The LSPR was affected by the plasma treatment, but it was completely recovered using subsequent annealing. It was found that the presence of defects increased the response for toluene and water while decreasing it for acetone.Graphene-covered silver nanoparticles were prepared directly on highly oriented pyrolytic graphite substrates and characterized by atomic force microscopy. UV–Vis reflectance spectroscopy was used to measure the shift in the local surface plasmon resonance (LSPR) upon exposure to acetone, ethanol, 2-propanol, toluene, and water vapor. The optical responses were found to be substance-specific, as also demonstrated by principal component analysis. Point defects were introduced in the structure of the graphene overlayer by O Noble metal nanoparticles (NPs) are widely used for chemical and biological sensing because of their local surface plasmon resonance (LSPR) ,2 and suThe synthesis of Ag NPs can be accomplished using a variety of strategies  dependin−7 mbar and an evaporation rate of 0.1 nm s−1. The deposited Ag films were covered with CVD graphene grown on copper foil (Graphenea), immediately after the opening of the evaporation chamber. We applied polymer tape as mechanical support to transfer large-area graphene samples. The copper foil was removed using an etchant composed of copper (II) chloride aqueous solution (20%) and hydrochloric acid (37%) in a 4:1 volume ratio. After rinsing and drying, the polymer tape with the graphene was pressed onto the evaporated Ag films. The tape was removed by lifting it with tweezers. To form nanoparticles, both bare and graphene-covered Ag thin films were annealed at 400 °C under an inert gas (Ar) atmosphere for 1.5 h. The obtained samples (samples #1 and #2) were characterized by tapping-mode AFM on a MultiMode 8 system , as well as SEM using a Thermo Scientific Scios2  instrument. Point defects were introduced in the atomic structure of the graphene overlayer (sample #2) by 5 s of O2 plasma treatment  at 50 W, followed by annealing (400 °C) in Ar gas for 60 min.Silver films of 7 nm nominal thickness were evaporated onto HOPG substrates at a background pressure of 5 × 102, 20% O2) and saturated volatile vapors through gas bubblers in the required ratio. During the measurements, a constant gas flow of 1000 mL/min was sustained through the cell. Vapor detection experiments were performed by varying the concentration and type of test vapor while tracking spectral variations over time. To purge the cell, a 20 s vapor flow at a given concentration was followed by a 60 s flow of synthetic air. In addition, before introducing the next vapor type, a 120 s purge was used to recover the initial reflectance of the sample.Optical reflectance and vapor sensing measurements were carried out by mounting the samples in an airtight aluminum box covered with a fused silica window to provide UV transmission. The samples were illuminated using an Avantes AvaLight DH-S-BAL light source. The initial reflectance of the samples in synthetic air was measured with an Avantes HS 1024 × 122TEC spectrometer  by capturing the specularly reflected signal (measured under 15°). For vapor sensing experiments, five types of volatile vapors were passed through the cell’s gas inlet and vented through the outlet: acetone, ethanol, 2-propanol, toluene, and water . Vapor concentration was adjusted by switching digital mass flow controllers  to pass synthetic air  separated by several nanometers, as shown in The adsorption of organic molecules to graphene is influenced by the presence of defects, as shown by recent calculations . This, i2O phases [This abrupt change in the optical characteristics is ascribed to the silver reacting with oxygen, and the formation of AgO or AgO phases . These oO phases .R = (R / R0) × 100%, where R0 is the initial reflectance of the sample in synthetic air. The calculated reflectance change spectra clearly showed an increasing signal as a function of the vapor concentration. A higher number of adsorbed molecules increased the effective refractive index of the medium more significantly. A positive peak followed by a negative peak represent a redshift of the LSPR. In this way, the original small changes in the LSPR could be effectively compared for all investigated samples and substances.In the following, we used both graphene-covered Ag NP samples in VOC-sensing experiments: sample #1 with pristine graphene, and sample #2 with a defected graphene overlayer. Saturated vapors of acetone, ethanol, 2-propanol, toluene, and water were diluted with synthetic air in ten different concentrations and the resulting wavelength shift of the LSPR peak was measured. As a control experiment, a bare HOPG surface was used in the same vapor sensing measurement, which resulted in only a slight decrease in the intensity as the vapor concentration was increased see . The effThe optical responses of graphene-covered Ag NPs obtained for saturated vapors are plotted in To investigate in more detail the VOC sensing data, principal component analysis (PCA) of the measured data sets was carried out and the resulting score plots were compared. As both samples showed a much higher response to acetone compared to the other four substances, and because the UV absorbance of this vapor was in the range of the LSPR, the data on acetone were omitted from the analysis. The PCA score plots of ethanol, 2-propanol, toluene, and water are shown in Here, each vapor had a unique trajectory. To facilitate the comparison, the data points were projected on the PC1–PC2 planes of the graphs. All trajectories originated from a common point, which was the data point of the initial synthetic air spectrum. Away from this, as the concentration of the vapors increased, the calculated points branched apart, resulting in a clear separation of the trajectories. This showed that the VOC detection by the graphene-covered Ag NPs was substance-specific. One can see on the PC1–PC2 projected plane that the third dimension is needed to properly separate the signal of ethanol and 2-propanol, as the trajectories are overlapping in the 2D projection. Furthermore, to observe the effect of defects in the graphene overlayer, we compared the maximal intensities of the peak (near the LSPR) in the reflectance change spectra to the maximal intensities obtained with the pristine graphene overlayer. These maximal peak intensities are plotted as a function of concentration in One can observe that there were differences in the maximal responses of the two samples, especially for acetone, water, and toluene. The defected graphene overlayer increased the sensitivity to water and toluene. This agrees with recent calculations showing that toluene  and wateWe investigated the morphology, optical, and vapor sensing properties of graphene-covered Ag NPs elaborated directly on HOPG substrates. We showed that the prepared hybrid nanostructures displayed pronounced optical responses upon exposure to organic vapors . The observed concentration-dependent shifts in the LSPR were substance-specific, as demonstrated by reflectance change spectra and PCA. We further showed that, by introducing structural defects in the graphene overlayer, the optical response of the graphene/Ag NPs increased for toluene and water, while it decreased for acetone detection. These findings can stimulate further research towards increasing the selectivity in VOC sensing.


