Porous Fluorocarbon from Rice Husk for the Efficient Separation of Gases

A porous fluorocarbon sorbent is synthesized from rice husk (RH) in a microwave reactor and then evaluated for the adsorption of different gases (CH₄, CO₂, and N₂). The fluorocarbon is characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), Raman spectroscopy, Thermal gravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS). Significant enhancement in the surface area of activated carbon material is obtained from 29 to 531 m² g^-1 after removing naturally present silica in RH. Results reveal that rice husk fluorocarbon (RHF) has a higher adsorption affinity for CO₂ (1.8 mmol g^-1) than that of the sulfonated rice husk (RHS) (1.4 mmol g^-1) at 298 K while the corresponding separation factor of CO₂/CH₄ is 4 and 3; respectively. Higher separation factors of 12 and 10 are observed for the binary system of CO₂/N₂, respectively. Quantum chemical density functional theory (DFT) calculations agree with the experimental observations. They reveal that RHF exhibits strong columbic interactions with considerable interaction energies of -87.85, -76.75, and -55.65 kcal mol^-1 with CO₂, CH₄, and N₂ gases; respectively. Finally, the adsorption process results are highly reproducible, with a small decrease in the adsorption capacity of less than 5% after repeated trials.