Chitosan has several shortcomings that limit its practical application for the adsorption of heavy metals: mechanical instability, a challenging separation and recovery process, and low equilibrium capacity. This study describes the synthesis of a magnetic xanthate-modified polyvinyl alcohol and chitosan composite (XMPC) for the efficient removal and recovery of heavy metal ions from aqueous solutions. The XMPC was synthesized from polyvinyl alcohol, chitosan, and magnetic Fe3O4@SiO2 nanoparticles. The XMPC was characterized, and its adsorption performance in removing heavy metal ions was studied under different experimental conditions. The adsorption kinetics fit a pseudo-second-order kinetic model well. This showed that the adsorption of heavy metal ions by the XMPC is a chemical adsorption and is affected by intra-particle diffusion. The equilibrium adsorption isotherm was well described by the Langmuir and Freundlich equations. The XMPC reached adsorption equilibrium at 303 K after approximately 120 min, and the removal rate of Cd(II) ions was 307 mg/g. The composite material can be reused many times and is easily magnetically separated from the solution. This makes the XMPC a promising candidate for widespread application in sewage treatment systems for the removal of heavy metals.

Environmental contextUranium-containing wastewaters have high potential to harm the environment and human health. We found that the combination of calix[4]arene with magnetic Fe3O4 particles produced good adsorption of uranium from wastewater. In addition, this material can be recycled and reused, so it has good prospects in practical applications for uranium remediation. AbstractA magnetic functionalised calix[4]arene composite consisting of Fe3O4 and calix[4]arene phosphonate derivative (CPD) was prepared through a facile self-assembly method. The composite was characterised by scanning electron microscopy (SEM), powder X-ray diffraction (PXRD) and Fourier transform infrared spectroscopy (FTIR). The as-synthesised Fe3O4/CPD composite was used to remove UVI from aqueous solutions under different conditions. Meanwhile, the adsorption isotherm, kinetics and thermodynamics were fitted and analysed. The results show that the Fe3O4/CPD composite may be a promising adsorption material for the separation and enrichment of UVI from aqueous solutions in the cleanup of environmental pollution.

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A coal-based activated carbon was treated chemically with nitric acid, sodium hydroxide and ammonia for its surface modification, and its adsorption capacity was investigated with bromate. Several techniques were used to characterize the physicochemical properties of these materials including BET, XPS, pHpzc and Boehm titration. The results indicated that the specific surface area of the activated carbon decreased after oxidation with nitric acid. But the amount of surface acidic oxygencontaining functional groups of the oxidized sample increased compared to the raw carbon and the points of zero charge (pHpzc) decreased. The specific surface area of the activated carbon also decreased after sodium hydroxide treatment and the points of zero charge increased. The changes of surface chemical properties after the ammonia treatment was opposite to the oxidized sample. As a result, the pHpzc of the carbon was increased to near pH9.3, the amount of surface basic groups was increased. Furthermore, the data of bromate adsorption on all the samples were fitted to the Langmuir isotherm model well which indicates monolayer adsorption. In addition, the adsorption capacity of ammonia treatment sample was the highest and its saturated adsorption capacity reached 1.55mg/g. A strong correlation was found between basic groups and adsorption capacity of bromate. Enhancement of basic groups was favorable for bromate removal.

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