Graphene-based Materials Research Articles

Comparative toxicological analysis of two pristine carbon nanomaterials (graphene oxide and aminated graphene oxide) and their corresponding degraded forms using human in vitro models

Despite the wide application of graphene-based materials, the information of the toxicity associated to some specific derivatives such as aminated graphene oxide is scarce. Likewise, most of these studies analyse the pristine materials, while the available data regarding the harmful effects of degraded forms is very limited. In this work, the toxicity of graphene oxide (GO), aminated graphene oxide (GO-NH2), and their respective degraded forms (dGO and dGO-NH2) obtained after being submitted to high-intensity sonication was evaluated applying in vitro assays in different models of human exposure. Viability and ROS assays were performed on A549 and HT29 cells, while their skin irritation potential was tested on a reconstructed human epidermis model. The obtained results showed that GO-NH2 and dGO-NH2 substantially decrease cell viability in the lung and gastrointestinal models, being this reduction slightly higher in the cells exposed to the degraded forms. In contrast, this parameter was not affected by GO and dGO which, conversely, showed the ability to induce higher levels of ROS than the pristine and degraded aminated forms. Furthermore, none of the materials is skin irritant. Altogether, these results provide new insights about the potential harmful effects of the selected graphene-based nanomaterials in comparison with their degraded counterparts.

Polymer-mediated vacancy defects of graphene sheets as high-performance cathode materials for aqueous zinc-ion hybrid supercapacitors

The electrochemical behavior of graphene sheets in energy storage system is closely related to its electronic structures. Specifically, structural vacancy defects can expose more active sites and enhance the electrochemical performance. However, it is still a challenging problem to realize valid defect regulation on improving the reaction kinetics of electrode materials. Herein, vacancy-defective graphene sheets were constructed through the thermal mediated method via intercalation of polyacrylonitrile nanofibers. The vacancy defects were generated from the NH3 gas resulting from polymer decomposition at gradient carbonization temperature. The obtained composites of the graphene sheets and carbon nanofibers demonstrate that the vacancy defects benefit to charge transport, allowing more electrons to pass through the interlayered structure, and enhance the adsorption capacitance during the reversible electrochemical process. In addition, the as-assembled Zn ion hybrid supercapacitors exhibit a high energy density of 129.9 Wh kg−1 and outstanding cyclic stability (99.8 % after 10,000 cycling). The confined polymer-mediated thermal modification strategy can afford abundant vacancy defective sites and exhibit promising outlook for constructing high-performance graphene-based electrode materials for Zn ion hybrid supercapacitors.

Unveiling the performance of graphene nanofiber additives in gypsum plasters: A solid vs liquid perspective

Graphene nanofibers (GNFs) are promising additives for the gypsum industry. However, their impact in different forms and configurations remains unexplored. This study delves into the effects of different types of GNF additives on the properties of gypsum plasters. Findings reveal that high-surface-area (HS) GNFs and liquid low-surface-area (LS) GNFs induced significant microstructural alterations. While rheology remained unaffected, GNFs accelerated gypsum hydration, leading to fast setting. Furthermore, these GNFs promoted the appearance of anhydrite, resulting in a porous matrix with shorter crystals and poor bonding. These microstructural changes significantly reduced both flexural and compressive strength, with losses of approximately 25%. The incorporation of surfactants further exacerbated these negative effects by limiting crystal formation and growth. Consequently, liquid GNF additives exhibited the lowest performance and durability attributes. While GNFs may impart improved thermal performance to gypsum components, their implementation can also lead to significant reductions in mechanical strength and durability. More research is required to develop additives that are more compatible and do not compromise the performance of the resulting components. Building practices interested in implementing graphene-based materials should focus on powdered additives with very low specific surface area (<100 m2/g) to minimize toxicity and negative impacts on strength and durability.

