Interlayer Spacing Of Graphene Oxide Research Articles

Swelling of Thin Graphene Oxide Film in Water Vapor Studied by In Situ Spectroscopic Ellipsometry.

Graphene oxide (GO) is obtained by the chemical treatment of graphene sheets, resulting in decoration with oxygen-containing functional groups. In the work presented here, we examined marked changes that occur in a thin film of parallel aligned GO sheets when exposed to water vapor at various pressures. It was found that exceptionally fast and substantial water uptake and release occur that is accompanied by major changes in GO interlayer spacing. These characteristics were obtained in situ with spectroscopic ellipsometry. At 99% relative humidity (RH) and 25 °C, the interlayer spacing became 1.41 nm, which recovers to ∼0.8 nm within 30 s when exposed to 10% RH. Besides layer thickness values, uniaxial optical constants for the GO vs RH were derived from the ellipsometry data. Molar refraction theory was applied that indicated monolayer water formation at ∼91% RH at 25 °C upon water adsorption. Our findings contribute to the understanding of the interaction between GO and its environment. The very outspoken effect of external water vapor pressure on GO water content, interlayer spacing, and optical properties can be utilized in sensing and separation devices, subnanometer positioning, chemical switches, and environmentally aware materials.

A cleaner lignin-induced 3D porous MXenes hybrid electrode with enlarged voltage and high capacitance retention

Conventional supercapacitors face narrow voltage and an inevitable reduction in capacitance retention during operation, significantly preventing its further commercial application. So, biomass-derived composite materials have attracted intensive attention, especially for pseudocapacitive supercapacitors. Herein, a high-end utilization strategy of lignin to induce a 3D porous layered MXenes/graphene oxide hybrid electrode (LGM2-80) and homologous gel electrolytes with low interface resistance for lignin-derived supercapacitors is demonstrated by a simple hydrothermal method. A more uniform distribution and smaller nanospheres ≈<10 nm of lignin prevent the restacking and increase the interlayer spacing of graphene oxide, also play an adhesive role between graphene oxide and MXene, guaranteeing the maximization of the pseudocapacitance effect between lignin and MXene. Consequently, the LGM2-80 electrode showed a wide operating potential (−0.7∼1.0 V), breaking through the bottleneck of MXene-derived devices with limited working voltage (typically≤0.6 V). Furthermore, the lignin-derived symmetric quasi-solid-state supercapacitor (LGM2-80//lignin gel//LGM2-80) possesses an excellent capacitance retention rate of 149 % at 5,000 cycles, which is far exceeding the current reported supercapacitors. This innovative use of lignin opens up new perspectives for ultra-voltage and ultra-high capacitance retention of advanced supercapacitors.

Fabrication of polydopamine/rGO Membranes for Effective Radionuclide Removal.

In this work, a novel polydopamine/reduced graphene oxide (PDA/rGO) nanofiltration membrane was prepared to efficiently and stably remove radioactive strontium ions under an alkaline environment. Through the incorporation of PDA and thermal reduction treatment, not only has the interlayer spacing of graphene oxide (GO) nanosheets been appropriately regulated but also an improved antiswelling property has been achieved. The dosage of GO, reaction time with PDA, mass ratio of PDA to GO, and thermal treatment temperature have been optimized to achieve a high-performance PDA/rGO membrane. The resultant PDA/rGO composite membrane has exhibited excellent long-term stability at pH 11 and maintains a steady strontium rejection of over 90%. Moreover, the separation mechanism of the PDA/rGO membrane has been systematically investigated and determined to be a synergistic effect of charge repulsion and size exclusion. Results have indicated that PDA/rGO could be considered as a promising candidate for the separation of Sr2+ ions from nuclear industry wastewater.

