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To evaluate the synergetic adsorption capacity of layered double hydroxide (LDH) and photocatalytic reduction property of TiO 2 for aqueous Cr(VI), the Fe 3 O 4 -ZnAl-LDH and TiO 2 composites (FLT) were prepared via sol-gel method. The removal efficiency of FLT composites for Cr(VI) changed with the mass ratio of Fe 3 O 4 -LDH/TiO 2 , and the optimal ratio was 20% (FLT-2). The adsorption efficiencies of 100 mg FLT-2 were 74% and 64% for 20 and 50 mg/L Cr(VI) solution, and the total removal ratios of Cr(VI) were all over 97% after UV irradiation. The experimental data of adsorption kinetic, adsorption isothermal, and photocatalytic reduction were consistent with the pseudo-second-order, Langmuir, and first-order reaction equations, respectively. From the X–ray photoelectron spectra analysis, FLT composites adsorbed Cr(VI) directly via surface complexation, also reduced aqueous Cr(VI) to Cr(III). The photocurrent and electrochemical impedance spectroscopy of FLT composites indicated the photo-induced electron-hole pairs were separated effectively. The regeneration results show that the FLT composites had good stability and reusability after five consecutive cycles. Therefore, FLT composites are promising materials in the disposal of wastewater containing Cr(VI). [ABSTRACT FROM AUTHOR]

[Display omitted] • CAL and PPy-CAL were prepared using hydrothermal and in situ polymerization methods. • The theoretical adsorption capacity of CAL-PPy for Cr(VI) was nearly twice than that of CAL. • CAL-PPy removed 100 mg/L of aqueous Cr(VI) efficiently and quickly. • Mechanisms included electrostatic attraction, anion exchange, complexation, and reduction. To efficiently remove high concentrations of hexavalent chromium (Cr(VI)), calcium–aluminum-layered double hydroxide (CaAl-LDH, denoted as CAL), and polypyrrole-modified CAL (CAL-PPy) were prepared by hydrothermal and in situ polymerization methods, respectively. The chemical structure, morphology, and elemental results indicated that the chain-like polypyrrole was decorated with hexagonal CAL. The specific surface area of CAL-PPy increased from 8.746 m2/g to 24.24 m2/g. The adsorption performances of CAL and CAL-PPy for aqueous Cr(VI) were investigated using batch equilibrium experiments. The decontamination process of aqueous Cr(VI) (100 mg/L) reached the equilibrium state within 50 min, and the kinetic data met the pseudo-second-order kinetic equation. The Langmuir model described the isothermal data properly, and the obtained theoretical adsorption capacity of CAL for Cr(VI) at 318 K was 34.06 mg/g, while that of CAL-PPy was 66.14 mg/g. The removal mechanisms involved electrostatic attraction, surface complexation, anion exchange, and reduction to low-toxicity Cr(III). Therefore, CAL and CAL-PPy have underlying applications in treating real wastewater containing Cr(VI). [ABSTRACT FROM AUTHOR]

A novel chromium (VI) ion-imprinted polymer (Cr(VI)-IIP) was prepared using surface ion imprinting technique on graphene oxide-mesoporous silica (GO-MS) nanosheets with 3-(2-amino ethyl amino) propyl trimethoxysilane as the functional monomer. The prepared Cr(VI)-IIP was characterized by Fourier transform infrared spectroscopy, scanning electronic microscopy, X-ray diffraction and thermogravimetric analysis. The prepared Cr(VI)-IIP was then applied to remove Cr(VI) ions from aqueous solution. The influences of functional monomer amount, contact time, initial Cr(VI) concentration, solution pH and temperature, on the adsorption performance of Cr(VI)-IIP were investigated. Adsorption experiments revealed that the sorption equilibrium was achieved within 5 min with a high adsorption capacity up to 438.1 mg g −1 , and the adsorption process followed pseudo-second-order kinetic model and Freundlich adsorption isotherm model. The Cr(VI)-IIP exhibited superior selectivity for Cr(VI) with respected to Cr(III), Mo(VI), PO 4 3− , SO 4 2− and NO 3 − . Moreover, Cr(VI)-IIP showed good reusability in five adsorption/desorption cycles. Results indicated that the synthesized Cr(VI)-IIP possessed excellent potential applications for the treatment of wastewaters containing Cr(VI). [ABSTRACT FROM AUTHOR]