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,Silicon Boride Powder
Silicon Boride (also known as boron silicide) is a lightweight ceramic compound made up of silicon and boron. There are silicon triboride, silicon tetraboride, silicon hexaboride, and so on.
Silicon hexaboride or hexaboron silicide is a glossy black gray powder. The chemical formula is SiB6. The molecular weight is 92.95. The relative density is 2.47 g/cm3, the melting point is 2200℃. The hardness is between diamond and ruby. Silicon hexaboride can conduct electricity. It is insoluble in water. When heated in chlorine and water vapor, the surface can be oxidized.
Physicochemical Properties of Silicon Boride Powder
The SiB6 crystal structure consists of interconnected icosahedrons (polyhedrons with 20 faces), icosahedrons (polyhedrons with 26 faces), and isolated silicon and boron atoms.
It is insoluble in water and resistant to oxidation, thermal shock, and chemical erosion. Especially under thermal shock, it has high strength and stability. The grinding efficiency is higher than boron carbide.
Surface oxidation occurs when SiB6 is heated in air or oxygen and is eroded at high temperatures by boiling sulfuric acid and fluorine, chlorine, and bromine. Borides are electrically conductive. Hexamborides have a low thermal expansion coefficient and high thermal neutron cross-section.
|Silicon Boride Powder Properties|
|Other Names||silicon hexaboride, SiB6 powder|
|Appearance||dark grey to black powder|
|Solubility in H2O||insoluble|
Preparation Methods of Silicon Boride Powder
The mixture of boron and silicon can be heated directly, the excess silicon can be removed with HF and HNO3, and the B3Si in the mixture can be decomposed with molten KOH.
Applications of Silicon Boride Powder
1 Used as various standard abrasives and grinding cemented carbide;
2 used as engineering ceramic material, sandblasting nozzle, manufacturing gas engine blade, and other special-shaped sintering parts and seals.
3. Used as an oxidant for refractories.
About Boron Carbide Powder
Boron carbide powder is hard, black, and shiny. Its hardness is lower than industrial diamond but higher than silicon carbide. Boron carbide is less fragile than most pottery. It has a large thermal neutron capture cross-section, and strong chemical resistance. It is not subject to attack by hot hydrogen fluoride and nitric acid. It is soluble in molten alkali and insoluble in water and acid. The relative density (D204) is 2.508 to 2.512. The melting point is 2350 ℃. The boiling point is 3500 ℃.
Physicochemical Properties of Boron Carbide Powder
Boron carbide does not react with acid and alkali solution and has high chemical potential. It has the properties of neutron absorption, wear-resistance, and semiconductor conductivity. It is one of the most stable substances to acids and is stable in all concentrated or dilute acid or alkaline water solutions. Boron carbide is basically stable under 800℃ in the air environment.
When some transition metals and their carbides coexist, they have special stability. The transition metals ⅳ, ⅴ, and ⅵ in the periodic table react strongly with boron carbide powder to form metal borides at 1000 ~ 1100℃. At higher reaction temperatures, it has been reported that boron carbide tends to nitride or react with transition metal oxides to form corresponding boron nitride and borides, which are mainly rare earth and alkaline earth metal hexaborides.
It has a Mohs hardness of about 9.5 and is the third hardest substance known after diamond and cubic boron nitride, which is harder than silicon carbide.
Due to the preparation method, boron carbide is easy to form carbon defects, resulting in a wide range of boron to carbon ratio changes without affecting the crystal structure, which often leads to the degradation of its physical and chemical properties. Such defects are difficult to be resolved by powder diffraction and often require chemical titration and energy loss spectrum.
|Boron Carbide Powder Properties|
|Other Names||B4C, B4C powder, black diamond, boron carbide powder|
|Appearance||gray black powder|
|Solubility in H2O||insoluble|
Boron carbide is suitable for hard materials of drilling, grinding, and polishing, such as hard alloy, ceramic wear parts including wear plate, pump parts, bearings, faucet, nozzle, valve parts engineering ceramics, biological ceramics, nuclear reactor pellet, lightweight body armor materials applications. Specifically,
1. Used to control nuclear fission. Boron carbide can absorb large amounts of neutrons without forming any radioactive isotopes, making it an ideal neutron absorber for nuclear power plants, where neutron absorbers control the rate of nuclear fission.
2. As abrasive materials. Boron carbide has been used as a coarse abrasive material for a long time. Because of its high melting point, it is not easy to cast into artifacts, but by melting at high temperatures, it can be machined into simple shapes. Used for grinding, drilling, and polishing of hard materials such as hard alloy and precious stone.
3. For coating coatings. Boron carbide can also be used as a ceramic coating for warships and helicopters. It is lightweight and has the ability to resist armor-piercing bullets penetrating the hot-pressed coating as a whole.