Irregularities in breathing patterns can be detected using breath monitor sensors, and this help clinicians to predict health disorders ranging from sleep disorders to heart failures. Variations in humidity during the inhalation and exhalation of breath have been utilized as a marker to detect breath patterns, and graphene-based devices are the favored sensing media for relative humidity (RH). In general, most graphene-based RH sensors have been used to explore resistance change as a measurement parameter to calibrate against the RH value, and they are prone to noise interference. Here, we fabricated RH sensors using graphene ink as a sensing medium and printed them in the shape of interdigital electrodes on glossy paper using an office inkjet printer. Further, we investigated the capacitance change in the sensor for the RH changes in the range of 10–70%. It exhibited excellent sensitivity with 0.03 pF/% RH, good stability, and high intraday and interday repeatability, with relative standard deviations of 1.2% and 2.2%, respectively. Finally, the sensor was embedded into a face mask and interfaced with a microcontroller, and capacitance change was measured under three different breathing situations: normal breathing, deep breathing, and coughing. The result show that the dominant frequency for normal breath is 0.22 Hz, for deep breath, it is 0.11 Hz, and there was no significant dominant cough frequency due to persistent coughing and inconsistent patterns. Moreover, the sensor exhibited a short response and recovery time (<5 s) during inhalation and exhalation. Thus, the proposed paper-based RH sensor is promising wearable and disposable healthcare technology for clinical and home care health applications. Abnormalities in the human respiration rate is a vital sign of health disorders. For a healthy adult at rest, the normal breathing rate ranges from 12 to 20 breaths per minute. By detecting irregularities in the breathing rate and respiration pattern, clinicians can predict acute events such as chronic obstructive pulmonary disease (COPD) , chronicIn general, there are two methods for measuring the respiratory rate, i.e., contact-based and contactless ones . ContactIn recent years, paper has been considered as a promising sensor substrate owing to its low cost, flexibility, lightweight, biodegradability, and disposability ,14. GreaThe ideal humidity level that comforts the human body is between 40% and 70% at the appropriate temperature . The humAnother consideration is the sensor readout, which can be either resistive or capacitive. Many humidity sensors are resistive-type ones, which respond to a change in the resistance with relative humidity ,38. HoweAccordingly, we present an inexpensive, disposable, and sensitive capacitive-and paper based humidity sensor for respiration sensing. The sensor was fabricated through one-step fabrication technique, which only required an inkjet printer, glossy paper, and graphene printing ink. In addition, the paper-based humidity sensor was designed with an interdigitated electrode (IDE) pattern to increase the effective sensing area and the capacitance of the sensor. The RH-sensing characteristics of the fabricated sensor were investigated in the range of 10–70% RH. To demonstrate that the sensor enables continuous, real-time breathing monitoring, the sensor was studied under three different breathing situations  and the respiratory frequency rates and patterns were analyzed.Graphene printing ink with a viscosity in the range of 10–20 cP was purchased from GO Advanced Sdn. Bhd. . A4 glossy inkjet photo paper (180 gsm) and dual-sided conductive copper tape (5 mm × 20 m) were obtained from INRO Electronic . The Arduino Mega2560 and BME680 environmental sensors were purchased from Cytron Sdn. Bhd. .−1 range using Raman Spectroscopy (Renishaw InVia Raman Microscope). The surface contact angles for a 20 μL droplet on the surfaces of glossy paper with printed graphene and without printed graphene were measured using a goniometer .All the paper sensors were prepared using Brother Model MFC-J200 inkjet printer. The surface morphology of graphene-printed glossy paper was characterized using a field emission scanning electron microscope (FESEM) . The chemical composition of the graphene-printed surface was characterized by X-ray photoelectron spectroscopy (XPS) . Raman spectra characterization with a 532 nm excitation was performed in the 3200–100 cmThe device fabrication protocol for the paper-based Inkjet-printed-graphene sensor is schematically shown in 3 with two peripheral holes that acted as the inlet and outlet. The inlet and outlet were always open for the continuous flow of gas mixture through the chamber to achieve a constant gas pressure. Purified nitrogen, N2, gas was supplied by a gas tank  at a pressure of 1.5 bar was regulated by both of the MFCs . During humidification, the N2 gas was flowed through a bubbler filled with deionized water into the sensing chamber at a fixed flow rate of 200 sccm, which was regulated by MFC2. The chamber was dehumidified by flowing dry N2 gas through the chamber at flow rate 711 sccm, which was regulated by MFC1. The fabricated paper sensor was placed in a homemade sensing chamber that was interfaced with the microcontroller for the humidity detection tests. Further, a data logging system was utilized to record the RH conditions using a PC. The operating ranges of the chamber for RH were controlled and monitored to stay within the range from 10% to 70%. The sensitivity of the sensor is expressed as Equation (1), where ΔC is the capacitance change due to the humidity, and ΔRH is the relative humidity variation [The RH sensing setup is illustrated in ariation .(1)S=[lThe description of the experimental setup used to investigate the response of the printed paper sensor to variable breath conditions is as follows: The paper sensor was embedded into a commercial KN94 mask for human respiration monitoring, as shown in FESEM was applied to examine the morphology of the printed sensing material at varied magnifications. The SEM images of the bare glossy paper (i–iii) and the graphene-printed glossy paper (iv–vi) at magnifications of 10 K, 20 K, and 50 K are shown in Hydrophilicity was investigated by measuring the water drop contact angle of the bare paper substrate and graphene ink film samples. 3 carbon and aromatic sp2 carbon are within the range of 284.5–285 eV [−) could be due to the water vapor on the graphene-printed paper surface and its origin in the surrounding environment [−1) and broad G-band (1584 cm−1), indicating the graphene layer that was inkjet printed onto the paper substrate [2 bonded carbon atoms in the graphitic structure [2 crystal structure due to oxidation [In addition, the elemental composition analysis on the energy dispersive XPS chart of the graphene-printed paper surface further confirms this result, illustrating the expected elemental peaks of carbon (C1s) and oxygen (O1s). From the XPS survey spectra in 5–285 eV ,45. The ironment . In Figuubstrate . The pretructure . The prexidation ,50.p value is 0.247 , which indicates that a not statistically significant difference occurred from day 1 to day 10. As a result, paper sensors can maintain good short-term stability during humidity testing. The repeatability of test on the paper sensor was evaluated by performing three cycles within the intraday (within same day) and interday (between days) range from 10% to 70% RH. The results of the paper sensor are considered to be highly repeatable, with relative standard deviations (RSD) of 1.2%  in terms of the capacitance (pF) value and the breathing pattern, with fast response and recovery times of 2.46 s ± 0.34 and 3.86 s ± 0.56 for the exhalation rise time, and 2.63 s ± 0.49 and 4.27 s ± 1.02 for the inhalation fall time under normal breathing and deep breathing conditions, respectively. The prototype sensor has a low cost, and it is disposable when it is used for frequent breathing pattern recognition. The sensor requires the simple inkjet printing of graphene ink on glossy paper using a typical office inkjet printer. The method is also suitable for mass production at a low cost. However, there are limitations in terms of aligning the layer features while one is printing multiple layers on same piece of paper. Furthermore, functionalized graphene ink for the selectively sensing of volatile organic compound molecules in breathe can be investigated in future studies.


