Synthesis of porous carbon xerogel adsorbents with tailored hierarchical porosity and morphology for the selective removal of sulfamethoxazole from water.

In this work, pellet-type carbon xerogel adsorbents (CXCs) were synthesized through sol-gel polymerization of resorcinol (R) and formaldehyde (F) using Cs2CO3 (Cs) as a catalyst for the removal of sulfamethoxazole (SMX), a hazardous water pollutant. The R/Cs ratio was varied at 100, 500, 1000, and 2000 (denoted CXCs100, CXCs500, CXCs1000, and CXCs2000), resulting in CXCs with a well-defined hierarchical porous structure composed of interconnected spherical particles. Increasing the R/Cs ratio led to larger spherical particle sizes, with pore diameters ranging from 60.7 to 126.6 nm, providing accessible and low flow resistance macroporosity. The maximum adsorption capacity was achieved in the CXCs100 sample (87.8 mg/g), which decreased with increasing R/Cs ratios due to a reduction in total pore volume and meso and macropore areas, indicating that adsorption occurred in macropores and wide mesopores, driven by π-π dispersive interactions. CXCs500 emerged as the optimal adsorbent, with a favorable adsorption capacity (72.0 mg/g) and adequate rigidity (315.9 MPa) to prevent adsorbent breakdown. The adsorption capacity decreased with increasing pH due to electrostatic interactions, and increased with temperature, indicating an endothermic process.