Temperature controlled swelling of graphene oxide for switchable dehumidification membranes

Variation of water permeance and interlayer spacing of graphene oxide (GO) is traced with in-situ X-ray diffraction upon its heating/cooling in dry (∼1000 Pa), humid (∼100 % RH) air and liquid water. Reversible variation of GO interlayer distance ranging 8.3-7.2 Å in dry air, 11-7.5 Å in humid air and 13.9-12.4 Å in liquid water is revealed in the temperature range of 25–80 °C. Accounting for GO layer thickness of ∼6 Å it corresponds manifold alterations of slit width with temperature and water vapor pressure, resulting in over 3 orders of magnitude variation of membrane performance. A typical rise of the permeance of 300–500 % within the temperature range at constant humidity is contraposed to a miserable increase in the activation energy for H2O transport, revealing the decisive impact of slit sizes on GO performance. The effect is addressed to entropy-driven variation of water absorption heat with slit sizes in GO. Variation of interlayer spacing of ∼10 % was also exposed with thermal dissociation of GO groups and H+ migration to the interlayer space as supported by semi-empirical calculations. Reversible structural changes in GO are successfully exploited for fabrication thermally switched membranes for dehumidification with initial permeance of ∼1.1·10−6 mol m−2 Pa−1·s−1 and its variation over 50 % at supplied power of ∼500 W/m2.

Interlayer control of graphene oxide membranes via ion bridges: A theoretical study

Interlayer spacing of graphene oxide (GO) membranes can be precisely controlled using cations, which has been extensively used in nanofiltration membrane. However, no report definitely discloses the specific performance of anion in treating GO membrane, although cations and anions naturally coexist in aqueous solution. Subjectively, anion might have weak/reverse effect in maintaining the interlayer of negatively charged GO, which is yet confirmed by no evidence. In this work, combining molecular dynamics simulations and density functional theory calculations, we have discovered a long-time unexplored effect that anion can also sustain the GO membrane interlayer — specifically, two types of ion bridges (confined within two neighboring GO sheets), one composed of one anion intercalated into two cations and the other composed of two anions sandwiched by two cations, can effectively and stably fix the interlayer spacing of GO membrane. Our calculations revealed that the ion bridges greatly enhance the interaction between two neighboring GO sheets, making them highly stabilize in aqueous solution. Moreover, free energy calculations and density functional theory calculations further confirm the critical role of ion bridge in controlling the interlayer spacing of GO membrane. Our findings highlight, for the first time, the undiscovered control of GO membrane interlayer with anions via forming an ingenious ion bridge, rather than the preconceived weak/reverse effect of anions, which could inspire the future application of anions (and ion bridge) in membrane design.

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.

Physicochemical transformation of graphene oxide during heat treatment at 110–200 °C

Graphene oxide (GO) was subjected to different heating pathways to investigate water removal at 110°C (GO-110), water removal followed by removal of surface groups at 140°C or 200°C (GO-110-140 or GO-110-200), and simultaneous removal of water and surface groups at 140°C or 200°C (GO-140 or GO-200). Physicochemical characteristics of GO samples at each stage were determined to quantify and understand the impact of each treatment pathway on porosity development, physical structure, or surface chemistry of GO. Surface elemental composition showed the following order for C/O ratio: GO-140-200 > GO-110-200 > GO-200, suggesting that a two-step heat treatment results in more oxygen removal from the surface, and FTIR profiles confirmed the lowest intensities of all functionalities for GO-140-200. Proton NMR spectra of as-received and heat-treated GO samples confirmed near complete removal of water and hydroxyl groups for samples treated at 200°C. XRD results showed that the interlayer spacing of GO reduced from 0.792 nm to the lowest values of 0.371 nm for GO-200 and 0.367 nm for GO-110-200. Porosity characterization revealed that only two pathways, GO-200 and GO-110-200, created a porous structure. Further analysis of data suggested that exfoliation is primarily triggered by decomposition of surface functionalities and release of a substantial volume of CO2/CO, but water vapor release helps to enhance the exfoliation. These results demonstrate that direct and rapid heat treatment of GO at 200°C (or higher temperatures) is the most effective option for developing a porous structure.

