Multilayer Graphene Oxide Membranes Research Articles

Photocatalytically self-cleaning graphene oxide nanofiltration membranes reinforced with bismuth oxybromide for high-performance water purification

Graphene oxide (GO) membranes have emerged as promising candidates for water purification applications, owing to their unique physicochemical attributes. Nevertheless, the trade-off between permeability and selectivity, coupled with their vulnerability to membrane fouling, poses significant challenges to their widespread industrial deployment. In this study, we introduce an innovative in-situ growth and layer-by-layer assembly technique for fabricating multilayer GO membranes reinforced with bismuth oxybromide (BiOBr) on commonly employed Nylon substrates. This method allows for the creation of two-dimensional lamellar membranes capable of photocatalytic self-cleaning and tunable nanochannel dimensions. The synthesized GO/BiOBr composite membranes exhibit remarkable water permeance rates (approximately 493.9 LMH/bar) and high molecular rejection efficiency (>99 % for Victoria Blue B and Congo Red dyes). Notably, these membranes showcase an enhanced photocatalytic self-cleaning performance upon exposure to visible light. Our work provides a viable route for the fabrication of functionalized GO-based nanofiltration membranes with BiOBr inclusions, offering a synergistic combination of high water permeability, modifiable nanochannels, and effective self-cleaning capabilities through photocatalysis.

Comparative Retention Analysis of Intercalated Cations Inside the Interlayer Gallery of Lamellar and Nonlamellar Graphene Oxide Membranes in Reverse Osmosis Process: A Molecular Dynamics Study.

Over the past decade, multilayered graphene oxide (GO) membranes have emerged as promising candidates for desalination applications. Despite their potential, a comprehensive understanding of separation mechanisms remains elusive due to the intricate morphology and structural arrangement of interlayer galleries. Moreover, a critical concern of multilayered GO membranes is their susceptibility to swelling within aqueous environments, which hinders their practical implementation. Therefore, this study introduces cation intercalation within GO laminates to elucidate the underlying factors governing swelling behavior and subsequently mitigate it. Moreover, this study performed nonequilibrium molecular dynamics simulations on the cation (Mg2+ or K+)-intercalated lamellar and nonlamellar GO membranes to understand the effect of the arrangement of GO sheets on the retention time of intercalated cations within GO layers, water permeance, and salt rejection mechanism in the reverse osmosis process using cation-intercalated GO membranes. Our results highlight that lamellar GO membranes exhibit higher water permeance, attributed to their well-defined interlayer gallery structure. On the other hand, nonlamellar GO membranes display superior salt rejection due to their complex interlayer gallery structure that impedes salt permeation. Moreover, the structural complexity of nonlamellar GO membranes contributes to greater stability by retention of the more intercalated cations for a longer time within the layers. Furthermore, it is observed that a higher percentage of Mg2+ cations remained inside the GO laminates as compared to K+ cations, hence resulting in the greater stability of the Mg2+-intercalated GO membrane in the aqueous environment.

Nanochannel characteristics contributing to ion/ion selectivity in two-dimensional graphene oxide membranes

Selective ion/ion transport is of great importance in environmental and energy applications. Nanofiltration membranes possessing sub-nanometer pore sizes and charge characteristics have garnered significant attention in effectively separating target ions. Nevertheless, the contributions of pore size, charge, and their combined impact on ion/ion separation have remained relatively unexplored. In this study, a well-defined example is presented using multilayered graphene oxide membranes with ordered interlayer nanochannels. These membranes were utilized to prepare diverse nanochannel types, each possessing distinct channel sizes and charge properties. A systematic investigation was conducted to discern their separation selectivity for mono-/di-valent ion pairs. The dominant factor governing mono-/di-valent ion selectivity was not found to be the channel pore size within the sub-nanometer scale. This could be because nanochannels are flexible and cannot strictly sieve ions based on their specific size. Instead, the difference in electrostatic effects between mono- and di-valent ions plays a more significant role in enhancing ion/ion selectivity within the subnanometer channel. This study offers certain insights into selective ion transport in two-dimensional membrane nanochannels, potentially assisting in the design of nanochannels with single-ion selectivity.

