Fabrication of efficient bipolar membranes with functionalized MOF interfacial layer for generation of various carboxylic acids via electrodialysis

Abstract

Stability and compatibility of two layers with each other are the major drawback of the bipolar membrane (BPM). Sulfonated poly (ether ether ketone) and quaternized poly phenylene oxide are taken as the cation exchange layer (CEL) and anion exchange layer (AEL) respectively to fabricate the bipolar membrane by layer-by-layer assembly. Different functionalized MOF (MIL-101 Cr) are prepared for the interfacial layer (IL) of BPM as water dissociation (WD) catalysts. Various analytical techniques (XRD, FT-IR, SEM, BET, XPS, TGA) are used to examine the chemical structure, textural properties and thermal stability of the synthesized catalysts. Two different catalytic sites of MOF as inorganic metal-ion and organic ligands facilitates the water dissociation rate. The effect of different IL (functionalized MOF) on performance of BPM is studied for the dissociation of NaCl into corresponding acid and alkali. BPM with bi-functionalized MOF as IL (BPM-BMOF) shows the better electro-chemical and physicochemical properties in term of ionic conductivity (8.02 mS cm−1) with 38.1 % water uptake, among the synthesized BPMs. The performance of BPM-BMOF is evaluated for the generation of different organic carboxylic acids from sodium carboxylates using bipolar membrane electrodialysis (BPMED). BPM-BMOF shows the 94.12 % acid generation with 0.496 g h−1 water dissociation rate using 0.2 M NaCl feed solution. The results suggest that product recovery (PR) and energy efficiency (ƞ) gradually reduces with higher homologous of sodium carboxylates under similar experimental conditions. The performance of BPM-BMOF with negligible co-ion leakage and stability made it industrially applicable for water splitting.