## 3 Results and Discussion
### Photocatalytic Degradation of Methyl Orange  
The photocatalytic degradation of MO was evaluated using TiO\({}_{2}\) and the TiO\({}_{2}\)/OLNCs nanocomposites (Figure 6). The reaction was first conducted in the absence of any photocatalyst, first in the dark for 30 min, and 120 min under light irradiation. Only a small amount of photodegradation of the MO (120 min) was observed in the absence of the photocatalyst. \begin{table}
\begin{tabular}{c c c c} \hline
**adsorbent** & **Surface Area (m\({}^{2}\)/g)** & **Pore Volume (cm\({}^{3}\)/g)** & **Average Pore Size (nm)** \\ \hline TiO\({}_{2}\) & 7.6 & 0.02 & 7.58 \\ TC-10 & 56.6 & 0.12 & 8.09 \\ TC-20 & 69.8 & 0.19 & 10.80 \\ TC-30 & 78.1 & 0.17 & 8.85 \\ TC-50 & 120 & 0.28 & 9.43 \\ \hline \end{tabular}
\end{table} 
Table 1: BET parameters for TiO\({}_{2}\) and the OLNCs/TiO\({}_{2}\) nanocomposite. Figure 5: UV-Vis spectroscopy scanning (**a**) of all the materials and bandgap energies for TiO\({}_{2}\) (**b**), TC-10 (**c**), TC-20 (**d**), TC-30 (**e**), and TC-50 (**f**) photocatalysts. A similar experiment was performed with TiO\({}_{2}\) in the dark, and an insignificant amount of MO was degraded. However, as expected, the TiO\({}_{2}\) catalyst was able to photodegrade the MO under light irradiation, with 44% of MO degraded after 120 min (Figure 6). The photocatalytic degradation of MO was then carried out with the composites (TiO\({}_{2}\)/OLNC). When the experiment was carried out in the dark, it was noted that all composites showed adsorption of the dye. Furthermore, as the OLNC content increased, the adsorption efficiency also increased. This suggests that the OLNCs assist with the MO adsorption process [22]. This is in line with the increased surface area as the mass of OLNCs increased, as shown in Table 1.  
However, the best photocatalytic result was found to be the composite with the lowest loading of OLNCs (Figure 6). This suggests that two effects are at play: (i) at low loadings, the OLNCs enhance the conductivity; but (ii) at high loadings, the carbon covers the active TiO\({}_{2}\) sites, i.e., the OLNCs cover the photoactive sites of the TiO\({}_{2}\), resulting in a decreased light transmittance and charge transfer, indicating that the surface area was not the major driving force in the photocatalytic degradation of MO [22]. Similar observations were made by [PERSON] et al. for the \(\text{CNOs}/\text{TiO}_{2}\) composites used for the degradation of rhodamine B. It was reported that the composite that showed the most effective photocatalytic activity was the composite with a 10% mass ratio of CNOs to TiO\({}_{2}\), due to the increased adsorption capacity of the composites compared to the bare TiO\({}_{2}\) (see Table S3), as calculated by Equation (S1). Figure S3 depicts the Langmuir (Equation (S2)) and Fruendlich (Equation (S3)) adsorption isotherms, which were selected to study the adsorption process. It can be seen from the figures that the experimental data fitted the Langmuir model for all the composite materials. This possibly indicates that the adsorption of the methyl orange was through a homogeneous surface coverage. Interestingly, for the bare TiO\({}_{2}\) material, the experimental data fitted the Fruendlich adsorption isotherm, possibly indicating that the adsorption pathway was through a heterogeneous surface coverage. The adsorption pathway was also studied using the intra-particle diffusion model, by plotting qt vs. t\({}^{1/2}\), as shown  
Figure 6: Photocatalytic degradation of MO using TiO\({}_{2}\), TC-50, TC-30, TC-20, and TC-10 photocatalysts. in Figure S4. It can be seen that all the catalysts show multiple linear regions that do not pass through the origin point. This indicates that the adsorption pathway involves a multiple-step mechanism. This involves (a) a bulk transport, as the catalyst is in contact with the dye; (b) film diffusion, where the dye molecules are transported to the boundary layer or film of the catalyst; and then (c) intra-particle diffusion of the dye molecules into the catalyst pores.