Biomimetic asymmetric GO/polymer nanocomposite membrane for energy harvesting

Energy harvesting based on salinity gradients between oceans and rivers can provide a clean, stable, and continuous electric output. However, it is highly dependent on the excellent performance of biomimetic ion-selective membranes. The graphene oxide (GO) membrane, as a 2D material-based layered-structure membrane, offers the possibility of efficient salinity gradient energy conversion. However, unstable stratification in aqueous solutions and the limited number of charged functional groups make practical applications difficult. A conventional symmetric structure will also reduce the effective salinity gradient owing to ion enrichment on the low-concentration side. In this study, we pre-modified GO to create an asymmetric ion-selective membrane with opposing charges. Hyperbranched polyethyleneimine (PEI) and polyacrylic acid (PAA) as surface charge donors and crosslinkers stabilise the interlayer spacing of GO and increase charge density, achieving up to 3.4 W/m2 power density under sea water and river water. Furthermore, theoretical calculations show that membranes with asymmetric structure and opposite charges can eliminate the effect of ion enrichment on the low-concentration side, thereby avoiding power consumption. This system contributes to a further step toward the application of salinity energy conversion.

Study on the Hydration and Physical Properties of Cement by M18 Polycarboxylate Superplasticizer Modified Graphene Oxide

Graphene oxide (GO) as a new nano-enhancer in cement-based materials has gained wide attention. However, GO is easy to aggregate in alkaline cement mortar with poor dispersibility. This hinders its application in practical infrastructure construction. In this work, GO-M18 polycarboxylate compound superplasticizer (GM) were obtained by compounding the M18 polycarboxylate superplasticizer with GO solution at different mass ratios. The dispersion of GM in alkaline solution was systematically studied. The phases and functional groups of GM were characterized by XRD and FTIR. The effects of GM on the cement mortar hydration and the formation of microstructure were investigated by measuring the heat of hydration, MIP, TG/DSC, and SEM. The results show that the long-chain structure of the M18 polycarboxylate superplasticizer can increase the interlayer spacing of GO and weaken the force between GO sheets. The modified GO can be uniformly dispersed in the cement slurry. GM can accelerate the early hydration process of cement, which can increase the content of Ca(OH)2 and decrease the grain size. It can optimize the pore size distribution of cement-based materials, increase the density of harmless and less harmful pores, thereby improving mechanical properties. Such methods can transform traditional cement-based materials into stronger, more durable composites, which prolong the life of cement-based materials and reduce the amount of cement used for later maintenance. This provides an idea for achieving sustainability goals in civil engineering.

Interlayer spacing control of boron nitride sheets with hydrated cations

Two-dimensional (2D) materials are widely used in various fields, among which the application prospect in filtering and purifying water resources is broad. An important factor in sieving water molecules and other substances is the interlayer spacing of 2D material membranes. The interlayer spacing of graphene oxide and graphene membranes can be controlled by hydrated cations because of hydrated cation–π interaction. Similarly, our simulations show that hydrated cations can also control the interlayer spacing between hexagonal boron nitride (h-BN) sheets, which are smaller than that of graphene oxide sheets and graphene sheets. The interlayer distances are 8.70, 8.62, 7.68, 8.21, 8.93, 8.11 and 8.18 Å for hydrated Li+, Na+, K+, Mg2+, Ca2+, Cu2+ and Zn2+, respectively. Both hydration energy and the radius of the hydrated cation are deciding factors for monovalent hydrated cations and divalent hydrated cations in affecting the h-BN layer spacing. Further calculations indicate that unlike graphene and graphene oxide dominated by the hydrated cation–π interaction, the interactions between h-BN sheets and hydrate cations are mainly hydrogen bonds. However, there is an obvious hydrated cation–π interaction between hydrated K+ and the h-BN sheets. Our results are helpful for future ion sieving applications using the h-BN membranes.

