Conventional thin-film composite membranes prepared via interfacial polymerization often exhibit molecular level ‘defects’ that can compromise their liquid separation performance. This research aimed to develop essentially ‘defect-free’ membranes with enhanced size-sieving properties through facile thermal modifications. Low-molecular weight, nitrogenous neutral organic micropollutants, including urea, 1H-benzotriazole, and N-nitrosodimethylamine, were selected as markers to evaluate membrane performance. 

The first methodology examined the sequential application of elevated interfacial polymerization temperature and heat-curing on thin-film composite membranes for efficient urea removal. This systematic study demonstrated that heat-curing effectively minimized ‘defects’ and promoted additional crosslinking. Under brackish water conditions, the modified membranes exhibited a water permeance of 0.8 LMH/bar and urea rejection of 76.7 %. Further optimization of feed solute concentration and transmembrane pressure improved urea rejection to 88.0 %, achieving the highest water/urea selectivity reported to date. Despite such improvements, this thermal modification led to a slight decrease in water permeance.

To overcome this limitation, a second methodology investigated the thermal treatment of hydrated thin-film composite membranes to enhance 1H-benzotriazole rejection. Thermally treated membranes exhibited an unexpected increase in water permeance from 1.0 to 1.6 LMH/bar, while simultaneously maintaining a lower pressure-independent solute flux. This thermal modification effectively produced essentially ‘defect-free’ membranes with enhanced transport properties. Under optimal thermal treatment and operating conditions, thermally treated membranes achieved 97.4 % 1H-benzotriazole rejection.

Lastly, a comparative study evaluated both heat-curing and thermal treatment of hydrated thin-film composite membranes for N-nitrosodimethylamine removal. Both thermal modifications enhanced rejection; however, thermally treated membranes achieved an outstanding rejection of 94.3 % while maintaining a relatively high water permeance of 1.6 LMH/bar. These membranes exhibited the highest N-nitrosodimethylamine rejection reported among state-of-the-art thin-film composite membranes. This research comprehensively demonstrated that the developed methodologies optimize membrane performance for the efficient rejection of a broad range of challenging nitrogenous neutral organic micropollutants, underscoring their potential for diverse advanced liquid separation applications.