Effect of oxygenic groups on desalination performance improvement of graphene oxide-based membrane in membrane distillation

Shear-aligned graphene oxide nanosheets incorporated PVDF composite membranes for selective dye rejection with high water flux

Membrane technology is crucial in addressing water pollution challenges, particularly in removing dyes from wastewater. This study presents a novel approach to fabricating shear-aligned graphene oxide (GO) nanosheets incorporated polyvinylidene fluoride (PVDF) membranes for achieving exceptional dye rejection efficiency while maintaining high water flux. The membranes were prepared by dispersing graphene oxide within a PVDF matrix and subsequent subjection to shear alignment techniques. Shear and flow-induced alignment were explored to achieve precise and controlled alignment of graphene oxide flakes within the PVDF matrix. The resulting membranes exhibited enhanced structural integrity and optimized molecular packing of PVDF and GO, enabling them to selectively reject dyes while allowing efficient water permeation. The fabricated membranes were extensively characterized using appropriate testing methods. The results demonstrated that the shear-aligned GO sheets infused PVDF composite membranes exhibited outstanding dye rejection (96-99%) performance, surpassing conventional membranes while maintaining high water flux. This innovative membrane fabrication approach holds significant promise for advanced water treatment applications, offering a sustainable solution for selective dye removal and efficient water purification.

Carbon-Based Nanocomposite Membranes for Membrane Distillation: Progress, Problems and Future Prospects

The development of an ideal membrane for membrane distillation (MD) is of the utmost importance. Enhancing the efficiency of MD by adding nanoparticles to or onto a membrane's surface has drawn considerable attention from the scientific community. It is crucial to thoroughly examine state-of-the-art nanomaterials-enabled MD membranes with desirable properties, as they greatly enhance the efficiency and reliability of the MD process. This, in turn, opens up opportunities for achieving a sustainable water-energy-environment nexus. By introducing carbon-based nanomaterials into the membrane's structure, the membrane gains excellent separation abilities, resistance to various feed waters, and a longer lifespan. Additionally, the use of carbon-based nanomaterials in MD has led to improved membrane performance characteristics such as increased permeability and a reduced fouling propensity. These nanomaterials have also enabled novel membrane capabilities like in situ foulant degradation and localized heat generation. Therefore, this review offers an overview of how the utilization of different carbon-based nanomaterials in membrane synthesis impacts the membrane characteristics, particularly the liquid entry pressure (LEP), hydrophobicity, porosity, and membrane permeability, as well as reduced fouling, thereby advancing the MD technology for water treatment processes. Furthermore, this review also discusses the development, challenges, and research opportunities that arise from these findings.

Composite 2D Material-Based Pervaporation Membranes for Liquid Separation: A Review

Today, chemistry and nanotechnology cover molecular separations in liquid and gas states by aiding in the design of new nano-sized materials. In this regard, the synthesis and application of two-dimensional (2D) nanomaterials are current fields of research in which structurally defined 2D materials are being used in membrane separation either in self-standing membranes or composites with polymer phases. For instance, pervaporation (PV), as a highly selective technology for liquid separation, benefits from using 2D materials to selectively transport water or other solvent molecules. Therefore, this review paper offers an interesting update in revising the ongoing progress of PV membranes using 2D materials in several applications, including solvent purification (the removal of water from organic systems), organics removal (the removal of organic molecules diluted in water systems), and desalination (selective water transport from seawater). In general, recent reports from the past 3 years have been discussed and analyzed. Attention has been devoted to the proposed strategies and fabrication of membranes for the inclusion of 2D materials into polymer phases. Finally, the future trends and current research gaps are declared for the scientists in the field.

Membranes Coated with Graphene-Based Materials: A Review

Graphene is a popular material with outstanding properties due to its single layer. Graphene and its oxide have been put to the test as nano-sized building components for separation membranes with distinctive structures and adjustable physicochemical attributes. Graphene-based membranes have exhibited excellent water and gas purification abilities, which have garnered the spotlight over the past decade. This work aims to examine the most recent science and engineering cutting-edge advances of graphene-based membranes in regard to design, production and use. Additional effort will be directed towards the breakthroughs in synthesizing graphene and its composites to create various forms of membranes, such as nanoporous layers, laminates and graphene-based compounds. Their efficiency in separating and decontaminating water via different techniques such as cross-linking, layer by layer and coating will also be explored. This review intends to offer comprehensive, up-to-date information that will be useful to scientists of multiple disciplines interested in graphene-based membranes.

Insights into the enhanced flux of graphene oxide composite membrane in direct contact membrane distillation: The different role at evaporation and condensation interfaces

Graphene oxide (GO) coating has recently been reported as a novel approach to increase membrane flux of membrane distillation (MD), yet the phenomena underlying the process are still not fully understood. In this study, a mathematical model based on capillary-film assumption was developed and validated with the results (R²>0.99) from a series of MD experiments. According to the model, when GO layer was placed at the evaporation interface, the temperature difference across the membrane surface increases significantly (44.2%∼92.0%) and the temperature polarization coefficient is increased greatly from 0.29∼0.38 to around 0.55. This leads to a big increase of driving force for higher heat flow and subsequently mass flux (17.8∼45.5%). However, the vapor pressure on membrane surface was decreased due to Kelvin effect of GO capillary pores, which has a negative influence on the driving force, accounting for about 26.9% to 52.6% drop in the achieved flux. In comparison, when GO layer was placed at the condensation interface, the temperature difference across the membrane surface decreases slightly (7.2∼12.2%), but the reduced vapor pressure on GO capillary pores due to Kelvin effect become the dominant factor affecting membrane flux, resulting in an increase mass flux of 12.4∼16.4%. The model developed in this study provides a theoretical foundation for understanding the role of GO coating on flux improvement, and can be used for further development of high flux membranes.

Membrane Distillation for the Production of Pharmaceutical-Grade Water-Investigation into the Application of AGMD and VMD

The production of pharmaceutical ingredients, intermediates and final products strongly depends on the utilization of water. Water is also required for the purification and preparation of reagents. Each specific application determines the respective water quality. In the European Union, the European Pharmacopeia (Ph. Eur.) contains the official standards that assure quality control of pharmaceutical products during their life cycle. According to this, the production of water for pharmaceutical use is mainly based on multi-stage distillation and membrane processes, especially, reverse osmosis. Membrane distillation (MD) could be an alternative process to these classical methods. It offers advantages in terms of energy demand and a compact apparatus design. In the following study, the preparation of pharmaceutical-grade water from tap water in a one-step process using MD is presented. Special emphasis is placed on the performance of two different module designs and on the selection of optimum process parameters.

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.

Large-pore-size membranes tuned by chemically vapor deposited nanocoatings for rapid and controlled desalination

Though membranes with pore size larger than 1 μm are much desired to increase the permeate flux of membrane distillation (MD), the vulnerability of large-pore-size membranes to pore wetting results in the penetration of saline water and consequent failure of MD operation. We report modification of large-pore-size membranes by chemically vapor deposited nanocoatings to achieve both high salt rejection and high permeate flux. The chemical vapor modification not only led to enhanced surface hydrophobicity and increased liquid entry pressure in membranes, but also significantly improved membrane wetting resistance at high temperature. Membranes with 1.0 and 2.0 μm pore size were successfully used for MD desalination with salt rejection higher than 99.99% achieved. Enlarging the pore size from 0.2 μm to 2.0 μm contributed to 48-73% enhancement in the permeate flux of the modified membranes. The modified large-pore-size membranes maintained the high permeate flux at elevated saline concentration and extended the operation time.