Applications of graphene electrophoretic deposition. A review

Biogenic synthesis of CuO/ZnO nanocomposite from Bauhinia variegate flower extract for highly sensitive electrochemical detection of vitamin B2

In this study, we report the preparation of bio-inspired binary CuO/ZnO nanocomposite (bb-CuO/ZnO nanocomposite) via the biological route using Bauhinia variegata flower extract following hydrothermal treatment. The prepared bb-CuO/ZnO nanocomposite was electrophoretically deposited (EPD) on indium tin oxide (ITO) substrate to develop bb-CuO/ZnO/ITO biosensing electrode which is employed for the determination of vitamin B2 (Riboflavin) through electrochemical techniques. Physicochemical assets of the prepared bb-CuO/ZnO nanocomposite have been extensively evaluated and make use of different characterization techniques including powder XRD, FT-IR, AFM, SEM, TEM, EDX, XPS, Raman, and TGA. Electrochemical characteristics of the bb-CuO/ZnO/ITO biosensing electrode have been studied towards vitamin B2 determination. Furthermore, different biosensing parameters such as response time, reusability, stability, interference, and real sample analysis were also estimated. From the linear plot of scan rate, charge transfer rate constant (Ks), surface concentration of electrode (γ), and diffusion coefficient (D) have been calculated, and these are found to be 6.56 × 10-1 s-1, 1.21 × 10-7 mol cm-2, and 6.99 × 10-3 cm2 s-1, respectively. This biosensor exhibits the linear range of vitamin B2 detection from 1 to 40 μM, including sensitivity and limit of detection (LOD) of 1.37 × 10-3 mA/μM cm2 and 0.254 μM, respectively. For higher concentration range detection linearity is 50-100 μM, with sensitivity and the LOD of 1.26 × 10-3 mA/μM cm2 and 0.145 μM, respectively. The results indicate that the bio-inspired nanomaterials are promising sustainable biosensing platforms for various food and health-based biosensing devices.

Theoretical investigations of the electronic and optical properties of a GaGeTe monolayer

Our study focused on exploring the electronic and optical characteristics of the GaGeTe monolayer using first-principles calculations. Our findings showed that this material has remarkable physical and chemical properties attributed to its unique band structure, van Hove singularities in the density of states (DOS), charge density distributions, and charge density differences. We also observed excitonic effects, multiple optical excitation peaks, and strong plasmon modes in the energy loss functions, absorption coefficients, and reflectance spectra, which contribute to its enriched optical response. Moreover, we were able to establish a close relationship between the orbital hybridizations of the initial and final states with each optical excitation peak. Our results suggest that GaGeTe monolayers hold great potential for various semiconductor applications, especially those involving optics. Furthermore, the theoretical framework we used can be applied to study the electronic and optical properties of other graphene-like semiconductor materials.

Intrinsically Conducting Polymer Composites as Active Masses in Supercapacitors

Intrinsically conducting polymers ICPs can be combined with further electrochemically active materials into composites for use as active masses in supercapacitor electrodes. Typical examples are inspected with particular attention to the various roles played by the constituents of the composites and to conceivable synergistic effects. Stability of composite electrode materials, as an essential property for practical application, is addressed, taking into account the observed causes and effects of materials degradation.

Electrophoretic-deposited MXene titanium coatings in regulating bacteria and cell response for peri-implantitis

Background: Two-dimensional(2D)MXenes have continued to receive increasing interest from researchers due to their graphene-like properties, in addition to their versatile properties for applications in electronic devices, power generation, sensors, drug delivery, and biomedicine. However, their construction and biological properties as titanium coatings to prevent peri-implantitis are still unclear.

Materials and methods: In this work, few-layer Ti₃C₂T_x MXene coatings with different thicknesses at varied depositing voltages (30, 40, and 50 V) were constructed by anodic electrophoretic deposition without adding any electrolytic ions. In vitro cytocompatibility assay was performed on preosteoblasts (MC3T3-E1) cell lines after the characterization of the coating. Meanwhile, the antibacterial activity against bacteria which are closely related to peri-implantitis including Staphylococcus aureus (S. aureus) and its drug-resistant strain MRSA was further investigated.

Results: MXene-coated titanium models with different thicknesses were successfully assembled by analyzing the results of characterization. The compounding of Ti₃C₂T_x could significantly improve the initial adhesion and proliferation of MC3T3-E1 cells. Moreover, the coating can effectively inhibit the adhesion and cell activity of S. aureus and MRSA, and MRSA expressed greater restricting behavior than S. aureus. The ability to promote antibacterial activity is proportional to the content of Ti₃C₂T_x. Its antioxidant capacity to reduce ROS in the culture environment and bacterial cells was first revealed.

Conclusion: In summary, this work shows a new avenue for MXene-based nano-biomaterials under the clinical problem of multiple antibiotic resistance.

