| In recent years,advanced oxidation techology based on persulfate activation has been widely studied and applied in the treatment of organic wastewater.Activation of persulfate by transition metal ions is considered to be one of the most efficient and feasible method which requires no external energy supply or consumption of chemical reagents.However,the activation by transition metals in homogeneous systems is limited due to loss of metal ions,inconvenient recovery,and inevitable sludge production.The use of solid-phase catalysts to construct heterogeneous activation systems is expected to overcome these shortcomings.Meanwhile,as an emerging two-dimensional(2D)layered material,MXene has been widely used in nanoscale due to its well-defined layered structure,good structural stability,excellent metal conductivity,abundant surface functional groups and Lewis acid sites.MXene has been considered as promising nanocatalyst support materials in the fields of performance improvement for composite nanomaterials,water purification,catalysis and so on.In view of the above background,in this thesis,three kinds of MXene-based environmental functional materials were prepared and applied to activate persulfate under simulated sunlight or photothermally activate persulfate under infrared light to degrade organic pollutants such as azo dyes,antibiotics,etc.in wastewater.The mechanisms of the prepared materials in the above reactions are presented,which provides theoretical basis and technical support for promoting the advanced oxidation technology based on persulfate to solve practical environmental problems.The specific research work is as follows:1.CoS nanoparticles were loaded onto Ti3C2 MXene by a simple hydrothermal method,and CoS/Ti3C2 MXene composites were prepared.By adjusting the loading amount of CoS,a composite sample with the best activation performance was obtained,namely 30%-CoS-TC.The experimental results show that the degradation performance of azo dye Rhodamine B(RhB)by activated persulfate(PMS)under simulated sunlight irradiation of 30%-CoS-TC composite has been greatly improved,and the degradation of RhB can be greatly improved with a lower catalyst concentration.The complete degradation of 20 mg L-1 RhB was achieved within 10 min,and the degradation activity remained basically unchanged after 4 cycles.The results of fluorescence test show that the electron-hole separation efficiency has been improved,thereby improving the photo-Fenton-like degradation activity of the composite catalyst.Through the chemical structure analysis of the material and the trapping agent experiment,we found that singlet oxygen(1O2)is the main active species for the degradation of pollutants in this system.MXene not only promoted the dispersion of CoS nanoparticles in the layer,but also promoted the circulation of CO(Ⅲ)/CO(Ⅱ),thus enhancing the activation of PMS for better degradation performance and the composite material showed good stability and repeatability.The material can also achieve good degradation effect in a wide pH range and low PMS concentration.This work provides a new idea for the design of advanced oxidation process based on PMS activation over MXene-based materials for degradation of organic pollutants.2.BiOCl/BiVO4/Ti3C2 MXene composite was sy nthesized by a hydrothermal method.The morphology and chemical composition of the composite were analyzed,which proved that the composite was successfully synthesized.The degradation of antibiotic pollutants by a series of BVCTC composite activated PMS under simulated sunlight was investigated.The experimental results showed that the reaction system had a good degradation effect on antibiotic pollutants sulfadiazine and tetracycline hydrochloride.Compared with BiOCl/BiVO4 material without Ti3C2 MXene,the ternary composite material with Ti3C2 MXene showed better performance for activating PMS to degrade antibiotics under simulated sunlight.Ti3C2 MXene can increase the surface active sites of materials and inhibit the recombination of photo-generated charge carriers.The ternary composite material has potential application in degradation of organic pollutants by activated persulfate.3.Pure Ti3C2 MXene(TC)was prepared by a HF etching method as a photothermal conversion material.Using the infrared(IR)light above 800 nm as a light source,and photothermal activation of peroxodisulfate(PDS)was applied to degrade antibiotic contaminants in wastewater.When the TC concentration was 1 g L-1,the reaction kinetic constant of the TC/PDS/IR system was 0.00984 min-1,which was 4 times that of the PDS/IR system and 7.6 times that of the TC/PDS system,and the degradation effect was significantly improved.Moreover,the TC photothermal conversion material prepared in the experiment showed excellent stability and was not easy to produce secondary pollution.The reaction mechanism in the process of photothermal activation of PDS to degrade organic matter by TC was discussed.At the same time,the experiment of active species quenching was carried out,and it was revealed that the active species that contributed to the degradation of organic matter in TC/PDS/IR system was mainly 1O2 rather than the conventional hydroxyl radical(·OH)or sulfate radical(SO4·-).This work provides a new idea for MXene materials to utilize infrared light for photothermal conversion to activate PMS for the degradation of antibiotics. |
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