Activation of peroxidase-like catalytic function of GO required hydrogen peroxide (H2O2) and ammonia (NH3) in pH 4.0 disodium hydrogen phosphate (Na2HPO4). Carbocatalytic abilities of GO were triggered in pH 4.0 deionised distilled water (ddH2O). Transmission electron microscope (TEM), scanning electron microscope (SEM), cyclic voltammetry (CV) and UV-Vis spectroscopy aided in qualitatively and quantitatively assessing GO/Ag nanocomposites. TEM and SEM analysis demonstrated the successful use of GO’s peroxidase-like and carbocatalytic properties to produce GO/Ag nanocomposite. UV-Vis analysis indicated a higher yield in optical density values for GO/Ag nanocomposites created using GO’s carbocatalytic ability rather than its peroxidase-like counterpart. Additionally, CV demonstrated that GO/Ag nanocomposite fabricated here is a product of an irreversible electrochemical reaction. Our study outcomes show new opportunities for GO as a standalone catalyst in biosensing. We demonstrate a sustainable approach to obtain graphene nanocomposites exclusive of harmful chemicals or physical methods.The present study evaluates the role of graphene oxide’s (GO’s) peroxidase-like and inherent/carbocatalytic properties in oxidising silver nitrate (AgNO Graphene is an ideal composite counterpart to create flexible electronics6, design batteries with enhanced storage capability7, prevent steel corrosion8, and shield aircraft from heat9. Real-world graphene applications have originated across several industries like the Inov-8 running trainers that employ thermal and mechanical qualities of graphene to improve their durability10. The famous sports equipment manufacturer, HEAD applied graphene to create stronger tennis rackets with lighter weight distribution10. The BAC-Mono formula racing car also uses graphene to boost strength and reduce the mass of its body parts by 20%11. Miniaturization of biochemical assays using graphene-based sensors for research and clinical purposes is now a reality with AGILER10012.Remarkable optical, thermal, mechanical, and electrical properties of graphene have captivated the imaginations of scientists worldwide10, HEAD10, BAC-Mono12, and AGILER10012 is the tip of an iceberg considering graphene’s estimated market size of $680 million by 202013. However, the reported market size for graphene was a mere $12 million in 2013, indicating that sales in the graphene industry are predominantly raw material driven14. Graphene’s annual production has peaked at 1200 tonnes per annum compared to 4600 tonnes per year of carbon fibre or carbon nanotubes14. Reported growth in the graphene industry may seem uninspiring but demonstrates the need for technological innovations that will increase graphene consumption. A surge in patent and scientific citation trends hint graphene nanocomposites as a promising area for research and application13. Unlike graphene, the role of graphene nanocomposites extends beyond improving the existing physiological properties of a host matrix13.Utilization of graphene by Inov-815. Currently, research on graphene nanocomposites heavily relies on physically or chemically coupling graphene with metal nanoparticles for utilization in a spectrum of catalytic processes24. Thus, understanding graphene’s role as a standalone heterogeneous carbon catalyst  to create nanocomposites by modifying inorganic or organic compounds is required. A simple PubMed search using the term “Graphene AND catalysis” will render over 2000 scientific articles, and the term “Graphene AND carbocatalysis” gives about ten results. Hence, less than 1% of research articles have explored graphene’s inherent or carbocatalytic properties.Catalytic properties of graphene nanocomposite help generate or store energy, reduce emission from modern automobiles, and remove pollutants from water, soil, and air26. However, pure graphene does not dissolve in organic or inorganic solvents27. Thus, researchers have functionalized the graphene surface with epoxy, hydroxyl, or carboxyl groups to obtain readily soluble graphene oxide (GO)28. Apart from GO’s carbocatalytic applications, the use of the peroxidase-like catalytic feature of GO29 is popular among researchers developing biochemical assays or biosensors to transform organic compounds30. Briefly, in the presence of hydrogen peroxide, GO can replace the horseradish peroxidase enzyme to reduce 3,3′,5,5′-Tetramethylbenzidine (TMB) from colourless to blue29. Surprisingly, GO’s peroxidase-like and carbocatalytic abilities are unexplored with the inorganic elements26.Density functional theory (DFT) calculations reveal the potential use of metal-free graphene to stabilize ground state molecules through non-covalent π-π interactionsAs a consequence, this study has investigated GO’s peroxidase-like and natural or carbocatalytic oxidation capabilities with inorganic compounds to show new opportunities for graphene as a standalone catalyst in biosensing. Specifically, the role of GO in changing silver nitrate to silver nanoparticles (Ag) to create GO/Ag nanocomposite without the use of extreme physical and chemical redox methods is explained here.29. Disodium phosphate (Na2HPO4), silver nitrate (AgNO3), hydrogen peroxide (H2O2), and ammonia (NH3) were purchased from Sigma-Aldrich, Finland29.Highly concentrated GO dissolved in water with over 95% monolayer content was purchased from Graphenea, Spain29 and facilitate the oxidation of aqueous AgNO3 to Ag nanoparticles. Therefore, GO/Ag nanocomposite synthesis was achieved by changing the concentration of GO in the presence of AgNO3 at a constant concentration and vice versa. Firstly, different GO concentrations  were independently introduced along with 100 mM H2O2, 0.1 mM AgNO3, and 40 mM NH3 to a final volume of 1 ml in 25 mM Na2HPO4 buffer at pH 4.0 and 37 °C. Secondly, several AgNO3 concentrations  were separately added with 100 mM H2O2, 40 µg GO, and 40 mM NH3 to a final volume of 1 ml in 25 mM Na2HPO4 buffer at pH 4.0 and 37 °C.GO surroundings were tailored to stimulate its peroxidase-like catalytic properties2HPO4, H2O2, and NH3 to create GO/Ag nanocomposite was assessed by lowering Na2HPO4 concentration  in the presence of 40 µg GO, 3.2 mM AgNO3, 100 mM H2O2, and 40 mM NH3 in total 1 ml solution. Particularly, the 0 mM Na2HPO4  experiment was performed with 40 µg GO and 3.2 mM AgNO3 in the presence and absence of 100 mM H2O2 and 40 mM NH3 at pH 4.0 and 37 °C. Without Na2HPO4, H2O2, and NH3, GO will depend on its natural abilities25 to convert aqueous AgNO3 to Ag nanoparticles.The need for Na3 to control for GO and vice versa. Thus, experimental controls have been referred to as GO alone or AgNO3 alone hereon. The reaction temperature for all experiments was maintained at 37 °C using a heat block, and each component was added at 15 min intervals29. The order in which each chemical was added to Na2HPO4 buffer was GO, H2O2, AgNO3, and NH3. Further, UV-VIS spectral analysis (Perkin Elmer Lambda 650) was performed between 300 nm to 700 nm 15 min after adding the last element. Specimens for changing GO and AgNO3 were performed in triplicates to measure average standard deviation across all wavelengths from 300 nm to 700 nm.In the case of experimental controls, all reaction components were included except AgNO3 alone,“Nanocomposite” refers to the GO/Ag nanocomposite absorbance at 450 nm and “Control” denotes matching GO or AgNO3 alone absorbance at 450 nm. The horseradish peroxidase (HRP) enzyme reacts with 3,3’,5,5’- tetramethylbenzidine (TMB) and is detectable at 450 nm that is extensively used for various biochemical applications32. As GO can mimic peroxidase-like activity29, the nanocomposite-to-control percentage measurements were performed at 450 nm. Equation 3. Following previously described set-up for CV33, an in-house CV was created using glassy carbon electrodes as the working and counter electrodes with an Ag/AgCl reference electrode (66-EE009) from Cypress systems. A Keithley electrometer series 2400 was utilized together with a homebuilt LabView measurement program to measure current (mA) between the working and counter electrodes, as well as difference in potential (V) between the working and reference electrodes. To avoid interference from dissolved O2, the electrolyte solution was purged with N2 gas. In all CV measurements, ±3 V was applied with a step size of 10 mV and scan rate of 38 mVs−1.Following equation was applied to measure the difference in absorbance between GO/Ag nanocomposite to GO or AgNOhttps://imagej.nih.gov/ij/ version 1.51) was utilized for measuring the average size of Ag nanoparticles on GO and adding a scale bar.Visualization studies were conducted to view the nanocomposite structures and aid in elemental analysis. