Ultrathin Polyamide Membrane with Decreased Porosity Designed for Outstanding Water-Softening Performance and Superior Antifouling Properties

Abstract

Poly(piperazine-amide)-based nanofiltration membranes exhibit a smooth surface and superior antifouling properties but often have lower Ca 2+ and Mg 2+ rejection due to their larger inner micropore and thus cannot be extensively used in water-softening applications. To decrease the pore size of poly(piperazine-amide) membranes, we designed and synthesized a novel monomer, 1,2,3,4-cyclobutane tetracarboxylic acid chloride (BTC), which possesses a smaller molecular conformation than trimesoyl chloride (TMC). The thickness of the prepared BTC−piperazine (PIP) polyamide nanofilm via interfacial polymerization is as thin as 15 nm, significantly lower than the 50 nm thickness of the TMC−PIP nanofilm. The surface characterization reveals that the BTC−PIP polyamide membrane exhibits an enhanced hydrophilicity, a smooth surface, and a decreased surface-negative charge. The desalination performance (both rejection and water flux) of these membranes in terms of Ca 2+ and Mg 2+ exceeds that of the current commercial water-softening membranes. In addition, the BTC−PIP polyamide membrane also exhibits superior antifouling properties compared to the TMC-based polyamide membrane. More importantly, molecular simulations show that the BTC−PIP membrane has a lower average pore size than that of the TMC−PIP membrane, which demonstrates an enhanced steric hindrance effect, as confirmed by desalination performance. Our results demonstrate that in the household and industrial water-softening market, BTC−PIP membrane with decreased porosity, enhanced hydrophilicity, and smooth surface is preferred alternative to the conventional TMC-based polyamide membranes.

Asymmetric polyamide nanofilms with highly ordered nanovoids for water purification

“…Upper-bound line represents the level of permeability and selectivity achieved by the currently prepared membranes. In order to illustrate the superiority of the asymmetric polyamide nanofilm between permeability and selectivity, we calculated related permeability/selectivity data of different types of polyamide membranes as currently reported in the literature, such as commercial polyamide membrane (Commercial membrane) 44 , crumpled polyamide membrane (IP with crumpled structure) 16,28,32 , polyamide membrane prepared by interlayer (Interlayer-IP) 20,21,26,[45][46][47][48] , traditional IP membrane (IP) 12,28,[49][50][51][52] , and mixed matrix polyamide membranes (MMMs) 14,[53][54][55][56][57][58][59][60] , as shown in Fig. 6a, b.…”

“…Combined the Eqs. (12) and (13), γ d S and γ p S can be obtained. Bringing these two parameters into the Eq.…”

“…Extensive efforts have been dedicated to tailoring the structural morphology of the polyamide dense layer. Tuning the monomer formula [12][13][14][15] , fabrication process [16][17][18][19] and porous support structural property 20,21 are the usual methods, which mainly generates two effects, one is to form a thinner polyamide dense layer, the other is to increase the specific surface area via nanoscale voids formation. The thinner polyamide dense layer aims to lower the resistance of water transport across the active layer, and thereby improve permeance.…”

Ultrathin Membranes for Separations: A New Era Driven by Advanced Nanotechnology

“…[4,9,[41][42][43][44][45][46] In addition, other monomers with novel structures, such as those hosting good chemical robustness, high microporosity, and solvent resistance have expanded the options for the development of innovative ultrathin PA membranes. [31,[47][48][49] Moreover, interfacial synthesis can also be leveraged to prepare COF and MOF membranes. Langmuir-Blodgett (LB) method is a common example to synthesize ultrathin 2D COF nanofilms at the air-water interface effectively.…”

Inner Surface Hydrophilic Modification of PVDF Membrane with Tea Polyphenols/Silica Composite Coating

“…Therefore, hydrophilic modification of the hydrophobic membrane is of vital importance. Many efforts such as blending [ 15 , 16 , 17 , 18 ], grafting [ 19 , 20 ], co-polymerization [ 21 , 22 , 23 , 24 ] and layer-by-layer assembly [ 25 , 26 , 27 ] methods have been devoted to improving the hydrophilicity of the membrane. However, these methods may require special equipment or complicated conditions, and have certain limitations in practical applications.…”