CN114100634B - Preparation method, product and application of magnetic multi-component iron-carbon composite Fenton-like catalyst - Google Patents

Preparation method, product and application of magnetic multi-component iron-carbon composite Fenton-like catalyst Download PDF

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CN114100634B
CN114100634B CN202111528238.8A CN202111528238A CN114100634B CN 114100634 B CN114100634 B CN 114100634B CN 202111528238 A CN202111528238 A CN 202111528238A CN 114100634 B CN114100634 B CN 114100634B
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CN114100634A (en
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马建青
朱佳皓
刘亮
赵燎原
许宁宁
应旭波
孙继传
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Ningbo Bicheng Ecological Technology Co ltd
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    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J27/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
    • B01J27/02—Sulfur, selenium or tellurium; Compounds thereof
    • B01J27/04—Sulfides
    • B01J27/043—Sulfides with iron group metals or platinum group metals
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/20—Catalysts, in general, characterised by their form or physical properties characterised by their non-solid state
    • B01J35/23—Catalysts, in general, characterised by their form or physical properties characterised by their non-solid state in a colloidal state
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/30—Catalysts, in general, characterised by their form or physical properties characterised by their physical properties
    • B01J35/33—Electric or magnetic properties
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/60—Catalysts, in general, characterised by their form or physical properties characterised by their surface properties or porosity
    • B01J35/61—Surface area
    • B01J35/613—10-100 m2/g
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    • B01J35/60—Catalysts, in general, characterised by their form or physical properties characterised by their surface properties or porosity
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    • B01J35/633—Pore volume less than 0.5 ml/g
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/72—Treatment of water, waste water, or sewage by oxidation
    • C02F1/722—Oxidation by peroxides
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/72—Treatment of water, waste water, or sewage by oxidation
    • C02F1/725—Treatment of water, waste water, or sewage by oxidation by catalytic oxidation
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
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    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
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    • C02F2101/30—Organic compounds
    • C02F2101/36—Organic compounds containing halogen
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2305/00—Use of specific compounds during water treatment
    • C02F2305/02—Specific form of oxidant
    • C02F2305/026—Fenton's reagent

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Abstract

The invention provides a preparation method, a product and application of a magnetic multi-component iron-carbon composite Fenton-like catalyst. The preparation method comprises the following steps: (1) Adding a carbon source into a ferrous sulfate aqueous solution, stirring and drying to obtain a precursor; (2) Calcining the precursor under the protection of nitrogen to obtain intermediate powder; (3) And (3) acid washing and activating the intermediate powder to obtain the magnetic multi-component iron-carbon composite catalyst. The preparation method of the magnetic multi-component iron-carbon composite Fenton-like catalyst is simple to operate and easy to realize industrialization. The magnetic multi-component iron-carbon composite Fenton-like catalyst prepared by the preparation method has high catalytic activity, can effectively improve the degradation rate of pollutants and has stable performance when being applied to the process of catalyzing, oxidizing and degrading organic pollutants, can be rapidly separated by an externally applied magnetic field, and has the advantages of simple operation, low cost, wide pH application range and higher practical value.

Description

Preparation method, product and application of magnetic multi-component iron-carbon composite Fenton-like catalyst
Technical Field
The invention belongs to the technical field of catalyst preparation, and particularly relates to a preparation method, a product and application of a magnetic multi-component iron-carbon composite Fenton-like catalyst.
Background
The rapid development of modern industry simultaneously discharges a large amount of wastewater into the environment, and particularly some refractory organic pollutants in the wastewater can bring great challenges to the traditional sewage treatment system. Fenton oxidation technology can degrade various organic matters by generating hydroxyl radicals with strong oxidability, and is considered as one of the most powerful technologies for treating refractory organic wastewater. The Fenton technology has the characteristics of wide application range and mild reaction conditions, and provides a low-cost and high-efficiency source for hydroxyl radicals; on the other hand, fenton oxidation systems utilize the environment-friendly oxidizing agent hydrogen peroxide, the final reaction product of which is water and carbon dioxide, also conforming to the concept of "green chemistry". However, the reaction needs to be carried out under strict acidic conditions, and a large amount of iron-containing sludge is generated in the process, so that secondary pollution problems can be caused.
