rGO Powders Research Articles

Photobiocidal Activity of TiO2/UHMWPE Composite Activated by Reduced Graphene Oxide under White Light.

Herein, we introduce a photobiocidal surface activated by white light. The photobiocidal surface was produced through thermocompressing a mixture of titanium dioxide (TiO2), ultra-high-molecular-weight polyethylene (UHMWPE), and reduced graphene oxide (rGO) powders. A photobiocidal activity was not observed on UHMWPE-TiO2. However, UHMWPE-TiO2@rGO exhibited potent photobiocidal activity (>3-log reduction) against Staphylococcus epidermidis and Escherichia coli bacteria after a 12 h exposure to white light. The activity was even more potent against the phage phi 6 virus, a SARS-CoV-2 surrogate, with a >5-log reduction after 6 h exposure to white light. Our mechanistic studies showed that the UHMWPE-TiO2@rGO was activated only by UV light, which accounts for 0.31% of the light emitted by the white LED lamp, producing reactive oxygen species that are lethal to microbes. This indicates that adding rGO to UHMWPE-TiO2 triggered intense photobiocidal activity even at shallow UV flux levels.

Structural, microstructural and optical characteristics of rGO-ZnO nanocomposites via hydrothermal approach

This paper describes the production and characterizations of reduced graphene oxide-zinc oxide (rGO-ZnO) nanocomposites fabricated via hydrothermal approach. Firstly, rGO powder was produced via modified Hummers' method and ZnO nanoparticles using chemical co-precipitation. The nanocomposites structural, microstructural and optical characteristics were determined using X-ray diffraction (XRD), infrared spectroscopy (FTIR), Raman spectroscopy and Ultraviolet–visible (UV–Vis) spectroscopy. The findings demonstrated the effective synthesis of rGO-ZnO nanocomposites with evenly distributed ZnO nanoparticles on the surface of reduced graphene oxide sheets. rGO-ZnO nanocomposites with different concentrations ratio rGO:ZnO in composition of 10:0. 7.5:2.5, 5:5, 2.5:7.5, and 0:10 (weight percentage) were formed. An average crystallite size (Davg) was observed to be decreasing with an increasing concentration of ZnO in to rGO from ∼13.96 nm to ∼21.36 nm which is supported by Williamson-Hall (W–H) extrapolation. The FTIR spectra showed the functional groups belongs to intrinsic and extrinsic vibrations v1 and v2 at ∼410 cm−1 for rGO and metal‒oxygen (Zn–O) stretching vibrations ∼400 cm−1 to ∼500 cm−1 for rGO-ZnO nanocomposites. On rising ZnO content in the rGO-ZnO nanocomposites, a slight variation in band positions was caused due to the microstructural changes. Raman spectroscopy revealed certain peaks (D, G, for rGO; E2, A1 (TO), LO for ZnO) in various compositions. The research demonstrates how the composition of a material affects its vibrational characteristics, which is crucial for customizing the material for certain applications. The optical energy band gap of rGO-ZnO 75 % was recorded to be ∼4.94 eV, and highest for rGO with 5.44 eV. The optical energy band gap decreased from 5.44 eV to 4.94 eV. This decrease can be attributed to the influence of the smaller crystallite size and fluctuations in microstructural properties caused by the rGO-ZnO nanocomposite. The obtained rGO-ZnO nanocomposites can be utilized for opto-electronic device applications.

Effect of dispersing graphene oxide with different specifications in water on lubrication performance

Graphene oxide (GO) and reduced graphene oxide (rGO) are known to exhibit low friction when dispersed in water or oil, although the underlying mechanism is not yet fully understood. In this study, five GO and rGO powders were used for friction tests in water dispersion. The structure of graphene (Raman spectrometry), the bonding state of carbon (XPS analysis), and the secondary particle size (dynamic light scattering) were measured to clarify the effects of these factors on the dispersibility of GO and rGO and on the friction coefficient. The results revealed that the smaller the secondary particle size, the higher the dispersibility, and the higher the ratio of -C-O- and C-OOH coordinated to GO and rGO, the lower the friction coefficient.