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) required 5 μl of sample on Formvar/carbon coated 200 mesh copper grids. In the case of TEM, digital micrographs were acquired with Jeol JEM-1400HC  that is equipped with Quemesa  bottom mounted CCD-camera. Chemical characterization for GO/Ag nanocomposite was achieved with Zeiss EVO-50XVP SEM that is integrated with Bruker Quantax 400 energy dispersive spectrometer (EDS). Elemental maps from EDS were obtained using Bruker AXS detector 3001 with energy resolution <133 eV . The counts per second values in elemental maps were normalized. Image J (https://products.office.com/en-in/ excel version 16.32 (19120802)), Microsoft PowerPoint (https://products.office.com/en-in/powerpoint version 16.16.3 (181015)), QtiPlot (https://www.qtiplot.com/ version 10.9), Adobe Photoshop 2020 (https://www.adobe.com/in/products/photoshop.html version 21.0.2), and Adobe Illustrator 2020 (https://www.adobe.com/in/products/illustrator.html version 24.0.1).All figures were created using Microsoft Excel  to 2.93% (160 µg GO/0.1 mM AgNO3). The decline in nanocomposite-to-control percentage is observed because varying GO concentrations in the presence of 0.1 mM AgNO3 produce spectra that are only GO dominant. However, as rising concentrations of AgNO3  are subjected to 40 µg/ml GO, 100 mM H2O2, and 40 mM NH3 in 25 mM Na2HPO4, a four-fold increase in absorbance is noted between AgNO3 alone and their respective GO/Ag nanocomposites  with 0.1 mM AgNO nm Fig. . Neverth nm Fig.  at 450 ntes Fig. .Figure 13 alone rises from 47% (40 µg GO/0.4 mM AgNO3) to 77% (40 µg GO/12.8 mM AgNO3). Therefore, varying AgNO3 amounts in the presence of 40 µg/ml GO yields spectra that are GO/Ag nanocomposite dominant  or at high AgNO3 concentration (40 µg GO/12.8 mM AgNO3) as depicted in Fig. 3 concentrations  alone  or AgNOone Fig.  were vis3 1.8 mM alo3 1.8 mM alo3 1.8 mM aloant Fig. , silver ant Fig. . Nucleatant Fig. . On incrted Fig. .Figure 23 to Ag nanoparticles  in the presence of 3.2 mM AgNO3, 100 mM H2O2, and 40 mM NH3 gradually decreases the background produced by AgNO3 controls 21, and cobalt (II) acetate (Co(CH3COO)2)22 include deionized distilled water19, ethanol22, 1% BSA17, citrate buffer16, or sulphuric acid23. Ultimately, blending of GO with metal nanoparticles demands the presence of chemical agents like hydroquinone17, hydrazine hydrate20, sodium borohydride (NaBH4)24, or ammonium hydroxide (NH4OH)22 to reduce and stabilize the metal clusters on GO surface. Alternatively, extreme physical methods such as autoclave22, annealing or heating at 60 °C to 600 °C23 have been reported to create metal nanoparticles over GO.The GO/Ag nanocomposite created in this study using only natural catalytic properties of GO is simple, resource-efficient, and swift compared to old techniques Fig. . Traditi15 and our research findings . Also, the size and density of Ag nanoparticles on GO is determined by the starting quantity of AgNO3  over a finite size of GO sheet  on the fabrication of carbon nanocomposites.Among various inorganic compounds, applications of silver nanoparticles in the biomedical field is widespread and ever-increasing due to its low-cost, abundance, and fascinating properties54. Currently, the lack of standardized health and safety guidelines to assess the toxic influence of unique graphene-based technologies on human health and the environment is staggering14. In Europe, the registration, evaluation, authorization, and restriction of chemicals (REACH) regulation (EC 1907/2006) by the European Agency for Safety and Health at Work instructs wellbeing at organizations that manufacture or import harmful chemicals55. Nonetheless, the REACH regulation only applies to establishments dealing with one tonne or more graphene per year14. In 2017, the International Organization for Standards (ISO) published ISO/TS 80004:13:201756 that only clarifies technical pre-requisites for a material to be deemed as graphene or otherwise.What plastic was for the 20th century, graphene is to the 21st century. The World Bank and the United Nations have adopted several sustainable development goals to reduce the risk that plastic poses to our environment and public healthGiven the inevitable mass application of graphene and missing guidelines to prevent public health hazards and environmental risks, the research community may become the frontline in consciously assessing the carbon footprint of their innovations. In the spirit of new opportunities for graphene in catalysis like biosensing, we show that using GO’s standalone catalytic abilities will reduce the widespread dependence on harmful chemicals and extreme physical methods to obtain graphene nanocomposites.


The capability of graphene-based biosensors used to detect biomolecules, such as DNA and cancer marker, is enormously affected by the quality of graphene. In this work, high quality and cleanness graphene were obtained by CVD based on acetic acid (AA) and ammonium persulfate (AP) pretreated copper foil substrate. Hall effect devices were made by three kinds of graphene which were fabricated by CVD using no-treated copper foil, AA pre-treated copper foil and AP pre-treated copper foil. Hall effect devices made of AA pre-treated copper foil CVD graphene and AP pre-treated copper foil CVD graphene can both enhance the sensitivity of graphene-based biosensors for DNA recognition, but the AA pre-treated copper foil CVD graphene improves more (≈4 times). This may be related to the secondary oxidation of AP pre-treated copper foil in the air due to the strong corrosion of ammonium persulfate, which leads to the quality decrease of graphene comparing to acetic acid. Our research provides an efficient method to improve the sensitivity of graphene-based biosensors for DNA recognition and investigates an effect of copper foil oxidation on the growth graphene. Graphen2 annealing and nitric acid treatment. They synthesized high quality and uniform graphene on Cu by this method which can effectively reduce the impurities on Cu. Raman mapping results showed that 98.3% of the mapped area exhibited monolayer characteristics with I2D/IG > 2 compared to 75% monolayer characteristics for that grown on untreated Cu foil [Owing to all these great properties, graphene has important research value as a biosensing application ,9,10,11. Cu foil . Jeong H Cu foil . Senyild Cu foil .2/Si substrate for fabrication of Hall effect biosensor by commonly-used PMMA. As shown by microscopy, the surface of AA pre-treated copper foil and the grown graphene were the cleanest and flattest among others. At the same time, AA grown graphene and AP grown graphene could both improve the sensitivity of the biosensors to detect DNA. At the same time, the sensitivity of the Hall effect biosensor fabricated by graphene grown on AA pre-treated copper foil for the detection of DNA was significantly (≈4 times) enhanced compared with that of non-treated graphene grown on pristine copper foil and the specificity of Hall effect biosensor made of graphene grown on AA pre-treated copper foil for the detection of DNA was also greatly enhanced (≈14 times) in comparison to graphene grown on pristine copper foil. This research offers a commercial and easy way to pre-treat the copper foil for the quality improvement of graphene which has a great influence on the sensing performance of the biosensors. The Hall effect biosensor also possesses an excellent sensitivity and specificity, which can effectively distinguish complementary target DNA from one-base mismatched DNA.In this work, we adopted a convenient and economical way to pre-treat the copper foil surface by chemical etching method attempting to optimize the roughness and cleanliness of copper foil as well as the growth quality of graphene and device sensitivity based on graphene grown on pre-treated copper foil. Before CVD growth, copper foils were immersed in acetic acid and ammonium persulfate separately for 10 s. Three kinds of graphene were used to produce graphene including, non-treated copper foil, AA pre-treated copper foil and AP pre-treated copper foil. After graphene growth ended, these three kinds of graphene were transferred onto SiO4S2O8) were purchased from Sinopharm Chemical Reagent Co. Ltd. . Si substrate with 300 nm-thick SiO2 coating was bought from Bokete Technology Co. Ltd. . PMMA as well as Silicone rubber was obtained from Micro Chem Co. Ltd.  and Dow Corning Co. Ltd.  separately. All the other chemical reagents used in this experiment, including PBS buffer solution, probe DNA (5′–AGG–TCG–CCG–CCC–3′), complementary target DNA (3′–TCC–AGC–GGC–GGG–5′) and one base-mismatched DNA (3′–TCC–AGC–GGC–AGG– 5′) were all purchased from Sangon Biotech Co. Ltd. .Copper foils with 25 µm thickness (purity: 99.8%) for the growth of graphene were obtained from Alfa Aesar Chemical  Co. Ltd. Acetic acid, ammonium persulfate  was introduced for the growth of graphene on Cu foil for 20 min at 1050 °C. The CVD tube was naturally cooled down and the graphene sheet was then transferred onto a target substrate for further investigation.Three kinds of graphene were synthesized on three kinds of Cu foil by the CVD method under the same reaction conditions. The Cu foils were firstly heated from 27 °C to 1050 °C in 60 min with a fixed rate. A continuous 20 sccm HThe surface topography was characterized using scanning electron microscope  and atomic force microscope . The quality of the graphene was studied by Raman spectroscopy . The chemical compositions of graphene were analyzed by X-ray photoelectron spectroscopy . The surface free energy was analyzed by a surface tension/dynamic contact angle measurement system . The room temperature Hall effect measurements were performed with the four-point probe method, which was based on the Van der Pauw theory in our self-built system.For each detection experiment with the Hall effect biosensor, a 100-μL drop of PBS buffer was added into the testing window and maintained for 2 h to remove the influence of PBS doping on graphene, as well as infiltrate the graphene surface. Then pre-immobilization of probe DNA was maintained on the graphene surface for 12 h as to substrate the influence of probe DNA and enable it to achieve the saturation adsorption on graphene. Rinsing was then done in 1 mL PBS buffer to remove any loosely bound DNA three