# Removal of Crotamiton from Reverse Osmosis Concentrate by a TiO\({}_{2}\)/Zeolite Composite Sheet
## 3 Results and Discussion
### Photocatalytic Degradation of Crotamiton by the F9/P25 Composite Sheet  
To clarify the photocatalysis of crotamiton by the F9/P25 composite sheet, the composite sheet was synthesized to be similar to the HSZ-385 composite sheet. Both F9 zeolite and the F9/P25 composite sheet did not remove crotamiton by adsorption (Figure S2). The F9 zeolite is a hydrophilic zeolite, whereas the Y-type zeolite HSZ-385 is a hydrophobic zeolite. This is further evidence that crotamiton is removed by HSZ-385 mainly through hydrophobic interactions. The photocatalytic degradation of crotamiton over time by the F9/P25 composite sheet is shown in Figure 3. Direct photolysis of crotamiton was not observed [31]. The removal efficiency of crotamiton from the RO concentrate was much lower than that from the ultrapure water. After 24 hr of UV irradiation, the majority of the crotamiton in the ultrapure water was degraded. In contrast, ca. 50% of the crotamiton was degraded in the RO concentrate. Linear relationships were found between In (\(C_{t}/C_{0}\)) and UV irradiation time (\(t\)) (Figure 3). Therefore, the first-order kinetic model shown in Equation (4) was used to evaluate the photocatalysis of crotamiton. In that equation, \(k_{1}\) is the pseudo-first-order rate constant. The \(k_{1}\) value for crotamiton removal from the RO concentrate by the F9/P25 composite sheet was 0.048 hr\({}^{-1}\), and was only half of that in the ultrapure water (0.092 hr\({}^{-1}\)). Obviously, the lower rate constant reflects the effect of other components in the RO concentrate on the photocatalytic degradation of crotamiton. Figure 3: Photocatalytic degradation of crotamiton using the F9/P25 composite sheet with ultraviolet irradiation (\(C_{0}\) = 10 mg/L). The inset shows the fitting results of the first-order kinetic model. Results are means \(\pm\) standard deviations (\(n\) = 2). \[\ln\left(C_{t}/C_{0}\right)=-k_{1}t \tag{4}\]  
UV absorbance is an important parameter affecting photocatalysis [10; 35]. The maximum output wavelength of the UV lamp in our study was 365 nm, and the RO concentrate had an absorbance of 0.049 cm\({}^{-1}\) at 365 nm (Table 1). Based on the Beer-Lambert law and the distance from the reactor surface to the sheet, the light transmittance was 82.1%. Therefore, after passing through the RO concentrate in the batch reactor, the light intensity at the sheet surface decreased by 17.9%, which is called the screening effect [36]. This effect contributed to the decrease in the photocatalytic degradation efficiency. Furthermore, the RO concentrate was light brown, and the color of the composite sheet surface changed from white to light brown after treatment of the RO concentrate. This color change could be caused by adsorption of coexisting materials on the sheet surface, and this could negatively affect the performance of TiO\({}_{2}\) photocatalysis through occupation of the active sites on the surface of TiO\({}_{2}\)[37]. The TiO\({}_{2}\) photocatalysis could be inhibited via the scavenger effect by coexisting ions [10; 38; 39; 40]. The ions Cl\({}^{-}\) and HCO\({}_{3}\)\({}^{-}\) have been found to inhibit photocatalysis through the hydroxyl radical and valence band hole scavenging [10; 40]. [PERSON] et al., reported a marked deactivation effect caused by added salts for two tested acidic drugs [41]. Furthermore, [PERSON] et al., suggested that coexisting matter could mitigate the generation of hydroxyl radicals through direct reactions with holes in the valence band and electrons in the conduction band of the photocatalyst [37]. As reported by [PERSON] et al., Cl\({}^{-}\) can cause agglomeration of TiO\({}_{2}\) particles in a slurry by suppressing the stabilizing effect of electrostatic repulsion, reducing the effective contact surface between the photocatalyst and the pollutants [42]. In this research, the TiO\({}_{2}\)/zeolite composite sheet was used instead of TiO\({}_{2}\) powder.