CN108607610B - Preparation method and application of magnetically-recoverable Fe-MOF photocatalyst - Google Patents
Preparation method and application of magnetically-recoverable Fe-MOF photocatalyst Download PDFInfo
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- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J31/00—Catalysts comprising hydrides, coordination complexes or organic compounds
- B01J31/16—Catalysts comprising hydrides, coordination complexes or organic compounds containing coordination complexes
- B01J31/1691—Coordination polymers, e.g. metal-organic frameworks [MOF]
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- B01J35/33—
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- B01J35/39—
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- 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
- C02F1/30—Treatment of water, waste water, or sewage by irradiation
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- 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
- C02F1/70—Treatment of water, waste water, or sewage by reduction
- C02F1/705—Reduction by metals
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- C02F2101/00—Nature of the contaminant
- C02F2101/10—Inorganic compounds
- C02F2101/20—Heavy metals or heavy metal compounds
- C02F2101/22—Chromium or chromium compounds, e.g. chromates
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- 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
- C02F2305/10—Photocatalysts
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Abstract
The invention discloses a preparation method and application of a magnetically recyclable Fe-MOF photocatalyst, wherein the preparation method comprises the following steps: (1) uniformly dispersing the 2-MI into methanol to obtain a 2-MI solution; mixing Fe (NO)3)3Uniformly dispersing in methanol to obtain Fe3+A solution; (2) adding the obtained 2-MI solution dropwise to the obtained Fe3+Stirring and uniformly mixing the solution to obtain suspension; (3) and standing, washing and vacuum drying the suspension in sequence to obtain the Fe-MOF photocatalyst. The photocatalyst has the advantages of simple preparation method, low price of raw materials, easy separation of photoproduction holes and electrons, certain magnetism, capability of realizing separation and recovery through an external magnetic field and high economic benefit.
Description
Technical Field
The invention relates to the technical field of photocatalytic materials, in particular to the technical field of visible light response photocatalytic materials, and specifically relates to a preparation method and application of a novel Fe-MOF photocatalyst.
Background
In recent years, global environment is seriously polluted by toxic heavy metals due to excessive discharge of pollutants generated in various industrial, agricultural and mining processes. Chromium (Cr) is a common contaminant in surface and groundwater and is widely used in the industries of electroplating, leather tanning, printing, painting, polishing, and the like. Cr (vi) contaminating aquatic ecosystems and drinking water sources can cause severe diarrhea and bladder, liver, kidney and skin cancer, seriously threatening the environment and human health. Even at relatively low concentrations, cr (vi) can be very harmful to humans due to its high toxicity, carcinogenicity, and bioaccumulation through the food chain.
Cr (iii) is environmentally friendly and has an important role for plant and human life, so the reduction of cr (vi) to cr (iii) is considered to be an effective strategy for removing cr (vi) from wastewater. And the photocatalyst is used for carrying out photocatalytic reaction, the condition is mild, and no secondary pollution is caused. The photocatalytic method is based on electron-hole pairs (e) generated under the irradiation of light of catalytic material with energy greater than the catalytic band gap--h+) These electrons migrating to the catalyst surface are able to reduce cr (vi) to cr (iii) in solution. TiO has been reported by many researchers2Photocatalytic reduction of Cr (VI) but TiO2The application of (2) is limited by the wide forbidden band width (3-3.2eV), and only ultraviolet light can be absorbed. Photocatalysts with visible light activity, e.g. CdS, SnS2，Ag2S and WO3It has been widely reported that these photocatalysts are not very active for reducing cr (vi), and the reduction process usually takes a long time. On the other hand, sulfide materials are generally not sufficient as photocatalysts due to photo-corrosion and may cause secondary pollution due to their high toxicity. Therefore, it is necessary to search for a novel visible light active photocatalyst.