Expanded interlayer spacing of graphene oxide achieved by electrostatic cation intercalation towards superior sodium ion storage

Expanded interlayer spacing of graphene oxide achieved by electrostatic cation intercalation towards superior sodium ion storage

Assembly of 2D-MoS2 with graphene layer for highly sensitive and selective gas detection at room temperature

Two-dimensional (2D) graphene has been regarded as a promising gas sensing material operated in room temperature. However, practical use of pure graphene as a gas sensor still faces problems owing to its insufficient sensitivity, selectivity and stability. In the present study, 2D-molybdenum disulfide (2D-MoS2) were successfully assembled with graphene oxide (GO) with the assistance of poly (diallyl dimethylammonium chloride) (PDDA). The intercalation of PDDA and stacking of 2D-MoS2 significantly expand the interlayer spacing of GO from 0.77 nm to 1.44 nm in the GO-PDDA-MoS2 composite. The rGO-PDDA-MoS2 sensing chip could be obtained by in-situ reduction of GO-PDDA-MoS2 pre-coated on an interdigital electrode in hydrazine vapor. The sensor exhibited excellent sensitivity, selectivity and stability for H2S and NO detection with a limit detection as low as 3 ppb and 5 ppb, respectively. The enhanced sensing performance could be ascribed to the increased gas accessibility and specific binding site resulted from the introduction of PDDA and 2D-MoS2. Furthermore, its potential application in the diagnosis of respiratory disease was demonstrated. Exhaled breath (EB) spiked with 50 ppb NO and 15 ppb H2S for simulating EB of asthma patients could be successfully discriminated from the normal EB.

2D vertical heterostructure membranes for lanthanide separation

The design and synthesis of separation materials for lanthanides with extremely similar properties have always been a significant challenge. Here, a two-dimensional (2D) metal–organic framework (MOF) with crystal faces similar to the [002] of ZIF-8, which theory suggests should not be stable, is predicted and synthesized by solvent evaporation between graphene layers to prepare a 2D vertical heterostructure membrane. Theoretically, the pristine cluster of 2D MOFs contains one small and 1/4 large crown pores, and the small pores can selectively adsorb lanthanide elements, causing the selective penetration of lanthanide ions. Experimentally, the selectivity of lanthanide is obtained through the membrane with La3+/Yb3+ ≈55.79 and La3+/Ce3+ ≈6.02. The interlayer entrapment of graphene stabilizes the structure of the 2D MOF, and the intercalation of the 2D MOF expands and fixes the interlayer spacing of graphene oxide, improving the stability in strong acids, the selectivity, and the ion transmittance of the membrane.

Two-dimensional sub-nanometer confinement channels enabled by functional carbon dots for ultra-permeable alcohol dehydration

Graphene oxide (GO) membranes have shown great promise in pervaporation dehydration of biofuels, expected to satisfy the demand of lower energy consumption. However, the swelling of interlayer spacing between GO nanosheets in aqueous environment, usually leads to deteriorated membrane separation performance and limited stability. Here, we report ultra-permeable sulfonated carbon quantum dots (SCDs)/GO composite membranes that are designed through strategically introducing the functional quasi-spherical nanoparticles - SCDs as water transport promoters and crosslinker into GO laminates. Well self-assembly stacked manner between SCDs and GO nanosheets created highly hydrophilic two-dimensional sub-nanometer confinement interlayer channels for fast water transport, while the crosslinking effect between SCDs and GO nanosheets producing a stable microstructure to maintain GO interlayer spacing against swelling. Furthermore, the SCDs occupied the vacancies around the ordered edges of GO nanosheets also resulted in an enhancement of water selective permeation. The microstructure evolution was confirmed by low-field nuclear magnetic resonance spectra. The prepared SCDs/GO membrane on polyethersulfone (PES) substrate with ∼150 nm selective layer exhibited a total flux of 5.88 kg m−2 h−1 and water/butanol separation factor of ∼4407 at 343 K, which outperforms the performance of state-of-the-art membranes reported to date. Meanwhile, the thin composite membrane showed long-term operation stability for 130 h when fed with 90 wt% butanol/water solution. This research provides a promising method for the selective water separation of high-performance GO membranes.

