Soybean hulls activated carbon for metronidazole adsorption: Thermochemical conditions optimization for tailored and enhanced meso/microporosity

Abstract

In this work, the use of soybean hulls as a residual biomass precursor for highly porous carbon materials through thermochemical treatments was assessed, aim to modify the surface chemistry and obtain enhanced chemistry and textural properties for the metronidazole (MTN) drug adsorption. Initially, the biomass was subjected to different chemical treatments followed by pyrolysis under fixed conditions. The modified carbon materials were evaluated in terms of residual surface charge, surface chemistry, and adsorption capacity. After determining the most appropriate chemical treatment, the optimized thermochemical conditions were investigated. Remarkable textural properties (Stotal= 1355.7 m2 g−1) of the activated carbon derived from dilute acid-alkali combined treatment (AC-CT) were achieved under the following conditions: T = 925 °C; t = 145 min and C= 0.3 mol L−1, which led to an increase in the adsorption capacity up to q= 51.25 mg g−1 (50% higher than the biochar). This increase in MTN adsorption performance is possibly related to the increase in the micropore area (SMICRO= 800.7 m2 g−1) and volume values, in addition to a tailored and narrow pore size distribution with an adequate size ratio to the MTN molecule (ØP/ØMTN= 2.3 – 2.6). Based on the results, it was identified that this tuned pore size distribution and the presence of surface oxygen groups provided adequate affinity to the MTN molecule due to H–bonds, π–interactions, and pore-filling effect retention mechanisms.