Surface engineered active photocatalysts without noble metals: CuS–ZnxCd1−xS nanospheres by one-step synthesis

CuS(y)–ZnxCd1−xS (where 0.3 ≤ x ≤ 0.8, 0% ≤ y ≤ 15.8%) nanospheres with a Zn and Cu-rich surface were synthesized via a one-step method in ethylene glycol. Structural, morphological and optical properties of the samples have been investigated by XRD, TEM, XPS, ICP, N2 physisorption and UV–vis DRS techniques. The cubic phased nanospheres of approximately 20–30 nm in diameter are comprised of nanocrystals of about 5 nm. Due to the reactivity difference among the metal ions in the organic solvent, the surface of the nanospheres was found enriched with Zn and Cu sulfide layers. In the absence of Cu, sample Zn0.65Cd0.35S gives a H2 production rate of 29 μmol/h under the irradiation of a 300 W Xenon lamp with a cut-off filter (λ ≥ 420 nm) in aqueous solutions containing S2− and SO32−. The activity, which can only be increased by four times by a traditional Pt cocatalyst for the as-prepared Zn0.65Cd0.35S sample, can be enhanced by around 20 times to 550 μmol/h and 624 μmol/h after adding 5.9 mol% and 11.1 mol% (metal basis) of Cu during the synthesis to form a Cu-rich surface. It is believed that the surface Cu2+ 3d impurity levels can function as the same role of the noble metal cocatalysts as charge accommodation sites for the charge separation, and hence increase the photocatalytic performance for water splitting.