Browsing by Subject "Hydrothermal"
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Item Open Access Effect of Au nano-particles on TiO2 nanorod electrode in dye-sensitized solar cells(Elsevier, 2012-05-26) Ghaffari, M.; Cosar, M. B.; Yavuz, H. I.; Ozenbas, M.; Okyay, Ali KemalAu nano particles (NPs) were deposited on vertically grown TiO2 nanorod arrays on FTO substrate by hydrothermal process. Metal nanoparticles were loaded onto the surface of TiO2 nanorods via photochemical reduction process under ultraviolet irradiation. X-ray diffraction (XRD), electron microscopy (FESEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) analysis were used to characterize the as-prepared Au/TiO2 nanorod composites. Current density-voltage (I-V) measurements were obtained from a two-electrode sandwich type cell. The presence of Au nanoparticles can help the electron-hole separation by attracting photoelectrons. Addition of Au nanoparticles to the TiO2 nanorod significantly increased the fill factor and J(SC) (short circuit current density). The application of Au NPs TiO2 nanorods in improving the performance of DSSCs is promising.Item Open Access Enhanced photocatalytic activity of homoassembled ZnO nanostructures on electrospun polymeric nanofibers: a combination of atomic layer deposition and hydrothermal growth(Elsevier, 2014) Kayaci, F.; Vempati S.; Ozgit Akgun, C.; Bıyıklı, Necmi; Uyar, TamerWe report on the synthesis and photocatalytic activity (PCA) of electrospun poly(acrylonitrile) (PAN) nanofibrous mat decorated with nanoneedles of zinc oxide (ZnO). Apart from a detailed morphological and structural characterization, the PCA has been carefully monitored and the results are discussed elaborately when juxtaposed with the photoluminescence. The present hierarchal homoassembled nanostructures are a combination of two types of ZnO with diverse optical qualities, i.e. (a) controlled deposition of ZnO coating on nanofibers with dominant oxygen vacancies and significant grain boundaries by atomic layer deposition (ALD), and (b) growth of single crystalline ZnO nanoneedles with high optical quality on the ALD seeds via hydrothermal process. The needle structure (~25. nm in diameter with an aspect ratio of ~24) also supports the vectorial transport of photo-charge carriers, which is crucial for high catalytic activity. Furthermore, it is shown that enhanced PCA is because of the catalytic activity at surface defects (on ALD seed), valence band, and conduction band (of ZnO nanoneedles). PCA and durability of the PAN/ZnO nanofibrous mat have also been tested with aqueous solution of methylene blue and the results showed almost no decay in the catalytic activity of this material when reused.Item Open Access Morphology-tailored synthesis of tungsten trioxide (Hydrate) thin films and their photocatalytic properties(ACS Publications, 2011-01-10) Jiao, Z. H.; Wang, J. M.; Ke, L.; Sun, X. W.; Demir, Hilmi VolkanTungsten trioxide hydrate (3WO(3)center dot H(2)O) films with different morphologies were directly grown on fluorine doped tin oxide (FTO) subsi:rate via a facile crystal-seed-assisted hydrothermal method. Scanning electron microscopy (SEM) analysis showed that 3WO(3)center dot H(2)O thin films composed of platelike, wedgelike, and sheetlike nanostructures could be selectively synthesized by adding Na(2)SO(4), (NH(4))(2)SO(4), and CH(3)COONH(4) as capping agents, respectively. X-ray diffraction (XRD) studies indicated that these films were of orthorhombic structure. The as-prepared thin films after dehydration showed obvious photcicatalytic activities. The best film grown using CH(3)COONH(4) as a capping agent generated anodic photocurrents of 1.16 mA/cm(2) fork oxidization of methanol and 0.5 mA/cm(2) for water splitting with the highest photoconversion efficiency of about 0.3% under simulated solar illumination.Item Open Access Seed layer assisted hydrothermal deposition of low-resistivity ZnO thin films(Materials Research Society, 2017) Chubenko, E.; Bondarenko, V.; Ghobadi, Amir; Ulusoy, Gamze; Topallı, Kağan; Okyay, Ali KemalIn this work, we describe the combination of hydrothermal and atomic layer deposition (ALD) for growing low-resistivity ZnO polycrystalline continuous films. The effect of the thickness of ALD seed layers on the morphology of the hydrothermal ZnO films was studied. It was shown that ZnO films hydrothermally deposited on very thin seed layer consist of separate nanorods but in the case of 20 nm seed layer ZnO films transform to uniform continuous layers comprising of closely packed vertically aligned crystallites. Photoluminescence spectra were shown to exhibit broad band behavior in the visible range, corresponding to radiative recombination processes via oxygen defects of ZnO crystalline lattice, and narrow band in the UV region, associated with band-to-band recombination processes. It was shown that the resistivity of the obtained ZnO films is decreased gradually with the increase of ZnO films thickness and determined by the presence of crystal lattice defects in the seed layer.