4. For the nozzle. It is used in the arms industry to make gun nozzles. Boron carbide is extremely hard and wear-resistant, does not react with acid and alkali, has high/low-temperature resistance, high-pressure resistance, density ≥2.46g/cm3; Microhardness ≥ 3500kGF /mm2, bending strength ≥400MPa, melting point is 2450℃. Because the boron carbide nozzle has the characteristics of wear resistance and high hardness, the boron carbide sandblasting nozzle will gradually replace the known carbide/tungsten steel and silicon carbide, silicon nitride, alumina, zirconia, and other materials of the sandblasting nozzle.
5. Others. Boron carbide is also used in the manufacture of metal borides and smelting of sodium boron, boron alloys, and special welding.
In today’s world, nanoparticles are playing a key role in making this world a better place by serving in different fields and industries through various means and sources. Aluminum oxide is a compound comprising aluminum and oxygen where its formula is known and written as Al2O3.
The entire chemical compound has diversity in its nature and possesses remarkable properties and characteristics which enable its production and applicability at a large scale. The prominent and most significantly used applications of aluminum oxide can be seen in the field of biomedical as they are being used in this field for quite a long time and benefiting this area of science immensely.
The improved characteristics of nanoparticles are the reason for them being utilized so much in industry and research than the bulk materials. Ultrafine particles of smaller sizes than 100 nm fabricates nanoparticles. The effects are because of its small size as a good amount of atoms are exposed on the surface when they are made from the nanoparticles. When they are made from a nanoscale, significant changes come in the behavior and performance of the materials. When they are composited from nanoparticles, enhancements are made, for instance, enhanced thermal conductivity, enhanced electrical conductivity, and enhanced strength and hardness.
Al2O3 is the chemical formula of Aluminum oxide, which is oxygen and aluminum’s chemical compound. Aluminum oxide is known as Aluminum (III) oxide and it occurs the most out of various other aluminum oxides. Commonly, it is known as alumina and can be identified as alundum, aloxite, or aloxide depending on certain applications or forms. Aluminum oxide is important for producing aluminum metal, as a refractory material because of its high melting point and as an abrasive because of its hardness.
Aluminum oxide nanoparticles
Nanosized aluminum oxide, also known as nanosized alumina, comes in the spherical form or the form of closely spherical nanoparticles, and oriented form or undirected fibers. Despite have spherical morphology, aluminum oxide nanoparticles look like white powder. They are graded as an irritant and highly flammable in both solid and liquid forms as they can be the factor in serious respiratory and eye irritation.
Properties of nanoscale colloidal alumina particles
Their fibers and particles are of a small diameter which is 2-10 nm. They have more than 100m2/g specific surface area. High defectiveness of the nanoparticles’ specific structure and material surface. Following are included in the nanoparticle’s specific structure and there is a possibility of modification in them; surface composition, structure, phase composition, degree of crystallinity, and pores’ size and volume.
Properties of the nanoscale fibers of aluminum oxide
20,000,000:1 is their length-diameter ratio. Their fibers are highly oriented. The fibers have a weak interaction among themselves. There are no surface pores in it. They have a high surface concentration of the hydroxyl groups
The dimensions and size of the nanoparticles heavily determine the nanoparticle’s physiochemical characteristics. When the size changes, there comes a difference in the atomic arrangement too in the nanoparticles. According to reports, nanoparticles have 3 distinctive layers and they are not pointed objects. The surface layer is the outermost and first layer. The surface layer is made up of metal ions or molecules and they are the reason for the functioning of the nanoparticle’s surface eventually. The shell layer is the 2nd layer and it is very different from the first and the third layer. The nanoparticle’s core is the last and third layer and it represents the nanoparticle’s basic chemical formula itself.
Thermal, magnetic, mechanical, optical, and electrical characteristics come in the general physicochemical properties. The energy levels and electrons determine the electric conductance, emission, and absorption, making optical and electronic characteristics symbiotic. Emission and spectra of absorbance are displayed by the nanoparticles. Nanoparticles’ capillary force, friction, adhesion, elastic modulus, hardness, and other mechanical characteristics are studied for facilitating these particles’ usage in the industry. When it comes to synthesizing wear resistance products, scientists use improved hardness. Long-lasting lubricants are designed by using low friction, and adhesion is used for the particle removal processes.
Nanoparticle’s thermal characteristics are determined by the kind of metal that makes up the nanoparticles. In comparison with most non-metallic compounds’ fluids or solids, a higher thermal conductivity is possessed by oxides of aluminum and metals like copper. When nanoparticles are added to these metal oxides and metals, it enables the fluid to have an enhanced thermal conductivity whereas it was a bad thermal conductor before.
Laser ablation, hydrothermal, sputtering, pyrolysis, sol-gel, and ball milling are among the many techniques that can be used to synthesize Aluminum oxide nanoparticles. However, the most commonly utilized method for the production of nanoparticles is laser ablation as it can be made in liquid, vacuum, or gas. Laser ablation offers many benefits in comparison with other techniques like high and rapid purity processes.
Moreover, one can easily collect the nanoparticles that are made through the laser ablation of materials in liquids as compared to the nanoparticles that are made through the laser ablation of materials in the gas state. A way was recently found by Max-Planck-Institut für Kohlenforschung, a chemist in Mülheim an der Ruhr for producing corundum (alpha-alumina), alumina’s extremely stable variant, in nanoparticle’s form by utilizing the simple mechanical method in a ball mill.
