CN115090332A

CN115090332A - MOFs photocatalyst capable of removing organic pollutants in high-salinity wastewater through visible light catalysis, and preparation method and application thereof

Info

Publication number: CN115090332A
Application number: CN202210907570.3A
Authority: CN
Inventors: 李倩; 王志炜; 周维芝
Original assignee: Shandong University
Current assignee: Shandong University
Priority date: 2022-07-29
Filing date: 2022-07-29
Publication date: 2022-09-23
Anticipated expiration: 2042-07-29
Also published as: CN115090332B

Abstract

The invention relates to an MOFs photocatalyst capable of removing organic pollutants in high-salinity wastewater through visible light catalysis, a preparation method and application thereof. The catalyst has a good removal effect on the antibiotic pollutant wastewater, can resist the influence of inorganic anions in an actual water body, reduces the generation of degradation byproducts, and is more suitable for the treatment of the actual wastewater.

Description

MOFs photocatalyst capable of removing organic pollutants in high-salinity wastewater through visible light catalysis, and preparation method and application thereof

Technical Field

The invention relates to an MOFs photocatalyst capable of removing organic pollutants in high-salinity wastewater through visible light catalysis, a preparation method and application thereof, and belongs to the technical field of chemistry and environment.

Background

The photocatalytic oxidation technology mostly uses a semiconductor as a catalyst, uses sunlight as driving energy to generate oxidative active substances (such as hydroxyl free radicals, superoxide free radicals and the like) and converts organic pollutants into nontoxic or low-toxic substances, and is a pollutant removal technology with strong oxidizability, energy conservation, high efficiency and thoroughness. At present, photocatalytic oxidation technologies represented by visible light catalytic technologies are often applied to wastewater treatment processes such as industrial organic wastewater and antibiotic pharmaceutical wastewater. However, in the application process of the traditional photocatalyst, the photoresponse is poor, the electron-hole recombination rate is high, the photon utilization rate is low, and the catalytic efficiency cannot reach the theoretical value. In addition, active substances generated in the photocatalytic oxidation process have extremely short service life, and quenching is easy to occur in the mass transfer process, so that the oxidative degradation of pollutants is greatly limited. Therefore, it is important to improve the performance of the photocatalyst.

The introduction of defects in a certain concentration range into the surface or bulk of an oxide semiconductor photocatalyst can effectively improve the efficiency of the photocatalyst. Even the band gap of the semiconductor is narrowed to a certain extent, and the effect of visible light absorption is expanded, so that the aim of improving the performance of the photocatalyst is fulfilled. More importantly, the introduction of defects, especially oxygen vacancies, is easier to capture photo-generated electrons, so that the recombination of the photo-generated electrons and holes is inhibited, and the photocatalytic degradation of pollutants is promoted.

The metal organic framework compounds (MOFs) are highly ordered porous crystalline materials and have wide application prospects in various fields such as adsorption, separation, catalysis and the like. Porphyrin MOFs have shown widespread application in photocatalytic applications due to their similar function as semiconductors. The organic linker in porphyrin MOFs can collect light by acting as an antenna and further activate the metal clusters via the linker for charge transition, thereby generating sufficient Reactive Oxygen Species (ROS). In addition, porphyrin MOFs also exhibit excellent adsorptivity, have abundant pores, can well collect target organic matters in water, and isolate the influence of humic acid and salt ions in complex environments by reducing the spatial distance between catalytic sites and organic matters.

However, in the process of photocatalysis of porphyrin MOFs, metal sites are easily masked by organic ligands and cannot play a catalytic role, so that the electron transfer efficiency in the process of photocatalysis is low; meanwhile, the sources of free radicals and non-free radicals in the system are single, the actual catalytic effect is poor, and the photocatalytic effect in high-salinity wastewater is poor.

Therefore, there is a need to develop a novel porphyrin MOFs photocatalyst which has high photocatalytic efficiency and can be used for degrading pollutants in a complex water environment.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides an MOFs photocatalyst capable of removing organic pollutants in high-salinity wastewater through visible light catalysis, and a preparation method and application thereof.