Nanoporous multilayer graphene oxide membrane for forward osmosis metal ion recovery from spent Li-ion batteries

The recovery of Li and rare metals from the spent electrodes of Li-ion batteries (LIBs) is becoming increasingly important. Herein, nanoporous multilayer graphene oxide (NMG) membranes were fabricated via the confined thermal annealing method to achieve Li-ion selectivity. A graphene oxide (GO) membrane was prepared by coating the membrane with an aqueous layer of GO liquid crystal via the scalable bar coating method, followed by hot-pressing. The influence of the GO interlayer spacing and nanopore presence on the ion separation performance was investigated. The NMG membrane shows different ion permeance phenomena depending on ion concentration. The permeation rate of divalent ions (Co, Ni, Mn) through the NMG membrane was faster than that of Li ions in solution with low ionic strength, whereas the membrane was Li-ion selective in mixed ionic solutions or at high ionic strength. This result indicates that electrostatic interaction by oxygen groups is important at low ionic strength, but size exclusion by interlayer spacing and adsorption by nanopore is critical at high ionic strength. The ion permeation mechanisms were further examined based on molecular calculations, which revealed that the binding energies between the divalent ions and nanopores or basal plane of graphene were high, resulting in slow ion permeation. When the NMG membrane was combined in a forward osmosis system, Li-ion can be separated continuously from the mixture solution simulated from the spent Li-battery electrode. This approach shows the high potential of nanoporous multilayer graphene membrane for Li extraction in particular with dense pore structure and around 7 Å of d-spacing.

Improving the separation performance for heavy metals by optimizing the structure of multilayered GO membrane

Graphene oxide (GO) membranes have significant application potential for heavy metal separation. Most previous studies only investigated GO membranes composed of nanosheets with a fixed number of layers and a specific size. In this study, the effects of the size of nanosheets and the number of layers on the membrane performance were investigated to optimize the structure of multilayered GO membranes. Large and small GO nanosheets (LG and SG) were used to construct the membrane. As the numbers of layers increase, the water permeability decreases to some extent, while the retention rate increases significantly. The membranes constructed with a small size of nanosheets have better performance. For membranes with an interlayer spacing of 0.8 nm, a number of layers of three, and a gap width of 1.23 nm, the water permeability of the SG membrane was only 3 % lower than that of the LG membrane, while the retention rate increased by 1.22 times. The number-density maps showed that a large amount of Cd2+ gathered around the hydroxyl, epoxy, and especially carboxyl groups, which helped improve the retention rate. The umbrella sampling indicated that the energy barrier for Cd2+ migrating across the gap of the membrane was much higher than that of water molecules, hence reducing the size of GO nanosheets could effectively improve the water permeability without significantly reducing the retention rate. In summary, the preparation of GO membranes from nanosheets with the smallest possible size and an optimal number of layers may help improve the overall performance.

Multilayered graphene oxide membranes for bioethanol purification: Microscopic insight from molecular simulation

Graphene oxide (GO) membranes have received considerable interest for separation. The channels in GO membranes are in an atomic scale and thus it is challenging to unravel underlying separation mechanism via experiment. In this study, we model multilayered GO membranes with various channel widths (W) and oxidation degrees (O/C), subsequently simulate their performance for bioethanol (an ethanol/water mixture) purification. In the sub-nm membranes with W = 0.75 nm, ethanol-selective permeation occurs at a low O/C but it changes to highly water-selective at a high O/C (with separation factor αH2O/EtOH of 5 and ∞ at O/C = 15% and 35%, respectively). In the wider membranes with W = 1.00 and 1.50 nm, moderate ethanol-selective permeation with αEtOH/H2O of 1–3 is observed. Detailed microscopic analysis reveals that ethanol and water differ in their intercalation and diffusion. In the wider membranes, both ethanol and water exhibit similar intercalation behavior and adopt Fickian diffusion, particularly at a low O/C ratio. In the sub-nm channels, both components feature sub-diffusion but ethanol has negligible diffusion at a high O/C = 35%. Depending on W, ordered structures with different layers are formed for ethanol and water. In the sub-nm channels, hydrogen bonds between water and channel are found to increase in number with increasing O/C ratio but their stability decreases. The microscopic insight provides quantitative understanding of bioethanol purification in GO membranes, and might facilitate the development of new GO membranes for important separation processes.