Optimization of Tensile Strength and Young's Modulus of CNT-CF/Epoxy Composites Using Response Surface Methodology (RSM)

Composites such as carbon fiber are used extensively by automotive, aerospace, marine, and energy industries due to their strong mechanical properties. However, there are still many areas it is lacking in testing, especially related to its electrophoretic deposition. In this research work, the tensile strength and Young's modulus of CNT-CF/epoxy composites were measured using the tensile test by varying the electrophoretic deposition (EPD) process parameters. Response surface methodology (RSM) was used to optimize the three main parameters in this EPD process: the volume ratio (water as the basis), deposition voltage, and time to obtain the maximum tensile properties of the composites. There were four volume ratios (0%, 20%, 80% and 100%) used in this design of experiment (DoE) with ratios' pairs of 0%, 100%, and 20%, 80%. For this study, water and methanol were used as the suspension medium. This design's deposition voltage and time were 10 to 20 V and 5 to 15 min. ANOVA further verified the responses' adequacy. The optimum conditions for the first Design of Experiment (DoE) (0% and 100%) were identified as a volume ratio of 99.99% water, deposition voltage of 10 V, and 12.14 min. These conditions provided the maximum strength of these composites with a tensile strength of 7.41 N/mm² and Young's modulus of 279.9 N/mm². Subsequently, for the second DoE (20% and 80%), tensile strength of 7.28 N/mm² and Young's modulus of 274.1 N/mm² were achieved with the ideal conditions: volume ratio of 44.80% water, deposition voltage of 10.04 V, and time of 6.89 min. It can be concluded that the ideal interaction between these three EPD parameters was necessary to achieve composites with good tensile properties.

Overcoming the rise in local deposit resistance during electrophoretic deposition via suspension replenishing

Nanomaterials have unique properties, functionalities, and excellent performance, and as a result have gained significant interest across disciplines and industries. However, currently, there is a lack of techniques that can assemble as-synthesized nanomaterials in a scalable manner. Electrophoretic deposition (EPD) is a promising method for the scalable assembly of colloidally stable nanomaterials into thick films and arrays. In EPD, an electric field is used to assemble charged colloidal particles onto an oppositely charged substrate. However, in constant voltage EPD the deposition rate decreases with increasing deposition time, which has been attributed in part to the fact that the electric field in the suspension decreases with time. This decreasing electric field has been attributed to two probable causes, (i) increased resistance of the particle film and/or (ii) the growth of an ion-depletion region at the substrate. Here, to increase EPD yield and scalability we sought to distinguish between these two effects and found that the growth of the ion-depletion region plays the most significant role in the increase of the deposit resistance. Here, we also demonstrate a method to maintain constant deposit resistance in EPD by periodic replenishing of suspension, thereby improving EPD’s scalability.

Enhanced Antibacterial and Osteogenic Properties of Graphene Oxide Loaded with Berberine on Biomedical Titanium

Internal implants are widely used in most orthopedic surgeries, of which titanium and its alloys are most widely used owing to the excellent corrosiveness resistance, low elastic modulus and good biocompatibility. However, implant failure still occurs for that titanium and its alloys themselves do not own antibacterial and osteogenic properties. In this work, we successfully fabricated berberine-loaded graphene oxide (GO) on the surface of biomedical titanium and systematically investigated its capabilities of antibacteria and osteogenesis. In vitro results showed that berberine had low antibacterial activity, but GO loaded with berberine on titanium (Ber&GO@Ti) exhibited superior antibacterial activity against Staphylococcus aureus (S. aureus) with the synergistic effect of GO and berberine. Meanwhile, Ber&GO@Ti performed satisfactory cytocompatibility and was capable of promoting osteogenic differentiation of MC3T3-E1 cells. In the vivo experiment, Ber&GO@Ti showed excellent antibacterial properties and inflammatory cells e.g., neutrophils had seldom been found. No visceral toxicity had been found. This multifunctional coating showed great potential in orthopedic implants.

Liquid Transport and Real-Time Dye Purification via Lotus Petiole-Inspired Long-Range-Ordered Anisotropic Cellulose Nanofibril Aerogels

Nowadays, large-scale oriented functional porous materials have been sought after by researchers. However, regulation of the long-range uniform and oriented structures of the material remains a challenge. Herein, ultralong anisotropic cellulose nanofibril (CNF) aerogels with uniformly ordered structures of pore walls inspired by lotus petioles were constructed by applying external speeds to counterbalance the growth driving forces of ice crystals. Based on the growth law of ice crystals, the ice crystals grew at a stable rate when the applied external speed was 0.04 mm/s, ensuring the consistent orientation of the large-scale CNF aerogel. The aerogel exhibited a rapid long-range directional transport ability to different liquid solvents, delivering ethanol up to 40 mm from bottom to top within 50 s. Moreover, by introducing rectorites with good cation-exchange properties, the resulting long-range composite possessed an enhanced adsorption capacity for methylene blue. Furthermore, aerogel successfully achieved real-time dye purification at a long distance, such as fast dye adsorption or selective adsorption. This flexible and straightforward strategy of fabricating ultralong oriented CNF aerogel materials is expected to promote the development of functional aerogels in directional liquid transport and sewage treatment.

