A facile synthesis of Zn_xCd_1−xS/CNTs nanocomposite photocatalyst for H₂ production

The sulfide solid solution has become a promising and important visible-light-responsive photocatalyst for hydrogen production nowadays. Zn_xCd_1−xS/CNT nanocomposites were synthesized to improve the dispersion, adjust the energy band gap, and enhance the separation of the photogenerated electrons and holes. The as-prepared photocatalysts were characterized by scanning electron-microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and UV-visible diffuse reflectance spectra (UV-visible), respectively. And the effects of CNTs on structure, composition and optical absorption property of the sulfide solid solutions were investigated along with their inherent relationships. For Zn_0.83Cd_0.17S/CNTs, sulfide solid solution is assembled along the CNTs orderly, with a diameter of 100 nm or so. XPS analysis shows that there is bonding effect between the solid solutions and the CNTs due to the strong adsorption of Zn²⁺ and Cd²⁺ on the surface of CNTs. There are two obvious absorption edges for Zn_0.83Cd_0.17S/CNTs, corresponding to two kinds of sulfide solid solutions with different molar ratios of Zn/Cd. The hybridization of solid solutions with CNTs makes the absorption spectrum red shift. The photocatalytic property was evaluated by splitting Na₂S + Na₂SO₃ solution into H₂, and the highest rate of H₂ evolution of 6.03 mmol h⁻¹g⁻¹ was achieved over Zn_0.83Cd_0.17S/CNTs. The high activity of photocatalytic H₂ production is attributed to the following factors: (1) the optimum band gap and a moderate position of the conduction band (which needs to match the irradiation spectrum of the Xe lamp best), (2) the efficient separation of photogenerated electrons and holes by hybridization, and (3) the improvement of the dispersion of nanocomposites by assembling along the CNTs as well.