Investigation On The Mechanisms Of Ag⁺/NO₃^- Synergistic Photocatalytic System For The Treatment Of Refractory Organic Pollutants

Nitrate ion（NO₃^-）is widely present in the water environment,it is an important form of nitrogen in nature.At present,NO₃^-residues with a pollution level ofμmoL^-1to mmoL^-11 can often be detected in various water bodies at home and abroad.Therefore,the research based on NO₃^-has become a hot spot in the international environmental protection field.Numerous studies have shown that NO₃^-has strong oxidizing properties,and catalysts or critical conditions play an important role in promoting NO₃^-oxidation.Therefore,the development of NO₃^-based catalytic system is a potential strategy for treating pollutants in water.In this thesis,Ag⁺and NO₃^-were used to construct a synergistic catalytic system.The typical refractory organics of antibiotics and dyes were selected as target pollutants to revealthephotocatalytic properties and degradation mechanism involved in Ag⁺/NO₃^-system.The investigations in the work mainly include the following aspects.（1）The photocatalytic performance and degraded mechanism of methylene blue（MB）by Ag⁺/NO₃^-system.The construction of photocatalytic system,photocatalytic performance,photocatalytic mechanism and degradation mechanism of methylene blue were studied.The results showed that the degradation rate of MB can reach 98%in 90 min under the optimum conditiaon ofthe pH 3.0,the catalyst dosage 10mmol/L,the xenon lamp 500 W（the ultraviolet light was removed by filter）.The photocatalytic mechanism showed that Ag⁺and NO₃^-have a synergistic effect on the photocatalytic degradation of MB,and the dominated free radical is hydroxyl radical（·OH）in Ag⁺/NO₃^-system.Moreover,the degradation mechanism of MB was analyzed by infrared chromatography（IR）,ultraviolet-visible spectroscopy（UV-vis）,and high performance liquid chromatography-mass spectrometry（HPLC-MS）,and the degradation kinetics of the MB was studied as well.In addition,some other typical dye contaminants were comparatively investigated by Ag⁺/NO₃^-system.The degradation rate of reactive brilliant red is 83%,and the degradation rate of direct blue can reach 98%.（2）Thephotocatalyticperformanceanddegradedmechanismof chloramphenicol（CAP）by Ag⁺/NO₃^-system.The construction of photocatalytic system,photocatalytic performance and mechanism and degradation mechanism of CAP were investigated.The results showed that 90%degradation rate of CAP was achieved with the optimal parameters of pH 3.0,the catalyst dosage 10 mmol/L,the xenon lamp 500 W（no filter）,the illumination time 90 min.The main active intermediates in the Ag⁺/NO₃^-photocatalyticsystem such as·OH,·NO₂ and·O^2-,were further investigated.It was found that the determined radical was·OH and Ag⁺and NO₃^-showed a synergistic effect in the photodegradaion of CAP.Furthermore,HPLC and HPLC-MS were used to analyze the degradation performance and degradation products of CAP.The degradation kinetics of CAP was in accordance with pseudo-first order kinetic model.Aditionally,by comparing and analyzing the degradation performance of several typical antibiotic pollutants in the system,the degradation rate of sulfadiazine and paracetamol can reach 90%in 90min.The research in the work,on the one hand,can provide reference and basis for the resource utilization of NO₃^-in water and the construction of homogenous photocatalyic process,on the other hand,it can also provide new treatment methods and techniques for the treatment of refractory organic pollutants such as dyes and antibiotics.The mechanism involved in the work is expected to be developed in the exploring of methods for pollution control in the real water environment.The purpose of"treating waste by waste"can be achieved by means of the direct or induced photodegradation of NO₃^-in the pollution system to remove organic pollutants.Therefore,the research is titled with certain theoretical significance and practical value.