Designing a novel N-doped adsorbent with ultrahigh selectivity for CO2: waste biomass pyrolysis and two-step activation

In the research, N-doped cost-effective carbon dioxide adsorbents with ultrahigh selectivity are prepared using waste walnut shell pyrolysis by two-step activation and urea modification. The carbonaceous adsorbent exhibits excellent pore structure due to the catalytic degradation of H3PO4 and the etching action of KOH. The optimized sample, HAC-850-1.5, shows high CO2 adsorption 5.13 mmol/g at 0 °C. The study also indicates that nitrogen content, Vm/Vt, and porous texture characteristics play indispensable parts in impacting the CO2 adsorption of these prepared N-doped porous materials under atmospheric pressure. Furthermore, prepared carbonaceous adsorbents possess other superiorities including reasonable Qst and good recyclability and stability. It should not be overlooked that the adsorbent has a selectivity of more than 800 for CO2/N2 at low pressure, which is highly promising in CO2 adsorption through flue gas when contrasted with diverse solid adsorbents.