Nickel nanoparticles supported on doped graphene-based materials for the ORR and HER in alkaline medium

In this work, Ni nanoparticles (NPs), with nominal metallic loading of 20 wt%, were deposited on graphene-based materials (GMs) doped with nitrogen and sulphur, in order to study their electrocatalytic activity towards the oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) in alkaline medium. Different chemical reducing agents were employed to synthesize the catalysts. Results indicate that the presence of heteroatoms in the GMs influences the activity of both the GMs and the Ni-based catalysts. Thus, best results were obtained for catalyst containing nitrogen and sulphur for the ORR which favours the direct four-electron pathway, whereas for the HER, the highest performance was observed for N-doped materials.

Theoretical study on the electrocatalytic CO2 reduction mechanisms using carbon-nanotube-supported carbon-based single metal atom catalysts

In this study, five Ni-doped carbon-based single metal atom catalysts supported by carbon nanotubes, which can be used for electrocatalytic CO2 reduction, were constructed. According to their structures, these catalysts include one Ni phthalocyanine (NiPc) molecule, two di- and tri-coordinated Ni-doped carbon nanoribbons, and two di-/tri-coordination Ni-doped graphene, which are denoted as NiPc/CNT, H2(H3)-Ni/CNT, 2(3)-Ni/CNT respectively. We first optimized their structures and studied the adsorption characteristics of CO2 on these catalysts with PBE+D3 method. Additionally, the electronic structure characteristics were then calculated, and the electrocatalytic mechanisms of CO2 reduction to CO, HCOOH, CH3OH and CH4 using these catalysts were studied in detail. It is found that the electrocatalytic activities of these five catalysts for reducing CO2 follow the order of 2-Ni/CNT>3-Ni/CNT>H3-Ni/CNT>H2-Ni/CNT>NiPc/CNT. As can be seen, the di-coordination catalysts perform best, followed by the tri-coordination catalysts, while the four-coordination NiPc-based catalyst performs worst. Moreover, graphene-based materials have stronger catalytic activities than their nanoribbon counterparts. Apart from these facts, these five catalytic materials may exhibit product selectivity at different limiting potentials, and specific reaction products can therefore be synthesized by controlling the potentials. We simultaneously investigated the mechanism of competing hydrogen evolution reactions in the electrocatalytic reduction of CO2 with five catalysts, and in order to inhibit the competing hydrogen evolution reactions and improve the efficiency of CO2 electrocatalytic reduction, the acidity of the solution can be appropriately reduced. We hope that our present work can provide a theoretical foundation for the future design and synthesis of novel carbon-based electrocatalyst for efficient CO2 reduction.

Effect of Nitrogen Dopant Agents in the Performance of Graphene-Based Cathodes for Li-S Batteries.

Lithium-sulphur (Li-S) batteries offer high energy density compared to lithium-ion batteries, emerging as a promising technology for the next generation of energy storage systems. The ongoing challenge is to improve their electrochemical performance, extend their useful life and mitigate some problems that persist in this technology, by the investigation in materials with diverse properties. This work seeks to elucidate the importance and repercussions associated with functionalisation of graphene-based materials through nitrogen incorporation (more than 9 wt.% N), employing different chemical agents such as ethylenediamine and ammonia. Herein, differences in both the textural properties and the chemical environment of nitrogen within the carbonaceous network are identified, resulting in distinct electrochemical behaviours. The electrochemical performance of electrodes prepared from ammonia-functionalised samples surpasses that of ethylenediamine-functionalised samples in terms of both efficiency and rate performance. Conversely, the ethylenediamine-functionalised samples excel in stability, showing exceptional values in capacity retention per cycle. The outcomes exceeded expectations in energy performance, allowing the Li-S cells to be subjected to ultra-high rate cycling while maintaining appropriate capacity values.

Graphene Failure under MPa: Nanowear of Step Edges Initiated by Interfacial Mechanochemical Reactions.

The low wear resistance of macroscale graphene coatings does not match the ultrahigh mechanical strength and chemical inertness of the graphene layer itself; however, the wear mechanism responsible for this issue at low mechanical stress is still unclear. Here, we demonstrate that the susceptibility of the graphene monolayer to wear at its atomic step edges is governed by the mechanochemistry of frictional interfaces. The mechanochemical reactions activated by chemically active SiO2 microspheres result in atomic attrition rather than mechanical damage such as surface fracture and folding by chemically inert diamond tools. Correspondingly, the threshold contact stress for graphene edge wear decreases more than 30 times to the MPa level, and mechanochemical wear can be described well with the mechanically assisted Arrhenius-type kinetic model, i.e., exponential dependence of the removal rate on the contact stress. These findings provide a strategy for improving the antiwear of graphene-based materials by reducing the mechanochemical interactions at tribological interfaces.

