l-Cystine-assisted hydrothermal synthesis of Mn1−xCdxS solid solutions with hexagonal wurtzite structure for efficient photocatalytic hydrogen evolution under visible light irradiation

Abstract

A series of Mn_1−xCd_xS solid solutions with hexagonal wurtzite structure have been fabricated with the assistance of L-cystine as the S source and chelating reagent via a facile hydrothermal route at a lower temperature (130 °C). The as-synthesized products are characterized by XRD, TEM, HRTEM, EDS, XPS, ICP, FTIR, UV-vis and BET techniques, while the photocatalytic activities of the solid solutions for H₂ evolution from water decomposition are evaluated in the presence of Na₂S–Na₂SO₃ as sacrificial reagents under visible light illumination. The photocatalytic H₂ evolution is found to be strongly dependent on the ratio of CdS to MnS as well as the band gap energies. Among all samples, the highest photocatalytic activity is observed on the Mn_0.24Cd_0.76S photocatalyst, with the rate of H₂-production of 10.9 mmol h⁻¹ g⁻¹, corresponding to an apparent quantum yield as high as 9.5% at 420 nm even in the absence of co-catalysts, which far exceeds that of CdS. Moreover, Mn_0.24Cd_0.76S solid solution also displays good stability and anti-photocorrosion capability during the photocatalytic reduction of water to hydrogen under visible light. The excellent photoactivity of Mn_0.24Cd_0.76S solid solution is mainly related to the band-gap structure as well as large specific surface area and high crystallinity. The proposed hydrothermal method using L-cystine as the S source provides a simple, cost-effective and environmentally friendly approach to fabricate other multi-component chalcogenide solid solutions.