Planer nano-graphenes from camphor by CVD

Recent Advances in Nanomaterial-Based Biosignal Sensors

Recent research for medical fields, robotics, and wearable electronics aims to utilize biosignal sensors to gather bio-originated information and generate new values such as evaluating user well-being, predicting behavioral patterns, and supporting disease diagnosis and prevention. Notably, most biosignal sensors are designed for body placement to directly acquire signals, and the incorporation of nanomaterials such as metal-based nanoparticles or nanowires, carbon-based or polymer-based nanomaterials-offering stretchability, high surface-to-volume ratio, and tunability for various properties-enhances their adaptability for such applications. This review categorizes nanomaterial-based biosignal sensors into three types and analyzes them: 1) biophysical sensors that detect deformation such as folding, stretching, and even pulse, 2) bioelectric sensors that capture electric signal originating from human body such as heart and nerves, and 3) biochemical sensors that catch signals from bio-originated fluids such as sweat, saliva and blood. Then, limitations and improvements to nanomaterial-based biosignal sensors is depicted. Lastly, it is highlighted on deep learning-based signal processing and human-machine interface applications, which can enhance the potential of biosignal sensors. Through this paper, it is aim to provide an understanding of nanomaterial-based biosignal sensors, outline the current state of the technology, discuss the challenges that be addressed, and suggest directions for development.

In situ Fe-doped thin carbon wires via AC high voltage arc discharge

This study explores the controlled, continuous production of thin carbon rods between graphite electrodes (continued electrode deposits) during an arc discharge of high voltage alternating current with a frequency of 50 Hz in liquid paraffin, along with in situ doping of the resulting material using a suspension of liquid paraffin and iron powder ( <10 μm). The surface morphology of the obtained carbon rod nanomaterials was characterized using scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX), scanning transmission electron microscopy (STEM) with EDX chemical composition analysis, X-ray microtomography (micro-CT), and atomic force microscopy (AFM). The AFM technique in scanning thermal microscopy (SThM) and conductive probe (CP) modes was employed to determine the temperature and electrical conductivity of the obtained nanostructures. Qualitative analysis was conducted using Raman spectroscopy, X-ray powder diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). This simple system for producing thin, stable carbon wires (< 1.2 mm thick) enables efficient and low-cost production and doping of these materials. The high-voltage alternating current (HVAC) arc discharge method for growing controlled, metal-doped electrode deposits presents a new approach to producing inexpensive, porous carbon nanomaterials for various scientific and technological applications.

Utilization of 2D materials in aqueous zinc ion batteries for safe energy storage devices

Aqueous rechargeable battery has been an intense topic of research recently due to the significant safety issues of conventional Li-ion batteries (LIBs). Amongst the various candidates of aqueous batteries, aqueous zinc ion batteries (AZIBs) hold great promise as a next generation safe energy storage device due to its low cost, abundance in nature, low toxicity, environmental friendliness, low redox potential, and high theoretical capacity. Yet, the promise has not been realized due to their limitations, such as lower capacity compared to traditional LIB, dendrite growth, detrimental degradation of electrode materials structure as ions intercalate/de-intercalate, and gas evolution/corrosion at the electrodes, which remains a significant challenge. To address the challenges, various 2D materials with different physiochemical characteristics have been utilized. This review explores fundamental physiochemical characteristics of widely used 2D materials in AZIBs, including graphene, MoS2, MXenes, 2D metal organic framework, 2D covalent organic framework, and 2D transition metal oxides, and how their characteristics have been utilized or modified to address the challenges in AZIBs. The review also provides insights and perspectives on how 2D materials can help to realize the full potential of AZIBs for next-generation safe and reliable energy storage devices.

Transparent Electronics for Wearable Electronics Application

Recent advancements in wearable electronics offer seamless integration with the human body for extracting various biophysical and biochemical information for real-time health monitoring, clinical diagnostics, and augmented reality. Enormous efforts have been dedicated to imparting stretchability/flexibility and softness to electronic devices through materials science and structural modifications that enable stable and comfortable integration of these devices with the curvilinear and soft human body. However, the optical properties of these devices are still in the early stages of consideration. By incorporating transparency, visual information from interfacing biological systems can be preserved and utilized for comprehensive clinical diagnosis with image analysis techniques. Additionally, transparency provides optical imperceptibility, alleviating reluctance to wear the device on exposed skin. This review discusses the recent advancement of transparent wearable electronics in a comprehensive way that includes materials, processing, devices, and applications. Materials for transparent wearable electronics are discussed regarding their characteristics, synthesis, and engineering strategies for property enhancements. We also examine bridging techniques for stable integration with the soft human body. Building blocks for wearable electronic systems, including sensors, energy devices, actuators, and displays, are discussed with their mechanisms and performances. Lastly, we summarize the potential applications and conclude with the remaining challenges and prospects.

Graphene-Based Wearable Temperature Sensors: A Review

Flexible sensing electronics have received extensive attention for their potential applications in wearable human health monitoring and care systems. Given that the normal physiological activities of the human body are primarily based on a relatively constant body temperature, real-time monitoring of body surface temperature using temperature sensors is one of the most intuitive and effective methods to understand physical conditions. With its outstanding electrical, mechanical, and thermal properties, graphene emerges as a promising candidate for the development of flexible and wearable temperature sensors. In this review, the recent progress of graphene-based wearable temperature sensors is summarized, including material preparation, working principle, performance index, classification, and related applications. Finally, the challenges and future research emphasis in this field are put forward. This review provides important guidance for designing novel and intelligent wearable temperature-sensing systems.

