Hexagonal Nanoplatelets Research Articles

Hydroxylated hexagonal boron nitride nanoplatelets enhance the mechanical and tribological properties of epoxy-based composite coatings

The relationship between microstructure and properties of hydroxylated hexagonal boron nitride nanoplatelets (denoted as OH-h-BN) reinforced epoxy composite coatings was still not clear. In this work, hexagonal boron nitride nanoplatelets (h-BN) were successfully hydroxylated to increase their dispersion and compatibility with the EP matrix, which was confirmed by the results obtained from FTIR, XPS, XRD and TEM. Subsequently, OH-h-BN reinforced epoxy resin (EP) composite coatings were prepared by means of a spraying process, and their curing characteristics, cross-linking density and mechanical and tribological properties were discussed. As a result, the EP/OH-h-BN composite coating took an excellent curing label in terms of the ‘Cure Index’ (CI) and had a cure enthalpy 1.5 times higher than that of the pure EP coating. Moreover, with the presence of OH-h-BN, the storage modulus (at 40 °C) and cross-linking density of the epoxy composite coating were enhanced by 56% and 43%, respectively. The tensile test outcomes presented approximately 16% and 138% improvements in the maximum tensile strength and elongation at break of the EP/OH-h-BN composite coating compared with pure EP coating. In addition, the friction coefficient and the wear rate were reduced by 27% and 58% because of the enhancement of mechanical strength of the EP/OH-h-BN composite coating and the formation of a continuous, dense and high load-carrying lubricating tribofilm on the dual steel ball.

Cobalt ferrite-modified sol-gel synthesized ZnO nanoplatelets for fast and bearable visible light remediation of ciprofloxacin in water

Currently, metal oxide photocatalysts is a green and facile tool for the elimination of emerging pollutants utilizing light illumination. Though, the wide bandgap energy (Eg), rapid recombination of photogenerated carriers, and photostability of these oxides represent critical issues before the actual application. Herein, we familiarise a sol-gel based synthesis of ZnO hexagonal nanoplatelets modified with CoFe2O4 (CFO) nanoparticles at minor loading (1.0–4.0 wt %) to yield CFO/ZnO nanoheterojunctions. The CFO/ZnO unveiled mesostructured surfaces at surface areas of 102–120 m2 g−1 and photoactive in the visible region with high. The CFO addition to ZnO reduced its Eg from 3.14 to 2.66 eV. The formed nanoheterojunctions were applied to remediate ciprofloxacin (CPF), as an antibiotic pollutant in wastewater. The 2.4 g L-1 3.0 wt % CFO-added ZnO exhibited a 100% removal of 10-ppm CPF within 45 min of visible-light irradiation and sustainable recycling ability for five consecutive runs at 97%. The sustainable performance of CFO/ZnO is ascribed to the suppression of photogenerated carriers and reduction of E by p-n nanoheterojunction formation. This study broadens the way for nanoheterojunction oxides for the destruction of pharmaceutical wastes under visible-light illumination.

A facile green synthesis of porous hexagonal cobalt pyrovanadate electrode for supercapacitors by deep eutectic solvent

Cobalt vanadate is a kind of promising electrode material for pseudo-supercapacitors because of their higher electrical conductivity, better electrochemical activity, and prominent specific capacitance than single metal oxides. In this paper, cobalt pyrovanadate (Co2V2O7) was primarily fabricated by a facile environment-friendly ionothermal method using a green deep eutectic solvent (DES) and followed the heat treatment in the air. The eutectic mixture discussed here was consisted of a hydrogen bond donor (urea) and acceptor (ChCl) in a 2:1 molar ratio. The as-prepared Co2V2O7 was porous hexagonal nanoplatelets, and its electrochemical performances were characterized by cycle voltammetry, galvanostatic charge/discharge and cycling stability tests in a three-electrode system with 2 M KOH electrolyte solution. The specific capacitance of the synthesized Co2V2O7 revealed 304 F g−1 at the current density of 1 A g−1. Surprisingly, it remained an excellent cycle performance with 103% in 100 charge/discharge cycles. Therefore, we have successfully presented a deep eutectic solvent derived routine to prepare porous hexagonal Co2V2O7 nanoplatelets electrode material.