The role of oxidation level in mass-transport properties and dehumidification performance of graphene oxide membranes

Here we report on gas and vapor transport properties of ultra-thin graphene oxide (GO) membranes, with various C:O ratios. Graphene oxide nanosheets with an average lateral size of 800 nm and C:O ratio ranging from 2.11 to 1.81 have been obtained using improved Hummers’ method by variation of graphite:KMnO4 ratio. Thin-film selective layers based on the obtained graphene oxide have been spin-coated onto porous substrates. To extend the C:O range to 2.60, thermal reduction of GO membranes was applied. A decrease in C:O ratio leads to significant water vapor permeance growth to over 60 m3(STP)·m−2·bar−1·h−1 while the permeance towards permanent gases reduces slightly. According to the permeation and sorption measurements, a decisive role of H2O diffusivity has been established, while the water sorption capacity of the graphene oxide stays nearly independent of C:O ratio in GO. The result is supported by semi-empirical modeling which reveals diminution of H2O jump activation barriers with both increasing GO interlayer spacing and its oxidation degree. The height of the activation barriers was found to vary up to an order of magnitude within the entire range of relative humidity (0–100% RH), lowering significantly for strongly oxidized GO. Our results evidence the necessity of attaining maximum GO oxidation degree for improving water transport in GO, especially at low partial pressures.

Charge Storage in Graphene Oxide: Impact of the Cation on Ion Permeability and Interfacial Capacitance.

The charge storage and membrane applications of graphene oxide (GO) materials are dictated by its intrinsic material properties. Structure-function relationships correlating periodic parameters, such as the hydrated ion radius and ion-GO interactions, are currently lacking yet are needed to provide insight on the charge storage and ion transport mechanism. We report the use of scanning ion conductance microscopy to measure the ion permeability of GO films and evaluate its relationship with the measured capacitance. We demonstrate that species (namely K+) with strong electrostatic interactions with the oxygen functionalities of GO provide the benefit of higher capacitance but suffer from inhibited ion mobility due to constriction of the GO interlayer spacing.

Capacitance Enhancement of Hydrothermally Reduced Graphene Oxide Nanofibers.

Nanocarbon materials present sp2-carbon domains skilled for electrochemical energy conversion or storage applications. In this work, we investigate graphene oxide nanofibers (GONFs) as a recent interesting carbon material class. This material combines the filamentous morphology of the starting carbon nanofibers (CNFs) and the interlayer spacing of graphene oxide, and exhibits a domain arrangement accessible for fast transport of electrons and ions. Reduced GONFs (RGONFs) present the partial removal of basal functional groups, resulting in higher mesoporosity, turbostratic stacking, and surface chemistry less restrictive for transport phenomena. Besides, the filament morphology minimizes the severe layer restacking shown in the reduction of conventional graphene oxide sheets. The influence of the reduction temperature (140–220 °C) on the electrochemical behaviour in aqueous 0.5 M H2SO4 of RGONFs is reported. RGONFs present an improved capacitance up to 16 times higher than GONFs, ascribed to the unique structure of RGONFs containing accessible turbostratic domains and restored electronic conductivity. Hydrothermal reduction at 140 °C results in the highest capacitance as evidenced by cyclic voltammetry and electrochemical impedance spectroscopy measurements (up to 137 F·g−1). Higher temperatures lead to the removal of sulphur groups and slightly thicker graphite domains, and consequently a decrease of the capacitance.

