Adsorption of volatile organic compounds on biochar: A review

Remarkable industrial advances and urbanization have resulted in rapid increase in aromatic volatile organic compound (VOC) generation, causing significant environmental contamination, human health hazards, and considerable resource waste. Hence, scientific VOC reduction methods are necessary. Adsorption is considered efficient and cost-effective in this regard because the adsorbent and adsorbate are retrievable and reusable. Owing to abundant feedstock, cost-effectiveness, and advantageous physical-chemical surface features, biochar demonstrates immense potential for effective VOC adsorption. Herein, typical methods for VOC adsorption, biochar production processes, key variables affecting VOC adsorption on biochar, VOC adsorption mechanisms on biochar, competitive adsorption of multicomponent VOCs on biochar, and comparison of activated carbon and biochar are discussed. The chemical, physical, and structural characteristics of biochar are affected by feedstock properties, production parameters (especially pyrolysis temperature), and modification methods. Surface structure and functional groups, specific surface area, pore volume, and pore size distribution of biochar affect VOC adsorption rate and capacity. Variable pore sizes within biochar enable selective physical adsorption of VOCs based on molecule size, while specific surface functional groups facilitate chemical adsorption. Biochar's capacity for the adsorption of mixed VOCs depends on adsorption affinity, vapor pressure, and VOC characteristics. High surface area per pore volume of biochar enhances VOC sorption, but competitive inhibition reduces the total adsorbed VOC mass, particularly for light VOCs. The results contribute to our understanding of the potential of renewable sources for VOC adsorption and underscore the need for further research to completely realize biochar as a sustainable solution for air pollution.