Among the different graphene derivatives, graphene oxide is the most intensively studied material as it exhibits reliable and repeatable resistive switching. The operative mechanisms that are responsible for resistive switching are being intensively investigated, and three models explaining the change in the resistive states have been developed. These models are grounded in the metallic-like filamentary conduction, contact resistance modification and the oxidation of/reduction in the graphene oxide bulk. In this work, using Al/GO/n-Si structures, we demonstrate that all three of these operative mechanisms can simultaneously participate in the resistive switching of graphene oxide. Multiple point-like conduction channels in the graphene oxide films were detected by the electron beam-induced current (EBIC) technique. At the same time, large areas with increased conductivity were also revealed by EBIC. An analysis of these areas by Raman spectroscopy indicates the change in the graphene oxide bulk’s resistive properties. The EBIC data along with the measurements of the capacitance–voltage characteristics provided strong evidence of the involvement of an aluminum/graphene oxide interface in the switching processes. In addition, by using Al/GO/n-Si structures, we were able to identify unique local properties of the formed conductive channels, namely the change of the charge state of a conductive channel due to the creation of negatively charged traps and/or an increase in the GO work function. The research and development of materials, devices and processes that are related to non-volatile resistive memory is of great interest due to the prospects of the important practical applications including large-volume memory arrays , systemsIn our previous work , the HRSIn this work, we used Al/GO/n-Si metal–insulator–semiconductor (MIS) structures to investigate the resistive switching mechanisms and determine the locations of the conductive channels in the graphene oxide films by the electron beam-induced current (EBIC) technique ,21. To tThe graphene oxide that was used in this work was synthesized by the oxidation of graphite using the modified Hummers’ method ,23, and −11 A to minimize the irradiation dose. To monitor the e-beam irradiation effect during the EBIC mapping, the switching characteristics were measured on more than 20 MOS structures before and after their irradiation with an electron beam. After the experiments on resistive switching and the EBIC characterization, the aluminum electrodes were chemically removed, and the underlying GO film was characterized using the SENTERRA Bruker Raman microscope at the laser wavelength of 532 nm. A schematic presentation of the MIS structure and the experimental setup for the current–voltage and EBIC measurements is given in AC and DC measurements, respectively. Note that the capacitance playing a major role during the C–V measurements at a frequency of 100 kHz had an infinite value during the DC voltage sweep. The presence and role of aluminum oxide are explained in The investigations of the resistive switching characteristics and operative switching mechanisms in the GO films were carried out on the MIS structures that were made on phosphorous-doped Si wafer pieces with the GO film thickness of 40 nm. The top electrodes of circular shape and 1 mm in diameter were made by the sputtering of Al or Pt; the ohmic contact to the bottom Si electrode was formed by scratching the InGa paste. The use of the MIS structures with the bottom electrode of the n-type silicon allows us to determine the charges in the graphene oxide, evaluate its dielectric permittivity and provide the injection of holes under the negative bias that was applied to the top electrode. The use of aluminum as a top metal electrode allows the experimental verification of one of the switching mechanisms that is listed above, whereas Al fusibility can be employed to visualize the conductive channels under a high current flow. The use of the MIS structures also makes it possible to apply the method of electron beam-induced current to detect the conductive channels that are formed during the resistive switching processes. The GO film switching characteristics were studied by the DC current–voltage measurements using the Keithley 2450 Source Meter. To evaluate the presence of the charge traps in the GO film, the capacitance–voltage (C–V) characteristics were measured using the Keithley 4200A-SCS parametric analyzer at 100 kHz. The EBIC study was carried out using the scanning electron microscope (SEM) Jeol JSM-840 and using the Keithly 428 current amplifier at room temperature with a beam energy that was in the range from 8 keV to 30 keV and a beam current that was lower than 10−10 A, can be caused by a non-uniformity of the Al film thickness or they may reflect the difference in the conductivity of the GO flakes. An increase in a negative voltage during the subsequent I–V measurements up to 10 V resulted in a sharp increase in the current at about −5 V  are formed at higher voltages, and they can be directly detected by the EBIC due to the formation of local rectifying barriers at the GO/Si interface. These local barriers over-compensate a barrier in the pristine GO film, as shown by the change in the diode polarity in To illustrate the formation and disappearance of the conductive channels in the Al/GO/n-Si MIS structure, The presence of the GO bulk traps for the holes was established by measuring the GO-based MIS capacitors . A notabWe have investigated the operative mechanisms that are responsible for the resistive switching in the graphene oxide-based MIS structures. To the best of our knowledge, the EBIC method was used for the first time to reveal the conductive channels that are formed in graphene oxide due to resistive switching. The employment of the EBIC method enabled us to detect multiple point-like conductive channels under applied voltages of both polarities. Some of these channels can be disrupted under the bias of a reversed polarity and that is typical for bipolar resistive switching, while some new conductive channels can be formed. In addition, by using the Al/GO/n-Si MIS structures, we were able to identify unique local properties of the conductive channels. These properties are associated with a change in the charge state of a conductive channel near/at the GO/Si interface. This change is caused by either the creation of negatively charged traps or an increase in the GO work function. By increasing the maximum current that is flowing through the MIS structure, the conductive channels can be visualized by local changes to the aluminum electrode morphology. At the same time, large areas with an increased conductivity are revealed by the EBIC, and they may indicate the change of the GO bulk resistive properties. The important role of aluminum oxide in resistive switching is revealed by the C–V characteristics. An unusual dependence of the accumulation capacitance of the Al/GO/n-Si MIS structure on the bias that is in depletion is explained by the presence of a thin aluminum oxide which is connected in a series with the graphene oxide. The drift of the oxygen vacancies that are accumulated in the top GO layer is believed to be responsible for the formation of conductive filaments in a thin aluminum oxide layer. The formation of the conductive channels results in an increase in the conductivity and electrical shortening of the aluminum oxide. The presence of traps for the holes in the GO bulk may affect the resistive switching processes by accumulating and releasing the positive charge.In conclusion, at least two out of three major resistive switching mechanisms, namely metallic-like filamentary conduction and contact resistance modification due to the drift of the oxygen vacancies can operate simultaneously in the graphene oxide-based MIS structures. The third mechanism which is related to the oxidation of/reduction in the graphene oxide bulk due to the sp2–sp3 transitions cannot be excluded from consideration, but it needs additional experimental verification. The conductive channels in the GO can be revealed by the EBIC only when the local rectifying barriers are formed near/at the GO/Si interface. The creation of negatively charged traps or the change in the value of the GO work function can be responsible for the formation of such rectifying barriers.


