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(a) SEM image of edge region of the HDTMA functionalized membrane. (b) X-ray di ff raction patterns recorded from HDTMA functionalized graphite oxide powder showing a set of (00 l ) peaks and the XRD image (inset) recorded from the HDTMA reacted membrane. Both samples recorded under solvent free (dry) conditions.
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The change of distance between individual graphene oxide sheets due to swelling is the key parameter to explain and predict permeation of multilayered graphene oxide (GO) membranes by various solvents and solutions. In situ synchrotron X-ray diffraction study shows that swelling properties of GO membranes are distinctly different compared to precur...
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... These types of shapes for the edges and surface of the membrane could be expected since the samples are prepared in water solution and then slowly dried from the fully hydrated state. A very similar lamellar texture of GO membrane samples pre- served even after a prolonged reaction in the methanol solu- tion of alkylammonium salts and drying (see Fig. 7a ...
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... described earlier by Dekany et al., 31 and performed the reaction with HDTMA at 60 °C both with powders and membranes. In this case, the expanded structure preserves even when methanol solution is removed, the alkylammonium ions are attached to the GO sheets. Inter- calation of GO membranes and powders at 60 °C appeared to be very similar, Fig. 7. Note that the lamellar texture of the GO membrane reacted with HDTMA in methanol solution and air- dried ( Fig. 7a) is very similar to the texture of pristine air dried GO membranes prepared using water solution (Fig. 1a). The expanded lattice with a set of (00ℓ) reflections up to 8-10 order was observed for both powders and membranes ...
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... membranes. In this case, the expanded structure preserves even when methanol solution is removed, the alkylammonium ions are attached to the GO sheets. Inter- calation of GO membranes and powders at 60 °C appeared to be very similar, Fig. 7. Note that the lamellar texture of the GO membrane reacted with HDTMA in methanol solution and air- dried ( Fig. 7a) is very similar to the texture of pristine air dried GO membranes prepared using water solution (Fig. 1a). The expanded lattice with a set of (00ℓ) reflections up to 8-10 order was observed for both powders and membranes (later with strong diffuse scattering); the interlayer distance is found at d(001) = 32-35 Å in good agreement with ...
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Citations
... Multilayered GO comprises five to ten layers, while material with eleven or more stacked layers is denoted as graphite oxide (Dreyer et al. 2010;Kumar et al. 2021). GO has outstanding properties, notably its hydrophilic nature, which allows it to disperse in numerous solvents, especially water (Klechikov et al. 2015). Additionally, graphene-based composites can be synthesised by modifying the oxygen-functionalized groups of GO (Zheng et al. 2022). ...
Graphene-based materials have gained significant attention due to their unique mechanical, chemical, thermal, and optical properties. Among these, Graphene oxide (GO) is one of the promising materials extensively studied. Unlike other graphene derivatives, GO is chemically modified with diverse oxygenated functional groups, rendering it more hydrophilic. It serves as a precursor for graphene synthesis. Notably, recent researchers have focused on synthesising GO using alternative low-cost carbon-rich materials such as coconut shells, sugarcane bagasse, tea, pine leaves and scrap tyres instead of graphite. These non-conventional carbon sources decrease the demand for costly, non-renewable graphite, increase reliability, and offer an eco-friendly approach to waste management. This comprehensive review aims to explore accessible methods for synthesising graphene oxide and highlight various alternative feedstocks utilising agricultural, industrial, and plastic waste as precursors. Furthermore, a comparative assessment of various production methods and their performance in different applications is outlined to provide insights for the commercialisation of GO in future applications.
... [5][6][7][8][9] Due to the atom-thick features of 2D nanosheets and sub-nano interbedded gaps, the lamellar membranes prepared using 2D nanosheets as building blocks show fast water permeation and high rejection e ciency. However, they suffer from poor stability because these membranes tend to swell in liquid water, [10,11] and it is di cult to obtain a strictly de ned aperture which is considered the ideal pore feature for membrane separations. Membranes with intrinsic one-dimensional (1D) long-range ordered nanochannels [12][13][14] have recently achieved ultrafast desalination and have been considered a promising alternative. ...
