Dynamics and mechanisms of atrazine adsorption on biogas-residue biochar with citric acid modification

•The surface mineral structures of biogas residue biochar and its transformance after citric acid modification was firstly detected.•A high-efficiency and stable biogas residue biochar for atrazine adsorption was prepared by citric acid modification.•The internal mechanism was analyzed for the enhanced adsorption of atrazine by citric acid modified biogas residue biochar.