New mechanistic insight into rapid adsorption of pharmaceuticals from water utilizing activated biochar

The presence of emerging pollutants especially hazardous chemicals and pharmaceuticals in aquatic environments is a matter of grave concern to human health and the environment. In this study, coffee bean waste (CBW) was utilized to synthesize pristine (${\text{CBW}}_{550}$) and activated (${\text{CBW}}_{550}^{\text{HPO}}$) biochars for the elimination of diclofenac (DF) and levofloxacin (LEV) from water. A facile two-step approach was used to synthesize ${\text{CBW}}_{550}^{\text{HPO}}$ using chemical pretreatment and pyrolysis under N₂ purging. BET results of ${\text{CBW}}_{550}^{\text{HPO}}$ revealed that chemical pretreatment increased surface area by approximately 160 times compared to ${\text{CBW}}_{550}$. The calculated ${\text{I}}_{\text{D}}/{\text{I}}_{\text{G}}$ ratio from Raman spectra confirmed that ${\text{CBW}}_{550}^{\text{HPO}}$ had a high functionalized surface. Different operational parameters such as contact time, pH, adsorbent dose, ionic strength, and adsorbate concentration were studied and optimized. Maximum Langmuir adsorption capacity of ${\text{CBW}}_{550}^{\text{HPO}}$ was found to be 61.17 and 110.70 mg/g for DF and LVX, respectively. Experimental results demonstrated that presence of NaCl in solution enhanced DF removal efficiency due to the salting-out effect. Electrostatic attraction, $\pi -\pi$ bonding, and hydrophobic interaction were prominently responsible mechanisms for the adsorption of DF and LVX. Furthermore, continuous-flow mode studies confirmed that ${\text{CBW}}_{550}^{\text{HPO}}$ can be successfully utilized in large-scale treatment applications.