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High permeance nanofiltration membranes with an ultra-low molecular weight cut-off (MWCO) in the range of 150–200 g mol−1 and selective towards small solutes are essential for ionic and molecular separation. Despite the market dominance of thin film composite poly(piperazine-amide) nanofiltration membranes, the higher MWCO (>250 g mol−1) limits their widespread applications in molecular-level discrimination. Herein, we report the fabrication of new carbo-cationic microporous poly(triaminoguanidinium-amide) nanofilm composite membranes from an alkaline solution of triaminoguanidinium chloride (TG) and hexane solution of trimesoyl chloride (TMC) via interfacial polymerization. The microporous (mean pore size ∼1.1–1.3 nm) structure of the nanofilm with a thickness down to ∼30 nm allows convective transport of water with permeance as high as 19.0 ± 0.5 L m−2 h−1 bar−1 (at 4 bar), and tunable salt rejection of MgCl2 (21.5–85%), NaCl (41.6–85%) and Na2SO4 (98.7–99.7%) with a high ion selectivity of ∼140 between NaCl and Na2SO4. The membranes exhibit a low MWCO of 163–200 g mol−1 for neutral solutes, low rejection of glycerol (∼32.0%), high rejection of NaCl (∼85%), and excellent stability at low pH. Such ultra-low MWCO membranes would boost their applications in antibiotic removal, desalination, wastewater treatment, and many industrial separation problems concerning separating small neutral solutes. [ABSTRACT FROM AUTHOR]

Membrane filtration is a key technology for producing freshwater sustainably. However, fouling is a major setback in this technology. Several studies have revealed that hydrodynamics significantly affects the fouling pattern. This review highlights the recent trends in the use of methods to visualize hydrodynamics and fouling in membrane filtration systems. These methods can be classified into invasive and non-invasive types. Invasive methods are predominantly used for root cause analysis of fouling and are more oriented towards industrial applications. The non-invasive methods such as computational fluid dynamics, biofouling simulation, and real-time fouling-monitoring are used to understand hydrodynamics in the membrane channel, the kinetics and mechanism of fouling deposition, etc., and aid substantially in laboratory-scale studies. These methods have shown great potential to predict membrane performance in real-scale applications. Since the non-invasive and invasive methods are "preventive" and "cure" types, respectively, the recent focus has shifted more towards non-invasive methods. This review paper comprehensively discusses these techniques along with an outline of the future scope of work. [ABSTRACT FROM AUTHOR]