Heteroatom-doped Carbon Quantum Dot Activated PMS For The Degradation Of Organic Pollutants In Water

Advanced oxidation based on peroxymonosulfate（PMS）is a new technology for degrading organic pollutants that have received more and more attention in the environmental field in recent years,due to its strong oxidation capacity,good stability,and wide application range.At present,the catalysts for activating PMS are mainly metal-based,non-metallic catalysts,and composite catalysts.As a new type of catalyst that can effectively activate PMS,non-metallic carbon materials have received wide attention because of their better chemical stability and environmental values.Carbon quantum dots（CQDs）,as a newly emerged class of nano-carbon materials,have attracted much attention due to their superior optical properties.In recent years,CQDs have also been increasingly used as photocatalysts in the field of photocatalytic activation of PMS.However,the disadvantages of CQDs,such as large forbidden band width and easy compounding of photogenerated electron-hole pairs,greatly limit their application in photocatalysis.In this thesis,a variety of doped carbon quantum dots were prepared by adding different dopants,and the photocatalytic performance of CQDs was improved by doping to enhance the efficiency of photocatalytic activation of PMS to degrade pollutants,and the mechanism of their photocatalytic activation of PMS was investigated.The results provide a good reference value for the modification of carbon quantum dots and their application in the field of degradation of organic compounds.The main contents are as follows:（1）Preparation of sulfur-chlorine co-doped carbon quantum dots（S-Cl-CQDs）and performance study of photocatalytically activated PMS.S-Cl-CQDs were prepared by hydrothermal method using maltitol and sulfoxide chloride as raw materials,and the S-Cl-CQDs were characterized in detail by infrared spectroscopy（FT-IR）,X-ray photoelectron spectroscopy（XPS）,and transmission electron microscopy（TEM）.The results show that the introduction of S and Cl can reduce the forbidden band width of CQDs,thus improving the absorption of light and promoting the photogenerated electron transfer;the fluorescence performance of the chlorine and sulfur co-doped CQDs is significantly improved,and the S-Cl-CQDs also have the excellent ability of photocatalytic activation of PMS.The degradation experiments showed that the degradation rate of methylene blue（MB）could reach more than 94%and that of methyl orange（MO）could reach 99%within 10 min with the dosage of S-Cl-CQDs at 0.5 g/L and the concentration of PMS at 0.4 mM.Through experiments and density flooding theory（DFT）calculations,the reasons for the good fluorescence and photocatalysis of S-Cl-CQDs were found:the sulfur-chlorine co-doping made the photogenerated electron-hole complex of S-Cl-CQDs easy,which enhanced the fluorescence performance;however,the presence of PMS promoted the separation of photogenerated electron-hole of S-Cl-CQDs and inhibited the photogenerated electron-hole complex of CQDs,which improved their photocatalytic performance.The results of this study will provide a good reference for the design and preparation of new CQDs（2）Preparation of Br-modified CQDs and photocatalytic activation of PMS for the degradation of rhodamine B were studied.Bromine-modified carbon quantum dots（Br-CQDs）were prepared,and the Br-CQDs were characterized in detail by FT-IR,XPS,and TEM.The results confirmed that the introduction of bromine could reduce the forbidden band width of the CQDs,thus improving the absorption of light and promoting photogenerated electron transfer.Under those to visible light,Br-CQDs can efficiently catalyze the activation of PMS to oxidize organic compounds such as rhodamine B.The effects of the amount number Br-CQDs,dye type,concentration,and initial pH on the oxidation of organic compounds by the system were investigated.The results of degradation experiments showed that the degradation of RhB was nearly 99%within 1 h at the dosage of Br-CQDs of 0.5 g/L and the concentration of PMS of 0.2mM.Meanwhile,the mechanism of organic degradation by Br-CQDs photocatalytic activation of PMS was investigated by radical burst experiments,and the results showed that superoxide radical(O₂^·-)was the main active substance.（3）Preparation of phosphorus-doped carbon quanta（P-CQDs）and photocatalytic activation of PMS for MB degradation were investigated.The P-CQDs were prepared using maltitol as the carbon source and phosphoric acid as the dopant.detailed characterization of the P-CQDs was carried out by FT-IR,XPS,and TEM,and the results confirmed that phosphorus successfully accessed the CQDs.under visible light irradiation,the degradation of MB was nearly 96%within 10 min at the dosage of P-CQDs of 0.5 g/L and the concentration of PMS of 0.4 mM.The effects of P-CQDs dosage,PMS concentration,and initial pH on the system degradation efficiency of MB were investigated.Meanwhile,the mechanism of MB degradation by P-CQDs photocatalytically activated PMS was investigated by free radical burst experiment,and the results showed that superoxide radical(O₂^·-)was the main active substance。...