Nanofiltration membranes featuring sub-1 nm channels have shown significant potential for desalination and ion separation. However, the construction of scalable membranes with tailorable one-dimensional (1D) sub-1 nm channels using a versatile and eco-friendly protocol remains a formidable challenge. In this study, we present an approach to tuning sub-1 nm channels using natural palygorskite (PAL) nanorods with carboxymethylcellulose (CMC) cross-linkers to control density and enhance stability of membrane. The sub-1 nm channels of the membrane were further regulated by an ion-imprinting technique to enable fast and selective transport of Li ⁺ . The resulting PAL-CMC hybrid (PCH) membranes only retained the natural 1D straight sub-1 nm channels of PAL nanorods by adjusting the CMC content, making them among the few membranes capable of ultra-fast water transport (> 25 L m − 2 h − 1 bar − 1 ) and exceptional salt retention (97.4% for Na 2 SO 4 and 86.2% for NaCl). Notably, PCH membranes regulated by ion-imprinting technique exhibit unprecedented Li ⁺ selectivity from ionic mixture solutions containing Mg ²⁺ , achieving a separation factor ( S Mg 2+ / Li + ) up to 32.5. Molecular dynamics simulations revealed rapid Li ⁺ transport through the sub-1 nm channel of PAL. These findings position PCH membranes as next-generation candidates for desalination and Li ⁺ extraction from lagoons.
... The synthesis of ultrasonically assisted chemical oxidation, followed by further reduction as rGO, provides a cheap and simple solution for coal-based MG derivatives. The synthesized products were characterized analytically by thermogravimetry, x-ray photoelectron spectroscopy [17], x-ray diffraction spectroscopy [18], electron microscopy [19], Raman spectroscopy, infrared FTIR spectroscopy, UV-vis spectroscopy [20], interfacial contact angle, etc. Utilizing these coal types to create valuable graphene and its derivatives not only enhances the commercial potential of the coal as a raw material but also offers an additional pathway for its sustainable utilization. ...
... By XRD ( figure 5(b)) analysis, there is a distinct peak at 2θ= 12.4°. This peak corresponds to 12.4°a nd indicates the (001) crystal plane, which further confirms the formation of GO [18]. After the thermal reduction of GO by VC, GO was reduced to rGO, and the rGO recovered the ordered crystal structure. ...
In our study, we selected three prevalent coal types from Xinjiang: Dahuangshan coal (referred to as Y-coal), Black Mountain coal (B-coal), and Kuche coal (K-coal). Initially, we assessed their morphological differences using electron microscopy. Subsequently, we evaluated the superiority of Y-coal through Thermogravimetric Analysis (TGA). Furthermore, we compared their performances using various electrochemical tests, including the J-V curve, dark current curve, open-circuit voltage curve, and Electrochemical Impedance Spectroscopy (EIS) curve. Ultimately, we investigated the potential of synthesizing graphene from Y-coal and its derivatives. The first step was the preparation of multilayer graphene (MG) by treating Y-coal with acid to obtain demineralized coal, followed by treatment in a tube furnace to obtain ultrafine powdered MG. The second step was then followed by successive oxidation and ultrasonication of the already obtained MG to obtain graphene oxide (GO). Finally, ascorbic acid (VC) was selected to treat GO to prepare an aqueous suspension of reduced graphene oxide (rGO). MG (2θ= 26.2°), GO (2θ= 12.4°) and rGO (2θ= 25.5°) were obtained by XRD analysis. C 1s and O 1S were analyzed by XPS spectra. The functional groups -OH, C=O, and -C=C-, which are unique to graphene and its derivatives, were comparatively analyzed using infrared spectroscopy. The change of π→π* was analyzed by the UV-Vis method. The absorbance was further found in combination with PL spectra. Immediately after, the morphology of graphite and its derivatives was analyzed by SEM, HRTEM, the physical properties by contact angle and BET, and finally the content of elements C and O by EDS. The successful demonstration of the superiority of the synthesized MG and its derivatives was achieved.
... The XRD measurement was conducted in 2θ range from 5° to 80° at the scan rate of 0.1°/min. Figure 1a of the XRD pattern depicts the precise diffraction point at 9.20°, which reveals the pure (001) plane of Graphene oxide (GO), as reported in the literature [27]. The distance between planes can be calculated using Bragg's equation [28]: ...
The in situ Nickel oxide-zinc oxide-doped reduced graphene oxide (NiO–ZnO/rGO) nanocomposite is synthesized by the hydrothermal method. NiO–ZnO/rGO nanocomposite-modified glassy carbon electrode (GCE) utilized as electrochemical sensor for dopamine sensing. Scanning electron microscopy (SEM), RAMAN spectroscopy, Transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were used for morphological and structural characterizations of NiO–ZnO/rGO nanocomposite. Further investigation of the redox response and the charge transfer characteristics of dopamine (DA) at NiO–ZnO/rGO-modified GCE tested using cyclic voltammetry and electrochemical impedance spectroscopy. The prepared GCE nanocomposite-modified electrochemical sensor show a linear response of redox peak current for DA in the concentration range of 0.0041–0.054 µM. The active electrochemical surface area of the sensor found to be 2.1 × 10⁻⁶ cm², with low detection limit of 0.0076 µM and high sensitivity of 12.19 µA L cm⁻² Mol⁻¹. The constructed sensor has close to 100% recovery toward DA in voluntarily collected human urine samples. The composite exhibits good reproducibility for sensing DA for month, which is an indication of their repeatability. Also designed sensors show 123% retention current to 100 cycles of CV indicates the good stability of the sensor to DA, which are crucial for the fabrication of further devices.
