Preparation And Photocatalytic Properties Of Cubic/Hexagonal Cadmium Sulfide Nanomaterial

Nowadays,with the increasing demand for energy to ensure human activities,the traditional ways to obtain energy supply is no longer able to meet the enlarged needs.Confront with energy crisis and environmental contamination,it is urgent to find alternative technologies for clean renewable energy.Photocatalysis,driven by sunlight over semiconductor materials,is an ideal solution for solar energy to chemical energy transformation.Many efforts have devoted to photocatalytic reactions such as water splitting for hydrogen production,CO₂ reduction for hydrocarbon production and pollutants degradation for environment remediation.However,developing highly efficient photocatalysts with visible light response is crucial but still challenging for promoting this technique to industry.Cadmium sulfide(Cd S)is a kind of semiconductor material with a narrow band gap ca.2.4 e V.The optical absorption band edge of Cd S reaches about 550 nm,which is readily for visible light response.Cd S has been widely used in the fields of energy conversion and environment remediation.However,Cd S still suffer from low efficiency and poor stability caused by photo-corrosion and carrier recombination.Studies have shown that the construction of phase/phase junctions can effectively promote charge separation,improve photocatalytic performance,and enhance the stability of photocatalysts.Cd S has several different crystal structures.Cubic Cd S(ZB-Cd S)is in a metastable state,only stable structure at lower temperature;hexagonal crystal Cd S(WZ-Cd S)is more stable than the cubic ones thermodynamically at high temperature.In this research,a one-step solvothermal method was developed to construct the cubic phase/hexagonal phase junction of Cd S using selected solvent to control the growth of crystals.The physical properties were characterized,proving that the synthesized Cd S consists of both cubic and hexagonal phase.The conditions were detailed investigated to uncover the influence on crystal growth and consistence of two phases.The catalytic performance of Cd S samples with different phase consistence were evaluated by HER reactions.With consciously tuning the ratio of two crystal phases,the best photocatalytic activity was obtained.We also gain a better knowledge on structure-efficiency relationship,which will contribute to our design for synthesizing high performance photocatalysts.(1)Cd S nanomaterials with hexagonal(WZ)and cubic(ZB)phases were synthesized by one-step solvothermal method.With the increase of EG/DMSO ratio,the product changed from single cubic phase to ZB/WZ phase coexistence.The characterization of XRD,TEM and UV-Vis showed that the Cd S nanomaterials prepared by this method had two-phase structure and grain size is about 3?5 nm,and it has good absorption to visible light.The effect of reaction time on the properties of the materials was studied by selecting the optimal solvent ratio.The results show that when the reaction time increases from 3 to 24 hours,the ZB/WZ phase coexists gradually,and there is a certain grain growth orientation.Under visible light irradiation,the optimal photocatalytic activity of the material is 7.96 mmol?g^-1?h^-1,and the quantum efficiency is 36.7%at420nm,which is three times of that of any single phase sample(cubic or hexagonal phase),and the material maintains good stability within 50 hours.The mechanism of photocatalytic hydrogen production was obtained by analyzing the energy band of the materials.WZ and ZB constructed the I-type heterojunction,which enhanced the separation efficiency of photogenerated electron hole and improved the photocatalytic performance of the material.(2)Several other solvents were mixed with DMSO to control the polarity of mixed solvents for further investigation on phase control and size effect of Cd S synthesis.The nanostructure of obtained catalysts was characterized by XRD,TEM,FTIR,Raman.The results show that the crystal structure and properties of Cd S nanomaterials are changed due to the difference of dielectric constant and polarity of different solvents,and the higher the polarity will lead to the formation of mixed crystal phase junction.The photocatalytic HER performance was carried out under visible light irradiation.The catalyst synthesized using H₂O/DMSO mixture as solvent gives best activity.62.04mmol?g^-1H₂ formed in 5 hours,which is 6 times higher than the catalyst synthesized in DMSO.However,the stability of the catalyst synthesized in H₂O/DMSO with high activity is not as good as the catalyst synthesized in EG/DMSO.One possible explanation is that the highly active phase was easily corroded under irradiation.