Investigation of the performance and properties of ZnO/GO double-layer supercapacitor

Composite electrode material was formed by mixing reduced graphene oxide (rGO) and zinc oxide (ZnO) compound, using the Hummers and green synthesis methods, respectively. Of rGO powder, 10 g was mixed with 10%, 20% and 30% ZnO, and composite electrodes were obtained by using 10% binder. The energy storage performance and structural characteristics of the supercapacitor were evaluated by analyzing the capacitance values of the synthesized electrodes. The structural characterization of ZnO/rGO composites was performed using X-ray diffraction and field-emission scanning electron microscopy. The electrochemical properties of the ZnO/GO electrodes were analyzed by cyclic voltammetry, electrochemical impedance and galvanostatic charge–discharge tests. The specific capacitance value of electrodes increased as zinc content increased in the ZnO/rGO composite material used to produce electrodes. The maximum specific capacitance values were measured at 5 mV/s scanning rate as 194.23 (rGO), 366.81 (10% ZnO), 383.18 (20% ZnO) and 410.48 F/g (30% ZnO). In conclusion, the use of composite material formed by the combination of ZnO nanoparticles obtained by green synthesis method from orange peel and graphene oxide increased the electrochemical efficiency of the supercapacitor.

Pad printing inks based on reduced graphene oxide and various cellulose binders: Rheological properties, printability and application in electrochemical sensors

AbstractPad printing is not a widely used printing technique, but it offers the possibility of a simple, fast, and low‐cost production of various high‐resolution electrode structures. Here, the pad‐printed reduced graphene oxide (rGO) electrodes are prepared from pad‐printable inks containing rGO powder and different concentrations of two cellulose‐based polymers: ethylcellulose and cellulose acetate butyrate. The applicability of rGO inks for pad printing is analyzed according to their rheological parameters and printability. Based on viscosity, storage (G′) and loss modulus (G″) values, 10 wt% of ethylcellulose and 15 wt% of cellulose acetate butyrate appear to be most suitable for pad printing. The effect of polymer concentration on rGO electrodes homogeneity and mechanical stability is also evaluated. Cyclic voltammetry measurements for [Fe(CN)6]3−/4− redox system are performed with rGO/cellulose inks pad‐printed onto transparent conductive oxide substrates with the best results when using ethylcellulose as a binder. Finally, the square‐wave voltammetric method assesses the viability of rGO electrodes for the fast detection of ascorbic acid (detection limit of 15 μM) coupled with satisfactory precision (4.5%, n = 5) and long‐term stability during electrochemical measurements.

Irradiated rGO electrode-based high-performance supercapacitors: Boosting effect of GO/rGO mixed nanosheets on electrochemical performance

Supercapacitors are seemed to be one of the most promising choices as an energy storage system. However, there is still a gap in enhancing its energy density values and cyclic stabilities throughout a facile approach. Herein, it was aimed to propose a facile and effective way to fabricate high-energy supercapacitor electrode material based on reduced graphene oxide (rGO) nanostructure. Bearing this in mind, the bulk rGO powder was irradiated by various beam sources including Co-60, Am-241, Na-22, and Sr-90, and the resultant irradiated rGO samples were utilized as the electrode active material to fabricate symmetrical supercapacitor cells. The irradiated rGO samples were characterized both physicochemically and electrochemically. The physicochemical characterizations revealed that as a consequence of the irradiation, both GO and rGO nanosheets were formed in the resultant powder and the d-spacing of the graphene nanosheets were expanded. The highest electrochemical performance metrics were acquired for Sr-90 irradiated rGO electrode-based supercapacitor cell with the specific capacitance value of 585.44F.g−1 at 0.2 A.g−1, and outstanding capacitance retention performance of 97.14% for the 5000th CV cycles at 200 mV.s−1. Moreover, the energy density and power density values were comparable to other commercial energy storage systems such as lead-acid and nickel-metal hybrid batteries. Hence, it can be speculated that these pioneering breakthroughs could pave the way for cutting-edge high-energy supercapacitors based on rGO-derivatives with superior electrochemical performance metrics, as well as engineering of high-performance rGO-based materials to be employed in various energy applications.