Metal-organic frameworks (MOFs) are a class of hybrid porous materials composed of metal-oxygen clusters and organic structural units, have a wide application prospect, and particularly, the application prospect of the MOFs in the field of photocatalysis is more and more concerned at present. Compared with the traditional photocatalyst, the MOFs has an ideal topological structure and a high surface area, the band gap of the MOFs is closely related to the HOMO-LUMO gap, and the HOMO-LUMO gap can be flexibly adjusted through reasonable modification of an inorganic unit or an organic linker in the synthesis process, so that the effective trapping of visible light is realized. In fact, some MOFs such as titanium, zirconium and iron-based MOFs have been demonstrated to have photocatalytic activity, and are used for dye degradation, water splitting and carbon dioxide reduction, and the like. Its main catalytic mechanism involves the transfer of photo-induced electrons from photo-excited organic linkers to metal-oxide clusters in MOFs and direct excitation by metal-oxide clusters. Despite the great progress made to date, the photocatalytic performance of MOFs has not been fully exploited. Especially, research on applying MOFs to photocatalytic reduction of Cr (VI) is few, the recovery and separation capability of many MOFs photocatalysts prepared at present is not taken into consideration, and the research on the MOFs photocatalysts is inhibited due to the cost problem.
Therefore, on the basis of the researched MOFs, the MOF photocatalyst with high visible light response is prepared by adjusting the organic ligand and the metal central atom, and the experiment has high research value on the efficient degradation of chromium-containing wastewater.
Disclosure of Invention
The invention provides a preparation method and application of a magnetically recyclable Fe-based MOF photocatalyst.
A magnetically recoverable Fe-MOF photocatalyst having an atomic ratio composition represented by formula (i):
[Fe(2-mim)3·nH2O] (Ⅰ)
a preparation method of a magnetically recoverable Fe-MOF photocatalyst comprises the following steps:
(1) uniformly dispersing the 2-MI into methanol to obtain a 2-MI solution; mixing Fe (NO)3)3Uniformly dispersing in methanol to obtain Fe3+A solution;
(2) adding the obtained 2-MI solution dropwise to the obtained Fe3+Stirring and uniformly mixing the solution to obtain suspension;
(3) and standing, washing and vacuum drying the suspension in sequence to obtain the Fe-MOF photocatalyst.
Prepared by one-step method at room temperature, 2-MI and Fe3+Dissolving in methanol respectively, mixing, and mixing to obtain Fe solution3+And 2-MI is subjected to coordination reaction at room temperature to generate a sample, and the sample is washed and dried after standing to finally prepare the Fe-MOF photocatalyst.
The invention realizes the [ Fe (2-mim) at room temperature by a one-step method3·nH2O]The preparation method is simple and easy to realize, and has excellent visible light catalytic activity and magnetic recoverable performance.
Preferably, the concentration of the 2-MI solution in the step (1) is 0.1-2 mmol/mL, and Fe3+The concentration of the solution is 0.05-0.2 mmol/mL. Further preferably, the concentration of the 2-MI solution in the step (1) is 0.8-1.2 mmol/mL; fe3+The concentration of the solution is 0.08-0.12 mmol/mL; most preferably, the concentration of the 2-MI solution in step (1) is 1 mmol/mL; fe3+The concentration of the solution was 0.1 mmol/mL.
Further, the volume fraction of methanol used as a solvent for preparing the 2-MI solution is 99.5%, and the stirring time is 30-60 minutes; preparation of Fe3+The volume fraction of the solvent methanol of the solution is 99.5%, and the stirring time is 60-120 minutes.
Preferably, Fe in step (2)3+Mixing ratio of the solution and 2-MI solution is Fe3+The molar ratio of the 2-MI to the 2-MI is 1: 20-1: 1. The mixing and stirring time is 60-120 minutes.
Further preferably, Fe3+Mixing ratio of the solution and 2-MI solution is Fe3+The molar ratio of the 2-MI to the 2-MI is 1: 15-1: 5. Most preferably, Fe3+Mixing ratio of the solution and 2-MI solution is Fe3+The molar ratio of the mixed solution to the 2-MI is 1: 10.
