Synthesis and Applications of Graphene Oxide

Green and Sustainable Ultrasound-Assisted Anodic Electrochemical Preparation of Graphene Oxide Dispersions and Their Antioxidant Properties

A fast method for preparing aqueous graphene oxide (GO) dispersions by electrochemical oxidation of a graphite anode without preliminary intercalation with oxidizing agents is proposed. Ultrasonic probing was used in the modulation mode of ultrasonic waves (work/rest) for more efficient graphite oxidation-exfoliation. It is shown that the 4/2 s mode of ultrasonic modulation is the most effective due to the probe material's low corrosion while maintaining the optimum synthesis temperature not exceeding 30-35 °C and achieving the best characteristics of the resulting product. Three cases of anodic oxidation of graphite to obtain graphene oxide were considered: (1) a combined cathode-anode compartment, (2) a split cathode-anode salt-bridged compartment, and (3) separated anode compartment with a 3.5 kDa dialysis membrane. It was determined that the approach to synthesis with a divided cathode-anode compartment makes it possible to obtain GO sheets with fewer defects compared to chemical methods or methods with a combined cathode-anode compartment and makes it possible to control the oxidation degree of the material (C:O ratio) by varying the current density. The prepared samples showed good stability for more than six months. The spectral and morphological characteristics were studied. Using chemiluminometry in the luminol/Co(II)/H₂O₂ system, the antioxidant properties concerning three key reactive oxygen species (H₂O₂, superoxide anion radical, and hydroxyl radical) were demonstrated. It was also shown that the prepared GO dispersions do not induce lipid and phospholipid peroxidation.

Fluorescence Properties of ZnOQDs-GO-g-C3N4 Nanocomposites

In this paper, the fluorescence properties of ZnOQD-GO-g-C₃N₄ composite materials (ZCGQDs) were studied. Firstly, the addition of a silane coupling agent (APTES) in the synthesis process was explored, and it was found that the addition of 0.04 g·mL^-1 APTES had the largest relative fluorescence intensity and the highest quenching efficiency. The selectivity of ZCGQDs for metal ions was also investigated, and it was found that ZCGQDs showed good selectivity for Cu²⁺. ZCGQDs were optimally mixed with Cu²⁺ for 15 min. ZCGQDs also had good anti-interference capability toward Cu²⁺. There was a linear relationship between the concentration of Cu²⁺ and the fluorescence intensity of ZCGQDs in the range of 1~100 µM. The regression equation was found to be F₀/F = 0.9687 + 0.12343C. The detection limit of Cu²⁺ was about 1.74 μM. The quenching mechanism was also analyzed.

Advances in two-dimensional engineered nanomaterials applications for the agro- and food-industries

Two-dimensional nanomaterials, such as graphene, transition metal dichalcogenides, MXenes, and other layered compounds, are the subject of intense theoretical and experimental research for applications in a wide range of advanced technological solutions, given their outstanding physical, chemical, and mechanical properties. In the context of food science and technology, their contributions are starting to appear, based on the advantages that two-dimensional nanostructures offer to agricultural- and food-related key topics, such as sustainable water use, nano-agrochemicals, novel nanosensing devices, and smart packaging technologies. These application categories facilitate the grasping of the current and potential uses of such advanced nanomaterials in the field, backed by their advantageous physical, chemical, and structural properties. Developments for water cleaning and reuse, efficient nanofertilizers and pesticides, ultrasensitive sensors for food contamination, and intelligent nanoelectronic disposable food packages are among the most promising application examples reviewed here and demonstrate the tremendous impact that further developments would have in the area as the fundamental and applied research of two-dimensional nanostructures continues. We expect this work will contribute to a better understanding of the promising characteristics of two-dimensional nanomaterials that could be used for the design of novel and feasible solutions in the agriculture and food areas. © 2023 Society of Chemical Industry.

