Controlled Localized Metal–Organic Framework Synthesis on Anion Exchange Membranes

Metal–organic framework (MOF) films can be used in various applications. In this work, we propose a method that can be used to synthesize MOF films localized on a single side of an anion exchange membrane, preventing the transport of the metal precursor via Donnan exclusion. This is advantageous compared to the related contra-diffusion method that results in the growth of a MOF film on both sides of the support, differing in quality on both sides. Our proposed method has the advantage that the synthesis conditions can potentially be tuned to create the optimal conditions for crystal growth on a single side. The localized growth of the MOF is governed by Donnan exclusion of the anion exchange membrane, preventing metal ions from passing to the other compartment, and this leads to a local control of the precursor stoichiometry. In this work, we show that our method can localize the growth of both Cu-BTC and ZIF-8 in water and in methanol, respectively, highlighting that this method can used for preparing a variety of MOF films with varying characteristics using soluble precursors at room temperature

Sustainable K+/Na+ monovalent-selective membranes with hot-pressed PSS-PVA saloplastics

Monovalent selective cation exchange membranes could play an important role in balancing the K+/Na+ ratio in agricultural feed streams to prevent the toxic effects of excess Na+ in the plant and soil systems, especially in greenhouses and dry areas. A polyelectrolyte complex of polystyrenesulfonate and polyvinylamine in the monomer ratio 1:2.5 is hot-pressed to form a dense saloplastic. The plastic takes up 42% w/w water when equilibrated, while ion-exchange capacity measurements show that it is negatively charged with a net ion-exchange capacity of 1.1 ± 0.4. Resistance measurements show a very promising preferred conductivity for K+ over Na+. This was confirmed by measuring K+ and Na+ transport through the membrane under diffusive conditions from an aqueous mixture of KCl and NaCl. Commercial membranes show resistance-based selectivities of 1.32 ± 0.1 to 1.19 ± 0.1, and diffusion based selectivities of 0.99 ± 0.1 to 0.78 ± 0.1. In contrast, the selectivities for the newly developed saloplastic membrane were 1.80 ± 0.33 for the resistance-based selectivity while the diffusion-based selectivity was 1.91 ± 0.1. The procedure is green as toxic solvents and/or halogenating agents, typically used to make cation exchange membranes, are not needed. This work thus highlights how monovalent selective membranes with a relevant K+/Na+ selectivity can be prepared by a simple and sustainable hot-pressing approach

Transport characterization and modelling of Donnan dialysis for ammonium recovery from aqueous solutions

Efficient recovery of ammonium, a valuable nutrient, from dilute streams is still an unsolved challenge. One possible approach to separate and simultaneously concentrate ammonium from low concentration streams is Donnan dialysis. To design a process, a mass transport model was utilized for both plate and frame and hollow fiber modules and compared to experiments. The chosen model was based on film theory, accounting for mass transport resistances in the liquid as well as the membrane phase to allow for a complete investigation of mass transfer limitations. Experimental data for the flux of ammonium and potassium using flat sheet Nafion-115 and FujiFilm type-2 and hollow fiber Nafion membranes was predicted very well by the model for several flow conditions and concentrations. The two stage ammonium removal could be predicted accurately from a starting concentration over two orders of magnitude in concentration. For the hollow fiber module case, liquid phase resistances on the draw side were more substantial vs. plate and frame due to the lower velocity. Both plate and frame and hollow fiber modules showed similar transport rates, up to 1[mol/(m2·h)]. In the investigated, non-optimized, laboratory system, an 80% removal of ammonium was achieved with a processing flow of 12.5 [L/(m2·h)]

Native protein recovery from potato fruit juice by ultrafiltration

Potato fruit juice, i.e. the stream resulting after the extraction of the starch from the potato, contains up to 2.5% [w/w] of proteins that are potentially valuable for the food market. However, today the recovery of protein from the potato fruit juice with reverse osmosis membranes results in a protein concentrate that is not suitable for human consumption. The described research shows that the use of ultrafiltration with additional diafiltration is able to produce a higher quality protein. Tests with the produced protein show that the quality depends on the rate of diafiltration used and that the product has functional properties that are equal or better than the compared commercial food product that are currently used