Preferably, the standing time in the step (3) is more than 20 hours, the vacuum drying temperature is 60-80 ℃, and the drying time is 10-12 hours. Washing is carried out by adopting ethanol and water respectively.
A most preferred preparation method comprises the following steps:
(1) uniformly dispersing the 2-MI into methanol to obtain a 2-MI solution; mixing Fe (NO)3)3Uniformly dispersing in methanol to obtain Fe3+A solution; the concentration of the 2-MI solution in the step (1) is 1mmol/mL, and Fe3+The concentration of the solution is 0.1 mmol/mL; fe3+Mixing ratio of the solution and 2-MI solution is Fe3+The molar ratio of the 2-MI to the 2-MI is 1: 10;
(2) adding the obtained 2-MI solution dropwise to the obtained Fe3+Stirring the solution for 60min to obtain a suspension;
(3) and standing the suspension for 24h, washing, and drying the suspension for 10h under the conditions of static vacuum and 80 ℃ to obtain the Fe-MOF photocatalyst.
The invention also provides the Fe-MOF photocatalyst prepared by the preparation method.
The invention also provides a method for degrading chromium-containing Cr (VI) wastewater, which comprises the following steps:
(1) adding the Fe-MOF photocatalyst of claim 5 into chromium-containing Cr (VI) wastewater to be treated, stirring in the dark until the adsorption is balanced, turning on a visible light source, and carrying out photocatalytic degradation;
(2) and after the reaction is finished, adding a magnetic field to recover the Fe-MOF photocatalyst, and washing and drying the Fe-MOF photocatalyst for cyclic utilization.
Preferably, the addition amount of the Fe-MOF photocatalyst is 0.1-0.5 g/L.
Preferably, the pH of the wastewater is adjusted to 2-5 in the step (1), and most preferably, the pH is adjusted to 2.
The invention aims to provide a preparation method of Fe-based MOF capable of being magnetically recycled and a visible light catalyst for treating chromium-containing wastewater. According to the invention, Fe is used as a central metal atom and 2-MI is used as an organic ligand for the first time, so that the MOFs photocatalyst with visible light response is prepared, and compared with the conventional common Fe-based MOFs or MOFs photocatalyst with other metal elements as central metal atoms, the MOFs photocatalyst can better promote electron-hole separation, improve the quantity of photo-generated electrons, has better visible light catalytic activity, has magnetism which is not possessed by other MOFs photocatalysts, and can be better recycled.
The invention has the following beneficial effects:
(1) the Fe-based MOF photocatalyst is simple in preparation method and low in cost;
(2) the Fe-based MOF photocatalyst has high visible light activity.
(3) The Fe-based MOF photocatalyst has magnetism and is easy to recover.
Drawings
FIG. 1 shows a photocatalyst [ Fe (2-mim) ]in the present invention3·nH2O]Images taken under a Scanning Electron Microscope (SEM).
FIG. 2 is a graph showing the effect of reducing Cr (VI) by MOFs synthesized by using Fe as a central metal atom and different organic ligands in example 2 of the present invention.
FIG. 3 is a graph comparing the effect of reducing Cr (VI) by MOFs synthesized by using 2-MI as an organic ligand and different central metal atoms in example 3 of the present invention.
FIG. 4 shows different Fe values in example 4 of the present invention3+And 2-MI ratio, the effect of the synthesized Fe-based MOF on reducing Cr (VI) is compared with that of the synthesized Fe-based MOF.
FIG. 5 is a graph comparing the effect of Fe-based MOF on Cr (VI) reduction at different pH values in example 5 of the present invention.
FIG. 6 is a graph showing the cycle performance of the effect of reducing Cr (VI) by Fe-based MOF in example 6 of the present invention.
