Review of the Adsorption of Sulfur-Containing Gaseous Pollutants by Biochar: Progress, Challenges, and Perspectives

Sulfur-containing gaseous pollutants (e.g., H2S, SO2, and COS) emitted from various industries are important sources of air pollution. Because of the advantages of a simple and clean process, renewability of adsorbent, and cheap raw materials, adsorption removal of sulfur-containing gaseous pollutants by biochar has a good development prospect. However, due to scarce active functional groups and active sites on biochar and an underdeveloped pore structure, the development and application of biochar are still limited in this field. Activation and modification of biochar are one of the most effective ways to raise biochar surface active sites and active functional groups, and improve the pore structure of biochar. This paper reviews the recent research progress of activation and modification methods of biochar for adsorbing sulfur-containing gaseous pollutants (H2S, SO2, and COS). Various activation and modification methods are classified and summarized, including acid/alkali activation, microwave activation, metal oxide modification, nitrogen doping modification, and other emerging modification methods. The main process parameters, advantages, and disadvantages of each modification and activation method are introduced in detail. The activation and modification mechanisms as well as the adsorption mechanisms of pollutants are also discussed and summarized. Among these methods, photochemical modification technology has the advantages of a simple and clean process and low energy consumption, and especially it can simultaneously produce oxygen-containing functional groups on the carbon surface and improve the biochar pore structure, showing superior development prospects. This review will provide needed guidance and inspiration for researchers in related areas to develop new biochar-based desulfurization adsorbents.