times. Afterwards, the target or one-base mismatched DNA varying from 1 pM to 100 nM were dropped onto the device in turn for hybridization with probes. For each concentration of target DNA, it took 3 h for hybridization, which was always followed by a rinsing step.2/Si substrate separately. In this process, PMMA played a role of the supporting layer. Firstly, a 100 nm-thick PMMA layer was spin-coated on graphene. Then, the subjacent Cu foil was removed through etching in a 0.1 M aqueous (NH4)2S2O8 solution for 5 h. After the removal, the graphene/PMMA layer was moved into deionized water three times for cleaning. The layer was then transferred onto the target substrate. Baked on a hot plate at 60 °C for 2 h, the sample would obtain a stronger bonding of graphene and the target substrate. Ultimately, the PMMA layer was removed through etching in acetone on a hot plate at 60 °C for 8 min. As shown in Scanning electron microscope (SEM) can directly reflect the micro-topography information of the sample surface. + in AA reacted with the oxide impurities on the surface of the copper foil so as to remove them from the surface of the copper foil. On the country, AP can not only remove the impurities on the surface of the copper foil but can also etch the copper foil to some extent, while AA Cu cannot directly react with Cu. Therefore, there appeared etching pits in some areas of the copper foil surface pre-treated by AP.The surface etching process of copper foils by AP and AA was illustrated in Then the graphene grown on three kinds of copper foils was observed by SEM. Through AFM, it can be observed from At the same time, the morphology of the graphene surface grown on the three types of copper foil were observed by AFM. As shown in 2 carbon atoms which can reflect the symmetry and crystallinity of graphene. The intensity ratio of G-band to D-band (IG/ID) represents the amounts of defects on graphene and structural regularity of the graphene. Larger IG/ID ratio means fewer defects, better structural regularity, and better quality of graphene. The 2D-band appears by the two-phonon participation in the resonance process. The intensity of the 2D-band is about twice that of the D-band. The appearance of 2D-band marks the electronic structure is dominated by Dirac-Weyl dispersion. The intensity ratio of 2D-band to G-band (I2D/IG) can help to verify the amount of graphene layers [2D/IG is greater than 2, graphene can be regarded as monolayer [−1, and the I2D/IG value was 2.12 indicating that this kind of graphene displayed obvious structural defects. The intensity of D peak was reduced for graphene grown on copper foil pre-treated by AP with 2D peak FWHM of 30.5 cm−1, and the I2D/IG value increased to 3.31. Almost no D peak can be seen in graphene grown on pristine copper foil pre-treated by AA which had the highest quality with the I2D/IG value of 3.74 and the FWHM of 27.9 cm−1 respectively. In general, the spectra of three kinds of graphene in this experiment all exhibited the characteristic peaks of high-quality single-layer graphene including a negligible D-band (≈1350 cm−1), an obvious G-band (≈1580 cm−1), and I2D/IG ration over 2. The value of IG/ID for pristine graphene, AP graphene and AA graphene are 6.08, 5.88 and 10.53 separately. Compared with the original graphene, AA can reduce the defects of graphene, and also improve the monolayer and surface cleanliness of graphene. According to the value of IG/ID, AP may increase some defects of graphene, which is caused by the etching of copper foil by AP directly, but the monolayer of graphene has been improved and the surface of AP graphene is cleaner. The monolayer and surface cleanliness of the graphene are the main influencing factors for the biosensor, so even if the defects are slightly improved, the performance of the biosensor can still be enhanced. In general, pre-treatment copper foil by AP and AA can both boost the monolayer and surface cleanliness of graphene while AA had the most positive effect on the improvement of graphene quality.The Raman spectrum of graphene is closely related to its molecular structure. The D-band is an important criterion for the degree of chemical modification of graphene. It can be used to determine the magnitude of defects in graphene. The increasement of D-band intensity means there are more defects on graphene . The G-be layers . If the onolayer . It can 2/V·s from 2/V·s and 942 cm2/V·s relatively which were 1.30 times and 1.80 times of the graphene grown on pristine copper foil. The sheet resistance of three kinds of graphene were 886 ohm/sq, 612 ohm/sq and 408 ohm/sq separately  between complementary target DNA and single-base mismatched DNA and a wide linear range from 1 pM to 100 nM. The device made of AA graphene processed an approximately 4 times higher sensitivity than pristine graphene device and an approximately 1.9 times higher sensitivity than AP graphene devices, respectively. Meanwhile, AP graphene can also improve the sensitivity of the device by 1.8 times compared to pristine graphene. In general, this work provides a deeper understanding of the relationship between surface quality of graphene, as well as copper foil and sensing performance of devices, enabling the advancement and optimization of graphene-based biosensors in the future.


The choice of the right material is essential in microwave processing. The carbon materials are good microwave absorbers, which allows them to be transformed by microwave heating into new carbon materials with adapted properties, capable of heating other materials indirectly. In this paper, the microwave heating of graphene as reinforcement of the lithium aluminosilicate (LAS) ceramics has been explored. LAS ceramics have a near-zero coefficient of thermal expansion and exhibit an effective and efficient heating by microwave. Nevertheless, we have found that the graphene did not show any significant response to the microwave radiation and, hence, the interaction as mechanical reinforcement with the LAS material is harmful. The possible benefits of graphene materials to microwave technology are widely known; however, the mechanism involved in the interaction of microwave radiation with ceramic-graphene composites with high dielectric loss factors has not been addressed earlier. The graphene oxide (GO) was supplied as slurry (3.2 wt % in distilled water).β-eucryptite powder were added into 100 mL of water and it was dispersed under continuous stirring for 30 min. Water suspensions of GO with two different contents (0.5 and 1 wt %) were gradually added into the 10 g of β-eucryptite suspensions under continuous magnetic stirring and then sonicated for 30 min in an ultrasonic probe . The final suspension was frozen in a liquid nitrogen bath and then dried in a freeze drier  for 24 h. The dried powder mixture was ground and sieved using 60 mesh.10 g of 111 mode with a resonant frequency of 2.45 GHz was selected as the heating cell for microwave. The electric field vectors are perpendicular to the cavity axis with the maximum electric field magnitude at the center, where the samples are located. LAS-GO powders with 0.5 and 1.0 wt % of GO were sintered under vacuum using this microwave technology . Cyl. Cyl111 2, H2O and hydrogen sulphur as SO2. The oxygen content was determined using a graphite furnace coupled with LECO VTF 900 equip. In total, 1 mg of LAS-GO powders composite was pyrolyzed to 1350 °C under a helium flow of 225 mL·min−1. The generated CO oxidizes to CO2 forming CuO, which was evaluated and thereby the oxygen content was obtained directly.The carbon, sulphur, hydrogen and nitrogen content were determined by combustion of 1 mg LAS-GO powders at 1050 °C . Under these conditions carbon is transformed into COThe composites sintered at different temperatures were found to have the following graphene contents: 0.45 and 0.90 wt % to LAS + 0.5 wt % GO and LAS + 1.0 wt % GO, respectively.Raman spectra were recorded using a Confocal Raman Microscope  with a 532 nm excitation laser. Up to 20 spectra were recorded along the whole thickness of the polished composites. The sintered samples were previously cut longitudinally in half cylinders with a diamond saw and polished  to 0.25 μm using SiC paper and diamond suspension.