Derivation of aluminum oxide
Recycled alumina and bauxite mineral are the two main sources of aluminum oxide. However, bauxite mineral, aluminum’s ore is the main significant source of aluminum oxide. Instead of being a mineral, Bauxite mineral is a sedimentary rock, made up of a mixture of aluminum compounds with other nonmetals, metals, and their oxides like quartz (SiO2), magnetite (Fe3O4), and hematite (Fe 2O3). Brazil, Jamaica, China, and Australia are bauxite’s biggest manufacturers. Alumina has one small natural source but due to its frequent characterization as a gem and because of its characteristics of reflection and light absorption in the visible range when it is mixed with transition metals, it leads to a beautiful and colorful crystal.
Recycling of virgin aluminum
One of the other easy methods to obtain aluminum oxide is to recycle virgin aluminum. Due to aluminum oxide’s characteristics of hardness and durability, one can’t see the existence of the dissimilarities in functionality and characteristics of the virgin Aluminum and its recycled counterparts. In recycling, energy is utilized in a very small amount and unrecyclable Aluminum oxide’s amount is 10%, which is very low and it makes this particular source an extremely fascinating one particularly for industries like the construction industry as they utilize aluminum oxide in huge amount. Sufficient aluminum oxide is provided by these 2 sources to the world but better techniques might be used for our planet’s sustainability as mining is included.
When the bauxite mineral is obtained, then the Bayer process is used for crushing it and then purifying it to Aluminum. Just moments after sodium hydroxide’s hot solution is used to wash the bauxite mineral, aluminum is produced, and then aluminum oxide is obtained. The obtained aluminum hydroxide later gets calcinated to alumina. Rarely corundum or obtained alumina bulk is used to develop alumina nanoparticles. Laser ablation is the preferred method for the production of nanoparticles because of its versatility in nanoparticle size and the different media. The used nanoparticles are mostly pure. On interaction with the solid, the laser beam produces a plasma and evaporates to molecules and their clusters.
Formation of fumes
A fume is produced by the evaporated particles and it is expanding with time. On further expanding, it interacts in the setup with an ambient gas or a different fluid that meets with it for forming alumina nanoparticles. X-ray diffraction (XRD), transmission electron microscopy (TEM), and emission spectroscopy were then used to analyze the nanoparticles for characterizing the collected type of nanoparticles.
Applications of Aluminum Oxide Nanoparticles
Aluminum nanoparticles have been utilized in ordered mesoporous aluminum oxide’s form to enhance Telmisartan’s oral delivery as a poor-water soluble compound. Telmisartan is an anti-blood pressure drug. Evaporation induced self-assembly method synthesized ordered mesoporous aluminum oxide. X-ray diffraction (XRD), scanning electron microscopy, and Fourier transforms infrared then characterized it and then its pores were loaded with Telmisartan through the usage of a solvent impregnation method. Loading efficiency of 45% was seen between the nanoparticles and the drug in results. Moreover, when ordered mesoporous aluminum oxide was being loaded, it led to the release of Telmisartan and its major dissolution.
Aluminum oxide-ibuprofen nanocomposite’s sol-gel was fabricated in another study for increasing ibuprofen’s bioavailability. This was the reason for the fabrication of nano-aluminum oxide by aluminum oxide alkoxide’s controlled hydrolysis, followed by loading of the nano-aluminum oxide particles with the ibuprofen that’s insoluble in water. Then, Thermogravimetric analysis, Fourier transform Raman spectroscopy, Emmett and Teller method, Brunauer, UV-Vis spectrophotometry, and XRD analysis was used to characterize the prepared nanocomposite.
Effect on solubility
In sol-gel nanocomposite’s form with the aluminum oxide, there was a major increase in ibuprofen’s solubility and controlled release. The main mechanism and reason behind these significant increases is some of the characteristics of the sol-gel nano-aluminum oxide’s surface for instance high density of hydroxyl groups, highly porous structure, and high surface area. In this study, the major revelation is of the suitability of the nano-aluminum oxide particle of this type as an efficient and effective drug delivery vehicle.
There have been recent reports on the usage of aluminum nanoparticles as novel platforms to detect various molecules. Aluminum oxide nanoparticles are utilized for sensing bovine serum albumin. Self-assembled anodic aluminum oxide modified LSPR (localized surface plasmon resonance) sensor’s surface for performing the biosensing. In self-assembled anodic aluminum oxide, a well-organized aluminum oxide nanohole structure was produced on an LSPR chip. Nanocarbon-modified aluminum oxide nanocrystal’s shell/core was utilized in another study for sensing the DNA in a competitive bioassay. Easy surface engineering was enabled by this carbon layer and that’s why it was utilized as a platform for increasing aluminum oxide nanocrystal’s surface reactivity, biocompatibility, and stability.
