Preparation and characterization of low fouling novel hybrid ultrafiltration membranes based on the blends of GO−TiO2 nanocomposite and polysulfone for humic acid removal

In this work, graphene oxide (GO)−TiO2 nanocomposite was synthesized by in situ sol−gel reaction at pH=2 using GO nanosheets suspension and titanium isopropoxide precursor. The synthesized GO−TiO2 nanocomposite was explored as a filler to fabricate improved antifouling novel hybrid ultrafiltration membranes for removal of humic acid from aqueous solution. Membranes were fabricated from polymer blend solutions containing polysulfone and GO−TiO2 with varied loading amount (0–5wt%) by the non-solvent induced phase separation (NIPS) method. Contact angle, atomic force microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy and outer surface zeta potential studies were conducted in order to characterise the membranes in terms of roughness, structure, surface properties and charge. The porous hydrophilic hybrid membranes were shown to have an asymmetric structure with improved surface roughness. The water permeability and antifouling capacity of hybrid membranes with 10ppm HA solution were dependent on the loading amount of GO–TiO2. Incorporation of GO–TiO2 nanocomposite was found to improve the antifouling characteristics of the membranes when challenged with HA solutions. Irreversible HA fouling was substantially reduced with increased loading of GO−TiO2 nanocomposite (wt%). The lowest irreversible fouling ratio (3.2%) was obtained for the membrane containing 5wt% nanocomposite (to total wt% of PSf, MG−5). Ultrafiltration of HA solutions of varied concentrations using hybrid membranes was studied at pH=7 and 1bar feed pressure. The removal efficiency of hybrid membranes for HA was controlled by the membrane surface charge concentration, porosity and HA exclusion. The membrane MG−5 had the highest HA removal efficiency for 10ppm HA solution at pH=7. [Display omitted] •GO−TiO2 nanocomposite was synthesized via in situ sol–gel method at pH=2.•Low fouling novel hybrid ultrafiltration membranes were fabricated by NIPS method.•Membranes had improved ability to reduce irreversible HA fouling.•Membranes were efficient in the removal of HA from 10 ppm solution

Defining Swelling Kinetics in Block Copolymer Thin Films: The Critical Role of Temperature and Vapour Pressure Ramp

We studied the kinetics of swelling in high-χ lamellar-forming poly(styrene)-block- poly(lactic acid) (PS-b-PLA) block copolymer (BCP) by varying the heating rate and monitoring the solvent vapour pressure and the substrate temperature in situ during solvo-thermal vapour annealing (STVA) in an oven, and analysing the resulting morphology. Our results demonstrate that there is not only a solvent vapour pressure threshold (120 kPa), but also that the rate of reaching this pressure threshold has a significant effect on the microphase separation and the resulting morphologies. To study the heating rate effect, identical films were annealed in a tetrahydrofuran (THF) vapour environment under three different ramp regimes, low (rT1 °C/min), medium (2rT3 °C/min) and high (rT>4 °C/min), for 60, 90 and 120 min, respectively, while the solvent vapour pressure and the substrate temperature were measured in real time. The translational order improved significantly with increasing the heating rate. The solvent mass uptake calculated for the different ramp regimes during annealing is linearly proportional to time, indicating that the swelling kinetics followed Case II diffusion. Two stages of the swelling behaviour were observed: (i) diffusion at the initial stages of swelling and (ii) stress relaxation, controlled at later stages. Films with a faster rate of increase in vapour pressure (rP>2 kPa/min) reached the pressure threshold value at an early stage of the swelling and attained a good phase separation. According to our results, highly ordered patterns are only obtained when the volume fraction of the solvent exceeds the polymer volume fraction, i.e., (φs≥φp), during the swelling process, and below this threshold value (φs=0.5), the films did not obtain a good structural order, even at longer annealing times

Electrochemical Applications of Two-Dimensional Nanosheets: The Effect of Nanosheet Length and Thickness

Although many electrochemical properties of 2D materials depend sensitively on the nanosheet dimensions, there are no systematic, quantitative studies which analyze the effect of nanosheet size and thickness on electrochemical parameters. Here we use size-selected WS₂ nanosheets as a model system to determine the effect of nanosheet dimensions in two representative areas: hydrogen evolution electrocatalytic electrodes and electrochemical double layer capacitor electrodes. We chose these applications, as they depend on the interaction of ions with the nanosheet edge and basal plane, respectively, and so would be expected to be nanosheet-size-dependent. The data show the catalytic current density to scale inversely with mean nanosheet length while the volumetric double layer capacitance scales inversely with mean nanosheet thickness. Both of these results are consistent with simple models allowing use to extract intrinsic quantities, namely the turnover frequency and the double layer thickness, respectively

Activated Graphene Oxide-Calcium Alginate Beads for Adsorption of Methylene Blue and Pharmaceuticals

The remarkable adsorption capacity of graphene-derived materials has prompted their examination in composite materials suitable for deployment in treatment of contaminated waters. In this study, crosslinked calcium alginate–graphene oxide beads were prepared and activated by exposure to pH 4 by using 0.1M HCl. The activated beads were investigated as novel adsorbents for the removal of organic pollutants (methylene blue dye and the pharmaceuticals famotidine and diclofenac) with a range of physicochemical properties. The effects of initial pollutant concentration, temperature, pH, and adsorbent dose were investigated, and kinetic models were examined for fit to the data. The maximum adsorption capacities qmax obtained were 1334, 35.50 and 36.35 mg g−1 for the uptake of methylene blue, famotidine and diclofenac, respectively. The equilibrium adsorption had an alignment with Langmuir isotherms, while the kinetics were most accurately modelled using pseudo- first-order and second order models according to the regression analysis. Thermodynamic parameters such as ΔG°, ΔH° and ΔS° were calculated and the adsorption process was determined to be exothermic and spontaneous

Thickness Dependence and Percolation Scaling of Hydrogen Production Rate in MoS₂ Nanosheet and Nanosheet–Carbon Nanotube Composite Catalytic Electrodes

Here we demonstrate that the performance of catalytic electrodes, fabricated from liquid exfoliated MoS₂ nanosheets, can be optimized by maximizing the electrode thickness coupled with the addition of carbon nanotubes. We find the current, and so the H₂ generation rate, at a given potential to increase linearly with electrode thickness to up ∼5 μm after which saturation occurs. This linear increase is consistent with a simple model which allows a figure of merit to be extracted. The magnitude of this figure of merit implies that approximately two-thirds of the possible catalytically active edge sites in this MoS₂ are inactive. We propose the saturation in current to be partly due to limitations associated with transporting charge through the resistive electrode to active sites. We resolve this by fabricating composite electrodes of MoS₂ nanosheets mixed with carbon nanotubes. We find both the electrode conductivity and the catalytic current at a given potential to increase with nanotube content as described by percolation theory