Nanoporous Graphene Oxide Research Articles

Magnesium Ion Gated Ion Rejection through Carboxylated Graphene Oxide Nanopore: A Theoretical Study.

While nanoporous graphene oxide (GO) is recognized as one of the most promising reverse osmosis desalination membranes, limited attention has been paid to controlling desalination performance through the large GO pores, primarily due to significant ion leakage resulting in the suboptimal performance of these pores. In this study, we employed a molecular dynamics simulation approach to demonstrate that Mg2+ ions, adhered to carboxylated GO nanopores, can function as gates, regulating the transport of ions (Na+ and Cl-) through the porous GO membrane. Specifically, the presence of divalent cations near a nanopore reduces the concentration of salt ions in the vicinity of the pore and prolongs their permeation time across the pore. This subsequently leads to a notable enhancement in salt rejection rates. Additionally, the ion rejection rate increases with more adsorbed Mg2+ ions. However, the presence of the adsorbed Mg2+ ions compromises water transport. Here, we also elucidate the impact of graphene oxidation degree on desalination. Furthermore, we design an optimal combination of adsorbed Mg2+ ion quantity and oxidation degree to achieve high water flux and salt rejection rates. This work provides valuable insights for developing new nanoporous graphene oxide membranes for controlled water desalination.

Enhancing the seawater desalination performance of multilayer reduced graphene oxide membranes by introducing in-plane nanopores: a molecular dynamics simulation study.

In this study, using MD simulation, the effect of creating in-plane nanopores in a reduced graphene oxide (rGO) membrane and the formation of a reduced nanoporous graphene oxide (rNPGO) membrane is proposed to increase salt rejection and water flux. To this end, the desalination performance of r1NPGO, r2NPGO and r4NPGO membranes, which have 1, 2 and 4 pore(s), respectively, with a diameter of 0.9 nm and the r1NPGO-3 nm membrane, which has 1 pore with an approximate diameter of 3.0 nm, was investigated and compared from a molecular point of view. The simulation results show that in the rNPGO membranes, by increasing the number of pores from 1 to 4, water flux increases by ∼6 times compared to the rGO membrane. Meanwhile, upon increasing the pore size from 0.9 to 3.0 nm, water flux is enhanced by ∼16 times compared to the rGO membrane. The simulation results also demonstrate that the rGO membrane has two paths for water penetration, which are called the interlayer pathway and in-slit pathway. Moreover, pores in the rNPGO membranes provide another additional path for water transfer by shortening the lateral size of the membranes. This path is referred to as the in-pore pathway. By increasing the size of the pore in the r1NPGO-3 nm membrane, the contribution of the in-pore pathway increases and plays an important role. Furthermore, the simulation results show that in all rGO and rNPGO membranes, the interlayer space acts as a barrier for ions. Therefore, complete salt rejection is observed. Interestingly, by increasing the pore size in the r1NPGO-3 nm membrane, this membrane still maintains complete salt rejection. The observed phenomenon can be a result of very high water flux in this membrane. By increasing water flux, the presence of water molecules around Na+ and Cl- ions decreases. As a result, the formation of Na+Cl- ionic clusters is strengthened in such a way that these clusters do not have the ability to pass through large pores of 3.0 nm.

CO2/CH4 separation through monolayer nanoporous graphene oxide supported ionic liquid membrane