−3 for LAS and graphene, respectively. The relative density was calculated by dividing the bulk density with the theoretical density of the powder mixture.The bulk density of the samples was measured by the Archimedes method (ASTM C373-88) with ethanol as the immersion medium using densities of 2.39 and 2.01 g·cmNanomechanical properties such as hardness and Young’s modulus of the sintered composites were obtained by the nanoindentation technique . To carry out indentations at very low depths, a Berkovich diamond tip was used with radius less than 20 nm. In order to ensure the quality of the tip throughout the experiment, pre- and post- calibration procedures were performed for this indenter ensuring the correct calibration of its function area and correct machine compliance. The nanomechanical properties of the sintered samples were evaluated from the load-displacement nanoindentation data using the widely accepted Oliver and Pharr model .The fracture surface sections and microstructure of the sintered samples have been studied using a Field Emission Gun Scanning Electron Microscope . Specimen microstructures were thermal etching during 30 min at 100 °C below the maximum temperature to reveal grain boundaries. The average grain sizes were measured using the linear interception from FE-SEM micrographs. Approximately 100 grains for each phase were studied [A complete Raman spectroscopy study was performed to evaluate and optimise the graphene thermal reduction by microwave radiation. Raman spectroscopy is a very useful technique in order to evaluate the thermal reduction of the graphene oxide (labelled as rG) along the composite.Electrical resistivity values of LAS and LAS-rG materials are summarized in Density values were very high and close to the theoretical values for monolithic LAS materials . HoweverH) and Young’s modulus (E) values as a function of penetration depth.Some mechanical tests were performed in order to study the behaviour of the composites obtained by microwave processing. The nanoindentation technique shows a common trend clearly detected in the behaviour of hardness  of the samples sintered by microwave at 1200 °C and 1250 °C is presented in 2g phonon of sp2 C atoms (G peak) and the breathing mode of k-point photons of A1g symmetry (D peak), respectively, were observed in all the samples [−1 and an additional peak at 2945 cm−1 ascribed to the G + D combination mode induced by disorder or the D + D’ band [ samples . The eff D’ band . The resAs a result of the reduction process, non-conductive graphene oxide was transformed into a conductive material. Electrical resistivity values of LAS and LAS-rG materials are summarized in The addition of very small amounts of graphene into the LAS matrix leads to an exponential increase in the electrical conductivity of the composite in comparison to the monolithic LAS.The percolation threshold of the as prepared composites was found to be around 1 wt %, therefore, when the graphene content increases there is an increase in the intersheet connections. In the case of CNTs or CNFs, quantities around 7–10 vol% are needed in order to make the ceramic composites electrically conductive . The conThe value of electrical resistivity obtained (~4 Ω·cm) with LAS + 1 wt % rG sintered by microwave (in both temperatures), is good enough to shape the nanocomposite using the electro discharge machining (EDM) technique ,34. ThisCarbon materials are, in general, very good absorbents of microwaves, i.e., they are easily heated by microwave radiation. This characteristic allows them to be transformed by microwave heating to give rise to new carbon materials or to be used as microwave receptors, in order to heat other materials indirectly, or to act as catalysts and microwave receptors in different heterogeneous reactions. As a consequence, in recent years, the number of processes that combine the use of carbon materials and microwave heating has increased in comparison to other methods that are based on conventional heating ,18.The blank hypothesis to be tested in this work is that graphene could have a great influence on the microwave sintering behavior of LAS composites, and therefore, this may mean an increase in their final density, even at a lower temperature. In previous works, it was found that the LAS is an excellent material to absorb the microwave energy and, on the other hand it is known that the graphene has a high dielectric loss factor compared with the LAS ceramic ,36.From the results obtained, it is clear that graphene as a second phase directly affects the resulting densities of the studied LAS composites. This can be due to some important factors: the poor adherence of graphene with the LAS matrix, the lack of heat transfer by conduction from the graphene to the ceramic matrix, the agglomeration of graphene or the absence of the microplasma effect . We willThe microplasma effect would cause an increase in the local temperature of the graphene platelets. Thus, graphene platelets should be heated rapidly due to (a) high absorption of microwave radiation and (b) transfer of heat to the LAS matrix. Due to the nature of volumetric heating of microwaves, all the graphene platelets might simultaneously absorb microwaves and the temperature of the LAS particles that surround the graphene should also increase. Hence, the heating rate of the mixture would be far better than the one of the pure components, and the positive result (and expected) will be an increase of the density values even at lower temperatures than the one of the dense LAS material (1200 °C). This evidently has not happened. Therefore, the graphene is not acting as a susceptor during the sintering process, as initially thought.To verify this fact, the sintering of the same material using conventional heating at 1200 °C in vacuum with 2 h of holding time has been carried out. The obtained density values were: LAS (89.5%), LAS + 0.5 wt % rG (90.2%) and LAS + 1.0 wt % rG (91.3%). The density values were very low for all the materials, even the LAS composites with graphene that showed similar values to the ones obtained by microwave processing. Therefore, it has been shown that despite having a high dielectric loss factor and be an excellent electrical conductor, graphene does not act as a good susceptor and does not improve the sinterability of the matrix. An important conclusion is that there was no effect due to the microplasma generated by the graphene in a microwave environment.H) and Young’s modulus (E) with penetration depth. The large dispersion of H and E for the initial 200 nm of penetration depth could be due to the implicit experimental variability of factors such as tip-sample interactions, sample roughness and tip rounding. As expected, the low densities recorded for the different composites, are reflected in a sharp drop in the mechanical properties compared to those achieved in monolithic LAS materials. At 1200 °C, the composites with 0.5 wt % rG, the mechanical values tend towards the same value with the depth test. However, composites with 1 wt % rG, both E and H show a greater dependence with the penetration depth and sintering temperature. Increasing the sintering temperature up to 1250 °C, results in a slight improvement of the mechanical properties, closer to the monolithic LAS. In both cases and keeping in mind the density values, is possible to affirm that the graphene as a second phase in composites leads to a decrease in the mechanical properties, proportional with the quantity of graphene. These data also confirm that graphene is not acting as a susceptor during microwave heating.The next figure  draws thβ-eucryptite grain size reached depending on the presence of graphene, and their percentage within the matrix. The grain size of LAS decreases with the graphene content, i.e., graphene inhibits the grain growth of the matrix, and this grain in the composites is less defined in comparison to the monolithic material. The grain size of the starting powder of LAS is, approximately, 1.0–1.5 µm and the β-eucryptite grain size reached in the monolithic material by microwave is less than 2 µm [han 2 µm ,8Up to now, the graphene that should be the responsible for the microwave absorption due to a high dielectric loss factor and so, generate heat and heat the other constituent(s) by conventional modes of heating, is the one that causes the poor adherence between the graphene sheets and the ceramic matrix leading to poor mechanical properties in the composites. A possible explanation, which should be thoroughly studied, in order to explain the bad results obtained in the properties of the composites sintered by microwave radiation, is the change in the crystal structure of graphene when a perpendicular electric field was applied . Some auThis is a supposition or proposed explanation made on the basis of limited evidence as a starting point for further investigation.The 7 K−1 is obtained and 160 °C to 300 °C the value drops to −1.208 × 109 K−1. Therefore, it would be expected that adding graphene in a matrix could lead to more negative CTE values.Su et al. , measureCTE values for composites obtained by microwave technology do not exhibit the expected behavior. In the case of the composites with 0.5 wt % of rG, the CTE values are slightly lower than those obtained for the LAS monolithic material for all the sintering temperatures. In the case of composites with 1 wt % of rG, the CTE values present the same order as those obtained for the LAS material.The study of the behavior of graphene as a second phase in LAS matrix composites obtained by a non-conventional microwave sintering technique has been carried out for the first time, to the best of our knowledge, in the current investigation. The graphene oxide has been reduced in a one-step by microwave radiation, and therefore, the LAS-rG composites show a high electrical conductivity with very low graphene contents. The dilatometric data, including cryogenic temperatures, show a controlled CTE with very low thermal expansion behavior at all temperatures. The addition of graphene as a second phase, leads to near-zero values. These characteristics could lead to a variety of ceramic materials to suit engineering applications.Nevertheless, the possible potential of graphene to act as a susceptor and help to heat others dielectric materials by microwave technique is null. The mechanisms and effects involved in the graphene during the application of a perpendicular electric field are still unknown. From these results it can be concluded that graphene, despite having a high dielectric loss factor and being a good candidate to contribute in the sintering process, does not improve the density and the final mechanical properties such as hardness and Young’s modulus of LAS-rG composites. This work will enrich the current graphene-microwave knowledge.


