Graphene Oxide Aqueous Dispersion Research Articles

A Journey from Structured Emulsion Templates to Multifunctional Aerogels

AbstractInterfacial jamming and assembly, facilitated by nanoparticle surfactant (NPS) complexation, demonstrate a remarkable efficacy in stabilizing multiphase systems, evident in structured liquid streams and structured Pickering emulsions. However, the utilization of structured liquid templates to tune multiple porosity levels of ultra‐flyweight aerogels is barely discussed. In this study, a structured Pickering emulsion is prepared through mixing an aqueous dispersion of graphene oxide (GO) with an organic (hexane) solution containing an active ligand. The emulsion is jetted into the same organic phase, resulting in “dual jamming”. This process produced worm‐like aerogels with porosity that can be precisely tailored at four different levels: i) voids between filaments, ii) cavities produced by evaporation of trapped hexane droplets, iii) pores generated from sublimation of water in the bulk of GO emulsion, and iv) microscopic regions trapped between GO flakes or fractures/holes within GO nanosheets. These aerogels exhibit ultra‐low density (1.67–2.3 mg cm−3), high compressibility, and shape recovery. The multi‐scale porosity, created by structural design, endows aerogels with a record‐level fluid sorption capacity (e.g., 615 g g−1 for chloroform). Additionally, the aerogels demonstrate an absorption‐dominant electromagnetic interference (EMI) shielding mechanism, achieving a remarkable specific EMI shielding (SSE/t) of 67 178 dB cm2 g−1.

Stable graphene oxide-based lyotropic liquid crystals for interfacial lubrication

Lyotropic liquid crystals have lubricating properties due to their ordered assembly and fluidity, whose mesogens are often characterized by amphiphilic properties. Despite the attention that graphene oxide (GO) has been studied as a novel amphiphilic lyotropic mesogen this decade, and GO applied as a lubrication additive has been demonstrated in both oil and water-based systems, little research reveals the interfacial lubrication of GO liquid crystals yet. This work reports that GO aqueous dispersion can form lyotropic liquid crystals above a specific critical concentration of 5.00 mg/mL, providing a form of stable water-based lubricant, which can keep stable for several months and can reduce friction by 37.3% and wear by 25.24%. The liquid crystal phase was verified by polarizing microscope and synchrotron radiation small-angle X-ray scattering, and its rheological properties and viscoelasticity were studied by interfacial rheometer. The formation of lyotropic liquid crystals can enhance the stability of GO aqueous dispersions at high density, simultaneously ensuring friction decrease and anti-wear effect. It is attributed to the stable nematic network by the ordered GO sheets. The ordered assembly structure bears vertical shear force, therefore, reducing the wear. It is also assumed that the wide lateral size of graphene oxide promotes the nematic phase thus smoothes the graphene oxide film composed spontaneously under the coincidence of lamellar liquid crystal and 2D layered material. Through this work, the interlayer lubrication of GO was optimized, and the problem of GO dispersion sedimentation was solved by self-assembly. The range of interfacial lubrication of GO aqueous dispersion has been expanded and the synergistic effect is conducive to the environmentally friendly lubricants.

Investigation of Graphene Oxide/Mesoporous Silica Supports for Enhanced Electrochemical Stability of Enzymatic Electrodes

