Assessment of electrochemical removal mechanisms of diverse transition metal dichalcogenides for caesium ion removal in wastewater treatment.

Abstract

Abstract Effective treatment of radioactive wastewater is crucial for broader nuclear energy adoption, with caesium radionuclides (most exist in the form of caesium chloride) presenting challenges due to their long half-life and biological hazards. Conventional adsorbents like zeolites and carbon-based materials, including graphene, face limitations in adsorption capacity due to the formation of electric double layers (EDL). This has led to the investigation of alternatives such as transition metal dichalcogenides (TMDs) e.g., MoS2, MoSe2, and WSe2, which offer promising galleries for caesium ion removal. Aside from extensively studied MoS2, there is limited research on the adsorption mechanisms and capacities of other TMDs like MoSe2 and WSe2. Here, we conduct a comparative study examining the removal mechanisms and capacities of exfoliated MoS2, MoSe2, and WSe2 nanosheets, alongside an evaluation of these properties in relation to graphene. Our investigation reveals distinct removal mechanisms and capacities among these three materials for capturing caesium ions in a variety of mechanisms. MoS2 nanosheets primarily utilise a pseudocapacitive charge storage mechanism via intercalation, as evidenced by a total charge storage of 0.78 C g1, with only 2.6% stored via EDL formation. In contrast, MoSe2 predominantly relies on EDL formation, with almost 60% of the total 0.54 C g1 charge storage attributed to this mechanism. Lastly, WSe2 exhibits a combination of both charge storage behaviours, with a total charge storage of 0.77 C g1, of which 14% is due to EDL formation. This research highlights the potential efficacy of TMDs as viable materials for caesium removal, offering an appealing alternative to conventional adsorbents and likely fostering advancements in water treatment technologies.