Potential role of biochar in advanced oxidation processes: A sustainable approach

Biochar, a multifaceted and sustainable carbonaceous material has gained extensive research attention over the past couple of decades in advanced oxidation processes (AOP) owing to its tunable physico-chemical properties. This review explores biochar and biochar based catalyst preparation strategies, its multifunctional role in AOPs with special emphasis on the mechanisms involved in the activation of hydrogen peroxide, persulfate and peroxymonosulfate as well as its sequence towards degradation process. Pyrolysis is the most widely employed method for biochar preparation as the desired properties can be acquired by wisely choosing pyrolysis temperature and feedstock. High conductivity, enormous surface area, active functional groups and porous structure obtained via pyrolysis instigate the biochar to function like a catalyst, a support and cathode material for the degradation of organic contaminants. Moreover, pyrolysed biomass contains persistent free radicals necessary for reactive oxygen species (ROS) generation which are the key contributors in AOPs. Biochar modified with metallic and non-metallic components play synergistic action in ROS generation, electron transfer, adsorption and oxidation of pollutants. Biochar based catalysts are less explored for sulphate radical mediated degradation of pollutants when compared to hydroxyl radical based degradation. Bottlenecks and research gaps that will open a way to explore novel and fruitful inventions in this field are provided finally.