Mesoporous silica materials (MSMs) are widely used materials in many applications due to their diverse pore structures. However, the electrical conductivity of MSMs is poor which limits their use in electrochemical applications. In this study, widely used MSMs of different structural properties such as MCM-41, MCM-48, SBA-15, and SBA-16 were synthesized and reinforced with graphene oxide (GO) to obtain conductive composite supports for enzyme immobilization. MSMs were first synthesized using a hydrothermal method and characterized by Fourier-transform infrared spectroscopy, X-ray crystallography, scanning electron microscopy/energy dispersive X-ray, and MAPPING techniques. Aqueous dispersion of GO:MSM composites were prepared with as-synthesized materials and coated on screen-printed electrodes (SPE). The best composites were chosen based on their electroanalytical performance. Glucose oxidase (GOx) was then immobilized on modified SPEs using a simple drop-casting method to produce enzymatic electrodes. The electroanalytical performance of the enzymatic electrodes was investigated using different glucose concentrations to demonstrate biocatalytic activity. Stability tests were performed using intraday and interday measurements which revealed that SPE/GO:MCM-41/GOx electrode showed a more stable performance (3-folds) than SPE/GO/GOx electrode. This study presents an investigation of MSM mixed with GO in enzymatic electrochemical systems providing insight into the use of such materials to preserve enzyme activity.Graphical

The Thermophysical and Physicochemical Properties of the Aqueous Dispersion of Graphene Oxide Dual-Beam Thermal Lens Spectrometry.

Modern heat-conducting materials require special attention to analyze their thermophysical properties. Compared to classical methods, thermal lens spectrometry (TLS) has advantages due to its high sensitivity to physical and chemical composition. To avoid a systematic error in the analysis of complex systems, it is necessary to realize the limits of the applicability of the method. This study considers the features of thermal-diffusivity measurements by TLS in the stationary state for dispersed systems with absorbances up to 0.05. The limits of applicability of the method in analyzing heterogeneous systems are shown, and a mathematical apparatus is proposed for indicating a systematic error in finding thermal diffusivity that does not exceed 1%. Graphene oxide (GO), which has attractive physicochemical properties, was used as the object of analysis. GO belongs to 2D objects, the study of which requires highly sensitive methods and special attention when discussing the results. The thermophysical properties of aqueous dispersions of graphene oxide in a wide range of concentrations (up to 2 g/L) and lateral sizes (up to 4 µm) were studied by TLS. It has been found that with increasing nanophase concentration, the thermal diffusivity of graphene oxide dispersions passes through a minimum, which can be used in solving thermal insulation problems. It has been established that prolonged laser irradiation of the dispersion leads to a change in thermal diffusivity, which indicates the photochemical reduction of graphene oxide.

Graphene oxide/ZnO nanocomposites applied in photocatalysis of dyes: Tailoring aqueous stability of quantum dots

Nanocomposites between ZnO Quantum Dots (QDs) and Graphene Oxide (GO) were synthesized by sol-gel method in isopropanol. The proportion of GO aqueous dispersion was evaluated and ZnO QDs were also prepared with addition of water, for comparison. Indeed, the GO or water addition had a huge impact in the ZnO QDs size and photoluminescence, once the greater the GO/water addition, the greater the ZnO QDs size (from 4.5 ± 0.1–23.8 ± 0.4 nm) and the 50 µL of GO (or water) added to the synthesis led to a higher intensity emission. The photocatalytic activity of the ZnO-based materials was evaluated for methylene blue (MB) and astrazon blue (AB) degradation in isopropanol and water using two different sources of light irradiation (fluorescence and Hg vapor lamps). Once again, the GO/water addition affected their photocatalytic behavior and stability in aqueous medium. The ZnO QDs/GO had an impressive photocatalytic performance in both sources of light irradiation in isopropanol and aqueous medium (99% and 93% of degradation after 30 min of irradiation with Hg vapor lamp, respectively). In addition, the photocatalytic activity of this nanocomposite was stable when submitted up to 5 photodegradation cycles and to higher MB concentrations, besides being successfully reused in aqueous medium.

