A commercially pure titanium sheet precipitated TiC in the surface layer was fabricated by anodic oxidation in NH 4NO 3 solution and heat treatment in air. The fabricated sheet showed relatively high photocatalytic activity in 0.1 M KI solution, which was close to the activity level of the P-25 particle made by Degussa Corporation. It exhibited photocatalytic activity in antifungal and antivirus tests under black light irradiation. The better photocatalytic activity under black light irradiation is considered to be related to the formation of anatase and rutile type titanium dioxides and rough surface. It also showed photocatalytic activity under visible light irradiation, which is considered to be attributable to carbon and nitrogen doping in titanium dioxide.
Since Honda and Fujishima discovered the electrolysis of water by titanium dioxide under irradiation [
Anodic oxidation of titanium substrate is commercially used to produce colored titanium sheets. The color of the anodized titanium substrate can be changed by varying the thickness of surface titanium oxide layer. And colored titanium sheets are mainly used as architectural materials.
Recently, the anodic oxidation method has been applied for making titanium dioxide with enhanced photocatalytic activity under ultra-violet (UV) or visual light irradiation. K. Onoda et al. reported that the anodization of a pre-nitridated titanium substrate in a mixed electrolyte composed of H2SO4, H3PO4, and H2O2 resulted in photocatalytic activity [
Concerning visual light response, Y. Mizukoshi et al. conducted research on the visible light response of sulfur-doped rutile titanium dioxide photocatalysts fabricated by anodic oxidation [
However, a few studies for effects of material factors on photocatalytic activity of anodized titanium substrate have been investigated. The authors have investigated the effects of a TiC precipitated in surface layer of titanium sheet on discoloration of titanium due to the growth of titanium oxide layer and it was found that TiC in surface layer enhanced the growth of titanium oxide layer on the titanium substrate under an atmospheric environment [
Commercially pure (CP) titanium sheets cold rolled to the thickness of 0.4 mm were heat treated in vacuum annealing furnace. The holding temperature and time were 873 K and 6 hours, respectively. And average raising rate was approximately 100 K/hour and cooling rate was nearly 50 K/hour. The concentrations of impurity elements in the CP titanium sheets are shown in
The titanium sheets were rinsed in acetone and immersed in 0.06 M NH4NO3 solution for anodic oxidation. The anodic oxidation was controlled by galvanostatically at 15 V, 24 V, 45 V and 80 V for 120 sec at room temperature. After the anodization they were rinsed in distilled water and air-dry. After these treatments, they were heated in air at 803 K for 3600 sec and air cooled. The average raising rate was 315 K/min and the average cooling rate 136 K/min, following which they were cut into 15 mm × 25 mm and 50 mm × 50 mm samples to be used for measuring photocatalytic activity.
Photocatalytic activity was measured using KI solution [
Photocatalytic activity of the anodized Ti samples was also investigated in antifungal and antivirus tests based on Japanese Industrial Standard (JIS) R-1705 (2008) [
O | H | C | Fe | N |
---|---|---|---|---|
0.0473 | 0.0022 | 0.008 | 0.025 | 0.004 |
× 50 mm size were used. Same size glass sheets were used as control. Aspergillus niger NBRC 105649 was used in the test. Intensity of black light was 0.8 mW/cm2 and irradiation time was 24 hour. And the antivirus test was conducted at Kitasato Research Center for Environmental Science. Anodized titanium sample of 50 mm × 50 mm size were used and glass sheets of the same size were used as a control. Influenza A virus was used in the test and the intensity of the black light was 0.1 mW/cm2 and the irradiation time was 8 hour.
Anodic oxidation layers on the titanium substrate were analyzed by X-ray diffraction (XRD; RINT1500, RIGAKU) measurement. For XRD measurement, incident angle of X-ray beam to surface was 1 degree to obtain structure of anodized oxidized layer on titanium substrate. Surface morphology of the anodized titanium sample was observed by scanning electron microscope (SEM; JIS-7000F, Jeol). Glow Discharge Spectroscopy (GDS; GD Profiler2, HORIBA Jobin Yvon) with Ar ion sputtering was conducted to investigate content of elements in oxide layers. X-ray photoelectron spectroscopy (XPS; Physical Electronics Quantum 2000 Scanning ESCA Microprobe, ULVAC-PHI Inc.) with Ar ion sputtering was conducted using monochromatized Al Kαradiation (1486.6 eV) to investigate the chemical states of O, C and N in anodized titanium oxide layer on titanium substrate.
The sample “Blank” was a control performed by irradiating a 0.1 M KI solution containing no samples with black light for the prescribed time. As shown in
In order to investigate crystal structure and surface morphogy of anodized titanium samples, XRD measurement and SEM observation were carried out for the titanium sample anodized at 45 V.
As
On the other hand, it has been considered that dual phase of anatase and rutile had better photocatalytic activity [
Next a surface morphology of the anodized and heat treated titanium sample was observed by SEM.
In order to investigate the photocatalytic activity of the anodized titanium sample at 45 V and heat treated in regards to fungal growth, an antifungal test was carried out. The obtained results were shown in
Next, photocatalytic activity under visible light such as white color LED light was investigated by using 0.1 M KI solution. The results obtained are shown in
The absorbance of Ti sample was clearly higher than blank (no sample), which indicates photocatalytic activity under visual light irradiation. Thus, a surface analysis of the titanium sample before and after anodization was carried out by GDS.
As shown in
As shown in
As R. Asahi et al. reported that doping of carbon and nitrogen into titanium oxide induced visible light response [
A commercially pure titanium sheet precipitated TiC in the surface layer fabricated by anodic oxidation in
NH4NO3 solution at 45 V and 80 V and heat treatment in air at 803 K showed relatively high photocatalytic activity in 0.1 M KI solution which was close to the absorbance value of P-25 particle. The anodized sample at 45 V and heat treated, showed good photocatalytic activity in antifungal and antivirus tests under black light irradiation. The better photocatalytic activity under black light irradiation is considered to be related formation of dual phase of anatase and rutile type titanium dioxide and rough surface. It also showed photocatalytic activity under visual light irradiation. It is considered that visible light response was caused by doping of carbon and nitrogen in titanium dioxide.