Modification Of Cadmium Sulfide Quantum Dots And Their Application In Photocatalysis

As China proposes to achieve peak carbon dioxide emissions before 2030,the further development and utilization of clean energy is a top priority.In recent years,the use of semiconductor photocatalysts to absorb light,and then to fix light energy into chemical energy through water splitting,carbon dioxide reduction,biomass conversion and other reactions has become a research hotspot.Cadmium sulfide quantum dots(CdS QDs)are an excellent light-absorbing material with a series of advantages,such as excellent energy band position,good visible light absorption ability,large specific surface area,abundant surface adjustable sites,extremely high extinction coefficient,etc.So,it is widely used in photocatalytic reactions.As a photocatalyst,for CdS QDs,two problems should be solved in the process of practical application:One is to inhibit the recombination of photogenerated carriers,promote the separation of photogenerated electrons and photogenerated holes,and improve their reactivity;the second is to inhibit the photocorrosion of cadmium sulfide and improve its reaction life.In this paper,we modified the synthesized CdS QDs by means of bulk doping,ligand grafting,coordinate bond anchoring,etc.,and greatly improved the photocatalytic efficiency or photocatalytic lifetime of cadmium sulfidebased catalysts by improving the separation of photogenerated electrons and holes.The main results achieved are as follows:1.Doping cadmium sulfide quantum dots with transition metal ions and using them as catalysts for photocatalytic reduction of carbon dioxide.We obtained Ni2+ and other transition metal ion-doped CdS QDs using a one-pot method to achieve a highly selective photocatalytic reaction of CO2(the products only have CO and CH4 without hydrogen).The catalyst has excellent durability at 60 hours.Doping Ni sites into the CdS lattice can effectively trap photoexcited electrons as surface catalytic sites and can greatly suppress the release of H2.This method can be extended to various transition metal sites,and this work provides a new reference for exploring quantum dot-based photocatalysts prepared from earth-abundant elements.2.By the method of ligand grafting,the ligands of CdS QDs are connected with the ligands of copper clusters to form an electron transport channel between the CdS QDs and the copper clusters(Cu clusters).Through fluorescence spectroscopy.X-ray photoelectron spectroscopy and other tests,we proved that at short wavelengths(<280 nm),Cu clusters would absorb light and transfer photogenerated charges to CdS to enhance the photoluminescence of CdS quantum dots;At longer wavelengths(～370 nm-450 nm),the photogenerated charges of CdS QDs are transferred to Cu clusters.This phenomenon is not limited to CdS QDs,but can also be extended to other quantum dots.In the photocatalytic splitting of water to produce hydrogen,the quantum dotcluster composite catalyst achieved a 40-fold increase in the yield of pure quantum dots.3.The-CS2 group was modified on the ligand of the ruthenium complex,and then connected to the cadmium sulfide quantum dots through coordination bonds,which was used as a photocatalyst for the photocatalytic oxidation of 5-hydroxymethylfurfural(HMF).The catalyst oxidizes HMF under different atmospheres to obtain completely different main products.Under argon,2,5-diformylfuran is obtained,while under air,5-hydroxymethyl-2-furancarboxylic acid is obtained.In both cases,we obtained high HMF conversion(>81%)and high major product selectivity(>90%).After validation,this system can be extended to the selective oxidation of other compounds with hydroxyl and aldehyde groups.