Mechanistic insights into methylene blue removal by boron-doped biochar derived from lycium barbarum stalks

Given the significant potential of biochar in addressing various environmental pollution issues, this study systematically investigated the preparation conditions of boron-doped biochar, characterized its surface physicochemical properties and adsorption performance toward methylene blue (MB) in aqueous solution under optimal conditions, and elucidated both the boron doping mechanism and the underlying adsorption mechanisms. B-doped biochar (LBC-B) exhibits a high specific surface area (1240.31 m 2 /g) and a total pore volume of 0.67 cm 3 /g, which the adsorption capacity reaches 906.64 mg/g, representing a 26.5% increase over that of LBC. Adsorption occurs primarily through monolayer chemical interactions at active sites via Lewis acid–base interactions, π–π stacking, hydrogen bonding, and electrostatic forces. LBC-B demonstrates enhanced adsorption capacity, greater resistance to variations in initial pollutant concentration, and good reusability. After doping, B-C bonded compounds and C-B-O containing functional groups are predominantly formed on the biochar surface. The gaseous byproducts generated during the process promote microporous structure development through an in situ gas evolution mechanism. Furthermore, the oxygen affinity of boron facilitates the incorporation of a higher density of oxygen-containing functional groups on the carbon material surface, thereby significantly enhancing its adsorption performance toward MB. This study systematically investigated the preparation conditions of boron-doped biochar, characterized its surface physicochemical properties and adsorption performance toward methylene blue (MB) in aqueous solution under optimal conditions, and primarily elucidated both the boron doping mechanism and the underlying adsorption mechanisms, including the influence of boron's oxygen affinity on MB adsorption. B-doped biochar (LBC-B) exhibits a high specific surface area (1240.31 m2/g) and a well-developed porous structure, which facilitate the adsorption of MB molecules onto its surface with a capacity of 906.64 mg/g. Adsorption occurs primarily through monolayer chemical interactions at active sites via Lewis acid–base interactions, π–π stacking, hydrogen bonding, and electrostatic forces. LBC-B demonstrates enhanced adsorption capacity, greater resistance to variations in pollutant concentration, and good reusability. During the doping process, B-C bonded compounds and oxygen-containing functional groups with C-B-O configurations are predominantly formed on the biochar surface. The gaseous byproducts generated during this process promote the development of a microporous structure via an in situ gas evolution mechanism. Furthermore, the oxygen affinity of boron facilitates the incorporation of a higher density of oxygen-containing functional groups on the surface of LBC-B, thereby significantly enhancing its adsorption performance toward MB. The findings are expected to provide key theoretical basis and data support for precisely regulating B-doping process parameters of biochar and doping mechanism, thus laying a foundation for the synthesis of heteroatom-doped biochar and its application in the remediation of organic dye-containing wastewater. • B-doped biochar exhibits a high specific surface area (1240.31 m 2 /g) and a well-developed porous structure, which facilitate the adsorption of MB molecules onto its surface with a capacity of 906.64 mg/g. • Due to the high oxygen affinity of boron, the oxygen-containing functional groups introduced onto the surface of boron-modified biochar during the modification process play a beneficial synergistic role in the adsorption of methylene blue. • During the doping process, B-C bonded compounds and oxygen-containing functional groups with C-B-O configurations are predominantly formed on the biochar surface. The gaseous byproducts generated during this process promote the development of a microporous structure via an in situ gas evolution mechanism. • Compared with the samples without biochar addition, B-doped biochar exhibits superior resistance to fluctuations in pollutant concentration and excellent reusability.