S-Scheme Co9S8@Cd0.8Zn0.2S-DETA Hierarchical Nanocages Bearing Organic CO2 Activators for Photocatalytic Syngas Production

Delicate modulations of CO2 activation and charge carrier separation/migration are challenging, yet imperative to augment CO2 photoreduction efficiency. Herein, by supporting diethylenetriamine (DETA)-functionalized Cd0.8Zn0.2S nanowires on the exterior surface of hollow Co9S8 polyhedrons, hierarchical Co9S8@Cd0.8Zn0.2S-DETA nanocages are fabricated as an S-scheme photocatalyst for reducing CO2 and protons to produce syngas (CO and H-2). The amine groups strengthen adsorption and activation of CO2, while the "nanowire-on-nanocage" hierarchical hollow heterostructure with an S-scheme interface boosts separation and transfer of photoinduced charges. Employing Co(bpy)(3)(2+) as a cocatalyst, the optimal photocatalyst effectively produces CO and H-2 in rates of 70.6 and 18.6 mu mol h(-1) (i.e., 4673 and 1240 mu mol g(-1) h(-1)), respectively, affording an apparent quantum efficiency of 9.45% at 420 nm, which is the highest value under comparable conditions. Ultraviolet photoelectron spectroscopy, Kelvin probe, and electron spin resonance confirm the S-schematic charge-transfer process in the photocatalyst. The key COOH* species responsible for CO2-to-CO reduction is detected by in-situ diffuse reflectance infrared Fourier transform spectroscopy and endorsed by density functional theory calculations, and thus a possible CO2 reduction mechanism is proposed.