The effects of the wet milling rotating speed on the number of graphene layers and graphene quality, and the conversion efficiency of graphite exfoliate to graphene, were investigated by scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). The results show that the number of few-layer graphene nanometer sheets (GNSs) (≤10 layers) gradually increases with the increase of rotational speed in the range of 160–240 rpm. The proportion of GNSs with 0–10 layers reaches more than 80% as the rotational speed is increased to 280 rpm. GNS defect types in the composite materials are marginal defects with minimal influence and almost no oxidation. In the range of 160–280 rpm, the intensity of graphite peak decreases and the conversion efficiency of graphene increases with the increase of rotational speed. This is the same as the experimental result obtained by HRTEM. Currently, graphene has great potential applications and is widely used in aerospace, electronics, energy, structural and mechanical engineering, environment, medicine, and packaging applications. The nano-graphene core-shell structure is an important research direction for the comprehensive performance and multiple functions of composite materials .4C as a sintering aid, added 0–5.0 wt.% GNSs as experimental raw materials, and sintered at 2130 °C for 1 h without pressure to prepare GNSs/SiC composites [x) under CmSn  conditions [8C12 in the gas phase measured by the infrared resonance enhanced multiphoton ionization technique with X = V, Nb, Zr based on first principles [2 to prepare graphene and one-dimensional graphite nanoscrolls. This study shows that graphene can be effectively obtained by mechanically shearing and exfoliating graphite in a certain medium. Ouyang et al. used plasma-assisted dry ball milling to promote the exfoliation of graphite and reduce its disorder [At present, the solid lubricant fillers used frequently mainly include graphite, carbon nanotubes, and graphene, but they have the disadvantages of low hardness and toughness. By combining solid lubricant with hard ceramic materials, the defects of low toughness and low thermal conductivity of ceramic particles can be remedied so that the lubricating effect of soft particles and the strengthening effect of hard particles can play a role together . The wramposites . Tang etmposites . When thmposites . Howevernditions . Gueorguinciples ,15 and Ginciples  developedisorder . Gorrasidisorder . Zhang edisorder . Comparedisorder . At presIn this paper, graphene-wrapped SiC nanocomposites were synthesized by wet milling method using graphite and SiC as raw materials . The effThis article is divided into three parts: introduction, materials and methods, and results. The introduction mainly collects the related research on graphene-wrapped composite materials in recent years and puts forward the research purpose of this article. The material and method part mainly explains the initial materials and specific steps of the experiment, and introduces the role of the relevant instruments in the experiment and specific parameters. The results part mainly summarizes and discusses the experimental results of SEM, HRTEM, Raman spectroscopy, FTIR, and XRD.3N4) milling ball was used as milling medium with a diameter of 5 mm, and the process control agent is ethanol and distilled water.The size of graphite flakes is about 10 μm, and for SiC nanoparticles, is about 50 nm. A silicon nitride  and distilled water solution (volume ratio = 7:3) are added to the milling jar as an abrasive medium or process control agent.The milling jar is clamped in the planetary ball mill with the clamping fixture, and the machine cover is covered. The rotating speed is set at 160 rpm, and the milling time is 50 h.When the wet ball milling is finished, the powder is dried in a vacuum drying oven and then tested.The rotational speed of the ball mill is adjusted to 200, 240, and 280 rpm, and the above steps repeated for the experiment.Graphene-wrapped SiC core-shell nanoparticles were synthesized using a planetary ball mill  at 220 V voltage and 16 A current in one step. The movement mode of the planetary ball mill is different from that of the ordinary ball mill. As shown in −1. The chemical bonds and functional groups of the composites were detected using a Fourier transform infrared spectrometer  in the spectrum range of 750–4000 cm−1, which provided a favorable basis for the quality detection of graphene.The powder after wet ball milling is dried in a vacuum drying oven . The initial materials before ball milling and the surface morphology of the composites after ball milling were observed by high resolution scanning electron microscope  at 5 kV voltage. The dispersion of graphene-wrapped SiC core-shell nanoparticles and the number of graphene layers at different rotational speeds were observed by high resolution transmission electron microscope  at 200 kV. For the detection of the conversion efficiency of graphite exfoliation to graphene, the X’Pert Powder X-ray diffractometer  was used to conduct qualitative and quantitative analysis of the composite material within the range of 2θ from 10–80°. The defect types and sizes of carbon-related materials were evaluated by Raman spectrometer  in the spectral range of 1000–2000 cmThe HRTEM morphologies of graphene-wrapped SiC nanoparticles at 160 and 280 rpm were observed  as shown in 6 times magnification) morphology of graphene-wrapped SiC nanoparticles at different speeds were randomly selected. From this figure, the graphene-wrapped SiC core-shell nanoparticle microstructure can be seen clearly. Single-layer graphene thickness is 0.335 nm and the number of layers of multilayer graphene can be calculated by HRTEM. It can be seen from As shown in Rafael Tadmor deduced the mathematical expression of the interaction energy between macroscopic objects with common geometric shapes by establishing the London–van der Waals interaction energy among different geometries , which pA is the Hamaker constant (2.38 × 10−19 j).This model can be compared to the graphite flakes and single-layer graphene in this experiment. When the shear force between the graphite flakes given by the milling ball is greater than the van der Waals force between the graphite flakes, the graphene will exfoliate from the graphite flakes. The calculation formula is as follows :(1)EA=−Ah1, h2 is the thickness of single-layer graphene at 0.335 nm, and d is the distance between two graphite layers at 0.335 nm. The calculation shows that the energy required to exfoliate a single layer of graphene from the graphite flake is 4.2 × 10−13 j. According to this method, the energy required for exfoliate 10 layers (3.35 nm) and 20 layers (6.7 nm) can be calculated.Most of the graphite flakes used in this experiment are 10 μm, which was set as the thickness of mmρ—The density of Si3N4 milling ball is 3100 kg/m3;The energy transfer from the milling ball to graphene was evaluated with the increase of ball milling speed. The calculation formula is as follows :(2)△E=π1mmd—The diameter of the milling ball is 5 mm;vmm1—The tangential velocity vmm1 of the faster milling media is 0.85 m/s;mm2v—The tangential velocity vmm1 of the slower milling media is 0.425 m/s;PY—The Young’s modulus of the final product is 230 GPa; mmY—The Young’s modulus of the milling media is 388 GPa.−8 j, which is enough to exfoliate all sizes of graphite into graphene. While ensuring that the structure of the graphite flake is not destroyed, as the speed of the ball milling increases, the tangential speed of the milling media is also constantly increasing. Therefore, the energy transferred from the milling media to the graphene is also increasing. When the ball milling speed is faster, the graphene will be exfoliated into fewer layers.The energy provided by the milling medium is 9.67 × 10The thickness of the produced GNSs was estimated from the number of layers of the GNSs in their TEM images. The layer number distribution of GNSs was obtained from 40 random HRTEM images, either standing alone or wrapping nanoparticle. As shown in In the process of counting the number of graphene layers, it was found that the number of GNSs that can be wrapped on SiC nanoparticles is often 7 layers or less, and the thick GNSs are almost all scattered in the composite material. Shown in The performance of graphene in tribological behavior is not only affected by the number of layers, but also related to the types of defects in grapheme. Wang et al. used molecular dynamics method to study the effect of vacancy defect and SW defect on the friction force of graphene. Simulation results show that the friction on graphene with both kinds of defects were obviously larger than perfect graphene in the defect regions, which was attributed to the increasing energy dissipation resulted from the extended interface barrier potential of graphene due to vacancy . Therefo−1), G peak (1580 cm−1), and D’ peak (1620 cm−1) [Shown in 20 cm−1) . 