The development of solid Fenton-like catalysts with high catalytic activity under neutral conditions is a major approach to solve the deficiencies of the traditional Fenton technology. The graphene material has rich specific surface area, and can improve Fenton reaction rate by dispersing active components, improving mass transfer rate and strengthening electron transfer. Meanwhile, pi-pi interaction can be generated with the aromatic ring, so that enrichment of pollutants on the solid phase surface can be realized, and degradation of the pollutants is accelerated. However, the current graphene has higher price, and the direct use of the material for treating wastewater has no practical significance. Some natural polysaccharide materials such as chitosan and the like have been reported to produce similar graphene structures at high temperatures. Wherein, the chitosan has wide sources and low price, and the molecular structure contains a large amount of-NH 2 and-OH groups, which can effectively bind metal ions by complexation. Therefore, the graphitized carbon supported Fenton-like catalyst prepared by using the material as a precursor is expected to reduce the preparation cost.
On the other hand, the separation and reuse performance is also an important factor limiting the use of the powder catalyst. The material can keep smaller size by constructing magnetic response characteristics, ensures mass transfer rate and catalytic activity, and is beneficial to rapid separation and recovery of the material, thereby effectively reducing use cost. In the prior report, magnetic particles and functional materials are compounded together by a dipping and calcining method, a coating method, an in-situ precipitation method and the like. By constructing the magnetic Fenton-like catalyst through a proper method, the treatment flow can be further simplified, and the application of the technology in treating the refractory organic wastewater is promoted.
Disclosure of Invention
In order to solve the problems in the prior art, based on the analysis, the invention provides a preparation method of a magnetic multi-component iron-carbon composite Fenton-like catalyst, which is simple to operate and easy to realize industrialization.
The invention also provides the magnetic multi-component iron-carbon composite Fenton-like catalyst prepared by the preparation method, which has higher Fenton-like catalytic activity under neutral conditions and can realize rapid separation by a magnetic field.
The invention also provides application of the magnetic multi-component iron-carbon composite Fenton-like catalyst in catalytic oxidative degradation of organic pollutants.
A preparation method of a magnetic multi-component iron-carbon composite Fenton-like catalyst comprises the following steps:
(1) Adding a carbon source into a ferrous sulfate aqueous solution, stirring and drying to obtain a precursor;
(2) And calcining the precursor, and then performing acid washing and activation to obtain the magnetic multi-component iron-carbon composite catalyst.
In the preparation method, long-chain polysaccharide with rich amino and hydroxyl groups can be selected as a carbon source, after ferrous complexation and sulfate radical crosslinking, a three-dimensional network structure is formed, and the carbon source is calcined under the condition of isolating oxygen and gradually converted into components such as merle, pyrrhotite and the like loaded by graphite carbon, and after surface inert components are removed, the Fenton-like catalyst with high reactivity and magnetism is formed. Complexing of carbon sources in the precursor can form a limiting effect on Fe atoms, and by reducing contact among Fe atoms during calcination, more nano particles are promoted to be formed, so that the dispersibility and catalytic activity of iron are improved, the redox atmosphere around the Fe atoms during calcination is influenced, and finally the chemical state of Fe is changed; the graphene-like structure formed after carbonization of the carbon source can accelerate electron transfer, and can realize degradation of pollutants on the surface of the catalyst through enhanced adsorption, so that the reaction can resist interference of other components in the system.
In the preparation method, in the step (1):
preferably, the ferrous sulfate aqueous solution is prepared by dissolving ferrous sulfate in water.
In order to prevent ferrous iron oxidation in the preparation process, nitrogen is preferably introduced into water to remove oxygen in the water before the preparation, the preparation process is kept sealed, and vacuum drying is adopted after the preparation is finished.
The time of introducing nitrogen is preferably 1 to 60 minutes before the preparation. More preferably 20 to 40 minutes.
Preferably, the carbon source is one or more of chitosan and cellulose.
Chitosan, also known as deacetylated chitin, is prepared from chitin widely existing in nature through deacetylation, and the different deacetylation degrees determine the amino groups in the molecule. Cellulose has the same carbon skeleton structure, but has no amino group in the molecule compared with chitosan.
Further preferably, the carbon source is chitosan (degree of deacetylation 91.2% or 69.3%).
