## 5 Reactor Systems and Process Parameters
### Operational Parameters  
Several operational factors must be carefully optimized to maximize the photocatalytic performance (Figure 11) [51, 60, 79, 99, 102, 145, 146, 147, 148, 149, 150]. 1. Catalyst loading strategies in reactor configurations  
The concentration of the photocatalyst significantly influences the degradation efficiency. Insufficient catalyst amount results in fewer active sites, limiting the generation of reactive oxygen species (ROS). Conversely, excessive catalyst loading can lead to particle agglomeration and increased solution turbidity, causing light scattering that reduces the photon penetration and hinders the photocatalytic activity. For example, [PERSON] et al. (2024) demonstrated that higher catalyst doses provide more active sites, accelerating degradation [151]. However, beyond an optimal point, the efficiency declines due to light scattering and reduced photon absorption [151]. [PERSON] et al. (2023) reported that increasing the concentration of g-C\({}_{3}\)N\({}_{4}\) from 0.1 to 1.0 g/L improved the degradation rate of rhodamine B, but further increases to 2.0 g/L resulted in reduced performance due to light scattering and reduced photoactivation efficiency [152]. A study performed by [PERSON] et al. (2021) evaluated the influence of light scattering by different TiO\({}_{2}\) catalysts on photonic energy absorption [153]. It was found that higher concentrations of TiO\({}_{2}\) particles led to increased light scattering, thereby reducing  
\begin{table}
\begin{tabular}{p{42.7 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline \multicolumn{1}{c}{**Photocatalyst**} & \multicolumn{1}{c}{**Target Pollutant**} & \multicolumn{1}{c}{**Light Source**} & \multicolumn{1}{c}{**Photocatalytic Performance**} & \multicolumn{1}{c}{**References**} \\ \hline \multicolumn{1}{c}{TiO\({}_{2}\)} & \multirow{4}{*}{Coke water} & UV radiation & At a light intensity of 400 mWcm\({}^{-2}\), the removal efficiency was 15\% at 60 min. & \multirow{4}{*}{[38]} \\  & & & At a light intensity of 1300 mWcm\({}^{-2}\), the removal efficiency was 30\% at 60 min. & & \\ \cline{3-5} \cline{5-5 the number of photons reaching active sites and diminishing the photocatalytic efficiency. For instance, [PERSON] et al. reported that increasing the g-C\({}_{3}\)N\({}_{4}\) dosage from 0.1 to 1.0 g/L enhanced the degradation of rhodamine B, but a further increase to 2.0 g/L reduced efficiency, due to excessive light scattering [152]. Additionally, it is important to recognize that the trade-offs associated with catalyst loading extend beyond photocatalytic efficiency. In slurry systems, high catalyst dosages may lead to increased operational complexity, due to the need for downstream separation and recovery of fine particles. These challenges are particularly relevant in scaling up to pilot and industrial levels, where process economy and sustainability are essential. Studies have highlighted that excessive catalyst use, while initially improving performance, may compromise process simplicity and increase sludge handling costs [151; 153]. Consequently, future design strategies should integrate optimization of catalyst dosage with reactor configuration and reuse potential to enhance both efficiency and practicality. Thus, determining an optimal catalyst concentration is essential for balancing active site availability and light absorption. 1. pH of the medium  
The pH level of the solution affects the surface charge of the photocatalyst and the ionization state of contaminants, influencing the adsorption behavior and ROS generation. Titanium dioxide (TiO\({}_{2}\)) typically exhibits higher photocatalytic activity in acidic to neutral pH ranges. At these pH levels, the TiO\({}_{2}\) surface is positively charged, promoting the electrostatic attraction with negatively charged pollutants, thereby enhancing degradation efficiency. However, the optimal pH can vary depending on the specific photocatalyst and target contaminant.