No abstract

Recently, graphitic carbon nitride (g-C 3 N 4 ) has been investigated as a photocatalyst for water splitting and organic dye degradation. In this study, we have developed a simple soft-chemical method of doping Zn into g-C 3 N 4 to prepare a metal-containing carbon nitride. The doping was confirmed by x-ray photoelectron spectroscopy, and diffusion reflectance spectra revealed a significant red shift in the absorption edge of Zn/g-C 3 N 4 . This hybrid material shows high photocatalytic activity and good stability for hydrogen evolution from an aqueous methanol solution under visible light irradiation (λ 420 nm). The hydrogen evolution rate was more than 10 times higher for a 10%-Zn/g-C 3 N 4 sample (59.5 µmol h −1 ) than for pure g-C 3 N 4 . The maximum quantum yield was 3.2% at 420 nm.

Under visible light irradiation (λ g 420 nm), photocatalytic water reduction for hydrogen generation was achieved over Eosin Y sensitized multiwalled carbon nanotube (MWCNT)/Pt catalyst with triethanolamine (TEOA) as the electron donor. The highest apparent quantum yield reached 12.14%. Dilute HNO 3 treated MWCNT catalyst exhibited a higher hydrogen generation rate than a concentrated HNO 3 treated one. Characterization results indicated that HNO 3 treatment led to formation of -COOH and -OH on MWCNT, which provided anchoring sites for Eosin Y. The results of photocurrent, photoluminescence, and photocatalytic experiments indicated that MWCNT trapped photogenerated electrons and inhibited the recombination of electron-hole pairs. MWCNT in catalyst might work as a charge-transfer carrier. The catalysts presented rather stable properties for hydrogen generation in a long-term run.

Developing photocatalysts with a high-efficiency charge separation remains a challenge in the solar hydrogen production. Herein, we devised and prepared a unique 2D/2D heterojunction of CuInS2/ZnIn2S4 nanosheets for solar hydrogen evolution. Structural characterizations reveal that the CuInS2/ZnIn2S4 2D/2D heterojunction with lattice match consists of the thin thickness of nanosheets and has a large interface contact area, boosting charges transfer and separation. Benefiting from the favorable 2D/2D heterojunction structure, the CuInS2/ZnIn2S4 2D/2D heterojunction photocatalyst with 5 wt % CuInS2 yields the highest H2 evolution rate of 3430.2 μmol·g–1·h–1. In addition, the apparent quantum efficiency of 5%CuInS2/ZnIn2S4 2D/2D heterojunction reaches 12.4% at 420 nm, which is high among the ZnIn2S4-based 2D/2D heterojunctions. The enhanced photocatalytic H2 evolution comes from the boosting charge separation. This work demonstrates that a 2D/2D heterojunction provides a potential way for significantly improving the solar hydrogen production performance of ZnIn2S4.