title: Co-modified MCM-41 as an effective adsorbent for levofloxacin removal from aqueous solution: optimization of process parameters, isotherm, and thermodynamic studies.
abstract: Antibiotics are emerging contaminants due to their potential risks to human health and ecosystems. Poor biodegradability makes it necessary to develop effective physical-chemical methods to eliminate these contaminants from water. The cobalt-modified MCM-41 was prepared by a one-pot hydrothermal method and characterized by SAXRD, N2adsorption-desorption, SEM, UV-Vis DR, and FTIR spectroscopy. The results revealed that the prepared 3% Co-MCM-41 possessed mesoporous structure with BET surface areas at around 898.5 m2g-1. The adsorption performance of 3% Co-MCM-41 toward levofloxacin (LVF) was investigated by batch experiments. The adsorption of LVF on 3% Co-MCM-41 was very fast and reached equilibrium within 2 h. The adsorption kinetics followed the pseudo-second-order kinetic model with the second-order rate constants in the range of 0.00198-0.00391 g mg-1min-1. The adsorption isotherms could be well represented by the Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) isotherm equations. Nevertheless, D-R isotherm provided the best fit based on the coefficient of determination and average relative error values. The mean free energy of adsorption (E) calculated from D-R model was about 11 kJ mol-1, indicating that the adsorption was mainly governed by a chemisorption process. Moreover, the adsorption capacity was investigated as a function of pH, adsorbent dosage, LVF concentration, and temperature with help of respond surface methodology (RSM). A quadratic model was established, and an optimal condition was obtained as follows: pH 8.5, adsorbent dosage of 1 g L-1, initial LVF concentration of 119.8 mg L-1, and temperature of 31.6 °C. Under the optimal condition, the adsorption capacity of 3% Co-MCM-41 to LVF could reach about 108.1 mg g-1. The solution pH, adsorbent dosage, LVF concentration, and a combination of adsorbent dose and LVF concentration were significant factors affecting the adsorption process. The adsorption thermodynamic functions were also determined. The negative ΔH0(-33.50 kJ mol-1) and ΔS0(-43.57 J mol-1K-1) suggested that the adsorption was an exothermic process accompanied by decreasing disorder. This study may indicate that 3% Co-MCM-41 is a promising adsorbent for removing emerging pollutants of LVF from water.
authors.affiliation: Key Laboratory of the Ministry of Education for Synthetic and Natural Functional Molecule Chemistry, College of Chemistry and Material Science, Northwest University, Xi'an, 710069, China.
authors.forename: Ting
authors.initials: T
authors.lastname: Jin
authors.affiliation: Key Laboratory of the Ministry of Education for Synthetic and Natural Functional Molecule Chemistry, College of Chemistry and Material Science, Northwest University, Xi'an, 710069, China.
authors.forename: Wenhua
authors.initials: W
authors.lastname: Yuan
authors.affiliation: Key Laboratory of the Ministry of Education for Synthetic and Natural Functional Molecule Chemistry, College of Chemistry and Material Science, Northwest University, Xi'an, 710069, China.
authors.forename: Yujie
authors.initials: Y
authors.lastname: Xue
authors.affiliation: State Key Laboratory Base of Eco-Hydraulic Engineering in Arid Areas, Xi'an University of Technology, Xi'an, 710048, China.
authors.forename: Hong
authors.initials: H
authors.lastname: Wei
authors.affiliation: Key Laboratory of the Ministry of Education for Synthetic and Natural Functional Molecule Chemistry, College of Chemistry and Material Science, Northwest University, Xi'an, 710069, China.
authors.forename: Chaoying
authors.initials: C
authors.lastname: Zhang
authors.affiliation: Key Laboratory of the Ministry of Education for Synthetic and Natural Functional Molecule Chemistry, College of Chemistry and Material Science, Northwest University, Xi'an, 710069, China. kebin68li@163.com.
authors.forename: Kebin
authors.initials: K
authors.lastname: Li
mesh_terms: D000327:Adsorption; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D064704:Levofloxacin; D012822:Silicon Dioxide; D012996:Solutions; D017550:Spectroscopy, Fourier Transform Infrared; D013696:Temperature; D013816:Thermodynamics; D014867:Water / Q000737:chemistry; D014874:Water Pollutants, Chemical; D018508:Water Purification / Q000379:methods*
chemical_list: C509968:MCM-41; D012996:Solutions; D014874:Water Pollutants, Chemical; D014867:Water; D064704:Levofloxacin; D012822:Silicon Dioxide
keywords: Adsorption; Cobalt-modified MCM-41; Levofloxacin; Response surface methodology