Surface Cleaning of 2D Materials: Boron Nitride Nanosheets (BNNS) and Exfoliated Graphite Nanoplatelets (GNP)

Abstract

and impurities using methodologies such as electrical current annealing, [5] thermal annealing/desorption, [6-12] washing with water, acids, bases, ethanol, [12-14] plasma treatment, [13] and etching of metals. [15] Electrical annealing is effective at cleaning the surfaces of 2D materials; however, it is very limited in that it can only treat small sample areas (few micrometer square). [5] Thermal annealing proved to be the most effective at removing the impurities from the surface of 2D materials; however, there are serious concerns with regard degradation of the 2D material as a function of time. Washing with acids/bases are not always desirable as they can alter surface chemistry and their use may negatively impact the environment. [15] The etching of metals procedure is too laborious and not readily suitable for large-scale applications. Almost without exception the top-down production of 2D materials requires the use of surfactants or dispersants (e.g., water, ionic liquids) to assist the exfoliation of some bulk material. By way of example, the pretreatment of BNNS and exfoliated graphite nanoplatelets (GNP) studied here contain trace water and surfactant (sodium cholate, SC), [16,17] mainly introduced during the exfoliation of the corresponding bulk materials (i.e., boron nitride and graphite) in a high pressure homogenizer. [18] Specifically, three cleaning procedures were adopted in an attempt to remove impurities (i.e., water and SC) from the surfaces of BNNS and GNP, namely washing with ethanol, water assisted-freeze drying, and freeze drying without addition of water. Ethanol (EtOH) was utilized as it can wash water away from the surface of the BNNS and GNP and interact with the ionic surfactant SC thus being removed. The freeze drying process was selected as the sublimation of iced-water from the surface of BNNS and GNP would ideally remove water and exfoliate the 2D material further. [19-23] Indeed, when ice sublimates, the layers and flakes surrounded by ice are pulled apart. Two specific procedures for freeze drying were realized; FD-(i)-freezing of a dispersion of BNNS or GNP in water in liquid nitrogen followed by freeze drying and FD-(ii)-freezing in liquid nitrogen of the as received BNNS or GNP powder followed by freeze drying. The latter was performed on the basis that the water present as impurity in the BNNS and GNP samples would be sufficient at creating an ice pattern cutting through the layered structure Surface impurities such as water and surfactants can significantly affect the properties of 2D materials. They disrupt the 2D material lattice structure and surface chemistry and also promote electron and phonon scattering. Strategies to clean the surfaces of 2D materials are therefore critical to achieving optimal properties. Boron nitride nanosheets (BNNS) and exfoliated graphite nanoplatelets (GNP) are treated using three procedures: washing with ethanol, water-assisted freeze-drying, and freeze-drying without addition of water in an attempt to remove two impurities-water and an ion...

Polytetrafluoroethylene Nanocomposites with Engineered Boron Nitride Nanobarbs for Thermally Conductive and Electrically Insulating Microelectronics and Microwave Devices

“…This was determined as ≈0.86% for OCF 3 , consistent with the amount (<1%) earlier determined by FTIR and reported in the supplier’s data. XPS spectra of PTFE and BNNB are consistent with those of PTFE and BNNT reported in the literature. , The surface functionalization of BNNBs with glycine was further confirmed by XPS analysis (Figure e,f). B 1s and N 1s peaks for pristine BNNB appear at 190.4 eV (B–N bond) and 397.9 eV (N–B bond). , After modification with glycine, the B 1s and N 1s peaks shifted to 191.1 and 398.3 eV, respectively, suggesting electronic interactions due to covalent bonding of N atoms from glycine to B atoms of BNNB.…”

“…XPS spectra of PTFE and BNNB are consistent with those of PTFE and BNNT reported in the literature. 38,39 The surface functionalization of BNNBs with glycine was further confirmed by XPS analysis (Figure 2e,f). B 1s and N 1s peaks for pristine BNNB appear at 190.4 eV (B−N bond) and 397.9 eV (N−B bond).…”

Boron nitride nanosheets supported highly homogeneous bimetallic AuPd alloy nanoparticles catalyst for hydrogen production from formic acid

“…Scherrer equation (equation ( 3)) was used on the 002 diffraction peak to evaluate the thickness of BNNS. Where D is related to the mean size of the ordered (crystalline) domains, K represents a dimensionless shape factor, λ is the x-ray wavelength angstrom (CuKα = 1.5406), β represents the line broadening at half the maximum intensity (FWHM) in radians, and θ is the diffraction angle in degrees [48,49]. So, by considering 2θ=26.8°, the thickness of BNNS was calculated at 8.…”

High Thermal Conductivity Polymer Composites Fabrication through Conventional and 3D Printing Processes: State‐of‐the‐Art and Future Trends

“…The presence of impurities on the surface of 2D materials, such as BNNS and carbon materials is deleterious due to their intrinsic thermal and electrical properties as they originate from electron and phonon scattering, which causes a decline in electrical and thermal conduction. [ 3 ]…”