Synthesis, characterization and mechanism analysis of modified crayfish shell biochar possessed ZnO nanoparticles to remove trichloroacetic acid

Abstract Trichloroacetic acid (TCAA), as one of the chlorine disinfection by-products, has three harmful effects of carcinogenesis, teratogenesis and mutagenesis towards human health. At present, several adsorbents have been applied to remove TCAA, and crayfish shell has rarely been served as a feedstock for biochar field. In this experiment, crayfish shell (CFS) biochar was creatively applied to remove TCAA as an adsorbent. The synthesis method was used to produce the ZnO-CFS600 from crayfish shell modified by ZnCl 2 solution. The removal efficiency of ZnO-CFS600 was determined by batch sorption. Based on the Langmuir model, the maximum adsorption capacity was 17.8 mg/g, which was a dramatical increase in adsorption compared with previous studies. And the adsorption equilibrium time is about 20 h according to the kinetics experiment. The adsorption of ZnO-CFS600 was affected by anion competitions. Low pH provided positive charge condition to enhance the adsorption capacity and the removal process was endothermic. The specific surface area of ZnO-CFS600 significantly increased compared with the companion unmodified biochar. The SEM images indicated that ZnO-CFS600 had a better pore structure and possessed numerous apparent ZnO nanoparticles. The result of XRF showed that there was an increase of Zn content with decrease of Ca on the CFS600 after modification, which led to the presence of ZnO nanoparticles with the size of 37.8 nm based on XRD analysis. FTIR spectra showed that the functional groups on biochar surface had changed. All these results came to the mechanism of ZnO-CFS600 that the removal of TCAA was mainly by surface adsorption, supplemented by electrostatic attraction. This point was vividly illustrated by the following figure. Conclusions of this study constituted a stepping stone to the potential application of modified crayfish shell biochar as an effective sorbent for TCAA.