Design Of Cesium Lead Bromide Quantum Dot Photocatalysts For Photocatalytic CO₂ Reduction

Photocatalytic reduction of CO₂ into value-added chemical fuels is a very promising approach to address energy crisis and global warming.Metal-halide perovskite has regarded as an ideal candidate for CO₂ reduction because of its high molar extinction coefficient,low exciton binding energy and high defect tolerance,etc..In addition,perovskites have suitable energy band positions for overcoming the thermodynamic requirements of CO₂ reduction.As a new emerged photocatalyst,perovskite has exhibited huge prospect in the fields of hydrogen production（H₂）,CO₂reduction,organic synthesis,pollutant degradation and so on.In particularly,CsPbBr₃quantum dots（QDs）have attracted extensive attention in the field of photocatalytic CO₂ reduction.However,the pristine CsPbBr₃ QDs generally have low photocatalytic performance due to their serious charge recombination,instability in water and polar solvents,and low adsorption/activation capacity of CO₂.To solve the above problems,we coupled CsPbBr₃ QDs with covalent triazine frameworks（CTF）and treated CsPbBr₃ with octyramine sulfate for CO₂ reduction,respectively.The specific research contents are as follows:1.Coupling CsPbBr₃ quantum dots with CTF-1 for visible-light-driven CO₂reduction.Firstly,the ligands on the surface of the catalyst were detected by Fourier transform-infrared spectroscopy.The morphology,crystal phase and surface chemical state of the samples were characterized by transmission electron microscopy,X-ray diffraction and X-ray photoelectron spectroscopy.The charges of CsPbBr₃ and CTF-1were analyzed by Zeta（ζ）potential.It was concluded that CPB/CTF-1 was successfully prepared and the CPB and CTF-1 were coupled by electrostatic self-assembly method.By analyzing their Tauc plots,the corresponding band gaps were obtained.Mott-Schottky curves at different frequencies were used to evaluate their conduction bands（CBs）,and it was confirmed that the CsPbBr₃/CTF-1 had the appropriate CB position to meet the thermodynamic requirement of CO₂ reduction.Then,the photocatalytic CO₂reduction was carried out over various photocatalysts,and the results showed that CPB/CTF-1-Ni exhibited good photocatalytic activity for CO₂ reduction under visible light irradiation.Finally,steady-state fluorescence,transient fluorescence,in-situ electron spin resonance spectrum and photocurrent response were used to study the photoelectric properties and mechanism of the catalyst.As a result,the superior photocatalytic performance of CPB/CTF-1-Ni can be mainly attributed to synergistic interactions between CsPbBr₃ and CTF-1,which possess efficient charge-transfer efficiency and strong CO₂ adsorption.Furthermore,effective visible-light harvesting and abundant catalytic sites also contribute to the enhanced photocatalytic performance.These findings highlight the great potential of using perovskite as a platform for developing highly efficient noble-metal free photocatalytic system.Our present work provides a new approach for modulating the catalytic properties of perovskite-based photocatalysts.2.Surface modification of CsPbBr₃ quantum dots with octyramine sulfate for photocatalytic reduction of CO₂.The CsPbBr₃quantum dots were treated with octyramine sulfate by ligand exchange approach to obtain SO₄-CsPbBr₃（SO₄-CPB）.Transmission electron microscopy,X-ray diffraction and X-ray photoelectron spectroscopy were used to characterize the morphology and surface chemical state of the catalysts.It was proved that the CsPbBr₃ quantum dots have strong affinity with octylamine sulfate.Moreover,the crystal structure of perovskite was well maintained after treatment.The catalytic performance and stability of SO₄-CPB were also studied,the SO₄-CPB showed good photocatalytic activity towards CO₂reduction,which is 4times of the pristine CsPbBr₃.Various characterizations,such as photocurrent response,electrochemical impedance and water tolerance,further indicated that the adopted surface modification methodcould effectively passivate the surface defects of CsPbBr₃ quantum dots,thus reducing the non-radiative recombination,promoting the separation of photogenerated electron-hole pairs,and improving the photocatalytic CO₂ reduction performance of CsPbBr₃ quantum dots.At the same time,this surface modification approach can effectively enhance the stability of CsPbBr₃ in polar solvents（H₂O）.This work provides a facile method to improve the stability and catalytic performance of perovskite.