Florescent nature of aluminum oxide
Aluminum oxide nanostructures and their fluorescent nature was implemented for various detection purposes like in vitro DNA detection, intracellular cargo monitoring, and cell imaging, for the purpose of them being used in biosensing applications. Moreover, there have been reports that aluminum nanoparticles have the ability of sensing chemicals. Just like this feature, aluminum oxide nanoparticles are also utilized with chitosan for detecting phenolic molecules as a nanocomposite. Aluminum nanoparticles were decorated on a chitosan film and then fabricated nanocomposite was loaded with horseradish peroxidase (HRP).
A modified pulse anodization process was used to fabricate aluminum oxide nanomaterial in the nanotubes’ form containing Thapsigarin, they were then loaded with Thapsigarin. An autophagy inhibitor, 3-methyladenine co-administered Thapsigarin for targeting autophagy signaling in both the normal and the cancerous cells. Aluminum oxide nanotube loaded with Thapsigarin displayed no cytotoxic effect in the normal cells however in the cancer cells, it induces autophagy signaling, referring to the ability of the aluminum oxide nanotubes for anti-cancer therapy as a new generation of the drug delivery vehicle. There have been reports on the anti-cancer characteristics of the spherical nano-aluminum oxide particles other than their suitability for cancer therapy. Rajan Y.C. et al. fabricated poly-glutamic acid-modified aluminum nanoparticles in this study and implemented them as cytotoxic agents for inducing the death of the cell in the prostate cancer cells. Aluminum nanoparticles displayed cell toxicity towards the treatment of PC-3 prostate cancer cells.
Surface potential and viability
In another study, increased surface zeta-potential was shown by the nano-petal AlNPs-treated mouse neuroblastoma Neuro-2a cells towards the negative values along with decreased viability. The shape of the utilized aluminum oxide nanostructures determines the zeta potential’s value and cell viability’s percentage. Cell toxicity of the highest level was showed by nano-petal aluminum oxide, followed by wedge-like nanoparticles and nanoplates. Aluminum nanoparticles showed the highest change in cell surface’s zeta potential.
AINPs are also utilized as an adjuvant in cancer immunotherapy in vivo and in vitro as an enhanced cancer treatment strategy in which aluminum nanoparticles were utilized as a cancer antigen carrier to dendritic cells’ autophagosomes, effectively presenting the delivered antigens to the T-cells. AlNPs applications lead to a major increase in the amount of the activated T-cells, resulting in provoking a significant cancer remission and potent anti-tumor activity of these cells. Moreover, it is proved in this study that when it comes to boosting cancer vaccines’ efficacy, the potential candidate is AINPs.
Aluminum nanoparticles exhibit strong antimicrobial activities due to their large surface area. Sadiq M. et al. proved aluminum nanoparticle’s anti-Escherichia coli (E. coli) property in his study, in which bacterium E. coli incubated 179 nm-sized-AlNPs of different concentrations. Scientists observed a mild anti-growth effect because of the electrostatic interaction between the bacterial cells and the nanoparticles. Moreover, a small decrease was seen in the bacterium’s extracellular protein content. In another study, aluminum nanoparticles displayed anti-growth effects which were originated from nanoparticle’s direct attachment to these bacterial cell walls.
Aluminum oxide as a silver nanocomposite
When utilized in aluminum oxide–silver nanocomposite’s form, great antimicrobial characteristics are shown by the aluminum oxide nanomaterials against Staphylococcus epidermis (S.epidermidis) and E.coli, which refers to the nano-aluminum oxide’s potential biomedical applications as the composite structures.
There was another research in which aluminum oxide nano-coatings, in the form of aluminum oxide core/Fe3O4/shell magnetic nanoparticles, displayed remarkable magnetically-derived photothermal killing effects on various drug-resistance, gram-positive and gram-negative bacterial isolates. The aluminum oxide shell is a recognizer of bacterial cells in this intelligently designed nanocomposite. Although, the Fe3O4 core subsequently kills the bacterial cells photothermally. In addition, a magnetic field is used to use the core Fe3O4 for guiding the nanoparticles towards the bacterial cells.
Treatment of other diseases
Vasoactive intestinal peptide conjugated Alpha-Aluminum nanoparticles and was utilized as anti-asthmatic nano-drugs for preventing the mouse model from getting allergic asthma. The vasoactive intestinal peptide was protected against enzymatic degradation in the asthmatic mouse model’s lung by using alpha-aluminum nanoparticles, and they displayed a strong anti-asthmatic activity than the non-conjugated vasoactive intestinal peptide and beclomethasone.
Nano-thrombolytic system has been used to explain AINPs’ potential advantages. AINPs sol-gel form was loaded with the thrombolytic enzyme streptokinase for showcasing this potential. When they have a size of less than 500 nm, an efficient and effective thrombolytic activity was seen on various samples by prepared streptokinase-aluminum nanoparticles along with streptokinase’s sustained release.
Bimolecular preservation and stabilization
According to Volodina V.K. et al’s study, protein molecules can be correctly folded by the aluminum nanoparticles and they can be the nano platform for that. Aluminum nanoparticles interact with the denatured negatively charged proteins electrostatically for being utilized as a renaturing material. They also prevent the misfolding and aggregation of the denatured negatively charged proteins. Until the un/misfolded protein folds correctly, the refolding process is kept under control by the aluminum nanoparticles in addition to the reaction.
