## 3 Results and Discussion
\begin{table}
\begin{tabular}{c c c c c} \hline \multirow{2}{*}{**Sample**} & \multicolumn{2}{c}{**Concentration of**} & **Heating** & **Duration of** & \multirow{2}{*}{**Thickness (nm)**} \\  & **TiO\({}_{2}\) Precursor (mM)** & **Temperature (\({}^{\circ}\)C)** & **Spraying (min)** & \\ \hline
1 & 3.42 & 460 & 12 & 94 \\
2 * & 6.83 & 460 & 12 & 101 \\
3 & 13.66 & 460 & 12 & 106 \\
4 & 6.83 & 500 & 12 & 99 \\
5 & 6.83 & 550 & 12 & 103 \\
6 & 6.83 & 460 & 6 & 75 \\
7 & 6.83 & 460 & 24 & 107 \\ \hline \end{tabular}  
* The standard parameters used in the preparation of TiO\({}_{2}\) layer on substrates by Spray-ILGAR method for the preparation of solar cells.  
\end{table} 
Table 1: Thickness of the TiO\({}_{2}\) layers on stainless steels prepared by Spray-ILGAR method by using different concentrations of TiO\({}_{2}\) precursor, different heating temperatures and different spraying durations. Figure 1: SEM image of TiO\({}_{2}\) on stainless steel by Spray-ILGAR technique using 6.83 mM of titanium diisopropylopoxide bis(acetylacetone) alcoholic solution, heated at 460 \({}^{\circ}\)C and spraying time of 12 min. Figure 4 shows the XRD pattern for the prepared titania on stainless steel by Spray-ILGAR method. However, only a small peak corresponding to the (101) reflection of anatase TiO\({}_{2}\) at 2\(\theta\) value of around 25\({}^{\circ}\) can be detected. The rest of the diffraction peaks are attributed to the stainless steel substrate [11]. This could be caused by the small amount and thin layer of TiO\({}_{2}\) present in the sample. As no further analysis using XRD was carried out, no conclusive results can be drawn from the XRD analysis. Figure 3: SEM images of TiO\({}_{2}\) on stainless steel by Spray-ILGAR technique using 6.83 mM of TiO\({}_{2}\) precursor, heating temperature of 460 \({}^{\circ}\)C and (**a**) shorter spraying time (6 min) and (**b**) longer spraying time (24 min). Figure 2: SEM images of TiO\({}_{2}\) on stainless steel using higher concentration (13.66 mM) ((**a**) and (**b**)) and lower concentration (3.42 mM) ((**c**) and (**d**)) of titanium diisopropyloxide bis(acetylacetone) alcoholic solution. The spraying duration used was 12 min and heating temperature of 460 \({}^{\circ}\)C.  
The photocatalytic results of the samples using different concentrations of TiO\({}_{2}\) precursor, different heating temperature and different duration of spraying time are summarized in Table 2. Based on the results, it was found that sample prepared with concentration of TiO\({}_{2}\) precursor of 6.83 mM, temperature of 550 \({}^{\circ}\)C and spraying time of 12 min took the shortest time (35 min) to completely degrade 500 ppm of acetaldehyde under UV irradiation. It would seem that out of the three parameters studied, the heating temperature played a slightly more important role. This could be caused by the crystallinity of the TiO\({}_{2}\) as the crystallinity of a photocatalyst influences the charge recombination rate and, consequently, on the photocatalytic activity [12]. However, as the crystallinity could not be properly determined using the XRD analysis carried out, this hypothesis could not be confirmed. Apart from the heating temperature, the concentration of the TiO\({}_{2}\) precursor also seems to play a crucial role, as the sample prepared with a concentration of TiO\({}_{2}\) precursor of 13.66 mM, temperature of 460 \({}^{\circ}\)C and spraying time of 12 min took the second shortest time (40 min) to completely degrade 500 ppm of acetaldehyde under UV irradiation. As discussed in the morphology analysis, samples prepared with higher concentration of the TiO\({}_{2}\) precursor showed a more compact and dense layer (Figure 2a,b). This would indicate that more TiO\({}_{2}\) (active sites) are available to be used in the photodegradation of acetaldehyde, hence the shorter time required.