Fabrication of robust and bifunctional cyclotriphosphazene-based periodic mesoporous organosilicas for efficient CO2 adsorption and catalytic conversion

Abstract The design and development of advanced functional materials for efficient absorption and selective conversion of carbon dioxide (CO2) remains a challenging research topic. In this work, novel cyclotriphosphazene-based periodic mesoporous organosilicas (PMO-CPF) with various contents of active components and tunable porosity were successfully prepared via direct co-condensation method, and their structures were characterized by FT-IR, solid-state 13C, 29Si and 31P NMR, XRD, N2 adsorption–desorption, HR-TEM and TGA techniques. The PMO-CPFs as-prepared were applied for CO2 adsorption and conversion into cyclic carbonates, and the adsorption capacity and catalytic behaviors were thoroughly investigated. The PMO-CPFs integrate the structural features of high specific surface area, Lewis basic units and multiple dual hydrogen bond donor (HBD) groups, which endow the materials with dual functions of CO2 adsorption and epoxide activation by forming dual hydrogen bonds. The optimum PMO-CPF-20 combining with tetrabutylammonium iodide (TBAI) showed an excellent activity for the cycloaddition of CO2 to propylene oxide (PO), and could afford 98% propylene carbonate (PC) yield with above 99% selectivity under the conditions of 90 °C and 2.0 MPa for 6.0 h. Moreover, the catalyst reusability and applicability to epoxides with different substituents were studied, and a feasible catalytic mechanism was finally proposed. The developed metal-free, robust and bifunctional mesoporous organosilicas here were suggested to be advanced materials for CO2 adsorption and subsequent catalytic conversion.