Synthesis And Characterization Of Photocatalysts Base On Cesium Lead Halide Perovskite Nanocrystals

With the exhaustion of petrochemical energy and the increasingly prominent environmental problems,it is urgent to develop new clean sustainable energy technologies.Converting carbon dioxide?CO₂?into chemical fuels with sunlight is a very promising approach,the key of this technique is to develop efficient visible-light response photocatalysts.As a new type of semiconductors,metal halide perovskites?e.g.,perovskites?are excellent candidate for photocatalytic reactions with many excellent photoelectronic properties,including strong visible light absorption,tolerance to defects,high absorption coefficient,tunable band gaps,low production costs and easy solution processing.Furthermore,most perovskites have suitable conduction band and valence band edges,which can meet the thermodynamic requirements of CO₂ reduction.In the last decade,perovskites have achieved great successes in the fields of solar cells and LEDs.As a new emerging research field,the perovskite-based photocatalysts has great progress,especially in CO₂ reduction.However,the catalytic performance of perovskites is still remain low,which is mainly due to the serious charge recombination and the lack of efficient catalytic active sites for targeting reaction.In view of the above problems,we proposed two strategies involving coupling cocatalysts and doping transition metal ions,which provide specific catalytic sites and regulate charge carrier kinetics of perovskites,respectively.The specific research contents are as follows:?1?High quality CsPbBr₃ nanocrystals?NCs?were synthesized via hot-injection method,and the coupling of metal complex?Ni?tpy??was used as catalytic site for photocatalytic CO₂ reduction.First,the as-synthesized CsPbBr₃ nanocrystals was modified with PF₆^-through ligand exchange?PF₆-CsPbBr₃?.Then the Ni?tpy?were immobilized onto the perovskites.The ligand species on the perovskite surface were detected by fourier transform-infrared spectra,and the assembly mechanism of CsPbBr₃-Ni?tpy?was analyzed by combining Zeta???potential.The morphology and phase of the samples were characterized by UV-vis absorption spectrum,X-ray photoelectron spectroscopy,transmission electron microscopy and X-ray diffraction.The energy band structure of CsPbBr₃ nanocrystals were calculated by Tauc plot and Valence-band X-ray photoelectron spectroscopy,which confirms that the energy band positions of perovskite satisfies the thermodynamic condition of CO₂ reduction.At the same time,the cyclic voltammetry of Ni?tpy?was dected in Ar and CO₂atmospheres,respectively,which indicated that Ni?tpy?had catalytic activity for CO₂reduction.The CsPbBr₃-Ni?tpy?catalytic system achieves a high yield?1724?mol/g?in the reduction of CO₂ to CO/CH4,which is approximately 26-fold higher than that achieved with the pristine CsPbBr₃ NCs.This work has developed a method for enhancing the performance of photocatalytic CO₂ reduction by immobilizing metal complexes on perovskite NCs.The methodology we present here provides a new platform for utilizing halide perovskite NCs for photocatalytic applications.Further investigations revealed the electron transfer kinetics between the CsPbBr₃ NCs and Ni?tpy?through time-resolved fluorescence decay?TRPL?and transient absorption?TA?spectra.We demonstrated that the coupling of metal complexes is a promising strategy to improve the photocatalytic properties of perovskite NCs.This strategy also provides a platform for designing precious metal-free photocatalysts for CO₂reduction..?2?We synthesized the Mn²⁺doped CsPbCl₃ nanocrystals through a modified hot-injection method andstudy the role of long-lived carriers regulated by Mn²⁺in CO₂.By doping Mn²⁺in CsPbCl₃,new energy levels can be introduced into the energy band of CsPbCl₃.These doped energy levels can effectively trap photogenerated charge carriers and prolong carrier lifetime?from nanoseconds to milliseconds?,thus suppressing electron-hole recombination and improving spatial separation of charge carriers.These long-lived charge carriers provide sufficient time for reaching the surface of perovskite for catalytic reactions.In this work,the morphology and phase of the catalyst samples were characterized by transmission electron microscopy,UV-vis absorption spectrum,X-ray photoelectron spectroscopy,and X-ray diffraction,revealing that the morphology and crystal structure of Mn:CsPbCl₃ nanocrystals remain intact.The PL lifetime of Mn:CsPbCl₃ centered at580 nm was remarkable prolonged to 1.77 ms.As a result,the catalytic performance of the Mn:CsPbCl₃ was 3 times higher than that of the CsPbCl₃.This work provides an new strategy for altering the charge carriers transfer routes for photocatalytic CO₂reduction.