# Improvement of Buildings' Air Quality and Energy Consumption Using Air Purifying Paints
## 3 Results
### Laboratory Photocatalytic Performance of the Photo-Powder  
The lab-scale tests provide information on the elimination of air pollutants due to both photolysis and photocatalysis on the photo-powder. To that end, experiments in the absence of the photocatalytic powder were initially performed in order to estimate background contribution. The photocatalytic effect is calculated by the subtraction of the side-effect pollutant elimination during the photocatalytic experiments. More specifically, the reactor was fed with NO and toluene in the absence of the photocatalyst with and without irradiation, respectively. Afterwards, the experiments were repeated but with the presence of the photocatalyst. Figure 11a,b present the elimination of NO and toluene under the irradiation of the photo-paint from Vis light. It is observed that by Time 30 (start of irradiation), a significant decrease in NO concentration was present while a less sharp but also important decrease is shown for toluene. The latter demonstrate the instant response and the significant efficiency of the photo-paint to degrade both pollutants. Side effects of pollutant removal such as adsorption on the chamber's walls and photolysis were calculated and results showed that both these mechanisms did not have significant contribution to pollutant removal during the lab-scale experiments. The evaluation of the photocatalytic activity was performed by calculating photocatalytic yield (% n, Equation (3)), photodegradation rate (r, Equation (4)), and deposition velocity (Vd, Equation (5)). The corresponding equations were used for toluene. Results in Table 2 are very promising and show a very active photocatalytic powder in terms of air pollutant degradation. \[\%\;n_{NO}^{total}=\frac{C_{NO}^{IN}-C_{NO}^{OUT,\;light}}{C_{NO}^{IN}}\times 100 \tag{3}\]  
where \(C_{NO}^{IN}\) is the concentration of NO at the reactor inlet. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Property** & **Value** & **Test Method** \\ \hline Viscosity at 25 \({}^{\circ}\)C (KU) & 95 & ASTM D 562 [46] \\ Density at 25 \({}^{\circ}\)C (kg/L) & 1.464 & ISO 2811 [47] \\ Fineness and dispersion & \textless{40} \(\upmu\)m & ASTM D1210 [48] \\ pH at 25 \({}^{\circ}\)C & 7.85 & ISO 787-9 [49] \\ PVC (\%) & 78 & Calculated \\ Usage rate for a 50 \(\upmu\)m dry film thickness (m\({}^{2}\)/kg) & 6.52 & Calculated \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Physicochemical Properties of photo-paint. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **Lab Scale—Photo-Powder under Vis Light** \\ \hline \hline \(\%\;\eta\) & NO & Toluene \\ \(\%\;\eta\) & 85.4 & 32.4 \\ r photo (\(\upmu\)g/m\({}^{2}\)s) & 15.8 & 0.01 \\ Vd (m/s) & 0.03 & 0.0001 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Photocatalytic parameters for lab-scale tests. The photocatalytic rate of yield of the material is calculated by the formula below (Equation (3)) and expressed in \(\mu\)gm\({}^{-2}\) s\({}^{-1}\):  
\[r_{NO}^{photo}=\frac{613\mathrm{F}}{\mathrm{S}}\Bigg{(}\frac{n_{\mathrm{NO}}^{ \mathrm{total}}}{\left(1-n_{\mathrm{NO}}^{\mathrm{total}}\right)}-\frac{n_{ \mathrm{NO}}^{\mathrm{dark}}}{\left(1-n_{\mathrm{NO}}^{\mathrm{dark}}\right)} \Bigg{)} \tag{4}\]  
where \(F\) is the gas flow (m\({}^{3}\) h\({}^{-1}\)); \(S\) is the area of the test surface (m\({}^{2}\)). The deposition velocity (Vd) was calculated as follows:  
\[Vd=r_{NO}/C_{in}\;NO \tag{5}\]  
The photocatalytic rate provides a more accurate measure of the photo-paint activity as it is taking under consideration not only the final and the initial concentration of the pollutant but also the sample's surface area and the irradiation time. To that end, compared with the % photocatalytic degradation, it is expressed as \(\mu\)g of converted NO/toluene per  
Figure 11: (**a**) Photocatalytic yields’ (% n) concentration profile versus time for the photo-oxidation of NO in the presence of the catalyst.