As a further preferable embodiment, the carbon source is chitosan having a degree of deacetylation of rich amino groups of 91.2%.
Preferably, the ratio of the amount of the substance of ferrous sulfate in the aqueous solution to the mass of the carbon source is 2 to 6mmol/g. Further preferably 4.5 to 5.5mmol/L.
Preferably, the stirring time is 2 to 5 hours. In addition to the complexation of the polysaccharide with ferrous iron during stirring, in chitosan systems, cross-linking reactions of sulfate groups to different molecular chains can also occur due to protonation of the amino groups. Thus, sufficient reaction time can ensure formation of three-dimensional network precursors. Wherein, magnetic stirring is selected for stirring.
More preferably, the stirring time is 3.5 to 4.5 hours.
In the preparation method, in the step (2):
preferably, the precursor is calcined under nitrogen. Specifically, the precursor is placed in a tube furnace and calcined under the protection of nitrogen.
More preferably, the calcination temperature of the precursor is 800-1000 ℃ and the heating rate is 3-10 ℃/min; the calcination time is 3-5 h. When the calcination temperature is too low, graphitization transformation of carbon is difficult, and sulfate radical is also difficult to reduce; when the calcining temperature is too high, the original graphitized carbon collapses, and the graphene structure is damaged.
Further preferably, the calcination temperature is 900 ℃, and the temperature rising rate is 5 ℃/min; the calcination time was 4h.
In order to prevent the powder from being scattered by the gas flow during the calcination, it is preferable that the precursor is placed in a crucible with a lid and placed in a tube furnace for calcination.
Preferably, the calcined powder is acid washed with dilute sulfuric acid for activation. The surface of the calcined iron component is easy to be coated by carbon, more active sites can be exposed through acid washing, the reactivity is improved, and meanwhile, unstable iron components and impurities are removed.
Preferably, the concentration of the dilute sulfuric acid is 0.5 to 25mmol/L.
The concentration of sulfuric acid is too high, so that the effective iron component in the catalyst is lost, and the magnetism of the catalyst is weakened. Further preferably 1 to 10mmol/L. Still more preferably 2.5mmol/L.
Preferably, the acid washing activation time is 0.5-24 h, and the temperature is 25-80 ℃.
Further preferably, the activation time is greatly reduced by increasing the temperature, the pickling activation time is 1.5 hours, and the activation temperature is 80 ℃.
Preferably, after the pickling activation is finished, washing the activated powder sample to be neutral, and drying to obtain the magnetic multi-component iron-carbon composite Fenton-like catalyst.
The magnetic multi-component iron-carbon composite Fenton-like catalyst prepared by the preparation method provided by the invention has good Fenton-like catalytic performance, the removal efficiency of 50mg/L acid red dye for 1 hour under neutral conditions reaches 99.9%, and after the reaction is finished, the rapid solid-liquid separation can be realized by an external magnetic field, and the catalyst has good use stability. The principle is that the components such as highly dispersed nano ferric oxide, ferrous sulfide and the like are formed after calcination and activation through coordination complexing of the chitosan ferrous and crosslinking of sulfate radical, and the chitosan ferrous has more active sites; fe (II) and Fe (III) exist on the surface of the catalyst at the same time, and under the existence of a graphene structure, the two can realize rapid circulation to continuously catalyze hydrogen peroxide to generate hydroxyl free radicals; meanwhile, the stable performance of the material is ensured by firmly bonding the iron component and the carbon carrier through C-S-Fe.
As a specific preferred aspect, a method for preparing a magnetic multi-component iron-carbon composite Fenton-like catalyst includes the following steps:
(1) Dissolving ferrous sulfate in water, adding a carbon source, stirring, drying to remove water to obtain a precursor, and calcining under the protection of nitrogen;
(2) And (3) placing the calcined powder into dilute sulfuric acid for activation, washing with water to neutrality, and drying to obtain the magnetic multi-component iron-carbon composite Fenton-like catalyst.
A magnetic multi-component iron-carbon composite Fenton-like catalyst prepared by the preparation method of any one of the above. The magnetic multi-component iron-carbon composite Fenton-like catalyst is applied to catalytic oxidative degradation of organic pollutants, and is simple to operate, high in degradation rate and stable in performance. The application of the magnetic multi-component iron-carbon composite Fenton-like catalyst in Fenton-like catalytic oxidative degradation of organic pollutants in wastewater.
