Display omitted ••Biochar was produced from Tenebrio molitor frass and modified by KOH.•• TMFBC-750A possessed high SBET of 1858.80m2g−1 with enhanced absorptivity.••The prevailing mechanisms of NEOs on BC were revealed.••TMFBC-750A realized efficient adsorption of NEOs in water. Neonicotinoid pesticides (NEOs) are the most widely used insecticides in the world and pose a serious threat to ecological systems. Thus, the development of an efficient and sustainable technique for their removal is urgently needed. In this study, a novel biochar was prepared by pyrolysis of Tenebrio molitor frass and activated with KOH at 650 (TMFBC-650A), 750 (TMFBC-750A) and 850 °C (TMFBC-850A). Among them, TMFBC-750A showed the best adsorption performance, and the adsorption capacities for thiacloprid (THI), nitenpyram (NIT) and dinotefuran (DIN) were 155.08 mg·g−1, 195.86 mg·g−1, 325.81 mg·g−1, respectively. The isotherms for the adsorption of NIT and THI fit the Langmuir model quite well, while DIN fits the Freundlich model. Moreover, the adsorption of THI, NIT and DIN was well fitted by the pseudofirst-order kinetic model. The physicochemical characterization analysis demonstrated that the adsorption process of NEOs by TMFBC might be mainly controlled by micropore filling, π-π electron donor–acceptor interactions and functional group interactions (H-bonding, covalent bonding and hydrophobic interactions). Additionally, the thermodynamic parameters suggested that NEO adsorption in this work was a spontaneous, endothermic and randomly increasing process. TMFBC also exhibited a high selective adsorption capacity regardless of solution pH and inorganic ion strength concentrations. The regenerated TMFBC (via synergistic ultrasound/ethanol) could sustainably and efficiently absorb NEOs in reuse cycles, suggesting that TMFBC has excellent reusability and stability. These results indicated that TMFBC can be a potential and sustainable adsorbent for neonicotinoid pesticide removal.