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[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]

Graphical abstract Abstract In this work, the magnetic alginate microsphere of Fe 3 O 4 /MgAl-LDH (Fe 3 O 4 /LDH-AM) was prepared by immobilizing the Fe 3 O 4 /LDH with calcium alginate (CA) and was used to remove Cd2+, Pb2+, and Cu2+ from aqueous solutions. The obtained Fe 3 O 4 /LDH-AM was characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, energy dispersive spectroscopy, X-ray photoelectron spectroscopy, and Brunauer-Emmett-Teller surface area determination. The results indicated that the surface groups of the alginate and LDH were retained and so was the crystal structure in the alginate microsphere. The adsorption performance of the Fe 3 O 4 /LDH-AM for Cd2+, Pb2+, and Cu2+ in aqueous solutions was evaluated by batch and column adsorption experiments. The effects of adsorption conditions, kinetics, isotherms, mechanisms, and potential applications were investigated. The adsorption kinetic data conformed to the pseudo-second-order kinetic equation, and the isotherm data fit well with the Freundlich and Langmuir isotherm models. The adsorption mechanism of Cd2+, Pb2+, and Cu2+ by the Fe 3 O 4 /LDH-AM entailed complexation and precipitation. The experimental breakthrough curves were correlated with the Thomas model. Moreover, the Fe 3 O 4 /LDH-AM displayed superior regeneration and reusability. These results suggest that the Fe 3 O 4 /LDH-AM is an efficient adsorbent for the removal of heavy metals and can be effectively employed in practical applications. [ABSTRACT FROM AUTHOR]

With the increase of sustainable development goal, the bio-based adsorption materials with high and selective dye removal are important for water treatment in the dyeing industry. In this paper, a bio-based adsorption foam composed of metal-organic frameworks (MOF) and polyethyleneimine (PEI)-modified cellulose was prepared by a three-step process, i.e., PEI modification of cellulose fibers (PC), MOF decoration of PEI-modified cellulose (MIL-53@PC), and in-situ foaming with polyurethane. PEI modification provides cellulose fiber with more active sites for both dye adsorption and MOF bonding. We found that MIL-53 crystals were tightly bonded on the surface of PC through hydrogen bonding. Because of the abundant adsorption sites (e.g., amines, iron oxide group), the MIL-53@PC demonstrated high adsorption capacity and selectivity for anionic dye (e.g., 936.5 mg/g for methyl orange) through electrostatic interaction and hydrogen bonding. Finally, MIL-53@PC particles were blended with a waterborne polyurethane prepolymer to prepare a three-dimensional hydrophilic foam (MIL-53@PC/PUF), which not only maintained high adsorption capacity and selectivity of MIL-53@PC and also improved its recyclability and reusability. The MIL-53@PC/PUF offers a promising solution for dye wastewater treatment. [Display omitted] • MIL-53@PC was fabricated via the ultrasonic method. • The maximum adsorption capacity of MIL-53@PC for MO was 936.5 mg/g. • The MIL-53@PC could selectively remove the anionic dyes from wastewater. • The MIL-53@PC/PUF broadened the practical application of powder adsorbent. [ABSTRACT FROM AUTHOR]

In this study, ammonium thiocyanate functionalized graphene oxide (ATGO)-supported nanoscale zero-valent iron composite (ATGO-nZVI) employed to extract Cr(VI) from aqueous solution, was successfully synthesized by chemical oxidative polymerization and sodium borohydride reduction method. Characteristics of X-ray diffraction and high-resolution transmission electron microscopy confirmed the high disperse and activity of nZVI after supported by ATGO. Batch experiments showed that the removal efficiency of ATGO-nZVI was higher than that of bared nZVI and ATGO. Furthermore, the stability of ATGO-nZVI composite was higher than that of nZVI, which was proved by the Tafel polarization curves. Dynamic experiments suggested that the removal process was confirmed to be in agreement with not only the pseudo-second-order model for adsorption but also Langmuir-Hinshelwood first-order model for reduction process, which revealed that the removal of Cr(VI) by ATGO-nZVI composite was dominated by chemical surface-limiting step. Considering the experiments and characterization, the removal mechanism containing rapid adsorption of Cr(VI) onto the ATGO-nZVI surface and reduction by nZVI was clarified. The above results suggested that ATGO-nZVI would become a promising remediation material for Cr(VI) pollution cleanup. [ABSTRACT FROM AUTHOR]