When the magnetic multi-component iron-carbon composite Fenton-like catalyst is used for catalytic oxidative degradation of organic matters, the magnetic multi-component iron-carbon composite Fenton-like catalyst is directly put into wastewater to be treated (wastewater to be treated), and hydrogen peroxide is added. And the pollutant removal rate is fast, the pH application range is wide, the operation is very simple, and the method has great practical value. Preferably, the organic pollutant is one or more of acid red dye and parachlorophenol.
As a further preference, the organic contaminant is an acid red 73 (AR 73) dye or p-chlorophenol.
In the catalytic oxidative degradation process, the wastewater to be treated is:
the addition amount of hydrogen peroxide is preferably 10-50 mmol/L. Further preferably 40mmol/L.
The addition amount of the magnetic multi-component iron-carbon composite Fenton-like catalyst is preferably 0.5-2 g/L. Further preferably 1 to 2g/L. Still more preferably 1.5g/L.
The concentration of the organic contaminant is preferably 10 to 100mg/L. More preferably 10 to 50mg/L. Still more preferably 50mg/L.
The pH value of the wastewater to be treated is preferably 2 to 9. When the pH value is less than 4, more iron is leached out, which is not beneficial to the stable use of the catalyst; when the pH exceeds 8, the hydroxyl groups gradually combine with hydrogen peroxide to form O 2 Inhibit the progress of the reaction. Therefore, it is more preferable that the pH of the wastewater is 4 to 8.
In order to ensure that the magnetic multi-component iron-carbon composite Fenton-like catalyst is uniformly dispersed in a reaction system, the reaction is oscillated by a constant-temperature oscillating box in the reaction process, and the solid-liquid separation is realized by an external magnetic field after the reaction is finished.
Compared with the prior art, the invention has the beneficial effects that:
the preparation method of the magnetic multi-component iron-carbon composite Fenton-like catalyst is simple to operate and easy to realize industrialization. The magnetic multi-component iron-carbon composite Fenton-like catalyst prepared by the preparation method has high catalytic activity, can effectively improve the degradation rate of pollutants and has stable performance when being applied to the process of catalyzing, oxidizing and degrading organic pollutants, can be rapidly separated by an externally applied magnetic field, and has the advantages of simple operation, low cost, wide pH application range and higher practical value.
Drawings
In fig. 1:
(a) (b) are scanning electron microscope images of C-900 in comparative example 2 at different magnifications, respectively;
(c) Scanning electron microscope images of Fe/C-800 in example 1 at different magnifications;
(e) Scanning electron microscope images of Fe/C-900 in example 2 under different magnifications;
(g) (h) are scanning electron microscope images under different magnifications of Fe/C-1000 in example 3;
(i) (j) are scanning electron microscope images under different magnifications of Fe/Ce-900 in example 4;
FIG. 2 shows Raman spectra of Fe/C-800, fe/C-900, fe/C-1000, and Fe/Ce-900 in examples 1 to 4;
FIG. 3 is an X-ray diffraction pattern (XRD) of Fe/C-800, fe/C-900, fe/C-1000, fe/Ce-900 of examples 1-4;
FIG. 4 is a comparison of the L-side X-ray fine structure spectra of Fe/C-800, fe/C-900, fe/C-1000, fe/Ce-900 in examples 1 to 4 with an iron standard sample;
FIG. 5 shows the addition of H to Fe/C-800, fe/C-900, fe/C-1000, fe/Ce-900 in examples 1 to 4 2 O 2 Catalytic degradation curve for dye AR73 without addition of H 2 O 2 Adsorption removal curve for dye AR73 for Fe/C-900 of example 2;
in fig. 6:
(a) Hysteresis loop for Fe/C-900 in example 2;
(b) Performing solid-liquid separation on the degraded product by a magnet; in the figure, the circle mark is the separated catalyst Fe/C-900;
FIG. 7 is a paramagnetic resonance chart of Fe/C-900 of example 2 using lutidine N-oxide (DMPO) as a trapping agent, wherein:
(a) Is DMPO-O in methanol system 2 - Map;
(b) Is a map of DMPO-HO. In water system.
