In this study, nitrogen-tailored hierarchical meso-/micro-porous activated carbons were successfully fabricated from cypress sawdust by H3PO4 activation with further nitrogen modification using three kinds of nitrogen source (i.e. nitic acid, urea and melamine). The produced carbons were used as adsorbents for CO2 capture. The physic-chemical properties of the produced carbons were characterized by N2 adsorption-desorption, fourier-transform infrared spectroscopy, scanning electron microscopy and X-ray photoelectron spectroscopy. The effects of pore structure and nitrogen content on CO2 adsorption were investigated. It was found that H3PO4 activation would turn cypress sawdust into mesoporous carbon (AC), nitrogen doping could induce the development of microporosity and also increase the basicity of the carbon framework, which favoured for CO2 adsorption. Among the nitrogen-tailed carbons, HNO3-treated activated carbon (AC-N) showed the highest V mic (0.127 cm3/g), the largest CO2 adsorption capacity (2.8 mmol/g at 273 K, 1 bar) and the best CO2/N2 selectivity as compared to urea and melamine treated ones. The adsorption experiments showed that the presence of microporosity and pyrrolic-N on the carbons were responsible for CO2 adsorption, the oxygen functional groups on AC-N might also contribute to higher CO2 uptake, and the mesoporous structure could favour for the fast mass transfer of CO2. The results of CO2 adsorption heat confirmed the high affinity of the prepared carbons to CO2. This study provides a strategy to produce hierarchical meso-/micro-porous activated carbons with enriched nitrogen functional groups, which favoured for CO2 adsorption.
Keywords: CO2 adsorption; Hierarchical structure; activated carbon; cypress sawdust; nitrogen functional groups.