Structure Regulation And Performance Study On Carbonized Polymer Dots/Semiconductor Nanocomposite Photocatalysts

Nowadays,we are facing serious energy crisis and environment pollution.Solar energy is abundant,renewable and clean.Photocatalytic technology can efficiently convert solar energy into chemical energy,which is promising to reduce the pressure of energy crisis and environment pollution.Carbonized polymer dots（CPDs）is an emerging carbon-based fluorescent nanomaterials with low cost,low toxicity,strong luminescence,easy modification,good biocompatibility,photobleaching resistance and high chemical stability.Besides,because of its excellent absorption and charge transfer properties,CPDs have great prospect in photocatalytic fields.Under this research background,this research paper is aimed at the preparation of high performance CPD-based composite photocatalysts for photocatalytic degradation of pollutants and hydrogen evolution.We realize the conversion of solar energy into chemical energy and provide efficient ideas for water purification and preparation of clean energy.A series of innovative researches have been conducted for modulation of light absorption and charge separation of TiO₂ and perovskites through coupling with CPDs.We fabricate a new type of CPD/TiO₂ photonic crystals（PCs）heterostructure photocatalyst,which shows high light harvesting,charge separation efficiency,and thus high-performance photocatalytic activity.Then,a generally efficient method is developed to enhance charge separation and lifetime of MAPbI₃ perovskite via coupling with CPDs.Finally,surface reaction kinetics can be further enhanced by doping with Pt co-catalyst traces,the optimized CPD/MAPbI₃/Pt hybrid photocatalytic system exhibits an impressive H₂evolution rate of 11497μmol h^-1 g^-1,and a STH conversion efficiency of 2.15%,which are among the highest values for metal halide perovskite photocatalysts.The detailed advances are introduced in three aspects:1.In chapter II,a new TiO₂ PCs/CPD heterostructure photocatalyst is fabricated.The energy level of CPDs matches well with TiO₂ PCs,forming a type-II heterojunction.The staggered energy levels are helpful for charge separation and thus suppressed charge recombination.Besides,the CPDs with band gap of 2.08 eV efficiently broaden the light absorption range of heterostructures.Therefore,the CPDs/TiO₂ PCs heterostructures exhibit excellent light absorption and charge separation efficiency,and thus photocatalytic performance.2.In chapterⅢ,in contrast to previous works on electron pathway modulation,we find that CPDs can promote charge separation and stabilization in methylamine lead triiodide（MAPbI₃）perovskites through hole extraction.Staggered energy levels are established between CPDs and MAPbI₃.Therefore,CPDs can extract holes of MAPbI₃to increase charge lifetime,which is proved by photoluminescence（PL）,time-resolved PL,transient absorption（TA）and transient photovoltage（TPV）measurements.Compared to pure MAPbI₃,the rate of visible light–driven photocatalytic HI splitting is increased by 34.5-fold after introducing CPDs.The in-situ TPV measurements reveal that CPDs can efficiently stabilize the photo-generated charges of MAPbI₃,thus leading to enhanced photocatalytic performance.3.On the base of last chapter,we find the presented strategy of hole extraction via CPDs can be universally applied to improve the performance of all previously reported electron-manipulated MAPbI₃–based photocatalytic systems,providing a novel,facile,and generally efficient way of enhancing their efficiency.Furthermore,the surface reaction kinetics can be further enhanced by doping with Pt co-catalyst traces,the optimized CPDs/MAPbI₃/Pt hybrid photocatalytic system exhibits an impressive H₂evolution rate of 11497μmol h^-1 g^-1,and a STH conversion efficiency of 2.15%,which are among the highest values for metal halide perovskite photocatalysts.In summary,this thesis mainly focuses on the preparation of CPD-based composite photocatalysts.We use the excellent light absorption and charge transfer properties of CPDs to improve light absorption and charge separation of CPDs/semiconductor composites.We achieve high performance hybrid photocatalysts for applications in t photocatalytic degradation and hydrogen evolution through CPD modification and modulation of surface reaction rate.