Syahriza Ismail

Formation of Zirconia and Titania Nanotubes in Fluorine Contained Glycerol Electrochemical Bath

The formation of self-aligned titania and zirconia nanotubes is achieved by the anodisation of Ti and Zr in a fluorine contained electrochemical bath. The anodic oxidation was performed at 30 V for 60 min in a two-electrode glycerol (15% water) bath containing varying amount of NH4F. Despite the fact that a self-aligned nanotubular structure is formed on both titanium and zirconium, the dimensions of zirconia and titania nanotubes are different under the same anodisation parameters. It appears that by using 30 V as the anodisation voltage, the diameter of zirconia nanotubes (30-60 nm) is much smaller compared to that of titania nanotubes (80-100 nm). The length of zirconia nanotubes in the bath consisting of 0.7 g NH4F is 3 µm whereas titania nanotubes formed in the same bath have a length of ~700 nm. The fundamental difference between the nanotubes formed on titanium and zirconium may be related to the rate of oxidation, initial oxide formation during anodisation, pits formation and rate of pits growth for pores formation and stabilisation. Moreover, investigation on the crystallinity of the nanotubes reveals that titania nanotubes are weakly crystalline with crystallite sizes of <5 nm. Whereas, zirconia nanotubes are much more crystalline in cubic modification. The stabilisation of the high temperature phase is thought to originate from the size of the nanotubes walls and the deficiency in oxygen during the growth of the anodic oxide by anodisation.

Formation and Mechanistic Study of Self-Ordering ZrO2 Nanotubes by Anodic Oxidation

Among all of the one dimensional nanostructures other than titania (TiO2) and carbon, zirconia (ZrO2) have started to gain interest due to its potential in catalytic and energy applications. ZrO2 nanotubes arrays have been prepared using electrochemical anodizing method of Zr foil in fluorine containing glycerol electrolyte. The morphology and structure of the ZrO2 nanotubes are strongly controlled by the applied electrochemical condition especially voltage. Nanotubes with diameter of 30 to 60 nm has been produced by controlling the anodization voltage from 10 to 40 V. The ZrO2 nanotubes formed in this method is partially crystalline even without the heat treatment. The wall thickness is ~10 nm. The self-aligned nanotubes produced by this method could be used for phocatalytic application. The degradation of methylene orange under UV light was successful when ZrO2 nanotubes made in 30 V is used.

Formation of Anodic Oxide Nanotubes in H2O2 - Fluoride Ethylene Glycol Electrolyte as Template for Electrodeposition of α-Fe2O3

Anodic oxidation of titanium (Ti), zirconium (Zr) and niobium (Nb) foils in fluoride ethylene glycol (EG) added to it 1 H2O2 as oxidant was done to produce oxide film with nanostructures at 40 V. Whilst arrays of aligned nanotubes were successfully formed on the surface of Ti and Zr respectively, anodic Nb2O5 was found to consist of nanoporous structure with pore size of ~ 20 nm. Despite long nanotubes were formed on both Ti (2 μm) and Zr (3 μm), the surface of the nanotubes suffered from severe dissolution, thinning the wall and collapsing them. Well defined, ordered surface structure of the nanotubes is required as they will be used as template for subsequent deposition of nanoparticles. This was achieved when Ti anodised in 5 ml H2O2 fluoride EG. With excess H2O2 etching at the surface occur more uniformly forming homogenous surface structure. α-Fe2O3 were then electrodeposited on this surface at-3 V from chloride solution and the mode of formation is believed to be due to electrogeneration of base at the surface of the TiO2.

Crystallization of TiO2 Nanotubes Arrays Grown by Anodization of Ti in Organic Electrolyte

The TiO2 anodized in organic electrolyte using 85% glycerol is used to investigate the crystalization of TiO2 nanotubes annealed in air. The anatase start to form at 300°C and rutile appear when the temperature about 600 °C. The phase transformation is dependent on the annealing time and temperature. The anatase can be form at low temperatures when the annealing time is prolonged. The morphology of the annealed TiO2 nanotubes changes as the function of the annealing temperature and the mechanism for the phase transformation of anatase to rutile is discussed.

Effect of Anodisation Parameters on the Formation of Porous Anodic Oxide on Ti, Zr and W

Ti, Zr and W foils were anodized in 85% glycerol + 15% water electrolyte added to it 0.5wt%NH4F (pH ~ 6) at 20V. Self-ordered nanotubular oxide structure was found on Ti and Zr whereas oxide on W is comprised of dual layer with compact inner layer and oxide precipitates as the outer layer. The mechanism of the formation of the nanotubes is discussed. The formation of bi-layer on W is attributed to the high degree of dissolution and precipitation of WO3 on the surface of the anodic oxide in the viscous glycerol solution. In aqueous bath, the precipitation is much reduced revealing WO3 with a more ordered porous structure. On Zr foil nanotubes formed are much smaller than on Ti with diameter of < 40 nm compared to 100 nm on Ti. The length of the nanotubes is in the range of 1–2(μm for both zirconia and titania nanotubes. Increasing the voltage increases the diameter of the nanotubes marginally and there exists a maximum voltage which could be applied on the foils before the nanotubular structure is destroyed. In 85% glycerol, the voltage must be kept at < 30V for both samples.

Bamboo Sawdust as a Reduction Agent in Leaching Applications: Characterization Studies

One of the promising and environmentally friendly hydrometallurgical processes for the recovery of manganese is acid leaching in the presence of carbohydrate as a reducing agent. The aim of this study is to characterize bamboo sawdust (BSD), in particular, the carbohydrate within, for possible usage as a reduction agent in acid leaching applications. Characterization were done using Malvern analyzer (particle size distribution), SEM (morphology), XRD (crystalline index) and FTIR (molecular framework). Detailed BSD constituents were also analyzed, to determine the cellulose, hemicellulose and lignin content. Results exhibited a wide size range distribution with a span value of 1.86, and geometric mean diameter of ~100 µm. The dominant composition, meanwhile, were cellulose (38.96%) hemicellulose (26.95%) and lignin (25.86%). The morphology characteristic by SEM revealed a smooth fibrous surface with multiple aligned bundles. The assessable crystalline index of cellulose was 56.12%. The molecular framework of cellulose, hemicellulose and lignin were clearly illustrated in BSD. The obtained characteristics are valuable information in utilizing BSD as a source of carbohydrate for leaching application.

Control Over the Growth of Titania Nanotubes by Anodisation of TI Foil in NH4F‐Containing Electrolyte

TiO2 nanotubes were produced by anodisation of pure titanium foil in a standard two‐electrode bath consisting of either 1 M Na2SO4 or glycerol solution containing 5 wt% NH4F. The effect of anodisation voltage applied to the foil was studied to investigate the possibility of controlling the dimensions of the nanotubes produced. It was found that, in both electrochemical baths the diameter of the nanotubes increases with increasing of the applied voltage. However, in 1 M Na2SO4 there appears to be a maximum voltage at which the nanotubular structure persists. The maximum applied voltage must be less than 30 V. Above this voltage, the nanotubular structure is destroyed leaving an oxide with porous‐like morphology. In glycerol bath, the maximum voltage is higher. The length of the nanotubes was also found to be dependent on the voltage. In glycerol, the length of the nanotubes increases from 200 nm to 700 nm as the anodisation voltage was increased from 10 to 30 V.