Single process of pulsed wire discharge for defect healing and reduction of graphene oxide

The defect healing and reduction of graphene oxide (GO) is a key determinant for expanding the commercial applications of the GO. This paper presents an efficient and defect healing reduction method through pulsed wire discharge (PWD) process in the GO dispersed solution in an organic solvent. The energy generated during the electric explosion allows the organic solvent to serve as a carbon precursor for simultaneous reduction and defect healing within one process. To investigate the reduction efficiency of solution-based PWD method and property changes due to structural recovery, two different conductive media such as copper wire and carbon fiber were used for explosion control. The copper wire acted as a very efficient conducting medium for the reduction of GO result in very low oxygen content of less than 1% in the GO after reduction, while the carbon fiber produced non-metal contaminated reduced graphene oxide (rGO), exhibiting excellent electrical conductivity. Electrical conductivity results of the prepared rGO powder revealed that, under the same density conditions of 0.5 g/cc, carbon fiber exhibited higher conductivity (2057.6 S/m).

Synthesis of Reduced Graphene Oxide by Ethyl Acetate and Its Utilization in Determining Hydroxychloroquine in Wastewater and Pharmaceutical Samples

AbstractAn easy and sensitive sensor made by carbon paste modified with reduced graphene oxide rGO‐CPE was developed for the detection of hydroxychloroquine (HCQ). Graphene oxide GO was reduced using ethyl acetate. Scanning electron microscope and X‐ray diffraction (XRD) were used for the characterization of rGO powder. The reduction of graphene oxide was confirmed by the disappearance of the identical peak of graphite in the XRD pattern. Herein, the modified electrode rGO‐CPE showed stronger electrochemical activity compared to bare CPE. The electrochemical behavior of HCQ was studied by cyclic voltammetry, electrochemical impedance spectroscopy, and chronoamperometry. The mechanism of the HCQ oxidation in the surface of rGO‐CPE was found to be controlled by an adsorption process with the transfer of 2 electrons. Furthermore, the standard heterogeneous rate constant (Ks) and the surface concentration of electroactive species (Γ) were calculated and the obtained values are 1.03×10−2 cm s−1 and 1.07×10−10 mol cm−2, respectively. Differential pulse voltammetry was used for HCQ quantification as a result a linear relationship between HCQ concentration and the oxidation peak current was obtained in the range from 1.0×10−7 to 8.0×10−6 mol L−1 and from 8.0×10−6 to 1.0×10−4 mol L−1, with a detection limit (LOD) of 6.29×10−8 mol L−1 and a sensitivity of 6.42 A L mol−1 cm−2. Moreover, the rGO‐CPE was successfully applied for the detection of HCQ in wastewater and pharmaceutical samples.

Pitting resistance of reduced graphene oxide-layered double hydroxide reinforced aluminum composite coating deposited by cold spraying

Cold spraying aluminum-based coatings are widely used for corrosion protection of metals such as steel and magnesium alloy. However, poor pitting resistance and short protection life are the shackles of aluminum-based coating. In order to solve this problem, this paper innovatively utilized the synergistic effect of reduced graphene oxide (rGO) and layered double hydroxide (LDH) to modify the coating efficiently. Al-GLG coatings were prepared by cold spraying rGO and LDH-modified aluminum powders. The structure, composition and corrosion resistance of the Al-GLG coating were analyzed and compared with that of unmodified Al-based coating and graphene-modified Al-based (Al-G) coating. As a result, the Al-GLG coating presents a continuous network GLG surrounding the deformed aluminum powder, and this special coating exhibits pitting resistance and long life. The corrosion current density of the Al-GLG coating is only 0.01287 μA·cm−2, which is three orders of magnitude lower than that of the Al-based coating, and its pitting potential is about −0.24 VSCE, which is over 540 mV higher than that of the Al-based coating. During the full immersion text, the Al-GLG coating keeps the largest Rc (7.21×104 Ω·cm2) and low-frequency impedance modulus|Z|0.01Hz (3.66×104 Ω·cm2). The corrosion resistance mechanism of the Al-GLG coating was investigated via field emission scanning electron microscope (FE-SEM), X-ray diffraction (XRD), Raman and X-ray photoelectron spectroscopy (XPS), respectively. The excellent pitting corrosion resistance of the Al-GLG coating is attributed to the synergistic effect of the shielding effect of reduced graphene oxide and the ion exchange inhibition effect of LDH.

