Porous nitrogen-doped biochar derived from ZIF-8-assisted pyrolysis of bamboo for efficient adsorption of SO2

Structural modification is a necessary means to improve the adsorption performance of biochar. A simple, efficient, and well-applicable modification method is often expected. In this study, zeolitic imidazolate framework (ZIF-8)-assisted pyrolysis of bamboo was employed to prepare modified biochar for improving its SO2 adsorption performance. The physicochemical characteristics of biochars before and after modification were investigated and their SO2 adsorption behaviors were examined using a fixed bed adsorption system. The results showed that the surface heteroatoms and pore structure parameters of biochar modified by ZIF-8-assisted pyrolysis were significantly improved, with nitrogen content and surface area increasing from 1.3 wt% and 49.6 m2/g to 4.2 wt% and 557.4 m2/g, respectively. Among all tested conditions, the modified biochar obtained through ZIF-8-assisted pyrolysis at 700 °C exhibited not only the highest SO2 adsorption capacity (166 mg/g) but also a remarkable increase (up to 121 %) compared with pristine biochar under identical pyrolysis temperature conditions. Moreover, it exhibited good regeneration performance, with an adsorption efficiency of over 93 % after 8 cycles of SO2 adsorption and desorption. Combined with characterization results regarding physical and chemical properties before and after SO2 adsorption, it can be concluded that improved pore structure and the presence of polar ZnO on the surface are primarily responsible for promoting SO2 adsorption onto modified biochar, resulting in the final existence as SO32− rather that SO42−.