Electrophoretic Deposition of Graphene Oxide on Stainless Steel Substrate

We demonstrated the deposition of the architecture of graphene oxide on stainless steel substrate and its potential environmental application. The synthesis and characterization of graphene oxide were described. The controlled formation of graphene oxide coatings in the form of the homogenous structure on stainless steel is demonstrated by scanning electron microscopy (SEM). The structure, morphology and properties of the material were assessed by Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, transmission electron microscopy (TEM) and atomic force microscopy (AFM). The morphology and stability of these structures are shown to be particularly related to the pre-treatment of stainless steel substrate before the electrophoretic deposition. This approach opens up a new route to the facile fabrication of advanced electrode coatings with potential use in environmental applications.

Corrosion performance of graphene oxide coated 304 SS in PEMFC environment

In this work, an electrophoretic deposition technique was used to deposit graphene oxide (GO) on 304 stainless steel. Its corrosion performance was evaluated in a simulated polymer electrolyte membrane fuel cell environment. The corrosion current density (icorr) and interfacial contact resistance (ICR) were measured at 8.9 µA/cm2 and 19.3 mΩ cm2, respectively. The icorr of GO coated 304SS is several orders lower than bare SS 304. Similarly, the ICR of GO coated 304SS is nearly half of bare 304SS at a compaction pressure of 150 N/cm2. The potentiodynamic polarization plot indicates the prevalence of multiple corrosion mechanisms. A prolonged corrosion study for 30 days immersed in the simulated PEM cell environment shows the formation of rounded pits that corroborate the activity of pitting corrosion.

The Plant-Like Structure of Lance Sea Urchin Spines as Biomimetic Concept Generator for Freeze-Casted Structural Graded Ceramics

The spine of the lance sea urchin (Phyllacanthus imperialis) is an unusual plant-akin hierarchical lightweight construction with several gradation features: a basic core-shell structure is modified in terms of porosities, pore orientation and pore size, forming superstructures. Differing local strength and energy consumption features create a biomimetic potential for the construction of porous ceramics with predetermined breaking points and adaptable behavior in compression overload. We present a new detailed structural and failure analysis of those spines and demonstrate that it is possible to include at least a limited number of those features in an abstracted way in ceramics, manufactured by freeze-casting. This possibility is shown to come from a modified mold design and optimized suspensions.

Variable-Angle Spectroscopic Ellipsometry of Graphene-Based Films

A review of the authors’ research works on Variable-Angle Spectroscopy (VASE) of graphene-based films is presented. The interaction of graphene oxide (GO) with magnetron-sputtered metals is a promising research area. VASE optical models of GO thin films deposited on magnetron-sputtered titanium (Ti), silver (Ag) and gold (Au) are discussed. Moreover, the optical properties of graphene nanoplatelet (GNPS) films and reduced graphene oxide (RGO) stabilized with Poly(Sodium 4-Styrenesulfonate) (PSS) films, which are less studied graphene-related materials, are shown. Finally, different optical behaviors of chemical vapor deposition (CVD)-grown monolayer, bilayer, and trilayer graphene films on silicon and polyethylene terephthalate (PET) substrates are recapitulated.

Electrophoretic-deposited Superhydrophobic Coatings

Electrophoretic deposition (EPD) is an excellent surface coating approach widely investigated for applications ranging from solar cells, batteries, electrochemical capacitors, solid oxide fuel cells, sensors, molecular sieves, corrosion-resistant coatings, and biomedical materials. On the other hand, superhydrophobic (SHPC) surfaces have enticed substantial recent research interest owing to their superb surface properties. Here, we provide a comprehensive review of electrophoretic-deposited SHPC coatings. Concise descriptions of EPD and superhydrophobicity are provided first, followed by a brief mentioning of works reported on electrophoretic-deposited SHPC coatings by one-step or two-step processing (§2.1). The next section (§2.2) delivers a comprehensive description of these reports based on the micro/nanoparticles used. Works reported in specific applications such as anti-corrosion, biomedical, and oil-separation are described in §2.3. Future scopes of research also presented.