Facile and extensible preparation of multi-layered graphene oxide membranes with enhanced long-term desalting performance

Graphene oxide (GO) membranes have been developed by stacking the nanosheets together for using as molecular sieve due to its two-dimensional (2D) capillaries. However, this technology is still far from being ready for large-scale production. Specifically, pure GO membranes exhibit poor resistance to cross-flow process, and the commonly used preparation techniques pose scale-up difficulties. Here, we report a durable membrane developed using dip-coating polydopamine (PDA), followed by spray-coating multi-layered GO (MLGO). The fast preparation speed of ~0.2 s cm−2 and large preparation area of 1400 cm2 per preparing cycle demonstrated the scalability of the method. Acting as a binder and stabilizer, PDA developed MLGO-substrate interaction and crosslinked the MLGO sheets. The modified oriented MLGO layer contributed up to 95.0% retention of Na2SO4 and showed enhanced stability in a 263-days soaking test and a nearly 800-h cross-flow test with the test area of 29.2 cm2. This work expands the possibilities for the GO membranes in practical applications.

Graphene Oxide Membrane: Recent Advancement in Waste Water Treatment and its Applications

World water resources are barely alive due to various factors such as rise in population, adverse changes in the environment and the effects of pollutants, which increase the demand for fresh-water. Numerous techniques have been developed to solve the problem of water inadequacy, but most of them are adverse with respect to the environment and economy. Graphene-oxide (GO) nanopore materials may be an effective solution for water-purification due to its properties of easy fabrication and modification. This next-generation membrane has high waterflux, selectivity, and permeability to selected molecules. In this discussion, we have covered the latest technologies and potential applications of GO for waterpurification, which shall help researchers to get quick ideas for future research to design and fabricate multi-layered GO membranes. This article gives a snapshot of current status and proposed strategies of graphene-membranes for water treatment with earlier information to wastewater management and stimulated progress in this area from 2017 to date. The future challenges and opportunities in this field have also been highlighted.

Liquid Flow through Defective Layered Membranes: A Phenomenological Description

We present a realistic phenomenological description of liquid transport through defective, layered membranes. We derive general expressions based on conventional models of laminar flow and extend the formalism to accommodate slip flow. We consider different types of defects including in-layer vacancies that provide an activation-free tortuous path through the membrane. Of the many factors that affect flow, the most important is the radius of in-layer vacancy defects, which enters in the fourth power in expressions for the flux density. We apply our formalism to water transport through defective multilayer graphene oxide membranes and find that the flow remains in the laminar regime. Our results show that observed high water permeability in this system can be explained quantitatively by a sufficient density of in-layer pores that shorten the effective diffusion path.

Superiority of Modified Polymeric Membrane with Nanomaterial on Temperature and Mechanical Stability and Application in Industrial Waste Water

In this paper, we investigated the superiotires of carbon-based nanomaterial polymer inclusion membrane (PIM-GO) against to polymer inclusion membrane and removed Cr(VI), a highly toxic element typically used in chromate conversion coating in the plating industry, from the chrome plating water by using a PIM-GO modified with graphene oxide (GO), which strengthens the mechanical structure and permeability of PIMs. We performed experiments to investigate the membrance performance and structural ability ofthe PIM-GO, and lastly compared its performance to that of the PIM. We observed the PIM-GO’s high selectivity and recovery (96.83%) in the removal of Cr(VI). GO added to the membrane structure caused a visible increase in the rate constant, permeability and flux.The PIM-GO affords opportunities to work with a wider range of pH levels, changes of which in membrane-based experiments with unmodified PIM shave caused significant decreases in flux and permeability. The ease of use, applicability, high permeability of the PIM-GO at high temperatures afford significant advantages over the unmodified membrane as well. The results of this study can aid the development of next-generation membranes with increased mechanical stability, the resistance to multilayered GO membranes, and the use of the membranes in industrial applications. Moreover, the high transport efficiency of the PIM-GO at temperatures exceeding room temperature is evidence of the improved thermal stability of the PIM-GO. In effect, our findings can inform the production of new membranes with increased mechanical stability, membrane lifetime, and usability in industrial applications.