Chinese Materia Medica and Jiangsu New Medical College record that Radix Veratri root is Liliaceae Veratrum taliense Loses. f. and the root of Veratrum stenophyllum Diels. According to traditional Chinese medicine (TCM) example, Radix Veratri is a Liliaceae plant Veratrum taliense. Another literature pointed out that the aliases of Veratrum taliense and Veratrum angustifolia are both Radix Veratri, and their effects are basically the same. The main active ingredient of Veratrum is veratramine, of which veratramine and Jervine are higher in content, reaching 24.60% and 21.28% of the total alkaloids, respectively. Veratrum alkaloids are both toxic and effective ingredients. In addition to its good clinical efficacy, attention should also be paid to its pharmacokinetic characteristics in vivo. It is particularly important to study the pharmacokinetic characteristics of veratramine and Jervine in vivo.  The goal of this study was to develop a simple and effective method for measuring veratramine and Jervine in rat plasma at the same time. This method was used to study the pharmacokinetic characteristics of veratramine and Jervine in the alcohol extract of Radix Veratri in rats, to provide a reasonable basis for the clinical use of Radix Veratri. m/z, Jervine quantitative ion pair was 426.2⟶114.1m/z, and Bullatine B (IS) quantitative ion pair was 438.2⟶420.1m/z. In the positive ion mode, the multireaction monitoring (MRM) mode was used to determine the blood concentration of veratramine and Jervine. DAS 3.3.0 was used to calculate the relevant pharmacokinetic parameters.  Eighteen SD rats were randomly assigned into three groups, half male and half female, and were given 0.04 g/kg, 0.08g/kg, and 0.16 g/kg Radix Veratri alcohol extract, respectively. Blood samples were collected at different time points and were analyzed by LC-MS/MS after protein precipitation. Bullatine was set as the internal standard; the plasma samples were extracted with ethyl acetate. After the sample was processed, acetonitrile-10 mM ammonium acetate, whose pH was adjusted to 8.8 with ammonia water, was taken as the mobile phase. Veratramine quantitative ion pair was 410.1⟶295.1r of three consecutive batches of the standard curve was greater than 0.995. Veratramine's lower quantification limit was 0.745 ng/mL, Jervine's was 1.11 ng/mL, and precision and accuracy were both less than 15%. The accuracy of veratramine was between 88.96% and 101.85%, and the accuracy of Jervine was between 92.96% and 104.50%. This method was adopted for the pharmacokinetic study of alcohol extracts of Radix Veratri. The results showed that only Cmax of veratramine female rats did not show linear kinetic characteristics in the dose range of Radix Veratri alcohol extract from 0.04 g/kg to 0.16 g/kg. For AUCt0‐ and Cmax of veratramine and Jervine, it could not determine whether the Radix Veratri alcohol extract showed linear kinetic characteristics within the dosage range of 0.04 g/kg~0.16 g/kg. Veratramine and Jervine showed obvious gender differences in the absorption and elimination stages. The absorption rate of veratramine and Jervine by male mice was about 10 times higher than that of female mice, and the elimination rate of male mice is about 20 times lower than that of female mice. It was suggested that the clinical application of the steroidal alkaloids veratramine and Jervine in Radix Veratri required rational use of drugs based on gender.  Veratramine had a good linear relationship in the concentration range of 0.0745~18.2 ng/mL, and that of Jervine was 1.11~108 ng/mL. The correlation coefficient  An LC-MS/MS analysis method suitable for the pharmacokinetic study of veratramine and Jervine in Radix Veratri in SD rats was established to provide a basis for in vivo pharmacokinetic studies. The pharmacokinetic characteristics of veratramine and Jervine in the alcohol extract of Radix Veratri were significantly different in female and male rats. During the clinical use of Radix Veratri, it should pay close attention to the obvious gender differences that may occur after the medication. Radix Veratri is also known as small Veratri, Veratrum, small brown bag, human hair, etc. The taste is bitter, cool in nature, and highly toxic. It has the effects of dispelling blood stasis and swelling, analgesic and hemostasis, lowering blood pressure –3, expecThe paper's organization paragraph is as follows: The materials and methods are presented first. Second are experimental results of the proposed work. Thirdly, it consists of the results and discussion sections. Finally, the research work is concluded.Veratramine and Jervine reference substances' purity was no less than 98%, which were purchased from Nanjing SenBeiJia Biological Technology Co., Ltd. . Bullatine B  was purchased from the Beijing Shengshikangpu Chemical Technology Research Institute (batch number: N-019-150906). Heparin sodium  was purchased from Aladdin (batch number: C162031). Ammonium acetate  was purchased from Aladdin (batch number: k1616041). Methanol  was purchased from MERCK (batch number: I0887507 717). Sinopharm Chemical Reagent Co., Ltd. provided analytical pure ethyl acetate (batch number: 20170824). Sichuan Xilong Chemical Co., Ltd. provided the ammonia  (batch number: 150324). The water was ultrapure water made by the Drug Safety Evaluation Center of Yunnan Institute of Materia Medica.μL. The mass spectrum parameters were as follows: veratramine m/z: 410.1⟶295.1, Jervine m/z: 426.2⟶114.1, and Bullatine B m/z: 438.2⟶420.1. Ion source parameters were as follows: CUR: 20.00 psi, IS: 5,500.00 V, TEM: 500.0°C, GS1: 50.0 psi, GS2: 50.0 psi, CAD: medium, and interface heater(ihe): on.The researchers used an API-3200 triple quadrupole tandem mass spectrometer and an electrospray ionisation ion source (ESI). Multiple reaction monitoring (MRM) was used to quantify the sample, which was separated on an Agilent ZORBAX Extend C18 column. The mobile phase was A (10 mmol/L ammonium acetate) and B (acetonitrile), 0-0.2 min, 10% B; 0.2-2 min, 10%-90% B; 2-5 min, 90% B; 5-5.1 min, 90%-10%B; and 5.1-7.5 min, 10%B. The flow rate was 0.4 mL/min, the column temperature was set to 20°C, and the measurement solution was 10 μg/mL, 553 μg/mL, 496 μg/mL, and 513 μg/mL. Diluted with methanol, the concentrations of veratramine were 0.745, 2.24, 6.70, 20.2, 60.5, and 182 ng/mL; those of Jervine standard working fluid were 11.1, 27.8, 69.5, 174, 434, and 1,080 ng/mL; those of veratramine were 0.745, 2.70, 25.6, and 143 ng/mL; and those of Jervine quality control working solution were 1.11, 31.6, 194, and 724 ng/mL. Quality control samples were used for precision, accuracy, matrix effect, recovery, and stability investigations. The same method was used to prepare Bullatine B (IS) internal standard working solution with a concentration of 128 ng/mL, and all working solutions were stored in a refrigerator at 2-8°C.5.45 mg and 5.53 mg of veratramine reference substance and 4.96 mg and 5.13 mg Jervine reference substance were taken, two copies each. Methanol was diluted to stock solutions with concentrations of 545 μL internal standard working solution was added into a 2 mL EP tube, blown and dried with nitrogen at room temperature, and added with 100 μL of plasma sample mixed in vortex for 2 min. Then, 40 μL 25% ammonia water was added and mixed in vortex for 1 min, and 1 mL ethyl acetate was added and mixed in vortex for 3 min and centrifuged at 6,000 r/min at room temperature for 10 min. 600 μL of the supernatant was taken and blown and dried with nitrogen at room temperature. It was reconstituted with 150 μL methanol and mixed in vortex for 2 minutes and centrifuged at 15,000 r/min at room temperature for 10 minutes, and the supernatant was taken for analysis.10 It was fully verified according to the US Food and Drug Administration's bioanalytical method verification guidelines, as illustrated in Figures y = 0.291x + 17.1 × 10−4 (r = 0.9965). The Jervine standard curve was y = 0.0462x − 5.51 × 10−3 (r = 0.9981). The lower limits of quantification of veratramine and Jervine were 0.0745 and 1.11 ng/mL, respectively, and those of RSD% were 5.49% and 0.12%, respectively.The standard curve was obtained by measuring no less than six points for each compound. The veratramine concentrations were 0.0745, 0.224, 0.670, 2.02, 6.05, and 18.2 ng/mL, respectively. The Jervine concentrations were 1.11, 2.78, 6.95, 17.4, 43.4, and 108 ng/mL, respectively. The lowest detectable concentration was used to define the lower limit of quantification. It was also repeated six times to ensure precision and accuracy. The veratramine standard curve was n = 6) and intraday (n = 6) were determined after four concentrations of quality control samples were measured, those of veratramine were 0.745, 2.70, 25.6, and 143 ng/mL, respectively, and those of Jervine were 1.11, 31.6, 194, and 724 ng/mL, respectively (The accuracy and precision of intraday (ectively . The absn = 6) was veratramine of 2.70, 25.6, and 143 ng/mL, respectively, and Jervine of 31.6, 194, and 724 ng/mL, respectively. The extraction recoveries of the two compounds were veratramine of 81.22%~94.42% and Jervine of 81.65%~87.98%  2015-030, and the laboratory animal quality certificate number was No. 51203500004128. There are 9 females and 9 males each, 7-8 weeks, the weight range of female rats was 200-230 g, and the weight range of male rats was 200-230 g. The weight difference of the grouped animals was not more than 20% of the average weight of all animals, and they were rolled into low, medium, and high dose groups, with half males and half females. Samples were collected at 0.15, 0.5, 1, 3, 6, 9, 18, 30, 48, 72, and 96 h before intragastric administration (0 h) and after administration. 0.3 mL of blood was collected from the rat's retroorbital venous plexus, placed in a centrifuge tube soaked in 2 mL of heparin sodium, and centrifuged  for 15 min, and the plasma was frozen and stored at -20°C for testing.t0‐, AUC0−∞, and T1/2. Cmax and Tmax adopted actual measured values, and other pharmacokinetic parameters adopted statistical moment parameters.The pharmacokinetic parameters were calculated using the DAS 3.3.0 pharmacokinetic program to calculate the main pharmacokinetic parameters AUCα · Dβ  was used for multidose linear relationship analysis. α, β, and the 90% confidence interval (90% CI) of the β value in the power function model were calculated using the DAS 3.3.0 pharmacokinetic program. The linear judgment interval after the criterion was changed using the DAS 3.3.0 pharmacokinetic program was 0.839-1.161, based on the bioequivalence criterion of 0.8 to 1.25. When the 90% CI of the β value fell within the linear judgment interval, the linear relationship was considered to be established; otherwise, the linear relationship did not hold.Power function model PK = The absorption rate of male mice was higher than that of female mice, and the elimination rate of male mice was lower than that of female mice, showing obvious gender differences in veratramine  and JervPower Model in the hypothesis test method was used according to the standard of 0.8~1.25, and the linear interval calculated by 1 ± ln(θL)/ln(DH/DL) < β < 1 ± ln(θH)/ln(DH/DL) should be between 0.839 and 1.161. The results of determinations of whether veratramine and Jervine in the alcohol extract of Radix Veratri showed linear kinetic characteristics within the dose range of 0.04 g/kg to 0.16 g/kg are presented in DAS 3.3.0 was employed, the In the initial selection of internal standards, the first selected compounds were aconitine, hypaconitine, Bullatine A, Wilforgine, and Bullatine B. The response of aconitine and hypaconitine could not reach the linear medium concentration, and the response was extremely unstable. Although Bullatine A and Wilforgine could achieve the required response, their chromatographic peaks were far from the target peak, and the analysis time was long, which increased the experimental cost. The peak shape of Bullatine B was good, it can be completely separated from the target peak, and it can be better dissolved in the sample. After testing, there was no Bullatine B in Radix Veratri, so Bullatine B was selected as the internal standard.Cmax of veratramine female rats did not show linear kinetic characteristics within the dosage range of 0.04 g/kg~0.16 g/kg of Radix Veratri alcohol extract. For others, it cannot be judged whether AUCt0‐ and Cmax were linear kinetic characteristics within the dosage range of 0.04 g/kg~0.16 g/kg of Radix Veratri alcohol extract.t0‐ and average Cmax of males were much higher than those of females. Female rats have considerably greater CLz/F clearance rates of veratramine and Jervine than male rats. However, there was no discernible variation in the half-life of veratramine in male and female rats, while the half-life of Jervine was considerably different in female and male rats. This was due to the fact that female rats had a considerably higher volume of veratramine dispersion than male rats, and Jervine was removed faster in female rats than in male rats. The above situation showed that after administration of the alcohol extract of Radix Veratri, veratramine and Jervine were more widely distributed in female rats than in male rats, but the clearance rate was much lower than that in female rats. In addition, at the dosage designed in this experiment, the average AUCt0‐ and average Cmax of males were much higher than that of females. The drug exposure in male rats was much higher than that of female rats, but the clearance rate was much lower than that of female rats. Male rats were more prone to accumulate toxicity in the course of long-term administration, and the symptoms of toxicity were greater than that of females.In the low-dose group, middle-dose group, and high-dose group, the average AUCThe blood drug concentration and main pharmacokinetic parameters of the Radix Veratri alcohol extract group were analyzed. The absorption rate of veratramine and Jervine by males was higher than that of female rats. Although Bullatine A and Wilforgine were able to provide the desired response, their chromatographic peaks were distant from the intended peak, and the analysis time was considerable, increasing the expense of the experiment. Male mice had a lower elimination rate than female mice, indicating clear gender differences. Finally, the clinical usage of the steroidal alkaloids veratramine and Jervine in Radix Veratri necessitates gender-based medication selection.


