Degradation of indometacin by simulated sunlight activated CDs-loaded BiPO4 photocatalyst: Roles of oxidative species

- A sunlight-driven CDs/BiPO4 photocatalyst was prepared firstly.
- The active mechanism of the CDs/BiPO4 composites was deduced suggesting the participation of reactive species in the degradation of Indometacin.
- O2− and h+ were the two critical reactive oxidative species to mediate or immediate the photocatalytic degradation and mineralization of IDM.
- The CDs/BiPO4 photocatalytic technology could effectively reduce the toxicity of the treated solution and by-products of Indometacin.

In this study, novel carbon dots/BiPO4 (CDBP) photocatalytic complexes were successfully synthesized via a facile hydrothermal-calcination synthesis strategy. The physicochemical properties of the synthesized samples were studied by X-ray diffraction (XRD), UV-vis diffuse reflectance spectra (DRS), Fourier infrared spectrometer (FT-IR), Raman spectrometer, scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), photoluminescence26spectra (PL), electrochemical workstation, etc. The activities of the CDBP were evaluated through the photocatalytic degradation of Indometacin(IDM) in an aqueous solution under simulated sunlight irradiation. With increasing concentrations of carbon dots (CDs), the photocatalytic activity of the CDBP initially increased, and then decreased. A CDs content of 3.0 wt% shows 12 times higher photocatalytic activity than that of pristine BiPO4. Reactive oxidative species, particularly O2− and h+, were the two critical reactive oxidative species to mediator immediate the photocatalytic degradation of IDM. A notable sign of 5, 5-dimethyl-1-pyrrolidone-N-oxyl(DMPOX) was observed through electron spin resonance spectroscopy(EPR) with CDBP as the photocatalyst, which indicated higher oxidability than pristine BiPO4 under simulated sunlight irradiation. This enhanced photocatalytic activity might due to high-efficiency charge separation, unique up-converted PL properties, as well as the bandgap narrowing of the CDs. Moreover, the byproducts of IDM were detected by HPLC-MS/MS and GC-MS, and the probable pathways were deduced. The acute toxicity at three trophic levels initially increased slowly and then decreased rapidly as the IDM dechlorination and total organic carbon(TOC) decreased during photocatalytic degradation.

shows the schematic photocatalytic mechanism of Indometacin for the CDs-doped BiPO4 composites under simulated sunlight irradiation. The photocatalytic activity of BiPO4 was enchanced by introduced CDs. This enhanced photocatalytic activity might have been due to high-efficiency charge separation, robust oxidization properties, unique up-converted PL properties, as well as the band gap narrowing of the CDs. As a promising alternative to conventional water treatment technology, CDs/BiPO4 photocatalytic technology performs excellently the mineralization of IDM.216