Probing the role of nickel dopant in aqueous colloidal ZnS nanocrystals for efficient solar-driven CO2 reduction

Photocatalytic CO2 reduction reaction (CO2RR) on a heterogeneous catalyst offers the possibility for CO2 abatement and emerges as a promising avenue for renewable carbonaceous fuels production at ambient temperature and pressure using solar light as the sole energy input. Here, we report a newly aqueous colloidal comprised of monodispersed Ni-doped ZnS (ZnS:Ni) nanocrystals as excellent visible-light-responsive photocatalysts for CO2RR into formate. The wavelength-dependent quantum yield shows a significant contribution of Ni doping for visible light activity. A high selectivity (>95%) of HCOOH production and remarkable quantum efficiency of 59.1% at 340 nm and 5.6% at 420 nm are obtained over ZnS:Ni (0.1%) colloidal nanocrystals modified by Cd2+. The proper balance between sulfur vacancies and extended visible light absorption of the constructed colloidal ZnS:Ni nanocrystals contributes to the prominent performance for CO2RR. However, excessive doping of Ni does not guarantee an increase of photocatalytic CO2RR due to a diminish of sulfur vacancies. The regulation of sulfur vacancies by Ni doping and their interplay on photocatalytic CO2RR activity are presented and discussed. This work provides an in-depth insight of the role of dopant on vacancy modulation in photocatalyst beyond light absorption and a guidance for design of the potential photocatalyst for CO2RR.