This study focuses on the facile preparation of ZnO-biochar (ZnO-BC) nanocomposite prepared by the hydrothermal approach as an efficient sonocatalyst for degradation and mineralization of gemifloxacin (GMF). Morphological and textural characteristics of bare biochar (BC), ZnO nanorods (ZnO NRs) and ZnO-BC nanocomposite were investigated using TEM, SEM and BET analyses. Moreover, XRD, FTIR, EDX and UV–vis DRS analyses were performed to study the crystalline structure, functional groups, elemental composition and optical properties of the samples, respectively. ZnO-BC nanocomposite showed better sonocatalytic performance than BC and ZnO NRs owing to its huge surface area, narrow band gap and enhanced sonoluminescence phenomenon. These properties led to the synergetic ability of ultrasonic irradiation and catalytic activity of ZnO-BC to generate reactive species and subsequent radical reactions. In addition, the effect of the addition of various gases and scavengers on the removal of GMF was evaluated. The GC–MS analysis was used to verify the generation of some intermediates and a possible pathway was proposed accordingly. 83.7% COD removal efficiency was observed within 90 min treatment confirming efficient mineralization of GMF solution. The phytotoxicity test was carried out using Lemna minor and the results proved that after the treatment process, a considerable toxicity removal of the GMF solution had occured.
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