Effects of ball milling on hydrochar for integrated adsorption and photocatalysis performance

[Display omitted] •Hydrochar was first treated by ball milling method as a convenient way.•BM-HC exhibited a superior combined MB removal rate of 95.22 % of MB in 30 min.•Ball milling can produce more furan structure and promote visible light absorption.•Possible removal mechanism and degradation pathway of MB was proposed.•Degradation intermediates of MB had a significant reduction in biotoxicity. In this study, hydrochar (HC) was firstly treated by ball milling for methylene blue (MB) removal through combined adsorption-photodegradation. The ball-milled bamboo hydrochar (BM-HC) exhibited a maximum adsorption capacity of 49.522 mg/g and a synergistic adsorption-photodegradation removal rate of 95.22% within 30 min, which was superior to those of pristine HC (20.530 mg/g, 79.47%). Compared with HC, BM-HC had smaller particle size, increased quantities of polyfuran rings, enhanced adsorption of visible light, which were favorable for the enhancement of adsorption capacity and photodegradation rate. The effect of the catalyst dosage, MB concentration, water matrix, pH, coexisting ions on MB photodegradation were examined. The possible synergistic adsorption and photodegradation mechanism of MB was illustrated. The foremost active specie in the synergistic removal of MB was h+. In addition, the possible degradation pathways of MB were proposed depending on the intermediates detected by Liquid chromatography-mass spectrometry (LC-MS), and the biotoxicity of MB and its intermediates was evaluated by Ecological Structure-Activity Relationship (ECOSAR) program. This work confirms that ball-milled hydrochar could be used as a potential catalyst for pollutants removal in water via synergistic adsorption and photocatalysis.