2 carbon atom and its interaction with iTO and iLO optical phonons promote the generation of G peak, which is a very rare Raman scattering process in graphene. As the D peak and G’ peak of the second-order double resonance Raman scattering process, iTO optical phonons will be generated under two inelastic scattering between valleys. Among them, the D peak is related to the scattering between iTO phonons and defect valleys, and the number is one. According to experience, the appearance of the D peak is caused by the deviation of the lattice of the graphite flake layer from the Brillouin zone, so the D peak reflects the defects of the graphene lattice. The G peak is due to the in-plane vibration produced by the σ bond bonding of carbon atoms [The vibration direction of the atom parallel to the plane of graphene is expressed as (i), the vibration direction perpendicular to the plane of graphene is expressed as (O), the vibration direction parallel to the direction of A–B carbon bond is expressed as longitudinal (L), and the vibration direction perpendicular to the direction of A–B carbon bond is expressed as (T). The in-plane vibration of spon atoms . D/IG is a recognized index for evaluating the strength of defects in carbon-related materials [D/IG intensity ratio of initial graphite is about 0.03, and the ID/IG intensity ratios in the experiments at 160, 200, 240, and 280 rpm are 0.41, 0.57, 0.59, and 0.68, respectively. Its value is much lower than that of the graphene prepared by redox method (ID/IG > 1) [D/IG > 1.5) [D/IG strength is related to the gradual thinning and exfoliation of graphite flakes into graphene and the generation of defects. There is no obvious D’ peak in the experiment with the rotational speed of 160 rpm. When the rotation speed is increased to 200 rpm, a faint D’ peak appears, which is a small part of the G peak and gradually increases with the increase of the rotational speed. According to the ratio of ID/ID’, information about the nature of the defect can be obtained. The defect types can be divided into sp3 hybridization-related defects (≤13), vacancy defects (≤7), and edge defects (≤3.5) [The intensity ratio Iaterials ,37. As c/IG > 1)  and dry G > 1.5) . From ths (≤3.5) . Accordi−1, and there is no C=O, –OH stretching vibration peak, and C–O–C vibration absorption peak related to graphene oxide [−1 are the absorption peaks of CO2 in the air.ne oxide ,41. Two It can be seen that the graphene conversion efficiency of the composites is very high after 50 h milling. With the increase of milling speed, the conversion efficiency of graphene increases gradually. At the same time, it can ensure the integrity of SiC nanoparticles to a certain extent.The conclusions obtained using SEM, HRTEM, Raman spectroscopy, FTIR, XRD, and other characterization methods for graphene-wrapped SiC core-shell nanomaterials may be equally applicable to other similar graphene-wrapped inherently nanostructure systems.In this paper, the rational speed of the ball milling was changed by wet ball milling, and the influence of different rational speeds on the number of graphene layers, quality, and conversion efficiency was analyzed.The results show that the graphene is well dispersed in SiC nanoparticles when the ball milling speed is in the range of 160–280 rpm, and graphene-wrapped SiC core-shell nanocomposites were synthesized.With the increase in ball milling speed, the proportion of few-layer graphene (≤10 layers) increases. When the rotational speed is 160–240 rpm, the proportion of few-layer graphene increases from 45% to about 70%. When the rotational speed is increased to 280 rpm, the proportion of few-layer graphene increases to more than 80%. At the same time, it is found that most of the GNSs wrapped on SiC nanoparticles are ≤7 layers.When the rotational speed is 160–280 rpm, the obtained graphene has relatively small defects, and the defect type is the edge defect that has the least impact on the quality of the graphene and, at the same time, it is almost not oxidized. Therefore, the graphene produced by wet ball milling has better quality.With the rotational speed increases, the peak intensity of graphite gradually decreases and the conversion efficiency of graphene gradually increases. When the rotational speed reaches 280 rpm, the conversion efficiency of graphene has reached an ideal state.The graphene-wrapped SiC core-shell nanocomposites prepared by wet ball milling have high quality. When there are more graphene layers, the anti-friction ability and self-lubricity are stronger. Therefore, in practical application, when the main purpose of the required materials is to reduce friction and wear, a lower ball milling rotational speed can be selected. If the composite material is for the purpose of improving the toughness, thermal conductivity, and optical properties, the ball milling rotational speed can be appropriately increased.


Meanwhile, the electro‐enhancing influence of OMe/OH groups could be switched off or inverted by conformational twisting. 267 conformational equilibrium constants measured across eleven solvents were found to be better predictors of reaction kinetics than calculated electrostatic potentials, suggesting utility in other contexts and for benchmarking theoretical solvation models.The description of substituents as electron donating or withdrawing leads to a perceived dominance of through‐bond influences. The situation is compounded by the challenge of separating through‐bond and through‐space contributions. Here, we probe the experimental significance of through‐space substituent effects in molecular interactions and reaction kinetics. Conformational equilibrium constants were transposed onto the Hammett substituent constant scale revealing dominant through‐space substituent effects that cannot be described in classic terms. For example, NO The description of substituents as electron donating or withdrawing leads to a perceived dominance of through‐bond influences. The situation is compounded by the challenge of separating through‐bond and through‐space contributions. Measurements of through‐space substituent effects question classic descriptions of substituent effects. Similarly, the computational prediction of solvent effects remains notoriously difficult.19F NMR signals corresponding to each conformer. The integral ratio corresponds to the conformational equilibrium constant, KX, which constitutes a quantitative assessment of the substituent effects on interactions occurring within the balances. Negative electrostatic potential over the X‐substituted ring would repel the electron‐rich carbonyl oxygen and contribute towards a preference for the H‐conformer in Figure KX for the 25 molecular balances shown in Figure 6]benzene , encodes the electronic effects of the X substituent on the position of the conformational equilibrium. These −log10(KX/KH) values are accordingly positive for classically “electron‐withdrawing” para‐substituents  and negative for “electron‐donating” para‐substituents . Such substituent effects are reflected in the calculated electrostatic potentials taken over the carbon positioned ipso to the conformationally exchanging formamide  for all 25 molecular balances in benzene ). The 3,5‐dinitrophenyl substituent in compound 1‐e =+1.00. Such behavior would classically be described as more electron‐withdrawing than the directly connected nitro substituent in compound 21‐NO (σp(conf)=+0.90). Strikingly, moving the two nitro groups such that they are positioned over the biaryl bond in compound 1‐d, results in a very large change in the determined Hammett substituent constant (σp(conf)=−0.17, orange in Figure σp(conf) can be attributed to the addition of a tert‐butyl group, but the σp=−0.20 for a tert‐butyl group,σp(conf) of −1.17 between 1‐d and 1‐e.The experimentally determined conformational equilibrium constants can be transposed onto the established σs Figure .2, 21 Heipso=−66 vs. −16 kJ mol−1, Figure 1‐d. Indeed, despite the large electrostatic change arising from differences in the proximity of the nitro oxygen atoms, these ESPipso values remain excellent predictors of the conformational preferences of the balances  provide insight into the large changes in substituent effects upon repositioning the nitro groups Figures  A,B. Theσp(conf)=−0.85, it might be tempting to describe the 2,6‐dimethoxyphenyl substituent in 1‐a as being even more “electron donating” than the amino group in 21‐NEt (σp(conf)=−0.66, red in Figure 1‐b (σp(conf)=+0.03, green in Figure ortho tert‐butyl groups, which sterically twist the OMe groups such that the oxygen lone pairs no longer point over the adjacent phenyl ring. Accordingly, the ESPipso value over the bridging phenyl ring in 1‐b was similar to the control compound 1‐H, which does not contain any OMe substituents  from +0.03 to +0.54 =+0.47). The electrostatic slices in Figure 1‐c.Remarkably, removing the capping methyl groups from compound 1‐a to 1‐c, ESPipso on the bridging ring changes by 78 kJ mol−1 and σp(conf) changes by ≈1.4 units =−0.11 and −0.37 vs. −0.17 and −0.85). Again, the negative sign of σp(conf) for the ortho‐nitrophenyl substituent runs counter to the traditional expectation that a nitro group is strongly electron withdrawing.Hammett constants determined in the mono‐1‐n) gave σp(conf)=+0.11, with the through‐space δ+ charge of the NH protons overcoming through‐bond resonant donor ability of the nitrogen lone pair .Positioning an amino group over the biaryl bond (meta‐methoxyphenyl substituent in 1‐k (σp(conf)=−0.31) exhibited an electro‐enhancing influence even though meta‐methoxy groups normally have net electron‐withdrawing character (σp=+0.12).meta‐nitrophenyl substituent (1‐j). However, ESP slices reveal that the bridging phenyl ring is located in the electro‐attenuated region when bonded to a meta‐nitrophenyl group, but in the electro‐enhanced region for the meta‐methoxyphenyl example .The  σp=+0.1.2 Surpripara‐substituted phenyl rings of balances 1‐h and 1‐i project their NO2 and OMe substituents along the same axis as the simple control balances 21‐NO and 1‐OMe. Accordingly, the signs and magnitude of their respective σp(conf) values (+0.72 and −0.15) are consistent with their substituent effects being projected in the same direction, but over a greater distance than the aforementioned control balances (σp(conf)=+0.72 vs. +0.90, and −0.15 vs. −0.25).The ortho to the biphenyl bond (1‐l and 1‐m) gave similar substituent effects to the control compounds 1‐H, 1‐Me, and 1‐Ph. Such findings also rule out electronic changes arising from “steric pressure”.Apolar methyl and ethyl groups positioned ipso values utilized in Figures 2=0.94, Figure S1D). Similarly, the same through‐space electrostatic potentials, in which through‐bond contributions are definitively absent, also correlated well with the experimental conformational equilibrium constants .Our observations are in accord with Wheeler and Houk's proposal that through‐space field effects, and not through‐bond polarization of the aryl π‐system, are the major determinants of non‐covalent interactions involving aromatic rings.Having convinced ourselves of the dominance of through‐space substituent effects over through‐bond polarization of the aryl π‐system, we next sought to examine whether such dominance is manifested in other contexts; namely solvent and reactivity