3D printed nanofiltration composite membranes with reduced concentration polarisation

3D printed nanofiltration (NF) composite membranes with surface patterns minimising the impact of concentration polarisation (CP) are presented here for the first time. The membranes consist of a NF polydopamine‐coated polyvinylidene fluoride (PVDF/PDA) selective layer on a 3D printed asymmetric wavy (patterned) support. The result is a wavy composite membrane with pure water permeance of 14 ± 2 LMH bar−1 and molecular weight cut-off of ∼550 Da, measured using a crossflow NF setup at a transmembrane pressure of 2 bar for Reynold number (Re) of 700, using a range of dyes (mass balance &gt;97% for all tests). The CP behaviour of the composite membranes was assessed by filtration of Congo red (CR) dye solution (0.01 g L−1), showing that the wavy pattern significantly reduced the impact of CP compared to the flat membranes, with a nearly tripling of the mass transfer coefficient and a 57% decline of the CP factor. Computational fluid dynamics showed that these significant performance improvements were due to improved hydrodynamics, with the maximum surface shear stress induced by the wavy structure (1.35 Pa) an order of magnitude higher than that of the flat membranes (0.18 Pa) at Re = 700. These results demonstrate that 3D printing is a viable technology route to reducing concentration polarisation in membrane nanofiltration applications.</p

Surface-controlled water flow in nanotube membranes

The independent effect of nanotube surface chemistry and structure on the flow of water under nanoscale confinement is demonstrated in this paper for the first time via the synthesis of novel carbon nitride nanotube (CNNT) membranes. Using a combination of experiments and high-fidelity molecular dynamics (MD) simulations, it is shown here that the hydrophilization of the sp 2 carbon structure, induced by the presence of the C-N bonds, decreases the pure water permeance in CNNTs when compared with pristine and turbostratic carbon nanotubes (CNTs). The MD simulations are based on a model true to the chemical structure of the synthesized nanotubes, built from spectroscopy measurements and calibrated potentials using droplet experiments. The effect on permeance is explained in terms of solid-liquid interactions at the nanotube wall with increased water viscosity and decreased surface diffusion near the CNNT wall, when compared to CNTs. A model directly linking the solid-liquid interactions to the water permeance is presented, showing good agreement with both experiments and MD simulations. This work opens the way to tailoring surface chemistry and structure inside nanotube membranes for a wide range of transport and separation processes. </p

Orange juice ultrafiltration:Characterisation of deposit layers and membrane surfaces after fouling and cleaning

The influence of feed condition and membrane cleaning during the ultrafiltration (UF) of orange juice for phytosterol separation was investigated. UF was performed using regenerated cellulose acetate (RCA) membranes at different molecular weight cut-off (MWCO) values with a 336 cm2 membrane area and a range of temperatures (10-40 °C) and different feed volumes (3-9 L). Fluid dynamic gauging (FDG) was applied to assess the fouling and cleaning behaviours of RCA membranes fouled by orange juice and cleaned using P3-Ultrasil 11 over two complete cycles. During the FDG testing, fouling layers were removed by fluid shear stress caused by suction flow. The cleanability was characterised by using ImageJ software analysis. A Liebermann-Buchard-based method was used to quantify the phytosterol content. The results show that RCA 10 kDa filters exhibited the best separation of phytosterols from protein in orange juice at 20 °C using 3 L feed with a selectivity factor of 17. Membranes that were fouled after two cycles showed higher surface coverage compared to one fouling cycle. The surface coverage decreased with increasing fluid shear stress from 0 to 3.9 Pa. FDG achieved 80-95% removal at 3.9 Pa for all RCA membranes. Chemical cleaning using P3-Ultrasil 11 altered both the membrane surface hydrophobicity and roughness. These results show that the fouling layer on RCA membranes can be removed by fluid shear stress without affecting the membrane surface modification caused by chemical cleaning.</p