Nanoporous graphene oxide (NPGO) with a single atomic layer thickness and good mechanical strength has been regarded as a promising candidate in gas separation. However, it is challenging to precisely control the pore size to match the target gas. In this work, the pore size was modulated by supporting ionic liquid (IL) on the monolayer NPGO membrane (NPGO-SILM). The separation performance and mechanism for CO2/CH4 in NPGO-[EMIM][BF4], NPGO-[EMIM][PF6] and NPGO-[EMIM][TF2N] were investigated by molecular dynamics simulation. It was found that the pore size of NPGO greatly affects the permeability and selectivity, and 5.6 Å is the most suitable pore size. After coating IL on NPGO, the CO2/CH4 selectivity is obviously enhanced. With the IL thickness increasing from 5 to 11 Å, the CO2 permeance decreased from ∼105 to ∼104 GPU, while the selectivity increased, and almost no CH4 passed through the membrane with 11 Å thickness. Among the studied three types of ILs, the NPGO-[EMIM][TF2N] membrane shows the best CO2/CH4 separation performance due to the strongest adsorption capacity between [TF2N] anion and CO2. The interaction energy, PMF and probability distribution results suggest that the improved selectivity is attributed to the synergistic effect of cations and anions. The anions are responsible for the adsorption of large amounts of CO2. At the same time, the cations are mainly distributed around the center of the NPGO pore because of the strong interaction between cation and NPGO, which would be favorable for dynamically adjusting pore size to allow the passage of CO2 and prevent CH4 from passing through the membrane.

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.

Scalable fabrication of nanoporous multilayer graphene oxide membrane for organic solvent nanofiltration

Nanoporous graphene is promising for the fabrication of high-performance organic solvent nanofiltration (OSN) membranes owing to the excellent chemical resistance of graphene in organic solvents. Moreover, the nanopores increase solvent permeance by providing diffusion channels. However, conventional chemical and physical etching methods are generally applicable on a laboratory-scale, and the large-scale fabrication of these structures is challenging. Herein, a large-area nanoporous multilayer graphene oxide (NMG) membrane was prepared using a combination of slot-die coating and confined thermal treatment. Graphene oxide (GO) was coated on polymeric supports using a slot-die coater, which is generally used for continuous coating in industry. Afterward, the GO membrane was treated using a hot-pressing method to activate the nanopores on the graphene surface and weld the polymeric support with the graphene layer. The interlayer and pore structure of GO were tuned by modulating the hot-pressing time, and its influence on OSN performance was systemically investigated. The optimized NMG membrane exhibited a high ethanol permeance of 300 Lm−2h−1bar−1 and a sharp molecular weight cut-off of 500 g/mol. Furthermore, the enhanced adhesion between graphene and the polymeric support enables mechanically stable membrane operation under cross-flow conditions for 30 days, which is the longest test time reported for two-dimensional material-based OSN membranes thus far.

Nanoporous Graphene Oxide-Based Quartz Crystal Microbalance Gas Sensor with Dual-Signal Responses for Trimethylamine Detection

This paper presents a straightforward method to develop a nanoporous graphene oxide (NGO)-functionalized quartz crystal microbalance (QCM) gas sensor for the detection of trimethylamine (TMA), aiming to form a reliable monitoring mechanism strategy for low-concentration TMA that can still cause serious odor nuisance. The synthesized NGO material was characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy to verify its structure and morphology. Compared with the bare and GO-based QCM sensors, the NGO-based QCM sensor exhibited ultra-high sensitivity (65.23 Hz/μL), excellent linearity (R2 = 0.98), high response/recovery capability (3 s/20 s) and excellent repeatability (RSD = 0.02, n = 3) toward TMA with frequency shift and resistance. Furthermore, the selectivity of the proposed NGO-based sensor to TMA was verified by analysis of the dual-signal responses. It is also proved that increasing the conductivity did not improve the resistance signal. This work confirms that the proposed NGO-based sensor with dual signals provides a new avenue for TMA sensing, and the sensor is expected to become a potential candidate for gas detection.