Droplet-Dispensed Graphene Oxide as Capacitive Sensing Elements for Flexible Pressure-Pulse Sensing Array

We report a novel flexible capacitive pressure-pulse sensor array developed by integrating droplet-dispensed graphene oxide (GO) sensing elements and flexible electronics. The utilization of droplet-dispensing technology enables the fabrication multiple capacitive sensing elements rapidly while producing sensitive pressure sensors with excellent repeatability. The dispensed droplet volume (GO aqueous dispersion) ranged from around 33.5 to 65.4 pL with diameter ranging from 40 to 50 μm. The size (i.e., footprint and dielectric material thickness) of a sensing element can be controlled by the total GO dispersed per droplet. The fabrication process and preliminary characterization of these GO capacitive sensors are discussed in this paper. Thus far, we have shown that these sensors have a sensitivity of ∼10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> kPa <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> , with the relative permittivity of the dispensed GO being ∼6 (measured at a frequency of 600 kHz). We have also demonstrated that the printed sensing elements can be used for human wrist pulse sensing. Hence the technology described in this paper could potentially be used in wearable electronics for healthcare applications.

Insights into the Stability of Graphene Oxide Aqueous Dispersions.

Understanding graphene oxide's stability (or lack thereof) in liquid solvents is critical for fine-tuning the material's characteristics and its potential involvement in future applications. In this work, through the use of structural and surface investigations, the alteration of the structural and edge-surface properties of 2D graphene oxide nanosheets was monitored over a period of eight weeks by involving DLS, zeta potential, XRD, XPS, Raman and FT-IR spectroscopy techniques. The samples were synthesized as an aqueous suspension by an original modified Marcano-Tour method centred on the sono-chemical exfoliation of graphite. Based on the acquired experimental results and the available literature, a phenomenological explanation of the two underlying mechanisms responsible for the meta-stability of graphene oxide aqueous dispersions is proposed. It is based on the cleavage of the carbon bonds in the first 3-4 weeks, while the bonding of oxygen functional groups on the carbon lattice occurs, and the transformation of epoxide and hydroxyl groups into adsorbed water molecules in a process driven by the availability of hydrogen in graphene oxide nanosheets.

Composite GO/Ceramic Membranes Prepared via Chemical Attachment: Characterisation and Gas Permeance Properties.

Graphene oxide (GO) oligo-layered laminates were self-assembled on porous ceramic substrates via their simple dip-coating into aqueous GO dispersions. To augment the stability of the developed composite GO/ceramic membranes and control the morphology and stacking quality of the formed laminate, short-((3-glycidoxypropyl)trimethoxy silane-GLYMO, (3-aminopropyl)triethoxy silane-APTES), and long-chain (polydopamine-PDA) molecules were involved and examined as interfacial linkers. A comparative study was performed regarding the linker's capacity to enhance the interfacial adhesion between the ceramic surface and the GO deposit and affect the orientation and assemblage characteristics of the adjacent GO nanosheets that composed the formed oligo-layered laminates. Subsequently, by post-filtrating a GO/H2O suspension through the oligo-layered laminate membranes, the respective multi-layered ones have been developed, whereas ethylenediamine (EDA) was used in the suspension as an efficient molecular linker that strongly bonds and interlocks the GO nanosheets. The definition of the best linker and approach was conducted on macroporous α-alumina disks, due to the use of inexpensive raw materials and the ability to fabricate them in the lab with high reproducibility. To validate the concept at a larger scale, while investigating the effect of the porous substrate as regards its micrometer-scale roughness and surface chemistry, specific chemical modifications that yielded membranes with the best gas permeability/selectivity performance were replicated on a commercial single-channel monolith with a ZrO2 microfiltration layer. XRD, Raman, ATR, FESEM, and XPS analyses were conducted to study the structural, physicochemical, surface, and morphological properties of the GO/ceramic composite membranes, whereas permeance results of several gases at various temperatures and trans-membrane pressures were interpreted to shed light on the pore structural features. Concerning the short-chain linkers, the obtained results ascertain that GLYMO causes denser and more uniform assembly of GO nanosheets within the oligo-layered laminate. PDA had the same beneficial effect, as it is a macromolecule. Overall, this study shows that the development of gas-separating membranes, by just dipping the linker-modified substrate into the GO suspension, is not straightforward. The application of post-filtration contributed significantly to this target and the quality of the superficially deposited, thick GO laminate depended on this of the chemically attached oligo-layered one.

