Synthesis Of Thin Film Composite Membranes Research Articles

Engraving Polyamide Layers by In Situ Self-Etchable CaCO3 Nanoparticles Enhances Separation Properties and Antifouling Performance of Reverse Osmosis Membranes.

Nanovoids within a polyamide layer play an important role in the separation performance of thin-film composite (TFC) reverse osmosis (RO) membranes. To form more extensive nanovoids for enhanced performance, one commonly used method is to incorporate sacrificial nanofillers in the polyamide layer during the exothermic interfacial polymerization (IP) reaction, followed by some post-etching processes. However, these post-treatments could harm the membrane integrity, thereby leading to reduced selectivity. In this study, we applied in situ self-etchable sacrificial nanofillers by taking advantage of the strong acid and heat generated in IP. CaCO3 nanoparticles (nCaCO3) were used as the model nanofillers, which can be in situ etched by reacting with H+ to leave void nanostructures behind. This reaction can further degas CO2 nanobubbles assisted by heat in IP to form more nanovoids in the polyamide layer. These nanovoids can facilitate water transport by enlarging the effective surface filtration area of the polyamide and reducing hydraulic resistance to significantly enhance water permeance. The correlations between the nanovoid properties and membrane performance were systematically analyzed. We further demonstrate that the nCaCO3-tailored membrane can improve membrane antifouling propensity and rejections to boron and As(III) compared with the control. This study investigated a novel strategy of applying self-etchable gas precursors to engrave the polyamide layer for enhanced membrane performance, which provides new insights into the design and synthesis of TFC membranes.

Naturally Derived Allylated Gallic Acid for Interfacially Polymerized Membranes

A naturally derived monomer, allylated gallic acid (AG), was herein proposed as a monomer for interfacially polymerized thin-film composite nanofiltration membranes. We investigated the synthesis of the thin-film composite polyester membranes by varying the concentration of the AG monomer and the reaction time with trimesoyl chloride. In addition, we demonstrated the synthesis of a polyesteramide film using a mixture of AG and m-phenylene diamine, although there are a few orders of magnitude differences in their reactivity. While membranes prepared using the classical polyamide process had a water permeance of 0.54 L m–2 h–1 bar–1 , the prepared polyesteramide and polyester films had water permeances of 12.3 and 47.6 L m–2 h–1 bar–1, respectively The rejection of dyes was larger than 700 g mol–1 and could be tuned to 327 g mol–1 by changing the chemical composition and reaction time. The retention of inorganic salts followed the order Na2SO4 > MgSO4 ≈ NaCl. Therefore, the membrane performance demonstrates the potential of the phenolic monomer to be integrated into the synthesis of thin-film composite membranes. Besides, the availability of the free allyl group holds potential for further modification and covalent binding onto the surface.

Use of Ionic Liquids and Co-Solvents for Synthesis of Thin-Film Composite Membranes.

Polyamide (PA) thin-film composite (TFC) membranes are commonly applied in reversed osmosis (RO) and nanofiltration (NF) applications due to their thin, dense top-layer, and high selectivity. Recently, the conventional organic phase (i.e., hexane) during interfacial polymerization (IP) was replaced by less toxic ionic liquids (ILs) which led to excellent membrane performances. As the high price of most ILs limits their up-scaling, the potential use of inexpensive Aliquat was investigated in this study. The thin-film composite (TFC) membranes were optimized to remove flavor compounds, i.e., ethyl acetate (EA) and isoamyl acetate (IA), from a fermentation broth. A multi-parameter optimization was set-up involving type of support, reaction time for IP, water content of Aliquat, and concentration of both monomers m-phenylenediamine (MPD) and trimesoylchloride (TMC). The membranes prepared using Aliquat showed similar fluxes as those prepared from a reference IL 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([C4mpyr][Tf2N]) but with better EA and IA retentions, even better than for a commercial RO membrane (GEA type AF). Finally, the recently introduced epoxide-curing of Bisphenol A diglycidyl ether (BADGE) with 1,6-hexanediamine (HDA) was investigated using Aliquat as organic phase. It is the first time this type of IP was performed in combination with an IL as organic phase. The resulting membrane was used in the filtration of a 35 µM Rose Bengal (RB) in 20 wt% dimethylformamide/ water (DMF/H2O) feed mixture. A well-crosslinked poly(β-alkanolamine) film was obtained with a > 97% retention.

Synthesis of thin-film composite forward osmosis membranes for removing organic micro-pollutants from aqueous solutions

Abstract In this study, a thin-film composite (TFC) forward osmosis membrane was synthesized and characterized with various concentrations (15%, 16%, 17% and 18%) of polysulfone for the removal of two organic micro-pollutants, namely phenol and benzene from the aqueous solutions. Synthesis of a thin-film composite membrane with a support layer carried out by dissolving an amount of polysulfone polymer and polyvinyl pyrrolidone in N-methyl,2-pyrrolidone via phase inversion process and a thin-film layer of the polyamide M-phenylenediamine (MPD) and 1,3,5-benzene trichloride by interfacial polymerization reaction for the fabrication of the TFC were examined. Water flux and reverse salt flux decreased with increasing the concentration of polysulfone polymer. The composite membranes with polysulfone at 16% and 17% had even higher efficiencies. Also, by increasing the concentration of the draw solution, further phenol and benzene could be removed. The highest rejection rates of phenol (polar) and benzene (nonpolar) were found to be 79% and 90%, respectively. The results showed the capability of the thin-film composite forward osmosis (TFC-FO) membranes for removing organic micro-pollutants from the aqueous solutions under different operating conditions, with the efficiency of removing nonpolar compounds being higher.