Furthermore, the c-GAFs were fabricated into strain sensors and showed better stability and sensitivity compared with GAF-based sensors. This work revealed the mechanism of the tunable conductivity and presented a facile and universal method for improving the electrical conductivity of macro-graphene materials in a controllable manner and proved the potential applications of such materials in flexible electronics like antennas, sensors, and wearable devices.Graphene and graphene-based materials gifted with high electrical conductivity are potential alternatives in various related fields. However, the electrical conductivity of the macro-graphene materials is much lower than their metal counterparts. Herein, we improved the electrical conductivity of reduced graphene oxide (rGO) based graphene assembled films (GAFs) by applying a series of compressive stress and systematically investigated the relationship between the compressive stress and the electrical conductivity. The result indicates that with increasing applied compressive stress, the sheet resistance increased as well, while the thickness decreased. Under the combined effect of these two competing factors, the number of charge carriers per unit volume increased dramatically, and the conductivity of compressed GAFs (c-GAFs) showed an initial increasing trend as we applied higher pressure and reached a maximum of 5.37 × 10 Graphene, as the thinnest two-dimensional material with a honeycomb lattice nanostructure that contains numerous double bonds, has been attracting prevalent attention ,2 in the3 S/m [7 S/m.Electrical conductivity is an extremely important fundamental property that represents the ability of the material to conduct current. It is also one of the determining properties of graphene and graphene-based materials for electrical applications such as sensors, electromagnetic shielding, antennas, and flexible electronics. Since the discovery of graphene, various efforts have been made to improve its electrical conductivity. For example, the relation between the distances among neighbor holes and the conductivity of graphene was predicted by simulation by Pavel et al. . To impr3 S/m . However5 S/m under the optimal compressive stress of 450 MPa and then decreased. Further, the obtained compressed graphene films were applied as strain sensors which showed good stability and sensitivity. This work provides general guidance on controlling the electrical conductivity for macro graphene materials to achieve different applications [Given the widest applicability of film materials within common macro graphene materials, this work investigated subsequent compression for improving the electrical conductivity based on graphene-assembled films (GAF) by thermal annealing. The result showed that the electrical conductivity of GAF could be regulated by applied pressure and peaked at 5.37 × 10ications ,35,36,37The GO powder purchased from Wuxi Chengyi Education & Technology Co., Ltd.  was dispersed in deionized water with solid contents of 2–4%. The obtained suspension was then stirred at 450 rpm for 4–6 h until it transformed into a gel. After carefully pouring the polyethylene terephthalate (PET) substrate into a glass mold at the proper height, the GO gel was dried up at room temperature until the GO film was formed. This newly formed GO film was peeled off from the PET substrate and then thermally annealed with the heating rate of 10 °C/min under argon shielding at 1300 °C for 2 h and 3000 °C for 1 h. The GAF was obtained after cooling to room temperature.The obtained GAF was cut into square or rectangular pieces and was then set between two PET films forming a sandwich-like structure (PET-GAF-PET) to avoid damage from the tiny machine marks on the metal plate on the test machine. The laminated structure was then compressed by a testing machine (MTS with force capacities from 1 to 3000 kN) at a speed of 0.2 mm/min until reaching the set pressure. The pressure was kept constant for 12 h. After the compression process, the PET films were peeled off from the GAF, and the c-GAF was obtained.The high-resolution transmission electron microscope  was used to observe the morphology of GO and rGO nanosheets. The cross-sectional images of GO and GAF were captured by the field-emission scanning electron microscope . The 3D reconstruction for surface morphology and cross-section of the c-GAF specimens were processed by the digital microscope . The sheet resistance of c-GAF was measured by the four-point probe system (RTS-9). The defects of molecular structures in GO and GAF were examined by the confocal Raman microscope .The c-GAFs were cut into rectangles (5 mm × 70 mm) and fabricated into strain sensors. The c-GAF strain sensors were fixed on the glass fiber-reinforced plastic (GFRP) by polydimethylsiloxane (PDMS). Foil gages (BE120-5AA) were fixed on the opposite sides of each GFRP specimen to indicate the deformations. All GFRP specimens with strain sensors were stretched by the universal testing machine  at a speed of 0.5 mm/min. The resistance of the c-GAF sensors was measured by a digital multimeter . The outputs of the foil gages were recorded by the strain gauge .2. When those gas compounds were expelled from the interior of the reduced GO film, micro-gasbags sprouted in assembled graphene nanosheets and contributed to the porous microstructures of GAF. The HRTEM image of GO nanosheets in −1 could be observed, which informs the defective carbon structure in GO film. After annealing at 3000 °C, the D peak can hardly be observed for GAF, and instead, the intensity of the G peak at 1600 cm−1 increases significantly, which indicates its higher crystallinity than GO film. In addition, the new-emerged 2D peak at 2700 cm−1 confirms the existence of graphene layers. The ratio of ID/IG was estimated to be 0.052, indicating the excellent crystal structure. The X-ray photoelectron spectroscopy (XPS) results further corroborate the much higher graphitization degree in GAF than in GO with diminished C-O peak and higher intensity of C-C peak at 284.5 eV  measurement was also conducted to characterize the functional groups as depicted in To characterize the molecular structures of the films before and after reduction systematically, Raman spectroscopy was applied. As presented in 284.5 eV b. The X-= 10.95° c indicatσ = Gl/A where G is the conductance which is the reciprocal of the resistance R, l, and A are the length and cross-sectional area of the specimen, respectively. However, the result of traditional methods to measure the resistance between any two gauging points can hardly expose the conductance of specimens in practice. To understand the rules about the electrical conductivity of the obtained GAFs, the sheet resistance which is only related to the thickness of the given material has been used. A four-point probe is a commonly used equipment to measure the sheet resistance for conductive materials, especially films with relatively large lateral dimensions. Once sheet resistance sR is obtained, the conductivity can be determined using σ = 1/sdR, where d is the thickness of the specimen. This formula indicates that the most effective way to improve the electrical conductivity is by reducing the sheet resistance and thickness of the specimen. Given that the dense structure provides a superior electric conductive network, compressing the specimen with flat plates might be a feasible method. Thus, we treated the graphene films under different flat compression loads by the universal test machine and measured the conductivity for each c-GAF to systematically investigate the relation between applied stress and electrical conductivity of c-GAF.Electrical conductivity is one of the most important indicators to evaluate the ability to conduct electricity. To a specific specimen, the electrical conductivity σ can be calculated by 5 S/m and then showed a decrease to 4.36 × 105 S/m with the stress of 550 MPa. Assume the symbol p as the compressive stress to describe the relationship between the conductivity and the applied pressure; the fit result is shown in σ = −7 × 10−10p4 + 8 × 10−7p3 − 0.0003p2 + 0.0436p + 1.4289. Together with the monotonically increasing sheet resistance , the damaged area could be observed, and the resistance increased dramatically. The sensor was broken completely when the strain approached about 0.60%; the resistance cannot be measured.In consideration of the mechanical properties of the c-GAF and GFRP, including elastic range and ultimate strain, the tensile tests for c-GAF strain sensors on GFRP were conducted by the test machine at a speed of 0.5 mm/min and maximum strain of 1%. During the stretching process, the resistance of different c-GAF strain sensors was collected at a frequency of 10 Hz by a data acquisition system, and the results are displayed in To verify the reliability of the c-GAF for application in strain sensor, the fatigue test with strain ranging from 0–0.6% (elastic range) was conducted with a c-GAF-450 sensor on the GFRP specimen. As depicted in 5 S/m to a maximum value of 5.37 × 105 S/m. It also proved that there is optimal stress at 450 MPa for c-GAF to gain the most excellent electrical conductivity, and further increasing the pressure resulted in decreasing conductivity. Furthermore, as part of the exploration of the application, comparative uniaxial tensile tests and fatigue tests for the performance of c-GAF sensors were conducted, which demonstrated the outstanding sensitivity and reliability of the c-GAF-450-based strain sensor. Based on the experimental results, our further work will focus on the conductive mechanism of the c-GAF and try to expose the rule of electrical conductivity theoretically.In summary, we proposed a universal strategy to tailor the electrical conductivity for the synthesized GAF by thermal annealing. The GAFs were compressed with stress ranging from 0 to 550 MPa to experimentally study the relation between the applied compress stress and the electrical conductivity. Encouragingly, by affecting both the thickness and the sheet resistance at the same time, the number of the charge carriers per unit volume was changed, and the electrical conductivity of the c-GAF was tunable ranged from 0.88 × 10