Facile formation of porous, multilayer reduced graphene oxide electrodes using electrophoretic deposition and flash sintering

A reduced graphene oxide (rGO) film is mechanically fragile; therefore, transferring it to another substrate without damage is crucial. Hence, a technique that facilitates the formation of an integrated rGO film that holds adhesion with the substrate is desired. Moreover, a rGO film on metal is promising as an electrode for energy storage devices. This work presents the formation of rGO film on copper using electrophoretic deposition (EPD) and flash sintering. Briefly, a stable aqueous dispersion of graphene oxide (GO) layers was used to form a uniform GO film on copper at a fixed deposition voltage and time duration. To reduce the GO film without detaching it from copper, pulse energy (1–10 J cm−2) was varied for a fixed exposure time (10 ms) and a single micropulse. At pulse energy of 6 J cm−2, the structural studies indicated turbostratic stacking (decreased interlayer spacing) and restored crystallinity (decreased peak intensity ratio of D and G bands). The morphology showed voids between stacked rGO layers and high roughness in the film. The reduction resulted in mesoporous and high surface area (373 m2 g−1) multilayer rGO film. Due to restored electrical conductivity, the rGO film showed a specific capacitance of 475.8 F g−1 at a scan rate of 2 mV s−1. An increase in contact angle from ∼66° to ∼81° also validated the reduction. The combination of EPD and flash sintering offers rapid and eco-friendly formation of binder-free rGO film on copper, promising as an electrode for supercapacitors.

(Invited) Controlling Void Space in Crumpled Graphene for High Stability Silicon Anodes

Silicon anodes are thought to soon replace graphite in next-generation Li-ion batteries due to silicon’s high capacity (3590 mAh/g for the Li15Si4 alloy at room temperature), availability and natural abundance. However, lithiation of silicon causes a large volume expansion (~300%) which can cause pulverization of the primary silicon particles, cracking and delamination of the bulk electrode and the formation of an unstable solid-electrolyte interface which must rebuild upon each cycle. Some combination of these effects leads to rapid anode failure via electrical isolation of active material and/or electrolyte depletion. To mitigate these challenges, clusters of silicon nanoparticles can be wrapped with flexible 2D-materials like graphene which can potentially act as a dimensionally and electrochemically stable, permeable barrier layers. This can be achieved in a scalable way via spray drying of aqueous dispersions of graphene oxide and silicon. In this talk, I will describe recent work from our group which aims to introduce a controlled amount of void space within the graphene protected silicon structures with the aim of engineering zero-strain silicon/carbon anode particles. In the absence of void space control, capillary forces acting during the spray drying process tightly wrap graphene around silicon clusters leaving little room for volume expansion. In one case, void space is introduced via incorporation of sacrificial polystyrene nanoparticles within the core by co-spray drying silicon, polystyrene and graphene oxide. In a second case, we do not use a sacrificial material but, instead, incorporate a responsive, cross-linked hydrogel within the core which can be expanded upon hydration to increase the volume of the graphene shell. When dehydrated, the gel shrinks to generate the required void space and acts as a Li-ion conducting, elastic binder within the core. In both cases, I will describe the systematic evolution of the crumpled graphene microstructure and its impact on anode performance in both half-cells and full Li-ion batteries.

Enhancing Humidity Performance: Effect of Electrode Material on Electrochemical Reduced Graphene Oxide (ERGO) Humidity Sensor