Detailed Description
The invention will be further illustrated with reference to the following examples:
the raw materials used in the examples:
chitosan (degree of deacetylation 91.2%) was purchased from Zhejiang gold shell biochemistry limited (Zhejiang jade ring);
ferrous sulfate heptahydrate (analytically pure) was purchased from national pharmaceutical group chemical reagent limited (Shanghai, china);
the water used in the experiment is ultrapure water (resistance is more than or equal to 18.2MΩ cm) -1 )。
Examples 1 to 3
100mL of ultra-pure water was added to a 250mL beaker, nitrogen was bubbled for 30min, oxygen was removed, and then 5.56g of FeSO was added 4 ·7H 2 And O, slowly adding 4g of chitosan after dissolving, sealing by a sealing film, and keeping continuous stirring for 4 hours. And (3) performing rotary evaporation on the stirred mixed system, removing most of water, and continuously drying in a vacuum drying oven at 80 ℃ for 8 hours to obtain the iron-carbon precursor. The precursor is put into a corundum crucible with a cover, and under the protection of nitrogen in a tube furnace, the temperature is 5 ℃ for min -1 The temperature rise rate of (C) was raised to a predetermined temperature (800 ℃, 900 ℃, 1000 ℃) in Table 1 and maintained for 4 hours.
And adding the calcined powder sample into enough 2.5mmol/L dilute sulfuric acid, activating for 1.5 hours at 80 ℃, separating by a magnet, washing with water for multiple times to neutrality, and drying to obtain the magnetic multi-component iron-carbon composite Fenton-like catalyst which is respectively marked as Fe/C-800, fe/C-900 and Fe/C-1000.
Table 1 calcination temperatures for each of examples 1 to 3
Examples Example expression Calcination temperature (. Degree. C.)
1 Fe/C-800 800
2 Fe/C-900 900
3 Fe/C-1000 1000
Example 4
100mL of ultra-pure water was added to a 250mL beaker, nitrogen was bubbled for 30min, oxygen was removed, and then 5.56g of FeSO was added 4 ·7H 2 And (3) slowly adding 4g of cellulose after dissolving, sealing by a sealing film, and keeping continuous stirring for 4 hours. And (3) performing rotary evaporation on the stirred mixed system, removing most of water, and continuously drying in a vacuum drying oven at 80 ℃ for 8 hours to obtain the iron-carbon precursor. The precursor is put into a corundum crucible with a cover, and under the protection of nitrogen in a tube furnace, the temperature is 5 ℃ for min -1 The temperature rise rate of (2) was raised to 900℃and maintained for 4 hours.
And adding the calcined powder sample into enough 2.5mmol/L dilute sulfuric acid, activating for 1.5 hours at 80 ℃, separating by a magnet, washing with water for multiple times to neutrality, and drying to obtain the magnetic multi-component iron-carbon composite Fenton-like catalyst which is marked as Fe/Ce-900.
Comparative example 1
Placing chitosan into corundum crucible with cover, and under the protection of nitrogen gas in tubular furnace at 5 deg.C for min -1 The temperature rise rate of (2) was increased to 900℃and maintained for 4 hours, designated C-900.
Characterization of the catalyst 1
The scanning electron micrographs in FIG. 1 give the surface topography of examples 1 to 4 and comparative example 1. As can be seen from fig. 1 (a) and (b), the pure chitosan of comparative example 1 has a smoother surface of the fine bulk material after high temperature calcination; and after the ferrous sulfate is added (examples 1-3), the calcined materials in (c) - (h) of fig. 1 are relatively porous. In fig. 1 (i) and (j), cellulose is used as a carbon precursor (example 4) and still retains a fibrous morphology after calcination, and the particles are loosely bound to the fibers, indicating that the cellulose has a weak binding capacity to iron, resulting in poor binding of the iron component formed after calcination to carbon.
The specific surface areas and pore volumes of examples 1 to 4 and comparative example 1 are shown in Table 2, and the specific surface area of comparative example 1 after calcination of pure chitosan reaches 624.494m 2 Per g, but with a pore volume of only 0.080cc/g, indicating that it is microporous; in examples 1 to 4, the specific surface area was 47.4 to 87.7m 2 Between/g, the pore volume is between 0.151 and 0.191cc/g, because the iron component with higher density is introduced, the specific surface area is reduced compared with that of comparative example 2, but the pore structure is more developed.