Homogeneous dispersion of boron nitride nanoplatelets in powder feedstocks for plasma spraying

Hexagonal Boron nitride nanoplatelet (BNNP) with the combination of excellent mechanical properties, high-temperature thermal stability, and self-lubrication is a promising strengthening agent in plasma-sprayed composite coatings. However, it is a significant challenge to produce plasma sprayable feedstocks with homogeneously dispersed BNNPs owing to the intrinsic agglomeration of BNNPs. In this research, three powder preparation processes (electrostatic interaction, ball milling, and shear mixing) were employed to disperse BNNPs in Ni-Cr-Cr2O3 (NCCO) powders. The shear mixing process presents a competitive advantage in powder preparation, providing stable shear force and achieving exfoliated BNNPs homogeneous distribution in the composite powders. The spray drying technique was finally utilized to obtain spherical agglomerated BNNP-NCCO feedstocks with characteristics of relatively smooth surface and uniform size distribution. Hence, shear mixing and spray drying processes are expected to produce large-scale spherical composite powders with a homogeneous distribution of 2D layered nanomaterials for industrial application.

Preparation of Al(OH)3-based layered structural material by shear alignment from aqueous dispersion of colloidal gibbsite platelets

Development of the technological and industrial capabilities to obtain hexagonal gibbsite nanoplatelets with a regularly well-defined configuration is an ongoing consideration that has not yet covered a required level of feasible architecture. Here we present a convenient method to synthesize the colloidal gibbsite particles based on a simple hydrothermal process from aluminum alkoxides in weak acid media. These colloids are near-regularly shaped and fairly monodisperse hexagons with an average diameter of 185 nm and a thickness of ~5.3 nm. The aqueous dispersion of gibbsite platelets can be shear-aligned to form highly ordered, continuous films on a substrate by an industrially adaptable method for producing large-area membranes. Overall, the modified synthesis method exhibits an excellent potential for scalable-up production with high quality in various practical applications. The aligned films also have outstanding properties due to the self-assemblies and interfacial physical interactions between adjacent gibbsite platelets and the possibility of industrial fabrication from those layered structural materials. Moreover, we prepare this shear-aligned membrane by the in-plane shearing method to introduce the great promise of disk-like-derived gibbsite as new gas-barrier material or surface-protective materials.

Earth-Abundant Electrocatalysts for the Oxygen Evolution Reaction of Water Splitting Using Nanostructured Layered Inorganic Materials

Nature uses solar energy and earth-abundant materials for splitting water into oxygen, in the oxygen evolution reaction (OER), and protons, which are then reduced into hydrogen in the hydrogen evolution reaction (HER). Hydrogen solar fuel produced in artificial photosynthesis schemes for water splitting could be used in fuel cells. Learning from nature, instead of using expensive catalysts such as platinum, cheaper alternatives (such as cobalt, iron, or nickel) would provide the opportunity to make solar energy even more competitive with fossil fuels. However, obtaining efficient catalysts based on earth-abundant materials is still a daunting task, particularly for the OER. Recent theory has shown that nanoscopic confinement of catalysts increases the stability and efficiency of catalysts for OER. We have designed and develop earth-abundant electrocatalysts for oxygen reduction and water splitting using nanostructured layered inorganic materials of zirconium phosphate (ZrP). We have demonstrated improved electrocatalytic activity of ZrP nanomaterials loaded with metal ions suitable for the OER of water splitting. Adsorbing Co or Ni catalysts on the ZrP nanoparticles surface proved to improved OER activity compared to intercalated catalysts. A comparison between adsorbed Co or Ni catalysts and those catalysts on exfoliated ZrP hexagonal nanoplatelets proved that those on exfoliated nanoplatelets were more active, with diminished overpotentials and reduced Tafel plot slopes as well as higher mass activities. More recently, comparison between Co and Ni catalyst on ZrP particles with different morphologies (hexagonal platelets, rods, cubes, and spheres) revealed that the more active Co catalysts are those on hexagonal ZrP platelets, whereas the best Ni catalysts are those on ZrP spheres. Finally, encouraging recent results with a cobalt porphyrin catalyst will be presented, as well as recent XAS operando results. These results demonstrate that ZrP nanoparticles are suitable supports for electrocatalysis of the OER and water splitting.Sponsored by NSF Center for Chemical Innovation in Solar Fuels CHE-1305124 and NSF-PREM Center for Interfacial Electrochemistry for Energy Materials (CIE2M) grant DMR-1827622.