Selective area multilayer graphene synthesis using resistive nanoheater probe

Graphene has been a material of interest due to its versatile properties and wide variety of applications. However, production has been one of the most challenging aspects of graphene and multilayer graphene (MLG). Most synthesis techniques require elevated temperatures and additional steps to transfer graphene or MLG to a substrate, which compromises the integrity of the film. In this paper, metal-induced crystallization is explored to locally synthesize MLG directly on metal films, creating an MLG-metal composite and directly on insulating substrates with a moving resistive nanoheater probe at much lower temperature conditions (~ 250 °C). Raman spectroscopy shows that the resultant carbon structure has properties of MLG. The presented tip-based approach offers a much simpler MLG fabrication solution by eliminating the photolithographic and transfer steps of MLG.

Wearable chemical sensors based on 2D materials for healthcare applications

Chemical sensors worn on the body could make possible the continuous, noninvasive, and accurate monitoring of vital human signals, which is necessary for remote health monitoring and telemedicine. Attractive for creating high-performance, wearable chemical sensors are atomically thin materials with intriguing physical features, abundant chemistry, and high surface-to-volume ratios. These advantages allow for appropriate material-analyte interactions, resulting in a high level of sensitivity even at trace analyte concentrations. Previous review articles covered the material and device elements of 2D material-based wearable devices extensively. In contrast, little research has addressed the existing state, future outlook, and promise of 2D materials for wearable chemical sensors. We provide an overview of recent advances in 2D-material-based wearable chemical sensors to overcome this deficiency. The structure design, manufacturing techniques, and mechanisms of 2D material-based wearable chemical sensors will be evaluated, as well as their applicability in human health monitoring. Importantly, we present a thorough review of the current state of the art and the technological gaps that would enable the future design and nanomanufacturing of 2D materials and wearable chemical sensors. Finally, we explore the challenges and opportunities associated with designing and implementing 2D wearable chemical sensors.

Graphene-Based Nanocomposites as Antibacterial, Antiviral and Antifungal Agents

Over the past decade, there have been many interesting studies in the scientific literature about the interaction of graphene-based polymeric nanocomposites with microorganisms to tackle antimicrobial resistance. These studies have reported variable intensities of biocompatibility and selectivity for the nanocomposites toward a specific strain, but it is widely believed that graphene nanocomposites have antibacterial, antiviral, and antifungal activities. Such antibacterial activity is due to several mechanisms by which graphene nanocomposites can act on cells including stimulating oxidative stress; disrupting membranes due to sharp edges; greatly changing core structure mechanical strength and coarseness. However, the underlying mechanisms of graphene nanocomposites as antiviral and antifungal agents remain relatively scarce. In this review, recent advances in the synthesis, functional tailoring, and antibacterial, antiviral, and antifungal applications of graphene nanocomposites are summarized. The synthesis of graphene materials and graphene-based polymeric nanocomposites with techniques such as pressurized gyration, electrospinning, chemical vapor deposition, and layer-by-layer self-assembly is first introduced. Then, the antimicrobial mechanisms of graphene membranes are presented and demonstrated typical in vitro and in vivo studies on the use of graphene nanocomposites for antibacterial, antiviral, and antifungal applications. Finally, the review describes the biosafety, current limitations, and potential of antimicrobial graphene-based nanocomposites.

High quality epitaxial graphene on 4H-SiC by face-to-face growth in ultra-high vacuum

Epitaxial graphene on SiC is the most promising substrate for the next generation 2D electronics, due to the possibility to fabricate 2D heterostructures directly on it, opening the door to the use of all technological processes developed for silicon electronics. To obtain a suitable material for large scale applications, it is essential to achieve perfect control of size, quality, growth rate and thickness. Here we show that this control on epitaxial graphene can be achieved by exploiting the face-to-face annealing of SiC in ultra-high vacuum. With this method, Si atoms trapped in the narrow space between two SiC wafers at high temperatures contribute to the reduction of the Si sublimation rate, allowing to achieve smooth and virtually defect free single graphene layers. We analyse the products obtained on both on-axis and off-axis 4H-SiC substrates in a wide range of temperatures (1300 °C-1500 °C), determining the growth law with the help of x-ray photoelectron spectroscopy (XPS). Our epitaxial graphene on SiC has terrace widths up to 10μm (on-axis) and 500 nm (off-axis) as demonstrated by atomic force microscopy and scanning tunnelling microscopy, while XPS and Raman spectroscopy confirm high purity and crystalline quality.

In-Situ Catalytic Preparation of Two-Dimensional BCN/Graphene Composite for Anti-Corrosion Application

In-situ catalytic growth of two-dimensional materials shows great potential for metal surface protection because of the impermeability and strong interaction of the materials with metal surfaces. Two-dimensional hexagonal boron-carbon nitrogen (h-BCN) is composed of alternating boron, carbon, and nitrogen atoms in a two-dimensional honeycomb lattice, which is similar to graphene. The corrosion caused by defects such as grain boundary of two-dimensional materials can be weakened by dislocation overlap via the transfer method. However, two-dimensional composite films prepared using the transfer method have problems, such as the introduction of impurities and poor adhesion, which limit their corrosion resistance. In this study, a layer of BCN/Gr two-dimensional composite was directly grown on the surface of copper foil using the CVD in-situ catalysis method, and its anti-corrosion performance was characterized by electrochemical and salt spray experiments. The results showed that the directly grown two-dimensional composite had better adhesion to the substrate and the advantage of grain boundary dislocation, thus showing a better anti-corrosion capability.

