Adsorption and desorption behaviors of antibiotic ciprofloxacin on functionalized spherical MCM-41 for water treatment

Abstract

Extensively used antibiotic ciprofloxacin increases in water environment, which is not efficiently removed by means of conventional adsorbents. MCM-41 has great potential for ciprofloxacin removal. There has been little research on ciprofloxacin removal by MCM-41 and their corresponding adsorption/desorption behaviors. In this study, amorphous SiO2, MCM-41 and diamine-functionalized MCM-41 were used as adsorbents to remove ciprofloxacin. In the adsorption process, their adsorption capacity followed the order of SiO2≪MCM-41< diamine-functionalized MCM-41. Ciprofloxacin adsorption behaviors were revealed through the analysis of adsorption isotherms and kinetics model: i. Adsorption process for MCM-41/diamine-functionalized MCM-41 mainly included three steps; and ii. Diamine-functionalized MCM-41 had higher adsorption capacity because of its more and stronger chemical-monolayer adsorption. In the desorption process, strong acid facilitated desorption by inhibiting the interaction between ciprofloxacin and diamine-functionalized MCM-41, and the mechanism was proposed and then supported by salt elution experiment. Last, the breakthrough bed volume and capacity of these absorbents were tested in column operation. Diamine-functionalized MCM-41 had better performance with 550 bed volume and 18.3 mg/g adsorption capacity in the treatment of 5.0 mg/L ciprofloxacin. Both batch and column results demonstrated that diamine-functionalized MCM-41 was highly efficient for ciprofloxacin removal. This study indicates great application prospect of mesoporous silica materials for ciprofloxacin removal and reveals their adsorption/desorption behaviors, which could provide guidance on adsorbent modification/regeneration for antibiotics removal.