Ultrasound-assisted method to improve the structure of CeO@polyprrole core-shell nanosphere and its photocatalytic reduction of hazardous Cr.

In this work, the CeO@polypyrrole (CeO@PPy) core-shell nanosphere has been synthesized via an ultra-sonication method using bath type (WUC-D22H, Daihan Scientific, Korea) and they are utilized for the photo-reduction of hazardous Cr to benign Cr. The ultrasonic frequency and power were 20 kHz and 100 W, respectively. The PPy shielded CeO in aqueous solution could prevent the dissolution of CeO and to improve the photocatalytic ability of CeO. X-ray diffraction was used to confirm the crystalline structure of as prepared CeO@PPy core-shell and FT-IR was used to identify the functional groups. The uniform sized core of PPy and shell of CeO were observed by transition electron microscopy. The ultrasonic assisted synthesized CeO@PPy core-shell exhibits a narrow bandgap (UV-DRS) and good reduction efficiency with higher reusability and stability compared to pure CeO, PPy and mechanical mixing of CeO@PPy. Moreover, the synergistic effect of CeO and PPy core-shell structure facilitate a higher electron transfer rate and prolong lifetime of photogenerated electron-hole pairs which can achieve good reduction rate of 98.6% within 30 min. In particular, the pH, catalyst, and Cr concentration effects were optimized in photocatalytic reduction reactions. Meanwhile, this photocatalysis with fast and effective electron transfer mechanism for the Cr reduction was elucidated. This method opens a new window for simple fabrication of conducting polymers-based metal oxide nanocomposite towards wastewater remediation and beyond.