Polyethylene oxide-intercalated nanoporous graphene membranes for ultrafast H2/CO2 separation: Role of graphene confinement effect on gas molecule binding

H2/CO2 separation is essential for various industrial applications, such as hydrocarbon steam reforming for H2 production. Herein, a layered composite membrane composed of nanoporous graphene (NG) and polyethylene oxide (PEO) is developed. The membrane demonstrates an ultrafast H2 permeability of ca. 32 240 barrer with a moderate H2/CO2 selectivity of 25, which far surpasses the upper bound of the separation performance demonstrated by existing membrane materials. The regularly layered structure is fabricated by facilitating the intercalation of PEO via an aqueous graphene-oxide liquid crystal (GOLC) scaffold. After preparing the layered GO/PEO membrane, hot pressing is conducted to activate dense nanopores on the basal plane of graphene, resulting in an NG/PEO membrane. The permeation of gas molecules is significantly enhanced owing to the presence of nanopores and expansion of the interlayer spacing by PEO. In contrast, CO2 permeation is lower than that of H2 owing to its strong binding interaction with PEO, and molecular simulations demonstrate that this CO2–PEO interaction is significantly enhanced owing to the confinement of PEO in the graphene interlayer spacing, particularly at d-spacing of approximately 7–8 Å.

Molecular dynamics study on electric field-facilitated separation of H2O/O2 through nanoporous graphene oxide membrane

The application of external stimuli, such as electric fields, could improve gas separation. Molecular dynamics (MD) simulations were conducted to analyze the dynamic electric field-facilitated separation process of H2O/O2 gas molecules through a double-layered nanoporous graphene oxide membrane. The computational results illustrated an enhanced gas permeation rate of 3.26 × 103 mol·m−2·s−1 for H2O molecules with an external electric field of 10−4 V·Å−1, and an enhanced selectivity of 1.44 over O2 molecules, which was 0.33 in the absence of the external electric field. The mechanism of enhanced H2O/O2 separation has also been illuminated by examining the variation in interaction energy with electric field strength. The electric field inhibits the hydrogen bond interactions between H2O molecules and H2O membranes. Accelerating desorption under electric fields would enable more adsorption sites on the membrane, thereby facilitating H2O molecules permeation.

Recent Advances in Graphene Oxide Membranes for Water desalination

Freshwater is one of the most important sources in daily life. However, freshwater resources are very scarce at present. As a consequence, water desalination remains an important challenge in solving the problem of the shortage of freshwater resources. As an effective technique, membrane-based desalination has been developed to be a mature solution to solve the problem of water desalination. Graphene oxide membranes have been considered important membrane materials for water desalination due to their high stability and high hydrophilicity. In such review, this paper will introduce three kinds of recently-developed graphene oxide membranes for water desalination, which respectively are mixed matrix membrane, reduced nanoporous graphene oxide membrane, and GO/C60 membrane. Firstly, the structure and characteristics of each membrane are introduced; then, the processes of how to make these membranes are described. Additionally, this study compares them with other novel methods for water desalination. In the end, on the basis of graphene oxide membranes, it could be seen that these three membranes are more promising.

Electrodialysis based direct air dehumidification: A molecular dynamics study on moisture diffusion and separation through graphene oxide membrane

To compromise shortages of traditional dehumidification methods, an electrodialysis based direct air dehumidification with higher efficiency and respondency was proposed. This technique could be accomplished via directional migration of charged water molecules and subsequent separation from air composition by the membrane. Notably, the water molecules diffusion and separation through the membrane are challenging and fundamental tasks to support the proposed novel dehumidification strategy. The purpose of this paper is to evaluate the dynamic diffusion behavior of water molecules across the double-layered nanoporous graphene oxide (2NPGO) membrane under the external electric field. Thence, molecular dynamics (MD) simulations of atmospheric gas, including water and nitrogen, were conducted. Once the electric field was applied, the self-diffusion coefficient of water increased from 2.421 × 10-9 m2·s−1 to 7.566 × 10-8 m2·s−1. In the presence of nitrogen, an electric field strength of 10-6 V/ Å would contribute to the increased permeation rate of 2.83 × 103 mol·m-2s−1 for water and a selectivity of 4.918 over nitrogen. Further study in hydrogen bond evolution and interaction energy variation versus electric field strength illustrated the mechanism of enhanced diffusion of water molecules.

