Mixed Matrix PVDF/Graphene and Composite-Skin PVDF/Graphene Oxide Membranes Applied in Membrane Distillation

Exploring the material and dielectric properties of poly(vinylidene fluoride) composites incorporated with graphene and graphene oxide

This study focuses on enhancing the structural, thermal, and dielectric properties of poly(vinylidene fluoride) (PVDF) nanocomposites loaded with graphene oxide (GO) and graphene (G), synthesized via solution casting. Characterization techniques, including X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric analysis (TGA), revealed significant enhancements due to the nanofillers. The crystallinity of PG composites increased to 60.39% from 49.21% in neat PVDF, transitioning from α to β phases, which is beneficial for high-performance electronics and energy storage. PG composites showed a dielectric constant (ε') of 10.50, higher than those of neat PVDF (ε' = 7.54) and PGO composites (ε' = 8.56). The dielectric loss (tan δ) for PG was low at 0.15, suitable for electronics. The AC conductivity of PG composites (2.22 × 10-7 S cm-1) was higher than those of neat PVDF (1.09 × 10-7 S cm-1) and PGO (1.65 × 10-7 S cm-1), enhancing their suitability for flexible electronics. Thermal stability assessments showed that PG composites had the highest degradation temperature at 471.04 °C, indicating improved thermal resistance. These enhancements are due to the effective dispersion and interaction of graphene-based nanofillers within the PVDF matrix. This study demonstrates that incorporating nanofillers into polymer composites significantly advances materials science by enhancing the dielectric properties for various industrial applications.

Novel Pilot-Scale Photocatalytic Nanofiltration Reactor for Agricultural Wastewater Treatment

Nowadays, the increased agro-industrial activities and the inability of traditional wastewater treatment plants (WWTPs) to eliminate recalcitrant organic contaminants are raising a potential worldwide risk for the environment. Among the various advanced water treatment technologies that are lately proposed for addressing this challenge, the development and optimization of an innovative hybrid photocatalytic nanofiltration reactor (PNFR) prototype emerges as a prominent solution that achieves synergistic beneficial effects between the photocatalytic degradation activity and size exclusion capacity for micropollutant molecules. Both these features can be contemporarily endued to a multitude of membrane monoliths. The physicochemical and the photoinduced decontamination properties of the titania materials were firstly determined in the powder form, and subsequently, the structural and morphological characterization of the obtained titania-modified membrane monoliths were accomplished. The PNFR unit can operate at high water recovery and low pressures, exhibiting promising removal efficiencies against Acetamiprid (ACT) and Thiabendazole (TBZ) pesticides and achieving the recycling of 15 m³/day of real agro-wastewater. The obtained results are very encouraging, demonstrating the integration of titania photocatalysts in a photocatalytic membrane reactor as a feasible technological solution for the purification of agricultural wastewater.

Effects of Co-Solvent-Induced Self-Assembled Graphene-PVDF Composite Film on Piezoelectric Application

A persistent purpose for self-powered and wearable electronic devices is the fabrication of graphene-PVDF piezoelectric nanogenerators with various co-solvents that could provide enhanced levels of durability and stability while generating a higher output. This study resulted in a piezoelectric nanogenerator based on a composite film composed of graphene, and poly (vinylidene fluoride) (PVDF) as a flexible polymer matrix that delivers high performance, flexibility, and cost-effectiveness. By adjusting the co-solvent in the solution, a graphene-PVDF piezoelectric nanogenerator can be created (acetone, THF, water, and EtOH). The solution becomes less viscous and is more diluted the more significant the concentration of co-solvents, such as acetone, THF, and EtOH. Additionally, when the density is low, the thickness will be thinner. The final film thickness for all is ~25 µm. Furthermore, the- crystal phase becomes more apparent when graphene is added and combined with the four co-solvents. Based on the XRD results, the peak changes to the right, which can be inferred to be more dominant with the β-phase. THF is the co-solvent with the highest piezoelectric output among other co-solvents. Most of the output voltages produced are 0.071 V and are more significant than the rest.

Asymmetric Cellulose/Carbon Nanotubes Membrane with Interconnected Pores Fabricated by Droplet Method for Solar-Driven Interfacial Evaporation and Desalination

Solar-driven interfacial water purification and desalination have attracted much attention in environmentally friendly water treatment field. The structure design of the photothermal materials is still a critical factor to improve the evaporation performance such as evaporation rate and energy conversion efficiency. Herein, an asymmetric cellulose/carbon nanotubes membrane was designed as the photothermal membrane via a modified droplet method. Under 1 sun irradiation, the evaporation rate and energy efficiency of pure water can reach up to 1.6 kg m−2 h−1 and 89%, respectively. Moreover, stable reusability and desalination performance made the cellulose/carbon nanotubes membrane a promising photothermal membrane which can be used for solar-driven desalination.

Characterization of PVDF/Graphene Nanocomposite Membranes for Water Desalination with Enhanced Antifungal Activity

Seawater desalination is a worldwide concern for the sustainable production of drinking water. In this regard, membrane distillation (MD) has shown the potential for effective brine treatment. However, the lack of appropriate MD membranes limits its industrial expansion since they experience fouling and wetting issues. Therefore, hydrophobic membranes are promising candidates to successfully deal with such phenomena that are typical for commercially available membranes. Here, several graphene/polyvinylidene (PVDF_G) membranes with different graphene loading (0–10 wt%) were prepared through a phase inversion method. After full characterization of the resulting membranes, the surface revealed that the well-dispersed graphene in the polymer matrix (0.33 and 0.5 wt% graphene loading) led to excellent water repellence together with a rough structure, and a large effective surface area. Importantly, antifungal activity tests of films indicated an increase in the inhibition percentage for PVDF_G membranes against the Curvularia sp. fungal strain. However, the antifungal surface properties were found to be the synergistic result of graphene toxicity and surface topography.

