# Removal of Crotamiton from Reverse Osmosis Concentrate by a TiO\({}_{2}\)/Zeolite Composite Sheet
## 3 Results and Discussion
### Behavior of the Degradation Intermediates during Photocatalysis  
The degradation intermediates were characterized following the methods described in our previous study [31]. We proposed that P25-catalyzed photodegradation of crotamiton could initially occur via hydroxylation of the aromatic ring, the double bond of the propenyl group, or the ethyl group. These reactions formed intermediates that we labeled as P189, P217, and P219. The peak areas of the intermediates were measured in the selected ion recording mode of LC/MS/MS. With the degradation of crotamiton, the intermediates gradually accumulated and reached their highest levels in the treatment using the F9/P25 composite sheet (Figure 7). Intermediate P219, which was produced by hydroxylation of the aromatic ring of crotamiton, was the most noticeable degradation intermediate. The peak area of P219 was higher than those for P189 and P217. After 24 hr of treatment, most of the P189 and P217 had disappeared. In contrast, the peak area of P219 was still high after 24 hr of treatment with the F9/P25 composite sheet. This result corresponded well to the high TOC/TOC\({}_{0}\) level revealed in Figure 4a, validating the assumption of the accumulation of degradation intermediates during the treatment by the F9/P25 composite sheet. Treatment with the HSZ-385/P25 composite sheet (Figure 8) was compared with that using the F9/P25 composite sheet. The peak areas for the three intermediates obtained with the HSZ-385/P25  
Figure 6: Removal of TOC in the solutions and the TOC derived from the residual crotamiton during the treatment by the HSZ-385/P25 composite sheet with ultraviolet irradiation in ultrapure water (**a**) and RO concentrate (**b**). Results are means \(\pm\) standard deviations (\(n=2\)). Figure 7: Changes in the peak areas of the major intermediates over time in ultrapure water when crotamiton was photocatalytically degraded using the F9/P25 composite sheet (\(C_{0}=10\) mg/L). The squares are P189 (retention time 5.2 min) and the circles are P217. The diamonds with a dashed line are P219 (retention time 5.0 min, secondary \(y\)-axis). composite sheet were clearly lower than those obtained with the F9/P25 composite sheet throughout the treatment, especially for intermediate P219. After 24 hr of treatment with the HSZ-385/P25 composite sheet, the majority of all three intermediates had disappeared. The lower peak areas of degradation intermediates as well as the lower TOC/TOC\({}_{0}\) ratios (Figure 6a) confirmed that the HSZ-385/P25 composite sheet captured the degradation intermediates. Moreover, changes in the peak areas for the major intermediates in the HSZ-385/P25 composite sheet were evaluated through desorption treatment for the composite sheet after the adsorption and photocatalysis experiment. The methanol solution with the composite sheet after ultrasonic treatment contained croatmiton, as well as large amounts of degradation intermediates, retained in the composite sheet (Figure 9). The peak area for P219 was higher in the composite sheet during treatment than that in the aqueous phase when using the HSZ-385/P25 composite sheet shown in Figure 8. Even if the efficiency of desorption of the intermediates from the sheet could not be confirmed without the standard of every detected intermediate, the high peak areas for the intermediates provided direct evidence of the adsorption of intermediates on the composite sheet. Figure 8: Changes in the peak areas of the major intermediates over time in ultrapure water when croatmiton was photocatalytically degraded using the HSZ-385/P25 composite sheet (\(C_{0}\) = 10 mg/L). The squares are P189 (retention time 5.2 min) and the circles are P217. The diamonds with a dashed line are P219 (retention time 5.0 min, secondary \(y\)-axis). Figure 9: Changes in the areas of the peaks for the major intermediates over time in the HSZ-385/P25 composite sheet after desorption when croatmiton was photocatalytically degraded using the HSZ-385/P25 composite sheet (\(C_{0}\) = 10 mg/L).