Biochars with excellent Pb(II) adsorption property produced from fresh and dehydrated banana peels via hydrothermal carbonization

•Facile one-step HTC to produce biochars with excellent adsorption performance.•Fresh and dehydrated banana peels were used to produce biochars via HTC.•As-obtained biochars had abundant surface oxygen containing groups.•The banana peel based biochar had lead adsorption capacity of 359 mg·g−1.

Fresh and dehydrated banana peels were used as biomass feedstock to produce highly effective sorbent biochars through a facile one-step hydrothermal carbonization approach with 20%vol phosphoric acid as the reaction medium. The elemental ratio of oxygen content of the two as-prepared biochars were about 20%, and the FT-IR analysis confirmed the existence of abundant surface functional groups such as hydroxyl and carboxyl which greatly enhanced the adsorption performance. The sorbents showed excellent lead clarification capability of 359 mg·g−1 and 193 mg·g−1 for dehydrated and fresh banana peels based biochars, respectively. The change of the CO/OCO and the appearance of PbO/PbOC on the surface after adsorption confirmed that the ion exchange might be the dominant mechanism. The dehydration and pulverization pre-treatment and the addition of phosphoric acid can benefit the formation of those functional groups and hydrothermal carbonization can be a promising method to transfer biomass like fruit peels into biochars with excellent adsorption performance.