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

3D printed composite membranes with enhanced anti-fouling behaviour

The fabrication of three dimensional (3D) printed composite membranes by depositing a thin polyethersulfone (PES) selective layer onto ABS-like 3D printed flat and wavy structured supports is presented here for the first time. The 50 mm disk supports were printed using an industrial 3D printer with both flat and double sinusoidal, i.e. wavy, surface structures. The thin selective layers were deposited onto the 3D supports via vacuum filtration. The resulting flat and wavy composite membranes were characterised and tested in terms of permeance, rejection, and cleanability by filtering oil-in-water emulsions of 0.3−0.5 vol% through a cross-flow (Reynolds number, Re = 100, 500 and 1000) ultrafiltration set-up under a constant transmembrane pressure of 1 bar. Results showed that pure water permeance through the wavy membrane was 30% higher than the flat membrane for Re = 1000. The wavy 3D printed membrane had a 52% higher permeance recovery ratio compared to the flat one after the first filtration cycle, with both membranes having an oil rejection of 96% ± 3%. The wavy 3D composite membrane maintained some level of permeation after 5 complete filtration cycles using only water as the cleaning/rinsing agent, whereas the flat one was completely fouled after the first cycle. Cleaning with NaOCl after the sixth cycle restored ~70% of the initial permeance for the wavy membrane. These results demonstrate that 3D printed wavy composite membranes can be used to significantly improve permeation and cleanability performance, particularly in terms of reducing fouling build-up, i.e. the main obstacle limiting more widespread adoption of membranes in industrial applications.</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

3D printed composite membranes with enhanced anti-fouling behaviour

The fabrication of three dimensional (3D) printed composite membranes by depositing a thin polyethersulfone (PES) selective layer onto ABS-like 3D printed flat and wavy structured supports is presented here for the first time. The 50 mm disk supports were printed using an industrial 3D printer with both flat and double sinusoidal, i.e. wavy, surface structures. The thin selective layers were deposited onto the 3D supports via vacuum filtration. The resulting flat and wavy composite membranes were characterised and tested in terms of permeance, rejection, and cleanability by filtering oil-in-water emulsions of 0.3−0.5 vol% through a cross-flow (Reynolds number, Re = 100, 500 and 1000) ultrafiltration set-up under a constant transmembrane pressure of 1 bar. Results showed that pure water permeance through the wavy membrane was 30% higher than the flat membrane for Re = 1000. The wavy 3D printed membrane had a 52% higher permeance recovery ratio compared to the flat one after the first filtration cycle, with both membranes having an oil rejection of 96% ± 3%. The wavy 3D composite membrane maintained some level of permeation after 5 complete filtration cycles using only water as the cleaning/rinsing agent, whereas the flat one was completely fouled after the first cycle. Cleaning with NaOCl after the sixth cycle restored ~70% of the initial permeance for the wavy membrane. These results demonstrate that 3D printed wavy composite membranes can be used to significantly improve permeation and cleanability performance, particularly in terms of reducing fouling build-up, i.e. the main obstacle limiting more widespread adoption of membranes in industrial applications.</p

A Fluctuation-Driven Mechanism for Slow Decision Processes in Reverberant Networks

The spike activity of cells in some cortical areas has been found to be correlated with reaction times and behavioral responses during two-choice decision tasks. These experimental findings have motivated the study of biologically plausible winner-take-all network models, in which strong recurrent excitation and feedback inhibition allow the network to form a categorical choice upon stimulation. Choice formation corresponds in these models to the transition from the spontaneous state of the network to a state where neurons selective for one of the choices fire at a high rate and inhibit the activity of the other neurons. This transition has been traditionally induced by an increase in the external input that destabilizes the spontaneous state of the network and forces its relaxation to a decision state. Here we explore a different mechanism by which the system can undergo such transitions while keeping the spontaneous state stable, based on an escape induced by finite-size noise from the spontaneous state. This decision mechanism naturally arises for low stimulus strengths and leads to exponentially distributed decision times when the amount of noise in the system is small. Furthermore, we show using numerical simulations that mean decision times follow in this regime an exponential dependence on the amplitude of noise. The escape mechanism provides thus a dynamical basis for the wide range and variability of decision times observed experimentally