The Trend of 2D Transistors toward Integrated Circuits: Scaling Down and New Mechanisms

2D transition metal chalcogenide (TMDC) materials, such as MoS₂ , have recently attracted considerable research interest in the context of their use in ultrascaled devices owing to their excellent electronic properties. Microprocessors and neural network circuits based on MoS₂ have been developed at a large scale but still do not have an advantage over silicon in terms of their integrated density. In this study, the current structures, contact engineering, and doping methods for 2D TMDC materials for the scaling-down process and performance optimization are reviewed. Devices are introduced according to a new mechanism to provide the comprehensive prospects for the use of MoS₂ beyond the traditional complementary-metal-oxide semiconductor in order to summarize obstacles to the goal of developing high-density and low-power integrated circuits (ICs). Finally, prospects for the use of MoS₂ in large-scale ICs from the perspectives of the material, system performance, and application to nonlogic functionalities such as sensor circuits and analogous circuits, are briefly analyzed. The latter issue is along the direction of "more than Moore" research.

Graphene and Its Derivatives: Synthesis and Application in the Electrochemical Detection of Analytes in Sweat

Wearable sensors and invasive devices have been studied extensively in recent years as the demand for real-time human healthcare applications and seamless human-machine interaction has risen exponentially. An explosion in sensor research throughout the globe has been ignited by the unique features such as thermal, electrical, and mechanical properties of graphene. This includes wearable sensors and implants, which can detect a wide range of data, including body temperature, pulse oxygenation, blood pressure, glucose, and the other analytes present in sweat. Graphene-based sensors for real-time human health monitoring are also being developed. This review is a comprehensive discussion about the properties of graphene, routes to its synthesis, derivatives of graphene, etc. Moreover, the basic features of a biosensor along with the chemistry of sweat are also discussed in detail. The review mainly focusses on the graphene and its derivative-based wearable sensors for the detection of analytes in sweat. Graphene-based sensors for health monitoring will be examined and explained in this study as an overview of the most current innovations in sensor designs, sensing processes, technological advancements, sensor system components, and potential hurdles. The future holds great opportunities for the development of efficient and advanced graphene-based sensors for the detection of analytes in sweat.

Graphene Properties, Synthesis and Applications: A Review

We have evaluated some of the most recent breakthroughs in the synthesis and applications of graphene and graphene-based nanomaterials. This review includes three major categories. The first section consists of an overview of the structure and properties, including thermal, optical, and electrical transport. Recent developments in the synthesis techniques are elaborated in the second section. A number of top-down strategies for the synthesis of graphene, including exfoliation and chemical reduction of graphene oxide, are discussed. A few bottom-up synthesis methods for graphene are also covered, including thermal chemical vapor deposition, plasma-enhanced chemical vapor deposition, thermal decomposition of silicon, unzipping of carbon nanotubes, and others. The final section provides the recent innovations in graphene applications and the commercial availability of graphene-based devices.

Graphene-Based Electrospun Fibrous Materials with Enhanced EMI Shielding: Recent Developments and Future Perspectives

As a result of advancements in electronics/telecommunications, electromagnetic interference (EMI) pollution has gotten worse. Hence, fabrication/investigation of EMI shields having outstanding EMI shielding performance is necessary. Electrospinning (ES) has recently been established in several niches where 1D nanofibers (NFs) fabricated by ES can provide the shielding of EM waves, owing to their exceptional benefits. This review presents the basic correlations of ES technology and EMI shielding. Diverse graphene (GP)-based fibrous materials directly spun via ES as EMI shields are discussed. Electrospun EMI shields as composites through diverse post-treatments are reviewed, and then different factors influencing their EMI shielding characteristics are critically summarized. Finally, deductions and forthcoming outlooks are given. This review provides up to date knowledge on the advancement of the application of graphene-based electrospun fibers/composite materials as EMI shields and the outlook for high-performance electrospun fibers/composite-based EMI shielding materials.

Removal of toxic metals from wastewater environment by graphene-based composites: A review on isotherm and kinetic models, recent trends, challenges and future directions

Access to clean water has reduced in recent years due to pollution and man-made activities. Wastewater treatment regimens are many such as electrocoagulation, adsorption, ozonation, membrane and advanced oxidation processes. Owing to economical, resource availability and ease of operation adsorption has upper hand over all other methods employed in wastewater treatment. Graphene based adsorbents attracted researchers due to their ability to play dual role as adsorbent and photo-catalysts. When it comes to removal of heavy metals and dyes graphene-based aerogels are successful. Graphene composites were predominantly synthesized by top-down and bottom-up approach methods. Graphene composites are mesoporous and have microporous structure on surface. Graphene has copper desorption efficiency of 90 % upon 10th consecutive cycle. Graphene based adsorbents have adsorption efficiency of 367, 246 and 106.3 mg^-1 for lead, zinc and cadmium respectively. Though graphene possesses numerous applications, this review was devoted towards heavy metals removal from aqueous environment. In detail, the synthesis routes and interaction mechanism were explained and also the adsorption isotherms, kinetics were added. This review will serve as support for future research directions on removal of wastewater contaminants (heavy metals).