According to literature reports, polysaccharides gradually carbonize under high temperature anaerobic conditions, and transition from amorphous carbon to graphitized carbon with increasing temperature will be beneficial for electron transfer and contaminant adsorption. However, as the temperature increases, the specific surface area and pore volume show a tendency to increase and then decrease (see table 2), because the carbonization degree is increased when the temperature increases to 1000 ℃, and the original pore structure is partially collapsed, so that the specific surface area and pore volume are maximized at 900 ℃.
Table 2 comparison of specific surface area and pore volume for examples 1-4 and comparative example 1
FIG. 2 shows the Raman spectra of the catalysts prepared in examples 1 to 4, wherein 1340cm -1 The peak at D band, representing disordered sp 3 Vibration of hybridized carbon, 1591cm -1 The peak at G band represents ordered sp 2 Vibration of hybrid carbon, intensity ratio I D /I G The graphitization degree of carbon in the material can be reflected. As can be seen from FIG. 2, the values of I of Fe/C-800, fe/C-900, fe/C-1000 and Fe/Ce-900 D /I G 0.91, 0.86, 0.89 and 1.01, respectively, indicating that the highest graphitization degree of the carbon at 900 ℃ by taking chitosan as a carbon precursor.
Characterization of the catalyst 2
The iron components in examples 1-4 were first characterized by XRD and the results are shown in FIG. 3. As can be seen in fig. 3, the XRD peaks are substantially similar in the four catalysts,characteristic crystal planes (100), (112), (114) and (300) of merle iron (FeS) at 29.8 °, 33.6 °, 43.1 ° and 53.1 °, respectively, are accompanied by pyrrhotite (Fe) at 43.6 ° 1-x S) characteristic crystal plane, while hematite (alpha-Fe) at 35.5 DEG is also present 2 O 3 ) Is a characteristic peak of (2).
In FIG. 4, the fine structure spectrum of the iron L side shows that the iron of the catalyst outer layer is closer to that of Fe 2 O 3 Rather than FeS in the bulk phase. It is inferred from this that, during calcination at high temperature, the reducing atmosphere such as CO, C, etc. formed by carbonization of chitosan reduces sulfate and forms a series of iron sulfides with iron, whereas during subsequent acid washing activation, surface FeS is oxidized under acidic and heating conditions and is converted into Fe during subsequent water washing and drying 2 O 3 . Thus surface Fe 2 O 3 May be the active site of the reaction, but alpha-Fe 2 O 3 The magnetic property is weak, and the introduction of iron sulfide, especially strong ferromagnetic pyrrhotite, increases the magnetic separation performance of the catalyst, and increases the content of Fe (II) on the surface, thereby being beneficial to the circulation process of Fe (III)/Fe (II) in Fenton-like reaction.
In addition to the above three forms of Fe/Ce-900 in example 4, a small amount of elemental iron is present, due to FeSO during surface calcination 4 The combination effect with cellulose is weaker, so that the cellulose is carbonized vigorously, the generated atmosphere is stronger in reducibility, and iron reduction is stronger.
Catalyst Performance test
Catalyst Performance test experiments were performed in 250mL Erlenmeyer flasks, with a quantity of prepared catalyst sample and hydrogen peroxide solution (H 2 O 2 30%) was added to 100mL of a solution containing acid red 73 dye (50 mg/L by mass volume concentration), the flask was sealed and placed in a constant temperature shaking oven, and the reaction was shaken at 25℃and 150 rpm. Except for the specific illustration, the AR73 (acid Red 73) solution did not adjust pH, the catalyst sample was dosed at 0.15g, the hydrogen peroxide was dosed at 0.4mL, and the catalytic degradation time was 1 hour. After the sample was taken out and filtered through a 0.45 μm filter, the absorbance was measured immediately at 508nm with an UV-visible spectrophotometerDegree, and calculate the dye residual concentration.
