Methods of production of carbon nanoparticles by laser reduction of graphene oxide
Graphene oxide is a monomolecular carbon-based material with attached oxygen-containing groups on its surface. There are a number of applications in which it is simultaneously required to obtain graphene oxide with high thermal and electrical conductivity, which can be provided by various functional groups on the surface [1-2]. To create this type of material, graphene oxide needs to be thermally reduced. The processed material has properties similar to so-called carbon nanowalls  that can be used to produce nanoparticles of graphene: the raw material to produce quantum dots, bioactive substances and so on.
The aim of this work is to study the effect of different temperature regimes on the reduction of graphene oxide under ambient conditions using laser radiation and its influence on the parameters of the final carbon nanoparticles.
To determine the influence of laser irradiation conditions, the following parameters are varied: frequency of laser pulses, scanning speed of a laser beam, average laser power. The obtained samples are dispersed by ultrasonic treatment in an aqueous solution. The nonlinear optical properties of the samples are analyzed using aperture and non-aperture Z-scan. The nonlinear part of the refractive index of the obtained solutions of nanoparticles is estimated.
Z-scanning is performed using a 0.1 W laser diode with a wavelength of 505 nm. A collecting lens focuses the radiation onto the sample, then the light that passes through the diaphragm (during aperture measurement) enters the photosensor. During the measurement, the sample is shifted along the optical axis with a step of 0.5 mm, while passing through the focus of the collecting lens. The nonlinear 3rd-order constants of carbon nanoparticle soputions were measured.
The size of nanoparticles was measured by indicatrix of the Rayleigh scattering. The average size of a nanoparticle was of 140+/-40 nm.
To estimate the film temperature under laser irradiation, the heat conduction equation is solved numerically in the approximation of a radially symmetric system.
 S.A. Evlashin, S.E. Svyakhovskiy, F.S. Fedorov et al. Ambient condition production of high quality reduced graphene oxide. ADVANCED MATERIALS INTERFACES, 1800737, 2018
 S.A. Evlashin, P. Dyakonov et al. Controllable laser reduction of graphene oxide films for photoelectronic applications. ACS applied materials & interfaces, 8(42):28880–28887, 2016.
 V. A. Krivchenko, K. V. Mironovich et al. Carbon nanowalls: the next step for physical manifestation of the black body coating. Scientific Reports, 3(1), 2013.
Lomonosov Moscow State University
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