Preparation Of Ion-Doped ZnS Photocatalyst And Its Performance In Hydrogen Production From Water Decomposition

The rapid development of industry has brought the problem of energy shortage,and fossil fuel combustion process emits a lot of waste gas,great harm to the environment,so it is urgent to develop renewable clean energy.Hydrogen,has the advantages of renewable and zero carbon emissions,is a very ideal green energy.Photocatalytic decomposition of water to produce hydrogen with semiconductor material is a very effective technology to convert solar energy into hydrogen energy.As a typical semiconductor,Zn S has been widely studied,but the wide band gap limits its absorption of sunlight and it has low carrier separation efficiency,resulting in poor photocatalytic performance of Zn S.Element doping is an effective strategy to broaden the optical absorption range of semiconductor materials and promote photogenerated carrier separation.In this paper,element doping was used to modify Zn S to enhance its photocatalytic decomposition activity of aquatic hydrogen,and the mechanism of enhancing its performance was systematically studied.Various metal ion doped zinc sulfide photocatalysts were prepared using hydrothermal method,and the phase composition,morphology,optical properties and electronic structure of the catalysts were analyzed by XRD,SEM,TEM,XPS,UV-vis DRS,PL,electrochemistry,etc.The photocatalytic performance of the catalysts was tested,and the reaction mechanism was studied.The main research contents and achievements of this paper are as follows:（1）A series of Zn S microspheres surface-doped with Co²⁺were synthesized by a simple hydrothermal reaction,and the effects of Co surface doping on the photocatalytic activity and electronic structure of Zn S were systematically studied.In the prepared Co-doped Zn S photocatalysts,the concentration of Co ion increases gradually from inside the sample to the surface.Co²⁺doping results in the formation of impurity levels above the valence band,and the conduction band moves upward,the band gap decreases,and the visible light absorption is enhanced,and the efficiency of carrier separation and migration is improved.The surface electronic structure of catalyst was changed,and reduces the absolute value of hydrogen binding free energy（ΔG_H）of adsorbed hydrogen atoms on the catalyst.Therefore,Zn S doped with Co surface showed higher photocatalytic hydrogen production activity than pure Zn S material.（2）The transition metal ions(Cu²⁺,Co²⁺)with valence states and ion radii similar to Zn²⁺were homogeneously and surfacely doped with Zn S by a simple hydrothermal reaction,respectively,named H-MZn S and S-MZn S(M=Cu²⁺,Co²⁺).The practical mole ratio of the dopant M in H-MZn S and S-MZn S is the same as that of Zn（determined by ICP）,and no vacancy is generated,which eliminates the interference of doping concentration and associated vacancy.Surprisingly,all of the ion surface-doped catalysts showed higher photocatalytic activity than the corresponding uniformly doped catalysts,including the decomposition of water to produce hydrogen and the reduction of CO₂to CH₄and CO.Experimental and theoretical results show that surface ion doping has greater advantages than uniform ion doping in accelerating charge separation and enlarging H₂evolution dynamics,even under the condition of reduced light absorption.In addition,Ag⁺and Cr³⁺were uniformly and surface-doped into Zn S,respectively,and associated vacancy were found.However,the photocatalytic performance of surface-doped catalysts was still superior to that of homogeneous doped catalysts.