Tribological properties of hexagonal boron nitride nanoparticles or graphene nanoplatelets blended with an ionic liquid as additives of an ester base oil

AbstractAntifriction synergies between an ionic liquid (IL) and nanopowders as additives of an ester base oil were analysed at rolling conditions. For this aim, two nanodispersions based on hybrid combinations of hexagonal boron nitride nanoparticles (h‐BN) or graphene nanoplatelets (GnP) with tri(butyl) ethylphosphonium diethylphosphate ionic liquid as additives in triisotridecyltrimellitate (TTM) base oil and the mixture of TTM and IL were analysed using two tribometer techniques. Film thickness characterisation and tribological tests were performed at rolling conditions [5% slide‐roll‐ratio (SRR)], under 50N and at operating temperatures of 30, 50 and 80°C. Stribeck curves showed that friction coefficients for the prepared lubricants are lower than those found for the TTM, being the best friction behaviour for the hybrid GnP nanolubricant. Furthermore, friction torque loss tests were performed in rolling ball bearings, observing that for the two hybrid nanolubricants lower friction torque values were obtained.

Synthesis of monophase two‐dimensional α‐Si3N4 nanoplatelets via an ionothermal route

AbstractMonophase α‐Si3N4 was prepared by a salt melt strategy using Si as a starting material. The results showed that molten salt enhanced the conversion of Si to monophase α‐Si3N4, and some as‐synthesized α‐Si3N4 nanoparticles had a hexagonal platelet morphology. The α‐Si3N4 hexagonal nanoplatelets had an average lateral dimension of about 170 nm and a thickness of about 5.2 nm. The nitridation of Si in molten salt was investigated by a thermal quenching method, and the silicon halide intermediate products were detected by X‐ray photoelectron spectroscopy. Silicon halides possessing higher reactive activity facilitated the nitridation of Si and nucleation of α‐Si3N4. Furthermore, the lattice mismatch between α‐Si3N4 and the salts was calculated, suggesting that the lateral growth of α‐Si3N4 nanoplatelets had been guided by the salt crystal structure. Based on the results, the relevant formation mechanism of α‐Si3N4 nanoplatelets was proposed.

Lithium‐Ion Batteries: Layered Heterostructure Ionogel Electrolytes for High‐Performance Solid‐State Lithium‐Ion Batteries (Adv. Mater. 13/2021)

Ionogel electrolytes with a layered heterostructure are developed by Mark C. Hersam and co-workers in article number 2007864, using hexagonal boron nitride nanoplatelets and two imidazolium ionic liquids with different electrochemical stability windows. Compared with ionogels using the individual ionic liquids, the layered heterostructure ionogels provide broadened electrochemical stability windows while maintaining desirable ionic conductivity, suggesting a promising electrolyte strategy for high operating voltages and rate performance in solid-state lithium-ion batteries.