Detailed Description
The invention will now be further described with reference to the drawings and specific examples.
The following raw materials were all commercially available products.
Example 1
MOF photocatalyst [ Fe (2-mim)3·nH2O]The preparation method comprises the following steps:
(1) dissolving 40mmol of organic ligand 2-MI in 50ml of methanol solution, and mixing and stirring for about 30 minutes to obtain uniform 2-MI methanol solution;
(2) 4mmol of Fe (NO)3)3·9H2Dissolving O in 50ml of methanol solution, and mixing and stirring to obtain uniform Fe3+A solution obtained by dropwise adding the uniform 2-MI methanol solution obtained in the step (1) to Fe3+Stirring and reacting in the solution for about 60 minutes to obtain a suspension;
(3) standing the reaction product prepared in the step (2) at room temperature for more than 20h, washing the reaction product by ethanol and water respectively, and then drying the washed reaction product at the static vacuum condition of 80 ℃ for 10h to finally prepare [ Fe (2-mim)3·nH2O]A photocatalyst.
FIG. 1 shows [ Fe (2-mim)3·nH2O]Images taken under a Scanning Electron Microscope (SEM). From the figure, it can be seen [ Fe (2-mim)3·nH2O]Is flaky, has different sizes and loose structure.
Example 2
Different organic ligands with Fe3+Different MOFs with Fe as the central atom can be formed. By changing the organic ligands, respectively with H, using the methods already reported2BDC、NH2-H2BDC and fumaric acid as organic ligands with ferric nitrate (nonahydrate) to prepare MOFs.
Taking the example of degrading chromium-containing Cr (VI) wastewater to test the activity of the catalyst, adding 100mL of chromium-containing Cr (VI) wastewater with the concentration of 80 mu mol/L into a reactor, adding 10mg of Fe-based MOF visible light catalyst prepared according to different proportions, continuously stirring without adjusting pH, stirring in the dark for 30min until the adsorption is balanced, turning on a visible light source, and sampling at intervals of 15 min.
As shown in FIG. 2, the Fe-based MOF prepared by the invention and using 2-MI as an organic ligand has the best effect of degrading Cr (VI) by visible light, and has only magnetic property.
Example 3
Different central metal atoms and the organic ligands 2-MI are capable of forming MOFs of different central metal atoms. With M (NO)3)X(where M ═ Ce, Co, Bi, Fe, Zn) provides the central metal atom, methanol is used as solvent, and a series of different central metal atoms are prepared in a single step by a method similar to the preparation of Fe-MOFThe MOFs of (1). And a comparison was made by following the chromium reduction procedure of example 2.
As shown in FIG. 3, the Fe-based MOF prepared by the invention and taking Fe as a central metal atom has the best visible light degradation Cr (VI) effect and only has magnetism.
Example 4
The generation amount and the generation state of the complex can be influenced by adjusting the molar ratio of the central metal atom Fe to the organic ligand3+The defects of (2) can cause the low generation speed and the low generation amount of the complex, and the low reduction efficiency; central metal atom Fe3+Too much will in turn lead to the presence of free Fe3+Since the production of Fe-based MOF is suppressed, resulting in a decrease in the efficiency of Cr (VI) reduction, we can change [ Fe (2-mim) in example 13·nH2O]In the preparation method, different ligand ratios are adjusted, a series of catalysts are prepared, and comparison is carried out according to the chromium reduction operation of example 2.
As shown in FIG. 4, Fe3+The reduction effect of Cr (VI) is best when the molar ratio of 2-MI is 1:10, so that the prepared Fe3+And 2-MI [ Fe (2-mim) 3. nH at a molar ratio of 1:102O]The photocatalytic activity is optimal.
