Surface Modification of a Thin-Film Composite (TFC) Nanofiltration Membrane with 3-Aminopropyltriethoxysilane (APTES) for Efficient Dye–Salt Separation

Abstract

Nanofiltration (NF) technology is attractive in desalting and concentrating dyeing wastewater in the textile industry. A highly efficient NF membrane is critical in reducing the cost of the process. Here, a facile and reliable approach to prepare an NF membrane for the selective separation of dye/salt is proposed by surface grafting of 3-aminopropyltriethoxysilane (APTES) on a fresh polyamide (PA) layer after interfacial polymerization (IP). A thin layer of APTES with a thickness of ∼64 nm was found successfully covalently bonded onto the PA surface via esterification and amidation reactions. The thin-film composite (TFC)-1.0 membrane grafted with 10% APTES achieved a high water permeance of 44.8 L m–2 h–1 bar–1, which was 4.7 times higher than that of the control TFC membrane. Interestingly, the rejection of monovalent salt (NaCl, 11.5%) and divalent salt (Na2SO4, 17.2%) decreased significantly, while the rejection for different dyes (Congo red, reactive blue-19, Coomassie blue G-250, and methyl blue) remained over 99.0%. These noticeable changes in separation performances could be attributed to the large pore size of the active layer, resulting from the interference of APTES on the post-cross-linking of a PA network. The poly­(ethylene glycol) (PEG) filtration experiments confirmed that the mean pore size of the membrane was enlarged significantly from 0.51 to 1.17 nm after surface modification. Finally, the modified membrane showed good long-term stability and excellent separation efficiencies in fractionation of a high salinity Congo red/NaCl (0.2/50 g L–1) mixture. Overall, this work provides a practical strategy to prepare a permeable and selective NF membrane for dye and salt separation by surface grafting of the nascent PA layer.

Progress of Ultrafiltration-Based Technology in Ion Removal and Recovery: Enhanced Membranes and Integrated Processes

“…Enhanced UF membranes with a thin separation layer deposition on the substrate surface can promote the ion selectivity. Using the UF membrane as support, the polyamide thin films prepared by interfacial polymerization (IP) is a common method (Figure b). − The composite thin layer prepared by IP can effectively reject ions due to the narrow ion migration channel and higher electrostatic interaction. Zhai et al used host–guest chemistry to modulate the IP reaction kinetics by depositing Noria (a macrocyclic polyphenol) with PEI on UF membranes .…”

Polyethylenimine Deposited on Phosphomolybdic-Acid-Loaded Polyacrylonitrile Membranes for Enhanced Dye/Salt Separation

“…1−3 Membrane technology provides an alternative to overcome this dilemma by separating organic dyes and salts from textile wastewater through size sieving. 4,5 The membrane separation process not only enables the purification of textile wastewater but also realizes the recycle of organic dyes and salts to achieve "zero discharge". 6 However, ultrafiltration (UF) is incapable of efficiently removing organic dyes owing to the overly large pore size (5.0−50.0 nm).…”

“…Textile wastewater contains high concentrations of carcinogenic organic dyes and inorganic salts, threatening aquatic organisms and human health, and these dyes and salts are inaccessible for effective treatment by traditional physical adsorption and bio- or chemical degradation. − Membrane technology provides an alternative to overcome this dilemma by separating organic dyes and salts from textile wastewater through size sieving. , The membrane separation process not only enables the purification of textile wastewater but also realizes the recycle of organic dyes and salts to achieve “zero discharge” . However, ultrafiltration (UF) is incapable of efficiently removing organic dyes owing to the overly large pore size (5.0–50.0 nm). − Although nanofiltration (NF) can isolate almost all dyes and part of the salts from textile wastewater, the further fractionation of dyes or salts from the mixture is still a barrier due to the overly small pore size (0.5–2.0 nm). , Therefore, a flexible membrane with moderate size between UF and NF is urgently needed for efficient recovery of textile wastewater.…”

TiO2-Decorated Photocatalytic Nanofiltration Membranes for Enhanced Self-Cleaning and Separation Performance

“…Nevertheless, secondary pollution of these technologies should be taken into consideration during the decontamination . Compared with the traditional techniques, membrane separation processes present remarkable separation efficacy, reduced energy consumption, and simple operation properties, , thereby standing out in treating such wastewater. Among them, nanofiltration (NF) membranes with nanoscale pore size, charged surface, and adjustable selective layer outperformed other related technologies to treat the dye wastewater. , Nevertheless, membrane fouling inevitably occurred caused by the adsorption and deposition of foulants, especially for their practical applications in treating wastewater with complex components, thereby ultimately restricting the operational efficiency and increasing the maintenance cost …”