Performance test example 1
Acid Red 73 (AR 73) is an azo dye which is widely used and difficult to degrade, so that the acid Red 73 is taken as a treatment object in the study, and example 2 (Fe/C-900) is selected as a catalyst sample to examine different catalyst dosages and H 2 O 2 Effect of the amount used on AR73 removal rate. Table 3 shows the effect of different catalyst amounts on acid Red 73 removal, which indicates that at H 2 O 2 When the addition amount is 50mmol/L, the AR73 removal rate gradually increases along with the increase of the Fe/C-900 dosage, but when the dosage is 1.5g/L, the removal rate reaches 99.2%, the removal effect is not changed greatly after the dosage is continuously increased, so that 1.5g/L is selected as the optimal catalyst addition amount.
TABLE 3 removal of AR73 at different catalyst levels
Catalyst addition (g/L) Removal rate (%)
0.5 33.8
1.0 82.0
1.5 99.2
2.0 100
2.5 100
Performance test example 2
Example 2 (Fe/C-900) was selected as a catalyst sample, and H was examined at the above-selected optimum catalyst amount 2 O 2 The effect of AR73 removal (see table 4). Table 4 shows that H 2 O 2 When the addition amount is 20-50 mmol/L, the removal rate of AR73 is higher than 98%, the trend of increasing firstly and then slightly decreasing is presented, and when the addition amount is 40mmol/L, the removal rate of AR73 reaches the highest value, which is 99.85%. Due to excessive H 2 O 2 Will react with the generated hydroxyl radical, thus, when H 2 O 2 When the addition amount was increased to 50mmol/L, the removal rate was rather lowered. Thus, the catalyst addition amount was determined to be 1.5g/L, H 2 O 2 The batch amount of 40mmol/L is the optimal treatment condition.
TABLE 4 different H 2 O 2 Removal rate of AR73 at the amount used
Performance test example 3
To verify the Fenton-like catalytic performance of each catalyst sample, samples were taken at intervals (sampling intervals of 0, 5, 10, 15, 20, 30, 40, 50 and 60 min) in the catalytic degradation experiments of examples 1-4 on AR 73. As shown in FIG. 5, after H is added 2 O 2 In the case of (C) the AR73 removal of example 2 (Fe/C-900) was 97.8% at 20min, but the chromaticity remained at this time, the AR73 removal rate was 99.9% after 60min, and the chromaticity was substantially removed. As a comparison, the removal rates of example 1 (Fe/C-800, example 3 (Fe/C-1000) and example 4 (Fe/Ce-900) were 95.1%, 57.9% and 91.3%, respectively, at 60min, thereby verifying that Fe/C-900 had the best removal effect on AR 73. In the absence of added oxidant H 2 O 2 When the catalyst is used, the catalyst can onlyExhibits an adsorption effect, as can be seen from FIG. 5, fe/C-900 (without adding an oxidizing agent H 2 O 2 ) The adsorption removal rate for AR73 at 60min was 63.1%, indicating that AR73 was the result of the combined adsorption and catalysis of the adsorbent in the above system.
FIG. 6 (a) shows the hysteresis loop of example 2 (Fe/C-900), and (b) shows a photograph of the degradation after completion of solid-liquid separation by a magnet. Since the saturation magnetization of Fe/C-900 reaches 5.08emu/g (see (a) of FIG. 6), as shown in (b) of FIG. 6, when an external magnetic field is applied, a rapid solid-liquid separation can be achieved; the residual magnetization was only 0.84emu/g, indicating that the catalyst powder was again dispersible in water when the external magnetic field was removed.
Performance test example 4
To verify the stability of the catalyst in use, after one AR73 catalytic degradation experiment was completed for example 2 (Fe/C-900), the magnet was separated, the supernatant was discarded, and the catalyst was redispersed in 100mL of 50mg/L AR73 solution, and the catalytic degradation experiment was performed under the above-mentioned optimal reaction conditions and circulated 12 times in total, and the results are shown in Table 5. As can be seen from Table 5, the Fe/C-900 was excellent in stability, and the AR73 removal rate was kept at 92.26% in the 12 th cycle, and was reduced by only 7.74% from the initial removal rate.
