Coalescing solar-to-chemical and carbon circular economy: mediated by metal-free porphyrin and triazine-based porous organic polymer under natural sunlight

Abstract

Harnessing renewable solar energy to valorize CO₂ has emerged as a promising and enduring solution to address energy and environmental challenges. However, achieving high efficiency and selectivity in the photocatalytic reduction of CO₂, without relying on metals, photosensitizers, or sacrificial agents, remains a formidable hurdle. In the continuing pursuit of sustainable synthesis, in this study, we present the development of a novel metal-free photocatalyst, composed of porphyrin and a triazine-based porous organic polymeric network (TPT-porp) for the photocatalytic reduction of CO₂ coupled with oxidative benzylamine homocoupling under natural sunlight for the first time. Astonishingly, we achieved an exceptional CO production rate, reaching 1786 μmol g⁻¹ h⁻¹, with an outstanding selectivity of >90% and selective oxidation of benzylamine, yielding N-benzylbenzaldimine with a conversion of 65% and selectivity exceeding 98% in 6 h of irradiation under natural sunlight. A remarkably high AQY of 9.34% (at λ = 430 nm) and solar-to-fuel conversion of 0.24% was attained for CO production. A series of controlled experiments, EPR studies, ¹³CO₂ labelling experiments, and DFT studies were employed to unravel the underlying mechanism of this dual photoredox process. In summary, our pioneering study opens up unprecedented avenues for the investigation of metal-free photocatalysts capable for dual photoredox processes, and these findings offer tremendous potential for advancing the field of sustainable photocatalysis.