Controllable Fabrication of PAN/NHVPO Composite Membranes and Highly Selective Adsorption Mechanism of Sr(Ⅱ) in Simulated Wastewater

Efficient removal of radioactive strontium ions (Sr²⁺) from wastewater is critical for the sustainable development of nuclear energy and ecological security. Metal oxalatophosphate open frameworks (MOPOFs) are promising adsorbents for Sr²⁺ capture, but their practical application is constrained by poor solid-liquid separation in powder form. To address this challenge, a novel polyacrylonitrile-based ammonium vanadium oxalatophosphate (PAN/70NHVPO) composite membrane was fabricated via airflow-assisted electrospinning, and its Sr²⁺ adsorption performance was systematically evaluated. The PAN/70NHVPO membrane exhibits excellent structural stability: thermogravimetric analysis confirms minimal mass loss in the temperature range of 86.7-334.2 ℃, and a Zeta potential absolute value exceeding 40 mV indicates high colloidal stability. Batch adsorption experiments show that the membrane maintains high Sr²⁺ removal rate over a wide pH range (2-11), reaching equilibrium within 280 min. The adsorption kinetics follow the pseudo-second-order model (R² = 0.993 2), suggesting chemisorption as the rate-limiting step, with intraparticle diffusion also influencing the process. The equilibrium data fit the Langmuir isotherm model well (R² = 0.991 8), giving a theoretical maximum monolayer adsorption capacity of 263.09 mg/g. Notably, the membrane displays remarkable selectivity for Sr²⁺: even in the presence of 200-fold excess Ca²⁺ (a major competing ion), the Sr²⁺ removal rate remains as high as 62.01%. Dynamic fixed-bed column experiments further validate its practical applicability, achieving >95% Sr²⁺ removal rate from simulated seawater. Combined with multiple characterization techniques and density functional theory (DFT) calculations, the adsorption mechanism is elucidated: Sr²⁺ first undergoes ion exchange with interlayer \mathrmN\mathrmH_4^+ in NHVPO, followed by the formation of stable coordination bonds with oxygen atoms in the P-O and V-O groups of the vanadium oxalatophosphate anionic layers. This study presents PAN/70NHVPO as a highly effective and selective adsorbent for Sr²⁺, and provides a comprehensive understanding of its adsorption mechanism, laying a solid theoretical foundation for its potential application in radioactive wastewater treatment.