Extreme pressure and anti-wear properties of polycarboxylate superplasticizer modified 3D porous graphene/SiO2 as water-based lubricant additives

Lubricants can effectively solve the large amount of energy loss and environmental pollution caused by frictional wear. Graphene-based materials water-based lubricants have attracted attention due to their excellent various properties. But their application is still hindered by many obstacles. In this paper, a novel polycarboxylate superplasticizer modified 3D porous graphene/SiO2 (PG/SiO2) nanomaterial was prepared as water-based lubrication additives. The base fluid with good cooling properties was obtained by adding Kunlun full synthetic grinding/cutting fluid to deionized water and diluting it to 5% by weight. It is found that PG/SiO2 had a good synergistic effect, which could effectively improve the extreme pressure performance (PB/PD), with the maximum improvement rates of 39.7% and 86.3%, respectively. Meanwhile, significantly enhance the friction reduction (35%) and anti-wear (72.2%) properties of the base fluid. The enhancement mechanism was revealed by experimental and characterization analysis. Due to the excellent mechanical properties of graphene itself and synergistic effects including the rolling bearing effect of PG/SiO2 and the buffering effect of SiO2 in its intercalation, the PG/SiO2 nanomaterials can significantly improve the extreme pressure performance of the base fluid. Further, theoretical calculations revealed the enhancement effects of the long chains of the polycarboxylate superplasticizer on the dispersibility and surface adsorption of graphene, and the modified graphene on the diffusive movement of water molecules.

Tuning thermal and graphitization behaviors of lignin via complexation with transition metal ions for the synthesis of multilayer graphene-based materials.

Thermal conversion of kraft lignin, an abundant renewable aromatic substrate, into advanced carbon materials including graphitic carbon and multilayer/turbostratic graphene has recently attracted great interest. Our innovative catalytic upgrading approach integrated with molecular cracking and welding (MCW) enables mass production of lignin-derived multilayer graphene-based materials. To understand the critical role of metal catalysts in the synthesis of multilayer graphene, this study was focused on investigating the effects of transition metals (i.e., molybdenum (Mo), nickel (Ni), copper (Cu), and iron (Fe)) on thermal and graphitization behaviors of lignin. During the preparation of metal-lignin (M-lignin) complexes, Fenton-like reactions were observed with the formation of Fe- and Cu-lignin complexes, while Ni ions strongly interacted with oxygen-containing surface functional groups of lignin and Mo oxyanions weakly interacted with lignin through ionic bonding. Different chelation mechanisms of transition metal ions with lignin influenced the stabilization, graphitization, and MCW steps involved in thermal upgrading. The M-lignin complex behaviors in each of the three steps were characterized. It was found that multilayer graphene-based materials with nanoplatelets can be obtained from the Fe-lignin complex via MCW operation at 1000 °C under methane (CH4). Raman spectra indicated that Fe- and Ni-lignin complexes experienced a higher degree of graphitization than Cu- and Mo-lignin complexes during thermal treatment.

Implications of graphene-based materials in dentistry: present and future.

Since the advent of nanoscience, nanobiomaterials have been applied in the dental industry. Graphene and its derivatives have attracted the most interest of all of them due to their exceptional look, biocompatibility, multiplication differential, and antibacterial capabilities. We outlined the most recent developments about their applications to dentistry in our review. There is discussion of the synthesis processes, architectures, and characteristics of materials based on graphene. The implications of graphene and its counterparts are then meticulously gathered and described. Finally, in an effort to inspire more excellent research, this paper explores the obstacles and potential of graphene-based nanomaterials for dental aspects.

