Nanofiltration Membranes for Water Treatment: A Review of Fabrication Methods and Performance Evaluation

Abstract

The increasing global water crisis, due to the shortage of fresh water and pollution caused by industry, agriculture, and pharmaceutical companies, has increased the need for water purification technologies. Presently, 2.2 billion people are estimated not to have access to safe drinking water, with water pollution having become an issue in every part of the world. Nanofiltration (NF) membranes can play a crucial role in solving the problem since they fill in the gap between reverse osmosis (RO) and ultrafiltration (UF) processes by being able to remove ions under pressure as low as 5-15 bar (whereas RO requires up to 10-80 bar). Importantly, the development of molecular engineering technologies, such as the creation of Janus microporous frameworks, cationic triazolyl heterocyclic compounds, sulfonated macrocyclic compounds (Noria), and different types of MOFs, succeeded in breaking the permeability-selectivity dilemma. Machine learning techniques, specifically those of an ensemble nature, e.g., Random Forest, XGBoost, show great promise in predicting membrane performance and optimizing membrane fabrication, yielding accuracy levels greater than 0.85 R² when predicting salt/dye separation performance. The global NF membrane market estimated to be valued at around $1.2 billion in 2024 is anticipated to experience a CAGR of 12-15% from 2024 to 2030, owing to the growing demand for water treatment in water-stressed regions and regulatory requirements. Some issues remain to be resolved, such as the problem of membrane fouling (that may lead to loss of membrane flux of between 30% and 70%), scalable manufacturing process, and chemical stability in the long term.