Granular silica pillared clay for levofloxacin and gemifloxacin adsorption from aqueous systems

The present study deals with the adsorption of levofloxacin (LVX) and gemifloxacin (GMX), two types of antibiotic contaminants from aqueous solutions. A granular silica pillared clay (GSPC) was prepared by intercalation of a cationic surfactant into the structural layers of local Na-saturated clay, followed by calcination and granulation with sodium alginate. The SiO₂ content of more than 90 wt%, mainly in the amorphous phase, Si–O–Si and –OH functional groups, d-spacing: 40.1 Å, specific surface area: 482 m² g⁻¹, and high mesoporous volume and total pore volume: 1.16 and 1.27 cm³ g⁻¹ were the characteristics of GSPC. The pseudo-second order kinetic model, film-diffusion, and intraparticle diffusion (at long contact times) models described the kinetic adsorption data well. The Sips and Langmuir models provided the best agreement with the experimental equilibrium data. Hydrogen bonding, π-π interaction, and cation exchange (at acidic pH) were the most important mechanisms in the adsorption of GMX and LVX. The higher adsorption capacity of GSPC towards GMX is due to the NH₂ groups involved in adsorption and the affinity for adsorption in multilayer mode. This property in competition with LVX in adsorption from a binary solution is beneficial for the superiority of the adsorption capacity of GMX over LVX.