Ultra-high-performance graphene-based bulk materials strengthened by Y-type connection structure

The strategic design and assembly of bulk graphene materials represent a pivotal advancement for harnessing the inherent properties of graphene in practical applications. However, fabricating high-strength graphene-based bulk materials from graphene powders presents a significant challenge, primarily due to interlayer slippage between the graphene layers. Here, a unique Y-type connection structure was found in few-layer graphene synthesized by self-propagating high-temperature synthesis (SHS) and subsequently retained in graphene-based bulk materials prepared by spark plasma sintering (SPS) process. The Y-type connection structure and defect-induced linkages serve to cross-link the graphene-based bulk materials. Consequently, the bulk material exhibited an ultra-high compressive strength, reaching 2.14 GPa, supported by Molecular dynamics (MD) simulations which demonstrated that the Y-type connection structure increases the shear modulus and the load transfer rate. The Y-type connection structure plays a vital role in reinforcing the strength of graphene-based bulk materials, offering valuable insights for the microstructural design and property augmentation of other graphene-derived materials. Besides it’s ultra-high compressive strength, the graphene-based bulk material also performs a low thermal expansion coefficient (0.5 × 10−6 K−1), high electrical conductivity (1.47 × 105 S·m−1) and exceptional EMI shielding capability.

Investigating tribological properties of electrophoretically deposited graphene nanoplatelets coatings on mild steel

The use of graphene-based materials to enhance the tribological properties of metal surfaces has garnered increasing interest in recent years. In fact, various studies have demonstrated that graphene-related materials, such as graphene nanoplatelets (GNPs), hold promise as solid lubricants. Electrophoretical deposition (EPD) is an interesting coating method to obtain a deposition of particles such as graphene as it is a simple, cheap and effective process with a low environmental impact. This study focusses on investigating the tribological properties of GNPs coatings obtained through anodic EPD on mild steel. Specifically, a combination of GNPs and deionized water as the deposition medium is introduced, allowing a cost-effective process with reduced environmental impact.Deposition time (5, 10 and 20 min) and concentration in the bath (0.5, 1 and 1.5 g/l) were varied in a full factorial plan to highlight their effects on coating performance. The coatings achieved demonstrated good adhesion with scratch break loads above 10 N and excellent tribological performances, with a friction coefficient of above 0.1. The results showed how concentration and process duration have two opposing effects on the adhesion and tribological characteristics of the coatings. The presence of an intermediate optimal condition, with 10 min deposition and a GNP concentration of 1 g/l, leading to an improvement in anti-wear properties of approximately 85 % and a coating break distance of over 80 m. An ANOVA analysis was developed to confirm the statistical significance of the process parameters in adhesion and tribology of the coatings.

Cerium doped graphene-based materials towards oxygen reduction reaction catalysis

With the global transition towards cleaner energy and sustainable processes, the demand for efficient catalysts, especially for the oxygen reduction reaction, has gained attention from the scientific community. This research work investigates cerium-doped graphene-based materials as catalysts for this process with density functional theory calculations. The electrochemical performance of Ce-doped graphene was assessed within the computation hydrogen electrode framework. Our findings reveal that Ce doping, especially when synergized with an oxygen atom, shows improved catalytic activity and selectivity. For instance, Ce doping in combination with an oxygen atom, located near a border, can be selective for the 2-electron pathway. Overall, the combination of Ce doping with structural defects and oxygenated functions lowers the reaction free energies for the oxygen reduction compared to pure graphene, and consequently, might improve the catalytic activity. This research sheds light from a computational perspective on Ce-doped carbon materials as a sustainable alternative to traditional costly metal-based catalysts, offering promising prospects for green energy technologies and electrochemical applications.