Ultrahigh flux of graphene oxide membrane modified with orientated growth of MOFs for rejection of dyes and oil-water separation

Metal organic frameworks (MOFs) has broad application prospect in separation, catalysis, and adsorption. By a facile green method, we successfully fabricated prGO@cHKUST-1 composite membrane with the modification of dopamine and orientated growth of MOFs. Mg/Al-layered double hydroxides (Mg/Al-LDHs) was used as a modulator to obtain cubic HKUST-1 (cHKUST-1) with excellent morphology and special properties. Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) etc. characterization illustrated successful synthesis of cHKUST-1 and composite membranes. Cubic HKUST-1 can tune the inter-layer spacing of graphene oxide (GO) leading increase in hydrophilicity and flux of the membrane. Meanwhile, the reduction effect of PDA and intercalation effect of MOFs could change the stacked way of GO layers, forming several fuzzy pores and more active sites on membrane surface. The prGO@cHKUST-1 membrane has an excellent rejection for methylene blue (MB) (99.5%) and Congo red (CR) (71.2%). Moreover, the modified membrane exhibited 10 and 5 times higher permeation flux than that of original GO membrane and prGO membrane, respectively. Thus, using orientated growth of MOFs to synthesize GO based composite membrane will provide useful insights in ultrahigh permeation flux membranes of dye and oil-water emulsion separation.

Graphene oxide nanofibers: A nanocarbon material with tuneable electrochemical properties

We report the electrochemical properties of a novel nanocarbon material obtained by chemical oxidation and ultrasound-assisted exfoliation of fishbone carbon nanofibers (CNF). The resulting material maintains its tubular morphology and presents a characteristic interlayer spacing of graphene oxide (above 0.75 nm). Thus, this is called graphene oxide nanofibers (GONF). The new rearrangement of the accessible sp2-carbon domains makes the GONF a potential alternative for electrochemical energy conversion/storage applications, showing a developed porosity and tuneable surface chemistry. The influence of the oxidation degree of GONF on its electrochemical behaviour in 0.5 M H2SO4 is reported. Cyclic voltammetry and electrochemical impedance spectroscopy evidenced a significant increase of the capacitance for GONF, being 4–27 times higher than that obtained for pristine CNF. An optimum in the capacitance (49.2 F g−1) was obtained using an oxidation ratio (OR = KMnO4/Sample) of 6 and 60 min of sonication. The latter is ascribed to the unique structure of this material containing both graphitic and graphene oxide domains. Higher OR or longer sonication times led to a partial loss of graphitic domains and higher contribution of micropores, which worsen the fast ion/electrolyte transport. Additionally, the optimized material exhibited an improved activity for the hydrogen evolution reaction.

NH2-Fe3O4-regulated graphene oxide membranes with well-defined laminar nanochannels for desalination of dye solutions

Graphene oxide (GO)-based nanofiltration membranes, featuring well-ordered microscopic structure, well-defined 2D nanochannels and superior molecular sieving ability, have attracted sustained research interest in molecular and ionic separation. However, most of current GO laminar membrane have a poor water flux and high rejection of both dyes and salts, which is not suitable for the dye/salt mixture separation. Herein, we report a vacuum filtration strategy to fabricate GO/NH2-Fe3O4 nanofiltration membranes with high water flux and excellent separation performance for dye/salts mixture by introducing NH2-Fe3O4. The NH2-Fe3O4 is not only worked as the rigid spherical nanospacer to tune GO interlayer spacing but also as crosslinkers to improve the stability of GO membrane in water. FTIR, XRD, SEM, zeta potential and contact angle were applied to analyze the chemical composition and morphology of as-prepared membranes. The effect of intercalated NH2-Fe3O4 nanoparticles on overall performance of the GO/NH2-Fe3O4 membranes was systematically investigated. The resulted membrane with 8 wt% of NH2-Fe3O4 loading has high water flux of up to 78 Lm−2 h−1, which is 4.8 times higher than that of pure GO membrane. Moreover, such membrane also displays high congo red rejection (94%) and low NaCl rejection (~15%), rendering the membranes promising for dye/salt mixtures separation.