influences.Ka values of benzoic acids in aqueous solution), even though the electronic effects of substituents can be modulated by the solvent.10(KX/KH) values for 267 substituent/solvent combinations were determined using 19F NMR spectroscopy spanning 25 molecular balances in eleven different solvents (Table 10(KX/KH) values of the simple control balances appear to be relatively insensitive to the solvent  values for the most polar substituent/solvent combinations deviate most strongly from the 1:1 line. For example, outliers in dimethylsulfoxide (DMSO) include compound 1‐a (red point), and those containing good H‐bond donors  differences in the intramolecular interactions between the O‐ and H‐conformers (ΔE), and ii) the change in Boltzmann averaged hydrogen‐bond donor and acceptor constants between each conformer (Δα and Δβ), as represented in Figure G=−RTlnKX as the αs and βs solvent H‐bond constants were varied) were fitted to the equation in Figure 2=0.85). Pleasingly, the dissected solvent‐independent ΔE values (Table S10) gave an improved correlation against the electrostatic potential over the ipso‐carbon  compared to the prior correlation against equilibrium constants determined in [D6]benzene . The improved correlation reaffirms the dominance of electrostatics in determining the conformational preferences of these molecular balances, while also showing that a simple empirical solvation model can partially account for the attenuating influence of the surrounding solvent.Hunter's α/β hydrogen‐bond model has found use in accounting for the influence of solvents on the conformational preferences of molecular balances.N‐methylation of substituted pyridines with methyl iodide as a model reaction .Having examined the transferability of the through‐space substituent effects in different solvents, we next sought to determine the significance of such effects on reaction kinetics. Inspired by previous work,n Figure  B. Such 2‐X mirrored several important trends observed in the molecular balance series 1‐X:The through‐space substituent effects on the chemical reactivity of compound series 2=0.85, Tables S14, S15). The most reactive control compound was 2‐OMe (50 % completion in ≈35 minutes), while 2‐CN was the least reactive (40+hours to 50 % completion).The experimentally determined rate constants correlate with electrostatic potentials as the X‐substituent was varied .The dimethoxyphenyl derivative ortho‐nitrophenyl compound 2‐f  exhibited similar reactivity to pyridine .The electronically neutral dimethyl‐ and diethylphenyl derivatives  was found to correlate strongly with electrostatic potential of the pyridine nitrogen atom (ESPN) . Despite the numerous commonalities outlined above, the −log10(KX/KH) values determined using molecular balances correlated surprisingly poorly with the −log10(kX/kH) pyridine rate data when both sets of data were determined in [D6]acetone  values determined in six of the eleven solvents examined were found to correlate more strongly with −log10(kX/kH)  values compiled in Table These common patterns are consistent with some transferability of through‐space substituent effects upon varying the X‐substituent. Supporting this assertion, the calculated electrostatic potentials taken over the ined in Dacetone  may also prove useful for benchmarking emerging theoretical solvation models.In conclusion, we have used synthetic molecular balances and a simple model reaction to quantify the importance of through‐space substituent effects on non‐covalent interactions and reaction kinetics, respectively Figure . Experimp Figure  C, left.p Figure . As antip Figure  and 5. Ns Figure . Even thThe authors declare no conflict of interest.As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re‐organized for online delivery, but are not copy‐edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors.SupplementaryClick here for additional data file.


The first wave of the Covid-19 pandemic hit Israel in late February 2020. The present study examines patterns of the first wave of Covid-19 morbidity in Israel at the macro level, during the period of late February to early June 2020, when the first wave has faded out. The analysis focuses on the significance of four sociodemographic variables: socioeconomic status, population density, rate of elderly population and minority status (Jewish / Arab identity) of the population in cities with 5000 residents or more. Additionally, we take a closer look into the association between morbidity rates and one SES component – home Internet access.The article is a cross sectional study of morbidity rates, investigated on a residential community basis. Following the descriptive statistics, we move on to present multivariate analysis to explore associations between these variables and Covid-19 morbidity in Israel.Both the descriptive statistics and regressions show morbidity rates to be positively associated with population density. Socioeconomic status as well as the size of elderly population were both significantly related to morbidity, but only in Jewish communities. Interestingly, the association was inverse in both cases. i.e., the higher the SES the lower the morbidity and the larger the elderly population, the lower the community’s morbidity. Another interesting result is that overall, morbidity rates in Jewish cities were consistently higher than in Arab communities.We attribute the low morbidity rates in communities with relatively small elderly populations to the exceptionally high fertility rates in ultra-orthodox communities that sustained increased rates of morbidity; the lower morbidity in Arab communities is attributed to several factors, including the spatial Jewish-Arab segregation. Israel’s first case of Covid-19 was diagnosed on February 26, 2020. On March 14, 2020, 200 cases were confirmed and additional 40–60 cases were being diagnosed daily. Two days later, on March 16, a general lockdown was declared. Mask wearing in public became obligatory on April 12th, but the requirement was hardly enforced for long weeks thereafter. Professionals offered polarized forecasts, ranging from a total of 10 deaths throughout the epidemic, to ten thousand deaths, accompanied by fatal shortage of ICU facilities, ventilators and medical staff. The first wave climaxed in early April with nearly 10,000 active cases and 500–700 additional confirmed cases a day. Since then, the spread started to slow down. Starting April 19, lockdown restrictions were gradually relaxed. As of early June 2020, Israel had roughly 2000 active cases, less than 300 deaths and a fatality rate of 1.67%, substantially lower than that of most West European countries and well below the world average of 6.15%.Scholars have suggested numerous variables that may affect the spread and scope of the pandemic, including medical resources, health coverage, life expectancy, employment rates, income inequality, levels of social connectedness and education, alongside religious affiliation, household size, population age composition, population density and ecological footprint . Of thisSocioeconomic status has often been mentioned in conjunction with rates of Covid-19 morbidity. In the UK, for instance, the disease appears to have spread along class lines. In the early stages of the outbreak, regions with higher SES were over-represented among the sick. Explanations attributed the excess to more frequent traveling and social contacts, alongside better access to testing ),Against this backdrop and the local discourse about the association between Covid-19 morbidity and the four scrutinized variables, we set off to explore the actual findings.This is a cross-sectional study, investigating all of Israel’s residential communities with more than 5000 people . It focuses on Israel’s cumulative Covid-19 morbidity figures since the beginning of national registration in February 23, 2020, up until June 2, 2020, when the first wave of the epidemic was considered to have been contained.Clalit Health Services, Israel’s largest HMO, which presented daily updates of Ministry of Health cumulative morbidity figures, by residential community.  The data includes approximately 197 municipalities in Israel.Data was retrieved from the official publication of Population density in every community, calculated as the number of residents divided by the community’s area of jurisdiction. As such, this is a continuous variable.3The communities’ SES, on a 1–10 (the highest) scale as defined by Israel’s Central Bureau of Statistics. This is calculated as continuous variable.4Proportion of local population aged 65+, thereafter called ‘elderly population’, calculated as the number of 65+ local residents divided by the community’s total population. This is a continuous variable.5Ethnic Nationality as a dichotomous variable, defining ‘Jewish’ and ‘Arab’ communities. This is a dichotomous variable.To supplement this data, we retrieved, for each community, several figures from Israel’s Central Bureau of Statistics’ publications. The added figures included:The dependent variable was the number of confirmed Covid-19 cases in each community in June 2, 2020, and their rate per thousand residents. This continuous variable may be challenged as it heavily depends on the testing policy at any given day. While acknowledging this limitation, we nonetheless consider the official morbidity rate a foundational indicator of local disease spread for several reasons. Morbidity rate was a major component in official assessments of the local spread of the epidemic and as such, was formative of related state policy. This centrality was enhanced by a report, published at the height of the epidemic first wave by the influential Advisory Team to the Center for National Security, that contended, on the basis of emerging local and global evidence, that the number of asymptomatically ill persons was not very large. In light of this clinical and policy shaping significance, we consider the Ministry of Health’s daily morbidity figures a valuable indicator for tracking the spread of Coronavirus in Israel.