Enhanced VOCs adsorption mechanism on biochar synthesized by one-step molten salt thermal treatment: Experimental and DFT insights.

Synthesizing high-performance biochar adsorbents through facile and sustainable methods represents an effective strategy for the removal of volatile organic compounds (VOCs). This study introduced a one-step thermal treatment method using molten salt for the rapid synthesis of biochar from biomass. Compared to conventional processes for activated carbon production, the proposed method offers a simpler and more energy-efficient route. Adsorption experiments demonstrated that biochar consistently achieved superior adsorption capacities for benzene, toluene, and chlorobenzene over business activated carbon across various temperatures and concentrations, specifically achieving a maximum adsorption capacity of 691.88 mg/g for chlorobenzene at 30 °C. Density Functional Theory calculations further indicated the adsorption mechanism at the molecular level, supporting the experimentally observed adsorption hierarchy, in which chlorobenzene exhibited stronger adsorption than toluene, followed by benzene. The results also confirmed that surface oxygen-containing functional groups played a crucial role in significantly enhancing the adsorption of VOCs. The presence of oxygen-containing functional groups increases the number of active sites and the electrostatic potential on the carbon surface, thereby enhancing the biochar adsorption capacity for VOCs. Notably, hydroxyl groups, acting via hydrogen bonding, and lactone groups, acting via electrostatic interactions, were particularly effective, with an overall efficacy order of hydroxyl > lactone > semiquinone. These findings imply that molten salt heat treatment is a rapid and clean method for synthetic biochar with high specific surface area reaching 1851.72 m2/g, a total pore volume of 0.92 cm3/g, and oxygen content of up to 15.20 %.