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 °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.