Summary of the invention:

the invention utilizes a simple hydrothermal method to prepare Hf-TCPP MOFs, monocarboxylic acids with different chain lengths are used for regulating and controlling the defect degree of the Hf-TCPP MOFs, defects are introduced into the porphyrin MOFs, the pore diameter of the porphyrin MOFs is enlarged, the capability of the catalyst for capturing electrons is enhanced, and the separation of photogenerated electrons and cavities is enhanced, so that the novel MOFs photocatalyst is obtained, and when the novel MOFs photocatalyst is used for removing organic pollutants in wastewater through visible light catalysis, more free radicals and non-free radicals can be generated, particularly in high-salinity wastewater, the degradation of pollutants can be promoted, and the novel MOFs photocatalyst can be suitable for degrading pollutants in a complex water environment. The catalyst has a good removal effect on the antibiotic pollutant wastewater, can resist the influence of inorganic anions in an actual water body, reduces the generation of degradation byproducts, and is more suitable for the treatment of the actual wastewater.

Detailed description of the invention:

in order to realize the purpose, the invention is realized by the following technical scheme:

the MOFs photocatalyst capable of removing organic pollutants in high-salt wastewater through visible light catalysis is characterized in thatHf ⁴⁺ And meso-tetrakis (4-carboxyphenyl) porphine H ₂ TCPP coordination, defect manufacturing by using monocarboxylic acid, and one-step hydrothermal synthesis to obtain crystals with regular morphology, wherein the microscopic morphology is a three-dimensional porous structure.

The preparation method of the MOFs photocatalyst comprises the following steps:

reacting HfCl ₄ Meso-tetrakis (4-carboxyphenyl) porphine H ₂ Stirring a mixture of TCPP, monocarboxylic acid and N, N-dimethylformamide DMF to obtain a mixed system; and heating the mixed system, cooling, filtering, washing and drying to obtain the defect-rich Hf-TCPP MOFs photocatalytic material.

Preference is given according to the invention to using HfCl in the mixture ₄ Has a concentration of 0.5-3.3g/L, meso-tetrakis (4-carboxyphenyl) porphine H ₂ The concentration of TCPP is 0.5-3.3 g/L.

Preference is given according to the invention to using HfCl in the mixture ₄ With meso-tetrakis (4-carboxyphenyl) porphine H ₂ The molar ratio of TCPP is (1-2): (1-2).

Preferably, according to the invention, the amount of DMF in the mixture is 100-500 mL.

Preferably, according to the invention, the monocarboxylic acid is formic acid, butyric acid or caprylic acid with a volume fraction of 88%.

Most preferably, the monocarboxylic acid is 88 volume percent formic acid.

Preferred according to the invention, HfCl ₄ The molar ratio of the medium Hf to the monocarboxylic acid is as follows: (1-3):(300-900).

Preferably, HfCl ₄ The molar ratio of the middle Hf to the monocarboxylic acid is as follows: (1-3):(400-620).

Most preferably, HfCl ₄ The molar ratio of the middle Hf to the monocarboxylic acid is as follows: 1.5:612.

When the monocarboxylic acid is formic acid, the obtained Hf-TCPP MOFs photocatalytic material is named Hf-TCPP-FA, when the monocarboxylic acid is butyric acid, the obtained Hf-TCPP MOFs photocatalytic material is named Hf-TCPP-BA, and when the monocarboxylic acid is caprylic acid, the obtained Hf-TCPP MOFs photocatalytic material is named Hf-TCPP-OA.

According to the invention, the preferred mixed system is prepared as follows:

reacting HfCl ₄ Adding the powder into N, N-dimethylformamide DMF, ultrasonic treating for 8-15min to dissolve completely, and adding meso-tetra (4-carboxyphenyl) porphin H ₂ Performing ultrasonic treatment on TCPP for 8-15min, and adding monocarboxylic acid for ultrasonic mixing for 8-15min to obtain a mixed system.

The monocarboxylic acid is uniformly dispersed in the MOFs structure in the synthesis process and is removed along with the replacement reaction; forming the defect-rich Hf-TCPP MOFs photocatalytic material.

According to the invention, the heating temperature of the mixed system is preferably 90-180 ℃, and after cooling, the mixed system is washed with DMF and acetone respectively.

