Correlation between geometrical and structural properties of mixed oxide ultrathin nanotubes and their solar water splitting performance
The objective of this study was to study the effect of Nb alloying with Ti on the photoelectrochemical performance of the resulted oxide upon anodization. In this regard, nanotubes were grown on Ti-Nb alloy via electrochemical anodization and their corresponding photocatalytic behavior was investigated and compared with those grown on an ordinary Ti substrate. After preparing and optimizing the nanotubes dimensions for the required geometrical structure, the as formed tubes were annealed at different temperatures and in air), then characterized with respect to their morphological, structural, and photoelectrochemical properties. From the morphological and structural point of view, optimized and well aligned ultra-thin wall nanotubes were successfully synthesized on the surface of Ti-Nb alloy. To the best of our knowledge, these dimensions have not been reported before. One of the challenges was that the oxide layer formed on the surface of the alloy was not precisely identified in literature, where some authors reported the formation of combination of individual oxides (TiO2 and Nb2O5), whereas, others claimed it was a mixed oxide TiNbOx. Raman and X-ray diffraction test results confirmed the formation of individual anatase and monoclinic Nb2O5 phases. Detailed XRD analysis was performed and the crystallite size as well as microstrain were calculated and found to be minimal indicating negligible effect of lattice induced tension or compression. It is worth mentioning that insignificant structural changes are favorable to maintain good electron mobility. Hence, point defect equations were deduced and it was found that that oxygen vacancies were the prevailing ionic defects rather than electronic Nb compensation. From the aforementioned results, ultrathin wall nanotubes formed on TiNb alloy were achieved, for the first time, with clear representation of the oxide layer composition. Such oxide layer showed better stability upon annealing at high temperatures. Although, UV-Vis test results showed small or negligible enhancement in the absorption, profile the photo-electrochemical measurements showed much higher photocurrent for Ti-Nb oxide alloy than bare TiO2 prepared at the same conditions for the sake of comparison. In conclusion, the Ti-Nb NTs showed enhanced stability over a wide range of temperatures, where the transition from anatase to rutile was shifted to higher temperature in addition to an increase in the photoconversion capability, resulting in a more efficient water splitting process.
Mechanical Engineering Department
MS in Mechanical Engineering
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(2017).Correlation between geometrical and structural properties of mixed oxide ultrathin nanotubes and their solar water splitting performance [Master's Thesis, the American University in Cairo]. AUC Knowledge Fountain.
Elsayed, Ayatullah Mohamed Adel Saleh. Correlation between geometrical and structural properties of mixed oxide ultrathin nanotubes and their solar water splitting performance. 2017. American University in Cairo, Master's Thesis. AUC Knowledge Fountain.