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Enhanced Photoinduced-Stability and Photocatalytic Activity of CdS by Dual Amorphous Cocatalysts: Synergistic Effect of Ti(IV)-Hole Cocatalyst and Ni(II)-Electron Cocatalyst

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journal contribution
posted on 2016-02-05, 00:00 authored by Huogen Yu, Xiao Huang, Ping Wang, Jiaguo Yu
CdS is one of the most well-known and important visible-light photocatalytic materials for water splitting to produce hydrogen energy. Owing to its serious photocorrosion property (poor photoinduced stability), however, CdS photocatalyst can unavoidably be oxidized to form S0 by its photogenerated holes, causing an obviously decreased photocatalytic performance. In this study, to improve the photoinduced stability of CdS photocatalyst, amorphous TiO2 (referred to as Ti­(IV)) as a hole cocatalyst was successfully loaded on the CdS surface to prepare Ti­(IV)/CdS photocatalysts. It was found that the resultant Ti­(IV)/CdS photocatalyst exhibited an obviously enhanced photocatalytic stability, namely, its deactivation rate clearly decreased from 37.9% to 13.5% after five cycles of photocatalytic reactions. However, its corresponding photocatalytic activity only showed a very limited increase (ca. 37.4%) compared with the naked CdS. To further improve its photocatalytic performance, the amorphous Ni­(II) as an electron cocatalyst was subsequently modified on the Ti­(IV)/CdS surface to prepare the dual amorphous-cocatalyst modified Ti­(IV)–Ni­(II)/CdS photocatalyst. In this case, the resultant Ti­(IV)–Ni­(II)/CdS photocatalyst not only exhibited a significantly improved photocatalytic activity and stability, but also could maintain the excellent photoinduced stability of CdS surface structure. Based on the experimental results, a synergistic effect of dual amorphous Ti­(IV)–Ni­(II) cocatalysts is proposed, namely, the amorphous Ti­(IV) works as a hole-cocatalyst to rapidly capture the photogenerated holes from CdS surface, causing the less oxidation of surface lattice S2– ions in CdS, while the amorphous Ni­(II) functions as an electron-cocatalyst to rapidly transfer the photogenerated electrons and then promote their following interfacial H2-evolution reaction. Compared with the traditional noble metal cocatalysts (such as Pt and RuO2), the present amorphous Ti­(IV) and Ni­(II) cocatalysts are apparently low-cost, nontoxic, and earth-abundant, which can widely be applied in the design and development of highly efficient photocatalytic materials.