P-N Coupled Semiconductor CoO/CdS Sensitized TiO₂as Photocatalyst For Hydrogen Production From Water Splitting Under Visible Light Irradiation

In recent years, with the global energy crisis and environmental pollution becoming moreserious, utilizing solar energy to produce hydrogen, which is a kind of clean, efficient andrenewable energy, from photocatalytic water splitting has attracted considerable attentions. Inthis work, we studied the preparation technique of CoO, prepared p-CoO/n-CdS and CdS/TiO₂composite photocatalysts, and synthesized CoO/CdS/TiO₂composite photocatalysts by usingp-CoO/n-CdS to sensitize TiO₂. The composite photocatalysts were characterized by XRD,UV-Vis, BET, SEM, TEM and Electrochemical workstation. The photocatalysis of productingH2from water splitting under visible light irradiation and the photocorrosion of CdS were alsodiscussed. The detailed contents are as follows:In this paper, the CoO particle was prepared by calcining cobaltous acetate in N₂atmosphere, and the preparating conditions of CoO were also investigated. The best preparatingcondition was calcined at300℃for3h with the flow rate of N₂being70ml/min. At thiscondition, the purity of CoO reaches the highest.A series of p-n coupled p-CoO/n-CdS photocatalysts with different mass ratios wereprepared by an impregnation method. The p-n coupled photocatalyst were characterized byXRD, UV-Vis, SEM, TEM, and electrochemistry technology. The photocatalytic activities ofthe photocatalysts under visible light irradiation were evaluated by photocatalytic hydrogenproduction. The results indicated that the photocatalytic activity of p-CoO/n-CdS was notablyincreased compared to that of CdS. The photocatalysts had higher hydrogen production ratewith Na₂SO3/Na₂S as sacrificial agent than HCOOH as sacrificial agent. When theconcentration of Na₂S was0.8M,0.7wt%CoO/CdS had the greatest hydrogen productionamount, with a hydrogen evolution rate of up to170.2μmol g^-1 h^-1. What’s more, thephotocatalysts had stabled photocatalytic activity and the photocorrosion rate of CdS wasreduced effectively by forming p-n coupled photocatalyst.Five kinds of TiO₂/CdScomposite photocatalysts with different mass ratios were preparedusing anatase TiO₂coupled with CdS. The composite photocatalysts were characterized byXRD, UV-Vis, SEM and electrochemistry technology. The result of hydrogen production fromwater splitting under visible light irradiation showed that TiO₂/CdS composite photocatalystshad higher photocatalytic activity than CdS. When the compound quantity of TiO₂was20wt%,the photocatalyst had the maximum hydrogen production rate, and it could reduce thephotocorrosion rate a little more effectively than pure CdS.Finally, CoO/TiO₂/CdS composite photocatalysts with different mass ratios were preparedby an impregnation method. The products were characterized by XRD, UV-Vis, BET, SEM andelectrochemistry technology. The photocatalytic property of the ternary compositephotocatalysts under visible light irradiation was investigated. The results showed that for theefficient separation of photoexcited electron-hole by p-n and n-n semiconductor, thephotocatalytic activity of CoO/TiO₂/CdS composite photocatalysts was much better than pureCdS, CdS/TiO₂and CoO/CdS, and they had good photocatalysis stability.0.7wt%CoO/TiO₂-20/CdS had the highest hydrogen production rate in the solution of Na₂SO3/Na₂Swith the value of276μmol·g^-1·h^-1, and0.9wt%CoO/TiO₂-20/CdS had the highest hydrogenproduction rate in the solution of28vol%HCOOH with the value of366.27μmol·g^-1·h^-1. And the photocorrosion of CdS in CoO/TiO2/CdS could be control more effectively.