Graphene: A Path-Breaking Discovery for Energy Storage and Sustainability

The global energy situation requires the efficient use of resources and the development of new materials and processes for meeting current energy demand. Traditional materials have been explored to large extent for use in energy saving and storage devices. Graphene, being a path-breaking discovery of the present era, has become one of the most-researched materials due to its fascinating properties, such as high tensile strength, half-integer quantum Hall effect and excellent electrical/thermal conductivity. This paper presents an in-depth review on the exploration of deploying diverse derivatives and morphologies of graphene in various energy-saving and environmentally friendly applications. Use of graphene in lubricants has resulted in improvements to anti-wear characteristics and reduced frictional losses. This comprehensive survey facilitates the researchers in selecting the appropriate graphene derivative(s) and their compatibility with various materials to fabricate high-performance composites for usage in solar cells, fuel cells, supercapacitor applications, rechargeable batteries and automotive sectors.

Reliable fabrication of transparent conducting films by cascade centrifugation and Langmuir-Blodgett deposition of electrochemically exfoliated graphene

Electrochemical exfoliation is an efficient and scalable method to obtain liquid-phase graphene. Graphene in solution, obtained through electrochemical exfoliation or other methods, is typically polydisperse, containing particles of various sizes, which is not optimal for applications. We employed cascade centrifugation to select specific particle sizes in solution and prepared thin films from those graphene particles using the Langmuir-Blodgett assembly. Employing centrifugation speeds of 3, 4, and 5 krpm, further diluting the solutions in different volumes of solvent, we reliably and consistently obtained films of tunable thickness. We show that there is a limit to how thin these films can be, which is imposed by the percolation threshold. The percolation threshold is quantitatively compared to results found in literature that are obtained using other, more complex graphene film fabrication methods, and is found to occur with a percolation exponent and percolative figure of merit that are of the same order as results in literature. A maximum optical transparency of 82.4% at a wavelength of 660 nm is obtained for these films, which is in agreement with earlier works on Langmuir-Blodgett assembled ultrasonic-assisted liquid-phase exfoliated graphene. Our work demonstrates that films that are in all respects on par with films of graphene obtained through other solution-based processes can be produced from inexpensive and widely available centrifugal post-processing of existing commercially available solutions of electrochemically exfoliated graphene. The demonstrated methodology will lower the entry barriers for new research and industrial uses, since it allows researchers with no exfoliation experience to make use of widely available graphene materials.

Nanomaterials with Excellent Adsorption Characteristics for Sample Pretreatment: A Review

Sample pretreatment in analytical chemistry is critical, and the selection of materials for sample pretreatment is a key factor for high enrichment ability, good practicality, and satisfactory recoveries. In this review, the recent progress of the sample pretreatment methods based on various nanomaterials (i.e., carbon nanomaterials, porous nanomaterials, and magnetic nanomaterials) with excellent adsorption efficiency, selectivity, and reproducibility, as well as their applications, are presented. Due to the unique nanoscale physical–chemical properties, magnetic nanomaterials have been used for the extraction of target analytes by easy-to-handle magnetic separation under a magnetic field, which can avoid cumbersome centrifugation and filtration steps. This review also highlights the preparation process and reaction mechanism of nanomaterials used in the sample pretreatment methods, which have been applied for the extraction organophosphorus pesticides, fluoroquinolone antibiotics, phenoxy carboxylic acids, tetracycline antibiotics, hazardous metal ions, and rosmarinic acid. In addition, the remaining challenges and future directions for nanomaterials used as sorbents in the sample pretreatment are discussed.

Novel charm of 2D materials engineering in memristor: when electronics encounter layered morphology

The family of two-dimensional (2D) materials composed of atomically thin layers connected via van der Waals interactions has attracted much curiosity due to a variety of intriguing physical, optical, and electrical characteristics. The significance of analyzing statistics on electrical devices and circuits based on 2D materials is seldom underestimated. Certain requirements must be met to deliver scientific knowledge that is beneficial in the field of 2D electronics: synthesis and fabrication must occur at the wafer level, variations in morphology and lattice alterations must be visible and statistically verified, and device dimensions must be appropriate. The authors discussed the most recent significant concerns of 2D materials in the provided prose and attempted to highlight the prerequisites for synthesis, yield, and mechanism behind device-to-device variability, reliability, and durability benchmarking under memristors characteristics; they also indexed some useful approaches that have already been reported to be advantageous in large-scale production. Commercial applications, on the other hand, will necessitate further effort.

Performance Assessment of Low-Temperature Solar Collector with Fullerenes C60 Manufactured at Low Cost in an Emerging Country

In this work, the performance of a low-temperature solar collector (LTSC) is evaluated, using carbon nanoparticles in water as working fluid. The nanoparticles used are crystallized fullerenes, with a red parameter of 1.42 nm ± 0.5 nm, with different volume fractions in water. The thickness of the carbon film was approximately 140 to 520 nm. The study is divided into three parts: modeling and simulation of an LTSC, low-cost production and characterization of nanoparticles, and thermal evaluation of the LTSC. For the study, fullerenes were produced by microwave synthesis from a terpenoid resin (Camphor) and the nanoparticles were characterized by scanning electron microscopy (SEM) and High-Resolution Transmission (HRTEM). Tests were carried out with different volumetric flow rates, 0.0111 LT/s, 0.0166 LT/s and 0.0194 L/s, and two volumetric concentrations, 0.035% and 0.063%. The results obtained from the fullerene nanofluid showed an improvement in the thermophysical properties compared to the properties of water. The performance results showed that the efficiency increases up to 47.2% compared to that of water, with a volume fraction of 0.063%, and a flow rate of 0.0194 LT/s.

