Selectivity Reversal from CO to Ethylene Products in CO2 Photoreduction via Electronic Modulation of SnS2 Using a Vinyl-Bridged Porous Organic Polymer.

Developing an efficient and robust photocatalyst for optimal C2+ product generation from carbon dioxide (CO2) is a pressing need in advancing solar fuel production. In this study, we designed an ionic vinylene-bridged conjugated porous organic polymer (Py-POP) enriched with charged pyridine groups via a quaternization-promoted Knoevenagel condensation reaction. The resulting positively charged polymeric framework with shape-persistent nanochannels enabled the uniform assembly of SnS2 units through ionic interactions mediated by amino and sulfhydryl groups. The hybrid porous photopolymer (SnS2@Py-POP) converts CO2 into ethylene with a rate of 34.7 μmol g-1 h-1 with a selectivity of ethylene around 78.7% under visible light photoirradiation, which outperforms all the C2 selective Sn-based photocatalysts. Our findings principally sheds light on the mechanism of selectivity reversal (from C1 to C2 product) by hybrid catalyst framework engineering. In-depth investigations by synchrotron-based X-ray absorption spectroscopy (XAS) and morphological analysis via high-resolution transmission electron microscopy (HRTEM) reveal the nature of interaction for hybrid heterostructure formation within the porous network. Electron transfer pathways were mapped using time-resolved photoluminescence (TRPL) and transient absorption spectroscopy (TAS), which revealed a Z-scheme electron transfer mechanism. This mechanism facilitates enhanced electron accumulation on the SnS2 layer, promoting efficient CO2 activation and subsequent C-C coupling, ultimately leading to ethylene formation. Furthermore, the ethylene formation mechanism has been investigated in detail by time-resolved diffuse reflectance infrared spectroscopy (TR-DRIFTS), corroborated with density functional theory (DFT). This study opens a new avenue for achieving selectivity reversal in a C1 selective photocatalyst through electronic modulation enabled by the formation of an inorganic-organic hybrid heterostructure.