Two different types of graphene materials were used as functional nanofillers for the mechanical and tribological improvement of silicon carbide/graphene nanocomposites. On the one hand is thermally reduced graphite oxide (TRGO) reduced at three different temperatures, and on the other hand is graphene made of three different organic precursors, which were directly coated on silicon carbide (SiC) platelets (GSiC). Additionally, benchmark materials were also used as carbon fillers. The SiC/graphene nanocomposites with 2 wt% filler content were manufactured by pressureless sintering (PLS). Some composites were produced with higher graphene contents of 4% and 8% and sintered by spark plasma sintering (SPS). Microstructural analyses were conducted using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Underwater lubrication, the SP sintered TRGO and GSiC materials with high graphene content have shown the most promising tribological performance. Furthermore, the reduced size of the homogeneously distributed nanoparticles promotes the formation of surface states, which improve the friction and wear properties. Reliability and efficiency of these components need to be improved by using high-performance ceramics with superior tribological and good mechanical properties. The main aim of this work is to develop novel, highly efficient materials on the basis of graphene-containing silicon carbide (SiC) nanocomposites and to demonstrate their suitability for technical applications such as slide bearings and face seals in aqueous media. SiC is an advanced ceramic material which is characterized by good mechanical and chemical properties as well as a superior resistance against wear ,2. For t3N4 ,9 and bo3N4  ceramics3N4 ,12, frac3N4  and vari3N4 , a few p3N4  or under3N4 . Though 3N4 ,17,18.As reported by Zhang et al. , mechanoThe research work presented in this paper follows on from the studies of Zhang et al.  investig3 (30 g) were suspended overnight in H2SO4 . At 0 °C, the KMnO4 (180 g) was added in portions within 2 h. The suspension was then stirred for 2 more hours at room temperature. The dispersion was poured slowly on ice water (1.4 L), and H2O2  was added. The resulting mixture was filtered in a buechner funnel. The solid filter cake was rinsed several times with deionized H2O (4 × 5 L) and concentrated HNO3 . The resulting sulphate and manganese impurities in the GO were largely removed by cross-flow filtration [−1) with nitrogen cooling. After milling, the drying procedure was repeated. The dry powder was reduced in a tube furnace at 600 °C, 800 °C and 1000 °C under nitrogen atmosphere  to yield a low-density powder. Accordingly, the produced thermally reduced graphite oxides are referred to as TRGO-600, TRGO-800 and TRGO-1000. To integrate the particles homogeneously into the ceramic matrix, TRGO dispersions  were produced in water. For this purpose, the dispersion was dispersed once in the high-pressure homogenizer  at 1000 bar after an ultrasonic bath pretreatment (2 × 15 min) [Graphite oxide (GO) was prepared by oxidizing graphite via the Hummers method . Graphitltration . After dH2O2 5%, 0 mL was For the preparation of GSiC, three different precursors were used: dopamine (GSiC-D) , furfury2/g, d90 = 2 µm, QSIL Ingenieurkeramik, Frankenblick, Germany) in tris(hydroxymethyl)–aminomethane solution  using an ultrasonic bath (15 min). Then the solution of dopamine hydrochloride (2.00 g) was added to the tris(hydroxymethyl)–aminomethane solution . After stirring the reaction mixture for 72 h the water was removed by freeze-drying. The powder was mortared and carbonated in the tube furnace  in a nitrogen atmosphere. The material was heated to a temperature of 150 °C at a rate of 5 K/min, maintained for 21 h, and then increased to 1000 °C at 5 K/min and thermolyzed for 6 h.Graphene-coated silicon carbide from dopamine (GSiC-D) was first prepared by dispersing SiC  in water (200 mL). This was followed by the addition of furfuryl alcohol (15 mL). Then, after 10 min stirring, p-TsOH (0.33 g in water 10 mL) was added. After 20 min of stirring, the reaction mixture was heated up to 80 °C and held at this temperature for 1 h. After 6 h, the mixture was stirred at 100 °C until the powder was dry. After crushing the powder with a mortar, it was carbonized in the tube furnace  in a nitrogen atmosphere. The material was heated up to a temperature of 150 °C at a rate of 5 K/min, maintained for 21 h, and then increased to 800 °C at 5 K/min and thermolyzed for 6 h.Graphene-coated silicon carbide from furfuryl alcohol (GSiC-F) was produced by dispersing SiC  in water (90 mL) by ultrasonic bath (2 × 15 min). Then the solution of D(+)-glucose (2.00 g in 10 mL water) was added. After predispersion by using an ultrasonic bath (2 × 15 min), the reaction mixture was completely dispersed under ice cooling via an ultrasonic lance. After freeze-drying, the powder was mortared and carbonated in the tube furnace  in a nitrogen atmosphere. The material was heated up to a temperature of 150 °C at a rate of 5 K/min, maintained for 21 h, then increased to 800 °C at 5 K/min and thermolyzed for 6 h.Graphene-coated silicon carbide from glucose (GSiC-G) was produced by dispersing SiC  and BG-grade M (GnP® Grade M–15) both delivered by XG sciences.Four different carbon fillers were chosen as commercially available benchmark materials: Graphite (KFL99.5 graphite AMG Mining), carbon black  and two types of benchmark graphene nanoplatelets (BG): BG-grade C  was performed by using a vario MICRO cube . The specific surface area was measured by the adsorption of nitrogen according to Brunauer–Emmett–Teller (BET) theory by using a Sorptomatic 1990 . The graphene content on top of the coated SiC-particles was measured by thermogravimetric analysis . The mass loss was determined as the filler content in comparison to pure SiC . Scannin2/g, d90 = 2 µm, QSIL Ingenieurkeramik, Frankenblick, Germany) and sintering aids  with the desired amount of graphene material in a planetary ball mill  for the duration of 4 h and a sharker mixer  for another 4 h. TRGO was incorporated in the form of a stable aqueous dispersion . After screening (grain size 63 μm), the sample was redried and granulated by freeze-drying. The granules (grain size < 180 μm) were then compacted to test plates  and sintered by a conventional solid phase sintering process using sintering parameters that generally lead to highly densified microstructures for silicon carbide ceramics . Test specimens were milled from the sintered plates.SiC/graphene nanocomposite slurries were prepared by blending SiC . SPS is a new technique and enables fast and energy-efficient sintering of ceramic parts. However, SPS is only possible with sufficient contents of electrically conductive fillers. This was the case for samples with 4% and 8% of graphene fillers. For this sintering process, the conductive powder (>20 Ωcm) was compacted between two highly conductive graphite punches . A current was applied to the punches (max. 10 V) until the sinter temperature 2050 °C was reached. The sample was then sintered at this pressure and temperature for 5 min in an argon atmosphere.The density of SiC/graphene nanocomposites was measured by using Archimedes’ method in water. The four-point bending strength (σ) values of ceramic nanocomposites were determined in accordance with DIN EN 843-1 on bars with dimensions 3 mm × 4 mm × 45 mm at ambient temperature and atmosphere. The fracture toughness was measured by the Single Edge V-notch Beam  method. The specimens with dimensions 3 mm × 4 mm × 45 mm were ground and polished by a 15 µm diamond grinding wheel before testing. A sharp V-notch using the razor blade and diamond paste  with total depth of between 0.8 mm and 1.2 mm was prepared. Electrical resistance measurements were performed on specimens with a dimension of 3 mm × 4 mm × 45 mm. The contact area of the specimens was coated with silver paste to assure good contact with the crocodile clip. The specific conductivity was calculated from these values.a: 0.65 µm, Hexaloy SA, Eagle Burgmann, Wolfratshausen, Germany) were performed using a standard pin-on-ring setup . The graphene-containing pins had a spherical tip with a radius of 5 mm and had dimensions of 10 mm × 4 mm × 4 mm in length, width and thickness. The contact geometry of a spherical tip ensures that an initial point of contact is established; thus, there is no risk of contact misalignment. The initial contact stresses were calculated according to Hertzian equations. The normal force and sliding speed were 50 N and 0.1 m/s; consequently, the initial contact pressure amounts measured up to 2.7 GPa. A drawback of the use of a spherical tip radius is that, due to wear of the pins, the contact area continuously increases during the sliding test, which leads to a continuous decrease in the contact pressure. In order to avoid hydrodynamic influence, which would affect the comparability of the results, the test duration was restricted to 4 h. It was therefore ensured that the contact pressures were at least 10 MPa throughout the whole test. The tests were conducted under water-lubricated conditions at room temperature and repeated twice. As reference material combination, SSiC pins without graphene (SSiC#137) were tested against SSiC face seal counter rings under the same conditions.Sliding tests of graphene-infiltrated SiC ceramics against commercially available SSiC face seal counter rings  to determine the wear volumes and wear mechanisms. In the SEM analyses, a low electric voltage of 3 kV and a SE detector were used to resolve surface changes due to wear with high contrast. For selected samples, atomic force microscopy (AFM) was carried out to detect tribologically induced layer formation on top of the surfaces .As it is apparent from As shown in the TEM images in The morphology and particle sizes of the four different benchmark materials are shown in The wear results of the pins are shown in In order to summarize the best results of the pin-on-ring tests, the COFs measured after 4 h are plotted in relation to the respective wear volumes for selected tribosystems in The worn surface of the reference material SSiC#137 is shown in In contrast, there is no microcracking on the surfaces of the TRGO-containing pins after sliding . Sinter Finally, A more surface-sensitive analysis was carried out with scanning electron microscopy using an in-lens detector and, additionally, AFM of the worn surfaces. A representative SEM image of a worn surface of a silicon carbide ring is shown in The starting point of this research work was the analysis of the tribological behavior of SiC ceramics containing graphene in aqueous media, in light of a technical application of these innovative materials for bearings in pumps. Therefore, two different types of graphene materials were chosen: thermally reduced graphite oxide (TRGO), reduced at three different temperatures , and graphene made from three different organic precursors, which was directly coated on SiC platelets . Additionally, four commercially available carbon benchmark materials were chosen as fillers.The material synthesis of SiC-based nanocomposites is very complex, since it depends on a lot of subsequent manufacturing steps, starting with powder synthesis, mixing and processing, shaping and sintering. Our goal was to reach considerable graphene contents to improve tribological properties without losing too much mechanical strength. Concerning the mechanical properties, it is very difficult to reach sufficient mechanical strength (>300 MPa) at higher graphene contents. The problem may be at this point that the carbon fillers act as a diffusion barrier during the sintering process, thus preventing densification and formation compact and pore-free microstructures. If agglomeration cannot be completely prevented, the formation of large microstructural defects is inevitable. In light of the mechanical properties see , it is nFocusing on the microstructural aspects, in the case of GSiC materials, the precursor has to be taken into account. As shown in the results, different numbers of graphene layers can be obtained on the SiC depending on the precursor. In accordance with the observed friction and wear behavior of GSiC-D and GSiC-G, the following applies: The