Generating promising materials for the conversion of CO2 to valuable industrial products under mild conditions is important for both ameliorating the greenhouse effect and sustainable development. Pillar[5]arene-incorporated materials have recently emerged as building frameworks to construct versatile functional polymeric materials. Herein, we demonstrate that highly efficient fixation of CO2 to cyclic carbonates can be achieved by employing a novel pillar[5]arene-based Co(III)-loaded covalent organic polymer (COP) as a heterogeneous catalyst (Co(III)–P5COP). The catalyst was created first by condensation of bromo-functionalized pillar[5]arene and a Schiff-base derivative (BHPD–OH) to afford the pillar[5]arene-based COP (P5COP), followed by loading Co(III) to prepare the target material bearing abundant salen–Co(III) sites. Results of catalysis with various substrates reveal excellent catalytic performance for CO2 cycloaddition with the conversion and selectivity of cyclic carbonate reaching up to 96 and 99%, respectively, under mild conditions of 30 °C and 1 atm CO2. Moreover, Co(III)–P5COP exhibits general applicability to other bulky epoxides. The polymeric pillar[5]arene-based catalysts could be easily recovered and reused without marked loss in their activity. Therefore, the marriage of Co(III)–salen and the pillar[5]arene platform constitutes a feasible approach to offering easily accessible and macrocycle-based new materials for the conversion of CO2 to valuable products.

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The production of tetraethyl orthosilicate (TEOS) from biomass provides a new way for TEOS production and biomass valorization. In this study, rice straw was treated using different fractionation methods, and the content, state, and reactivity of Si in the treated samples were investigated. It was found that acid treatment and ethanol extraction kept most Si in the biomass, while alkali treatment caused significant Si loss. Si was mainly present in the SiOx, Si−O−C, and Si−O−Si states in the surface of raw rice straw, cellulose and Klason lignin. The results showed that the Si−O−Si state in rice straw was beneficial for the formation of TEOS. The removal of lipids from rice straw facilitated the production of TEOS, giving the highest TEOS yield of 76.2 %. In contrast, the production of TEOS from other samples became difficult; the simultaneous conversion of the three organic components of rice straw also facilitated the production of TEOS.

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