Preparation of composite photocatalyst with tunable and self-indicating delayed onset of performance and its application in polyethylene degradation

The photocatalyst can be used as additives to plastic to increase the degradability of plastic products. However, the performance of photocatalyst cannot be delayed resulting in the unstable performance of plastic products during their usage. Even though when the delay can be realized, there is no color changing to indicate whether the performance starts or not. This hinders the industrial application of photocatalytic technology in plastic degradation. In this study, a new type of composite photocatalyst, TiO₂@amylose/polyiodide/hydroxyethyl cellulose (T@AIH), is elaborately designed with self-indicating delayed onset of performance. T@AIH is prepared via the wet chemistry method. The periods before and after onset are named stable stage and active stage, respectively. The T@AIH is blue at stable stage, and the color changes to white when the photocatalytic performance of T@AIH starts. The length for the stable stage and reaction rate for the active stage are tunable. The properties of T@AIH at different stages are characterized. The results suggest that efficient I₃⁻/I₅⁻ interconversion of polyiodide in amylose helical pitch plays a key role in electron-hole recombination, resulting in the stable stage. High diffusivity of polyiodide in HEC plays a crucial role in initiating the active stage and making it happen simultaneously with color changing. The performance of sample T@A_0.1IH on low density polyethylene (LDPE) degradation is tested. This study proposes a new photocatalyst to increase the degradability of plastic in a self-indicating and delayed-onset way for the first time.