Understanding the effect of natural deep eutectic solvent compositions on the performance and characteristics of reverse osmosis membrane: Experimental and life cycle assessment

The effect of different natural deep eutectic solvent (NDES) compositions was investigated on the characterization and performance of reverse osmosis (RO) membranes. Thymol (Th) as a hydrogen bond acceptor and long-chain acids (LCAs) and short-chain acids (SCAs) were chosen as hydrogen bond donors. NDESs were characterized and identified by FTIR and NMR spectroscopy. NDESs were then utilized as a co-solvent in the organic phase of the co-solvent-assisted interfacial polymerization (CAIP) process. The characterization of the fabricated membranes was evaluated using SEM, FESEM, XPS, EDS, ATR-FTIR, water contact angles, and MPD diffusion experiments. The NDES co-solvent directly influenced the diffusion rate of the m-phenylenediamine (MPD; see graphical abstract) monomer and modified the membrane morphology by altering the thickness of the reaction zone. Moreover, the hydraulic tests showed that the best NDES-modified membrane exhibits double the water flux compared to the unmodified membrane, achieving a NaCl rejection of 97.6 %; also, demonstrated a selectivity of 6 for Li⁺/Mg²⁺. Also, the 24-hour experiment revealed that the TAA CAIP membrane, with only an eight percent reduction in flux, possesses remarkable antifouling features. Furthermore, the CAIP membrane had much higher chlorine resistance than commercial and IP membranes. Life cycle assessment (LCA) indicated that the impacts of the TAA membrane were reduced to half of the unmodified membrane from a membrane performance perspective. This study confirmed that using a very small amount of NDES provides a high-performance RO membrane along with high resistance against fouling and chlorine, which could be used for industrial applications.