Characterization of amphoteric bentonite-loaded magnetic biochar and its adsorption properties for Cu2+ and tetracycline

To realize simultaneous adsorption of heavy metal and antibiotic pollutants by a BC-based recyclable material, Fe3O4 magnetic biochar (MBC) was prepared by co-precipitation method. Then different ratios of dodecyl dimethyl betaine (BS-12)-modified bentonite (BS-B) were loaded on the surfaces of biochar (BC) and MBC to prepare BS-B-loaded BC and MBC composites, called BS-B/BC and BS-B/MBC, respectively. The physicochemical and structural properties of the composites were characterized by scanning electron microscopy, Fourier transform infrared spectrometry, thermogravimetric analysis, specific surface area (SBET) analysis, and vibrating sample magnetometry, and the adsorption efficiencies of BS-B/BC and BS-B/MBC to Cu2+ and tetracycline (TC) were studied. The following results were obtained. (1) Compared with BS-B/BC, BS-B/MBC had decreased pH and cation exchange capacity (CEC) and increased SBET. The pH, CEC, and SBET of BS-B/BC and BS-B/MBC decreased with the increase in the BS-12 proportion of BS-B. The surface of BS-B/MBC became rough after Fe3O4 loading. (2) The residual rate of BS-B/MBC was higher than that of BS-B/BC after high-temperature combustion, and the residual rate decreased with the increase in the BS-12 proportion of BS-B. The 2D infrared spectra showed that Fe3O4 and BS-12 were modified on the surface of BS-B/MBC. MBC and BS-B/MBC had splendid magnetism and could be separated by external magnetic field. (3) Compared with unmagnetized ones, the adsorption effects of Cu2+ and TC on different BS-B/MBCs improved, and the average adsorption rate reached the largest value of 91.92% and 97.76%, respectively. Cu2+ and TC adsorptions were spontaneous, endothermic, and entropy-increasing processes. The pH and SBET of the material had a great influence on Cu2+ and TC adsorptions, respectively, than CEC.