One-Step Synthesis of In Situ Sulfur-Doped Porous Carbons for Efficient CO2 Adsorption

Abstract

Porous carbons for CO2 capture were synthesized from a sulfur-rich bituminous coal via a one-step method concurrently including carbonization and KOH activation. The activation parameters were controlled by varying KOH/coal mass ratios (1:1, 2:1, and 3:1) and temperatures (700 °C, 800 °C, and 900 °C) to optimize their CO2 capture performance. The surface physicochemical structural properties of these porous carbons were characterized by applying a Brunauer–Emmett–Teller (BET) surface area analysis, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy, and Raman spectroscopy. The results show that the SBET of sample SCC-800-3 is as high as 2209 m2/g, the CO2 adsorption capacity of sample SCC-700-2 at normal temperature and pressure reaches 3.46 mmol/g, and the CO2/N2 selectivity of sample SCC-700-1 reaches 24. The synergistic effect of moderate activation conditions ensures optimal pore evolution without compromising sulfur species retention. Furthermore, these porous carbons also demonstrate excellent cycling stability and thermal stability. The fitting of the adsorption isotherm model for all samples were further conducted. Adsorption isotherm modeling demonstrated superior fitting accuracy with the dual-parameter Freundlich and tri-parametric Redlich–Peterson formulations across all samples, indicating that the CO2 capture by high-sulfur coal-based porous carbons belongs to multilayer adsorption and the carbon surface is heterogeneous. The CO2 adsorption on porous carbon exhibits spontaneous, exothermic behavior according to the thermodynamic data. These findings confirm the great potential of high-sulfur coal-based porous carbons on the capture of CO2. The presenting research provides a strategy that leverages the synergistic effect of in situ sulfur doping and milder activation conditions, achieving the high-efficiency utilization of high-sulfur coal resources and developing low-cost CO2 capture materials.