Aminoguanidine-based polyamide nanofiltration membranes for purifying natural surface water: Superior anti-fouling properties and ultra-high organic matter/minerals selectivity

The current challenges of piperazine-based nanofiltration (NF) membrane technology for high-quality drinking water include improving selectivity for organic maters and minerals, as well as reducing membrane fouling. In this investigation, a series of innovative polyamide (PA) NF membranes were meticulously synthesized through the reaction of aminoguanidine nitrate (AN), serving as an aqueous phase monomer, with 1,3,5-benzotriacontanoyltrichloride (TMC). The AN was found to exhibit high reactivity and low diffusivity during interfacial polymerization (IP) when used as an aqueous phase monomer. This optimization greatly enhanced the structural integrity, mechanical properties and surface physical properties of the NF film. Notably, the PA-AN-0.5 NF membranes manifested enhanced hydrophilicity, elevated negative surface charge density, and a comparatively loose microstructure. These attributes culminated in superior permeability rates (18.8 LMH/bar) and Ca²⁺/SO₄²⁻ selectivity ratios (68.9) relative to alternative configurations. The exceptional mineral/organic selectivity demonstrated by PA-AN-0.5 NF membranes during natural surface water filtration significantly bolsters their commercial viability for producing drinking water. Furthermore, the AN-modified membrane demonstrated exceptional anti-scaling and anti-fouling properties, thereby establishing the PA-AN-0.5 NF membrane as a highly promising candidate for cost-effective purification processes aimed at producing high-quality drinking water from surface sources.