The need for high-performance and novel technologies for selective treatment of radionuclides in water has recently stimulated broad research. In this study, we examined the ability of carbon nanotube (CNT) membranes in selective removal of strontium (Sr 2+ ) and cesium (Cs + ) from water and wastewater. In single-metal systems that contained only Sr 2+ , Cs + or their competitive metal ions, the distribution coefficients ( K d ) of functionalized CNT membranes for divalent cations, i.e., Sr 2+ , Ca 2+ , and Mg 2+ , were measured as 4.41 mmol g −1 , 2.14 mmol g −1 , and 1.30 mmol g −1 , respectively, and those for monovalent cations, i.e., Cs + , K + and Na + , were 0.81 mmol g −1 , 0.79 mmol g −1 , and 0.81 mmol g −1 , respectively. When Cs + or Sr 2+ co-existed with a competing cation, both pristine and functionalized CNT membranes showed excellent selectivity to Sr 2+ over Mg 2+ and Ca 2+ while their selectivity to Cs + over K + and Na + diminished. Moreover, the CNT membranes remained their selectivity for Sr 2+ in a wastewater effluent despite the complex water composition. Overall, the selectivity sequence of the CNT membranes for divalent cations support the occurrence of inner-sphere complexation on CNT surfaces, while that for the monovalent cations was probably determined by electrostatic interactions. This study demonstrates that Ar/O 2 plasma treatment is a greener technology for the production of CNT functionalized membranes for selective removal of contaminants from water to achieve “fit-for-purpose” treatment.
Radioactive strontium (Sr 2+ ) and cobalt (Co 2+ ) in nuclear wastewater pose significant environmental risks, leading the need of developing effective remediation strategies. In this study, a poly (triazine imide) (PTI) composite intercalated with bromide (Br − ), referred to as PTI/LiBr, synthesized via a molten salt method, is introduced as a novel adsorbent for the removals of Sr 2+ and Co 2+ . PTI/LiBr composite exhibited rapid adsorption and high efficiency for both radionuclides, driven by electrostatic interactions and partial exchange of Li + ions. The removal efficiency for Sr 2+ and Co 2+ exceeded 95 % within 30 min. Adsorption kinetics followed a pseudo-second-order model, while isotherm analysis indicated that Sr 2+ adsorption aligned with the Freundlich model and Co 2+ adsorption followed the Langmuir model. The adsorption process was confirmed to be spontaneous and endothermic. The γ-radiation tolerance tests verified the structural stability and high adsorption efficiency of the material under ionizing radiation conditions. Additionally, DFT-based wave function and charge density analyses showed a stronger and more stable interaction between PTI/LiBr and Co 2+ compared to Sr 2+ , which might be driven by favorable magnetic interactions and significant charge transfer. This study highlights the potential of PTI/LiBr as a robust and efficient adsorbent for mitigating radioactive pollutants in complex aqueous environments.
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