Preparation of epichlorohydrin modified corn starch biochar and its adsorption performance on imidacloprid from water

Imidacloprid is a commonly used neonicotinoid pesticide. Imidacloprid widely exists in aqueous environment due to its usage, high water solubility, and long half-life. This poses a potential threat to the ecological safety and human health. Biochar is a solid product obtained from biomass pyrolysis. It has the characteristics of wide source, low energy consumption, easy regeneration, and environmental friendliness, etc, and has been widely concerned in the field of adsorption. In this study, epichlorohydrin modified corn starch biochar (ECSB) was prepared by crosslinking epichlorohydrin with corn starch as raw material. Scanning electron microscopy etc was applied to characterize the structure of ECSB, study the adsorption behavior of ECSB towards imidacloprid, and investigate the adsorption mechanism. The results showed that ECSB had abundant pore structure, with the specific surface area of 285 m²/g and pore volume of 0.162 cm³/g, which were 46.5 and 31.4 times higher than those of unmodified corn starch biochar (CSB), respectively. The maximum adsorption capacity of ECSB for imidacloprid was 70.9 mg/g, which was 112 times higher than that of CSB. Adsorption of imidacloprid by ECSB was in accordance with the quasi-second-order kinetic and Langmuir isothermal model, and was an endothermic, entropy-increasing, and spontaneous process. The presumable adsorption mechanism was mainly attributed to the pore-filling action. Moreover, the adsorption capacity of ECSB still reached 96.6% of the original one after five regenerations using a co-processing technology of ultrasound cavitation and reagent extraction. This study can provide research ideas and theoretical basis for the treatment of environmental imidacloprid wastewater and the development and application of corn starch.