Biochar-based activation of peroxide: multivariate-controlled performance, modulatory surface reactive sites and tunable oxidative species

• Intrinsic knowledge on modification of biochar and ROS generated on its surface were included. • Reactive sites on biochar to activate peroxide were comprehensively summarized. • Co-doping of redox-metals and heteroatoms emerged as a novel strategy to modify biochar. • Boron doped biochar with satisfactory reactivity was firstly involved in review papers. • Future prospects and research needs were proposed based on the summary. Recently, biochar emerged as a promising peroxide activator due to its chemical-saving/facile synthesis processes, high efficiency, tunable physicochemical properties and capacity to endow both radical and non-radical oxidative species. However, serious knowledge gaps and controversies have been raised on the mechanism to modulate reactive sites on its surface and dominated reaction pathways in biochar-involving systems. Insight understanding of the activation processes will remarkably advance its functional synthesis and application in practical wastewater treatment. Therefore, this paper aims to provide an up-to-date review on application and modification of biochar activator to alter their reactive sites and physicochemical properties and design their synthesis processes to achieve a satisfactory performance. Also, formation of reactive oxidative species on various reactive sites was discussed. Lastly, future research directions on evaluation and improving the physicochemical properties of biochar catalysts were proposed as well as their potential applications in real wastewater systems.