Hydrophobic poly(vinylidene fluoride) / siloxene nanofiltration membranes

Hydrophobic, chemically resistant nanofiltration (NF) polymeric membranes could provide major improvements to a wide range of processes, from pharmaceutical manufacturing to hazardous waste treatment. Here, we report the fabrication of the first poly (vinylidene fluoride) (PVDF) NF membranes retaining their hydrophobicity and surface chemistry. This was achieved by incorporating in the polymer 2D siloxene, which induce a compaction of the PVDF chains, resulting in low free volume and a highly ordered microstructure. Siloxene nanosheets were obtained from deintercalation of Ca from CaSi2 using HCl, followed by exfoliation and size fractionation, with average lateral dimension of 1–2 μm and thickness of 3–4 nm. The resulting membranes, containing 0.075 wt% of siloxene, have a pure water permeance of 22 ± 2 L m-2 h-1 bar-1 and molecular weight cut-off (MWCO) of 530 Da. The same membrane also showed stable hexane permeance of 11 L m-2 h-1 bar-1 for 24 h with MWCO of around 535 Da. These results supersede the performance of commercial NF membranes, expanding the potential application of nanofiltration to processes requiring stable, chemically resistant and hydrophobic nanofiltration membranes.</p

Hydrophobic poly(vinylidene fluoride) / siloxene nanofiltration membranes

This dataset contains all the data used in the manuscript "HYDROPHOBIC POLY(VINYLIDENE FLUORIDE) / SILOXENE NANOFILTRATION MEMBRANES". The dataset includes: - All materials characterisation data necessary to fully characterise the membranes produced. - Individual data files for pure water permeance and dye and salt rejection tests, inclusive of mass balances. - Calibration data. The dataset integrates the quantitative information already provided in the manuscript and the online supplementary information.Materials Characterisation: The nanosheet morphology with elemental mapping was investigated by high-resolution TEM (JEM-2100Plus, JEOL) with EDS detector (X-Max detector, Oxford Instruments) and SAED was also obtained. The average thickness of the nanosheets was measured by AFM (Asylum Research Jupiter XR, Oxford Instruments). FTIR analysis was performed on siloxene-embedded KBr pellets using a Frontier FTIR spectrometer (Perkin Elmer) and Raman spectra were recorded with a RM1000 Raman Microscope (Renishaw) at 532 nm. XRD (D8-Advance PXRD, Bruker) with Cu Kα1 radiation source was operated at 40 kV and 40 mA (0.015° step size) to examine the crystallinity and phase of the siloxene powders. XPS was performed using a K-alpha+ spectrometer (Thermo Fisher Scientific) with survey scans recorded at 150 eV (1 eV step size) and high-resolution scans at 40 eV (0.1 eV step size). Hydrophilicity of the membranes was assessed using water contact angle goniometer (OCA15, Date Physics) in sessile mode at room temperature. 1 μL droplets of water were used and the values reported are the average of ten measurements at different positions. The surface zeta potential of each membrane sample was measured using a Zetasizer Nano (ZS, Malvern Instruments Ltd.) with the surface ζ accessory at neutral pH = 7.0. A tracer solution was prepared by adding a low concentration of polystyrene in 10 mM NaCl solution. Each sample was measured at least three times and the reported values were the average of the measurements. The surface roughness of the membrane samples was assessed by AFM (AFM Multimode IIIA, Bruker) in tapping mode over scan areas of 5 × 5 μm2. ATR-FTIR (Frontier, Perkin Elmer) was employed to characterize the chemical bonds on the membrane surface. The spectra were collected in the wavenumber range of 4000 to 600 cm-1 by accumulating 10 scans at a resolution of 4 cm-1. The distributions of siloxene on membrane surfaces were investigated by Raman mapping (RM1000 with inVia system, Renishaw) at 532 nm [25]. Areas of 100 × 100 μm2 were scanned on each membrane sample with the line mapping technique. XRD (D8-Advance PXRD, Bruker) with Cu Kα1 radiation source (1.5406 Å) was operated at 40 kV and 40 mA (0.015° step size) to examine the compactness of the PVSi membrane samples. The obtained spectra were analyzed using CrystalDiffract software (CrystalMaker Software Ltd, UK). 2 theta values are reported in Table 3 with 4 significant figures for ease of readability, whereas the original values have 6. The melting behavior of each membrane sample was characterized using differential scanning calorimetry (DSC Q20, TA Instruments). The samples were heated from room temperature (⁓ 20 °C) to 220 °C with a ramping rate of 10 °C min-1. The percentage crystallinity of PVDF in each sample was determined by crystallinity (%)=(ΔH_m)/(∆H_m^0 )×100% (1) where ΔHm is the enthalpy associated with membrane melting and ΔH0m is the theoretical melting enthalpy of 100% crystalline PVDF, which is 104.7 J g-1. The reported data were the average of three measurements taking from the same membrane sample. The dynamic mechanical properties of the membrane samples were analyzed using dynamic thermo-mechanical analysis (DMA1, Mettler Toledo) in auto-tension mode. The samples were cut into 20 × 5 mm2 strips. The sample strips were heated from – 80 °C to 145 °C with ramping rate of 3 °C min-1 in air. The data recorded were the average of three measurements. Membrane performance: Pure water and hexane permeation tests were conducted using a dead-end filtration cell (Sterlitech Corporation) connected with a 5 L feed tank. The operating pressure was fixed at 2 bar with compressed air. All the samples were compacted for 3 h prior to sample collection. The permeance, K (L m-1 h-1 bar-1), of the membrane was calculated by using Equation 2: K= V/∆t∆pA (2) where K is the permeance, V is the permeate volume, A is the effective membrane area (i.e., 14.6 cm2), Δt is the time for permeate collection and Δp is the operating pressure (i.e., 2 bar). After the pure water or solvent test, the membrane sample was transferred into a cross-flow cell for the rejection tests of different dyes and salts. The concentrations of all the dye feed solutions were 0.01 g L-1, whereas the concentrations of salt solutions were 1 g L-1 except for NaCl, which was 2 g L-1. The concentrations of dyes and salts in the feed, permeate and retentate solutions were measured by UV-visible spectrophotometer (Cary 100, Agilent) and conductivity meter (Thermo Fisher), respectively. The rejection of the tracer was calculated using Equation 3: R=(1-C_p/C_f )×100% (3) where R is the rejection, Cp and Cf are the tracer concentrations in the permeate and feed solutions, respectively. The mass balance for each rejection test was also calculated according to mass balance (%)=(C_p V_p+C_r V_r)/(C_f V_f )×100% (4) where Cr is the tracer concentration in the retentate solution, Vp, Vr and Vf are the volume of permeate, retentate and feed solutions, respectively. For all the filtration/separation tests, at least three samples were tested for each membrane and the average value was recorded

