Güler, Seval Hale; Safa, Hasan

In this study, BNNSs were synthesized via liquid-phase exfoliation method. Hexagonal boron nitride powders were used as the starting material. The production of boron nitride nanosheets was optimized. For this purpose, different sonication parameters and the effects of different solvents have been investigated. Different sonication power and time parameters of the homogenizer (Sonics Vibra-cell VCX, 750 W) used as the sonication parameter have been changed. In this stage, they were subjected to sonication process first for 1-1.5-2 hours at 25% sonication power, 1-1.5-2-4 hours at 50% sonication power, and 1-1.5-2-4-6-8 hours at 75% sonication power. As a result of particle size analysis, time/sonication power parameters were determined as 2 h-75%, 2 h-50%, 4 h-75%, 2 h-50%. The obtained samples were sedimented with centrifuge process, washed with distilled water to remove solvent, and dried. Different solvents were compared in the best power–time relationship. These solvents are dimethylformamide (DMF), isopropyl alcohol, N-methyl pyrrolidone, ethylene glycol. The best results were obtained in DMF. The synthesized BNNS samples were subjected to particle size (Malvern), scanning electron microscope (Zeiss, Gemini Supra 55), transmission electron microscope (Jeol Jem-1011), Fourier transform infrared spectroscopy (Thermo Scientific Nicolet™ iS™ 5), Raman (WITech alpha 300R), x-ray photoelectron spectroscopy (Specs-Flex), and x-ray diffraction analysis (PANalytical Empyrean).

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Güler, Ömer; Ayhan, Hakan; Başgöz, Öyküm; Yavuz, Çağdaş; Albayrak, M. Gökhan; Evin, Ertan; Safa, Hasan; Yahia, Ibrahim S.

In this study, titanium dioxide (TiO2)-based graphene nanoplatelets (GNPs)-reinforced composite materials were produced and the electrical and optical properties of the composite materials were investigated. Graphene, which was used as a reinforcing material, was produced by using liquid-phase exfoliation method. While the TiO2 used as matrix material was commercially available for the first group of samples, it was produced by using the sol–gel method for the second group of the samples. Different rates of graphene were added to the TiO2 powders which were commercially available and produced by using sol–gel method. GNPs used as a reinforcing material were subjected to TEM analysis. The resulting composite materials were structurally examined in SEM and XRD. Then, the changes in electrical conductivity of these composites under the impact of temperature were measured. UV–Vis spectrometers of the samples were taken and their optical properties were determined. When temperature-based electrical examination of the produced composite materials was performed, an increase was observed on the electrical conductivity values in both groups of samples as a result of addition of the reinforcing element. In addition, TiO2-containing composites produced by using sol–gel method had lower electrical conductivity comparing with commercially purchased TiO2-containing composites especially at high temperatures. In the optical measurements, it was observed that there was an increase in the optical bandgap energy range values with GNPs reinforcement but a decrease in the reflectance values.

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