... Fig. 2(a,b,c) illustrates the results of the FE-SEM assessment used to examine the composition and surface characteristics of the different amine-functionalized GO and MMT clay nanomaterials. Large, leaf-like, two-dimensional nanosheet structures made of stacked layers of GO and clay can be found in the amine-functionalized GO and MMT clay nanofillers [42,43]. The appearance of layered and sheet-like structures in all three nanomaterials obtained from FE-SEM images supports the functionalization of the nanomaterial with 2D nanosheet structures. ...
... A distinguishing feature of porous media is the threedimensional interconnected network of capillary channels, often with nonuniform sizes and shapes 42 (Fig. 3). [43][44][45][46][47][48][49][50][51][52][53][54] Despite the inherent complexities of these substrates, some characteristics of fluidic movement can be approximated by separate formulae. For example, the flow rate (Q P ) within a porous structure is characterized by Darcy's law, which accounts for the hydraulic conductivity of the substrate. ...
... 123 These materials have also historically been difficult to integrate within microfluidic devices as the graphitic surface does not bind readily to polymers, 114 among other potential microdevice materials. However, GO or rGO composites may offer an alternative means for microfluidic integration beyond a reliance on adhesives, 47 in addition to imparting novel characteristics such as enhanced tensile strength. 115 Finally, although lamellar GO flakes remain heavily favored as a membrane substrate, alternative porous structural formats offer novel avenues for microdevice applications, including the use of GO microfibers 117 as a culturing scaffold for organ-on-adisc, 124 asymmetric bilayers for integrated power generation, 125,126 or hydrogels for sensors 127 and catalysis. ...
Centrifugal microfluidics has evolved into a sophisticated technology capable of enabling the exploration of fundamental questions in such fields as protein analysis, environmental monitoring, and live cell handling. These microdevices also hold unique potential for translating promising academic research into many real-world scenarios, with several products already available on the market. Yet, in order to fully realize this potentially transformative technology, there remains an outstanding need to incorporate simple to operate world-to-chip interfaces alongside the integration and automation of complex workflows. This requires cost-effective and versatile materials that are, ideally, already commercially available. Membranes not only meet these exigencies, they are also capable of enhancing the inherent advantages of microdevices when thoughtfully combined. This review provides an overview of the importance of these two technologies and the manifold benefits upon their unification. The fundamental principles governing fluid flow with centrifugal actuation, as well as within porous membranes, are briefly covered in addition to a comment on their relative advantages compared to classical microdevices and porous media. The major subtypes in membrane composition, preparation, and microfluidic integration strategies are next discussed in detail, along with their relativistic capabilities and drawbacks. This is followed by recent examples in the literature displaying the enormous versatility membranes have already demonstrated within microfluidic devices, highlighting recent centrifugal microdevices wherever possible. Finally, recommendations for areas where the incorporation of these materials still face challenges, as well as possible new avenues for exploration, are also provided.
... The fabricated GO membranes exhibited high rejection rates for organic dyes with molecular weights of approximately 500 Da, and the permeation flux of water exceeded that of most commercially available nanofiltration membranes. In addition to being stable and extremely hydrophilic in a variety of organic solvents, such as acetone and methanol, GO membranes are suitable for the nanofiltration of organic solvents, owing to their layer spacing, which can be precisely controlled [16][17][18]. Huang et al. prepared GO composite membranes on ceramic hollow fiber supports via vacuum aspiration, which exhibited high flux and separation factors in the dehydration of dimethyl carbonate [19]. ...
Graphene oxide (GO) has attracted attention as an excellent membrane material for water treatment and desalination owing to its high mechanical strength, hydrophilicity, and permeability. In this study, composite membranes were prepared by coating GO on various polymeric porous substrates (polyethersulfone, cellulose ester, and polytetrafluoroethylene) using suction filtration and casting methods. The composite membranes were used for dehumidification, that is, water vapor separation in the gas phase. GO layers were successfully prepared via filtration rather than casting, irrespective of the type of polymeric substrate used. The dehumidification composite membranes with a GO layer thickness of less than 100 nm showed a water permeance greater than 1.0 × 10−6 mol/(m2 s Pa) and a H2O/N2 separation factor higher than 104 at 25 °C and 90–100% humidity. The GO composite membranes were fabricated in a reproducible manner and showed stable performance as a function of time. Furthermore, the membranes maintained high permeance and selectivity at 80°C, indicating that it is useful as a water vapor separation membrane.
