Preparation And Properties Of Cd-based Semiconductor Materials For Photocatalytic Reduction Of Uranium

There are two main problems limiting the development of nuclear energy.The first is the limited available amount of uranium,which would only cover about 70years of global nuclear energy consumption.Secondly,the process of nuclear energy development and utilization accompanied a serious pollution to environment,especially a large amount of radioactive uranium mainly in the form of hexavalent uranium（U（VI））with great migration poured into water.However,the detection and recovery U（VI）from uranium-containing wastewater is still a challenge.Therefore,this study takes CdS nanobelts and CdSe nanosheets as example,through simply element doping,greatly improving the photocatalytic reduction ability of U（VI）.According to the bandgap structure analysis of materials,we summarize the reasons for their efficient photocatalytic reduction of U（VI）.The main conclusions are as follows:（1）In order to improve extraction amount of U（VI）by CdS nanobelts photocatalyst,we synthesized CdS_xTe_1-x nanobelts capped by ethylenediamine（EDA）,which provided amino groups as the adsorption sites.Specifically,the incorporation of Te^2-narrowed the bandgap of CdS-EDA nanobelts,accompanying with the reducing chemical valance of Cd²⁺,further modulating the Cd²⁺ligand complexation with EDA.The balanced the factors of amino groups and bandgap revealed that the optimum photocatalytic activity of CdS_xTe_1-x nanobelts was achieved at a 5%of Te^2-doping,and the CdS_0.95Te_0.05-EDA nanobelts exhibited a considerable U（VI）removal ratio of 97.4%with a remarkable equilibrium U（VI）extraction amount on per weight unit of the adsorbent（q_e）of 836 mg/g.This adsorption-photoreduction process offers an ultrahigh uranium extraction capacity over wide uranium concentrations.（2）For the CdSe nanosheets photocatalyst with narrow bandgap structure,due to the low concentration of photogenerated carrier,which leading the low utilization of photogenerated electrons.The crystal structure of pristine CdSe nanosheets was the mixture of sphalerite and wurtzite,through the elemental doping of Ag into CdSe nanaosheets,the crystal structure of Ag doped CdSe nanosheets gradually changed tosphalerite.The change of crystal structure narrowed the bandgap of CdSe nanosheets and meets the energy of photocatalytic reduction of U（VI）,which enhanced the light absorption ability and improved the generation and utilization of photoelectrons and holes.In photocatalytic reduction of U（VI）,the 3%Ag-CdSe nanosheets exhibited a considerable selectivity of U（VI）with a remarkable q_e of 765.2 mg/g.This strategy that through elemental doping to change the crystal structure of materials,further optimize the bandgap structure,which can be applied to other materials with multiple crystal structures.To enhance the utilization rate of photogenerated carriers of semiconductor materials,we optimized the semiconductor bandgap structure through simple element doping and improved the photocatalytic reduction efficiency of CdS nanobelts and CdSe nanosheets.This study summarizes the relationship between the bandgap structure of semiconductor materials and the photocatalytic reduction of uranium,and hopes to develop other semiconductor materials for the application of photocatalytic reduction of uranium.