In-situ growth of single-crystal plasmonic aluminum–lithium-graphene nanosheets with a hexagonal platelet-like morphology using ball-milling

Metal-graphene nanocomposites and plasmonic metal nanoparticles are two nanoscience fields of a rapidly growing interest due to their potential in advanced applications. In this study, we combine both fields by synthesizing plasmonic aluminum-lithium-graphene nanosheets (Al–Li-GNSs) with anisotropic morphologies using a simple ball-milling technique. Structural analysis using SEM and TEM revealed that the Al–Li-GNSs nanoparticles are single-crystals with a hexagonal platelet-like morphology of a ∼300–500 nm diagonal and a ∼60 nm thickness. Electron diffraction analysis indicated that the as-milled platelets have an FCC structure with (111) top and bottom facets and revealed the presence of 1/3(422) and 1/3(220) forbidden reflections. UV–Vis spectroscopy of the hexagonal Al-based nanoplatelets was found to exhibit plasmonic resonance absorption bands in the UV region at a wavelength of 214 nm and 345 nm. In this report, we confirm the feasibility of building epitaxial plasmonic metal-graphene systems inside bulk metal-graphene composites using a simple milling process.

Tribological properties of graphene nanoplatelets or boron nitride nanoparticles as additives of a polyalphaolefin base oil

In this work, antifriction and antiwear capabilities of hexagonal boron nitride nanoparticles (h-BN) or graphene nanoplatelets (GnP) as additives of a polyalphaolefin neat oil (PAO 40) were studied at pure sliding conditions. For this purpose, eight PAO 40 nanodispersions were prepared: four nanodispersions with h-BN and four others based on GnP. The mass concentrations of these dispersions are 0.25, 0.50, 0.75 and 1.00 wt% of h-BN and 0.05, 0.10. 0.25 and 0.50 wt% of GnP, having all of them a good stability against sedimentation (at least 96 h). Tribological assays were carried with prepared nanolubricants as well as with PAO 40 base oil at 20 N load. All nanolubricants based on h-BN or GnP showed lower friction coefficients in comparison to the non-additivated neat oil, with a maximum decrease in friction of 21% for the 0.50 wt% GnP nanodispersion. Regarding the produced wear, all disks lubricated with nanolubricants showed lower wear than those lubricated using PAO 40. The greatest wear reduction in wear track width (22%) was also achieved for the 0.50 wt% in GnP nanolubricant. Moreover, through the confocal Raman microscopy and roughness analyses of worn disks it can be concluded that the wear reductions are due to the surface repairing and tribofilm formation mechanisms.

Mechanical and thermal properties of 3D-printed epoxy composites reinforced with boron nitride nanobarbs

In this work, new boron nitride-reinforced epoxy-based composite inks for direct-ink write (DIW) additive manufacturing are presented. Printed composites are characterized for thermal conductivity, flexure, and impact energy, along with optical and electron microscopy. The new inks utilize boron nitride nanobarbs (BNNBs), a novel form of boron nitride nanotube, where the surface is decorated with hexagonal boron nitride nanoplatelets. BNNBs are shown to improve the thermal conductivity of the printed composites up to 32%, the strength up to 34%, and stiffness up to 44%. Anisotropy was observed in all measurements, suggesting that the BNNBs become aligned during printing.

Preparation of Boron Nitride Nanoplatelets via Amino Acid Assisted Ball Milling: Towards Thermal Conductivity Application.

Hexagonal boron nitride nanoplatelets (BNNPs) have attracted widespread attention due to their unique physical properties and their peeling from the base material. Mechanical exfoliation is a simple, scalable approach to produce single-layer or few-layer BNNPs. In this work, two amino acid grafted boron nitride nanoplatelets, Lys@BNNP and Glu@BNNP, were successfully prepared via ball milling of h-BN with L-Lysine and L-Glutamic acid, respectively. It was found that the dispersion state of Lys@BNNP and Glu@BNNP in water had been effectively stabilized due to the introduction of amino acid moieties which contained a hydrophilic carboxyl group. PVA hydrogel composites with Lys@BNNP and Glu@BNNP as functional fillers were constructed and extensively studied. With 11.3 wt% Lys@BNNP incorporated, the thermal conductivity of Lys@BNNP/PVA hydrogel composite was up to 0.91 W m−1K−1, increased by 78%, comparing to the neat PVA hydrogel. Meanwhile, the mechanical and self-healing properties of the composites were simultaneously largely enhanced.

