Efficient and reusable mesoporous silica structures for ciprofloxacin removal from water media

The present study aimed to evaluate the potential of mesoporous silica structures, synthesized by the sol-gel method, and using an inorganic precursor, in adsorbing the antibiotic ciprofloxacin (CIP) from water. The structures with the largest surface area and smallest pore size were selected for adsorption tests. Under optimal adsorption conditions, the results showed better correlation with the Langmuir isotherm for the non-porous SiO2 (SiO2-3) and with the Freundlich isotherm for the mesoporous SiO2 (M0.5-SiO2-3 and M1.5-SiO2-3). The kinetic parameters for all analyzed particles had a better fit to the pseudo second-order model. The highest adsorption capacity value obtained was 47.24 mg/g for M1.5-SiO2-3. The thermodynamic parameters indicated that the adsorption was spontaneous, endothermic, and mostly occurred through physical and multilayer adsorption mechanisms. By the analysis of intraparticle diffusion it is clear that a multistep adsorption process occurs, and therefore an adsorption mechanism was proposed. The influence of temperature, pH and presence of salt on the adsorption process was evaluated. The results show that increasing temperature favours adsorption, and that pH and the presence of ions directly influence the adsorption capacity of CIP, indicating that the major interactions controlling the process are mainly electrostatic. Reusability experiment was carried out for M1.5-SiO2-3, being possible to identify that after 5 adsorption-desorption cycles, the adsorbent still has significant CIP adsorption capacity. Based on the results the feasibility of synthesizing mesoporous structures, using a facile method, with high CIP adsorption capacity was demonstrated.