The investigation of detection and sensing mechanism of spicy substance based on human TRPV1 channel protein-cell membrane biosensor

The transient receptor potential vanilloid 1 (TRPV1) is a key target for the spicy taste sensor and analgesic drug development. However, the human TRPV1-associated signaling remains to be obscure. In this study, we overexpressed human TRPV1 (hTRPV1) in HEK293T cells and explored its signaling activated by spicy substances. A cell membrane biosensor was constructed by using the cells highly expressed hTRPV1 through a layer-by-layer assembly. Our results showed that the activation constants by capsaicin, allicin and sanshool, the active components of chili pepper, garlic and mountain pepper, were K_{a, capsaicin} = 3.5206 × 10^-16 mol/L, K_{a, allicin} = 5.0227 × 10^-15 mol/L, K_{a, sanshool} = 1.7832 × 10^-15 mol/L. Obviously, the order of the sensitivity mediated by hTRPV1 was capsaicin > sanshool > allicin. The affinity values of the three spicy substances with hTRPV1 analyzed by molecular docking simulation also displayed the same law. Most importantly, some amide bonds and their similar groups and even benzene rings of spicy compounds were fund to be critical in the spicy sensing process. In addition, Glu570 in the active pocket of hTRPV1 plays an important role in identifying spicy substances. The elucidation of the detailed mechanism mediated by hTRPV1 in spicy sensing will lay a theoretical foundation to design rational strategies for screening of potential analgesics.

Graphene-assembly liquid crystalline and nanopolymer hybridization: A review on switchable device implementations

Two-dimensional graphene and its hybrid derivatives combined with liquid crystals, polymers, and nanomaterials enable the formation of hybrid nanocomposites possessing extraordinary and unique properties. Among others, these assemblies could exhibit stimulus-induced optical and electrical changes, which are essential for many new switchable device technologies. The current review deals straight forward and versatile techniques of the fabrication of exclusive graphene self-assembly of liquid crystalline polymer nanocomposite which exhibiting novel emerging equities as well as unique functionalities. Unique design makes hybrid composite matrix multidomain structures serve as both alignment and conductive layers, thus sustaining novel switchable device fabrication mechanism. Exhibited ultra thin-film nanocomposite based smart switchable devices are promising candidates for diverse applications in the field of stretchable electronics, energy storage, photodetectors, high contrast displays, and optoelectronics. Furthermore, the brand new device implementation through novel materials have the potentials of cost-effective production, large-area compatibility and scalability, and seamless heterogeneous integration.

Microextraction on a screw for determination of trace amounts of hexanal and heptanal as lung cancer biomarkers

Solid phase microextraction on a screw was utilized for the extraction of hexanal and heptanal as lung cancer biomarkers from urine samples. Reduced graphene oxide (rGO) was coated on the surface of a stainless-steel set screw by electrophoretic deposition method. The screw was located inside a glass cover, and the created channel acted as the sample solution flow pass. A 5 mL glass syringe was connected to a syringe pump to direct the sample and the eluent through the channel. The extraction procedure was followed by gas chromatography/mass spectrometry (GC/MS) for separation and determination of the extracted aldehydes. The effective parameters on the extraction efficiencies of the analytes were identified and optimized. Under the optimal extraction conditions, the extraction time was as short as 10 min. The calibration curves indicated good linearity (R² > 0.97) within the concentration range of 1.0-50 μg L^-1. The obtained limits of detection (LODs) for hexanal and heptanal were down to 0.4 and 0.3 μg L^-1, respectively. Considering the repeatability, simplicity, and eco-friendliness of this simple extraction method, it can be efficiently used for preconcentration of aldehydes in different samples.

Electrophoretic deposition of polymers and proteins for biomedical applications

This review is focused on new electrophoretic deposition (EPD) mechanisms for deposition biomacromolecules, such as biopolymers, proteins and enzymes. Among the rich literature sources of EPD of biopolymers, proteins and enzymes for biomedical applications we selected papers describing new fundamental deposition mechanisms. Such deposition mechanisms are of critical importance for further development of EPD method and its emerging biomedical applications. Our goal is to emphasize innovative ideas which have enriched colloid and interface science of EPD during recent years. We describe various mechanisms of cathodic and anodic EPD of charged biopolymers. Special attention is focused on in-situ chemical modification of biopolymers and crosslinking techniques. Recent innovations in the development of natural and biocompatible charged surfactants and film forming agents are outlined. Among the important advances in this area are the applications of bile acids and salts for EPD of neutral polymers. Such innovations allowed for the successful EPD of various electrically neutral functional polymers for biomedical applications. Particularly important are biosurfactant-polymer interactions, which facilitate dissolution, dispersion, charging, electrophoretic transport and deposit formation. Recent advances in EPD mechanisms addressed the problem of EPD of proteins and enzymes related to their charge reversal at the electrode surface. Conceptually new methods are described, which are based on the use of biopolymer complexes with metal ions, proteins, enzymes and other biomolecules. This review describes new developments in co-deposition of biomacromolecules and future trends in the development of new EPD mechanisms and strategies for biomedical applications.

