Effects of Wet Chemical Oxidation on Surface Functionalization and Morphology of Highly Oriented Pyrolytic Graphite

Abstract

The knowledge of chemical functionalization for area selective deposition (ASD) is crucial for designing the next generation heterogeneous catalysis. Surface functionalization by oxidation was studied on the surface of highly oriented pyrolytic graphite (HOPG). The HOPG surface was exposed to with various concentrations of two different acids (HCl and HNO3). We show that exposure of the HOPG surface to the acid solutions produce primarily the same -OH functional group and also significant differences the surface topography. Mechanisms are suggested to explain these strikingly different surface morphologies after surface oxidation. This knowledge can be used to for ASD synthesis methods for future graphene-based technologies.

Investigating the Relationship between Adhesion Forces and Surface Functionalization Using Atomic Force Microscopy

“…In the OH-functionalized HOPG image (Figure C), graphitic islands and trenches are observed to decorate the surface, produced from oxidation with concentrated HNO 3 . This shows that when HOPG is exposed to concentrated HNO 3 , the surface is oxidized and changes the morphology of the HOPG surface. ,,, It should be noted that Figure B shows slight interference in the image, which may have been due to environmental noise and Figure C shows an AFM streak, which is an error in the scanning of the image. Streaks are common AFM artifacts and may have occurred due to vibrational noise experienced by the probe during scanning.…”

“…Graphene-based technologies and other 2D materials are intensely investigated as potential new materials in the aforementioned fields of semiconductor design and catalysis, as well as in the broad field of nanotechnology. ,− Highly oriented pyrolytic graphite (HOPG) has been used in the field of surface science as a model graphene surface, due to its sp 2 -hybridized carbon network, ease of preparation, and well-defined surface sites, such as the planar graphene terrace and step-edge defects . Because of its surface structure, HOPG is known to be hydrophobic and air-stable. , Additionally, treatment of graphene and related carbon nanomaterials with oxidizers produces graphene oxide of various morphologies. , Similar surface treatments can be used to produce (hydroxy) functionalized graphite . The surface oxidation causes the delamination of the graphitic surface by etching away sheets of graphene, resulting in trenches, holes, and various defects in the surface. − …”

“…Because of its surface structure, HOPG is known to be hydrophobic and air-stable. , Additionally, treatment of graphene and related carbon nanomaterials with oxidizers produces graphene oxide of various morphologies. , Similar surface treatments can be used to produce (hydroxy) functionalized graphite . The surface oxidation causes the delamination of the graphitic surface by etching away sheets of graphene, resulting in trenches, holes, and various defects in the surface. − …”

“…In our previous work, we and others , have observed that HOPG becomes functionalized with OH groups, through surface oxidation, as observed by X-ray photoelectron spectroscopy. We have also observed that when the HOPG surface is exposed to concentrated nitric acid, the surface topography is drastically affected, producing large trenches on the HOPG surface on the nanoscale compared to untreated HOPG. , These topographical features and roughness were quantified in this lab experiment in comparison to the flat HOPG surface, the unfunctionalized surface with no oxygen groups, and sputter-deposited gold, a metallic surface that is also unreactive in ambient air. In this study, force-pull measurements (force–displacement curves) are used to quantify the adhesion force, which is defined as how much force is required to pull the tip away from the surface .…”

Simple, controllable and environmentally friendly synthesis of FeCoNiCuZn-based high-entropy alloy (HEA) catalysts, and their surface dynamics during nitrobenzene hydrogenation

“…The other three signals at 286.1 eV, 287.1 eV, and 288.3 eV are attributed to the oxygenated groups C -O, C--O and C-OOH, respectively. These oxygenated groups were expected as a result of the pretreatment of the graphite support prior to the alloys deposition, and have an important role in the electric performance of the catalysts, since these oxygenated functional groups may improve the dispersion of the substrate [69], the amount of surface defects and adsorption sites [70,71], and may enhance the electrical conductivity of the laminar graphite structures [69]. The signal at 284 eV was attributed to the C--C bond in the graphite sheets.…”