The Fe-based materials were considered very attractive for the treatment of wastewater using peroxymonosulfate (PMS) activation. However, the difficulties to restore the active Fe 2+ oxidation state restrict them to attained sustainable efficiency. In this work, a new strategy was introduced to accelerate the regeneration of Fe 2+ state through constructing an electron-rich MoS 4 2− centre in the inter-layers of FeMgAl layered double hydroxide (MoS 4 -LDH) catalyst. The dual centre MoS 4 -LDH catalyst was found more efficient as clear from the observed atrazine (ATZ) degradation rate of 0.117 min −1 , 100 times higher than the Fe 3+ /PMS or 25–50 times higher than the Fe based single centre NO 3 -LDH/PMS, CO 3 -LDH/PMS or S 2 O 4 -LDH/PMS systems, respectively. This boosted efficiency was related to the electron-rich MoS 4 2− centre which allows the constant electron transfer to reduce the electron-deficient Fe 3+ center at MoS 4 -LDH surface and thereby accelerating the Fe 2+ /Fe 3+ redox cycle during reaction. Furthermore, the MoS 4 -LDH/PMS system exhibited a broader effective pH (3.0–9.0), good stability and minimum influence of background electrolyte or organic matter. The degradation pathway of ATZ based on free radical (SO 4 – and OH), involving the redox cycles of Fe 3+ /Fe 2+ and Mo 6+ /Mo 4+ was proposed for the activation of PMS . This work highlighted the essential role of MoS 4 2− moiety, to accelerate the Fe 3+ reduction at the surface of the LDH catalyst through the continuous feeding of electrons.
Kiran Gupta,Jiang-Bo Huo,Jia-Cheng E. Yang,Ming-Lai Fu,Baoling Yuan,Zhangxu Chen
We introduced (MoS 4 ) 2− moiety into the lamellar layers of Ca 0.66 Al 0.34 (OH) 2 (NO 3 ) 0.34 ⋅yH 2 O to fabricate Ca 0.66 Al 0.34 (OH) 2 (MoS 4 ) 0.17 ⋅yH 2 O (CA-MoS 4 ⋅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-MoS 4 ⋅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-MoS 4 ⋅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 NH 2 + 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 (MoS 4 ) 2− moiety offers stability to the CA-MoS 4 ⋅LDH structure to avoid its solubility under ambient environments.
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