Graphene Nanoplatelets with different morphologies and the influence on the measured functionalization degree.
Source: BAM
Graphene has some unique electric, optical, and thermal properties due to the structure of one single carbon monolayer. In contrast to graphene deposited on a substrate, graphene as powder does not exist as single ideal monolayer, but usually as stacks of several layers. When such kind of graphene will be chemically modified, which means functionalized, it is important to know, which layer from the stack will be functionalized. Such functionalization is important for the application of graphene, but also for the risk for environment and health. For example, the solubility of graphene in water can be influenced.
For the investigation of the chemical composition of graphene, and, herewith, of the functionalization of such two-dimensional structures, X-ray photoelectron spectroscopy (XPS) is a prominent method. Hereby, the sample is irradiated by X-rays; because of this irradiation, electrons are emitted. By measuring the number and the energy of the electrons, the chemical composition in the outermost first layers of the samples of a few nanometers can be determined. If the energy of the X-rays will be increased, deeper layers of the samples can be investigated. BAM is one of the few sites in Europe, where such an instrumentation is installed, which allows measurements with X-rays of lower energy (1.5 keV) and of so-called hard X-rays with a higher energy (5.5 keV) at the same location of the sample. Thereby, a non-destructive depth profile can be performed at complex samples like graphene nanoplatelets with different morphologies.
In a recently published study, platelets with a particle-like structure of about 100 nm were compared with stack of platelets of a few mircrometers. At these stack-like structure a higher degree of functionalization in the outermost layer of the stack than in the inner layers was detected. As expected, this effect was not so significant at the smaller particles. With this experimental approach, the functionalization of the graphene nanoplatelets can be investigated and und understood, which is important for the application and the risk assessment of graphene, and, herewith, for the safe use of graphene.
Influence of the Morphology on the Functionalization of Graphene Nanoplatelets Analyzed by Comparative Photoelectron Spectroscopy with Soft and Hard X-Rays
Giovanni Chemello, Xenia Knigge, Dmitri Ciornii, B.P. Reed, A.J. Pollard, C.A. Clifford, T. Howe, N. Vyas, Vasile-Dan Hodoroaba, Jörg Radnik
published in Advanced Materials Interfaces, article number 2300116, pages 1 bis 8
BAM Materials Chemistry
BAM Surface Analysis and Interfacial Chemistry