For uranium extraction from seawater, development of new stable and reusable sorbents with high affinity and good selectivity for U(VI) is required. Herein, a new phosphate-functionalized polyethylene (denoted PO₄/PE) was synthesized via a simple Ar-jet plasma treatment of PE in concentrated H₃PO₄ and was employed in U(VI) extraction from seawater. The prepared PO₄/PE shows superior performance in the extraction of trace U(VI) from seawater. The adsorption process followed the second-order kinetics model and the Langmuir model. The maximum adsorption capacity of PO₄/PE for U(VI) reaches 173.8 mg/g at pH 8.2 and 298 K. PO₄/PE can be effectively regenerated by 0.1 mol/L Na₂CO₃ and reused well even after eight cycles. Experimental results offer a new approach for U(VI) uptake from seawater.

β-Cyclodextrin modified graphene oxide (denoted as β-CD–GO) was synthesized and applied as a sorbent to remove Co(II) from aqueous solution. The synthesized β-CD–GO was characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM/EDX), Fourier transform infrared (FT-IR) spectroscopy, Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) in detail, and the results of the characterization indicated that β-CD was successfully grafted onto the surface of GO. The effects of pH, ionic strength, competing ions and solid content on the sorption of Co(II) onto the β-CD–GO nanocomposites were investigated. The results indicated that Co(II) sorption on β-CD–GO was strongly dependent on pH and independent of ionic strength under the experimental uncertainties. The sorption isotherms of Co(II) on β-CD–GO could be described well by the Langmuir model. The thermodynamic data (ΔH⁰, ΔS⁰ and ΔG⁰) calculated from the temperature-dependent sorption isotherms suggest that the sorption of Co(II) on β-CD–GO is a spontaneous and endothermic process. The maximum sorption capacity of Co(II) on β-CD–GO (72.4 mg g⁻¹) at pH = 6.0 ± 0.1 and T = 303 K was much higher than that of Co(II) on GO (47.39 mg g⁻¹) and other sorbents. The abundant oxygen-containing functional groups of modified β-CD on the GO surface can improve the sorption capacity of β-CD–GO for Co(II). The results indicate that β-CD–GO is a promising material for the removal and enrichment of Co(II) from wastewater.

During the amidoximation process, transformation details of poly(acrylonitrile) (PAN) to poly(amidoxime) (PAO) is critical for optimizing amidoximation conditions, which determine the physicochemical properties and adsorption capabilities of PAO-based materials. Although the optimization of amidoximation conditions can be reported in the literature, a detailed research on the transformation is still missing. Herein, the effect of the amidoximation conditions (i.e. temperature, time, and NH₂OH concentration) on the physicochemical properties and adsorption capabilities of PAO was studied in detail. The results showed that the extent of amidoximation reaction increased with increasing temperature, time, and NH₂OH concentration. However, a considerably high temperature (>60 °C) and a considerably long time (>3 h) could result in the degradation and decomposition of PAO's surface topologies and functional groups, and then decrease its adsorption capability for U(VI). The optimal amidoximation condition was 3 h, 60 °C and 50 g L⁻¹ NH₂OH. At this condition, the PAO obtained presented the highest adsorption capability for U(VI) under experimental conditions. These results provide pivotal information on the transformation of PAO-based materials during the amidoximation process.

In order to explore the effect of –OH functional groups in Cs⁺ adsorption, we herein used the low temperature plasma-induced grafting method to graft chitosan onto carbon nanotubes (denoted as CTS-g-CNTs), as raw-CNTs have few functional groups and chitosan has a large number of –OH functional groups. The synthesized CTS-g-CNT composites were characterized using different techniques. The effect of –OH functional groups in the Cs⁺ adsorption process was evaluated by comparison of the adsorption properties of raw-CNTs with and without grafting chitosan. The variation of environmental conditions such as pH and contact time was investigated. A comparison of contaminated seawater and simulated groundwater was also evaluated. The results indicated that: (1) the adsorption of Cs⁺ ions was strongly dependent on pH and the competitive cations; (2) for CNT-based material, the –OH functional groups have a positive effect on Cs⁺ removal; (3) simulated contaminated groundwater can be used to model contaminated seawater to evaluate the adsorption property of CNTs-based material. These results showed direct observational evidence on the effect of –OH functional groups for Cs⁺ adsorption. Our findings are important in providing future directions to design and to choose effective material to remedy the removal of radioactive cesium from contaminated groundwater and seawater, crucial for public health and the human social environment.