Effect of the Temperature and Concentration of NaOH on the Formation of Porous TiO[sub 2]

Abstract

The influence of the temperature and concentration of NaOH on the formation of porous TiO 2 was investigated. The porous TiO 2 was obtained only after a 24-h immersion in 5 M NaOH at 353 K. The X-ray diffraction pattern indicated that the porous layer consisted of a mixture of anatase and rutile types of TiO 2 . During immersion in the NaOH solution, the anodic and cathodic reactions proceed at the same time on the titanium. From the cathodic polarization measurements, the cathodic reaction proceeded mainly the hydrogen evolution reaction. Therefore, a part of the adsorbed hydrogen penetrated into the titanium. The penetration of hydrogen confirmed with a glow discharge optical emission spectroscopy. The hydrogen evolution reaction continues during immersion in the 5 M NaOH solution at 353 K. However, the hydrogen evolution did not proceed in the low concentration of NaOH solution or at below 283 K. In addition, although the hydrogen evolution continues during immersion in 5 M NaOH solution at 303 or 333 K. As a result, the content of hydrogen in the titanium is insufficient to form the porous TiO 2 layer so that the porous layer is not produced on the titanium. Titanium dioxide ͑TiO 2 ͒ has favorable optical properties and a good stability in corrosive environments. Since O'Regan and Grätzel 1 reported the high-efficiency solar cell based on dyesensitized porous TiO 2 films in 1991, porous TiO 2 has become one of the most interesting materials in the field of solar cells and photoelectrochemistry. Since then, many researchers have vigorously investigated the formation of porous TiO 2 in order to use it as a material to convert photoenergy into electric energy. 2-6 Porous TiO 2 is also an attractive material in the field of biomaterials. This is because the porous TiO 2 can enhance the adhesion between an artificial bone, which is based on a titanium alloy, and calcium phosphate. [7][8][9][10] Although these properties, such as energy conversion efficiency and adhesion resistance, may be influenced by the structure of the porous TiO 2 , such as porosity, film thickness, and so on, the factor controlling these parameters has not been defined in detail. This is because the mechanism of the preparation for porous TiO 2 in alkaline solution has not yet been clarified. Generally, the porous TiO 2 was prepared by immersing in alkaline solution at high temperature for several hours. 8-12 However, we reported that the formation of porous TiO 2 was strongly dependent on the initial surface conditions of the titanium and the porous layer was only obtained in the presence of TiH 2 or a hydrogen-absorbed layer in the titanium before immersion in NaOH solution. 13,14 Therefore, we have proposed that the surface condition of titanium before immersion is an important factor for the formation of porous TiO 2 .In this study, we prepared the porous TiO 2 on the surface of titanium by immersing it in an alkaline solution in order to investigate the influence of the solution temperature and the concentration of NaOH on the formation...

Structural, optical, and magnetic study of Ni-doped TiO2 nanoparticles synthesized by sol–gel method

“…There exist various methods of producing titania nanoparticles, such as sol-gel process, electrochemical coating, hydrothermal process, hydrolysis, microemulsion method, thermolysis, flame aerosol process, chemical vapor deposition, etc. [27][28][29][30][31][32][33][34][35]. Sol-gel method is often employed as it offers the advantages such as precise control over the stoichiometry, low-temperature synthesis, high crystallinity, and high purity [36][37][38].…”

Hydrogen evolution on porous Ni cathodes modified by spontaneous deposition of Ru or Ir

“…For these reasons, these materials have been extensively investigated [1]. Most attention has been devoted to Raney-Ni, obtained by leaching a non-noble metal (Zn or Al in most cases) from variously prepared alloy or composite precursors [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. Owing to the multiplicity of the preparation methods, variable overpotentials were reported for hydrogen evolution at Raney-Ni electrodes.…”

Correlation of microstructure and catalytic activity of crystalline Ni–Co–Y alloy electrode for the hydrogen evolution reaction in alkaline solution

“…The improvement consisted in targeting several fields of interest such as the intrinsic nature of the reaction [1], electrode composition [2][3][4][5][6][7][8][9][10], surface morphology [11][12][13][14], structural, chemical and electronic properties [15][16][17][18][19][20][21][22][23] physico-chemical and electrochemical activation treatment [24][25][26].…”