Effects of UV Light Treatment on Functional Group and Its Adsorption Capacity of Biochar

This study aimed to investigate the impact of UV treatment on the surface functionality and adsorption capacity of biochar, with the goal of enhancing its effectiveness as an adsorbent for toluene. The surface and near-surface functionality and structure of biochar were studied to evaluate the impact of UV treatment by utilizing X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and Brunauer–Emmett–Teller (BET) techniques. Biochar was generated by pyrolyzing wood chips at 900 °C without any oxidant injection in order to increase their carbon content. To boost biochar’s adsorption capability, UV irradiation on the biochar is utilized before and during the penetration process. Toluene was selected as the target absorbing material. The equilibrium adsorption capacity and rate were simulated using the Wheeler equation. It was found that the adsorption capacity of biochar increased significantly after pretreatment with ultraviolet light irradiation with a wavelength of 254 nm and an intensity of 280 μW/cm2 and reached a saturated state after 15 h. SEM and XPS showed that the UV-biochar modification technology not only improved the pore structure of biochar, but also increased the content of -O-containing functional groups on the surface of biochar and improved the adsorption capacity of biochar. The experimental results for sample M50_Uu demonstrated significant improvement in adsorption performance. The adsorption saturation time increased by 80%, and the equilibrium adsorption capacity rose from 12.80 mg/g to 54.60 mg/g. The main reason for the adsorption capacity increase by UV treatment is functional group formation, of which rate linearly increases with pretreatment energy until 11 W·hr/gbiochar, after which the increase rate is slow.