Graphene-based materials for effective adsorption of organic and inorganic pollutants: A critical and comprehensive review

Water scarcity has been felt in many countries and will become a critical issue in the coming years. The release of toxic organic and inorganic contaminants from different anthropogenic activities, like mining, agriculture, industries, and domestic households, enters the natural waterbody and pollutes them. Keeping this in view in combating the environmental crises, removing pollutants from wastewater is one of the ongoing environmental challenges. Adsorption technology is an economical, fast, and efficient physicochemical method for removing both organic and inorganic pollutants, even at low concentrations. In the last decade, graphene and its composite materials have become the center of attraction for numerous applications, including wastewater treatment, due to the large surface area, highly active surface, and exclusive physicochemical properties, which make them potential adsorbents with unique physicochemical properties, like low density, chemical strength, structural variability, and the possibility of large-scale fabrications. This review article provides a thorough summary/critical appraisal of the published literature on graphene-, GO-, and rGO-based adsorbents for the removal of organic and inorganic pollutants from wastewater. The synthesis methods, experimental parameters, adsorption behaviors, isotherms, kinetics, thermodynamics, mechanisms, and the performance of the regeneration-desorption processes of these substances are scrutinized. Finally, the research challenges, limitations, and future research studies are also discussed. Certainly, this review article will benefit the research community by getting substantial information on suitable techniques for synthesizing such adsorbents and utilizing them in water treatment and designing water treatment systems.

Noble Metals Functionalized on Graphene Oxide Obtained by Different Methods-New Catalytic Materials

In recent years, research has focused on developing materials exhibiting outstanding mechanical, electrical, thermal, catalytic, magnetic and optical properties such as graphene/polymer, graphene/metal nanoparticles and graphene/ceramic nanocomposites. Two-dimensional sp² hybridized graphene has become a material of choice in research due to the excellent properties it displays electrically, thermally, optically and mechanically. Noble nanomaterials also present special physical and chemical properties and, therefore, they provide model building blocks in modifying nanoscale structures for various applications, ranging from nanomedicine to catalysis and optics. The introduction of noble metal nanoparticles (NPs) (Au, Ag and Pd) into chemically derived graphene is important in opening new avenues for both materials in different fields where they can provide hybrid materials with exceptional performance due to the synergistical result of the specific properties of each of the materials. This review presents the different synthetic procedures for preparing Pt, Ag, Pd and Au NP/graphene oxide (GO) and reduced graphene oxide (rGO) composites.

Recyclable GO-Arginine Hybrids for CO2 Fixation into Cyclic Carbonates

New covalently modified GO-guanidine materials have been realized in a gram-scale synthesis and purified by an innovative microfiltration. The use of these composites in the fixation of CO₂ into cyclic carbonates is demonstrated. Mild operating conditions, high yields (up to 85 %), wide scope (15 examples) and recoverability/reusability (up to 5 cycles) of the material account for the efficiency of the protocol. Dedicated control experiments shed light on the activation modes exerted by GO-l-arginine during the ring-opening/closing synthetic sequence.

Age- and Lifespan-Dependent Differences in GO Caused DNA Damage in Acheta domesticus

The rising applicability of graphene oxide (GO) should be preceded by detailed tests confirming its safety and lack of toxicity. Sensitivity to GO of immature, or with different survival strategy, individuals has not been studied so far. Therefore, in the present research, we focused on the GO genotoxic effects, examining selected parameters of DNA damage (total DNA damage, double-strand breaks-DSB, 8-hydroxy-2'-deoxyguanosine-8-OHdG, abasic site-AP sites), DNA damage response parameters, and global methylation in the model organism Acheta domesticus. Special attention was paid to various life stages and lifespans, using wild (H), and selected for longevity (D) strains. DNA damage was significantly affected by stage and/or strain and GO exposure. Larvae and young imago were generally more sensitive than adults, revealing more severe DNA damage. Especially in the earlier life stages, the D strain reacted more intensely/inversely than the H strain. In contrast, DNA damage response parameters were not significantly related to stage and/or strain and GO exposure. Stage-dependent DNA damage, especially DSB and 8-OHdG, with the simultaneous lack or subtle activation of DNA damage response parameters, may result from the general life strategy of insects. Predominantly fast-living and fast-breeding organisms can minimize energy-demanding repair mechanisms.

