# Removal of Crotamiton from Reverse Osmosis Concentrate by a TiO\({}_{2}\)/Zeolite Composite Sheet
## 3 Results and Discussion
### Adsorption and Photocatalytic Degradation of Croatmiton by the HSZ-385/P25 Composite Sheet  
In our previous research, we found that P25 was effective for photocatalytic degradation of croatmiton [31]. The HSZ-385/P25 composite sheet prepared in the present study combines adsorption and photocatalysis processes, which makes it possible to regenerate the adsorbent during treatment. To clarify the adsorption and degradation performance of croatmiton by the HSZ-385/P25 composite sheet, the mass of croatmiton in the composite sheet (\(M_{in\_sheet}\)) was determined together with the mass of croatmiton in the aqueous phase (\(M_{in\_water}\)). The mass of croatmiton in the system (\(M_{in\_system}\)) was calculated as the sum of the residual mass of crotamiton in both the aqueous phase and in the sheet, which was the mass of undecomposed crotamiton remaining in the system. The masses of crotamiton in different phases were plotted against time (Figure 5) for solutions with initial croamiton concentrations of 10 mg/L in ultrapure water (Figure 5a), 10 mg/L in RO concentrate (Figure 5b), and 120 mg/L in RO concentrate (Figure 5c). Although similar trends were observed for \(M_{in\_water}\) in ultrapure water and RO concentrate (Figure 5a,b) with an initial crotamiton concentrations of 10 mg/L, the trends for \(M_{in\_sheet}\) were very different. The highest value of \(M_{in\_sheet}\) (ca. 0.12 mg) was observed after 3 hr treatment of crotamiton in the ultrapure water, and this then decreased with time (Figure 5a); at most, only 23% of the initial crotamiton was accumulated in the sheet, and all the croamiton was eventually degraded by photocatalysis. In removing of crotamiton from the RO concentrate, much more crotamiton (0.34 mg) was accumulated in the composite sheet after 6 h treatment (Figure 5b). After that, the mass of croamiton in the sheet gradually decreased, and finally 0.25 mg remained in the sheet at 24 hr. The higher removal rate obtained with adsorption compared with photocatalysis led to the accumulation and long retention time of croamiton in the composite sheet. In the treatment of both RO concentrate and ultrapure water, crotamiton could be effectively removed from the aqueous phase, thus purifying the water. The adsorption process was not greatly affected by the water matrix, but inhibition of photocatalysis resulted in low crotamiton degradation in the RO concentrate when using the HSZ-385/P25 composite sheet. Removing of croamiton from the RO concentrate with an initial crotamiton concentration of 120 mg/L was investigated (Figure 5c). The \(M_{in\_sheet}\) values were maintained at a low level throughout the treatment, and the maximum accumulation of croamiton in the sheet was only 6.7% of the initial croamiton mass in the aqueous phase. A rapid decrease was observed in \(M_{in\_system}\), showing that rapid decomposition of crotamiton occurred with the low initial crotamiton concentration. Inhibition of the degradation process with high initial croamiton concentrations may be attributed to competition from intermediates produced by croamiton degradation [37]. [PERSON] et al., found that the target material (trichloroethylene) saturated the composite catalyst surface and reduced photon efficiency, leading to photocatalyst deactivation [45]. [PERSON] et al., showed that the degradation rates of codeine and methamphetamine increased with increasing initial concentration (100-250 mg/L) [44; 46]. With the initial concentration at microgram per liter levels, the degradation rate may not be limited by the availability of catalytic sites but by contaminant concentration. Figure 4: Removal of TOC in the solutions and the TOC derived from the residual crotamiton during the treatment by the F9/P25 composite sheet with ultraviolet irradiation in ultrapure water (**a**) and RO concentrate (**b**). Results are means \(\pm\) standard deviations (\(n=2\)).