## 3 Results and Discussion
### The Photocatalytic Performance of Modified CA Membranes
#### 3.10.1 Photodegradation of KP in Deionized Water
The cost associated with cleaning water is one of the factors that limit the wide-scale use of membranes and photocatalysis. The details of how the Electrical energy consumption (E\({}_{\text{EC}}\)) was calculated are given in S11, Equation (S5). Here, it was observed that the high removal efficiency (also, the high rate constant) of CTG-500 translated into the process requiring the least amount of electrical energy to treat 1 L of 10 ppm KP than all the other materials tested in this work. Additionally, utilizing the CTG-500 membrane in the dark required lesser energy than all the other tested materials albeit in the dark. The electrical energy consumption followed a reverse trend to that of removal efficiency, i.e., in the order of decrease in consumption, CTG-500 > CTG-500 (in the dark) > CTG-300 > CTG-100 > CA > PA > photolysis. These results further signify the synergy between membrane technology and photocatalysis. Furthermore, it indicates that the increased hydrophobicity of the membranes positively affects the energy consumption of the process. 10.2 Photodegradation of KP in Drinking and Groundwater Using CTG-500 and Costs Associated with the Process  
The photodegradation of KP (as a contaminant model) in different water qualities was evaluated by utilizing 1% CuO/TiO\({}_{2}\)@GCN (9:1) (0.5 wt%) blended in the CA matrix to form CTG-500 membrane. The characteristics of the water matrixes are given in Supplementary Information S12, Table S1) This was done to investigate the applicability of the material into real water qualities to evaluate applicability in the real world. The results are plotted and shown in Figure 9 and Table 4 The photocatalytic membrane showed rapid removal of KP producing 94.0 and 94.8% efficiency in drinking and groundwater, respectively, higher than when it was tested in a distilled water matrix. This was attributed to the matrix of the drinking water and groundwater containing ions and organic matter (Table S1) that blocked the pores on the membrane preventing KP from flowing through, thus increasing the filtration of KP [55; 56]. Furthermore, the ions in drinking and groundwater allowed for a higher residence time for KP to be photodegraded on the surface of the membrane [55; 56]. Unfortunately, this caused the fouling of the membrane which resulted in a reduced flux which in turn reduced the volume of water treated per hour. This resulted in a significant increase in electrical energy consumption (Table 4). \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Membrane ID** & **Rate Constant/h\({}^{-1}\)** & **Degradation Efficiency/\%** & **E\({}_{\text{EC}}\)/kWh/m\({}^{3}\)** \\ \hline CTG–500 (Groundwater) & 0.508 & 94.8 & \(1.69\times 10^{4}\) \\ CTG–500 (Drinking water) & 0.568 & 94.0 & \(1.52\times 10^{4}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Rate constants and energy consumption of the filtration process. Figure 9: (a) Simultaneous filtration and photodegradation of KP (10 ppm, pH 5 for 5 h) in different water grades using CTG—500 membrane and (b) their reaction kinetics. 3.10.3. Photocatalytic Degradation of KP Drinking and Groundwater: Antifouling and Regeneration Studies in Drinking and Groundwater  
The reusability and anti-fouling ability of the membranes are vastly necessary to assess their applicability in water treatment. The CTG-500 which exhibited better removal efficiencies was subjected to reusability studies for five cycles of the membrane filtration process using KP as a target contaminant in drinking and groundwater. To recycle the membrane, it was flushed with water in between the cycles and immersed in deionized water under the presence of light irradiation for 12 h. The results are shown in Figure 10.  
The findings showed that the CTG-500 membrane possessed good reusability performance under visible light than in the dark. The removal of KP in drinking and groundwater in the first cycle was high, exhibiting 91.4 and 85.1% efficiencies for 5 h under visible light irradiation, respectively.