Continuous Synthesis of Nanodroplet-Templated, N-Doped Microporous Carbon Spheres in Microfluidic System for CO₂ Capture

Microporous carbon has been widely known as a probable material to capture greenhouse gases. This work provides a facile synthesis of monodisperse biomass-derived microporous carbon spheres (CSs) for effective CO2 capture. The spheres were synthesized by a novel continuous microfluidic strategy from oil-in-water-in-oil ((O1/W2)/O2) emulsions. O1 nanodroplets could be self-assembled into the cores of micelles, which were formed by chitosan and surfactant F127 in the W2 phase through high-speed liquid-phase shearing. The obtained O1/W2 emulsion can be further sheared into a sphere by the O2 phase. After carbonization, nanodroplet-templated pores shrank to micropores and ultramicropores. The optimal sample showed the developed pore structure with a Brunauer–Emmett–Teller (BET) surface area of 576 m2/g and microporous volume of 0.22 cm3/g. Compared with O1 free CS, the dynamic adsorption capacity of CO2 was improved to 1.20 mmol/g from 0.42 mmol/g. The CO2 capture capacity, cycling stability, isosteric heats, and mass diffusion coefficient of CSs were evaluated as well. The results demonstrate that microporous CSs are promising candidates for CO2 capture with low cost and a green synthesis route, which was achieved via continuous microfluidic strategy using sustainable biomass chitosan as a carbon precursor and droplets as templates.