A Novel NH2-MIL-101(Fe)/Silica Xerogel Composite for Ciprofloxacin Removal: Structural, Kinetic, and Thermodynamic Insights

Abstract

The main objective of this study was to demonstrate adsorption of the ciprofloxacin (CIP) on NH2-MIL-101(Fe)/silica xerogel composite. The composites were synthesized with varying loadings of NH2-MIL-101(Fe) into the silica xerogel using the sol-gel method. The addition of NH2-MIL-101(Fe) to silica xerogel structure increased the surface area up to 1092.8 m(2) g(-1). Optimum adsorption parameters including pH, contact time, and adsorbent dosage were optimized as 6.1, 180 min, and 0.3 g L-1, respectively. Adsorption isotherm and kinetic models were implemented to equilibrium data. Langmuir isotherm and pseudo-second-order kinetic model well matched adsorption data. A high adsorption capacity of 185.2 mg g(-1) was obtained using a low adsorbent dosage at 298 K. The thermodynamic data exhibited that CIP adsorption on the composite was exothermic and spontaneous. The impact of ionic strength on adsorption was examined using NaCl and CaCl2. The adsorption efficiency remained almost the same in presence of both monovalent and divalent cation. CIP adsorption was studied under the influence of dissolved organic matter, and adsorption efficiency decreased with increasing humic acid concentration. The adsorption-desorption cycles demonstrated the reusability of the composite, maintaining about 50% of its initial adsorption efficiency after four cycles.