Synthesis And Properties Exploration Of Zn_0.2Cd_0.8S-based Photocatalysts

In the context of increasing global energy demand,declining fossil fuel reserves and increasingly harsh climate,photocatalytic hydrogen evolution has become a potential technology for renewable energy.The development of new photocatalysts with visible light response,high photostability,low cost and high efficiency has become a current research focus.ZnxCd1-xS solid solution is widely used in the application of hydrogen evolution reaction by water splitting due to its advantages such as adjustable band gap and suitable conduction band potential.On the one hand,this project improves the photocatalytic hydrogen production performance of Zn0.2Cd0.8S by adjusting the process parameters in the preparation process.On the other hand,it combines Zn0.2Cd0.8S with graphene oxide(GO)and graphitic carbon nitride(g-C3N4),and suppress the rapid recombination of photogenerated electron-hole pairs through the interaction of two semiconductor materials.(1)Zinc acetate dihydrate(Zn(CH3COO)2·2H2O),cadmium acetate dihydrate(Cd(CH3COO)2·2H2O)and thiourea were used as raw materials.Hydrofluoric acid(HF)was used as morphology control agent to realize the controlled growth of dendritic Zn0.2Cd0.8S with exposed {002} active faces.The effects of reaction temperature and time on the morphology and properties of Zn0.2Cd0.8S were studied.The results shown that the addition of HF made Zn0.2Cd0.8S grow in the direction perpendicular to the c-axis and expose {002} active faces to promote the improvement of hydrogen production performance.When the reaction temperature was 180 ℃and the reaction time was 18 h,the flakes of Zn0.2Cd0.8S were the largest and thinnest,and the average hydrogen production rate was the highest,reaching 3100.3 μmol h-1 g-1.It can be concluded that the dendritic Zn0.2Cd0.8S solid solution was a promising visible-light-driven photocatalyst.(2)The prepared pure-phase Zn0.2Cd0.8S photocatalyst was compounded with GO by a two-step method to obtain a Zn0.2Cd0.8S/rGO composite material.The effects of reaction time,amount of GO and surfactants on the photocatalytic performance of Zn0.2Cd0.8S/rGO materials were studied.The results shown that the addition of GO made the photoinduced electrons in Zn0.2Cd0.8S transfer to GO,confined electrons and holes in different phases,and promoted the separation of electrons and holes.At the same time,the addition of GO increases the visible light absorption intensity of the photocatalyst.The photocatalytic performance of Zn0.2Cd0.8S/rGO was the best when reacting for 18 h,adding 2 mg of graphene,and without surfactants,reaching 4514.7 μmol h-1 g-1.(3)Zn0.2Cd0.8S and g-C3N4 were compounded to form Zn0.2Cd0.8S/g-C3N4 material.By constructing a type Ⅱ heterojunction,the photoinduced electrons of g-C3N4 with a more negative conduction band potential were transferred to the conduction band of Zn0.2Cd0.8S,and the holes in the valence band of Zn0.2Cd0.8S with a more positive valence band potential were transferred to the valence band of g-C3N4.The results shown that the construction of type Ⅱ heterojunction realized the efficient separation of photoinduced electrons-holes pairs,thereby improving the performance of hydrogen evolution reaction by water splitting.The hydrogen production efficiency of Zn0.2Cd0.8S/g-C3N4 with 40 wt%of g-C3N4 was the highest,reaching 21.73 mmol h-1 g-1,which was 16 and 7 times higher than that of single phase g-C3N4 and Zn0.2Cd0.8S.