Renewable N-doped microporous carbons from walnut shells for CO2 capture and conversion

The development of advanced porous carbon-based materials is a burgeoning field, especially for CO2 capture and utilization. In this research, renewable, microporous granular nitrogen-doped carbons were prepared by KOH activation of melamine modified walnut shells making use of two different protocols at a relatively low pyrolysis temperature (650 °C). The microporous carbons had a 0.6–1.5 nm micropore size and exhibited high surface areas of 949–2847 m2 g−1. Furthermore, the synthesized microporous carbons manifested a good capacity to capture CO2 owing to the existence of a large number of narrow micropores and nitrogen-bearing functionalities. The equilibrium CO2 capture capacities of these carbons at 1 atm were respectively in ranges of 4.1–6.6 and 2.7–4.0 mmol g−1 at 0 °C and 25 °C. Even in a CO2/N2 mixture, it exhibited a high selectivity for the capture of CO2 with a separation factor of 19. Thanks to its excellent CO2 adsorption capability, the incorporation of Ag(0) nanoparticles makes it serve as an efficient catalyst for the conversion of propargylic alcohols with CO2 into carbonates via a cycloaddition reaction under mild conditions. The sorbent has a multitude of advantages including the ease of its synthesis, high CO2 uptake capacity, low cost, regenerability, and selectivity, which demonstrate that great potential is manifested by nanoporous nitrogen-doped carbon for CO2 capture and utilization.