Graphene Oxide and Biomolecules for the Production of Functional 3D Graphene-Based Materials

Graphene and its derivatives have been widely employed in the manufacturing of novel composite nanomaterials which find applications across the fields of physics, chemistry, engineering and medicine. There are many techniques and strategies employed for the production, functionalization, and assembly of graphene with other organic and inorganic components. These are characterized by advantages and disadvantages related to the nature of the specific components involved. Among many, biomolecules and biopolymers have been extensively studied and employed during the last decade as building blocks, leading to the realization of graphene-based biomaterials owning unique properties and functionalities. In particular, biomolecules like nucleic acids, proteins and enzymes, as well as viruses, are of particular interest due to their natural ability to self-assemble via non-covalent interactions forming extremely complex and dynamic functional structures. The capability of proteins and nucleic acids to bind specific targets with very high selectivity or the ability of enzymes to catalyse specific reactions, make these biomolecules the perfect candidates to be combined with graphenes, and in particular graphene oxide, to create novel 3D nanostructured functional biomaterials. Furthermore, besides the ease of interaction between graphene oxide and biomolecules, the latter can be produced in bulk, favouring the scalability of the resulting nanostructured composite materials. Moreover, due to the presence of biological components, graphene oxide-based biomaterials are more environmentally friendly and can be manufactured more sustainably compared to other graphene-based materials assembled with synthetic and inorganic components. This review aims to provide an overview of the state of the art of 3D graphene-based materials assembled using graphene oxide and biomolecules, for the fabrication of novel functional and scalable materials and devices.

Graphene-Based Nanomaterials for Biomedical Imaging

Graphene is sp²-hybridized carbon structure-based two-dimensional (2D) sheet. Graphene-based nanomaterials possess several features such as unique mechanical, electronic, thermal, and optical properties, high specific surface area, versatile surface functionalization, and biocompatibility, which attracted researcher's interests in various fields including biomedicine. In this chapter, we particularly focused on the biomedical imaging applications of graphene-based nanomaterials like graphene oxide (GO), reduced graphene oxide (rGO), graphene quantum dots (GQDs), graphene oxide quantum dots (GOQDs), and other derivatives, which utilize their outstanding optical properties. There are some biomedical imaging modalities using Graphene-based Nanomaterials, among which we will highlight fluorescence imaging, Raman imaging, magnetic resonance imaging, and photoacoustic imaging. We also discussed the brief perspectives and future application related to them.

Atomically Thin 2D van der Waals Magnetic Materials: Fabrications, Structure, Magnetic Properties and Applications

Two-dimensional (2D) van der Waals (vdW) magnetic materials are considered to be ideal candidates for the fabrication of spintronic devices because of their low dimensionality, allowing the quantization of electronic states and more degrees of freedom for device modulation. With the discovery of few-layer Cr2Ge2Te6 and monolayer CrI3 ferromagnets, the magnetism of 2D vdW materials is becoming a research focus in the fields of material science and physics. In theory, taking the Heisenberg model with finite-range exchange interactions as an example, low dimensionality and ferromagnetism are in competition. In other words, it is difficult for 2D materials to maintain their magnetism. However, the introduction of anisotropy in 2D magnetic materials enables the realization of long-range ferromagnetic order in atomically layered materials, which may offer new effective means for the design of 2D ferromagnets with high Curie temperature. Herein, current advances in the field of 2D vdW magnetic crystals, as well as intrinsic and induced ferromagnetism or antiferromagnetism, physical properties, device fabrication, and potential applications, are briefly summarized and discussed.

Graphene as a Piezoresistive Material in Strain Sensing Applications

High accuracy measurement of mechanical strain is critical and broadly practiced in several application areas including structural health monitoring, industrial process control, manufacturing, avionics and the automotive industry, to name a few. Strain sensors, otherwise known as strain gauges, are fueled by various nanomaterials, among which graphene has attracted great interest in recent years, due to its unique electro-mechanical characteristics. Graphene shows not only exceptional physical properties but also has remarkable mechanical properties, such as piezoresistivity, which makes it a perfect candidate for strain sensing applications. In the present review, we provide an in-depth overview of the latest studies focusing on graphene and its strain sensing mechanism along with various applications. We start by providing a description of the fundamental properties, synthesis techniques and characterization methods of graphene, and then build forward to the discussion of numerous types of graphene-based strain sensors with side-by-side tabular comparison in terms of figures-of-merit, including strain range and sensitivity, otherwise referred to as the gauge factor. We demonstrate the material synthesis, device fabrication and integration challenges for researchers to achieve both wide strain range and high sensitivity in graphene-based strain sensors. Last of all, several applications of graphene-based strain sensors for different purposes are described. All in all, the evolutionary process of graphene-based strain sensors in recent years, as well as the upcoming challenges and future directions for emerging studies are highlighted.