A major target of next-generation vaccines and immunotherapy is autophagy induction because of autophagy’s central role in presenting the antigens to the T lymphocytes. AINPs have been researched as an autophagy inducer because of this reason. Cysteine peptidase A and B were conjugated in one study to Aluminum nanoparticles and they were utilized as leishmania vaccine for inducing autophagy in the macrophages. When these nanoparticles were administered, fast internalization is shown of the conjugated nanoparticles by leishmania-infected macrophages. Aluminum nanoparticles can also be used to design an anti-HIV vaccine as they are effective and efficient nano-adjuvants to provoke mucosal and systematic immunity. A peptomer was covalently conjugated onto the aluminum nanoparticles, leading to a nanoconjugate of 300 nm that can cause a strong immunologic reaction in mucus.
The nanoparticles are still being utilized for drug delivery purposes in various fields of medicine. Dosage’s accuracy determines the nanoparticle’s power in delivering the drugs into the body and they can release it in very certain locations at a set time in the body, which leads to fewer side effects as the drugs’ therapeutic efficiency will increase. Fewer side effects will be caused as compared to the number of side effects that will be caused if current methods are used for the delivery of the drug.
Alumina nanoparticles are a good option for IV delivery of the drug into body parts because of their durability. The durability of the nanoparticle matters here as such body parts has extremely low pH, making it easy to degrade the nanomaterials before nanomaterials reach their desired location. The most concerning thing right now is aluminum toxicity as recently people have been linking cancer and aluminum. However until now, aluminum has shown no carcinogenic effect so that link has not been proven, still one should take care while adding aluminum nanoparticles for delivery of the drug.
AINPs are attractive and efficient nanomaterials because of a number of their great characteristics. Some of them are mentioned below:
(i) Due to having known methods of manufacture, they are easily available.
(ii)They can be easily conjugated with molecules of other origins like biological and chemical molecules because of their vast surface area.
(iii) AINPs can interact easily with biological interfaces, enabling them to be utilized for biological purposes.
(iv) In harsh, complicated non-biological environments and other numerous conditions, AINPs are stable enough for being utilized.
(v) They are ideal nanomaterial when it comes to developing various nanomaterials because of the fact that their surface functionalization protocols are very clear.
Aluminum oxide nanoparticles have gained popularity and prominence in the field of biomedical specifically as they are serving this field for a long time. This enables these nanoparticles to fight and combat a series of deadly diseases as well which is a huge achievement for such tiny particles. Their excellent nature in which they are present and then molded into the form that can be used for beneficial purposes is a very hard and tiring process but once achieved can work wonders for the industries as well as the humans.
Graphene particles are by far the best-known particles that are serving as one of the best catalyzers in the industry. When boron is doped with graphene by going through different processes it becomes and forms boron-doped graphene particles which serve various purposes in the industry.
The characteristics and properties which are exhibited by boron-doped graphene particles are highly rich in their content and are capable of exhibiting a lot of valuable processes. Technological applications have only increased over time and enhanced the entire purpose of forming these boron-doped graphene particles.
Graphene-based nanomaterial, boron-doped graphene (BG), is a carbon atom’s single sheet organized in a hexagonal lattice. When the boron atom impurities are added into pure graphene, the bandgap opens, redox reactions accelerate, catalytic ability enhances, and the activation region on its surface increases. All of these alterations give various applications to it in sensors, ultracapacitors, semiconductor devices, fuel cell chemistry, and other technologies.
Using electron-withdrawing (boron) or electron-donating groups (phosphorus, nitrogen), to dope graphene is significant to change graphene’s electrical characteristics. Graphene sheet’s electron density changes when they are doped with electron-withdrawing (electron acceptors, p-type) or electron-donating (n-type, electron donors) groups and thus also affects graphene sheet’s electrochemical characteristic. Doping level plays a very important part as carrier density is very significant to tune the material’s performance.
One of the other major problems is manufacturing doped materials for synthesizing scalable methods to doped material’s large quantities. In this article, a technique is showed for the scalable formation and tunable doping levels by graphene oxide’s exfoliation at various temperatures in the BF3 atmosphere. There are also investigations on p-doped material’s electrochemical characteristics and their comparison with the ones that the literature presents.
Nitrogen and boron-doped graphene
Unusual electrocatalytic effects are displayed by nitrogen-doped graphenes toward oxygen and H2O2 reduction which have extremely significant usages for applications in fuel cells and biosensing. In comparison with graphene, large capacitance is possessed by nitrogen-doped graphenes. Similar effects were displayed by boron-doped graphene, being increased capacitance and electrocatalytic toward oxygen reduction. According to observations, it doesn’t matter which atoms are doped in graphene as these characteristics are improved. Compound oxidation is easy with increased doping of materials with electron-deficient components, whereas reduction turns difficult.
