Focusing on the high-valued utilization of the widespread silicon-rich waste biomass, a sustainable route by simultaneous utilization of carbon and silicon from silicon-rich rice husk was proposed in this work. Specifically, porous carbon-zeolite composite with hierarchical porous structure of micro/meso pores (carbon) and ultra-microporous pores (Na-X zeolite) was in situ prepared by a facile one-pot method. The obtained porous carbon-zeolite composite (PC2-Z) had a higher yield of 67.66% compared to the porous carbon without silicon (PC2) of 43.33%. Moreover, due to the high ultra-micropore volume of the PC2-Z sample (up to 0.181 cm3/g), it exhibited high dynamic CO2 adsorption capacity of 1.81 mmol/g and CO2/N2 selectivity of 9.80 (1 bar), which were higher than 1.67 mmol/g and 7.01 (1 bar) for PC2, respectively. PC2-Z also showed good regeneration efficiency above 99% after ten cycles. Furthermore, the economic and energy consumption assessment of this utilization route was conducted. Overall, a facile one-pot route was developed to prepare highly efficient composite absorbents from silicon-rich biomass, which can be widely used in different environmental applications.