LAUSR

Abstract We herein have developed a simple and economical approach for the synthesis of pure SiO2 nanoparticles from rice husk. Accordingly, the rice husk was acid-leached, and silica was subsequently extracted with 2 M sodium hydroxide solution. The silica gel was then precipitated by titration of the extract with sulfuric or nitric acid until pH reached 4, 5, or 7. The results evidenced that the sequence of addition of the acids (required for acid-leaching and titration steps), calcination temperature, and pH of the titrated media played an essential role for tuning the phase purity, yield, and crystallite size of the synthesized SiO2 nanoparticles. The products were elucidated by XRD, FE-SEM, TEM, EDS, FT-IR, BET, and thermal analysis techniques. The optimized conditions: HNO3 and H2SO4 acid sequence addition, pH 7, and 600 or 800 °C calcination temperature, produced pure amorphous SiO2 or SiO2 nanostructure with 14 nm average crystallite size. The produced SiO2 products showed good adsorption capacity (ca. 190 and 30 mg/g) for the removal of ciprofloxacin (CIP) drug from aqueous solutions. As such, various factors influencing the adsorption process were examined. The adsorption results fitted well the pseudo-second-order kinetic and Langmuir isotherm models. The determined thermodynamic constants (ΔHo = 9.9 4 kJ/mol, ΔGo = −19.55 kJ/mol, and Ea = 27.24 kJ/mol) exhibited that the adsorption of CIP drug using the as-prepared SiO2 nano-adsorbent was an endothermic, physisorption, and spontaneous process. The present investigation demonstrated that the SiO2 nano-adsorbent is a good candidate for the removal of CIP drug from the environmentally polluted water.