Molecular simulations of phenol and ibuprofen removal from water using multilayered graphene oxide membranes

We present here non-equilibrium molecular dynamic simulations concerning the separation of phenol and ibuprofen as impurities compounds (ICs) in water by novel graphene oxide (GO) membranes. The coupling between water permeability and impurity rejection is studied as a function of membrane thickness and concentration, focusing on the underlying molecular phenomena. Results show that water permeability decreases as the number of layers increases. Moreover, molecular sieving can be achieved by tuning the number of GO layers and the surface chemistry of the sheet: water flow through layers is up to 20% faster than that in graphene layers, because of strong hydrogen bonded interactions with the oxygenated groups. Analysis of the simulation results suggests that upon adsorbing on the GO surface, the translational motion of ICs in water would be supressed. Nevertheless, hydrophilicity affects the permeability for membranes with high O/C ratio, owing to these strong hydrogen bonds. Furthermore, 100% rejection for the ICs can be obtained for most of the GO membranes with four layers. This study elucidates the important role of hydrophilic interactions in GO membranes to become ideal candidates for removal of organic pollutants from water, showing the applicability of molecular simulations to obtain molecular insights into this problem.

Insights on the mechanism of water-alcohol separation in multilayer graphene oxide membranes: Entropic versus enthalpic factors

Experimental evidence has shown that graphene oxide (GO) can be impermeable to liquids, vapors and gases, while it allows a fast permeation of water molecules. Theoretical studies to understand the filtration mechanisms come mostly from water desalination, while very few works have been dedicated to alcohol dehydration. In this work, we have investigated the molecular level mechanism underlying the alcohol/water separation inside GO membranes. A series of Molecular Dynamics and Grand-Canonical Monte Carlo simulations were carried out to probe the ethanol/water and methanol/water separation through GO membranes composed of multiple layered graphene-based films with different interlayer distance values and number of oxygen-containing functional groups. Our results show that the size exclusion and membrane affinities are not sufficient to explain the selectivity. Besides that, the favorable water molecular arrangement inside GO 2D-channels forming a robust H-bond network and the fast water permeation are crucial for an effective separation mechanism. In other words, the separation phenomenon is not only governed by membrane affinities (enthalpic mechanisms) but mainly by the geometry and size factors (entropic mechanisms). Our findings are consistent with the available experimental data and contribute to clarify important aspects of the separation behavior of confined alcohol/water in GO membranes.

Molecular Insight into Water Desalination across Multilayer Graphene Oxide Membranes.

Transport of ionic solutions through graphene oxide (GO) membranes is a complicated issue because the complex and tortuous structure inside makes it very hard to clarify. Using molecular dynamics (MD) simulations, we investigated the mechanism of water transport and ion movement across multilayer GO. The significant flow rate is considerably influenced by the structural parameters of GO membranes. Because of the size effect on a shrunken real flow area, there is disagreement between the classical continuum model and nanoscaled flow. To eliminate the variance, we obtained modified geometrical parameters from density analysis and used them in the developed hydrodynamic model to give a precise depiction of water flow. Four kinds of solutions (i.e., NaCl, KCl, MgCl2, and CaCl2) and different configurational GO sheets were considered to clarify the influence on salt permeation. It is found that the abilities of permeation to ions are not totally up to the hydration radius. Even though the ionic hydration shell is greater than the opening space, the ions can also pass through the split because of the special double-deck hydration structure. In the structure of GO, a smaller layer separation with greater offsetting gaps could substantially enhance the membrane's ability to reject salt. This work establishes molecular insight into the effects of configurational structures and salt species on desalination performance, providing useful guidelines for the design of multilayer GO membranes.

Phase-selective graphene oxide membranes for advanced microfluidic flow control.

For the first time, we harness the unique phase-selectivity of chip-integrated graphene oxide (GO) membranes to significantly enhance flow control on centrifugal microfluidic platforms. In this paper, we present novel processes for the assembly of these GO membranes into polymeric microfluidic systems and demonstrate that multilayer GO membranes allow the passage of water while blocking pressurized air and organic solutions.

In-Situ ESEM and EELS Observation of Water Uptake and Ice Formation in Multilayer Graphene Oxide.

Graphene oxide (GO) is hydrophilic and swells significantly when in contact with water. Here, we investigate the change in thickness of multilayer graphene oxide membranes due to intercalation of water, via humidity-controlled observation in an environmental scanning electron microscope (ESEM). The thickness increases reproducibly with increasing relative humidity. Electron energy loss spectroscopy (EELS) reveals the existence of water ice under cryogenic conditions, even in high vacuum environment. Additionally, we demonstrate that freezing then thawing water trapped in the multilayer graphene oxide membrane leads to the opening up of micron-scale inter-lamellar voids due to the expansion of ice crystals.