These observations are contrary to the old reports on the boron-doped graphene that catalyzes the oxygen’s electrochemical reduction. Cyclic voltammetry, prompt γ-ray analysis, X-ray photoelectron spectroscopy, Raman spectroscopy, and scanning electron microscopy, are used to characterize it in detail.
Graphene oxide’s thermal exfoliation was done to manufacture boron-doped graphenes in an atmosphere at 1000 °C in N2, 800 °C in N2, and with boron trifluoride diethyl etherate in N2/H2 at 1000 °C. Graphene oxide goes through many stages, exfoliation, deoxygenation (manufacturing CO2, CO, H2O, organic molecules), and then its simultaneous doping with boron. Cyclic voltammetry (CV), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and prompt γ-ray analysis (PGAA), are used to characterize resulting boron-doped graphenes for studying the electrocatalytic characteristics of it towards oxygen reduction and its capacitance. Here, there are all abbreviations of all boron-doped graphenes as B-G.
Thermal shock treatment
There were investigations on the Graphene oxide’s thermal shock treatment in the BF3 atmosphere and how it results in Graphene oxide’s exfoliation. SEM studied boron-doped graphene’s (B-G) morphology. SEM images are shown of boron-doped graphenes and those graphenes are made by exfoliation. A typical exfoliated structure is shown by all of these materials just like how it was shown in previous studies and this structure also assures graphite oxide’s successful thermal exfoliation in the BF3 atmosphere. Exfoliation temperature’s effect was consequently studied upon the amount of graphene used to dope boron through PGAA. (prompt γ-ray analysis)
Trace levels of elements
One of the best methods to determine the element’s trace level is PGAA. Boron’s absolute content in samples was determined comparatively to the liquid standard of H3BO3 with the known concentration of boron. In N2/H2 atmosphere, graphite oxide’s exfoliation at 1000 °C resulted in graphene’s doping at 23 ppm boron levels, whereas boron’s larger amount was introduced on graphite oxide’s exfoliation in the atmosphere of nitrogen, 590 ppm at 1000 °C, and 140 ppm boron at 800 °C.
According to the result, graphene can be doped with boron atoms of a higher amount if the exfoliation temperature was higher. A major decrease was observed in the concentration of boron for GO exfoliated in the atmosphere with hydrogen. Thus, boron’s successful doping into the graphene sheets is confirmed by this result.
Characterization of density
Raman spectroscopy is used by us for characterizing the defect density in boron-doped graphene by determining the doping level that boron did on Graphene. Defects are present and indicated by the D band at almost 1350 cm−1 because of the sp3 -hybridized carbon atoms. A G band is shown by the graphene sheet’s pristine sp2 lattice carbon atoms at almost 1560 cm−1. The carbon structure’s degree of the disorder can be indicated through the usage of the ratio between D and G band intensities (ID/IG). 0.732, 0.632, and 0.903 are the ID/IG ratio for 590 ppm B-G, 140 ppm B-G, and 23 ppm B-G, respectively.
Sizes of crystallites
D- and G- band intensities can be used to estimate various material’s average crystallite sizes (La) by applying this equation, 1.20 =× × × λ − L II 2.4 10 / a 10 laser 4 G D. In this equation, ID and IG are Raman D and G band’s intensities, and the excitation laser’s wavelength is denoted by λlaser in nanometers. The crystallite sizes in graphenes that are doped with boron are then calculated. La is 23.0 nm of 590 ppm B-G, 26.6 nm of 140 ppm B-G, and 18.6 nm of 23 ppm B-G. At 2700 and 1620 cm-1, both the 2D band and D’ band are displayed by all three boron-doped graphenes indicating disorder of low degree in their carbon structure.
XPS was used to consequently determine boron-doped graphene’s elemental compositions as it is a chemical analysis method and is beneficial for determining the bonding arrangement and the elemental composition. The obtained high-resolution XPS of C 1s and wide scan of C 1s for three graphenes referred to the fact that there was a removal of most of the oxygen-containing groups and the preparation of the thermally reduced graphenes was successfully done.
According to wide scan XPS, for 590 ppm B-G, the C/O ratio is 16.1, for 140 ppm B-G, the C/O ratio is 8.9, and for 23 ppm B-G, 14.2 is the C/O ratio. Huge insight is given of the residual oxygen-containing group’s chemical composition by high-resolution XPS of the C 1s signal. They exhibit different and various energy levels. When made at 800 °C in N2, 1000 °C in N2/H2, and 1000 °C in N2, boron-doped graphenes possess C-C bonds, C−C bonds, C−O bonds, CO bonds, and O−CO bonds, respectively. XPS can determine the residual oxygen-containing groups in the reduced graphene. However, trace amounts of boron can’t be measured by XPS as it is not sensitive enough.