Highly selective and ultra-low power consumption metal oxide based hydrogen gas sensor employing graphene oxide as molecular sieve

The excellent gas sensing performance of metal oxide based nano- and microstructures, including a fast response time and good sensitivity, is typically limited by their low selectivity. Therefore, novel approaches and strategies are required to gain a precise control of the selectivity. Here, we introduce a nanoporous few-layer graphene oxide (GO) membrane with permeability only to specific gas molecules to improve the selectivity of individual zinc oxide microwires (ZnO MWs) toward hydrogen (H2) gas. The fabricated GO-covered ZnO MWs showed ultra-low power consumption (60−200 nW) and an excellent room temperature H2 gas sensing properties with fast response (114 s) and recovery (30 s) times, and a low detection limit of ∼4 ppm, while no gas response was measured to all other tested gases. As proposed, the gas sensing mechanism is based on selective sieving of H2 gas molecules through the GO membrane and further diffusion to the Schottky contacts, resulting in a decreased barrier height. Being based on a bottom-up fabrication approach, the presented results could have great potential for further technological applications such as high-performance and highly selective ultra-low power metal oxide-based gas sensors, opening new opportunities for the design of nanosensors and their integration in wireless and portable devices.

Mass Transfer Through Graphene-Based Membranes

The problems related to the transport of gases through nanoporous graphene (NG) and graphene oxide (GO) membranes are considered. The influence of surface processes on the transport of gas molecules through the aforementioned membranes is studied theoretically. The obtained regularities allow finding the dependence of the flux of the gas molecules passing through the membrane on the kinetic parameters which describe the interaction of the gas molecules with the graphene sheets. This allows to take into account the influence of external fields (e.g., resonance radiation), affecting the aforementioned kinetic parameters, on the transport of gas molecules through the membranes. The proposed approach makes it possible to explain some experimental results related to mass transfer in the GO membranes. The possibility of the management of mass transfer through the NG and GO membranes using resonance radiation is discussed.

Nanotechnology in water and wastewater treatment. Graphene – the nanomaterial for next generation of semipermeable membranes

In recent decades, novel and promising graphene-based materials (i.e., carbon nanotubes, nanoporous graphene and graphene oxide) suitable to be used in preparation of high-capacity membranes for water desalination and water and wastewater treatment have been developed. After detail recognition of properties of nanoporous graphene and graphene oxide-based materials, the general conclusion on preparation of membranes made of only graphene or only graphene oxide as well as other composite materials involving these nanomaterials has been given. Novel composite membranes containing nanoporous graphene and, first of all, graphene oxide can be divided into two groups: (i) freestanding membranes made only of graphene or only of graphene oxide, and (ii) polymeric/ceramic membranes modified with the use of graphene-based nanomaterials. The modification of polymeric membranes can be achieved either by introduction of a nanomaterial onto a membrane surface or its addition to a membrane casting solution followed by membrane formation from a polymer and a nanomaterial mixture. Membranes based on nanomaterials enable to obtain significantly higher water/permeate fluxes than currently used thin film composite polyamide membranes. The future prospect of membranes based on nanoporous graphene and graphene oxide in regard to the final separation efficiency and commercial scaling up has been discussed.

Design and application of nanoporous graphene oxide film for CO2, H2, and C2H2 gases sensing

Nanoporous Graphene Oxide (NGO) film sensor is designed by combining the modified Hummer method and the spray pyrolysis technique. The structural, morphological, and optical characterizations of the prepared NGO sensor are carried by FTIR, XRD, SEM, and UV–vis spectrophotometer. Based on the morphological study, a homogenous and uniform NGO film with two-dimensional nanoporous structure is prepared. The structural study reveals the existence of high density of oxygen functional groups on a typical GO surface with d-spacing ˜0.82 nm. The optical characterization shows intensive and broad absorption band around 335 nm. The NGO film is used as a detector for CO2, H2, C2H2 gases at room temperature (20 °C). The response, response and recovery times, and selectivity of the NGO sensor are investigated. Also, the effect of gases concentrations on the resistance of the film is studied. The response and selectivity of the NGO film are in order CO2 > H2 > C2H2. The sensor response is 37.04, 16.16, and 2.87% at 60 SCCM for CO2, H2, and C2H2, respectively. The response time is ˜25, 100, and 100 s @ 10 SCCM for CO2, H2, and C2H2, respectively. At concentrations of 30 SCCM, the recovery time is 241.4, 437.2, and 674.7 s for C2H2, H2, and CO2, respectively. Finally, a simple mechanism is explained to show the sensing approach.