Reduced graphene oxide (rGO) possesses remnant oxygen functional groups, hydrophilic characteristics, and a large surface area, making it a one-of-a-kind material with unique qualities that are attributed to the reduction of graphene oxide (GO)process.There are numerous ways that can be utilized in the reduction process; however, it has not yet been completely examined which method is the most efficient in terms of reducing the oxygen-containing functional group from the GO. This is owing to the fact that a successful reduction technique has the potential to broaden the scope of rGO's applicability across a wide range of industrial sectors. This study entails an investigationthe effect of humidity performance on different metal materials such as Pt, Au, Ag, and Cu with fixedfingers spacing of 5um on the reduced graphene oxide (rGO) by electrochemical deposition (ECD) from GO aqueous dispersion. A combination of experimental measurements using humidity chamber, Raman spectroscopy, Electrochemical Impedance Spectroscopy, andScanning Electron Microscopyhave revealed the performance of rGO as the humidity sensor.According to the findings, a good humidity performance was displayed in rGO/Pt, as demonstrated by higher sensitivity and greater response towards humidity which is found to be around 10 times higher response than GO in Hummer’s method, as reported in the literature.These characteristics are both facilitated by the higher ionic conductivity of the material.

Corrosion behavior of Q235 steel in graphene oxide aqueous dispersion

Conductive metals can speed up the self-assembly and reduction process of graphene oxide (GO) in liquid media, but there is little available information about the effect of this process on the corrosion rate of metal substrates. The corrosion performance of Q235 steel in GO aqueous solution was studied by comparing the influence of different GO concentrations and immersion times on the corrosion rate of steel. The result found that a GO layer will be formed on the surface of steel when immersing in the GO aqueous dispersion, which has a shielding effect on the diffusion process of ions and electrons, and effectively inhibits the steel corrosion. However, this inhibition effect of GO layer will disappear with the self-reduction of GO, which increasing the defect density and conductivity of the sedimentary layer on steel and thus the corrosion rate of steel will increase with the immersion time and the GO concentration in solution.

Graphene paper with electrodeposited NiCo2S4 nanoparticles as a novel flexible sensor for simultaneous detection of folic acid and ascorbic acid

We studied the production and electrochemical performance of NiCo2S4 electrodeposited reduced graphene oxide (rGO) paper for use as a freestanding flexible electrode for the simultaneous determination of folic acid (FA) and ascorbic acid (AA). Production of rGO paper was achieved through vacuum filtration of the aqueous dispersion of graphene oxide, followed by chemical reduction in hydrogen iodide solution. NiCo2S4/rGO paper material was fabricated with a simple approach using electrodeposition of hydrothermal synthesized NiCo2S4 nanoparticles directly on rGO paper. The physicochemical properties of as-prepared flexible NiCo2S4/rGO paper were characterized by means of field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and X-ray powder diffraction patterns. This freestanding paper electrode demonstrated high sensitivity, a wide linear range, and a low detection limit towards the simultaneous detection of FA and AA. NiCo2S4/rGO paper sensor, possessing easy preparation, low cost, and high flexibility, was tested in real samples with promising recoveries. This study exhibited that the approach of the electrodeposition of bimetallic sulfides on freestanding graphene paper substrates has great potential to develop high-performance flexible electrochemical sensors.

Facile synthesis of crumpled-paper like CoWO4-CoMn2O4/N-doped Graphene hybrid nanocomposites for high performance all-solid-state asymmetric supercapacitors

In this work, for the first time, the synergetic effect of CoWO4-CoMn2O4/N-doped graphene (CCNG) hybrid nanocomposites as active electrode materials with high conductivity and fast transmission of electrons/ions are investigated for high performance supercapacitor. The crumpled- paper like CCNG nanostructure is synthesized by an efficient and simple hydrothermal route via adding a certain amount of CoWO4-CoMn2O4 and a defined amount of urea as a reducing agent into the aqueous dispersion of graphene oxide (GO). The obtained CCNG hybrid nanocomposites represent excellent electrochemical efficiencies with a high specific capacitance of 4133.3 F g−1 at a current density of 2 A g−1. Besides, the proposed electrode exhibits the excellent specific energy density of 116.25 WhKg−1, specific power density of 2250 Wkg−1 and superior cycling stability by retaining 96.96% of their original capacitance after 5000 cycles. Furthermore, using CCNG as positive electrode and activated carbon (AC) as negative electrode is designed for an asymmetric supercapacitor (ASC). The assembled ASC device provides a superior specific capacitance of 281.58 mF g−1 at the applied current density of 1 mA g−1 and delivers the energy density of 56.31 mWh kg−1 at the power density of 600 mWkg−1.