... The XRD measured inter-plane distances in the mHGO and GO thin films were carefully summarized in the review paper [10]. The XRD data for the swollen BGO membranes (mBGO) may be found in [22][23][24]. The existing data make it possible to argue that membranes sorbed less and swelled less than powders. ...
... These data are presented in Table 4 separately. HGO, powder 0.35± 0.03 12.0 a HGO, membrane 0.16± 0.03 8.8 a HGO, powder [15] 0.34± 0.01 HGO, powder [22] 14.0 b HGO, membrane [22] 9.0 b a Measured after the IM experiment, 30 days; b Measured in direct contact with liquid CH3 CN, ≈30 min [22]. ...
... These data are presented in Table 4 separately. HGO, powder 0.35± 0.03 12.0 a HGO, membrane 0.16± 0.03 8.8 a HGO, powder [15] 0.34± 0.01 HGO, powder [22] 14.0 b HGO, membrane [22] 9.0 b a Measured after the IM experiment, 30 days; b Measured in direct contact with liquid CH3 CN, ≈30 min [22]. ...
The comparative study of sorption of polar substances acetonitrile and water into powders and membranes (>10 μm thick) of modified Hummers (HGO) and Brodie (BGO) graphite oxides was performed using isopiestic method (IM) and differential scanning calorimetry (DSC). Additional sorption data were obtained for pyridine and 1-octanol. Sorption measurements were accompanied by conventional XRD and XPS control. Electron paramagnetic resonance (EPR) was additionally used to characterize ordering of the membranes. The impact on sorption of synthetic procedure (Brodie or Hummers), method of making membranes, chemical nature of the sorbent, and method of sorption was systematically examined. It was demonstrated that variations in synthetic procedures within both Hummers and Brodie methods did not lead to changes in the sorption properties of the corresponding powders. Sorption of acetonitrile and pyridine was reduced by approximately half when switching from powders to membranes at ambient temperature. DSC measurements at a lower temperature gave equal sorption of acetonitrile into HGO powder and membranes. Water has demonstrated unique sorption properties. Equal sorption of water was measured for HGO membranes and powders at T = 298 K and at T = 273 K. It was demonstrated that lowering the orientational alignment of the membranes led to the increase of sorption. In practice this could allow one to tune sorption/swelling and transport properties of the GO membranes directly by adjusting their internal ordering without the use of any composite materials.
... Due to its unique atomic thickness and micrometer lateral dimensions, 2D materials have increasingly been explored as a fundamental medium to establish separation technologies [11][12][13][14]. Graphene oxide (GO), the oxidative form of graphene, is rated at a high level due to its unique permeation path, large surface area, outstanding anti-fouling properties, high chemical tolerance, high hydrophobicity [15,16]. It is a single layer of carbon monoatomic on the basal planes and sides, formed in a honeycomb with oxide groups (epoxide, carboxyl, and hydroxyl) [17,18]. ...
Presently carbon allotropes namely graphene, graphene oxide (GO) and reduced graphene oxide (RGO) are being extensively utilized for water purification applications. The presence of myriad types of oxygen functional groups in the GO, however, makes this material very hydrophilic, allowing it to absorb water and to swell in moist or watery environments and to significantly damage its intended performance. In contrast, fully reduced graphene oxide membranes are not stable due to fewer oxide groups which are mainly responsible for GO flakes stacking. In the present work, the aforementioned problems are overcome by optimizing the oxygenated functional groups to develop mildly reduced graphene oxide (MRGO) membrane over PVDF (polyvinylidene fluoride) support. GO is reduced by L-Ascorbic Acid (LAA) with different amounts of wt.% and an optimized MRGO membrane is achieved at 10 wt.% of LAA, which is stable and showing comparatively lower swelling than GO membrane. All related structural and optical characterizations like XRD, SEM, EDAX, Raman, FTIR, and Contact angle have been done to evaluate the effect of mild reduction of GO. The studies are indicative of their potential application in water purification.
... 50 However, information about the change of inter-layer distance is extremely difficult to collect for few-layered GO membranes. X-ray diffraction (XRD) is the most common method to evaluate averaged interlayer distance in multilayered GO membranes 13,14 but it is rather difficult to employ for 2-3 layered GO films, and almost impossible for individual micrometer sized bilayered flakes. Therefore, the XRD data obtained on GO membranes with thickness corresponding to tens of layers were often directly applied to interpretation of results with few-layered membranes. ...
