Function of tannin and droplet template in microfluidic system to synthesize carbon capsules for carbon dioxides capture: Promoting hierarchical porous structure and nitrogen content

Abstract

Nitrogen(N)-doped porous carbon is one of the most efficient materials for carbon dioxide (CO₂) capture, but its synthetic techniques face certain limitations in the synergy of N doping and pore formation. This study proposes a simple microfluidic approach to synthesize N-doped porous carbon capsules (CCs) using chitosan (CTS) as bio-carbon and N precursor, with tannin serving as N-doping promoter by enabling amination reaction with CTS through droplet-templated pore-forming strategy. Compared to CCs synthesized without droplet templates and tannin, the optimum sample showed a developed hierarchical pore structure, with micropore volume increasing from 0.155 cm³/g to 0.26 cm³/g. Moreover, the optimum sample exhibited increased micropore and mesopore volumes, and the N content rose from 2.46 at.% to 3.67 at.% simultaneously, the corresponding CO₂ uptake amount raised from 1.03 mmol/g to 1.40 mmol/g. Compared to the sample without tannin, the optimized sample exhibits a breakthrough adsorption capacity that is 1.13 times higher. These results demonstrated that, owing to its crosslinking with surfactant Pluronic® F127 and inhibitory effect on N-containing compound release, tannin enhances in-situ N incorporation in CTS to increase surface N content, and synergistically with droplet-template improve hierarchical pore structure of CCs. This work provides a facile approach for N-doped porous bio-carbon applicable to CO₂ capture.