tribological properties are improved if SiC is coated with only few graphene layers so that the filler can be distributed finer within the matrix.From the results obtained, meaningful correlations can be made between the size of the specific surface and the mechanical and tribological properties. The specific surface area of BG-grade C is significantly increased compared to the other benchmark materials, and a significantly improved tribological behavior can be observed. A high specific surface area of the graphene correlates with good mechanical and tribological properties, as they are distributed homogeneously in the SiC matrix, resulting in a defect-free microstructure. For normally sintered SiC ceramics containing 2% TRGO, however, no influence of the specific surface on the tribological behavior can be observed. It is assumed that here the difference in the specific surface is not large enough to significantly affect friction and wear.In addition, the positive influence of SPS sintering leads to improved microstructural properties, which have a positive effect on mechanical and tribological performance. A necessary condition for this sintering process is the sufficiently high electrical conductivity of the ceramic green body. This can be improved by increasing the filler content and by a homogeneous distribution of the graphene in the SiC matrix.In this respect, ceramics with already good tribological properties such as 4% GSiC-containing SiC nanocomposites provided evidence that they are predestined for this process.2O to form strongly hydrated silica layers on the sliding surfaces [Tribochemical reactions: It is well-known that, under water lubrication, SiC reacts chemically with Hsurfaces ,29. ThesSurface passivation by graphenization: There is a strongly growing interest in liquid superlubricity, which means lubricated frictional contacts with extremely low friction coefficients (lower than 0.01) ,31,32. AIn general, the results of the rotating pin on disc tribotests in water show that tribological improvements, i.e., reduction of friction and lower wear rates, can be achieved with increasing the filler content. Furthermore, the tribological experiments show that a homogeneous distribution of small graphene particles in the SiC matrix is desirable in order to guarantee favorable friction and wear properties. On the one hand, the homogeneous distribution ensures that graphene is provided reliably and uniformly on the tribologically stressed surface, which is a fundamental prerequisite for the formation of a carbon-containing tribological film. This layer, in turn, has a friction-reducing effect, as it was verified in previous experimental works  and atomOur present results have shown that pure SiC ceramics actually may show low and stable friction under water lubrication. However, at high contact pressures, these low-friction conditions that completely depend on silica formation may become unstable . In contIn this paper, various SiC/graphene ceramic composites were examined to explore their potential as materials for face seals. Therefore, three groups of composites containing TRGO, GSiC and benchmark materials as carbon fillers were produced and tribologically tested under water-lubricated conditions. In addition to sufficiently good mechanical strength and fracture toughness, all composites—except graphite—show better friction and wear performances in an aqueous environment than the SSiC#137 reference material without graphene. Significant improvement (better than 20%) was observed for higher filled and SPS-treated samples such as all SiC + GSiC-F  materials, SiC + 4% GSiC-D , SiC + 3% TRGO-600, SiC + 4% TRGO-1000 (SPS) and SiC + 4% TRGO-600 (SPS). The results show that, besides the increase in the filler content, a homogeneous distribution of small graphene particles that are well-bonded to the ceramic matrix is necessary to achieve excellent results.With respect to previous and recent publications on wear mechanisms, we propose as a combined tribological mechanism: (1) The tribochemical formation of strongly hydrated silica acting as lubricious oxides, and (2) the release graphene during the wear process leading to partial surface graphenization and therefore chemical passivation.This material approach will therefore be very interesting in the future to develop tribological systems that may even enable stable liquid superlubricity, i.e., friction coefficients lower than 0.1.


The present paper analyses the properties of printed polylactic acid (PLA) samples with admixtures of graphene nanopowder (GNP) at wt. 1%, 2% and 4%. The pure polylactide and admixed polylactide printed samples were examined to determine their chemical-physical properties, stiffness, and strength parameters. The tests of tensile, dynamic mechanical analysis (DMA), difference thermogravimetric (TG), and differential scanning calorimetry (DSC) were executed before and after UV (ultraviolet) treatment. The first part of the paper shows the process of manufacturing granulates and filaments mixed with graphene. The second part of the paper concerns the results of the tests made on printed samples. The analysed samples were printed using a Prusa i3 MK3 printer. It transpired that the content of graphene at 1% improved the mechanical parameters of the printed composite by organising its structure. Increasing the amount of graphene caused the values of the measured parameters to drop. This research indicates how important it is to determine the optimal values of nanoadditives in biopolymers. The industry of manufacturing printed materials, commonly called 3D printing or additive manufacturing (AM), is being strongly developed in many branches. 3D printing technology, by reason of low costs and flexibility, can be applied in prototyping phases. The simplest materials taken into consideration are various polymers. The most-used method of 3D printing is fused deposition modelling (FDM), which relies upon forming a printed shape by using melted wire (filament) under certain physical conditions. Currently, PLA filament is often used in 3D printing because this material is characterised not only by good thermo-plasticity and moderately high mechanical properties, but also by good biodegradability and compatibility. PLA, regarded as biodegradable biopolymers, can be produced from plants, bacteria, mushrooms, or crustacean shells. To enhance the general strength and stiffness of polymers, some reinforcements are applied and added into the structure of polymers. These reinforcements are mostly additives such as glass, graphite, carbon, or organic fibres. Therefore, many recent works have explored the influence of different reinforcements in polymers, especially on their mechanical properties. Sanes et al. , analyseBased on the above-mentioned literature, there is a lot of research on graphene-modified polymers, but there are few analyses that concern the influence of the addition of significant amounts of graphene used in PLA samples, especially those printed from own prepared filament; therefore, this work provides a new look at these and their results. Previously, we performed similar research for samples of small additives of graphene , in whicThe first step of preparation of the samples was based on manufacturing the filament from PLA pellets  and graphene nanoplatelets . The melting temperature in the case of pure PLA and PLA admixed with graphene nanopowder (GNP) was set in the range of 180–185 °C and 150–170 °C, respectively. Setting the parameters of manufacturing pure PLA filament allowed us to achieve PLA wire with the correct diameter of 1.7–1.8 mm. Achieving the correct diameter was essential to create adequate samples during printing. An effective technique for manufacturing the PLA filament was associated with a cooling system which enabled a very fast decrease in the temperature of the hot PLA wire coming from the extruder nozzle. In the case of PLA filament with additives of GNP, the batch to extruder was adequately prepared. The schematic illustration of admixing the batch composed of PLA and graphene pellets is displayed in The addition of graphene decreased (slightly but noticeably) the flow of the mixture due to the increase in compounding density (PLA filament/graphene), which resulted in an uneven outflow of polymer from the printing nozzle. By increasing the temperature in composite PLA/graphene, the blends decreased in viscosity. In this case, the printing temperature was also set as low as possible to improve and even the outflow of the composite from the nozzle and avoid excessive degradation. Every sample was printed out using the Prusa i3 MK3 printer with a parameter setting of 100% infill. The printing trajectory was set to be 0–90° along the longitudinal axis of samples. The main printing parameters were assumed: velocity 10–70 mm/s and a single printing layer of 0.05 mm. To investigate the structure of samples, microscopic examinations were performed by employing a Leica s9i microscope with a maximum magnification of 16×. The tensile tests on samples were performed using a Shimadzu AS-X testing machine based on standard UNE EN ISO 527-1:2020-01. These tests were carried out with a constant velocity of moveable traverse of 2 mm/min. As a result of stretching the samples, the plots of force vs elongation were obtained. The dimensions of the samples were based on a standard: L = 80 mm, a1 = 15 mm, w1 = 5 mm, w = 10 mm, and mean thickness t = 4 mm . Mean we2. It is worth mentioning that the average power of UV radiation obtained on the earth coming from the sun is 62 W/m2. This means that one hour of material ageing in an applied container corresponds to about 5645 h of an exposure to a solar radiation. The prepared container was connected to a vacuum pump, forcing airflow. As a result, the ozone formed in the chamber was pumped out. The method was based on loose arrangements of samples on special bases. The entire irradiation process lasted 4 h. A four-hour exposure is equivalent to approximately one year of exposure to solar radiation [One method of determining a material’s life is treating the sample with UV radiation, determining the material’s ageing. The tested samples were placed on an appropriate stand in a glass specially lined with reflective foil. The closed container with the investigated samples was subjected to ultraviolet lamp action with a power of 35 W/cmadiation .With the aim of thermal stability determination, thermogravimetric analysis (TGA) and DTG analyses were used. Thermogravimetric analyser-TGA 550 Discovery of TA Instruments were applied for measures. The tests were conducted in an atmosphere of nitrogen in the scope of temperature from 40 °C to 600 °C with a heating velocity of 10 °C/min.DMA (DMA 850 Discovery of TA Instruments) was used by mounting the sample on the device, but the middle part of the sample was subjected to oscillating motion with a frequency of 10 Hz and amplitude of 10 µm. Firstly, the sample was cooled down to −60 °C and subsequently was heated up with a velocity of 5 °C/min to a temperature of 80 °C.DSC tests were performed by means of scanning the differential calorimeter from the Mettler Toledo company. For controlling and data elaborations, STARe Thermal software was applied. The tests