In this work, g-C 3 N 4 /rGO nanocomposites were synthesized to use them as photocatalysts in Li-ion oxygen batteries by aiming at the reduction of the charging potential efficiently under photoassisted conditions. Fourier transform infrared (FTIR) spectra showed that novel C�C bonds formed between g-C 3 N 4 and rGO during the decomposition of melamine and that the formation of these bonds was assumed to cause a red shift in the optical absorption band edge. The competition between the narrowing in the optical band gaps of the nanocomposites as a result of the red shift due to the presence of rGO and the degradation in the visible light utilization as a result of favorably absorbed incident light by rGO instead of g-C 3 N 4 pointed out that the g-C 3 N 4 /3% rGO nanocomposite has the optimum light absorbance efficiency. The photoassisted charging tests indicated that the g-C 3 N 4 /3% rGO nanocomposite reduced the charging potential effectively, especially at higher current densities, and improved the cyclic discharge− charge performance of the Li-ion oxygen batteries considerably. KEYWORDS: g-C 3 N 4 /rGO, nanocomposites, photocharging, Li-ion oxygen batteries, photocatalyst
The effect of the deep cryogenic treatment on the micro-structure and mechanical properties (tensile strength, toughness, residual stress and fatigue strength) of the medium carbon spring steel, which is subjected to different heat treatment steps, is investigated. Deep cryogenic treatment causes spring steel to keep compressive residual stress more efficiently due to an increase in the density of the crystalline defects, retardation in the stress relief after the phase transformations and nano-cluster carbide formations. If deep cryogenic treatment is applied before the tempering then the homogeneously distributed fine carbides form after the tempering and the grains remain relatively fine. The microstructure with homogeneously distributed fine carbides and fine grains cause spring steels to have simultaneously enhanced tensile strength, ductility and fatigue strength. If deep cryogenic treatment is applied after the conventional heat treatment (quenching + tempering), however, the coarse carbides form in the micro-structure and the improvement in the mechanical properties of the spring steel is limited.
Graphene was synthesized by the chemical vapor deposition (CVD). Initially ratios of Ar, H2 and CH4 gases were optimized to get a single layer graphene by CVD. Raman characterizations showed that the optimized synthesis conditions provided I2D/IG ratio as 3 that this ratio indicated the formation of the single layer graphene. The synthesized single layer graphene was mixed with melamine at the certain ratios to obtain the graphene/graphitic-C3N4 (g-C3N4) semiconductor composites. All the synthesized composites were prepared as the photo-electrode to be used in the photo-assisted charging of the lithium-ion oxygen battery. The photo-current levels produced by the photo-electrodes were determined by the linear sweep voltammetry technique.
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