Enhanced Scratch Performance of Plasma Sprayed Hydroxyapatite Composite Coatings Reinforced with BN Nanoplatelets

In recent years, research on hydroxyapatite (HA) coatings has been driven by the demands of clinical applications. However, the intrinsic brittleness of HA limits its potential in the use for the load-bearing implant. To improve mechanical properties of the HA coating itself, a HA composite coating reinforced with hexagonal boron nitride nanoplatelets (BNNP) was fabricated using plasma spray, and its scratch behavior was investigated in this research. Typical brittle fractures such as microcracks both in and beyond the residual groove and material chipping were observed in the HA coating, while stronger and tougher BNNP/HA coatings exhibited a dominant role in protecting them from scratch damage through resisting plastic deformation and brittle microfracturing. Moreover, easier grain sliding within a splat and splat sliding at the splat boundaries due to the presence of BNNPs, and the nature porosity at different length scales of the as-sprayed HA composite coatings would provide significant self-lubricating effects to reduce the lateral force during scratching and alleviate the contact damage. Therefore, the addition of BNNPs renders HA coating with low scratch friction and enhanced tolerance to surface damage, which is naturally beneficial for the long-term durability and reliability of the implants.

Effect of Hexagonal Boron Nitride Nanoplatelet on Crystal Nucleation, Mechanical Behavior, and Thermal Stability of High‐Density Polyethylene‐Based Nanocomposites

AbstractHexagonal boron nitride nanoplatelets (BNNP) significantly enhance the mechanical and thermal properties of high‐density polyethylene. In order to ensure superior dispersibility of BNNP, two different techniques, colloidal solution, and solvent blending, are used for fabricating nanocomposites. Compared to solvent blending, the colloidal solution‐based fabrication technique has superior dispersion capabilities for nanofillers in the PE matrix, which helps in improving the thermal stability and crystallinity in synthesized nanocomposites. A significant increase in the rate of crystallization of polyethylene (PE) is reported at 1% weight fraction of BNNP, which further increases with the increase in weight percentage of BNNP. BNNP acts as a new source of nucleating sites for crystallization in PE that also reduces the size of secondary structures spherulites. Enhanced tensile strength and Young’s modulus of BNNP/PE nanocomposites are reported with the increase in weight contribution of BNNP in the range of 1% to 5%.

Pinning of the Fermi Level in CuFeO2 by Polaron Formation Limiting the Photovoltage for Photochemical Water Splitting

AbstractCuFeO2 is recognized as a potential photocathode for photo(electro)chemical water splitting. However, photocurrents with CuFeO2‐based systems are rather low so far. In order to optimize charge carrier separation and water reduction kinetics, defined CuFeO2/Pt, CuFeO2/Ag, and CuFeO2/NiOx(OH)y heterostructures are made in this work through a photodeposition procedure based on a 2H CuFeO2 hexagonal nanoplatelet shaped powder. However, water splitting performance tests in a closed batch photoreactor show that these heterostructured powders exhibit limited water reduction efficiencies. To test whether Fermi level pinning intrinsically limits the water reduction capacity of CuFeO2, the Fermi level tunability in CuFeO2 is evaluated by creating CuFeO2/ITO and CuFeO2/H2O interfaces and analyzing the electronic and chemical properties of the interfaces through photoelectron spectroscopy. The results indicate that Fermi level pinning at the Fe3+/Fe2+ electron polaron formation level may intrinsically prohibit CuFeO2 from acquiring enough photovoltage to reach the water reduction potential. This result is complemented with density functional theory calculations as well.

Monitoring the multiphasic evolution of bismuth telluride nanoplatelets

Bismuth telluride hexagonal nanoplatelets originate from electronically distinct thicker Bi-rich triangular nanoplatelets while being centrally knitted by Te nanorods.