Example 5
Different pH values have great influence on the adsorption and photocatalytic effect of the MOF photocatalyst, and the existing state of chromium ions is different under different pH values. The pH of the solution was about 4.64 when not adjusted. To investigate the effect of pH on the catalysts prepared according to the invention, the pH of the chromium reduction solution of example 2 was varied, adjusted to pH 2 with 1M sulfuric acid solution, adjusted to pH 8 and 10 with 1M sodium hydroxide solution and compared according to the chromium reduction procedure of example 2.
As shown in fig. 5, the reduction effect of cr (vi) is the best at pH 2, and the reduction effect of the MOF photocatalyst prepared by the present invention gradually decreases with increasing pH.
Example 6
In practical applications, catalyst recovery and recycle performance are critical factors. Most of the existing photocatalysts have no good recycling effect and are difficult to recycle. In order to investigate that the MOF photocatalyst prepared by the invention has magnetism and can be recovered under an external magnetic field and test the cycle performance of chromium reduction, on the basis of the chromium reduction operation in the example 2, the chromium reduction operation in the example 2 is repeated by washing and drying the catalyst again after the catalyst is recovered, and the change of the Fe-based MOF prepared after four cycles on the chromium reduction performance is compared.
As shown in FIG. 6, after five cycles, the reduction effect of Cr (VI) is not obviously reduced, and the Fe-based MOF photocatalyst prepared by the invention is considered to have good cycle performance and can carry out continuous photocatalytic degradation on chromium-containing wastewater.
As can be seen from the above examples, the Fe-based MOF photocatalyst prepared by the invention has excellent visible light catalytic activity.
The above description is only an embodiment of the present invention, but the technical features of the present invention are not limited thereto, and any person skilled in the relevant art can change or modify the present invention within the scope of the present invention.
Claims (5)
1. A magnetically recoverable Fe-MOF photocatalyst, characterized in that the preparation method comprises the steps of:
(1) uniformly dispersing 2-methylimidazole in methanol to obtain a 2-methylimidazole solution; mixing Fe (NO)3)3Uniformly dispersing in methanol to obtain Fe3+A solution;
(2) the resulting 2-methylimidazole solution was added dropwise to the resulting Fe3+Stirring and uniformly mixing the solution to obtain suspension; fe3+Mixing ratio of the solution and 2-methylimidazole solution is Fe3+The molar ratio of the 2-methylimidazole to the 2-methylimidazole is 1: 15-1: 5;
(3) and standing, washing and vacuum drying the suspension in sequence to obtain the Fe-MOF photocatalyst.
2. The Fe-MOF photocatalyst according to claim 1, wherein the concentration of the 2-methylimidazole solution in the step (1) is 0.1-2 mmol/mL, and Fe3+The concentration of the solution is 0.05-0.2 mmol/mL.
3. The Fe-MOF photocatalyst according to claim 1, wherein the standing time in the step (3) is more than 20 hours, the vacuum drying temperature is 60-80 ℃, and the drying time is 10-12 hours.
4. A method for treating wastewater containing chromium Cr (VI) is characterized by comprising the following steps:
(1) adding the Fe-MOF photocatalyst of claim 1 into chromium-containing Cr (VI) wastewater to be treated, stirring in the dark until the adsorption is balanced, turning on a visible light source, and performing photocatalytic degradation;
(2) and after the reaction is finished, adding a magnetic field to recover the Fe-MOF photocatalyst, and washing and drying the Fe-MOF photocatalyst for cyclic utilization.
5. The treatment method of claim 4, wherein the Fe-MOF photocatalyst is added in an amount of 0.1-0.5 g/L.
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| CN110038636B (en) * | 2019-04-11 | 2021-11-30 | 浙江工商大学 | AgI/Ag-Ce-2MI composite photocatalyst and preparation and application thereof |
| CN110037052B (en) * | 2019-04-11 | 2021-01-12 | 浙江工商大学 | Photocatalytic bactericide and preparation method and application thereof |
| CN111254707B (en) * | 2020-02-25 | 2022-03-18 | 南通大学 | Preparation method of Fe-MOF-loaded activated carbon fiber material |
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