TiO2/GO-coated functional separator to suppress polysulfide migration in lithium-sulfur batteries.

Lithium–sulfur batteries render a high energy density but suffer from poor cyclic performance due to the dissolution of intermediate polysulfides. Herein, a lightweight nanoporous TiO2 and graphene oxide (GO) composite is prepared and utilized as an interlayer between a Li anode and a sulfur cathode to suppress the polysulfide migration and improve the electrochemical performance of Li/S batteries. The interlayer can capture the polysulfides due to the presence of oxygen functional groups and formation of chemical bonds. The hierarchically porous TiO2 nanoparticles are tightly wrapped in GO sheets and facilitate the polysulfide storage and chemical absorption. The excellent adhesion between TiO2 nanoparticles and GO sheets resulted in enhanced conductivity, which is highly desirable for an efficient electron transfer process. The Li/S battery with a TiO2/GO-coated separator exhibited a high initial discharge capacity of 1102.8 mAh g−1 and a 100th cycle capacity of 843.4 mAh g−1, which corresponds to a capacity retention of 76.48% at a current rate of 0.2 C. Moreover, the Li/S battery with the TiO2/GO-coated separator showed superior cyclic performance and excellent rate capability, which shows the promise of the TiO2/GO composite in next-generation Li/S batteries.

Adsorption and competition investigation of phenolic compounds on the solid-liquid interface of three-dimensional foam-like graphene oxide

Phenolic contaminants existed widely in ecological environment. Due to the various structure and functional groups, the interaction behavior of phenolic organic compounds with adsorbent was complex and changeable. Therefore, the exploration of adsorption and competition about phenolic compounds on solid-liquid interface in aqueous solution is of great significance. Herein, through a simple sugar-blowing route and post-oxidation modification, a free-standing, large-scale nanoporous three-dimensional graphene oxide (3D GO) was achieved. The synthesized 3D GO possessed hierarchical interconnected porous structure and abundant active sites, which showed excellent removal performance for many phenolic compounds. The maximum adsorption capacity (qmax) was 135.6 mg/g, 191.3 mg/g, 237.7 mg/g, 398.6 mg/g, 420.9 mg/g and 585.8 mg/g for phenol, 2-chlorophenol (2-CP), 4-chlorophenol (4-CP), 2,4-dichlorophenol (DCP), bisphenol-A (BPA) and 2,4,6-trichlorophenol (TCP) at 25 °C respectively. The competitive adsorption between BPA and TCP on 3D GO was also explored. Batch adsorption experiments and characterization revealed that the outstanding performance benefited from various factors, including structural advantage, electrostatic interaction, π-π interaction, hydrophobic effect, hydrogen bond, the synergy of heteroatom and the new active sites of preferential adsorbed organics. The cost-effective and highly active 3D GO adsorbent showed great promising in environmental field, and supplied insight to understand the underlying behavior of phenolic compounds on the solid-liquid interface.

Thermally Reduced Nanoporous Graphene Oxide Membrane for Desalination.

Graphene-based laminar membranes open new avenues for water treatment; in particular, reduced graphene oxide (rGO) membranes with high stability in aqueous solutions are gaining increased attention for desalination. However, the low water permeability of these membranes significantly limits their applications. In this study, the water permeability of thermally reduced GO membrane was increased by a factor of 26 times by creating in-plane nanopores with an average diameter of ∼3 nm and a high density of 2.89 × 1015 m-2 via H2O2 oxidation. These in-plane nanopores provide additional transport channels and shorten the transport distance for water molecules. Meanwhile, salt rejection of this membrane is dominated by both the Donnan effect and the size exclusion of the interspaces. Besides, the water permeability and salt rejection of the thermally reduced nanoporous GO membrane can also be simply tuned by adjusting the thermal treatment time and membrane thickness. Additionally, the fabricated membrane exhibited a relatively stable rejection of Na2SO4 during the long-term testing. This work demonstrates a novel and effective strategy for fabricating high-performance laminar rGO membranes for desalination applications.

