The Generation Of Singlet Oxygen By Lead-free Halide Perovskite For Photocatalysis Of Organic Oxidation

Oxygen conversion into highly reactive substances is usually called reactive oxygen species（ROS）.ROS mainly includes four kinds:superoxide free radicals（·O₂^-）,hydrogen peroxide（H₂O₂）,hydroxyl free radicals（·OH）and singlet oxygen（¹O₂）.ROS is an important substance in many physical,chemical and biological systems because it has different oxidation capacities and can oxidize different reactants specifically.Among them,¹O₂ has the advantage of high selectivity compared with other reactive oxygen species,which has attracted wide attention in many fields.For example,¹O₂ plays an indispensable role in the degradation of organic pollutants,synthesis of organic chemicals,and photodynamic therapy（PDT）for cancer.There are many effective ways to produce singlet oxygen,including the photosensitization pathway,chemical pathway,and enzyme-catalyzed reaction pathway.Among them,photosensitization to produce ¹O₂ has the advantage of simplicity and controllability,which is the focus of research in this field.The production of ¹O₂ by photosensitization is strongly dependent on the properties of photosensitizers.The main problems of photosensitizers currently used are that they are easy to photodegrade to lose activity,and their quantum yields are low.In response to these problems,a new type of lead-free halide perovskite photosensitizer with high efficiency for ¹O₂ generation was developed and applied to the selective oxidation of organic matter in this thesis.The details are as follows:（1）In this paper,we found for the first time that non-lead halogenated perovskite Cs₃Sb₂Br₉ nanocrystals with good light absorption ability can effectively produce ¹O₂.The formation of ¹O₂ was directly demonstrated by near-infrared phosphorescence emission spectra and specific chemical capture techniques.The quantum yield of ¹O₂produced by Mn-doped Cs₃Sb₂Br₉ nanocrystals reaches 0.38,which is higher than those of most precious metal or semiconductor nanocrystals.We propose that ¹O₂generation by Cs₃Sb₂Br₉ nanocrystals is achieved by charge transfer mechanism through free radical annihilation experiments.The mild and efficient ¹O₂ produced by Cs₃Sb₂Br₉ nanocrystals can selectively oxidize anisole to an important medical intermediate sulfoxide.Through manganese doping of Cs₃Sb₂Br₉ nanocrystals,the photogenerated carrier separation efficiency was improved,and the conversion and selectivity of the oxidation of anisole to sulfoxide reach up to 90%and 99%,respectively.（2）Considering that two-dimensional materials have better stability and more unsaturated active sites than three-dimensional materials,we prepared Cs₃Sb₂Br₉nanosheets by hot injection method.It is proved that Cs₃Sb₂Br₉ nanosheets can also convert oxygen into ¹O₂ by means of near-infrared phosphorescence emission spectra and specific chemical capture techniques.Studies on the oxidation of anisole to sulfoxide shown that Cs₃Sb₂Br₉ nanocrystals have higher activity than Cs₃Sb₂Br₉nanocrystals.In addition,Cs₃Sb₂Br _XI_9-X nanosheets were prepared by halogen iodide doping,which widened the spectrum response range and further improved the photocatalytic performance of anisole oxidation to sulfoxide.