Prussian Blue Analogues (PBAs), which are characterized by their open structure, high stability, and non-toxic properties, have recently been the subject of research for various applications, including their use as electrode precursors for capacitive deionization, gas storage, and environmental purification. These materials can be readily tailored to enhance their affinity towards gases for integration with sensing devices. An improved understanding of PBA-gas interactions is expected to enhance material development and existing sensor deposition schemes greatly. The use of inverse gas chromatography (IGC) is a robust approach for examining the relationship between porous materials and gases. In this study, the adsorption properties of (functionalized) hydrocarbons, i.e., probe molecules, on the copper hexacyanoferrate (CuHCF) lattice were studied via IGC, demonstrating that alkylbenzenes have a higher affinity for this material than n-alkanes. This difference was rationalized by steric hindrance, π–π interactions, and vapour pressure effects. Along the same line, the five isomers of hexane showed decreasing selectivity upon increased steric hindrance. Enthalpy values for n-pentane, n-hexane and n-heptane were lower than that of toluene. The introduction of increased probe masses resulted in a surface coverage of 46% for toluene. For all n-alkane probe molecules this percentage was lower. However, the isotherms of these probes did not show saturation points and the observed linear regime proves beneficial for gas sensing. Our work demonstrates the versatility of CuHCF for gas sensing purposes and the potential of IGC to characterize the adsorption characteristics of such a porous nanomaterial.

We investigated in detail the permeation selectivity in the electro-dialysis of Na⁺, K⁺, Mg²⁺ and Ca²⁺ in both binary and quaternary mixtures using a supported liquid membrane (SLM). The SLM consisted of the organic liquid 2-nitrophenyl octyl ether (NPOE) containing a lipophilic anion, i.e. tetrakis[3,5-bis(trifluoromethyl)phenyl]borate, as the cation-exchanging site, which was used to fill the pores of the supporting membrane Accurel^R. We first determined the electro-phoretic mobilities of the migrating cations in single salt solutions, yielding: Na⁺ > K⁺ > Mg²⁺ > Ca²⁺. This order reflects the different size of the migrating cations. The monovalent cations Na⁺ and K⁺ migrate in the dehydrated state and the divalent cations Ca²⁺ and Mg²⁺ migrate in a (partly) hydrated state, a conclusion was supported by Karl Fisher titrations. Both binary and quaternary salt experiments showed a permeation selectivity in the following order: K⁺ > Na⁺ > Ca²⁺ > Mg²⁺. Since this order does not correlate with the order of electro-phoretic mobilities, we have determined the ion-exchange selectivity constant (K_ex) and found: K⁺ > Ca²⁺ > Mg²⁺ ≈ Na⁺. We conclude that the overall permeation selectivity is determined by the combination of ion-exchange selectivity and electro-phoretic mobility of the cations present in the membrane.

Organic solvent nanofiltration (OSN) is gradually expanding from academic research to industrial implementation. The need for membranes with low and sharp molecular weight cutoffs that are able to operate under aggressive OSN conditions is increasing. However, the lack of comparable and uniform performance data frustrates the screening and membrane selection for processes. Here, a collaboration is presented between several academic and industrial partners analyzing the separation performance of 10 different membranes using three model process mixtures. Membrane materials range from classic polymeric and thin film composites (TFCs) to hybrid ceramic types. The model solutions were chosen to mimic cases relevant to today's industrial use: relatively low molar mass solutes (330–550 Da) in n-heptane, toluene, and anisole.