According to the invention, the temperature of the drying treatment is preferably 60-180 ℃, and the drying time is preferably 6-24 h.

The MOFs photocatalyst is applied to catalytic degradation of pollutants in high-salt and/or humic acid-containing complex water, and is added into a pollutant solution, and after dark adsorption saturation, visible light of the MOFs photocatalyst is irradiated at room temperature to perform visible light catalytic degradation.

According to the present invention, preferably, the light irradiation light source is a xenon lamp.

According to the invention, the mass-volume ratio of the MOFs photocatalyst to the water body is preferably as follows: 5-50 mg: 50-200 mL.

According to the invention, the concentration of the pollutants in the water body is preferably 5-30mg/L, the pollutants are Norfloxacin (NOR) antibiotics, and the catalytic degradation time is 0.5-3 h.

Preferably, according to the invention, the pH of the application system is from 4 to 9.

According to the invention, the system is preferably promoted to degrade in the high-salinity water body, the salt in the high-salinity water body is sodium chloride, sodium sulfate, sodium bicarbonate or sodium nitrate, and the concentration of the salt is 5-500 mM.

Preferably, according to the invention, the catalytic system has the capacity to withstand the environmental disturbances, the degrading effect of NOR not being significantly inhibited in the presence of humic acid in the range of 2 to 10 mg/L.

According to the optimization of the invention, the Hf-TCPP MOFs photocatalytic material is recycled by centrifugally collecting after photocatalytic degradation, washing with deionized water, soaking and washing with absolute ethyl alcohol, centrifugally collecting again and freeze-drying.

According to the invention, the rotation speed of centrifugal collection is 5000r/min, the washing times of deionized water are 3 times, and the circulation times are 6 times.

The recycling finds that the catalyst still has good photocatalytic performance after 6 times of recycling of the catalytic material, which shows that the Hf-TCPP MOFs photocatalytic material has the recycling property, the stability and the recyclability.

According to the invention, after defects are introduced into the porphyrin MOFs, the Hf-O cluster has stronger electropositivity, more anions can be enriched, and ionic bonds Hf-Cl are formed, so that anions and organic pollutants are isolated, and free anions are prevented from quenching free radicals. In the photocatalysis process, the coexisting anions can play the role of an additional electron donor to transport electrons to the Hf-O cluster to form more lower valence Hf (III). The reduced metal can further react with dissolved oxygen by reducing to generate more superoxide radicals.

The invention has the technical characteristics and advantages that:

1. the defect-rich Hf-TCPP MOFs photocatalytic material adopts Hf and H ₂ TCPP coordination, defects are manufactured by using monocarboxylic acid, a three-dimensional porous visible light catalytic material is synthesized, and a new method and a new thought are provided for synthesizing MOFs photocatalyst with porous defects.

2. The defect-rich Hf-TCPP MOFs photocatalytic material provided by the invention has the advantages that the adsorption capacity of pollutants is obviously enhanced, the contents of free radicals and non-free radicals are obviously improved, the types of the free radicals are rich, and biological-resistant pollutants in a water body can be quickly removed.

3. The invention uses the defect-rich Hf-TCPP MOFs photocatalytic material as a visible light catalyst, generates a large amount of free radicals and non-free radicals while generating photocatalysis, is particularly suitable for degrading pollutants in a complex water environment, and has good removal effect on antibiotic organic pollutant wastewater; can resist the influence of inorganic anions in the actual water body, and is more suitable for the treatment of the actual wastewater.

4. The defect-rich Hf-TCPP MOFs photocatalytic material can efficiently degrade environmental pollutants in high-salt water, and can promote to generate more free radicals under the condition that the concentration is 500mM high-salt, so that the degradation of the pollutants is promoted to be improved.

5. The defect-rich Hf-TCPP MOFs photocatalytic material has good visible light response capability and excellent catalytic performance, can effectively degrade antibiotic organic pollutants, and realizes reasonable development and utilization of visible light energy.

