Enhancement of ciprofloxacin sorption on chitosan/biochar hydrogel beads

Biochar is effective in water treatment but it is hard to retrieve or separate biochar powder from aqueous solutions. In this study, the removal of ciprofloxacin from aqueous solutions was investigated using chitosan/biochar hydrogel beads (CBHB). The results showed that the adsorption rate was almost independent of the temperature and occurred at the homogeneous sites of adsorbent thus obeying the Langmuir model. The equilibrium time was varying for different initial concentrations and found to be 48 h for maximum one. The maximum sorption was found to be >76 mg/g of adsorbent out of 160 mg/L as initial concentration. Adsorption obeyed the second-order mechanism with leading role of intra-particle diffusion and outer diffusion. Adsorption capacity decreased from 34.90 mg/g to 15.77 mg/g in the presence of 0.01 N Na₃PO₄ whereas other electrolytes such as NaCl, Na₂SO₄, NaNO₃ with same concentration did not affect the sorption capacity. However, increased concentration of NaCl reduced the sorption capacity to some extent. CBHB showed a mixed mechanism by removing CIP through π-π electron donor-acceptor (EDA) interaction, hydrogen bonding and hydrophobic interaction. The reformation of CBHB with methanol and ethanol instead of water decreased its sorption capacity to 32.69 mg/g and 29.29 mg/g. Adsorption decreased by little after every regeneration of CBHB and was still >64 ± 0.68% (25.73 mg/g) after 6th regeneration. The efficacy of CBHB for CIP removal proved that CBHB is an economical and sustainable adsorbent.