Influence of Laboratory Synthesized Graphene Oxide on the Morphology and Properties of Cement Mortar

The introduction of Graphene Oxide (GO), a nanomaterial, has shown considerable promise in improving the mechanical properties of cement composites. However, the reasons for this improvement are not yet fully understood and demand further research. This study aims to understand the effect of laboratory-produced GO, using Tour's method, on the mechanical properties and morphology of cement mortar containing GO. The GO was characterized using Fourier-transform infrared spectroscopy, X-ray Photoelectron Spectroscopy (XRD), X-ray powder diffraction, and Raman spectroscopy alongside Scanning electron microscopy (SEM). This study adopted a cement mortar with GO percentages of 0.02, 0.025, 0.03, 0.035, and 0.04 with respect to the weight of the cement. The presence of GO in cement mortar increased the density and decreased the consistency and setting times. At the optimum of 0.03% GO viscous suspension, the mechanical properties such as the 28-day compressive strength, splitting tensile strength, and flexural strength were enhanced by 41%, 83%, and 43%, respectively. In addition, Brunauer-Emmett-Teller analysis indicates an increase in surface area and volume of micropores of GO cement mortar, resulting in a decreased volume of mesopores. The improvement in properties was due to increased nucleation sites, calcium silicate hydrate (CSH) density, and a decreased volume of mesopores.

Biogenic synthesis of reduced graphene oxide from Ziziphus spina-christi (Christ's thorn jujube) extracts for catalytic, antimicrobial, and antioxidant potentialities

In the current work, various concentrations of the aqueous extract of Ziziphus spina-christi were employed for the phytoreduction of graphene oxide (GO). The green synthesized reduced graphene oxide (rGO) was characterized through UV-Vis spectrometry, Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy, and energy-dispersive X-ray spectroscopy (SEM-EDX). Gas chromatography-mass spectrometry (GC-MS) denoted the presence of numerous phytoconstituents including ketones, terpenoids, fatty acids, esters, and flavonoids, which acted as reducing and capping agents. The obtained results indicated the increase in rGO yield and shape with increasing the extract concentration. The optimized rGO was instantaneously ~100% removed methylene blue (MB) from the water at 5 mg L-1. However, the removal efficiency was slightly declined to reach 73.55 and 65.1% at 10 and 15 mg L-1, respectively. A powerful antibacterial activity for rGO particularly against gram-negative bacteria with a high concentration of 2 × 108 CFU mL-1 was confirmed. Furthermore, rGO demonstrated promising and comparable antioxidant efficiency with vitamin C against DPPH free radical scavenging. While vitamin C recorded 13.45 and 48.4%, the optimized rGO attained 13.30 and 45.20% at 12 and 50 μg mL-1, respectively.

High-Throughput Preparation of Uncontaminated Graphene-Oxide Aqueous Dispersions with Antioxidant Properties by Semi-Automated Diffusion Dialysis

A semi-automated diffusion-dialysis purification procedure is proposed for the preparation of uncontaminated graphene oxide (GO) aqueous dispersions. The purification process is integrated with analytical-signal processing to control the purification degree online by several channels: oxidation-reduction potential, conductivity, and absorbance. This approach reduces the amounts of reagents for chemical treatment during dialysis. The total transition metal (Mn and Ti) content was reduced to a sub-ppb level (assessed by slurry nebulization in inductively coupled plasma optical atomic emission spectroscopy). Purified aqueous GO samples possess good stability for about a year with a zeta-potential of ca. -40 mV and a lateral size of ca. sub-µm. Purified GO samples showed increased antioxidant properties (up to five times compared to initial samples according to chemiluminometry by superoxide-radical (O₂^-) generated in situ from xanthine and xanthine oxidase with the lucigenin probe) and significantly decreased peroxidase-like activity (assessed by the H₂O₂-L-012 system).

Graphene Synthesis Techniques and Environmental Applications

Graphene is fundamentally a two-dimensional material with extraordinary optical, thermal, mechanical, and electrical characteristics. It has a versatile surface chemistry and large surface area. It is a carbon nanomaterial, which comprises sp² hybridized carbon atoms placed in a hexagonal lattice with one-atom thickness, giving it a two-dimensional structure. A large number of synthesis techniques including epitaxial growth, liquid phase exfoliation, electrochemical exfoliation, mechanical exfoliation, and chemical vapor deposition are used for the synthesis of graphene. Graphene prepared using different techniques can have a number of benefits and deficiencies depending on its application. This study provides a summary of graphene preparation techniques and critically assesses the use of graphene, its derivates, and composites in environmental applications. These applications include the use of graphene as membrane material for the detoxication and purification of water, active material for gas sensing, heavy metal ions detection, and CO₂ conversion. Furthermore, a trend analysis of both synthesis techniques and environmental applications of graphene has been performed by extracting and analyzing Scopus data from the past ten years. Finally, conclusions and outlook are provided to address the residual challenges related to the synthesis of the material and its use for environmental applications.