Hydrogel membranes: A review

Hydrogel membranes (HMs) are defined and applied as hydrated porous media constructed of hydrophilic polymers for a broad range of applications. Fascinating physiochemical properties, unique porous architecture, water-swollen features, biocompatibility, and special water content dependent transport phenomena in semi-permeable HMs make them appealing constructs for various applications from wastewater treatment to biomedical fields. Water absorption, mechanical properties, and viscoelastic features of three-dimensional (3D) HM networks evoke the extracellular matrix (ECM). On the other hand, the porous structure with controlled/uniform pore-size distribution, permeability/selectivity features, and structural/chemical tunability of HMs recall membrane separation processes such as desalination, wastewater treatment, and gas separation. Furthermore, supreme physiochemical stability and high ion conductivity make them promising to be utilised in the structure of accumulators such as batteries and supercapacitors. In this review, after summarising the general concepts and production processes for HMs, a comprehensive overview of their applications in medicine, environmental engineering, sensing usage, and energy storage/conservation is well-featured. The present review concludes with existing restrictions, possible potentials, and future directions of HMs.

Immobilization Techniques for Aptamers on Gold Electrodes for the Electrochemical Detection of Proteins: A Review

The development of reliable biosensing platforms plays a key role in the detection of proteins in clinically and environmentally derived samples for diagnostics, as well as for process monitoring in biotechnological productions. For this purpose, the biosensor has to be stable and reproducible, and highly sensitive to detect potentially extremely low concentrations and prevent the nonspecific binding of interfering compounds. In this review, we present an overview of recently published (2017–2019) immobilization techniques for aptamers on gold electrodes for the electrochemical detection of proteins. These include the direct immobilization of thiolated aptamers and the utilization of short linkers, streptavidin/biotin interaction, as well as DNA nanostructures and reduced graphene oxide as immobilization platforms. Applied strategies for signal amplification and the prevention of biofouling are additionally discussed, as they play a crucial role in the design of biosensors. While a wide variety of amplification strategies are already available, future investigations should aim to establish suitable antifouling strategies that are compatible with electrochemical measurements. The focus of our review lies on the detailed discussion of the underlying principles and the presentation of utilized chemical protocols in order to provide the reader with promising ideas and profound knowledge of the subject, as well as an update on recent discoveries and achievements.

Progress in supercapacitors: roles of two dimensional nanotubular materials

Overcoming the global energy crisis due to vast economic expansion with the advent of human reliance on energy-consuming labor-saving devices necessitates the demand for next-generation technologies in the form of cleaner energy storage devices. The technology accelerates with the pace of developing energy storage devices to meet the requirements wherever an unanticipated burst of power is indeed needed in a very short time. Supercapacitors are predicted to be future power vehicles because they promise faster charging times and do not rely on rare elements such as lithium. At the same time, they are key nanoscale device elements for high-frequency noise filtering with the capability of storing and releasing energy by electrostatic interactions between the ions in the electrolyte and the charge accumulated at the active electrode during the charge/discharge process. There have been several developments to increase the functionality of electrodes or finding a new electrolyte for higher energy density, but this field is still open to witness the developments in reliable materials-based energy technologies. Nanoscale materials have emerged as promising candidates for the electrode choice, especially in 2D sheet and folded tubular network forms. Due to their unique hierarchical architecture, excellent electrical and mechanical properties, and high specific surface area, nanotubular networks have been widely investigated as efficient electrode materials in supercapacitors, while maintaining their inherent characteristics of high power and long cycling life. In this review, we briefly present the evolution, classification, functionality, and application of supercapacitors from the viewpoint of nanostructured materials to apprehend the mechanism and construction of advanced supercapacitors for next-generation storage devices.

Additive-Free Electrophoretic Deposition of Graphene Quantum Dots Thin Films

The electrophoretic deposition (EPD) of graphene-based materials on transparent substrates is highly potential for many applications. Several factors can determine the yield of the EPD process, such as applied voltage, deposition time and particularly the presence of dispersion additives (stabilisers) in the suspension solution. This study presents an additive-free EPD of graphene quantum dot (GQD) thin films on an indium tin oxide (ITO) glass substrate and studies the deposition mechanism with the variation of the applied voltage (10-50 V) and deposition time (5-25 min). It is found that due to the small size (≈3.9 nm) and high content of deprotonated carboxylic groups, the GQDs form a stable dispersion (zeta-potential of about -35 mV) without using additives. The GQD thin films can be deposited onto ITO with optimal surface morphology at 30 V in 5 min (surface roughness of approximately (3.1±1.3) nm). In addition, as-fabricated GQD thin films also possess some interesting physico-optical properties, such as a double-peak photoluminescence at about λ=417 and 439 nm, with approximately 98 % visible transmittance. This low-cost and eco-friendly GQD thin film is a promising material for various applications, for example, transparent conductors, supercapacitors and heat conductive films in smart windows.