Vitamin C aqueous solution assisted in-situ reduction of graphene oxide in flexible thermoplastic polyurethane

Graphene oxide (GO) is usually used as a precursor of reduced GO (rGO) in polymer matrices for improving their properties. However, reduction degree of GO in conventional melt mixing is usually limited. In this work, thermoplastic polyurethane (TPU)/rGO nanocomposite is prepared via water-assisted mixing extrusion with vitamin C (VC) aqueous solution injection. In situ chemical reduction (ISCR) by the VC and in situ thermal reduction (ISTR) by the thermal energy from both extruder barrel heating and screw shear are simultaneously enhanced for the GO, which are indicated by disappearances of O–H peak at the FTIR spectrum and O–C=O peak at the XPS spectrum of the rGO powder extracted from the prepared nanocomposite. Thus high reduction degree of the GO is obtained (with C/O atom ratio of 9.83 for the extracted rGO powder). This is attributed to the following two aspects: (1) TPU chains plasticized by water can better intercalate into GO galleries, thus enhancing the stripping of oxygen-containing groups from GO surface and the ISTR of the GO; (2) the screw shear action helps to disperse the VC of the injected VC aqueous solution in the TPU melt and increase the contact between the VC and GO, therefore enhancing the ISCR of the GO. The prepared TPU/GO nanocomposite exhibits enhanced dielectric permittivity.

Stabilization of marble wastes using cement and nano materials for subgrade applications

Marble has been widely used as a construction material for many centuries. Due to its wide use, managing of marble wastes has become a pressing issue for authorities as of the environmental threat driven by its increased stockpiles in roadside or abandoned lands. This study investigates a new use of marble waste in weak field soils as subgrade application using additive based stabilization. Raw marble waste was first stabilized with Fly ash based – Portland Pozzolana Cement (PPC) having various PPC content (0.5 to 10%) to investigate the behaviour changes of physical and mechanical characteristics. Then, the modified matrix with cement (1% and 10%) was further stabilized using nano materials of 0.1% reduce Graphene Oxide (rGO) powder by weight in order to enhance the strength properties. The improvements in strengths and mechanisms were characterised using detailed morphological studies to identify new formations of elements, functional groups and microstructure changes during stabilization process. Results showed significant increase of strength in the modified matrix (800% increase of CBR and 3 MPa increase of UCS from negligible strength) compared to raw marble waste due to the efficacy of adopted stabilization in the current study. Outcomes revealed that the novel marble matrix derived from this research using wastes and additives does not only indicate great potential in replacing weak subgrade soil which usually is the route problem for many road defects, but also provides an efficient solution for waste management crisis.

Effect of MWCNTs additive on preservation stability of rGO powder

Effect of MWCNTs additive on preservation stability of rGO powder

Study on Preparation and Properties of Ultrahigh Molecular Weight Polyethylene Composites Filled with Different Carbon Materials.

The development of ultrahigh molecular weight polyethylene (UPE) has been restricted due to its linear structure and low thermal conductivity. In this paper, graphene oxide (GO) was prepared by the modified Hummers method, and then UPE/reduced graphene oxide (rGO) powder was prepared by reduction with hydrazine hydrate. UPE/natural graphite (NG), UPE/carbon nanofiber (CNF), and UPE/rGO are prepared by hot compression molding. With the increase of thermally conductive fillers, the high density of the composite makes the thermal conductivity of the crystal structure more regular and the thermal conductivity path increases accordingly. Both TGA and SEM confirmed the uniform dispersion of carbon filler in epoxy resin. Among the three composites, UPE/NG has the best thermal conductivity. When the NG filling content is 60 phr, the thermal conductivity of the UPE/NG composite is 3.257 W/(mK), outperforming UPE/CNFs (0.778 W/(mK) and pure UPE (0.496 W/(mK) by 318.64 and 556.65%, respectively. UPE/CNFs have the best dielectric properties. Comparison of various carbon fillers can provide some references for UPE’s thermal management applications.

