(MoS4)2− intercalated CAMoS4⋅LDH material for the efficient and facile sequestration of antibiotics from aqueous solution

Abstract

We introduced (MoS4)2− moiety into the lamellar layers of Ca0.66Al0.34(OH)2(NO3)0.34⋅yH2O to fabricate Ca0.66Al0.34(OH)2(MoS4)0.17⋅yH2O (CA-MoS4⋅LDH), a stable and efficient adsorbent for removal of two envoy Fluoroquinolones (FQs), Ciprofloxacin (CIP) and Ofloxacin (OFL), from contaminated aquatic sources. Various characterization tools, such as X-ray diffraction (XRD), Scanning electron microscopy, Energy dispersive X-ray spectrometer, transmission electron microscopy, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy and Thermogravimetric analyses etc. were applied to confirm structural and compositional changes during the synthesis and adsorption properties of CA-MoS4⋅LDH. The efficiency of adsorbent was investigated by evaluating different parameters including contact time, pH of solution, initial concentration of pollutant, and effect of temperature. By using CA-MoS4⋅LDH as adsorbent, we found more efficient removal of CIP than that of OFL due to the steric hindrance. The highest uptake of 707.20 mg/g and 476.74 mg/g of CIP and OFL, respectively, was found at pH of 6 with improved kinetics and easily reusability for these representative antibiotics models so far. Removal kinetics of both FQs were found to better follow the pseudo-second-order kinetic model than the pseudo-first-order. The Langmuir adsorption isotherm was employed to understand the removal process, suggesting monolayer chemisorption mechanism. The adsorbate-adsorbent interaction revealed remarkable features originate from the combination of weak hydrogen bond interaction between thio group and NH2+ group of antibiotic and electrostatic interaction between positive LDH layer and COO− group of antibiotic as well, and anion exchange mechanisms, which were also confirmed by XRD, FTIR, XPS and Raman spectrum etc. obtained after adsorption. It is proposed that all (MoS4)2− moiety offers stability to the CA-MoS4⋅LDH structure to avoid its solubility under ambient environments.