Electrophoretic Deposition of WS2 Flakes on Nanoholes Arrays-Role of Used Suspension Medium

Here we optimized the electrophoretic deposition process for the fabrication of WS₂ plasmonic nanohole integrated structures. We showed how the conditions used for site-selective deposition influenced the properties of the deposited flakes. In particular, we investigated the effect of different suspension buffers used during the deposition both in the efficiency of the process and in the stability of WS₂ flakes, which were deposited on an ordered arrays of plasmonic nanostructures. We observed that a proper buffer can significantly facilitate the deposition process, keeping the material stable with respect to oxidation and contamination. Moreover, the integrated plasmonic structures that can be prepared with this process can be applied to enhanced spectroscopies and for the preparation of 2D nanopores.

Dopamine-functionalized cyclodextrins: modification of reduced graphene oxide based electrodes and sensing of folic acid in human serum

A mandatory step in any sensor fabrication is the introduction of analyte-specific recognition elements to the transducer surface. In this study, the possibility to anchor β-cyclodextrin-modified dopamine to a reduced graphene oxide based electrochemical transducer for the sensitive and selective sensing of folic acid is demonstrated. The sensor displays good electrocatalytic activity toward the oxidation of folic acid. The strong affinity of the surface-confined β-cyclodextrin for folic acid, together with favorable electron transfer characteristics, resulted in a sensor with a detection limit of 1 nM for folic acid and a linear response up to 10 μM. Testing of the sensor on serum samples from healthy individuals and patients diagnosed with folic acid deficiency validated the sensing capability. Graphical abstract.

“Click” Chemistry on Gold Electrodes Modified with Reduced Graphene Oxide by Electrophoretic Deposition

The coating of electrical interfaces with reduced graphene oxide (rGO) films and their subsequent chemical modification are essential steps in the fabrication of graphene-based sensing platforms. In this work, electrophoretic deposition (EPD) of graphene oxide at 2.5 V for 300 s followed by vapor treatment were employed to coat gold electrodes uniformly with rGO. These interfaces showed excellent electron transfer characteristics for redox mediators such as ferrocene methanol and potassium ferrocyanide. Functional groups were integrated onto the Au/rGO electrodes by the electro-reduction of an aryldiazonium salt, 4-((triisopropylsilyl)ethylenyl)benzenediazonium tetrafluoroborate (TIPS-Eth-ArN) in our case. Chemical deprotection of the triisopropylsilyl function resulted in propargyl-terminated Au/rGO electrodes to which azidomethylferrocene was chemically linked using the Cu(I) catalyzed “click” chemistry.

Simultaneous Silicon Oxide Growth and Electrophoretic Deposition of Graphene Oxide

During electrophoretic deposition of graphene oxide (GO) sheets on silicon substrates, not only deposition but also simultaneous anodic oxidation of the silicon substrate takes place, leading to a three-layered material. Scanning electron microscopy images reveal the presence of GO sheets on the silicon substrate, and this is also confirmed by X-ray photoelectron spectroscopy (XPS), albeit that the carbon portion increases with increasing emission angle, hinting at a thin carbon layer. With increasing applied potential and increasing conductivity of the GO solution, the carbon signal decreases, whereas the overall thickness of the added layer formed on top of the silicon substrate increases. Through XPS spectra in which the Si 2p peaks shifted under those conditions to 103-104 eV, we were able to conclude that significant amounts of oxygen are present, indicative of the formation of an oxide layer. This leads us to conclude that GO can be deposited using electrophoretic deposition, but that at the same time, silicon is oxidized, which may overshadow effects previously assigned to GO deposition.

Triple phase boundary and power density enhancement in PEMFCs of a Pt/C electrode with double catalyst layers

Exploring efficient approaches to design electrodes for proton exchange membrane fuel cells (PEMFCs) is of great advantage to overcome the current limitations of the standard platinum supported carbon (Pt/C) catalyst. Herein, a Pt/C electrode consisting of double catalyst layers (DCL) with low Pt loading of around 0.130 mg_Pt cm⁻² is prepared using spray and electrophoresis (EPD) methods. The DCL electrode demonstrated a higher electrochemical surface area (ECSA-52.5 m² g_Pt⁻¹) and smaller internal resistance (133 Ω) as compared to single catalyst layer (SCL) sprayed (37.1 m² g_Pt⁻¹ and 184 Ω) or EPD (42.4 m² g_Pt⁻¹ and 170 Ω) electrodes. In addition, the corresponding DCL membrane electrode assembly (MEA), which consists of a Pt/C DCL electrode at the anode side and a Pt/C sprayed electrode at the cathode side, also showed improved PEMFC performance as compared to others. Specifically, the DCL MEA generated the highest power density of 4.9 W mg_Pt⁻¹, whereas, the SCL MEAs only produced 3.1 and 3.8 W mg_Pt⁻¹, respectively. The superior utilization of the Pt catalysts into the DCL MEA can originate from the enrichment of the triple phase boundary (TPB) presented on the Pt/C DCL electrode, which can strongly promote the adsorbed hydrogen intermediates' removal from the anode side, thus improving the overall PEMFC performance.