Catalytic ozonation membrane reactor integrated with CuMn2O4/rGO for degradation emerging UV absorbers (BP-4) and fouling in-situ self-cleaning

• The combination of CuMn 2 O 4 and rGO enhanced the catalytic ozonation. • Coating times and calcination temperature determined catalytic membrane properties. • [Ozone] and TMP affected the degradation of micropollutants significantly. • Self-cleaning and catalytic ozonation are catalytic ceramic membrane superiority. To develop degradation efficiency of emerging ultraviolet absorbers (benzophenone-4, BP-4) and in-situ self-cleaning of membrane fouling in membrane filtration, a novel CuMn 2 O 4 /rGO catalytic ceramic membrane (CR/CM) was fabricated and used in catalytic ozonation membrane reactor (COMR) for water purification. Firstly, the CuMn 2 O 4 /rGO powder catalyst was optimized, according to the performance of catalytic ozonation BP-4. After that, the potential reaction sites was proposed as surface oxygen defect in CuMn 2 O 4 /rGO. Secondly, the optimized CuMn 2 O 4 /rGO powder was deposited on the surface of ceramic membrane by the vacuum negative pressure method. The thickness and roughness of the active layer were adjusted by changing the coating times. The best fabrication condition was twice surface coating. The performance of this CR/CM mainly depended on [ozone] and transmembrane pressure (TMP). The optimum reaction parameters were [ozone] = 20 mg/L and TMP was 0.20 bar. Compared with the pristine ceramic membrane coupled with ozonation, the degradation efficiency of BP-4 increased by 61.3%, the self-cleaning efficiency of catalytic membrane was 52.87%. The proposed COMR, gave a full play to the respective advantages of membrane filtration and catalytic ozonation technology, including degrading micro-organic pollutants effectively and alleviating membrane fouling.

Facile Green Synthesis of Reduced Graphene Oxide in L-cysteine Solution and its Structural, Morphological, Optical and Thermal Characteristics

The current research reports a cost-effective, efficient ad green reducing agent (L-cysteine) to reduce the graphene oxide (GO) for large-scale reduced graphene oxide (rGO) synthesis. Fabrication of rGO was performed by the reduction of GO using different concentrations from L-cysteine. Synthesis of rGO was noticed by change in color of GO solution from brown to black. For additional confirmation, the structural, morphological, optical and thermal properties of synthesized rGO were analyzed using powder X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscope (SEM), energy dispersive X-ray Spectroscopy (EDX) atomic force microscopy (AFM), thermogravimetric analysis (TGA) and ultraviolet-visible spectrophotometer (UV-Vis). The XRD, FTIR and EDS results showed the oxygen-containing groups such as hydroxyl, carbonyl, and epoxy. The UV-Vis spectrum for GO exhibited an absorbance peak at 233 nm which undergoes a red shift of the absorbance peak to 265, 273 and 278 nm due to reduction of GO to rGO using 5, 8 and 10 mg/L of L-cysteine respectively. XRD patterns demonstrated the disappearance of the characteristics peak of GO (11.1) and reinforced this appearance of peak around ~26, indicating the efficient reduction of GO and restoration of graphene sp2 hybridized structure. Furthermore, FTIR spectroscopy showed the gradual disappearance of band at 1745 cm-1 assigned to GO as L-cysteine concentration was increased. The thermal stability of the GO was much lower than those of all the rGO powders where the increased concentration of L-cysteine resulted in enhanced more thermal stability and higher C/O ratio in rGO. The SEM images confirmed the successful structurally exfoliation of two dimensional rGO sheets and showed the folded, curled and flake-like morphology of the graphene nanosheets.

Reduced graphene oxide as reinforcement in aluminium nanocomposites prepared by powder metallurgy

This study investigated the use of reduced graphene oxide (rGO) obtained by chemical route as a reinforcement phase in aluminium matrix nanocomposites (AMNCs) fabricated by powder metallurgy. Mechanical milling of a mixture of aluminium and rGO powders was able to form homogeneous and highly densified composites, allowing an effective interaction between matrix and reinforcement to establish. The effect of rGO content (ranging for 0.01 to 1.0 wt%) on the mechanical properties of rGO-AMNCs was investigated. Microhardness, elastic modulus and yield strength increase gradually up to 0.5 wt% with respective gains of 308%, 61% and 86%.