Fouling resistant 2D boron nitride nanosheet – PES nanofiltration membranes

A novel fouling-resistant nanofiltration mixed-matrix membrane was obtained by the incorporation of 2D boron nitride nanosheets (BNNS) in polyethersulfone (PES). The addition of just 0.05 wt% of BNNS into the PES matrix led to a 4-fold increase in pure water permeance with a 10% decrease in the rejection of the dye Rose Bengal; up to 95% rejection of humic acid and nearly 100% flux recovery over two cycles in cross-flow fouling tests without the need for chemical cleansing. This performance is attributed to the uniform distribution of the BNNS in the PES matrix, observed via Raman mapping, and the surface chemistry and structure of the BNNS, which hydrophilised the polymer matrix and reduced its surface roughness. The low amount of BNNS filler needed to render the mixed-matrix membrane fouling-resistant opens the way to its use in waste-water treatment applications where organic fouling remains a major challenge.</p

Jet energy measurement with the ATLAS detector in proton-proton collisions at root s=7 TeV

The jet energy scale and its systematic uncertainty are determined for jets measured with the ATLAS detector at the LHC in proton-proton collision data at a centre-of-mass energy of √s = 7TeV corresponding to an integrated luminosity of 38 pb-1. Jets are reconstructed with the anti-kt algorithm with distance parameters R=0. 4 or R=0. 6. Jet energy and angle corrections are determined from Monte Carlo simulations to calibrate jets with transverse momenta pT≥20 GeV and pseudorapidities {pipe}η{pipe}<4. 5. The jet energy systematic uncertainty is estimated using the single isolated hadron response measured in situ and in test-beams, exploiting the transverse momentum balance between central and forward jets in events with dijet topologies and studying systematic variations in Monte Carlo simulations. The jet energy uncertainty is less than 2. 5 % in the central calorimeter region ({pipe}η{pipe}<0. 8) for jets with 60≤pT<800 GeV, and is maximally 14 % for pT<30 GeV in the most forward region 3. 2≤{pipe}η{pipe}<4. 5. The jet energy is validated for jet transverse momenta up to 1 TeV to the level of a few percent using several in situ techniques by comparing a well-known reference such as the recoiling photon pT, the sum of the transverse momenta of tracks associated to the jet, or a system of low-pT jets recoiling against a high-pT jet. More sophisticated jet calibration schemes are presented based on calorimeter cell energy density weighting or hadronic properties of jets, aiming for an improved jet energy resolution and a reduced flavour dependence of the jet response. The systematic uncertainty of the jet energy determined from a combination of in situ techniques is consistent with the one derived from single hadron response measurements over a wide kinematic range. The nominal corrections and uncertainties are derived for isolated jets in an inclusive sample of high-pT jets. Special cases such as event topologies with close-by jets, or selections of samples with an enhanced content of jets originating from light quarks, heavy quarks or gluons are also discussed and the corresponding uncertainties are determined. © 2013 CERN for the benefit of the ATLAS collaboration

Measurement of the inclusive and dijet cross-sections of b-jets in pp collisions at sqrt(s) = 7 TeV with the ATLAS detector

The inclusive and dijet production cross-sections have been measured for jets containing b-hadrons (b-jets) in proton-proton collisions at a centre-of-mass energy of sqrt(s) = 7 TeV, using the ATLAS detector at the LHC. The measurements use data corresponding to an integrated luminosity of 34 pb^-1. The b-jets are identified using either a lifetime-based method, where secondary decay vertices of b-hadrons in jets are reconstructed using information from the tracking detectors, or a muon-based method where the presence of a muon is used to identify semileptonic decays of b-hadrons inside jets. The inclusive b-jet cross-section is measured as a function of transverse momentum in the range 20 < pT < 400 GeV and rapidity in the range |y| < 2.1. The bbbar-dijet cross-section is measured as a function of the dijet invariant mass in the range 110 < m_jj < 760 GeV, the azimuthal angle difference between the two jets and the angular variable chi in two dijet mass regions. The results are compared with next-to-leading-order QCD predictions. Good agreement is observed between the measured cross-sections and the predictions obtained using POWHEG + Pythia. MC@NLO + Herwig shows good agreement with the measured bbbar-dijet cross-section. However, it does not reproduce the measured inclusive cross-section well, particularly for central b-jets with large transverse momenta.Comment: 10 pages plus author list (21 pages total), 8 figures, 1 table, final version published in European Physical Journal