Pt/C double catalyst layers (DCL), serving as an anodic electrode, have been utilized in a PEMFC application for the first time.

Functionalized graphene oxide coating on Ti6Al4V alloy for improved biocompatibility and corrosion resistance

The present study focused on the development of magnesium-functionalized graphene oxide (FGO) coating on titanium alloy (Ti6Al4V) by electrophoretic deposition. Graphene oxide (GO) was synthesized by modified Hummers' method and functionalized with magnesium ions. X-ray diffraction, infrared spectroscopy (IR) and Raman spectroscopy were employed to confirm the synthesis of GO and GO-coatings on Ti6Al4V. Functionalization of GO with Mg ions was confirmed by energy dispersive X-ray spectroscopy. The surface morphology of coated samples was examined through scanning electron microscopy. Reduction of FGO coating (labelled as rFGO) by heating at 200 °C was confirmed by IR. The rFGO coated Ti6Al4V was found to be hydrophilic in nature as determined by contact angle measurement which showed reduction in the contact angle of Ti6Al4V from 95.4° to 42.1°. The percent cell viability over the coated sample was appreciably improved compared to as-received Ti6Al4V sample owing to hydrophilicity of the former. The positive shift in open circuit potential and increase in polarization resistance was observed after coating Ti6Al4V samples with FGO. The significant decrease in the corrosion current density and negative polarization loop in the reverse scan of samples also confirmed the improved corrosion resistance of rFGO-coated Ti6Al4V over uncoated Ti6Al4V in the PBS solution. Furthermore, the impedance spectroscopy revealed that the preferential adsorption of ionic species (indicated by large R_ads) at the surface improved the barrier characteristics of rFGO coated samples and exhibited an order of magnitude higher R_ct compared to as-received samples.

Atomic layer oxidation on graphene sheets for tuning their oxidation levels, electrical conductivities, and band gaps

Graphene sheets that can exhibit electrical conducting and semiconducting properties are highly desirable and have potential applications in fiber communications, photodetectors, solar cells, semiconductors, and broadband modulators. However, there is currently no efficient method that is able to tune the band gap of graphene sheets. This work adopts an efficient atomic layer oxidation (ALO) technique to cyclically increase the oxidation level of graphene sheets, thus, tuning their electrical conductance, band-gap structure, and photoluminescence (PL) response. The O/C atomic ratio as an increasing function of the ALO cycle number reflects two linear regions: 0.23% per cm2 per cycle (0-15 cycles) and 0.054% per cm2 per cycle (15-100 cycles). The excellent correlation coefficients reveal that the ALO process follows a self-limiting route to step-by-step oxidize graphene layers. The interlayer distance of ALO-graphene sheets shows an obvious increase after the ALO treatment, proved by X-ray diffraction. As analyzed by X-ray photon spectroscopy, the hydroxyl or epoxy group acts as a major contributor to the interlayer spacing distance and oxidation extent in the initial ALO stage, as compared to carbonyl and carboxyl groups. The ALO mechanism, based on Langmuir-Hinshelwood and Eley-Rideal models, is proposed to clarify the formation of oxygen functionalities and structural transformation from pristine graphene sheets to oxidized ones during the ALO cycle. With a tunable oxidation level, the electrical resistivity, semiconductor character, and PL response of ALO-graphene samples can be systematically controlled for desired applications. The ALO approach is capable of offering a straightforward route to tune the oxidation level of graphene sheets or other carbons.

Effects of Graphene Nanoplatelet Size and Surface Area on the AC Electrical Conductivity and Dielectric Constant of Epoxy Nanocomposites

Epoxy nanocomposites reinforced with various grades of multilayer graphene nanoplatelets (GNPs) are manufactured and tested. The effects of size, surface area, and concentration of GNP, as well as alternating current (AC) frequency on the electrical and dielectric properties of epoxy nanocomposites are experimentally investigated. GNPs with larger size and surface area are always beneficial to increase the electrical conductivity of the composites. However, their effects on the dielectric constant are highly dependent on GNP concentration and AC frequency. At lower GNP concentration, the dielectric constant increases proportionally with the increase in GNP size, while decreasing as the AC frequency increases. At higher GNP concentration in epoxy, the dielectric constant first increases with the increase of the GNP size, but decreases thereafter. This trend is also observed for varying the processed GNP surface area on the dielectric constant. Moreover, the variations of the electrical conductivity and dielectric constant with the GNP concentration and AC frequency are then correlated with the measured interfiller spacing and GNP diameter.