Experimental and Simulation Research on the Preparation of Carbon Nano-Materials by Chemical Vapor Deposition

Carbon nano-materials have been widely used in many fields due to their electron transport, mechanics, and gas adsorption properties. This paper introduces the structure and properties of carbon nano-materials the preparation of carbon nano-materials by chemical vapor deposition method (CVD)—which is one of the most common preparation methods—and reaction simulation. A major factor affecting the material structure is its preparation link. Different preparation methods or different conditions will have a great impact on the structure and properties of the material (mechanical properties, electrical properties, magnetism, etc.). The main influencing factors (precursor, substrate, and catalyst) of carbon nano-materials prepared by CVD are summarized. Through simulation, the reaction can be optimized and the growth mode of substances can be controlled. Currently, numerical simulations of the CVD process can be utilized in two ways: changing the CVD reactor structure and observing CVD chemical reactions. Therefore, the development and research status of computational fluid dynamics (CFD) for CVD are summarized, as is the potential of combining experimental studies and numerical simulations to achieve and optimize controllable carbon nano-materials growth.

Thermal strain engineering of mechanical properties in Si-based hybrid sheets via molecular dynamics simulations

The mechanical properties of pristine and defective Si-based hybrid sheets are studied using molecular dynamics calculations for a temperature ranging from 100 to 800 K, in conjunction with a variable strain rate. When increasing temperature, the melting phase of the hybrids occurs from the solid to the liquid phase, while the increase in the strain rate enhances their elastic parameters. The absence of plastic stage reveals that the fracture pattern is brittle in these 2D materials. Under the uniaxial loading, the systems stretch, resulting in the failure of the crystalline skeletons that lose their rigidity with anisotropic behavior observed only for SiC. In defective hybrids, the point defects reduce the values of fracture strength and strain without affecting the brittle behavior of the sheets. The results impart that coupling high temperature to SiC material offers new possibilities for MEMS devices, whereas SiGe is a promising candidate for microelectronic devices.

Green Synthesis of Nanomaterials

Nanotechnology is considered one of the paramount forefronts in science over the last decade. Its versatile implementations and fast-growing demand have paved the way for innovative measures for the synthesis of higher quality nanomaterials. In the early stages, traditional synthesis methods were utilized, and they relied on both carcinogenic chemicals and high energy input for production of nano-sized material. The pollution produced as a result of traditional synthesis methods induces a need for environmentally safer synthesis methods. As the downfalls of climate change become more abundant, the scientific community is persistently seeking solutions to combat the devastation caused by toxic production methods. Green methods for nanomaterial synthesis apply natural biological systems to nanomaterial production. The present review highlights the history of nanoparticle synthesis, starting with traditional methods and progressing towards green methods. Green synthesis is a method just as effective, if not more so, than traditional synthesis; it provides a sustainable approach to nanomaterial manufacturing by using naturally sourced starting materials and relying on low energy processes. The recent use of active molecules in natural biological systems such as bacteria, yeast, algae and fungi report successful results in the synthesis of various nanoparticle systems. Thus, the integration of green synthesis in scientific research and mass production provides a potential solution to the limitations of traditional synthesis methods.

Overcoming barriers in photodynamic therapy harnessing nano-formulation strategies

Photodynamic therapy (PDT) has been extensively investigated for decades for tumor treatment because of its non-invasiveness, spatiotemporal selectivity, lower side-effects, and immune activation ability. It can be a promising treatment modality in several medical fields, including oncology, immunology, urology, dermatology, ophthalmology, cardiology, pneumology, and dentistry. Nevertheless, the clinical application of PDT is largely restricted by the drawbacks of traditional photosensitizers, limited tissue penetrability of light, inefficient induction of tumor cell death, tumor resistance to the therapy, and the severe pain induced by the therapy. Recently, various photosensitizer formulations and therapy strategies have been developed to overcome these barriers. Significantly, the introduction of nanomaterials in PDT, as carriers or photosensitizers, may overcome the drawbacks of traditional photosensitizers. Based on this, nanocomposites excited by various light sources are applied in the PDT of deep-seated tumors. Modulation of cell death pathways with co-delivered reagents promotes PDT induced tumor cell death. Relief of tumor resistance to PDT with combined therapy strategies further promotes tumor inhibition. Also, the optimization of photosensitizer formulations and therapy procedures reduces pain in PDT. Here, a systematic summary of recent advances in the fabrication of photosensitizers and the design of therapy strategies to overcome barriers in PDT is presented. Several aspects important for the clinical application of PDT in cancer treatment are also discussed.

Remediation of emerging environmental pollutants: A review based on advances in the uses of eco-friendly biofabricated nanomaterials

The increased environmental pollutants due to anthropogenic activities are posing an adverse effects and threat on various biotic forms on the planet. Heavy metals and certain organic pollutants by their toxic persistence in the environment are regarded as significant pollutants worldwide. In recent years, pollutants exist in various forms in the environment are difficult to eliminate by traditional technologies due to various drawbacks. This has lead to shifting of research for the development of cost-effective and efficient technologies for the remediation of environmental pollutants. The adaption of adsorption phenomenon from the traditional technologies with the modification of adsorbents at nanoscale is the trended research for mitigating the environmental pollutants with petite environmental concerns. Over the past decade, the hidden potentials of biological sources for the biofabrication of nanomaterials as bequeathed rapid research for remediating the environmental pollution in a sustainable manner. The biofabricated nanomaterials possess an inimitable phenomenon such as photo and enzymatic catalysis, electrostatic interaction, surface active site interactions, etc., contributing for the detoxification of various pollutants. With this background, the current review highlights the emerging biofabricated nano-based adsorbent materials and their underlying mechanisms addressing the environmental remediation of persistent organic pollutants, heavy metal (loid)s, phytopathogens, special attention to the reduction of pathogen-derived toxins and air pollutants. Each category is illustrated with suitable examples, fundamental mechanism, and graphical representations, along with societal applications. Finally, the future and sustainable development of eco-friendly biofabricated nanomaterial-based adsorbents is discussed.

