In this work, the reducing power of three reductants: hydrazine (chemical), ascorbic acid (mild) and the extract of Amaranthus hybridus (green) were investigated. Graphene oxide (GO) was synthesized by modified Hummer's method and was reduced by hydrazine (RGO-HZ), ascorbic acid (RGO-AA) and the extract of Amaranthus hybridus (RGO-AH). GO, RGO-HZ, RGO-AA and RGO-AH were characterized using Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy and ultraviolet visible spectrometry. The FTIR spectra showed the presence of oxygen functionality groups in GO which were reduced in all RGOs. The morphological properties showed that RGOs sheets were exfoliated forming clusters with roughened surfaces while the optical energy band gaps of 2.19, 3.90, 3.60, and 3.20 eV were estimated for GO, RGO-HZ, RGO-AA and RGO-AH respectively. It can be concluded that the three reductants demonstrated good reducing capacities. The ascorbic acid and the extract of Amaranthus hybridus, apart from being environmentally friendly, can also be good substitutes for the dangerous chemical hydrazine.

Graphene Oxide (GO) was chemically synthesized from Natural Flake Graphite (NFG). The GO was chemically reduced to Reduced Graphene Oxide (RGO) using hydrazine monohydrate. Thin films of GO and RGO were also deposited on sodalime glass substrate using spray pyrolysis technique (SPT). The samples were characterized using Fourier Transform Infrared (FTIR) spectroscopy, Scanning Electron Microscopy (SEM) with Energy Dispersive X-Ray (EDS) facility attached to it, UV-Visible Spectrometry and Four-Point probe. The FTIR spectra showed the addition of oxygen functionality groups in GO while such groups was drastically reduced in RGO. SEM micrograph of GO thin film showed a porous sponge-like structure while the micrograph of RGO thin film showed evenly distributed and well connected graphene structure. The EDX spectrum of RGO showed that there was decrease in oxygen content and increase in carbon content of RGO when compared to GO. The optical analysis of the GO and RGO thin films gave a direct energy bandgap of 2.7 eV and 2.2 eV respectively. The value of sheet resistance of GO and RGO films was determined to be 22.9 × 10 6 Ω/sq and 4.95 × 10 6 Ω/sq respectively.

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a b s t r a c tSurface texturing or topographical design is one of the primary techniques to control friction and wear performance of surfaces in tribological contact. Laser surface texturing (LST), whereby a laser beam is used to produce regular arrays of dimples on a surface, has been demonstrated to reduce friction in conformal lubricated contacts. Friction and wear behavior under boundary lubrication is also known to be dependent on the formation and durability of the tribochemical film formed from lubricant additives. In this paper, the effects of LST on the formation and durability of tribochemical films and its consequent impacts on friction and wear behavior in various lubrication regimes were evaluated. Friction and wear tests that cycled through different lubrication regimes were conducted with both polished and LST treated surfaces using a synthetic lubricant with and without model additives of ZDDP and MoDTC mixture. In the base oil without additives, LST produced noticeable reduction in friction in all lubrication regimes. However, with low-friction model additives, friction was higher in tests with LST due to significant differences in the tribochemical film formation in the polished and LST surfaces, as well as the sliding counterface. Continuous tribo-films were formed on ball conterface rubbed against polished surfaces while the films were streaky and discontinuous in ball rubbed against LST surfaces. LST produced more wear on the ball counterface in both base and additized oils. No measurable wear was observed in both the polished and LST flat specimens.