In this study, rice husk-based activated carbon (RHAC) was prepared using a dry silica etching method instead of conventional toxic solvents to remove the silica component present in rice husk. Ammonium fluoride was used to prepare carbide (char) and simultaneously etch the silica present in rice husk. Chemical activation was then performed with potassium carbonate (K2CO3). This resulted in RHAC with a specific surface area of 1924.9 m2/g and micropores of 0.67 cm3/g. This is due to the removal of silica by ammonium fluoride and the simultaneous introduction of nitrogen and fluorine into the carbon skeleton. These introduced nitrogen and fluorine functional groups retained some of their heteroelements even after activation. The CO2 adsorption properties of RHACs were also analyzed to study the effect of pore structure and surface functional groups on CO2 adsorption. The results showed that RHACs exhibited CO2 adsorption up to 5.50 mmol/g and good CO2 selectivity for CO2/N2 gas mixtures. This was attributed to the ultra-micropore distribution below 0.7 nm and semi-ionic C-F bonds. Therefore, this study provides new possibilities for the preparation of activated carbon using rice husk and its application in CO2 adsorption.