Solvent‐Free Ball Milling Synthesis of Water‐Stable Tin‐Based Pseudohalide Perovskites for Photocatalytic CO ₂ Reduction

A pseudohalide (SCN^-) tin-based perovskite material using a solvent-free ball milling method is developed. The synthesized perovskite exhibits long-term water stability and demonstrated significant photocatalytic activity in reducing CO₂ to CO under light irradiation. The structural transition from nanoparticles to planar perovskites is achieved by varying the ratios of dimethylammonium (DMA) and formamidinium (FA) cations, which is confirmed by X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses. The surface elemental distribution, absorption spectra, band gap and energy levels estimations using energy-dispersive X-ray spectroscopy (EDS), Kubelka-Munk function, and ultraviolet photoelectron spectroscopy (UPS) are thoroughly investigated. These findings indicated that the incorporation of DMA cations increased the band gap and shifted the absorption spectra toward the blue region. The optimal photocatalytic performance is observed for the perovskite composition with a 50% DMA cation ratio (DMA_0.5FA_0.5SnI(SCN)₂), achieving a CO production yield of 285 µmol g^-1 with 12 hours irradiation in humid environment. The efficiency is critically dependent on the ball milling speed and duration, with 400 rpm and 1 hour being the optimal conditions. This research highlights the potential of environmentally friendly synthesis methods in developing stable and efficient lead-free perovskites as photocatalytic materials, contributing to the goal of net-zero carbon emissions.