Single crystal CdS nanowires with high visible-light photocatalytic H2-production performance

Abstract

Single crystalline hexagonal CdS nanowires were prepared by a solvothermal method using ethylenediamine as a solvent. Pt/CdS nanocomposites were produced by different reduction methods and characterized by X-ray diffraction, transmission electron microscopy, high-resolution transmission electron microscopy, UV-visible spectroscopy, nitrogen absorption, pulse H₂ chemisorption and X-ray photoelectron spectroscopy. The photocatalytic performance of the as-synthesized Pt/CdS nanocomposites was evaluated towards H₂ generation from a lactic acid aqueous solution under visible light (λ ≥ 420 nm). The sample prepared by the NaBH₄ reduction method showed a higher photocatalytic H₂-production activity than the sample prepared by the photo-reduction deposition method. A remarkable H₂-production rate of 1.49 mmol h⁻¹ with a quantum efficiency (QE) of 61.7% was first achieved on the former with a small amount of Pt (0.3 wt%) as a co-catalyst. The photocatalytic activity difference of the samples is because reduction methods influence the size and dispersion of Pt nanoparticles (NPs), which further influence the photocatalytic H₂-production activity. The sample from the NaBH₄ reduction method contains smaller Pt NPs (ca. 1–2 nm) and has higher Pt dispersion (72%), thus resulting in the higher H₂-production activity. Further experiments showed that the one-dimensional nanostructure markedly enhanced the photocatalytic H₂-production activity of CdS. After ball milling of the nanowires, which leads to destruction of their structure, the photocatalytic H₂-production activity of CdS decreases by more than 30%. The underlying mechanism for the observed photocatalytic H₂-production performance of Pt/CdS nanocomposites was discussed.