Graphene-Based Materials Immobilized within Chitosan: Applications as Adsorbents for the Removal of Aquatic Pollutants

Graphene and its derivatives, especially graphene oxide (GO), are attracting considerable interest in the fabrication of new adsorbents that have the potential to remove various pollutants that have escaped into the aquatic environment. Herein, the development of GO/chitosan (GO/CS) composites as adsorbent materials is described and reviewed. This combination is interesting as the addition of graphene to chitosan enhances its mechanical properties, while the chitosan hydrogel serves as an immobilization matrix for graphene. Following a brief description of both graphene and chitosan as independent adsorbent materials, the emerging GO/CS composites are introduced. The additional materials that have been added to the GO/CS composites, including magnetic iron oxides, chelating agents, cyclodextrins, additional adsorbents and polymeric blends, are then described and discussed. The performance of these materials in the removal of heavy metal ions, dyes and other organic molecules are discussed followed by the introduction of strategies employed in the regeneration of the GO/CS adsorbents. It is clear that, while some challenges exist, including cost, regeneration and selectivity in the adsorption process, the GO/CS composites are emerging as promising adsorbent materials.

Exploration of the form factors of turbulence kinetic energy transfer for shear exfoliation of graphene

Mass production of defect-free and large-lateral-size 2D materials via cost-effective methods is very important. Recently, shear exfoliation has shown great promise for large-scale production due to its simple operation, environmental-benignity and wide adaptability. However, a long-standing challenge is that with the production of more nanosheets, a ceiling yield and shattered products are encountered, which significantly limits their wider application. The method and efficiency of energy transfer in fluid is undoubtedly the key point in determining exfoliation efficiency, yet its in-depth mechanism has not yet been described. Thus, a thorough investigation of turbulence energy transfer is critically necessary. Herein, we identify two main factors that critically determine the exfoliation yield and provide a statistical analysis of the relationship between these factors and the exfoliation yield. In the initial shearing process, the coexistence of the 2D nanosheets and raw particles is the dominant factor; as time passes, the dimensional change of raw materials gradually has a greater influence on the energy transfer. These factors together lead to attenuated efficiency and a power function relationship between yield and exfoliation time. This investigation gives a statistical explanation of shear exfoliation technology for 2D material preparation and provides valuable insights for mechanical exfoliating high-quality 2D materials.

Recent advances of monoelemental 2D materials for photocatalytic applications

As a sustainable environmental governance strategy and energy conversion method, photocatalysis has considered to have great potential in this field due to its excellent optical properties and has become one of the most attractive technologies today. Among 2D materials, the emerging two-dimensional (2D) monoelemental materials mainly distributed in the -IIIA, -IVA, -VA and -VIA groups and show excellent performance in solar energy conversion due to their graphene-like 2D atomic structure and unique properties, thereby drawing increasing attention. This review briefly summarizes the preparation processes and fundamental properties of 2D single-element nanomaterials, as well as various modification strategies and adjustment mechanisms to enhance their photocatalytic properties. In particular, this article comprehensively discusses the related practical applications of 2D single-element materials in the field of photocatalysis, including photocatalytic degradation for contaminants removal, photocatalytic pathogen inactivation, photocatalytic fouling control and photocatalytic energy conversion. This review will provide some new opportunities for the rational design of other excellent photocatalysts based on 2D monoelemental materials, as well as present tremendous novel ideas for 2D monoelemental materials in other environmental conservation and energy-related applications, such as supercapacitors, electrocatalysis, solar cells, and so on.

Effect of the Pressure of Reaction Gases on the Growth of Single-Crystal Graphene on the Inner Surfaces of Copper Pockets

Single-crystal graphene has attracted much attention due to its excellent electrical properties in recent years, and many growth methods have been proposed, including the copper pockets method. In the copper pockets method, a piece of copper foil is folded into a pocket and put into a chemical vapor deposition (CVD) system for the growth of graphene. The dynamic balance of evaporation and deposition of copper on the inner surfaces of the copper pockets avoids high surface roughness caused by the evaporation of copper in open space, such as the outer surfaces of copper pockets. Much lower partial pressure of methane in the copper pockets and lower surface roughness reduce the nucleation density of graphene and increase the size of single-crystal graphene. It is found that the growth pressure is closely related to the size of single-crystal graphene prepared by the copper pockets method; the higher the growth pressure, the larger the size of single-crystal graphene. It is also found that the growth pressure has an effect on the inner surface roughness of the copper pockets, but the effect is not significant. The main factor affecting the size of the single-crystal graphene is the change in the volume of the copper pockets caused by the change in the growth pressure, and the volume of the copper pockets determines the content of methane in the copper pockets. According to the above law, the size of single-crystal graphene prepared by the copper pockets method can be enlarged by increasing the growth pressure. The size of single-crystal graphene can be enlarged in a wide range as the growth pressure can be increased in a wide range. In our experiments, when the growth pressure reached 450 Pa, single-crystal graphene with a diameter of 450 μm was prepared.