were executed in the nitrogen atmosphere at a flow of 30 mL/min.This subsection presents the results of the tension of considered samples before and after UV treatment. The application of UV rays caused the supply of high-energy radiation to the PLA crystal lattice, which resulted in the shortening of the main PLA polymer lattice (degradation by electromagnetic radiation). Shorter chains are easier to change position in relation to other chains that build the polymer structure (lower coefficient of viscous friction). Shorter chains and the current energy available in the system (from UV radiation) caused the possibility of PLA crystallization. This situation meant that after UV, an increase in PLA strength was noted; however, this is a negative situation in the long term, as DMA tests proved that the storage module for non-aged samples was higher in the entire range of temperature. Static tests showed only the resistance of the crystal lattice at one temperature (room temperature), with the possibility of easy lattice relaxation (low test speed). There were no chain movements, and the main factor determining high strength was the quality and quantity of the crystal phase in the 3D print. The changes in the network were also indicated by a large dispersion in the static test of prints after ageing.Based on the data obtained from mechanical tests, it can be noticed that the statistical dispersion of the obtained results increases with the amount of graphene in PLA. This may indicate that the dispersion of the nanoclave in the PLA matrix deteriorated despite the use of solvent dispersion in DCM prior to granulation.This subsection presents the results of TGA. Taking into account that the greatest differences in the rate of weight loss were recorded in pure PLA samples compared to pure PLA after UV radiation. The reason for this is primarily the translucency of the PLA transparent radiation and the penetration of high-energy UV radiation of the PLA chains’ presence in the depths of the sample. The degradation and shortening of the polymer chains are the fastest in this case, because degradation takes place throughout the volume of PLA. Graphene retains and disperses high energy from radiation, and in addition blocks UV rays from penetrating into the PLA/graphene biocomposite. With the increase in graphene content, the thermal stability slightly increases .Based on the results of DMA, graphene applied in printed samples decreases the value of behaviour modulus a,b. ThisThe samples containing 4% graphene lost the value of a loss modulus after the ageing process. This can be explained by the fact that if the content of graphene in the PLA sample is too great, and then the graphene might have become a simple insertion. The loss moduli were also subjected to change under the influence of graphene presence and the ageing process. The single graphene decreased a loss modulus, meaning that in composite, more crystal phase exists than in the structure of a pure PLA sample. The UV process hydrolysed the PLA chains; therefore, the loss modulus was lower after the ageing process. In the case of modulus loss, composites with 1% and 2% graphene were characterised slightly by greater values of loss moduli after the UV process. It transpired that shorter chains in the presence of 1% or 2% graphene could easily move to each other at small distances. The characteristic values of DMA are shown in DMA studies on modified (plasticized) PLA are known in the literature ,28. In tThe DSC study of the produced composites allowed us to determine the changes in the structure of the PLA polymer under the influence of UV radiation, under the influence of the addition of graphene and its amount in PLA (ii), under the influence of graphene content on changes in the structure of the PLA/graphene composite, and the influence of UV radiation (iii). Graphene has a significant influence on the structure in which PLA crystallises. The research shows that the best amount of graphene tested in PLA is 1%. This significantly increased the energy of cold crystallisation (10% ↑). This means that graphene acts as a nucleation centre to accelerate PLA to form a crystalline phase. With the increase in the amount of graphene in PLA, the value of cold crystallisation energy decreased, which proves that above 1% graphene, the nanoadditive forms aggregate or there is too much of it between PLA chains, making it difficult to crystallise the polymer chains . The presence of graphene in the PLA matrix delayed the effects of degradation under the influence of UV light. Exposing pure PLA to UV action caused a slight decrease in the energy of cold crystallisation and a slight increase at the beginning of cold crystallisation. Adding 1% graphene to PLA increased the energy of cold crystallisation by 10%. This amount of additive made the ability to form PLA crystals under the influence of graphene the most effective even after degradation. The addition of 4% graphene in PLA is characterised by similar values of cold crystallisation energy to the raw PLA samples not subjected to UV treatment. With the increase in graphene content, the glass transition temperature and the energy of this transformation of the tested printed PLA polymer decreased. With 1% graphene, the decrease in the energy and temperature of this transformation was the most noticeable—by as much as 4 °C in the case of temperature and the decrease in energy value by as much as 0.1 J/gK (decrease of 20%). The glass transition temperature drop for PLA samples with 2% and 4% graphene was at the level of 5 °C and 6 °C, compared to the glass transition temperature of pure PLA. The energy value of this transformation was maintained at the level of the energy value of the composite containing 1% graphene; interestingly, the decrease in the phase transition energy of the glass transition was at the level of composites containing 1% PLA. The decrease in temperature (and thus the reduced amount of energy) of the glass transition, as well as the value of the energy of this phase transition, was caused by the increase in the distance between PLA chains due to the presence of 2D graphene. Graphene allows the polymer chains to slide between each other because it allows the chains to slide on their surface, and the increase in the interchain distance meant that the phase changes associated with the glass transition required lower energy values. Exposing pure PLA to UV action caused a decrease in the glass transition start temperature. The data obtained from the DSC test are summarized in The addition of graphene stopped this temperature drop; the strongest effect was in the case of 1% graphene in the PLA matrix, and the sample containing 4% graphene had almost identical glass transition parameters to the pure PLA sample after UV treatment. In the case of the scattering of UV radiation on the carbon nanoadditive, one would obtain an increase in UV resistance along with an increase in the amount of graphene in the composite with an increase in its amount. There was a decrease in parameters , which means that the enhancement of the UV resistance by graphene is on a structural basis, and its too-high presence in the PLA matrix may lead to a decrease in this resistance compared to pure PLA. The phase transition energy, which is melting from the solid phase to the liquid phase of PLA, was at a similar level for PLA, PLA 2% and PLA 4% graphene. The melting energy for the PLA 1% composite was 20% higher, which proves that in these samples, graphene acted as a nucleation centre, facilitating the formation of PLA crystal structures. The temperature of the beginning of the PLA melting transformation was similar for all samples. The addition of graphene in the PLA matrix did not change the nature of the PLA melting transformation in the composite. The fusion energy values and the temperature range over which this transformation occurred were similar. This means that the degree of degradation of PLA and the hydrolysis of the biopolymer chains under the influence of light was not great because graphene causes the non-transparency of the PLA/graphene composite, and thus the degradation progress is lower, as it takes place only on the surface and propagates deep into composite much slower than in the case of raw light-transparent PLA samples).The presence of GNP in PLA samples caused a slight decrease in Young’s moduli before UV radiation. However, after UV ageing, this parameter was greater compared to pure PLA (before radiation). Of course, after UV treatment, pure PLA was characterised by a weaker Young’s modulus and maximum stress. The content of GNP 1%, 2%, and 4% in samples indicated comparable strength;DMA results on GNP samples showed a decrease in storage modulus. The lowest drop of storage modulus was observed for 4% GNP samples. The greatest decrease in storage modulus was noticed for the sample with 2% graphene. It is seen that the loss modulus of aged samples containing 4% GNP decreased;TG results proved that the presence of GNP in samples enhanced thermal stability. The content of graphene of at least 1% positively affects the growth of weight loss.Graphene has a significant influence on the structure in which PLA crystallises. This is due to its direct influence on the formed crystal structure of the polymer. With the increase in the amount of graphene in PLA, the value of the cold crystallisation energy decreases, which proves that graphene can form aggregates;With the increase in the content of graphene, the glass transition temperature and the energy of this transformation of the tested printed PLA polymer decreases, and the exposure of pure PLA to UV action causes a decrease the temperature of the glass transition at the beginning;The presence of graphene in the PLA matrix delays the effects of degradation under the influence of UV light. The addition of graphene does not change the nature of the PLA melting transformation in the composite. This means that the degree of PLA degradation and the hydrolysis of the biopolymer chains under the influence of light is not great and is related to the transparency of the printed composite;Graphene changes the rheology of the bioplastic filament and requires a higher pre-production temperature. It also dissipates UV energy in the composite and protects PLA chains against radiation penetration into the composite.This paper presents the results of mechanical and physical-chemical parameters of printed pure PLA and PLA admixed with GNP. We determined the influence of graphene on the mechanical properties and the modulus of elasticity. In our research, we investigated the loss or improvement of the properties of biocomposites as a function of temperature and time after exposure to UV radiation in the ageing chamber. Based on the DSC and TG studies, the changes taking place in the structure of the biopolymer were determined. This allowed us to determine the real impact of graphene on the PLA matrix, which we have looked at comprehensively: graphene does not have significant influence on mechanical properties; therefore, graphene should not be added as modificator. We also described the degradation process of PLA in the presence of graphene. The essential aspects of graphene addition can be stated as: