A Novel, Cost-Effective Post-Doping Method to Produce Nitrogen-Doped Activated Carbon from Rice Husk for CO2 Adsorption

Abstract

Nitrogen-doped activated carbon (N-doped AC) from agricultural waste offers a low-cost route to solid sorbents for post-combustion CO2 capture. However, there are limited straightforward and scalable methods for producing N-doped AC with a large surface area, high nitrogen content, and strong CO2 adsorption. Thus, this study aims to synthesize rice husk-derived N-doped AC by optimizing the surface morphology and nitrogen functionality to enhance CO2 capture efficiency and to quantify adsorption, correlating the gains with BET surface area and microporosity. Rice husk was carbonized via pyrrole-assisted pyrolysis at 450 ℃ for 45 min with a 90 min dwell, the carbonized rice husk was then activated chemically using a 4:1 ratio of KOH to carbonized rice husk, heated to 800℃ at a ramp rate of 15 ℃ per min under a flow of N2 gas at 150 ml/min for 60 min, Subsequently, N- doping was performed by immersing the activated carbon in a urea solution with a mass ratio of 4:1 (urea solution to AC) at 600℃ for 60 min. The obtained N-doped AC exhibits a remarkable surface area of 2986.6 m²/g and a significantly enhanced CO₂ adsorption capacity of 6.5 mmol/g under ambient conditions. Incorporating approximately 6% nitrogen into the carbon structure optimizes its porosity and structural properties. The integrated carbonization, activation, and urea post- doping sequence provides a reproducible pathway to high-performance, waste- derived CO2 sorbents, highlighting rice husk as a viable feedstock and underscoring the synergistic roles of micro/mesoporosity and nitrogen functionalities in boosting physisorption-dominated CO2 capture.