Drawings

FIG. 1 is an SEM image of different MOFs photocatalytic materials;

FIG. 2 is an XRD spectrum of different MOFs photocatalytic materials;

FIG. 3 is an XPS spectrum of different MOFs photocatalytic materials;

FIG. 4 is a graph of the degradation of NOR by different MOFs photocatalytic materials in the visible light catalytic system of application experiment example 2;

FIG. 5 is a graph of the degradation of NOR by different MOFs photocatalytic materials in a visible light photocatalytic high-salt system in application Experimental example 2;

FIG. 6 is a graph showing the degradation of NOR at different pH values using the visible light catalytic system of Experimental example 1;

FIG. 7 is a graph showing the degradation of NOR in the presence of different trapping agents in Experimental example 1;

FIG. 8 shows ESR spectra of different actives and defects in application example 1;

FIG. 9 is a graph showing the effect of different concentrations of anions on catalytic degradation in Experimental example 1;

FIG. 10 is a graph showing the effect of humic acid of various concentrations on catalytic degradation in Experimental example 1;

FIG. 11 is a graph showing the effect of recycling the MOFs photocatalytic material in example 1 of the present invention.

Detailed Description

The present invention will be further described with reference to the following detailed description of embodiments thereof, but not limited thereto, in conjunction with the accompanying drawings.

The starting materials used in the examples are all conventional commercial products.

Example 1

The preparation of the MOFs photocatalyst capable of removing organic pollutants in high-salt wastewater through visible light catalysis:

(1) 481mg of HfCl ₄ ，500mg H ₂ TCPP dissolved in 300mL DMF and as HfCl ₄ The molar ratio to monocarboxylic acid is: 1.5:612 formic acid with a volume fraction of 88% was added and finally the mixture was transferred to a 500mL round bottom flask;

(2) the mixture was heated at 120 ℃ for 24h, cooled to room temperature, and after harvesting the product by centrifugation and washing with DMF;

(3) adding the product into 1.25% hydrochloric acid solution, heating at 90 deg.C for 12h, and repeating for 3 times;

(4) the product is filtered, washed by DMF and methanol respectively, and soaked in methanol for 24h, and repeated for 2 times;

(5) and filtering the product, and drying the product in a vacuum oven at 100 ℃ for 12 hours to obtain a dark purple crystal to obtain the defect-rich Hf-TCPP MOFs photocatalytic material, which is recorded as Hf-TCPP-FA.

The SEM image of the Hf-TCPP-FA photocatalytic material is shown in FIG. 1, and it can be seen from FIG. 1 that the Hf-TCPP-FA photocatalytic material is a three-dimensional porous structure, the XRD of the Hf-TCPP-FA photocatalytic material is shown in FIG. 2, and the XPS diagram is shown in FIG. 3. The application of the Hf-TCPP-FA photocatalytic material for removing organic pollutants in high-salt wastewater through visible light catalysis is as follows:

adding an Hf-TCPP-FA photocatalytic material into high-salt wastewater containing pollutants, stirring the high-salt wastewater under the irradiation condition of a visible light source at room temperature, quickly generating a large amount of free radicals and non-free radicals by a system to perform catalytic degradation on the pollutants, wherein the catalytic degradation time is 1h, 5mg of the Hf-TCPP-FA photocatalytic material is added into every 100mL of the wastewater, and the concentration of the pollutants in the wastewater is 10 mg/L.

Application example 1:

adding the Hf-TCPP-FA photocatalytic material in example 1 into simulated wastewater with norfloxacin antibiotic concentration of 10mg/L, adding 5mg of the Hf-TCPP-FA photocatalytic material into every 100mL of wastewater, applying visible light source for irradiation to form a photocatalytic system, changing the concentrations of pH, salinity, anions and humic acid of the system respectively, and testing:

1. effect of different pH conditions on the catalytic System

The influence of different pH conditions on the catalytic system, and the result is shown in FIG. 6, under the irradiation condition of a visible light source, in the initial pH range of pH 3-9, when the pH is 3, the degradation of NOR is obviously inhibited, and the NOR degradation effect is obviously improved along with the increase of the pH, which indicates that the catalyst has better effect in a slightly alkaline environment.

