Squaramide-derived framework modified periodic mesoporous organosilica: A robust bifunctional platform for CO2 adsorption and cooperative conversion

Novel periodic mesoporous organosilica with different concentrations of squaramide-derived framework (PMO-SAF) were prepared and structurally characterized. They were applied to CO2 capture and conversion into cyclic carbonates under mild and metal/solvent-free conditions. The PMO-SAFs as prepared possess favorable structure features of high specific surface area, Lewis basic units and dual hydrogen bond donor groups, they showed interesting synergistic effects for both CO2 adsorption and epoxide activation. By regulating structure of the PMO-SAFs, an enhanced CO2 uptake capacity was obtained under a low CO2 pressure. The catalytic behaviors of PMO-SAFs on the model cycloaddition of CO2 to propylene oxide, including reaction parameters optimization, catalyst reusability and versatility were investigated in detail, and excellent yield (98%) and selectivity (99%) to propylene carbonate were obtained under the optimized reaction conditions of 90 degrees C and 2.0 MPa for 7.0 h. Moreover, the PMO-SAF-catalyzed reaction mechanism was proposed according to the results obtained. The special design of the PMO-SAFs endows the material with robust structure, dual-functions of CO2 adsorption and transformation, displaying great significance to the design of multi-functional nanomaterials.