Effect of graphene reinforcement on hybrid bioceramic coating deposited on the produced porous Ti64 alloys

Porous-Ti64 alloys (P-Ti64), produced at various porosities by hot-pressing technique with the help of Mg spacer, were coated by hybrid-Graphene Oxide (rGO) reinforced-hydroxyapatite (HAp), using the sol–gel method. The synthesized rGO powder was used in reinforcing HAp by the Modified Hummers method having 30 µm particle size and nano (nm) scale layer thickness. Hybrid coatings were executed on Ti64 substrates in four different groups as single-HAp, HAp reinforced with 0.5 wt%, 1.0 wt% and 1.5 wt% rGO for three different porosities (41, 52, and 64%) were characterized by FT-IR, Raman, XRD and SEM. The average 21 µm coating film thicknesses were obtained and desirably, the only superficial pores of the substrates were closed by coating material rather than the inner connected open pores. It was also shown that 0.5 wt% and 1.0 wt% rGO reinforcements into HAp prevented crack formation on the Ti64 surfaces, whereas 1.5 wt% rGo reinforcement and single-HAp coatings caused. The highest adhesion strength values were achieved at low porosities (41–52%) and of 0.5–1.0 wt% rGO reinforcements through the adhesion tests.

Effect of the particle size of graphene oxide powders on the electrochemical performance of graphene-based supercapacitors

Graphene has been extensively investigated as an electrode material for high-performance supercapacitors due to its high electrical conductivity and large surface area. Because conventional graphene-based supercapacitors use reduced graphene oxide (rGO) in a powder form, the particle size can be one of the important factors affecting the supercapacitor performance. In this study, the effect of the particle size of graphene oxide (GO) powders was studied for the electrochemical performance of graphene-based supercapacitors. The GO powders with three different particle size distributions were used for the electrochemical tests after reducing the GO powders using simple microwave irradiation. The chemical characteristics and specific surface areas of the rGO powders synthesized by microwave irradiation (MWrGO) were nearly the same for all cases. However, the supercapacitor using the MWrGO powders with a medium size showed a higher specific capacitance (109.1 F g−1) with a lower internal resistance and efficient charge transfer. This work provides an effective method to enhance the electrochemical performance of the MWrGO powders.

Investigation of electrochemical reduction effects on graphene oxide powders for high-performance supercapacitors

This study aims to investigate the electrochemical reduction effects on graphene oxide (GO) powders with various bias voltages and treatment times. Phosphate-buffered saline solution was used as the electrolyte in the electrochemical reduction process. The experimental results showed that the GO powders were reduced to produce the best reduced GO (rGO) powders as using a bias of −17.5 V for 2 h. After the analysis of Raman spectra for GO and rGO powders, the intensity ratios of the D and G bands increased from 0.85 to 1.08, respectively. The carbon to oxygen ratios increased from 0.4 to 1.79 measured by an X-ray photoelectron spectroscopy. Moreover, the electrical conductivity obviously increased from 7.92 × 10−4 to 4.16 × 10−1 S/cm. Fourier transform infrared spectra revealed the disappearance of oxygen-containing functional groups in rGO powders. According to the cyclic voltammetry analysis, the specific capacitance of the rGO powders could reach 183 F/g at the scan rate of 100 mV/S in 1 M KCl electrolyte solution. This specific capacitance value was 16 times higher than that obtained with the GO powders. The results indicated that the produced high-quality rGO powders could be used for high-performance supercapacitors.

Flexible and Stretchable Temperature Sensors Fabricated Using Solution-Processable Conductive Polymer Composites.

Accurate monitoring of physiological temperatures is important for the diagnosis and tracking of various medical conditions. This work presents the design, fabrication, and characterization of temperature sensors using conductive polymer composites (CPCs) patterned on both flexible and stretchable substrates through both drop coating and direct ink writing (DIW). These composites were formed using a high melting point biopolymer polyhydroxybutyrate (PHB) as the matrix and the graphenic nanomaterial reduced graphene oxide (rGO) as the nanofiller (from 3 to 12 wt%), resulting in a material that exhibits a temperature-dependent resistivity. At room temperature the composites exhibited electrical percolation behavior. Around the percolation threshold, both the carrier concentration and mobility were found to increase sharply. Sensors were fabricated by drop-coating PHB-rGO composites onto ink-jet printed silver electrodes. The temperature coefficient of resistance was determined to be 0.018 /°C for pressed rGO powders and 0.008 /°C for the 3 wt% samples (the highest responsivity of all composites). Composites were found to have good selectivity to temperature with respect to pressure and moisture. Thermal mapping was demonstrated using 6 × 7 arrays of sensing elements. Stretchable devices with a meandering pattern were fabricated using DIW, demonstrating the potential for these materials in healthcare monitoring devices.