Reduced Graphene Oxide–Metal Oxide Nanocomposites (ZrO2 and Y2O3): Fabrication and Characterization for the Photocatalytic Degradation of Picric Acid

Herein, reduced graphene-oxide-supported ZrO2 and Y2O3 (rGO-ZrO2 and rGO-Y2O3) nanocomposites were synthesized by hydrothermal method and used as the catalysts for photodegradation of picric acid. The structural and morphological properties of the synthesized samples were characterized by using an X-ray diffractometer (XRD), scanning electron microscope (SEM) with energy dispersive absorption X-ray spectroscopy (EDAX), UV-Vis spectrophotometer, Raman spectrophotometer and Fourier transformation infrared spectrophotometer (FT-IR) techniques. In this work, the wide band gap of the ZrO2 and Y2O3 was successfully reduced by addition of the reduced graphene oxide (rGO) to absorb visible light for photocatalytic application. The performance of as synthesized rGO-ZrO2 and rGO-Y2O3 nanocomposites in the photocatalytic degradation of picric acid were evaluated under UV light irradiation. The photodegradation study using picric acid was analyzed with different energy light sources UV (254, 365 and 395 nm), visible light and sunlight at different pH conditions (pH = 3, 7 and 10). The photocatalytic activity of rGO-ZrO2 and rGO-Y2O3 nanocomposites showed excellent photocatalytic activity under optimum identical conditions with mild variations in pH 3. Compared to rGO-Y2O3, the rGO-ZrO2 nanocomposite showed a better action, with a degradation percentage rate of 100, 99.3, 99.9, 100 and 100% for light conditions of UV-252, 365, 395, visible and sunlight, respectively. The excellent degradation efficiency is attributed to factors such as oxygen-deficient metal oxide phase, high surface area and creation of a greater number of hydroxyl groups.

The Anticancer Efficacy of Thiourea-Mediated Reduced Graphene Oxide Nanosheets against Human Colon Cancer Cells (HT-29)

The current research focuses on the fabrication of water-soluble, reduced graphene oxide (rGO) employing thiourea (T) using a simple cost-effective method, and subsequently examining its anticancer characteristics. The cytotoxicity caused by graphene oxide (GO) and T-rGO is investigated in detail. Biological results reveal a concentration-dependent toxicity of GO and T-rGO in human colon cancer cells HT-29. A decrease in cell viability alongside DNA fragmentation is observed. Flow cytometry analysis confirms the cytotoxic effects. The novelty in this work is the use of raw graphite powder, and oxidants such as KMNO₄, NaNO₃, and 98 percent H₂SO₄ to produce graphene oxide by a modified Hummers method. This study demonstrates a simple and affordable procedure for utilising thiourea to fabricate a water-soluble reduced graphene oxide, which will be useful in a variety of biomedical applications.

Performance Improvement with an Ultrathin p-Type Interfacial Layer in n-Type Vertical Organic Field-Effect Transistors Based on Reduced Graphene Oxide Electrode

Vertical organic field-effect transistors (VOFETs) with a large current on/off ratio and easy fabrication process are highly desirable for future organic electronics. In this paper, we proposed an ultrathin p-type copper (II) phthalocyanine (CuPc) interfacial layer in reduced graphene oxide (rGO)-based VOFETs. The CuPc interfacial layer was sandwiched between the rGO electrode and the N,N'-dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C8) organic layer. The introduced CuPc interfacial layer not only decreased the off-current density of the device but also slightly enhanced the on-current density. The threshold voltage of the device was also effectively improved and stabilized at around 0 V. The obtained device exhibited a current on/off ratio exceeding 106, which is the largest value reported for rGO-based VOFETs. The vertical electron mobility of the PTCDI-C8 layer estimated by the space-charge-limited current technique was 1.14 × 10-3 cm2/(V s). However, it was not the main limiting factor for the current density in this device. We totally fabricated 48 devices, and more than 75% could work. Besides, the device was stable with little performance degradation after 1 month. The use of low-cost, solution-processable rGO as work-function-tunable electrode and the application of an ultrathin CuPc interfacial layer in VOFETs may open up opportunities for future organic electronics.

