Melamine-assisted hierarchical nitrogen-doped biochar from garlic peel hydrochar as efficient adsorbent for tetracycline removal

The acumulation of antibiotics in water shows high risk towards human health, and it is important to form hierarchical porous biochar with prominent superiority in mass transfer to improve removal ability. Here, garlic peel as biowaste was converted into mesoporous biochar under the assistance of melamine, showing surface areas of 3011 m²/g with main mesopores at around 2.4 nm and acting as useful adsorbent for tetracycline (TC) removal. The important variables including initial concentration, contact time and co-existing ions are studied in detail, and adsorption behavior is better described by pseudo-second-order and Langmuir model with spontaneous endothermic process. Significantly, the maximum TC capacity is up to be 1304.5 mg/g, much larger than most type of adsorbents with close surface areas due to synergetic effect of pore-filling, H-bonding and π-π static interaction. This work highlights a useful guidance to design hierarchically porous biochar for the effectively TC removal from aquatic environment.