Pristine Graphene Inks for 3D Printed Supercapacitors with High Capacitance

The 3D printing of 2D materials, such as graphene, transition metal dichalcogenides and M-Xenes, offers a cost-efficient and sustainable route for the fabrication of integrated electronics and advanced energy devices with arbitrarily complex architectures. In particular, the assembly of 2D materials into rationally designed three-dimensional electrodes can enhance the charge transport kinetic and increase the electrochemically-active surface area, resulting in superior electrochemical performance.Graphene has long been considered a promising active material for carbon-based supercapacitors, owing to its high intrinsic capacitance, superior mechanical strength and flexibility, and excellent electrical conductivity. However, because of the limited processability of pristine graphene in water, the 3D printing of graphene supercapacitors has either relied on inks containing high boiling solvents and electrochemically inactive binders, or on aqueous dispersions of graphene oxide, which must be thermally reduced at elevated temperatures (>1000°C) after printing.In this work we demonstrate a new class of 3D printed supercapacitors obtained from aqueous inks of pristine graphene, without the need of functional additives or high-temperature processing to achieve high capacitance. With an electrical conductivity of ~1370 S m-1 and rationally designed architectures, the symmetric supercapacitors can achieve an exceptional areal capacitance of 1.57 F cm-2 at 2 mA cm-2 which is retained over 72% after repeated voltage holding test. The areal power density (0.968 mW cm-2) and areal energy density (51.2 μWh cm-2) outperform many carbon-based supercapacitors previously reported, indicating the feasibility of this approach for the fabrication of efficient energy storage devices.

Investigations of structural and dynamical mechanisms of ice formation regulated by graphene oxide nanosheets.

Recent research indicates that graphene oxide (GO) nanosheets can be used to regulate ice formation by controlling critical ice nucleus growth in water at supercooling temperatures. In addition, the study of ice formation mechanisms regulated by GO nanosheets, a good model system for antifreeze proteins (AFPs), will shed light on how AFPs regulate ice formation in nature. In this work, time-resolved small-angle x-ray scattering (TR-SAXS) and quasi-elastic neutron scattering (QENS) experiments were carried out to investigate the structural and dynamical mechanisms of ice formation regulated by GO nanosheets. Strikingly, a transient intermediate state was observed in TR-SAXS experiments that only exists in the aqueous dispersions with a larger GO size (11 nm). This serves as evidence that the size of GO is critical for regulating ice formation. Elastic neutron scattering results indicate that ice is formed in all samples and thermal hysteresis occurs in GO aqueous dispersions in both H2O and D2O. The structural and dynamics information about water molecules in GO, extracted from QENS, reveals different dynamical behaviors of water molecules in GO aqueous dispersions when approaching the ice formation temperature.

Nitrogen and Sulfur Co-Doped Graphene as Efficient Electrode Material for L-Cysteine Detection

Two graphene samples co-doped with nitrogen and sulfur were synthesized by the hydrothermal method using thiourea as doping and reducing agent for graphene oxide (GO). An appropriate amount of thiourea was added to the aqueous dispersion of GO, previously sonicated for 30 min. The mixture was poured into an autoclave and placed in the oven for 3 h, at 120 and 200 °C. The samples were denoted NSGr-120 and NSGr-200, respectively, in agreement with the reaction temperatures. They were next morphologically and structurally characterized by advanced techniques, such as SEM/TEM, XPS, XRD, and FTIR. According to XPS analysis, the NSGr-120 sample has higher amounts of heteroatoms in comparison with NSGr-200, indicating that the reaction temperature is a crucial factor that affects the doping degree. In order to reveal the influence of the doping degree on the electrochemical performances of graphene-modified electrodes, they were tested in solutions containing L-cysteine molecules. The electrode with the best electrocatalytic performances, GC/NSGr-120, was tested to detect L-cysteine in a pharmaceutical drug, proving its applicability in real sample analysis.