Performance of PVDF Based Membranes with 2D Materials for Membrane Assisted-Crystallization Process

Membrane crystallization (MCr) is a promising and innovative process for the recovery of freshwater from seawater and for the production of salt crystals from the brine streams of desalination plants. In the present work, composite polymeric membranes for membrane crystallization were fabricated using graphene and bismuth telluride inks prepared according to the wet-jet milling (WJM) technology. A comparison between PVDF-based membranes containing a few layers of graphene or bismuth telluride and PVDF-pristine membranes was carried out. Among the 2D composite membranes, PVDF with bismuth telluride at higher concentration (7%) exhibited the highest flux (about 3.9 L∙m-2h-1, in MCr experiments performed with 5 M NaCl solution as feed, and at a temperature of 34 ± 0.2 °C at the feed side and 11 ± 0.2 °C at the permeate side). The confinement of graphene and bismuth telluride in PVDF membranes produced more uniform NaCl crystals with respect to the pristine PVDF membrane, especially in the case of few-layer graphene. All the membranes showed rejection equal to or higher than 99.9% (up to 99.99% in the case of the membrane with graphene). The high rejection together with the good trans-membrane flux confirmed the interesting performance of the process, without any wetting phenomena, at least during the performed crystallization tests.

Advantages, limitations, and future suggestions in studying graphene-based desalination membranes

The potential of novel 2D carbon materials such as nanoporous single-layer graphene and multilayer graphene oxide membranes is based on their possible advantages such as high water permeability, high selectivity capable of rejecting monovalent ions, with high salt rejection, reduced fouling, and high chemical and physical stability. Here we review how the field has advanced in the study of their performances in various desalination approaches such as reverse osmosis, forward osmosis, nanofiltration, membrane distillation, and solar water purification. The research on making high-performance graphene membranes which started with reverse osmosis applications is seemingly evolving towards other directions.

The use of carbon nanomaterials in membrane distillation membranes: a review

Membrane distillation (MD) is a thermal-based separation technique with the potential to treat a wide range of water types for various applications and industries. Certain challenges remain however, which prevent it from becoming commercially widespread including moderate permeate flux, decline in separation performance over time due to pore wetting and high thermal energy requirements. Nevertheless, its attractive characteristics such as high rejection (ca. 100%) of nonvolatile species, its ability to treat highly saline solutions under low operating pressures (typically atmospheric) as well as its ability to operate at low temperatures, enabling waste-heat integration, continue to drive research interests globally. Of particular interest is the class of carbon-based nanomaterials which includes graphene and carbon nanotubes, whose wide range of properties have been exploited in an attempt to overcome the technical challenges that MD faces. These low dimensional materials exhibit properties such as high specific surface area, high strength, tuneable hydrophobicity, enhanced vapour transport, high thermal and electrical conductivity and others. Their use in MD has resulted in improved membrane performance characteristics like increased permeability and reduced fouling propensity. They have also enabled novel membrane capabilities such as in-situ fouling detection and localised heat generation. In this review we provide a brief introduction to MD and describe key membrane characteristics and fabrication methods. We then give an account of the various uses of carbon nanomaterials for MD applications, focussing on polymeric membrane systems. Future research directions based on the findings are also suggested.

Grafting Thin Layered Graphene Oxide onto the Surface of Nonwoven/PVDF-PAA Composite Membrane for Efficient Dye and Macromolecule Separations

This study investigates the permeance and rejection efficiencies of different dyes (Rhodamine B and methyl orange), folic acid and a protein (bovine serum albumin) using graphene oxide composite membrane. The ultrathin separation layer of graphene oxide (thickness of 380 nm) was successfully deposited onto porous polyvinylidene fluoride-polyacrylic acid intermediate layer on nonwoven support layer using vacuum filtration. The graphene oxide addition in the composite membrane caused an increased hydrophilicity and negative surface charge than those of the membrane without graphene oxide. In the filtration process using a graphene oxide composite membrane, the permeance values of pure water, dyes, folic acid and bovine serum albumin molecules were more severely decreased (by two orders of magnitude) than those of the nonwoven/polyvinylidene fluoride-polyacrylic acid composite membrane. However, the rejection efficiency of the graphene oxide composite was significantly improved in cationic Rhodamine B (from 9% to 80.3%) and anionic methyl orange (from 28.3% to 86.6%) feed solutions. The folic acid and bovine serum albumin were nearly completely rejected from solutions using either nonwoven/polyvinylidene fluoride-polyacrylic acid or nonwoven/polyvinylidene fluoride-polyacrylic acid/graphene oxide composite membrane, but the latter possessed anti-fouling property against the protein molecules. The separation mechanism in nonwoven/polyvinylidene fluoride-polyacrylic acid membrane includes the Donnan exclusion effect (for smaller-than-pore-size solutes) and sieving mechanism (for larger solutes). The sieving mechanism governs the filtration behavior in the nonwoven/polyvinylidene fluoride-polyacrylic acid/graphene oxide composite membrane.