Ionic Liquid-Assisted Production of Biochar with High Cu²⁺ Removal Efficiency: Effect of Pyrolysis Temperature and CaCO₃ Content in Biomass

Application of biochar to treat heavy metal polluted wastewater has received increasing attention. However, the adsorption ability of biochar for metal metals is still limited. Ionic liquid (IL) is an organic solvent, which is regarded to have catalysis on biomass during pyrolysis. In this study, a representative IL, 1-butyl-2,3-dimethylimidazolium triflate was selected to co-pyrolysis with wastepaper to acquire biochars with high removal rates for Cu²⁺. Meanwhile, the enhancement mechanisms by IL were clarifed, and the effects of pyrolysis temperature and CaCO₃ in biomass on IL modification were explored. Results showed IL increased micropores of biochar, enhanced the functional groups such as -OH, CO₃^2- and C-O on biochar surface, meanwhile generated CaF₂ crystals. Compared to 350°C and 600°C, the IL-modified biochar produced at 700°C showed the highest removal rate of Cu²⁺, close to 100%. The adsorption mechanisms of IL-modified biochar on Cu²⁺ were that porous structure of IL-modified biochar provided enough adsorption sites, and the F^- from IL reacted with Cu²⁺ to form CuF₂ precipitation. CaCO₃ in biomass weakened the modification effect of IL by isolation the organic component of biomass with IL. This study proposed an innovative method to produce biochars with highly efficient removal rate of Cu²⁺, which was of great significance to control heavy metal pollution in water bodies.