2. Analysis of active species in photocatalytic systems

To validate the active species in the photocatalytic system, quenching experiments and electron paramagnetic resonance Experiments (ESR) were performed. The results are shown in FIG. 7, where isopropanol and furfuryl alcohol are taken as OH and ¹ O ₂ after the quenching agent of isopropanol and furfuryl alcohol is added, the concentration of the system after the isopropanol and the furfuryl alcohol are respectively 10mmol/L, and the degradation of NOR is obviously inhibited. As shown in FIG. 8, ESR results indicate that, in the photocatalytic process, a large amount of OH and OH can be generated ¹ O ₂ OH and ¹ O ₂ is the main active substance for NOR degradation under the irradiation of visible light.

3. Effect of different anions on photoreactive systems

In order to verify the resistance to the influence of natural environment background, different anions, Cl and SO with different concentrations are added into simulated wastewater ₄ ^2- And NO ₃ Influence on the reaction system, as shown in fig. 9, the addition of anions has a significant effect on promoting the overall degradation system. This is mainly because, after addition of salt ions, OH content increases significantly, and OH has a non-selective attack characteristic, which accelerates degradation of NOR.

4. Influence of high-salt water body on different catalysts

In order to verify the influence of the high-salinity water body, different salts are added into the simulated wastewater, and the influence of the different salts on the photocatalytic system is explored. As shown in FIG. 9, in a high-salinity water body of 500mM, the degradation effect of NOR is improved to a certain extent, and the performance of the Hf-TCPP MOFs photocatalytic material with abundant defects is improved most obviously.

5. Influence of humic acid of different concentrations on photoreaction system

In order to verify the influence of resisting the natural environment background, the influence of different concentrations of humic acid on the reaction system is explored. As shown in FIG. 10, in humic acid water of 2-10mg/L, the degradation effect of NOR is not obviously inhibited, which shows that the Hf-TCPP MOFs photocatalytic material has the capability of resisting the interference of complex environment.

6. Cyclic use of catalyst

In order to verify the stability of the catalyst, the effect of using the catalyst in pure water and high-salt water by circulating 6 times respectively was studied. As shown in FIG. 11, after 6 cycles, the performance of the Hf-TCPP-FA photocatalytic material for removing NOR is only slightly reduced, which indicates that the catalyst has good cyclicity.

Example 2

The difference between the preparation of the Hf-TCPP MOFs photocatalytic material described in example 1 is that:

the operation and the amount of the formic acid with the volume fraction of 88% were completely the same as those of example 1 except that the butyric acid was replaced by the formic acid, and the obtained product was designated as Hf-TCPP-BA.

The SEM image of Hf-TCPP-BA is shown in FIG. 1, the XRD is shown in FIG. 2, and the XPS image is shown in FIG. 3.

Example 3

the same operation and amount as in example 1 were repeated except that 88% by volume of formic acid was replaced with octanoic acid, and the obtained product was designated Hf-TCPP-OA.

The SEM image of Hf-TCPP-OA is shown in FIG. 1, XRD is shown in FIG. 2, and XPS is shown in FIG. 3.

Comparative example 1

The preparation of the photocatalytic material described in example 1 was the same, except that:

the operation and amount were the same as in example 1 except that no formic acid was added, and the obtained product was designated as Hf-TCPP.

The SEM image of Hf-TCPP is shown in FIG. 1, XRD is shown in FIG. 2, and XPS is shown in FIG. 3.

Application example 2:

5mg of the photocatalytic material samples of examples 1 to 3 and comparative example 1 were placed in 100mL of a 10mg/L NOR solution and adsorbed at room temperature. At the end of the adsorption (30min), photocatalytic degradation was carried out. In the degradation process, 1mL of samples are taken at time intervals of 5-15min, and the concentration of the samples is measured by using a high performance liquid chromatograph, so that the catalytic behavior of the process is researched.

