High Performance and Selective Sequestration of Cd(II) from Water by Layered Thiophosphate

The extensive use of toxic cadmium (Cd) in energy conversion and industrial applications ranging from solar cells and battery appliances to paints and pigments contaminates water bodies. However, the upper limit of Cd contamination in drinking water is to be only 3 ppb by the WHO and 5 ppb by the USA-EPA, which underscores the need for cost-effective, efficient, and ppb level capture of Cd from contaminated water. Leveraging the selectivity due to Lewis's hard-soft acid-base (HSAB) theory, we have achieved swift and highly selective capture of Cd(II) ions from aqueous mediums using layered potassium manganese thiophosphate (K-MnPS₃). K-MnPS₃ effectively removes Cd(II) ions from extremely dilute aqueous solutions (ppb levels), achieving a maximum sorption capacity of 405.43 mg/g and a removal rate exceeding 97% within 20 min. Even in the presence of competing ions such as Na⁺, Mg²⁺, Ca²⁺, and Pb²⁺, K-MnPS₃ remains selective. Additionally, it operates efficiently across a wide pH range (1.78-11.19) with a high distribution coefficient (∼10⁴ mL/g). Breakthrough experiments using a 1 wt % K-MnPS₃ and 99 wt % sand column showed complete breakthrough of Cd(II) after 62 h, leading K-MnPS₃ as a promising candidate for Cd(II) removal from industrial effluents.