Influence of activation conditions on the physicochemical properties of activated biochar: a review

The biochar produced from agricultural crop residues through thermochemical processes helps in crop waste management. Biochar has paid more attention due to its distinctive features such as high organic carbon content, stable structure, large surface area, and cation exchange capacity. The biochar obtained from crop residues can be readily converted into activated biochar. This review paper systematically summarised the preparation of activated biochar, characterisation, and analytical techniques of activated biochar based on more than 150 literatures published in the last 10 years. The physicochemical properties of activated biochar varies according to the type of feedstock, pyrolysis condition, and mode of activation. The selection of the activation method mainly depends on its further end environmental application. Physical activation or steam purging at high temperature creates pores inside biochar. Gas purging increases the surface area and pore volume, although steam activation is not much suitable to improve the BC surface functionality as compared to chemical and impregnation activation. Sulphuric and oxalic acid–modified biochar was found to be most suitable for the soil amendment. Alkaline activation enhances the surface area and oxygen-containing functional group in activated biochar. Metal oxide–modified biochar had better surface functionalities than did physical- and chemical-activated biochar and better sorption of organic and inorganic contaminants from potable water and waste water. In summary, activated biochar has a wide environmental prospect in remediation.