Evaluation of Upscaling the Selective Electrophoretic Deposition of Reduced Graphene Oxide on Miniaturized Au Interdigital Electrodes from Chip-to Wafer-Level

Today’s novel materials challenge the research industry to enhance the performance and to reduce the power consumption of microchips as well as to develop new sensor principles. All this applies pressure on the investigation of new economical mass production technologies for the integration into standard process sequences or on top of state-of-the-art CMOS devices. Since the discovery of graphene in 2004, many different variations have been investigated, thus the number of publications of graphene-based content grew from a few in 2004 exponential to 1.2 million only in 2019, according to Google Scholar analysis. The deposition of graphene-based materials at wafer-level is still difficult to do economically on standard SEMI wafers up to 8” diameter. In this publication, the selective electrophoretic deposition (EPD) of reduced graphene oxide flakes (rGO) will be shown. This technique is a very promising deposition method for large scale fabrication. The EPD of rGO particles is the only known way to create 3D surface topologies for an enhanced sensing area of electrochemical sensor applications e.g. biosensors. The electrical and chemical properties of this novel material provides a broad range of applications for possible sensor solutions [1, 2]. Firstly, the deposition will be shown on chip scale to gain optimum parameters in suspension preparation and EPD deposition time/voltage for a uniform particle deposition over the sensor area. Shortcuts from particles between the transmission lines or co-deposition on reference electrodes have to be avoided. This leads to a high selectivity in rGO particle deposition on Au-structures. Afterwards designs and experiments have been made on array level and a proof of concept wafer-level deposition with a low volume suspension is demonstrated. In previous work, the adhesion of rGO on Au structures in electrochemical sensors with a liquid flow, showed a migration of the deposited particles with the friction of the liquid [3]. Therefore, standard separation of particle agglomeration or splitting of primary particles with ultra sonic sonotrodes are not sufficient to gain highly concentrated suspensions with homogenous target particle distributions (&lt; 0,5µm ≤ 1µm ≥ 5µm). For this reason, a novel particle crushing preparation by ball milling is introduced and enhanced selectivity with an improved adhesion is demonstrated. A full process of the preparation of the colloidal suspension with the definition of target particle sizes with an optimum zeta potential will be provided and the cathodic electrophoretic deposition shown [4, 5]. For the evaluation of the deposition experiments, stereo microscopy is used to reveal the selectivity on the interdigital electrode (IDE) structures (sensor area) and scanning electron microscopy (SEM) analysis is used to characterize particle sizes and 3D topography, in terms of primary and secondary particles (agglomerates). For this study, IDE structures with 15 different geometry variations (3µm to 15µm lines and spaces) are used that were manufactured [6] to evaluate the rGO deposition on chip level. A novel multisensory array design with eight sensing areas are presented, combined with wafer-level deposition as a proof of concept on a 200mm wafer.

Adsorption capacity of pollutants from water by graphene and graphene-based materials: a bibliographic review

The increase in the contamination of water systems by endocrine disruptive chemicals is of great concern once they pose risk to human and animal lives. The need for materials to adsorb these pollutants are of great concern. Graphene, a newly discovered material from the carbonaceous group, has been demonstrating interesting applications in contaminants removal from water. Therefore, this study aimed to review manuscripts regarding the adsorption capacity of herbicides and pesticides, bisphenol A, and carbamazepine from water using graphene or graphene-based materials as an adsorbent. Research of manuscripts was performed in Science Direct, Wiley Online Library, and Periódicos Capes database regarding the application of this nanomaterial in the removal of these pollutants from water. This review demonstrated that graphene itself or hybrid with other materials is very efficient in removing these contaminants, with high-efficiency rates. However, new studies can be performed to improve graphene applications and effectiveness.

Autoclave-mediated reduction of graphene oxide for enhanced conductive films

A highly efficient and environmentally friendly method for producing high-quality reduced graphene oxide (rGO) films is explored. It consists of a scalable autoclave process devoid of hazardous reductants. In detail, the reduction of four distinct graphene oxide materials, whose O/C ratio varied from 0.28 to 0.58, through an autoclave-mediated hydrothermal process at 200 °C and 12 bars pressure is carried out. This employs overheated steam as a heat carrier, without any additional solvents or reducing agents. Upon mild annealing (80 °C), the final rGO films result being robust, self-supporting, and electrically conductive. This study investigates the impact of both the initial GO’s oxidation degree and the volume distribution on the efficacy of the hydrothermal process in synthesizing rGO systems. Furthermore, a comparison between films, created through both hydrothermal autoclave-mediated and thermal oven-mediated methods, is conducted, by assessing their electrical, morphological, chemical, and structural properties. Films produced via the autoclave method display notably improved electrical surface resistivity (3.34·102 Ω/sq) compared to the traditional thermal treatments (6.71·105 Ω/sq). These promising results emphasize the potential of this eco-friendly route as a foundation for scalable and sustainable fabrication of valuable graphene-based conductive materials.

