## 3 Experimental
### Bacterial Activity
#### 3.3.2 Cellulose Breakdown  
The role of the materials comprising the filter was further explored and it was found that the bacterial contamination that led to RedOx reactivity with oxidising NO\({}_{2}\) was related to the formation \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline \multirow{2}{*}{**Sample**} & \multicolumn{5}{c}{**Cultured Extract**} \\ \cline{2-6}  & **Total Viable Count (TVC) of Aerobic Bacteria (\(\text{cfu}\cdot\text{g}^{-1}\text{sample}\))** & **Observed Growth** & **Nitrite (mg-cm\({}^{-3}\))** & **Organism** & **Score** \\ \hline Uncated NP substrate non-sterilised 1 & \(>10^{5}\) & yes & 50 & - & - \\ \hline Uncated NP substrate thermally sterilised & \(74\times 10^{3}\) & yes & 50 & _Bacillus_ sp. 3  & 1.839 \\ \hline Uncated NP substrate non-sterilised & \(>10^{5}\) & yes & 50 & _Enterobacter kobei_ & 2.349 \\ \hline Coated NP substrate non-sterilised & \(>10^{5}\) & yes & 50 & _Bacillus cereus_ & 2.081 \\ \hline Coated NP substrate thermally sterilised 1 & \(8\times 10^{3}\) & yes & 50 & - & - \\ \hline Coated NP substrate treated with H\({}_{2}\)O\({}_{2}\) & \(>10^{5}\) & yes & 50 & _Enterobacter kobei_ & 2.320 \\ \hline GCC non-sterilised 2 & \(4\times 10^{3}\) & - & - & - & - \\ \hline MNFC non-sterilised & \(>10^{5}\) & yes & 50 & _Bacillus licheniformis_ & 2.057 \\ \hline Laboratory bacteria-free control & - & no & 0 & - & - \\ \hline \hline \end{tabular}  
* 1 Bacteria grew as a complete thin film, so no discrete colonies could be separated. 2 Microparticle turbidity prevented observation. 3 Score below 2.0 can only be used for genus identification.  
\end{table} 
Table 10: Results of microbial analysis identifying contamination levels and genus/species. Figure 24: Experimental exposures of the variously treated filters shown as the period connected between sampling the outdoor air only: (**a**) thermal sterilisation prevented regeneration of the RedOx capacity but did not fully oxidise the sample, (**b**) treatment with 0.1 w/w% H\({}_{2}\)O\({}_{2}\) pre-oxidised the sample, such that the regeneration was prevented and the sample showed no RedOx capacity, (**c**) comparing the light and dark samples eliminates any possibility that the mechanism was driven by photon catalysis. of alcohol (-OH) due to cellulose breakdown and could be oxidised to aldehyde (Equation (2)). This is followed by oxidative conversion to carboxylic acid (Equation (3)). This reaction pathway is like that of the unwanted oxidation of wine. (2)  
(3)  
The action of pre-oxidising using H\({}_{2}\)O\({}_{2}\) is to pre-run the reaction parallel to Equation (2), following Equation (4), to saturate the transformation from alcohol to aldehyde and to complete the transformation to carboxylic acid (Equation (5)). In this way, the filter action for the desired absorption of NO\({}_{2}\) rather than conversion to NO could be preserved. (4)  
(5)  
The Fourier transform infrared (FTIR) spectroscopic analysis result, shown in Figure 25, confirmed this assumption with respect to the loss of the H-C=O band at 2830 cm\({}^{-1}\). (6)  
Figure 25: The Fourier transform infrared (FTIR) spectral analysis of recycled newsprint substrate that illustrates the action of pre-oxidation by removing the H-C=O stretch band. Following pre-oxidation by H\({}_{2}\)O\({}_{2}\), the desired mechanism of NO\({}_{2}\) sorption and formation of nitrate was restored, and the presence of retained N species was confirmed by both EDS and electron energy loss spectroscopy (EELS), which is more sensitive. The results are shown in Table 11, and TEM image selection and EDS spectra are exemplified in Figure 26. The sample material for analysis was scraped from the filter surface, dispersed to high dilution (1000 \(\times\)) in ethanol to reduce particle number per sample volume, and studied in a JEM-2200 FS 200 kV double Cs corrected transmission electron microscope (TEM) (JEOL Ltd., Akashima, Tokyo, Japan).