‘marginal effect’ of each of the study’s variables on local morbidity rates.Data is presented in two stages. First, descriptive statistics outline the distribution of the research variables and the average figures. In the second section, a multivariate analysis is carried out, in order to assess the association between each variable and a community’s Covid-19 morbidity. The regression data is then used to estimate the Looking at Israel’s morbidity rates by SES Fig. , we obseBnei Brak, Elad, Kiryat Yearim, Emanuel, Rechasim in rank 2 and Beit Shemesh, and Zefat in rank 3), which have indeed suffered the highest morbidity in the country. SES level 1 is also populated by orthodox communities. However, it also includes numerous peripheral Arab Bedouin communities. These communities were relatively less affected than communities in the two subsequent levels, as illustrated in Fig. Notably, the SES levels 2 and 3 sustained the highest morbidity rates in Israel. These categories include numerous Jewish orthodox communities  but a mere 8.9% of elderly residents. Jerusalem and Haifa, in contrast, with evidently larger proportions of elderly residents (12.3 and 27% respectively), had strikingly lower morbidity rates: 4.16 and 0.61 per 1000 respectively. A more systematic look into the communities with the highest morbidity rates  of the inter-community morbidity rate variance in Israel at the community level, by SES, density, elderly population and minority status. As shown, SES turned out to be statistically insignificant, but population density, size of elderly population and minority status emerged as significantly associated with morbidity rates. The association of each variable with COVID-19 communities’ morbidity rates is presented in Fig. The regression model thus predicts 38.1% , namely, 2.4 additional patients per 100,000 persons. As for the percentage of a community’s elderly residents, as suggested by the descriptive statistics, the regression shows a significant inverse association between this variable and communities’ morbidity rates, i.e., the smaller the elderly population, the higher the local rate of morbidity (b = − 9.16). In terms of minority status, despite their lower SES and minority status, Arab communities sustained lower morbidity rates, i.e., Jewish communities suffered 1.68 higher morbidity rates compared to Arab communities . Moreover, the Jewish-Arab gap in morbidity proved persistent. Figures The nearly horizontal SES line visualizes the lack of statistically significant association between this variable and the rate of morbidity in Israel. Population density, in contradistinction, emerged as significant, affirming the public discourse that linked crowdedness with increased morbidity. Indeed, population density emerged as the strongest association with communities’ morbidity rates (β = 0.439). A 100 person increase per kmb = − 9.1. In termThe calculation is based on the regression model, assuming that all other variables are held constant. The figures demonstrate that the higher the population density, the higher the community’s morbidity rates and the larger the elderly population, the lower the morbidity rate. Equally important: at any given value of population density or size of elderly population, the gap in morbidity rate between the Jewish and Arab cities persists, with morbidity rates consistently lower in Arab communities.In the light of the emergent gap in morbidity between Arab and Jewish communities, we divided our calculation and produced the average values of the scrutinized sociodemographic variables alongside Covid-19 morbidity rates in Jewish vs. Arab communities. Table The table reveals a clear Jewish-Arab difference: with communities twice or more richer, denser and older, Israel’s Jewish cities sustained 2.6 times the morbidity of their Arab counterparts. Whereas these figures accord with international findings regarding population density and proportion of elderly residents, the higher morbidity in richer cities is exceptional. In other words, Israel’s Arab communities, despite being much poorer and despite belonging to an underprivileged minority, sustained less than half the morbidity of their wealthier Jewish neighbors. Therefore, we examined how these variables are associated with morbidity in Jewish vs. Arab communities. The linear regression analysis presented in Table The analysis shows that when considered on its own, SES (Model 1) becomes significant in the Jewish communities though not in the Arab ones. Thus, in Israel’s Jewish communities SES was associated with morbidity in a manner similar to that observed elsewhere, i.e., poorer communities were more vulnerable to the virus than wealthier ones. More concretely, a rise in one SES rank in a Jewish community was associated with a reduction of 0.373 sick person per 1000. In the Arab sector, no such association was found. However, once the other variables are added (Model 2), the association of SES with morbidity once again becomes statistically insignificant also in the Jewish sector. Population density (Model 2), however, proved significant and equally influential in both sectors.The third variable, proportion of elderly population, also emerged as statistically insignificant in the Arab communities but significant and inversely associated with morbidity in Jewish communities, i.e., a smaller elderly population was associated with higher morbidity. Another substantial inter-sectorial difference related to the explained variance. While explaining nearly 38% of the variance in morbidity rates in Jewish communities, Model 2 accounts for less than 11% in Arab settlements. The model thus reaffirmed the lay perception that population density was positively associated with morbidity rates. However, in contrast to international findings, SES was statistically insignificant to morbidity rates in the Arab communities and even in the Jewish sector, the association was weak.Finally, some Israeli commentators attributed the high morbidity rates in some ultra-orthodox communities to the scarcity of home and mobile Internet access in these communities, that wish to maintain but minimal contact with their non-orthodox surrounding.  This virtual detachment was assumed to underlie the communities’ lack of awareness and belated application of the protective measures and lockdown guidelines. We therefore zoomed in on this specific component of the SES index and conducted a specific linear regression.The general regression revealed no association with internet access. Sector specific analyses Table  found thHowever, the latter association was substantial: a 10% increase in home internet access in Jewish communities was associated with a morbidity decline of 0.3 person per 1000. The resemblance to SES patterns is reasonable, given the fact that internet access is a component of the SES index.Figure We now turn to discuss the observed trends and particularities and propose some lines of explanation.opulation density was the only variable that emerged as statistically significant to morbidity in the entire Israeli population. In Arab communities, the lower density - 2037 vs. 3853 persons per km2 – might have contributed to the lower morbidity. The association of SES with communities’ morbidity solely in Jewish cities probably reflects the relatively narrow range of SES distribution of Israel’s Arab communities, which are largely clustered at the lower end of the SES scale. However, in the Jewish sector, too, SES was significant only when analyzed on its own and then, too, the association was moderate: massive differences in morbidity were observed among communities with similar SES7The current analysis revealed increased morbidity rates in dense, low SES Jewish communities with small elderly populations and low access to household Internet. This description befits first and foremost Jewish Orthodox communities. As mentioned, these communities have indeed suffered the highest morbidity rates in Israel. More generally, pelderly population is probably the most peculiar finding of the present study. Israel’s population is much younger than that of other industrialized countries. The main reason for the gap is the local fertility rate of 3.11 children per woman, which is nearly twice the OECD average of 1.7.Ibe. BeyondBeyond this particular difference, the analysis revealed that when density level, SES or size of elderly population are held constant as average, the prediction of morbidity rate in the Jewish communities is 1.68 times higher than in Israel’s Arab communities. This lower morbidity rate among the country’s poor minority population, as compared to the wealthier majority group, counters findings from other countries. Moreover, multi-generation households, another variable associated with higher morbidity, as mentioned, are more prevalent in Israel’s Arab communities than in Jewish ones ) As of May 20, 2020, there were a total of 1040 confirmed Covid-19 cases and five deaths in Arab communities in Israel, since the outbreak of the epidemic .To sum up, Arab communities in Israel were relatively less affected by the Covid-19 epidemic than Jewish communities, despite their relative poverty, minority status and prevalent multi-generational households. Lower population density and smaller families, alongside highly efficient community self-organization and collaboration with state bodies resulted in exceptionally low morbidity and mortality rates. In contradistinction, high morbidity was observed in Israel’s poor, crowded Orthodox communities, especially ones with very small elderly populations.The observed trends and differences may possibly offer an insight about potential state measures and the protection and inclusion that they have offered to marginalized communities in the context of pandemics. A comparison with morbidity patterns during Israel’s second wave of Covid-19 morbidity may reveal how different containment measures have affected the health and lives of various subpopulations across the social ladder.The first limitation of the current study is the focus on confirmed cases. As noted, this figure closely depends on the prevalence of testing. Moreover, assessments of the proportion of asymptomatic ill people vary widely from eight to 54% . Additi