The influence of membrane charge and porosity upon fouling and cleaning during the ultrafiltration of orange juice

The ultrafiltration of orange juice has been performed to separate phytosterols from proteins. Commercial regenerated cellulose acetate (RCA) ultrafiltration membranes of different molecular weight cut offs (MWCOs) of 10 kDa, 30 kDa and 100 kDa were fouled with orange juice and cleaned with Ultrasil 11 over two operational cycles. Fouling and cleaning mechanisms were investigated by using surface zeta potential, Brunauer-Emmet-Teller (BET) analysis and Fourier transform infrared (FTIR) analysis. The RCA conditioned membranes displayed zeta potential values of −0.2 to −31.5 mV. Fouling caused RCA membranes to have a greater magnitude of negative surface charge and cleaning restored the membrane surface charges close to its pristine state. Fouling increased both the total surface area and the total pore volume of all membranes. The total surface area and total pore volume for RCA 100 kDa after fouling increased by 102% and 185%, respectively. Pore area and volume distributions revealed that the porosities were returned close to the original level after cleaning. The recovery flux ratios of RCA 10, RCA 30 and RCA 100 decreased after fouling by 27%, 6% and 10% respectively; and changes were 25%, 9% and 1% respectively after cleaning. The charge of membrane surfaces after two operational cycles and the IR intensity of RCA membrane deposits, varied with MWCO such that RCA 30 &gt; RCA 100 &gt; RCA 10. Ultrafiltration using RCA 10 kDa membrane displayed the best separation efficiency, with 32 ± 4% rejection of phytosterols. and 96 ± 1% rejection of proteins. Changes in membrane surface charge and porosity have been found to affect the RCA membrane performance due to fouling and cleaning during the isolation of phytosterols from orange juice.</p

Towards next generation “smart” tandem catalysts with sandwiched mussel-inspired layer switch

In this paper, we prepared a novel reactor with switchable ability to address present challenges in tandem catalyst. By introducing mussel-inspired moiety, this goal was achieved via preparing a “smart” polymer reactor which can open or closes the entry tunnel of the targeted substrate in cascade reactions. The catalyst consisted of two functional layers acting as tandem catalytic parts and one smart layer with mussel-inspired moieties as a controlled middle switch. The top and the bottom layer were made of molecularly imprinted polymers and catalytic components, like acidic parts and metal nanoparticles, respectively. The middle layer made of polymeric dopamine (PDPA) and acrylamide with self-healing ability will allow or inhibit the intermediate product for the reaction, thus controlling the process of the tandem catalysis. As a result, the novel catalyst exhibited self-controlled tandem catalysis, which provides new opportunities to design smart tandem catalysts, showing a promising prospect in this area