Preparation And Photocatalytic Properties Research Of High Efficient Photocatalyst Based On BiOCl

In recent years,the continuous increase of CO₂ concentration in the atmosphere has led to a serious carbon cycle imbalance,and water pollution has caused a serious threat to the biological chain.The above issues pose serious challenges to the development of human society.Among many solutions,Semiconductor photocatalytic technology plays an important role in many aspects such as CO₂ photocatalytic conversion and water pollutant degradation.Layered bismuth oxyhalide has attracted extensive attention as a photocatalyst,and has become a promising photocatalytic material due to its unique layered structure,nontoxicity,and suitable band gap.Therefore,in this thesis,high-efficiency photocatalysts were prepared based on Bi OCl materials.The main research conclusions of the thesis are as follows:1.Under the condition of PVP-assisted synthesis,hydrothermal and solvothermal methods were used to control the influence of different chlorine sources and dissolution mediation on the morphology and band gap of Bi OCl.Under simulated sunlight,the photoreduction performance of Bi OCl samples to CO₂conversion was investigated.The results showed that the CO yield of Bi OCl（HCl-DG）reached 369.87μmol/g/h,and the activity was significantly higher than other Bi OCl samples.The outstanding catalytic activity is attributed to the small surface structure size and loose distribution of Bi OCl（HCl-DG）,which is more favorable for CO₂ adsorption,and has a higher valence band position（1.29 e V）and a smaller band gap（3.25 e V）,this also leads to its stronger electron reduction ability.Finally,the photocatalytic reduction mechanism of CO₂ is explained by FT-IR and VB-XPS.After the photoresponse of Bi OCl（HCl-DG）,the electrons on the VB transition to the CB.Since Bi OCl（HCl-DG）has a higher valence band,the reduction ability of e^-on the CB is stronger,and e^-react with the CO₂adsorbed on the catalyst surface,formed a series of intermediates,such as CO₂^*,COOH^*,which react with e^-to form CO,and finally CO is desorbed from the catalyst surface.2.During the synthesis of Bi OCl,the effect of HCl concentration on the photocatalytic performance of Bi OCl was investigated by adding different amounts of HCl.The photocatalytic oxidation of Rhodamine B was mainly used to evaluate the catalyst performance.The results showed that with the increase of HCl addition,the band gap of Bi OCl was gradually narrowed,and the oxidative degradation ability of rhodamine B was gradually enhanced.The degradation efficiency of Bi OCl-8 reached99%in 60 min.This is mainly due to the narrower band gap（3.08 e V）of Bi OCl-8resulting in better photoresponse of the catalyst.Meanwhile the·O₂^-formed by photogenerated electrons with dissolved oxygen in water,and the·OH produced by the reaction with H₂O which effectively promoted the oxidation of Rhodamine B.Bi OCl-8 also showed good CO₂ photoreduction activity,and the CO generation rate reached347.45μmol/g/h.The enhanced photocatalytic activity of Bi OCl-8 is attributed to its narrow band gap（3.08 e V）leading to excellent photoresponsivity,photogenerated electrons as the photocatalytic fast-determining factor,and e^-react with dissolved oxygen in water under illumination conditions yields high concentrations of·O₂^-.Which effectively promoted the oxidation of Rhodamine B,and the e^-direct reduction also endowed the catalyst with outstanding CO₂ photoreduction activity.3.Bi OCl/Bi-MOF composite with the co-shared Bi atoms were successfully prepared by in situ synthesis.The Bi OCl/Bi-MOF-0.2 sample formed by shared Bi atoms showed the highest CO（456.67μmol/g/h）,which is about 1.24 and 2.41 times higher than the original Bi OCl and Bi-MOF,and the stability of the material is also greatly improved.After 12 h of the cyclic reaction under humid air,the CO generation rate with Bi OCl/Bi-MOF is 145.25μmol/g/h.The enhanced photocatalytic activity is ascribed to the tightly contacted interface between Bi OCl and Bi-MOF through the shared Bi atoms,which enhances the charge carrier separation and transfer under solar light illumination.In addition,the rich functional groups,the large specific surface area,and the more oxygen vacancy contribute also to the enhanced CO₂ adsorption.Finally,a detailed photocatalytic reaction pathway of CO₂ to CO with Bi OCl/Bi-MOF composite catalyst is proposed by the in stiu infrared technology.