Combustible elemental analysis
Boron-doped graphene’s elemental composition can be determined by using combustible elemental analysis as it is very beneficial for measuring the accurate content of combustible elements present in the bulk material. Further, more insight regarding the bonding character and composition of graphene sheets is provided when it is combined with XPS. 5.54 atom % of O, 9.63 atom % of H, and 84.83 atom % of C, was contained by 590 ppm B-G. 7.69 atom % of O, 10.03 atom % of H, and 82.28 atom % of C were contained by 140 ppm B-G. 7.48 atom % of O, 10.04 atom % of H, and 82.48 atom % of C were contained by 23 ppm B-G. Moreover, there was no nitrogen in any of the samples.
Four-point measurements of compressed tablets studied resulting boron-doped material’s electrical resistivity. 13 ppm B-G, 140 ppm B-G, and 590 ppm B-G, has the electrical resistivity of 9.5 × 10−5 Ωcm, 2.1 × 10−5 Ω cm, and 2.3 × 10−4 Ωcm. According to these results, the electrical resistivity is increased by boron’s higher content which is in accordance with boron’s electron acceptor characteristics. There was an investigation on the boron-doped graphene’s electrocatalytic activity toward oxygen reduction reaction (ORR). In both N2 saturated 0.1 M KOH aqueous solution and air, cyclic voltammograms were recorded at 3 of the boron-doped surfaces. A major reduction peak is observed. There was no electrochemical reduction in N2- saturated KOH solution, and the reduction peak for air-saturated KOH solution was ∼−460 mV.
Oxygen’s reduction originates ∼−460 mV reduction peak. Reduction of oxygen with different levels of doping was recorded by Cyclic voltammograms. For Graphenes with boron dopant’s increasing concentrations, reduction peak shifts to increasingly negative potentials. Thus, for boron-doped graphene, the electrocatalytic activity towards the reduction of oxygen would be lower if the doped boron atoms are more, and vice versa. This is in agreement with hole-doping electrochemistry’s general concept but also in contrast to the past observations.
Weight specific capacitance
Cyclic voltammetry capacitive charge-discharge current was used to determine the boron-doped graphene’s weight-specific capacitance. ν C = I (2), is used to express the capacitance. In this equation, ν is the scan rate (mV/s, can be expressed as dE/dt), I is current (A), and C is capacitance (F). There were investigations on the capacitances of boron-doped graphenes. The investigations were being done by measuring the current With scan rates of 400, 200, 100, 75, 50, and 25 mV/s and at 0.15 V of applied potential. Boron-doped graphene’s weight-specific capacitances are 10.3, 10.7, and 11.7 at 1000 °C in N2, 800 °C in N2, and at 1000 °C in N2/H2. These weight-specific capacitances refer to the fact that when the amount of doped boron atoms increases, the weight-specific capacitance decreases.
In comparison to non-doped parts
As compared to its non-doped counterparts, N-doped graphenes and B-doped graphenes exhibit higher capacitance contrary to the previous claims. No theoretical background explanation is present here whereas, in both hole and electron doping cases, improved capacitance should be expected. In Han et al.’s paper, the utilized method was based on a famous hydroboration reaction from organic chemistry. With the BH2 group being covalently bonded to the backbone of graphene, the production of sp3-hybridized carbon can be imagined from such a reaction’s mechanism. Attaining carbon’s direct substitution with boron through the methods that Han et al. presented, is impossible.
Surface plasmon resonance
Optical sensors, surface plasmon resonance (SPR) biosensors, gained a lot of attention because of their benefits like non-invasive measurements, room temperature real-time measurements, and high sensitivity. At the metal-dielectric interface, SPR is very sensitive to refractive index alteration. Because of the analyte’s presence, sensitivity in detection is exploited if there is any kind of change at the interface. Typically in SPR biosensors, gold is utilized as a resonant layer because of its chemical stability, where a higher shift of resonant angle with a change in refractive index is exhibited by gold. Although, biomolecule’s adsorption or detection at low concentrations is extremely difficult or even impossible at times because of gold’s inertness.
Single crystalline gold surface
At increased temperatures and pressures or under high vacuumed (UHV) conditions, the single-crystalline gold surface doesn’t specifically measure small molecules adsorption. Such molecules are NH3, NO, O2, H2, and CO. There have been investigations of the physically and chemically modified gold layer in various studies regarding improved detection and adsorption mechanisms, like CNTs, gold nanocrystal, kinked/stepped gold surface gold nanorods, and graphene oxide coupled with gold nanoparticles.
There have been investigations on some of the novel materials like MOS2, Au/Ag/Au/chitosan-graphene oxide (RGO), and graphene, for improving SPR sensor’s selectivity and sensitivity. In all of these novel materials, the most promising material is graphene because of its excellent and remarkable characteristics like high surface-to-volume ratio and high mobility that are advantageous for biomolecule’s effective adsorption in comparison with gold. An improved SPR response is displayed by the doped graphene oxide (GO) that is enriched on the gold layer’s top with abundant defect sites. Although, chemical doping causes the modulation of the optical bandgap and GO’s Fermi energy which leads to alteration in the optical characteristics like dielectric constants and refractive index. SPR sensing techniques can monitor these variations.