Engineering multiple defects for active sites exposure towards enhancement of Ni3S2 charge storage characteristics

A promising strategy of multiple defects by engineering edges and vacancies simultaneously into the Ni3S2 structure significantly enhances the charge storage. In this work, vacancy scheming not only increases the interplanar spacing for greater availability of active sites but also improves the rate capability from 47% to 60%. Owing to enhance free electrons after vacancies, the resulting Ni3S2 (SNS) shows less band gap which in turn escalates the kinetics of charge storage. Furthermore, edges (thickness ~20–30 nm) of hexagonal nanoplatelet form during reduction treatment also contributes towards the additional exposure of active sites to the ions. This synergism imparts Ni3S2 with improved conductivity (one order) and large carrier concentration further augments energy density and cyclic stability. Charge storage in S vacancy induced Ni3S2 (SNS ~ 2994.46 F g−1) outperform the Ni3S2 (NS ~ 840.34 F g−1) by a factor 3. Whereas, the energy density obtained for SNS electrode is 4 times higher than NS. In addition, disorder structure in SNS lowers the surface energy and thus results in better stability with 88.72% retention. Moreover, asymmetric device SNS//LRGONR shows outstanding electrochemical performance of 53.38 Wh kg−1@997.45 W kg−1. This simplistic approach might shed new light on designing active site rich charge storage materials.

High-Modulus Hexagonal Boron Nitride Nanoplatelet Gel Electrolytes for Solid-State Rechargeable Lithium-Ion Batteries.

Solid-state electrolytes based on ionic liquids and a gelling matrix are promising for rechargeable lithium-ion batteries due to their safety under diverse operating conditions, favorable electrochemical and thermal properties, and wide processing compatibility. However, gel electrolytes also suffer from low mechanical moduli, which imply poor structural integrity and thus an enhanced probability of electrical shorting, particularly under conditions that are favorable for lithium dendrite growth. Here, we realize high-modulus, ion-conductive gel electrolytes based on imidazolium ionic liquids and exfoliated hexagonal boron nitride (hBN) nanoplatelets. Compared to conventional bulk hBN microparticles, exfoliated hBN nanoplatelets improve the mechanical properties of gel electrolytes by 2 orders of magnitude (shear storage modulus ∼5 MPa), while retaining high ionic conductivity at room temperature (>1 mS cm-1). Moreover, exfoliated hBN nanoplatelets are compatible with high-voltage cathodes (>5 V vs Li/Li+) and impart exceptional thermal stability that allows high-rate operation of solid-state rechargeable lithium-ion batteries at temperatures up to 175 °C.

High-Quality Hexagonal Nonlayered CdS Nanoplatelets for Low-Threshold Whispering-Gallery-Mode Lasing.

Low threshold micro/nanolasers have attracted extensive attention for wide applications in high-density storage and optical communication. However, constrained by quantum efficiency and crystalline quality, conventional semiconductor small-sized lasers are still subjected to a high lasing threshold. In this work, a low-threshold planar laser based on high-quality single-crystalline hexagonal CdS nanoplatelets (NPLs) using a self-limited epitaxial growth method is demonstrated. The as-grown CdS NPLs show multiple whispering-gallery-mode lasing at room temperature with a threshold of ≈0.6 µJ cm-2 , which is the lowest value among reported CdS-based lasers. Through power-dependent lasing studies at 77 K, the lasing action is demonstrated to originate from a exciton-exciton scattering process. Furthermore, the edge length- and thickness-dependent lasing threshold studies reveal that the threshold is inversely proportional to the second power of lateral edge length while partially affected by vertical thickness, and the lasing modes can be sustained in NPLs as thin as 60 nm. The lowest threshold emerges with the thickness of ≈110 nm due to stronger energy confinement in the vertical Fabry-Pérot cavity. The results not only open up a new avenue to fabricate nonlayered material-based coherent light sources, but also advocate the promise of nonlayered semiconductor materials for the development of novel optoelectronic devices.