Title : Counterion-directed assembly of oriented 1 nm-intrinsic porous polyoxometalate thin films for precise molecular separation

Precise control of pore size at the angstrom scale is critical for advancing membrane technologies capable of high-resolution separations. Biological membranes, such as aquaporins, achieve exceptional selectivity through well-defined nanopores. In contrast, conventional polymer membranes possess disordered, dynamic pore networks due to inefficient chain packing, leading to a fundamental permeability–selectivity trade-off. While crystalline porous materials like MOFs, COFs, and zeolites offer fixed and uniform pores, their practical application is hindered by limited mechanical strength, processability challenges, and difficulty in fabricating large-area, defect-free films while preserving their structural order. Here, Counterion-directed supramolecular assembly of polyoxometalates, a class of crystalline thin-film membranes assembled from crown-type polyoxometalate (POM) clusters, [P_?W_??O_???]??? (P₈). These P₈ clusters contain intrinsic ~1 nm pore defined with crystallographic precision, ideal for molecular sieving By functionalizing P₈ with alkylammonium counterions ([C_nH_2n⁺1]?N?,n = 4, 7, 10), we direct supramolecular self-assembly into continuous, defect-free thin films with ordered, permanent porosity. Tuning the alkyl chain length adjusts the extrinsic porosity (E?) between clusters without disrupting the intrinsic pore network (I?). Shorter chains (Q₄P₈) enable dual-path transport via I? and E?, whereas longer chains (Q₇P₈, Q₁₀P₈) restrict transport solely through I?, enabling precise molecular sieving. These ultrathin selective layers (~30-500 nm) can be fabricated over large areas (~50 cm²). POMbranes demonstrate single-digit pore selectivity and tenfold higher separation efficiency for molecules differing by only 100-200 Da compared to state-of-the-art membranes, offering a scalable strategy to translate molecular design into practical, high-performance separation technologies.

Dr. Priyanka Dobariya completed her Ph.D. in Chemistry at CSIR-Central Salt and Marine Chemicals Research Institute (CSMCRI), Bhavnagar, India. She designs porous functional materials (polyoxometalates, hydrogen-bonded organic frameworks and microporous polymers) as thin-film membranes for molecular separation, resource recovery and electrocatalysis. She has published 14 peer-reviewed articles, including two first-author papers in the Journal of the American Chemical Society, and has filed four patent applications. Her 1-nm-pore “POMbrane” work was featured by EurekAlert (AAAS), The Hindu and Times of India. She received CSMCRI’s Best Female Research Scholar Award 2026 and several best-poster awards.