Post-Treatment of Nanofiltration Polyamide Membrane through Alkali-Catalyzed Hydrolysis to Treat Dyes in Model Wastewater

Abstract

This research focused on the influence of post-treatment using alkali-catalyzed hydrolysis with a full-aromatic nanofiltration (NF) polyamide membrane and its application to the efficient removal of selected dyes. The post-treated membranes were characterized through Fourier transform infrared spectroscopy, goniometry, and zeta-potential analysis to analyze the treatment-induced changes in the intrinsic properties of the membrane. Furthermore, the changes in permeability induced by the post-treatment were evaluated via the measurement of water flux, NaCl rejection, and molecular weight cutoff (MWCO) under different pH conditions and post-treatment times. Major changes induced by the post-treatment in terms of physicochemical properties were the enhancement of permeability, hydrophilicity, and negative charge due to the hydrolysis of the membrane’s amide bonds. Four different dyes were selected as representative organic pollutants considering the MWCO of the post-treated membranes. Compared with the pristine NF membrane, membranes post-treated at pH 13.5 showed better water flux with similar rejection of the target dyes. On the basis of these results, the proposed post-treatment method for NF membranes can be applied to the removal of organic pollutants of various size.

Removal of Different Dye Solutions: A Comparison Study Using a Polyamide NF Membrane

“…This technology is based on the separation of compounds by size and charge, as the membrane acts as a filter that retains the molecules which are larger than the pore and allows the water to pass through. In the last decade, more than 65% of research works have been based on the fabrication strategies of nanoporous membranes and their applications in the field of water purification [ 7 , 8 , 9 , 10 , 11 , 12 ]. According to Wang et al the solute and water permeability play important roles in the membrane performance.…”

Chemical Cleaning Process of Polymeric Nanofibrous Membranes

“…It was found that an alkali-catalyzed hydrolysis PA membrane was observed after post-treatment at pH 14 for 28 days [ 26 ]. Herein, PA6 PNM was kept in NaOH for 24 h, which did not show any changes.…”

“…Under extreme pH conditions, the structure of amide bonds in polyamide can be easily destroyed by an acid or base. Since hydrogen or hydroxide ions react with oxygen/nitrogen or carbon atoms in amide bonding, this can abate the resonance structure of an amide and cause hydrolysis of the amide bond [ 26 ]. Moreover, under strong acidic and alkaline conditions, the charged groups in the membrane matrix can cause internal charged repulsion, resulting in expansion of the membrane structure and pores.…”

Improving the Structural Parameter of the Membrane Sublayer for Enhanced Forward Osmosis

“…In general, no obvious peculiarities were visible in the diagrams, except for the significant change in the intensities of the O-H band in the 3000-3680 cm −1 region between the TFC FOs and their support membranes. It is postulated that the increases in intensity may have helped increase the surface hydrophilicities of the TFC FO membranes, as evidenced by the CA measurements, that is, MS2 > MS1 > MS3 [34,35]. The weak peaks observed at 1660 cm −1 and 1550 cm −1 in TFC FO membranes correspond to amide I (C = O stretching) and amide II (N-H bending), both due to the formation of product groups during the IP reaction.…”