Search

High‐precision separation with increased water permeability is critical for efficient membrane‐based water treatment processes. To achieve high selectivity toward different targeted species while allowing rapid water transportation, the structure of the membrane polyamide selective layer requires delicate regulation. Herein, an effective approach to systematically expand the pore size of polyamide layers by incorporating ammonium ion‐modified carbon dots (CDs) into the polyamide network is developed. The ammonium ions with different alkyl chain lengths attached to the CDs create nanochannels of different sizes in the network to lower the energy barrier for water transportation while maintaining high selectivity to targeted species. When the alkyl chain length of the ammonium ions reaches eight carbon atoms (i.e., C8 ions), the amphiphilic C8‐CDs induce the formation of the ridged nanostructure on the membrane surface and hence the increased membrane filtration area. The resultant thin‐film nanocomposite (TFN) membrane, denoted as the TFN‐C8‐CDs membrane, demonstrates a higher Na2SO4 rejection of 98.9% and NaCl/Na2SO4 selectivity of 83.1 than the pristine polyamide membrane, together with a tripled pure water permeability of 29.0 L m−2 h−1 bar−1. Herein, a viable approach for ingeniously designing the nanochannels and surface nanostructure of polyamide membranes for more efficient filtration processes is provided. [ABSTRACT FROM AUTHOR]

In this work, we explored the practicability of a nanochannel-based biomimetic membrane (NBM) incorporating pillar[5]arene water channels for seawater reverse osmosis (SWRO) desalination. Two classes of peptide-attached biomimetic channels, (pR)-pillar[5]arenes (pRPH) and (pS)-pillar[5]arenes (pSPH) were integrated into the selective layer of SWRO membranes via interfacial polymerization on the top side of a polysulfone (PSf) support membrane. Here, pSPH is a non-identical stereoisomer of pRPH and was used as a negative control to pRPH to elucidate the flux enhancement effect contributed by pRPH. The optimized NBM presented a water permeability of 2.52 L m-2 h-1 bar-1 and 99.5% rejection under SWRO testing conditions of 50 bar applied pressure and 32,000 mg/L NaCl as feed solution. The 62% permeability increment with reference to the control membrane is hypothesized to originate from hybrid polyamide layers that were rougher with more voids (higher effective surface area and lower hydraulic resistance for water transport) as well as the conceivable water transport pathways provided by the pRPH channels. The simulation results from module-scale modelling suggest that the optimized NBM could lead to 7.2% savings in specific energy consumption of the membrane unit stage (or reduce the required membrane area by 25%) with respect to the commercial SWC4-LD membrane. The performance of the optimized NBM was further assessed in a one-week desalination test using an actual seawater feed gathered from an SWRO plant in Singapore. The robust NBM exhibited stable performance and ∼28% higher water flux (42 L m-2 h-1) than SWC4-LD with a comparable rejection of 99.3%, suggesting the feasibility of pillar[5]arene-based biomimetic membranes for seawater desalination. [Display omitted] • pRPH nanochannel-based biomimetic membrane (NBM) was used for SWRO application. • pRPH channels were incorporated into the PA layer via interfacial polymerization. • High permeability of 2.52 Lm-2h-1bar-1 (99.5% NaCl rejection) was reported in SWRO. • The energy and footprint savings achievable was quantified by module-scale modelling. • The NBM exhibited stable flux in a 7-day desalination test using real seawater. [ABSTRACT FROM AUTHOR]

Nanoscale characteristics of the polyamide layer are key towards the high desalination performance of thin-film composite reverse osmosis (TFC-RO) membranes. Further advancements in the performance of TFC membranes necessitate a comprehensive understanding of the desired polyamide characteristics and its formation mechanisms. Empirical evidence has shown that the properties of the support layer is as equally important as the interfacial polymerization (IP) conditions in the fabrication of high permselectivity TFC membranes for desalination. Herein, we discuss the properties of polyamide layers formed using identical IP conditions over support membranes of different polymers and chemistries (polyethersulfone, polyetherimide and polysulfone) under fairly similar surface pore properties. The characteristics of the polyamide layers formed thereon displayed different physicochemical properties. It is postulated that the support membrane chemistry actually affects the IP reaction and polyamide formation by controlling the amine diffusion speed as well as the breadth of the IP reaction zone (i.e., the region between the interface and the furthest point in which the reaction occurs). Transmission electron microscopy analyses further revealed the nanoscale differences in the polyamide layer (heights ranging from 50 to 200 nm), including intrinsic thickness of basal layer (~10–35 nm) and leaf-like top layer (~20–85 nm), as well as the presence of nanovoids. Finally, we propose a conceptual model to underline the role of support membrane chemistry in the IP reaction, and consequently the formation mechanism of the nanoscale polyamide features. The mechanistic insights from this study are expected to provide more understanding towards a better control over the fabrication of polyamide layers for TFC membranes. The findings in this work are also expected to facilitate tailoring polyamide layers for specific osmotically driven processes. [Display omitted] • Support membrane chemistry affects MPD diffusion and partitioning extent in IP. • TEM and SEM analyses revealed changes in the polyamide (PA) nanoscale morphology. • PA layer of TFC-PES membrane was thin and smooth without any nanovoids. • PA layer of TFC-PSf membrane had thick base, thin leaves and multi-layer nanovoids. • PA layer of TFC-PEI membrane had thin basal layer with clumpy roof-like top layer. [ABSTRACT FROM AUTHOR]

This study examined the feasibility and performance of a nanochannel-based biomimetic membrane (NBM) for brackish reverse osmosis (RO) desalination. Two types of peptide-attached synthetic nanochannels, (pR)-pillar[5]arenes (pRPH) and (pS)-pillar[5]arenes (pSPH), were incorporated into liposomes. pSPH is a diastereomer of pRPH and was used as a negative control (i.e. mutant) to pRPH in this work. The nanochannel-containing liposomes (e.g. pRPH-liposomes) were then immobilized into the active layer of the RO membranes via in situ interfacial polymerization on the top of a polysulfone support membrane to form NBM-pRPH membranes. To maximize the potential and benefits of the NBM-pRPH membrane, the physical characteristics of the polyamide layer was further tuned using some additives and the eventual membrane was named as NBM-pRPH-A. The NBM-pRPH-A membrane exhibited a water permeability of 6.09 L m−2 h−1 bar−1 and 98.2% NaCl rejection under a 15.5 bar applied pressure using 2000 mg L−1 as feed solution. The 62% flux increment with respect to the pristine control is postulated to arise from a thinner, less cross-linked (more free volume) and more hydrophilic active layer as well as the possible supplementary transport pathways of the pRPH-liposomes. The performance of the NBMs under differential feed pressures and temperatures further exemplifies the water permeation property of the pRPH nanochannels. Accordingly, the NBM-pRPH-A gave a water permeability higher than commercial RO membranes tested in this work (DuPont BW30 and Hydranautics ESPA2) as well as other RO membranes reported in the literature. This study provides a tangible foundation for the development of NBMs for brackish RO desalination. [Display omitted] • Synthetic pRPH nanochannel-based biomimetic membrane was used for BWRO application. • pRPH-liposomes were incorporated onto the PA layer via interfacial polymerization. • STEM-EDX analysis revealed the existence of liposomes in the PA layer. • High permeability of 6.09 Lm−2h−1bar−1 (98.2% NaCl rejection) was reported in BWRO. • RO tests under increasing ΔP and temperature suggested water transport across pRPH. [ABSTRACT FROM AUTHOR]