Ammonium molybdophosphate functionalized copolymer micelles for efficient Cs⁺ adsorption

The ammonium molybdophosphate (AMP) with excellent ability of separation and extraction for radioisotope ¹³⁷Cs and Cs⁺ in saline has a high solubility in water, which avoids its adsorbent role to extract Cs⁺ from enhydrous solutions directly. In our paper, the copolymers as the carrier of AMP are prepared via RAFT (reversible addition-fragmentation chain transfer) polymerization, and the AMP is covalently located in shell or core of self-assembled copolymer micelles for efficient Cs⁺ adsorption. The influence of the initial concentration of Cs⁺, the pH value and the dosage of adsorbents, and the adsorption performance of Cs⁺ is evaluated. The initial concentration of Cs⁺ has little effect on the adsorption effect, and the optimal pH of the solution is 7.0. The adsorption–desorption cycles indicate that the micelles have excellent stability and capability for regeneration. The adsorption process of Cs⁺ follows the quasi-second-order kinetic model, and the adsorption equilibrium is reached within 3 h. And the equilibrium adsorption capacities are 8.49 mg/g (AMP in shell of micelle) and 9.34 mg/g (AMP in core of micelle), respectively. According to the Langmuir adsorption model, the maximum adsorption capacity of Cs⁺ on micelles is 71.79 mg/g and 164.20 mg/g, respectively, and the adsorption process is single-layer adsorption. The principle of Cs⁺ selective adsorption is the Cs⁺ and NH₄⁺ exchange reaction in the gaps of the AMP. The results show that micelle with AMP loaded in shell is considered to be the more suitable adsorbent for separating and extracting Cs⁺.