Carbon Nanomaterials for Electro-Active Structures: A Review

The use of electrically conductive materials to impart electrical properties to substrates for cell attachment proliferation and differentiation represents an important strategy in the field of tissue engineering. This paper discusses the concept of electro-active structures and their roles in tissue engineering, accelerating cell proliferation and differentiation, consequently leading to tissue regeneration. The most relevant carbon-based materials used to produce electro-active structures are presented, and their main advantages and limitations are discussed in detail. Particular emphasis is put on the electrically conductive property, material synthesis and their applications on tissue engineering. Different technologies, allowing the fabrication of two-dimensional and three-dimensional structures in a controlled way, are also presented. Finally, challenges for future research are highlighted. This review shows that electrical stimulation plays an important role in modulating the growth of different types of cells. As highlighted, carbon nanomaterials, especially graphene and carbon nanotubes, have great potential for fabricating electro-active structures due to their exceptional electrical and surface properties, opening new routes for more efficient tissue engineering approaches.

Surface Modification Techniques of Titanium and its Alloys to Functionally Optimize Their Biomedical Properties: Thematic Review

Depending on the requirements of specific applications, implanted materials including metals, ceramics, and polymers have been used in various disciplines of medicine. Titanium and its alloys as implant materials play a critical role in the orthopedic and dental procedures. However, they still require the utilization of surface modification technologies to not only achieve the robust osteointegration but also to increase the antibacterial properties, which can avoid the implant-related infections. This article aims to provide a summary of the latest advances in surface modification techniques, of titanium and its alloys, specifically in biomedical applications. These surface techniques include plasma spray, physical vapor deposition, sol-gel, micro-arc oxidation, etc. Moreover, the microstructure evolution is comprehensively discussed, which is followed by enhanced mechanical properties, osseointegration, antibacterial properties, and clinical outcomes. Future researches should focus on the combination of multiple methods or improving the structure and composition of the composite coating to further enhance the coating performance.

Recent Advancements and Future Prospects in Ultrathin 2D Semiconductor-Based Photocatalysts for Water Splitting

Ultrathin two-dimensional (2D) semiconductor-mediated photocatalysts have shown their compelling potential and have arguably received tremendous attention in photocatalysis because of their superior thickness-dependent physical, chemical, mechanical and optical properties. Although numerous comprehensions about 2D semiconductor photocatalysts have been amassed up to now, low cost efficiency, degradation, kinetics of charge transfer along with recycling are still the big challenges to realize a wide application of 2D semiconductor-based photocatalysis. At present, most photocatalysts still need rare or expensive noble metals to improve the photocatalytic activity, which inhibits their commercial-scale application extremely. Thus, developing less costly, earth-abundant semiconductor-based photocatalysts with efficient conversion of sunlight energy remains the primary challenge. In this review, it begins with a brief description of the general mechanism of overall photocatalytic water splitting. Then a concise overview of different types of 2D semiconductor-mediated photocatalysts is given to figure out the advantages and disadvantages for mentioned semiconductor-based photocatalysis, including the structural property and stability, synthesize method, electrochemical property and optical properties for H2/O2 production half reaction along with overall water splitting. Finally, we conclude this review with a perspective, marked on some remaining challenges and new directions of 2D semiconductor-mediated photocatalysts.

Tribology of 2D Nanomaterials: A Review

The exfoliation of graphene has opened a new frontier in material science with a focus on 2D materials. The unique thermal, physical and chemical properties of these materials have made them one of the choicest candidates in novel mechanical and nano-electronic devices. Notably, 2D materials such as graphene, MoS2, WS2, h-BN and black phosphorus have shown outstanding lowest frictional coefficients and wear rates, making them attractive materials for high-performance nano-lubricants and lubricating applications. The objective of this work is to provide a comprehensive overview of the most recent developments in the tribological potentials of 2D materials. At first, the essential physical, wear and frictional characteristics of the 2D materials including their production techniques are discussed. Subsequently, the experimental explorations and theoretical simulations of the most common 2D materials are reviewed in regards to their tribological applications such as their use as solid lubricants and surface lubricant nano-additives. The effects of micro/nano textures on friction behavior are also reviewed. Finally, the current challenges in tribological applications of 2D materials and their prospects are discussed.

Carbon Nanomaterials as Versatile Platforms for Biosensing Applications

A biosensor is defined as a measuring system that includes a biological receptor unit with distinctive specificities toward target analytes. Such analytes include a wide range of biological origins such as DNAs of bacteria or viruses, or proteins generated from an immune system of infected or contaminated living organisms. They further include simple molecules such as glucose, ions, and vitamins. One of the major challenges in biosensor development is achieving efficient signal capture of biological recognition-transduction events. Carbon nanomaterials (CNs) are promising candidates to improve the sensitivity of biosensors while attaining low detection limits owing to their capability of immobilizing large quantities of bioreceptor units at a reduced volume, and they can also act as a transduction element. In addition, CNs can be adapted to functionalization and conjugation with organic compounds or metallic nanoparticles; the creation of surface functional groups offers new properties (e.g., physical, chemical, mechanical, electrical, and optical properties) to the nanomaterials. Because of these intriguing features, CNs have been extensively employed in biosensor applications. In particular, carbon nanotubes (CNTs), nanodiamonds, graphene, and fullerenes serve as scaffolds for the immobilization of biomolecules at their surface and are also used as transducers for the conversion of signals associated with the recognition of biological analytes. Herein, we provide a comprehensive review on the synthesis of CNs and their potential application to biosensors. In addition, we discuss the efforts to improve the mechanical and electrical properties of biosensors by combining different CNs.