Water-polyamide chemical interplay in desalination membranes explored by ambient pressure X-ray photoelectron spectroscopy

Abstract

<p>Using ambient-pressure XPS, we investigate the chemical interaction between water and polyamide membranes, to understand water transport in desalination membranes.</p>

Unlocking the potential of polymeric desalination membranes by understanding molecular-level interactions and transport mechanisms

“…Several studies have recognized the significance of local cationcarboxyl interactions, illustrated in Figure 7b, on membrane performance but the molecular details of these interactions are not well understood. 13,59,88,89 Cation-carboxyl interactions are speculated based on the presence of carboxyl groups identified in dry PA membranes by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). [89][90][91] Since the pKa of a carboxyl group is below the neutral pH usually experienced in water treatment, carboxylic acids are assumed to deprotonate to carboxylates, resulting in PA's negative surface charge and repulsion of cations.…”

“…13,59,88,89 Cation-carboxyl interactions are speculated based on the presence of carboxyl groups identified in dry PA membranes by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). [89][90][91] Since the pKa of a carboxyl group is below the neutral pH usually experienced in water treatment, carboxylic acids are assumed to deprotonate to carboxylates, resulting in PA's negative surface charge and repulsion of cations. However, as mentioned in Section 2, it is probable that only surface groups deprotonate due to nanoconfinement in the membrane interior, changing the pKa to 9.5.…”

Effects of Amphiphilic Polypeptoid Side Chains on Polymer Surface Chemistry and Hydrophilicity

“…58 Molecular adsorption of water is known to occur on organic surfaces, from alcohol and carboxylic acid-terminated self-assembled monolayers to highly cross-linked model layer-by-layer polyamide membranes. 51,53,54 Unsurprisingly, polymer surfaces interact differently with water, with a high degree of water uptake seen on Figure 1. Hydrophobic PDMS-based and hydrophilic PEO-based block copolymers modified with an amphiphilic polypeptoid sequence were previously shown to be efficacious for algae and diatom fouling prevention.…”

“…APXPS has grown from characterizing surface chemistry and interactions for applications like catalysis and surface science − to include fields such as electrochemistry, ,, environmental science, ,− biology, , and polymer and membrane sciences. ,, It has potential for characterizing water interactions with the surfaces of varying materials, but nearly all studies have been performed on crystalline, well-defined substrates with minimal restructuring capability. For instance, water adsorption and dissociation have been explored on metal and oxide surfaces such as copper, , silver, TiO 2 , , SiO 2 , Al 2 O 3 , and MgO .…”

“…For instance, water adsorption and dissociation have been explored on metal and oxide surfaces such as copper, , silver, TiO 2 , , SiO 2 , Al 2 O 3 , and MgO . Molecular adsorption of water is known to occur on organic surfaces, from alcohol and carboxylic acid-terminated self-assembled monolayers to highly cross-linked model layer-by-layer polyamide membranes. ,, Unsurprisingly, polymer surfaces interact differently with water, with a high degree of water uptake seen on hydrophilic poly­(sodium styrene sulfonate) films with varying counterions . Notably, water mixing was observed throughout the probed polymer interface, rather than isolated in multilayers above the substrate.…”