 2+ -Silica adsorption materials can be used to treat MG-Cr(VI) binary wastewater. 2+ -Silica has better degradation and removal effect than EDDS-Silica material and its degradation rate is also significantly improved.

[0061] Example 3: Removal of total iron and total chromium from binary simulated wastewater using EDDS-Silica adsorption material

[0062] The reaction solution in Example 1 was filtered and 0.3 g of EDDS-Silica material was added. The mixture was sealed and placed in a constant temperature water bath shaker. After reaction at 200 r / min and 25° C., the mixture was filtered and the supernatant was taken for determination.

[0063] Inductively coupled plasma atomic emission spectrometry (ICP-AES) was used to determine the total chromium concentration in the solution before and after adsorption, as well as the total iron concentration after adsorption, using deionized water as a blank solution. The total chromium removal rate was calculated according to the following formula.

[0064]

[0065] Where: C0—initial concentration, mg / L; C e —Concentration at equilibrium, mg / L.

[0066] Figure 2 (d) is the total chromium and residual total iron content in the solution after treatment. The removal rate of total chromium can reach more than 85%, showing a good removal effect, which is attributed to the excellent metal chelating properties of the hexadentate ligand EDDS. Figure 2In (d), it can be seen that the residual total iron content in the treated wastewater is 1.76 mg / L and 1.4 mg / L respectively, both of which meet the national emission standards (the "Iron and Steel Industry Water Pollution Emission Standard" stipulates 10 mg / L, the "Coal Industry Pollutant Emission Standard" stipulates 7 mg / L, the "Electroplating Pollutant Emission Standard" stipulates 5 mg / L (existing enterprises) and the "Water Quality Standard for Wastewater Discharge into Urban Sewers" stipulates 5 mg / L).

[0067] EDDS-Co 2+ The mechanism of degradation and removal of MG-Cr(VI) in binary wastewater system by -Silica adsorption material is as follows Figure 3 As shown, EDDS-Co 2+ -Silica treatment of simulated wastewater, EDDS-Co 2+- Silica can chelate Fe in FENTON reagent 2+ ( Figure 3 ①) in the paper, expanding the pH application range of FENTON-like degradation while avoiding the formation of iron sludge. 2+ with Fe 2+ The catalytic synergy is more conducive to the realization of FENTON-like, thereby increasing the degradation rate. The characteristics of this material in the degradation and adsorption of MG and Cr (VI) in the binary system are: (1) EDDS-Co 2+ -Silica as a Fenton-like catalyst effectively promotes H2O2 to produce HO·( Figure 3 ②) in the above, ensuring that Fe 2+ and Fe 3+ 、Co 2+ and Co 3+ The efficient cycle of redox reactions between the two groups, the synergistic catalysis of Co-Fe more efficiently promotes the degradation of MG to achieve the purpose of removal ( Figure 3 (2) Cr(VI), which has strong oxidizing properties, can also participate in the FENTON reaction system ( Figure 3 ④) in the above will further promote the degradation of MG, thus improving the degradation rate of MG. It can be seen that there is a positive synergistic effect between MG and Cr(VI). (3) By utilizing the metal chelating properties of EDDS, on the one hand, the hydrolysis of trivalent iron ions can be avoided, thereby expanding the pH application range of this method; on the other hand, the residual iron ions in the Fenton reagent and various forms of chromium in the solution can be effectively removed. Figure 3 ⑤) in the figure to ensure that the contents of the two meet the environmental emission requirements.

[0068] In summary, the method proposed in the present invention is to convert EDDS-Co 2+-Silica metal composite Fenton-like solid catalyst is used for efficient degradation and synergistic removal of MG and Cr(VI) in wastewater. The results show that in a binary simulated wastewater system, the EDDS-Co 2+ The proposed method combines the FENTON reaction catalytic properties of EDDS with the metal chelation properties of MG and Cr(VI), while utilizing the positive synergistic effect of MG and Cr(VI). This method demonstrates excellent degradation and removal efficiency in the treatment of simulated MG-Cr(VI) wastewater. Furthermore, the solid composite material is easily recyclable and eliminates secondary pollution. In practical applications, the materials used can be flexibly selected based on the specific conditions and emission standards of the industrial wastewater. The proposed method has broad application prospects in the treatment of industrial wastewater from the leather and textile industries, among others.

[0069] The above content is only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. Application of a metal composite Fenton-like solid catalyst in the synergistic degradation and removal of malachite green and Cr(VI) in wastewater, characterized in that: The structural formula of the catalyst is as follows: The catalyst was prepared by adsorbing CoCl2·6H2O solution on EDDS-Silica adsorbent for 2 h. The catalyst utilizes the metal chelating properties of the hexadentate ligand EDDS and Co 2+ A stable metal complex is formed and grafted onto a silica gel matrix using a spacer arm to prepare a metal composite Fenton-like solid catalyst.

2. The use according to claim 1, characterized in that The preparation of the metal composite Fenton-like solid catalyst comprises the following steps: Take EDDS-Silica adsorbent and adsorb CoCl2·6H2O solution for 2 h to obtain the metal composite Fenton-like solid catalyst EDDS-Co 2+ -Silica; The adsorption of CoCl2·6H2O solution was carried out at 30°C and 200 r / min; the concentration of CoCl2·6H2O solution was 1 mmol / L and the pH value was 4.64; the ratio of CoCl2·6H2O solution to EDDS-Silica adsorbent was 20 mL:1 g.

3. The use according to claim 2, characterized in that The preparation method of the EDDS-Silica adsorbent comprises: 1) Synthesis of γ-GLDP-EDDS Add EDDS to water, adjust the pH value of the system to 10.0-11.0, add γ-GLDP dropwise under stirring, let it stand for 1 hour, and then stir at 65°C for 12 hours; 2) Preparation of EDDS-Silica Adsorbent The upper layer solution after the γ-GLDP-EDDS reaction was taken and allowed to stand, the pH value was adjusted to 4.0, silica gel was added, ultrasonicated for 3-5 minutes, reacted at 90-95°C for 2 hours, washed and dried to obtain EDDS-Silica adsorbent.

4. The use according to claim 3, characterized in that In step 1), the ratio of EDDS to water is (3-6) g: (40-80) mL, and the ratio of added γ-GLDP to EDDS is (2-4) mL: (3-6) g.

5. The use according to claim 3, characterized in that In step 2), the average particle size of the silica gel used is 7-15 μm.

6. The use according to claim 3, characterized in that In step 2), cleaning and drying are performed by rinsing with 10% HAc three times, then washing with water until neutral, and drying at 60°C for 24 h.

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