The effect of different photocatalytic materials on NOR removal is shown in fig. 4;

different Hf-TCPP MOFs photocatalytic materials are applied to different high-salinity water bodies (500mM NaCl and Na) ₂ SO ₄ 、NaNO ₃ And 50mM NaHCO ₃ ) The performance of removing the NOR in the process is shown in FIG. 5: (a) Hf-TCPP, (b) Hf-TCPP-FA, (c) Hf-TCPP-BA, (d) Hf-TCPP-OA;

the effect of different catalytic materials on the removal of NOR in different concentrations of anionic environment is shown in fig. 9: (a) NaCl, (b) Na ₂ SO ₄ ，(c)NaHCO ₃ ，(d)NaNO ₃ 。

Claims

1. The MOFs photocatalyst capable of removing organic pollutants in high-salt wastewater through visible light catalysis, wherein the MOFs photocatalyst is Hf ⁴⁺ And meso-tetrakis (4-carboxyphenyl) porphine H ₂ TCPP coordination, defects are manufactured by using monocarboxylic acid, crystals with regular appearance are obtained by one-step hydrothermal synthesis, and the microscopic appearance is a three-dimensional porous structure.

2. The process for the preparation of the MOFs photocatalysts according to claim 1 comprising the steps of:

3. The method of claim 2, wherein the HfCl is present in the mixture ₄ In a concentration of 0.5-3.3g/L, meso-tetrakis (4-carboxyphenyl) porphine H ₂ TCPP concentration of 0.5-3.3g/L, HfCl ₄ With meso-tetrakis (4-carboxyphenyl) porphine H ₂ TCPP molar ratio is (1-2): (1-2).

4. The method according to claim 2, wherein the amount of DMF in the mixture is 100-500mL, the monocarboxylic acid is 88% by volume of formic acid, butyric acid or caprylic acid, and preferably the monocarboxylic acid is 88% by volume of formic acid.

5. The method of claim 2, wherein HfCl is used as a carrier ₄ The molar ratio of the middle Hf to the monocarboxylic acid is as follows: (1-3) (300-900), preferably, HfCl ₄ The molar ratio of the middle Hf to the monocarboxylic acid is as follows: (1-3) (400- ₄ The molar ratio of the middle Hf to the monocarboxylic acid is as follows: and 1.5:612, heating the mixed system to 90-180 ℃, cooling, washing with DMF (dimethyl formamide) and acetone respectively, and drying at 60-180 ℃ for 6-24 h.

6. The method of claim 2, wherein the mixed system is prepared by:

reacting HfCl ₄ Adding the powder into N, N-dimethylformamide DMF, ultrasonic treating for 8-15min to dissolve completely, and adding meso-tetra (4-carboxyphenyl) porphin H ₂ And (3) carrying out ultrasonic treatment on TCPP for 8-15min, and then adding monocarboxylic acid to carry out ultrasonic mixing for 8-15min to obtain a mixed system.

7. The application of the MOFs photocatalyst of claim 1, which is applied to the catalytic degradation of pollutants in a complex water body with high salt content and/or humic acid content, wherein the MOFs photocatalyst is added into a pollutant solution, and after the adsorption of the MOFs photocatalyst is saturated in a dark state, the MOFs photocatalyst is irradiated by visible light at room temperature to perform the catalytic degradation of the visible light.

8. The application of claim 7, wherein the light irradiation source is a xenon lamp, and the mass-to-volume ratio of the MOFs photocatalyst to the water body is as follows: 5-50 mg: 50-200mL, the concentration of the pollutant in the water body is 5-30mg/L, the pollutant is Norfloxacin (NOR) antibiotic, the catalytic degradation time is 0.5-3h, and the pH value of the application system is 4-9.

9. The use of claim 7, wherein the system is promoted to degrade in a high-salt water body, wherein the salt in the high-salt water body is sodium chloride, sodium sulfate, sodium bicarbonate or sodium nitrate, and the salt concentration is 5-500 mM; the catalytic system has the capability of resisting the interference of complex environment, and the degradation effect of NOR is not obviously inhibited in the presence of 2-10mg/L humic acid.

10. The application of claim 7, wherein the photocatalytic degradation is performed by centrifugal collection, the photocatalytic degradation is performed by washing with deionized water, the photocatalytic degradation is soaked and washed with absolute ethyl alcohol, the photocatalytic degradation is performed by centrifugal collection again and then freeze drying is performed, so that the recycling of the Hf-TCPP MOFs photocatalytic material is realized, the centrifugal collection rotation speed is 5000r/min, the washing frequency of the deionized water is 3 times, and the cycle frequency is 6 times.