## 3 Results and Discussion
### The Photocatalytic Performance of Modified CA Membranes  
#### 3.10.1 Photodegradation of KP in Deionized Water  
The synthesized membranes, along with the pristine CA and the support (polyamide, PA) were used for the simultaneous filtration and degradation of KP in distilled water. Photolysis (without the membranes but in the presence of light) experiments were also conducted as a control. The photolysis experiment showed insignificant removal of KP (5.6%). Therefore, in experiments that involve the membranes, the reduction is attributable to the presence of the membranes (Figure 8 and Table 3). The reduction in the concentration of KP was calculated using Equation (S4) in Supplementary Document S10. The pristine membrane CA and the PA support exhibited low removal efficiencies, under 40% (Figure 8 and Table 3). Figure 7: Recyclability of the as-prepared membrane and pure water permeability in the presence and absence of visible light. The photocatalytic membranes, i.e., samples CTG-100, CTG-300 and CTG-500, were found to have removal efficiencies higher than the pristine membranes. It was also observed that the removal efficiency of the photocatalytic membranes increased with an increase in the concentration of the photocatalyst (1% CuO/TiO\({}_{2}\)@GCN (1:9)) loaded onto the CA membrane (Figure 8 and Table 3). The trend was justified because a decrease in the concentration of the photocatalyst loaded onto the CA membranes meant that the membranes were more hydrophilic (Figure 5) with smaller pores and inferior water uptake (Figure 6 and Table 2). Therefore, in the case of CTG-100, because of its low concentration of the photocatalyst, its pores were blocked quicker by the contaminant molecules thus reducing its filtration rate. This results in the formation of a thin layer of contaminant molecules forming on the surface of the photocatalytic membrane. This hinders the penetration of light, thus reducing the photocatalytic efficiency of the photocatalytic membranes. Given that CTG-500 outperformed all the other membranes presented in this work, its removal efficiency without light was assessed. Here, the same experiment as above was conducted in the absence of light. It was found that its removal efficiency had decreased slightly from 83.9% to 78.1%. The total organic content (TOC) which is a measure of the amount of organic compounds in the sample was measured to determine the amount of KP degraded in these experiments. Here, it was found that the TOC measured for the sample filtered in the dark was 42% higher than the TOC obtained when the same experiment was conducted in the presence of light. This indicates that 42% of KP was degraded instead of simply being adsorbed onto the membrane. The TOC of the original KP test solution was only 0.8% less than that of the experiments conducted in the dark, indicating that the experimental conditions in this work (other than light) did not have an effect on the degradation of KP. These results indicate that the impressive removal efficiency of CTG-500 is a result of a synergy between filtration and photocatalysis. Figure 8: (**a**) Simultaneous filtration and photodegradation of KP (10 ppm, pH 5 for 5 h) using CTG—100, CTG—300, and CTG—500 membranes and (**b**) their reaction kinetics. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Membrane ID** & **Rate Constant/h\({}^{-1}\)** & **Degradation Efficiency/\%** & **E\({}_{\text{EC}}\) Costs/m\({}^{3}\)** \\ \hline
**CTG–100** & 0.141 & 46.1 & \(5.92\times 10^{4}\) \\
**CTG–300** & 0.181 & 61.5 & \(4.63\times 10^{4}\) \\
**CTG–500** & 0.390 & 83.7 & \(2.18\times 10^{4}\) \\
**CTG–500 (in darkness)** & 0.315 & 78.1 & \(2.69\times 10^{4}\) \\
**CA** & 0.095 & 38.3 & \(8.75\times 10^{4}\) \\
**PA supporting membrane** & 0.085 & 35.3 & \(9.78\times 10^{4}\) \\
**Photolysis** & 0.012 & 5.6 & \(6.88\times 10^{5}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The removal efficiency of the different membranes and electrical energy consumption associated with the process.