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 S 0 by its photogenerated holes, causing an obviously decreased photocatalytic performance. In this study, to improve the photoinduced stability of CdS photocatalyst, amorphous TiO 2 (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 S 2− 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 H 2 -evolution reaction. Compared with the traditional noble metal cocatalysts (such as Pt and RuO 2 ), 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.

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Compared with stable-phase hexagonal CdS, the metastable cubic CdS photocatalyst usually shows a lower H2-evolution performance under visible-light irradiation. Thus, the widely reported high-performance CdS photocatalysts are mainly focused on the hexagonal phase, while the cubic-phase CdS with a high H2-evolution activity has seldom been concerned. In this study, a direct precipitation method in a sulfur-rich Na2S–Na2SO3 system has been developed to prepare the suspensible cubic-phase CdS nanocrystal (c-CdS-NC) photocatalyst with a high H2-evolution activity. In this case, the resultant c-CdS-NC with a small crystal size (ca. 5 nm) and high specific surface area (>75.23 m2/g) exhibits a stable and suspensible photocatalysts due to the massive and preferential adsorption of S2–/SO3 2– ions on the nanocrystal surface. Photocatalytic results indicated that the suspensible c-CdS-NC photocatalysts clearly exhibited an obviously higher H2-evolution performance (0.36 mmol h–1) than the traditional hexagonal CdS (0.14 mmol h–1) by a factor of 2.6 times. Based on the present results, a S2–/SO3 2–-mediated mechanism was proposed for the enhanced H2-evolution performance of the suspensible c-CdS-NC, namely the massive adsorbed S2– ions on the suspensible c-CdS-NC surface not only promote the rapid capture of photogenerated holes but also can work as the effective active sites for H2-evolution reaction. The present work may provide important insights for developing high-performance photocatalytic materials.

Metal chalcogenophosphates are receiving increasing interest, specifically as promising infrared nonlinear optical (NLO) candidates. Here, a rare-earth chalcogenophosphate Eu 2 P 2 S 6 crystallizing in the monoclinic noncentrosymmetric space group Pn was synthesized using a high-temperature solid-state method. Its structure features isolated [P 2 S 6 ] 4À dimer, and two types of EuS 8 bicapped triangular prisms. Eu 2 P 2 S 6 exhibits a phase-matchable second-harmonic generation (SHG) response � 0.9 × AgGaS 2 @2.1 μm, and high laser-induced damage threshold of 3.4 × AgGaS 2 , representing the first rare-earth NLO chalcogenophosphate. The theoretical calculation result suggests that the SHG response is ascribed to the synergetic contribution of [P 2 S 6 ] 4À dimers and EuS 8 bicapped triangular prisms. This work provides not only a promising high-performance infrared NLO material, but also opens the avenue for exploring rareearth chalcogenophosphates as potential IR NLO materials.