Enhancements in graphene’s characteristics
According to recent literature, huge enhancements have been seen in the characteristics of graphene by doping graphene with various heteroatoms like Boron (B), Nitrogen (N), Oxygen (O)< and Fluorine (F). In numerous applications like improved photogenerated catalysis, solar cells, Li-ion batteries, and supercapacitors, there have been reports of the boron-doped graphene oxide. Also, numerous methods like chemical vapor deposition (CVD), arc-discharge process, and hydrothermal method have been used to dope graphene-based materials, where for tuning graphene’s electronic and optical characteristics, stable atomic substitution with carbon is extremely required. At high temperatures, GO is mostly lessened thermally among the reduction methods. Although, high-density defects are produced by reduction at high temperatures on the basal planes and edge, deteriorating graphene’s optical and electrical characteristics.
In post-treatments, there were decorations of each of the as-synthesized materials with platinum catalyst nanoparticles of 60 wt % that were made in the already reported procedure by utilizing a metal-organic Pt (acac) 2 precursor. The powdered support materials were briefly mixed uniformly in a glass vial of 4.5 mL with Pt(acac)2 in suitable ratios for yielding 60 wt% Pt. The mixture was heated under a low vacuum of 600 Torr for 16 hours at 210 C in an N2-H2O atmosphere, resulting in Pt metal nanoparticle’s deposition onto the support.
An anode-supported configuration was used to fabricate solid acid fuel cells. Mesh discs of 2.85 cm2 of Sintered 304 stainless steel functioned as the anode current collectors. There have been some previous reports on the architecture of the cell and after this, it was confirmed as the architecture of this cell was completely identical to the one in previous reports. CDP’s mechanical mixture formed identical anodes with 1.0 mg/cm2 (Pt) Pt loading. For all of the tested cells, those identical anodes with a Pt loading of 1.0 mg/cm2 (Pt), inhouse synthesized 60 wt% Pt supported on naphthalene (a fugitive binder), and carbon black (Cabot Crop., Vulcan XC-72R), by weight, in a 3:1:1 ratio.
A CDP membrane was possessed by each cell. The membrane’s thickness was 50 μm, and it was laminated at 125 MPa to the anode. Experimental cathodes of 25 mg of a 3:1 by CDP’s weight mixture and 60 wt% of Pt supported on CB9Ar, CH5Ar, or SWCNHs were implemented at 30 MPa pressure to the dense CDP membrane. 1.3 mg/cm2 was the experimental cathode’s areal Pt loading.
At 250 C temperature, ultrahigh purity H2 and the air was used to conduct cell testing by utilizing stainless steel test rigs, each at 75 C dew point. Bio-Logic VSP potentiostat was used to record polarization curves from open circuit potential to 0 V by scanning the cell potential at 10 mV s-1. At 0.8 V, each cell faced a multi-step cyclic testing protocol which included potentiostatic electrochemical impedance spectroscopy (EIS) spectrum for attaining the average high-frequency area-specific resistance (ASR), polarization curve’s recording, at 0.6 V a 30-minute potentiostatic hold, and then this protocol repeated. At 0.6 V, the cells were held after 30 cycles.
The polarization curves were corrected by using ASR for effects of membrane ohmic resistance, yielding iR-free polarization curves. For the formulation of each cathode, the results were averaged across multiple cells comprising two replicates at least.
There were performances of electron energy-loss spectroscopy (EELS) and transmission electron microscopy (TEM) imaging in a Zeiss Libra 200MC (0.1 nm is the information limit). ImageJ software was used to make an estimate of the dimensions of the nanoparticle from the TEM micrographs for calculating their cross-sectional areas and for tracing their parameters. There were derivations of the same area’s effective nanoparticle diameters. There have been many reports on the standard deviations and mean dimensions.
Sizes of the flake were measured by using a similar procedure, but by utilizing the square approximation. The concentration of the boron was determined by using EELS, and the background spectra were fit by utilizing the combination of a polynomial model and a power law. A polynomial model is, E−r + aE2 + bE + c, where E is energy, whereas r, c, b, and a, are fitting parameters. An In-lens detector was used to perform scanning electron microscopy (SEM) imaging at 3kV with a Zeiss Auriga 40. Pore size analyzer and Quantachrome Micromeritics surface area were used to perform BET surface area analyses. At 10 C/min ramp rate in air, Q50 from TA instruments was used to perform thermogravimetric Analysis (TGA).
Moreover, a continuous scan was done to carry out X-ray diffraction (XRD) measurements on a two-circle high-resolution X-ray powder diffractometer through the usage of Cu-Kα1 radiation (1.54059Å) with ½° fixed divergence slit.
A custom microscope-based system was used to perform Raman spectroscopy at 532 nm of excitation wavelength. The laser beam was focused by using a 100X objective with ~1 μm spot size on the sample, and ~0.5 mW was the measured power of the laser at the sample location. Spectral peak fitting was applied along with Gaussian/Lorentzian line shapes.
A lot of detailed processes are carried out to form these boron-doped graphene particles which are not only serving in the technological industries but are also paving way for the upcoming technologies which can be buckled up by the use of boron-doped graphene particles. Hence, these are excellent means of promoting technology and technology-based industries.
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