Preparation Of Two Kinds Of CdS Nanorod Herterogeneous Structures And Their Photocatalytic Performances For Hydrogen Production

While global structure of energy updating,green,clean,sustainable,new energies represented by solar are taking more and more important role in social development.The conversions from solar to chemical energies,such as thermal energy,electricity and hydrogen energy,are mostly accomplished by semiconductor cells which makes usage,transportation and storage of solar available.Cadmium sulfide is a kind of semiconductor with narrow band gap and able to be excited by visible light??<520 nm?which is suitable for catalyzing the decomposition of H₂O and producing hydrogen.But,one of CdS disadvantages is easy to be oxidized by photogenerated holes leading to the instability under illumination.In this work,heterogenous structure was composed by two methods based on CdS nanorod arrays to promote photocatalytic performance and stability,corresponding to hydrogenated thermal treatment and hydrolyzation.Simultaneously,the reaction mechanism and influence of heterogenous structure were analyzed combining characterization results.The main contents and conclusions were shown as follow.?1?While heating and injecting H₂/N₂,CdS were able to react with electric coating of FTO producing nanocomposites which contained CdS/SnS/SnO₂ ternary heterogeneous structure.Based on systematic research of temperature and time during hydrogenation,the optimal hydrogenating conditions were 450?and 2 h related to CdS NRAs-H₂-2 whose photocurrent was 12 mA·cm^-2,which is 1.5 times than CdS NRAs-N₂.As shown in the results of photocatalytic hydrogen production under visible light??>400 nm?,the initial and five-cycles speed of hydrogen production to the optimal CdS NRAs-H₂-h were 23.3?mol·cm^-2·h^-11 and23.7?mol·cm^-2·h^-1.To CdS NRAs-N₂,the initial and five-cycles speed were 20.0?mol·cm^-2·h^-1and 11.5?mol·cm^-2·h^-1.Therefore,heterogenerous structure formed during hydrogenation was beneficial to improve photocatalytic avtivity of CdS and especially to stability.Within heterojunction energy bands alignning like staires,the photogenerated electrons of CdS could rapidly transfer to SnO₂ and photogenerated holes of CdS could transfer to SnS which could suppress CdS self-corrosion and restrain recombination of chargers.Hydrogenated thermal treatment was a simple way to synthesis nanocomposites aiming at improvement of photocatalytic performance.?2?TiO₂ coating was loaded on the surface of CdS nanorods by hydrolyzation with the formation of CdS/TiO₂ binary heterogeneous structure.The key of TiO₂ coating being uniform was absorbing surfactant before hydrolyzation whose thickness was controlled by reaction time.The acid environment caused by TiCl₃ hydrolyzing could corrode the surface of CdS nanorods formatting holes.On the one hand,acid corrosion leaded to the amount of CdS decreasing and surface trapes increasing.On the other hand,interface between CdS and TiO₂ was enlarged which accelerated formatting compact heterogeneous structure.Sample CdS@TiO₂-72persisted optimal photocatalytic performance with 72 hours of hydrolyzation and its five-cycle speed of hydrogen production was 28.4?mol·cm^-2·h^-11 which was approximate 68%of initial speed.As to CdS NRAs-N₂,its five-cycle speed of hydrogen production was 8.86?mol·cm^-2·h^-11 which was approximate 36%of initial speed.Thus,CdS@TiO₂heterogeneous structure loaded on the surface of CdS nanorods could efficiently enhance photocatalytic activity and stability of CdS.As shown in structure analyzing,partial photoelectrons of CdS would transfer to the conduction band of TiO₂ which stimulated the separation of photogenerated chargers.Simultaneously,the diffusion of CdS self-oxidative products was depresssed because of tight cottony TiO₂ coating,such as S,etc.Whatsmore,CdS mainly aborted visible light which was scattered and transmitted by cottony TiO₂ coating so the stability of CdS could be enhanced in a way.