From Waste to Functional Materials: A Multifunctional Electromagnetic Interference Shielding Composite from Waste Rock Wool

Electromagnetic interference (EMI) shielding materials are effective in eliminating unwanted electromagnetic interference and reduce the potential harm to human health. Among them, the EMI shielding materials fabricated from wastes but with multiple functions are particularly attractive. However, it is always a great challenge to integrate multiple functions into one EMI shielding material, especially when using the wastes as raw materials. Here, a multifunctional EMI shielding composite was fabricated from waste rock wool, which is one of the fast-growing solid wastes in the world. The waste rock wool was converted into a valuable EMI material by simply dip-coating the rock wool into a graphene oxide aqueous dispersion and a following chemical reduction by hydrazine hydrate. The obtained rock wool/reduced graphene oxide (RW-rGO) composites showed excellent EMI shielding performance (>25 dB) and good hydrophobicity (water contact angle >130°). Moreover, the RW-rGO composites exhibit good thermal insulation and fire-retardant ability. We believe that the strategy for fabricating RW-rGO composites not only provides an effective way to solve the problem of waste rock wool pollution but also can promote the large-scale manufacturing of multifunctional EMI shielding materials.

Cost effective biosynthetic approach for graphene exhibiting superior sonochemical dye removal capacity

Green synthesis of graphene using leaf extracts as sustainable reducing and capping agents is a thrust area of research owing to its simplicity, eco-friendly nature and the ease of access to graphene. Moringa (Moringa oleifera Lam) plant is widely cultivated in India owing to its important medicinal and nutritional values. Inspired by these reports, herein we report a simple, green and economic synthesis of graphene, Moringa leaf extract employed reduced graphene oxide (MRGO) with excellent dye removal efficiencies. The MRGO is prepared by refluxing a mixture of aqueous dispersion of graphene oxide and Moringa leaf extract for 10 h. Further, we elucidated the role of synthesized MRGO in the removal of methylene blue (MB) and rhodamine B (RB) dyes through the sonochemical method. This as-synthesized material exhibited excellent dye removal efficiencies of about 93% and 87% against MB and RB dyes, respectively. Graphene with huge surface area expedited the better adsorption of dye molecules, thus, facilitated the better removal of the latter. Therefore, the superior dye removal efficiencies of MRGO were attributed to its adsorption capacity. This cost-effective synthetic approach of MRGO nanomaterial has a great potential for the innovative applications in water purification technology and find its place in further industrialization.

The synthesis of Ag3PO4 under graphene oxide and hydroxyapatite aqueous dispersion for enhanced photocatalytic activity

The development of Ag3PO4 photocatalyst for organic pollutant degradation is very challenging due to excellent activity under visible light exposure. The research aims to synthesize Ag3PO4 under graphene oxide (GO) and hydroxyapatite (HA) as a phosphate ion source for Rhodamin B degradation. The Ag3PO4/GO was prepared using the precipitation method with the starting material of graphene oxide aqueous dispersion, AgNO3, and hydroxyapatite suspension. The structure, absorption, morphology, and element composition of photocatalysts were studied using XRD, DRS, SEM, and EDX. Photocatalytic abilities of the samples were tested using RhB oxidation under blue light exposure. The results exhibited that GO improves the crystallinity andvisibleabsorption spectrum of Ag3PO4. Incorporating GO on Ag3PO4 decreases the ratio of O/Ag and O/P leading to a defect formation. The reaction mechanism on the surface of the photocatalyst was mainly run by holes and superoxide radical ions. The modification of Ag3PO4 using hydroxyapatite and GO improved photocatalytic activity.