TABLE 5 removal of AR73 during recycle of example 3
Number of cycles Removal rate (%)
1 100
2 100
3 99.97
4 99.88
5 99.70
6 99.08
7 99.25
8 99.85
9 99.66
10 98.81
11 97.64
12 92.26
Performance test example 5
The pH is an important factor affecting the Fenton reaction effect, and therefore, the removal of AR73 at different pH values (2-9) (50 mg/L AR73 solution pH of about 6.8) was examined in this study, and the results are shown in Table 6. As can be seen from Table 6, the removal rate of AR73 was extremely high under acidic and neutral conditions, indicating that the catalyst had good catalytic performance and was able to participate in the reaction normally. When the pH is more than 7, the AR73 removal rate gradually decreases with the increase of the pH, and the activity of the AR73 is reduced; at ph=8, AR73 still had a removal rate of 95.9%; whereas when ph=9, the AR73 removal rate was reduced to 85%. Table 6 also shows the exudation of Fe in the solution after the reaction at the corresponding pH, and when the pH is less than or equal to 3, the exudation rate of Fe is more than 2mg/L, indicating that the catalyst does not maintain good stability under the pH condition. When the pH is not less than 4, the amount of iron exudation is small, particularly at neutral conditions (ph=7) of only 0.399mg/L. Therefore, the pH of Fe/C-900 is preferably 4 to 8 in view of the combination of the AR73 removal rate and the iron leaching amount.
TABLE 6 removal rate of AR73 and iron exudation under different pH conditions
Performance test example 6
In order to explore the reaction mechanism, the free radical in the reaction was determined by paramagnetic resonance method using lutidine N-oxide (DMPO) as a capturing agent. FIG. 7 (a) shows DMPO-O in methanol system 2 - The quartet is shown in FIG. 7 (b) as the quartet of DMPO-HO in water system. FIG. 7 shows that Fe/C-900 can catalyze H 2 O 2 Production of HO & O 2 - For degradation of contaminants.
The reaction mechanism can be summarized by combining the above characterization and performance test analysis: fe/C-900 utilizes graphitized carbon to attract organic pollutants to the surface of the catalyst, and simultaneously with the circulation of Fe (II) and Fe (III), hydrogen peroxide is decomposed on the iron component to generate HO and O 2 - Oxidative degradation of the organic material on the catalyst surface, by which means HO in the system can be prevented - And the like, and realizes the efficient removal of pollutants under neutral and weak alkaline conditions.

Claims (7)

1. The preparation method of the magnetic multi-component iron-carbon composite Fenton-like catalyst is characterized by comprising the following steps of:
(1) Adding a carbon source into a ferrous sulfate aqueous solution, stirring and drying to obtain a precursor;
(2) Calcining the precursor, then carrying out acid washing activation, and after the acid washing activation is finished, washing the activated powder sample to be neutral and drying to obtain the magnetic multi-component iron-carbon composite catalyst;
in the step (2), the precursor is calcined under the protection of nitrogen;
acid washing and activating the calcined powder by adopting dilute sulfuric acid;
wherein the concentration of the dilute sulfuric acid is 0.5-25 mmol/L;
the pickling and activating time is 1.5h, and the activating temperature is 80 ℃;
the calcination temperature is 800-1000 ℃, and the temperature rising rate is 3-10 ℃/min; the calcination time is 3-5 h.
2. The method for preparing the magnetic multi-component iron-carbon composite Fenton-like catalyst according to claim 1, wherein the carbon source is one or more of chitosan and cellulose.
3. The preparation method of the magnetic multi-component iron-carbon composite Fenton-like catalyst according to claim 1, wherein in the step (1), the ratio of the amount of ferrous sulfate in the aqueous solution to the mass of the carbon source is 2-6 mmol/g.
4. A magnetic multi-component iron-carbon composite Fenton-like catalyst, characterized by being prepared by the preparation method of any one of claims 1-3.
5. Use of the magnetic multi-component iron-carbon composite Fenton-like catalyst according to claim 4 for Fenton-like catalytic oxidative degradation of organic pollutants in wastewater.
6. The use according to claim 5, wherein the organic contaminant is one or both of an acid red dye and p-chlorophenol.
7. The application of claim 5, wherein in the catalytic oxidative degradation process, the addition amount of hydrogen peroxide in the wastewater to be treated is 10-50 mmol/L; the addition amount of the magnetic multi-component iron-carbon composite Fenton-like catalyst is 0.5-2 g/L; the concentration of the organic pollutants is 10-100 mg/L; the pH value of the wastewater is 2-9.
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