Self-assembly of graphene hollow microspheres anchored with FeNi3/NiFe2O4 nanocrystal for highly efficient electromagnetic wave absorption

The graphene-based electromagnetic wave absorption materials have attracted extensive attention due to their lightweight, strong absorption, broadband, and thin thickness. In this work, graphene hollow microspheres anchored with FeNi-coupled nanocrystal (GHMs@FeNi3/NiFe2O4) were synthesized using water-in-oil (W/O) emulsification and high-temperature calcination. The GHMs@FeNi3/NiFe2O4 microspheres have a homogeneous spherical morphology and a pronounced hollow structure, and the FeNi-coupled nanocrystals are homogeneously embedded in a spongy shell assembled by rGO nanosheets. Owing to the optimized impedance matching and enhanced attenuation, the GHMs@FeNi3/NiFe2O4 composites exhibit outstanding microwave absorption ability, particularly in the Ku band. The minimum reflection loss (RLmin) value can reach −58.96 dB at 14.43 GHz with a matching thickness of 2.25 mm, and the effective absorption bandwidth (lower than −10 dB) is up to 6.29 GHz (11.71–18 GHz) covering the whole Ku band. We believe that our work provides an idea for the design of high-performance absorbing composite materials.

Heat transfer behavior of graphene-based photothermal conversion materials prepared with tube array-porous network composite structure

In order to solve the problems of low energy utilization and poor structural stability of photothermal conversion materials, a graphene-based photothermal conversion material was prepared, which was structurally integrated with a light-absorbing upper layer and a heat insulating base. During the preparation process, a tightly arranged nanotube array upper layer was constructed on the basis of graphene films by microimprinting technology, and a porous aerogel base was molded by a fixed-point titration and multiple-foaming method. The results show that the light trap constructed from graphene hollow nanotubes can significantly increase the number of light reflections and reduce light reflectivity. Meanwhile, the length of the nanotubes is directly proportional to the light-absorbing capacity of the material, which can increase the light-absorbing rate to more than 98% under the embossing conditions of 85 kN and 8h. In addition, the porous aerogel insulation base can effectively improve the photothermal conversion effect, and a photothermal conversion efficiency of 87% and a water evaporation rate of 1.3 kg/(m2 h) can be achieved at a base thickness of 6 mm.

Environmental and Health Impacts of Graphene and Other Two-Dimensional Materials: A Graphene Flagship Perspective.

Two-dimensional (2D) materials have attracted tremendous interest ever since the isolation of atomically thin sheets of graphene in 2004 due to the specific and versatile properties of these materials. However, the increasing production and use of 2D materials necessitate a thorough evaluation of the potential impact on human health and the environment. Furthermore, harmonized test protocols are needed with which to assess the safety of 2D materials. The Graphene Flagship project (2013-2023), funded by the European Commission, addressed the identification of the possible hazard of graphene-based materials as well as emerging 2D materials including transition metal dichalcogenides, hexagonal boron nitride, and others. Additionally, so-called green chemistry approaches were explored to achieve the goal of a safe and sustainable production and use of this fascinating family of nanomaterials. The present review provides a compact survey of the findings and the lessons learned in the Graphene Flagship.

Large-area, size-controlled and transferable graphene oxide-metal films for humidity sensor

The lack of low-cost methods to synthesize large-area graphene-based materials is still an important factor that limits the practical application of graphene devices. Herein, we present a facile method for producing large-area graphene oxide-metal (GO–M) films, which are size controllable and transferable. The sensor constructed using the GO–M film exhibited humidity sensitivity while being unaffected by pressure. The relationship between the sensor’s resistance and relative humidity followed an exponential trend. The GO–Mg sensor was the most sensitive among all the tested sensors. The facile synthesis of GO–M films will accelerate the widespread utilization of graphene-based materials.