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Ali, Ghafar,Yoo, Seung Hwa,Kum, Jong Min,Kim, Yong Nam,Cho, Sung Oh IOP Pub 2011 Nanotechnology Vol.22 No.24
<P>We present a novel and straightforward approach to fabricate large-scale and robust free-standing TiO<SUB>2</SUB> nanotube (TNT) membranes. Simply by blowing N<SUB>2</SUB> gas onto as-anodized TNTs that are wetted with methanol, free-standing TNT membranes are produced. The approach also provides homogeneous and honeycomb-like Ti substrates after the detachment of TNT membranes. Through the second anodization of the honeycomb-like Ti substrates following the N<SUB>2</SUB> blowing, TNT membranes comprising hexagonally close-packed and regularly ordered TNTs with clear open ends can be achieved. Characterization of the free-standing TNT membranes using Raman spectroscopy and a high-resolution transmission electron microscope reveals that anatase TiO<SUB>2</SUB> and crystalline graphitic carbon are embedded in the bottom surface of the free-standing TNT membranes. </P>
Fabrication of complete titania nanoporous structures via electrochemical anodization of Ti
Ali, Ghafar,Chen, Chong,Yoo, Seung Hwa,Kum, Jong Min,Cho, Sung Oh Springer 2011 Nanoscale research letters Vol.6 No.1
<P>We present a novel method to fabricate complete and highly oriented anodic titanium oxide (ATO) nano-porous structures with uniform and parallel nanochannels. ATO nano-porous structures are fabricated by anodizing a Ti-foil in two different organic viscous electrolytes at room temperature using a two-step anodizing method. TiO<SUB>2 </SUB>nanotubes covered with a few nanometer thin nano-porous layer is produced when the first and the second anodization are carried out in the same electrolyte. However, a complete titania nano-porous (TNP) structures are obtained when the second anodization is conducted in a viscous electrolyte when compared to the first one. TNP structure was attributed to the suppression of F-rich layer dissolution between the cell boundaries in the viscous electrolyte. The structural morphologies were examined by field emission scanning electron microscope. The average pore diameter is approximately 70 nm, while the average inter-pore distance is approximately 130 nm. These TNP structures are useful to fabricate other nanostructure materials and nanodevices.</P>
Rapid synthesis of TiO<sub>2</sub> nanoparticles by electrochemical anodization of a Ti wire
Ali, Ghafar,Kim, Hyun Jin,Kum, Jong Min,Cho, Sung Oh IOP Pub 2013 Nanotechnology Vol.24 No.18
<P>We present a simple and novel strategy to synthesize TiO<SUB>2</SUB> nanoparticles (NPs) based on electrochemical anodization of a Ti wire in an aqueous KCl electrolyte. The Ti wire is very rapidly and directly converted to TiO<SUB>2</SUB> NPs by the anodization process, allowing mass production of TiO<SUB>2</SUB> NPs. The size of the synthesized NPs can be readily tuned by changing the concentration of the electrolyte. We found that the field-assisted etching related to a strong electric field and the rapid etching rate caused by chloride ions play important roles for the formation of TiO<SUB>2</SUB> NPs. This approach can also be applied to the mass production of other semiconducting metal oxide NPs such as tungsten-oxide NPs. TiO<SUB>2</SUB> NPs showed higher photocatalytic activity compared to Degussa (P 25) under the same conditions. The higher photocatalytic activity of TiO<SUB>2</SUB> NPs is attributed to the polymorphism. We believe that our approach can be used in broad areas including biomedical applications, photovoltaics, optics, and electronics.</P>
Ali, Ghafar,Park, Yang Jeong,Kim, Hyun Jin,Cho, Sung Oh Springer 2014 NANOSCALE RESEARCH LETTERS Vol.9 No.1
<P>This work reports the formation of self-organized Zircaloy-4 (Zr-4) oxide nanotubes in viscous organic ethylene glycol (EG) electrolyte containing a small amount of fluoride salt and deionized (DI) water via an electrochemical anodization. The structure, morphology, and composition of the Zr-4 oxide nanotubes were studied using X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), EDX, and XPS. SEM results showed that the length of the nanotubes is approximately 13 μm, and TEM results showed that the inner diameter of the Zr-4 oxide nanotubes is approximately 20 nm with average wall thickness of approximately 7 nm. XRD and selected area electron diffraction pattern (SAED) results confirmed that the as-anodized Zr-4 oxide nanotubes have cubic crystalline structure. Both cubic and monoclinic phases were found after annealing of Zr-4 oxide nanotubes. The tubular structure morphology of Zr-4 oxide nanotubes did not remain intact after annealing which is attributed to the elimination of F species from the annealed nanotubes.</P>
Tariq Ali,Saima Mohyuddin,Ghafar Ali,Muhammad Ibrar,Faiza Summer,Sajid Iqbal,Yi Xie,Muhammad Maqbool 대한금속·재료학회 2022 ELECTRONIC MATERIALS LETTERS Vol.18 No.1
Self-organized and vertically oriented TiO2nanotubes (TNTs) were synthesized via anodization of Ti sheet in a glycerolbasedused electrolyte. Graphite (Gt) is doped in TNTs by physical vapor deposition (PVD) under Ar-atmosphere at 700 °Cusing polyvinyl alcohol (PVA) as a precursor. The samples were characterized using FESEM, HRTEM, XRD, Raman,XPS, and UV–vis diffuse reflectance spectroscopy. HRTEM, XRD, and Raman analysis confirm the suppression of phasetransformation from anatase to rutile due to Gt doping. The UV–vis absorption properties and photocatalytic activity of thepristine and Gt-doped TNTs have been investigated. The bandgap absorption edge of Gt-doped TNTs shifts towards a higherwavelength (~ 550 nm) compared to the pristine TNTs (~ 390 nm). Moreover, the Gt-doped TNTs show strong absorptionin the visible region. This makes it a good candidate for energy-storing applications. It has been found that Gt-doped TNTsdisplay two-fold enhanced photocatalytic activity for methyl orange (MO) degradation compared to pristine. The enhancedphoto-degradation of Gt-doped TNTs is ascribed to the higher absorptivity, better crystallinity, and lower bandgap of TNTsdue to Gt doping. The enhanced photo-degradation ability of Gt-doped TNTs can be used to clean industrial wastewater.