A Facile Fabrication of CdSe/ZnS QDs-Block Copolymer Brushes-Modified Graphene Oxide Nanohybrid with Temperature-Responsive Behavior

In this paper, we described a straightforward one-step chemical method for the synthesis of semiconductor quantum dots(QDs)-block copolymer brushes functionalized graphene oxide(GO) fluorescence nanohybrids. The azobenzene-terminated block copolymer poly(N-isopropylacrylamid)-b-poly(styrene-co-5-(2-methacryoylethyloxymethyl)-8-quinolinol)(PNIPAM-b-P(St-co-MQ)) was modified on the surface of GO sheets via host-guest interactions between β-cyclodextrin-modified GO and azobenzene moieties, and simultaneously CdSe/ZnS QDs were integrated on the block copolymer brushes through the coordination between 8-hydroxyquinoline units in the polymer brushes and CdSe/ZnS QDs. The resulting fluorescence nanohybrid exhibited dual photoluminescence at 620 nm and 526 nm, respectively, upon excitation at 380 nm and LCST-type thermo-responsive behavior which originated from the change in the PNIPAM conformation in the block copolymer brushes of GO sheets.

Research on Graphene and Its Derivatives in Oral Disease Treatment

Oral diseases present a global public health problem that imposes heavy financial burdens on individuals and health-care systems. Most oral health conditions can be treated in their early stage. Even if the early symptoms of oral diseases do not seem to cause significant discomfort, prompt treatment is essential for preventing their progression. Biomaterials with superior properties enable dental therapies with applications in restoration, therapeutic drug/protein delivery, and tissue regeneration. Graphene nanomaterials have many unique mechanical and physiochemical properties and can respond to the complex oral microenvironment, which includes oral microbiota colonization and high masticatory force. Research on graphene nanomaterials in dentistry, especially in caries, periodontitis therapy, and implant coatings, is progressing rapidly. Here, we review the development of graphene and its derivatives for dental disease therapy.

Electrical and Structural Properties of CVD-Graphene Oxidized Using KMnO4/H2SO4 Solution

We report the electrical properties of graphene grown via chemical vapor deposition (CVD-graphene) and oxidized using a KMnO4/dilute H2SO4 mixture. CVD-graphene was successfully oxidized without any pores or peeling off from the substrates. When the H2SO4 concentration was increased, the electrical resistance of the oxidized graphene (OG) increased. In particular, OG-20 shows a nonlinear current–voltage curve similar to that of a diode owing to direct tunneling through the interfaces between the nanosized sp2 and sp3 regions. The changes in electrical properties occurred because of structural evolution. As the H2SO4 concentration increased, the number of oxygen functional groups (epoxide/hydroxyl and carboxyl groups) in the OG increased. In addition, a reduction in the average distance between defects in the OG was determined using Raman spectroscopy. Oxidation using a KMnO4/dilute H2SO4 mixture results in CVD-graphene with modified electrical properties for graphene-based applications.

Efficiency of marketable decontamination agent and graphene oxide on 99mTc and 131I spillages in nuclear medicine department

Dealing with open sources of radioactive substances in nuclear medicine is a daily task since contamination due to radioactive spills may happen frequently. Proper and safe decontamination management is a vital procedure. However, regular purchase of decontamination agents incurs high costs and might be toxic due to their chemical properties. The purpose of this study is to compare graphene oxide, which is an environmentally friendly carbon-based material and marketable decontamination agent, in decontaminating radioactive spillage. Samples of pure 99mTc and 131I from the laboratory were spilled on a petri dish. The spill was immediately decontaminated with a marketable decontamination agent swab and varying concentrations of graphene oxide swab. The initial radioactivity of each swab containing 99mTc and 131I was measured using a dose calibrator. The absorbance spectra of each sample were analysed using an ultraviolet-visible spectrophotometer. The morphology image of graphene oxide was observed under field emission scanning electron microscope. For decontamination using a marketable decontamination agent, the radioactivity of 131I was slightly higher, whereas that of 99mTc was slightly lower than the high concentration of graphene oxide. The absorbance spectra of 99mTc and 131I that had been decontaminated using graphene oxide were observed at a range of 200 nm to 250 nm due ???* to the transition.