Green synthesis of porous biochar with interconnected pore architectures from typical silicon-rich rice husk for efficient CO2 capture

Abstract

Carbon capture is an effective solution to reduce the emitted CO2 from the burning of fossil fuels. However, the intrinsic tradeoff between activator selection and narrow pores for CO2 capture, as well as the difficult design of pores according to the biomass natural structure, greatly limits the CO2 capture capacity. To overcome those issues, for the first time, porous biochar with precisely narrow pores (0.36 and 0.59 nm) and nanocapsules structure was assembled by coupling the merit of typical silicon-rich waste rice husk and low-corrosive potassium citrate for CO2 adsorption application. The narrow ultramicropore was obtained and verified by CO2 and N2 molecular probes. Potassium citrate activated biochar exhibited an excellent gravimetric CO2 capture capacity of 1.55 mmol/g, which was 1.35 and 2.04 times higher than potassium citrate self-assembled and KOH-activated samples, respectively. The as-synthesized potassium citrate activated biochar exhibited high CO2/N2 selectivity of 37.80 (1 bar, 25 °C) and regeneration efficiencies above 99 % after 10 cycles. In combination with TG-FTIR, SEM and XRD, key CO2 capture mechanisms were proposed: 1) CO2 is encapsulated in the nanocapsules structure (∼1 μm) and enters the interior carbon matrix skeleton with narrow ultra-micropores (Vultra = 0.213 cm3/g); 2) CO2 tends to be absorbed in interconnected channel formed by tailoring the external SiO2 nanoparticles and internal organic carbon. This strategy could provide a new insight to guide the pores design according to biomass natural structure for efficient CO2 capture.