Xie, Yi,Ali, Ghafar,Yoo, Seung Hwa,Cho, Sung Oh American Chemical Society 2010 ACS APPLIED MATERIALS & INTERFACES Vol.2 No.10
<P>A sonication-assisted sequential chemical bath deposition (S-CBD) approach is presented to uniformly decorate CdS quantum dots (QDs) on self-organized TiO<SUB>2</SUB> nanotube arrays (TNTAs). This approach avoids the clogging of CdS QDs at the TiO<SUB>2</SUB> nanotube mouth and promotes the deposition of CdS QDs into the nanotubes as well as on the tube walls. The photoelectrochemical and photocatalytic properties of the resulting CdS-decorated TNTAs were explored in detail. In comparison with a classical S-CBD approach, the sonication-assisted technique showed much enhancement in the photoelectrochemical and photocatalytic activities of the CdS QDs-sensitized TNTAs.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2010/aamick.2010.2.issue-10/am100605a/production/images/medium/am-2010-00605a_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am100605a'>ACS Electronic Supporting Info</A></P>
Chen, Chong,Ali, Ghafar,Yoo, Seung Hwa,Kum, Jong Min,Cho, Sung Oh Royal Society of Chemistry 2011 Journal of materials chemistry Vol.21 No.41
<P>A thin layer of CuInS<SUB>2</SUB> and CdS quantum dots (QDs) is deposited on TiO<SUB>2</SUB> nanotube arrays (TNTs) to form CdS/CuInS<SUB>2</SUB>/TNTs photoelectrodes. The CuInS<SUB>2</SUB> layer is prepared by a successive ionic layer absorption and reaction method, and the CdS QDs are deposited by a chemical bath deposition method. The CuInS<SUB>2</SUB> layer acts as both a co-sensitizer and an energy barrier layer between TNTs and CdS QDs. The deposited CuInS<SUB>2</SUB> layer significantly extends the visible-light response of CdS-sensitized TNTs into 500–700 nm wavelength range. As a consequence, the photoelectrochemical response of the CdS/CuInS<SUB>2</SUB>/TNTs electrodes is much improved compared with CdS sensitized TNTs. The CdS/CuInS<SUB>2</SUB>/TNTs electrodes exhibit a maximum power conversion efficiency of 7.3%, which is a 120% improvement compared with the highest efficiency of 3.3% for CdS/TNTs electrodes in our study. The improved efficiency is mainly due to the increased absorbance and the reduced recombination between the photoinjected electrons and the redox ions from the electrolyte, resulting from the formation of a CuInS<SUB>2</SUB> layer.</P> <P>Graphic Abstract</P><P>Using CuInS<SUB>2</SUB> as a co-sensitizer and an energy barrier layer to improve conversion efficiency of CdS quantum dot-sensitized TiO<SUB>2</SUB> nanotube-arrays. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c1jm13616j'> </P>
Song, Er Hong,Ali, Ghafar,Yoo, Sung Ho,Jiang, Qing,Cho, Sung Oh Springer 2014 NANOSCALE RESEARCH LETTERS Vol.9 No.1
<P>Using density functional theory calculations, we have investigated the effects of biaxial tensile strain on the electronic and magnetic properties of partially hydrogenated graphene (PHG) structures. Our study demonstrates that PHG configuration with hexagon vacancies is more energetically favorable than several other types of PHG configurations. In addition, an appropriate biaxial tensile strain can effectively tune the band gap and magnetism of the hydrogenated graphene. The band gap and magnetism of such configurations can be continuously increased when the magnitude of the biaxial tensile strain is increased. This fact that both the band gap and magnetism of partially hydrogenated graphene can be tuned by applying biaxial tensile strain provides a new pathway for the applications of graphene to electronics and photonics.</P>