An overview of graphene-based hydroxyapatite composites for orthopedic applications

Hydroxyapatite (HA) is an attractive bioceramic for hard tissue repair and regeneration due to its physicochemical similarities to natural apatite. However, its low fracture toughness, poor tensile strength and weak wear resistance become major obstacles for potential clinical applications. One promising method to tackle with these problems is exploiting graphene and its derivatives (graphene oxide and reduced graphene oxide) as nanoscale reinforcement fillers to fabricate graphene-based hydroxyapatite composites in the form of powders, coatings and scaffolds. The last few years witnessed increasing numbers of studies on the preparation, mechanical and biological evaluations of these novel materials. Herein, various preparation techniques, mechanical behaviors and toughen mechanism, the in vitro/in vivo biocompatible analysis, antibacterial properties of the graphene-based HA composites are presented in this review.

High capacity lithium ion batteries composed of cobalt oxide nanoparticle anodes and Raman spectroscopic analysis of nanoparticle strain dynamics in batteries

Cobalt nanoparticle thin films were electrophoretically deposited on copper current collectors and were annealed into thin films of hollow Co₃O₄ nanoparticles. These thin films were directly used as the anodes of lithium ion batteries (LIBs) without the addition of conducting carbons and bonding agents. LIBs thus fabricated show high gravimetric capacities and long cycle lives. For ≈1.0 μm thick Co₃O₄ nanoparticle films the gravimetric capacities of the batteries were more than 800 mAh g^-1 at a current rate of C/15, which is about 90% of the theoretical maximum. Additionally, the batteries were able to undergo 200 charge/discharge cycles at a relatively fast rate of C/5 and maintain 50% of the initial capacity. In order to understand the electrochemistry of lithiation in the context of nanoparticles, Raman spectra were collected at different stages of the electrode cycles to determine the chemical and structural changes in the nanomaterials. Our results indicate that initially the electrode nanoparticles were under significant strain and as the battery underwent many cycles of charging/discharging the nanoparticles experienced progressive strain relaxation.

Simultaneous Suppression of Metal Corrosion and Electrolyte Decomposition by Graphene Oxide Protective Coating in Magnesium-Ion Batteries: Toward a 4-V-Wide Potential Window

Despite remarkable developments in electrolyte systems over the past 2 decades, magnesium-ion batteries still suffer from corrosion susceptibility and low anodic limits. Herein we describe how graphene oxide (GO), coated onto non-noble metals (Al, Cu, and stainless steel) via electrophoretic deposition, can solve this problem. In all phenyl complex electrolytes, GO coating results in a significant suppression of corrosion and extends the anodic limits (up to 4.0 V vs Mg/Mg²⁺) with no impact on reversible Mg plating/stripping reactions. The same effect of GO coating is also established in magnesium aluminum chloride complex electrolytes. This remarkable improvement is associated with the electrostatic interaction between the ionic charges of electrolytes and the surface-functional groups of GO. In addition, GO coating does not aggravate the cathode performance of Mo₆S₈, which allows the use of non-noble metals as current collectors. We also discuss the role of GO in increasing anodic limits when it is hybridized with α-MnO₂.

Freeze Casting for Assembling Bioinspired Structural Materials

Nature is very successful in designing strong and tough, lightweight materials. Examples include seashells, bone, teeth, fish scales, wood, bamboo, silk, and many others. A distinctive feature of all these materials is that their properties are far superior to those of their constituent phases. Many of these natural materials are lamellar or layered in nature. With its "brick and mortar" structure, nacre is an example of a layered material that exhibits extraordinary physical properties. Finding inspiration in living organisms to create bioinspired materials is the subject of intensive research. Several processing techniques have been proposed to design materials mimicking natural materials, such as layer-by-layer deposition, self-assembly, electrophoretic deposition, hydrogel casting, doctor blading, and many others. Freeze casting, also known as ice-templating, is a technique that has received considerable attention in recent years to produce bioinspired bulk materials. Here, recent advances in the freeze-casting technique are reviewed for fabricating lamellar scaffolds by assembling different dimensional building blocks, including nanoparticles, polymer chains, nanofibers, and nanosheets. These lamellar scaffolds are often infiltrated by a second phase, typically a soft polymer matrix, a hard ceramic matrix, or a metal matrix. The unique architecture of the resultant bioinspired structural materials displays excellent mechanical properties. The challenges of the current research in using the freeze-casting technique to create materials large enough to be useful are also discussed, and the technique's promise for fabricating high-performance nacre-inspired structural materials in the future is reviewed.