Recent progress in gas separation using functionalized graphene nanopores and nanoporous graphene oxide membranes

Carbon nanomaterials such as nanopores graphene, functionalized graphene and graphene oxide membranes and so forth, have attracted much attention for not only scientific interest but also various application expectations. Gas separation, including gas storage, carbon dioxide capture, flue gas purification and natural gas sweetening through nanopores is of great interest and the porous materials particularly nanoporous graphene, functionalized graphene nanopores and nanoporous graphene oxide membranes are widely utilized in this phenomenon. Nanoporous graphene, functionalized graphene nanopores and nanoporous graphene oxide membranes with narrow pore distribution, provide exciting opportunities in gas separation processes. These membranes are an excellent platform for developing size-selective membranes and exhibit unique gas separation properties. This paper reviews potential applications of nanoporous graphene, functionalized graphene nanopores and nanoporous graphene oxide based membranes for gas separation on the basis of theoretical studies. The properties of porous graphene have been discussed in first section. The second and third sections provide the recent advances in theoretical studies of nanoporous graphene, functionalized graphene nanopores and nanoporous graphene oxide membranes in gas separation, respectively.

Enantioselective addition of diethylzinc to aromatic aldehydes catalyzed by chiral BINOL-functionalized nanoporous graphene oxides

The supporting material on which an asymmetric catalytic reaction takes place has proved to be an important component which could influence the efficiency and sometimes enantioselectivity of a heterogeneous asymmetric reaction. On the other hand, graphene oxide (GO) has attracted broad attentions because of its unique characteristics and potential applications in many fields. However, GOs have been rarely employed as the supporting materials for heterogeneous catalytic reactions, especially those enantioselective reactions. Herein, a new type of GO-based heterogeneous catalyst was prepared for enantioselective addition of diethylzinc to aromatic aldehydes. To produce this GO catalyst, commercial GO was firstly oxidized in an acidic environment to make nanoporous GOs and then enantiopure (R) or (S)-NH2-BINOLs were attached (covalently) onto the nanoporous GOs, and this GO-BINOL was subsequently treated by using Ti(OiPr)4. The as-prepared GO-BINOL-Ti catalyst displayed good reactivity (99%) and modest enantioselectivity (45% ee) in the following asymmetric addition reactions. We expect this preliminary demonstration could inspire the research by using GO as heterogeneous catalytic supports and could improve the enantioselectivity later.

Non-noble Co anchored on nanoporous graphene oxide, as an efficient and long-life catalyst for hydrogen generation from sodium borohydride

Non-noble metal Co nano catalyst anchored on novel nanoporous graphene oxide (PGO) was successfully prepared for hydrolysis of NaBH4. The PGO was obtained by calcinating graphene oxide (GO) and Na2MoO4. During calcination, Na2MoO4 etched GO planes and plenty of nanopores with an average size of 20 nm was imported on the surface of GO. The nanopores provided binding sites for exactly-sized Co nanoparticles (NPs) to locate in GO, which could strengthen interaction between the Co NPs and PGO. The as-prepared Co/PGO exhibited a glorious catalytic activity on NaBH4 hydrolysis in alkaline condition, with a high hydrogen generation rate (HGR) 5955 mLH2⋅min−1⋅gM−1 at room temperature. Furthermore, The PGO facilitated reusability of the catalyst Co particles, with a retention rate 73% in HGR after five cycles. This work provided a potential strategy for preparing an efficient and non-noble catalyst for hydrogen generation from NaBH4 hydrolysis.