| With the increasing degree of industrialization, more and more organics is put into modern production and life, which cause a large number of organic residues in the aquatic environment, and the environmental pollution resulted from these organic residues is becoming increasingly serious. In recent years, photocatalysts as a kind of"green" energy material have attracted wide attention for photodegradation of organic contaminants under sunlight illumination. The ability to obtain high performance and low cost semiconductor photocatalytic materials are of critical importance to effective use the solar energy through photocatalysis. Quantum dots have the advantages of small size, large specific surface area, strong light response ability, unique electronic state and optical absorption performance. Therefore, combined with the advantages of quantum dots and CdSe semiconductors, the choice of CdSe quantum dots as photocatalytic materials to degrade organic pollutants in environmental wastewater has a good application prospect. However, due to the existence of some defects in the single CdSe quantum dots, the application scope is seriously restricted, such as easy agglomeration, poor light corrosion resistance and low stability. In order to surmount the shortcomings of CdSe quantum dots, this topic adopts modified by the various modification techniques. Ion doping technique was used to overcome the problem that CdSe photogenerated electrons and holes easily recombine; Combined with the plasma resonance effect of noble metal nanoparticles, the separation efficiency of photoelectrons and holes as well as the utilization ratio of light energy was improved;Selecting the appropriate carrier to prepare the load-composite multi-component photocatalytic material to solve the problem of CdSe semiconductor material adsorption capacity is poor, the stability is not high and so on. At the same time, the physical and chemical properties of modified CdSe photocatalytic materials and the reaction mechanism of environment organic pollutants photodegradation were systematically studied by a variety of analytical methods.Specific research work is as follows:(1) Using cetyltrimethylammonium chloride as the surfactant, vesicular CdSe nano-semiconductor materials were synthesized by soft template method and water bath reflux. The forming mechanism of vesicle like structure was analysed by TEM and other test methods. The physical and chemical properties of vesicular CdSe nano-semiconductor materials were characterized by XRD, TEM and TGA.Compared with the particle structure CdSe quantum dot material, the vesicular structure has a large specific surface area and rich pore structure. The results of degradation experiments show that the CdSe quantum dot photocatalytic material exhibits excellent photocatalytic activity for tetracycline hydrochloride (TC · HCl).The photocatalytic degradation mechanism was analyzed by the experiment of active substance capture.The cycle efficiency of the catalyst was investigated by cyclic degradation experiment.(2) Ion co-doped quantum dot photocatalystwere synthesized by a simple one-step hydrothermal method using mercaptopropionic acid as a modifier. Different metal ions doped CdSe quantum dot photocatalytic materials were prepared by adjusting the ion doping and ion doping ratio. TEM study found that the prepared metal ions doped CdSe quantum dot material, nanoparticle size uniform, spherical distribution, the average size of nanoparticles of about 8nm. UV-vis DRS showed that all the ions doped CdSe quantum dots have strong optical response in the visible range. Compared with single CdSe quantum dots, the band gap of metal ion doped CdSe quantum dots decreases. At the same time, taking TC · HCI solution as the target wastewater, the mechanism of photocatalytic degradation was discussed in detail and the effect of different conditions on photocatalytic degradation. By investigating the types of metal ions and the ratio of metal ion doping, we conclude that 3%Co-4%K/CdSe quantum dots have the best photocatalytic performance.Within 30 min, the degradation rate of tetracycline hydrochloride reached 78.4%.The intermediate process of TC · HCl degradation was analyzed by measuring the mass spectra of the solutions at different times.(3) A simple hydrothermal method was utilized to combine the Al2TiO5 ceramic material with CdSe quantum dots to construct the heterojunction composite material.On the basis of the above results, nano Ag particles modified CdSe quantum dots loaded Al2TiO5 composite photocatalysts were prepared. The physical and chemical properties of the photocatalyst were characterized by XRD, TEM, electrochemical methods, etc. The photocatalytic activity of the prepared composite photocatalyst was verified by the typical methylene blue dye (Methylene blue, MB) solution as the degradation target. The influence of the introduction ratio of Al2TiOs on the photocatalytic performance of the composites was investigated. Active factors of photocatalytic degradation were analyzed by the activity trapping experiment and mechanism of photocatalytic degradation of organic dyes was discussed in detail.(4) Using bamboo charcoal as raw material, bamboo biochar was prepared by oxygen free carbonization. The physical and chemical properties of bamboo biochar were verified by XRD, SEM and specific surface area. With the bamboo biochar as the carrier, the soluble metal salt solution as the metal source, sodium borohydride as the reducing agent, in-situ growth method and hydrothermal method with the combination of successful preparation of metal ion doped CdSe quantum dot loaded bamboo biochar composite photocatalyst. The photocatalytic activity was verified by photocatalytic degradation of tetracycline hydrochloride solution. The influence of the addition of biochar on the properties of the prepared composites was investigated. The impact of the ratio of metal ions on the properties of the prepared materials was investigated. We conclude that the addition of biochar is 35 wt% and the Co doping ratio is 3%-7% for the optimum doping ratio. In addition, the mechanism of photocatalytic degradation of antibiotics was discussed through a variety of experimental methods, revealing the essential reason for improving the photocatalytic performance. |
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