Carbon dots modifier for highly active photocatalysts based on ZnO porous microspheres

The multi-band light active carbon dots (CDs) as the sensitizers, three-dimentional porous zinc oxide (ZnO) microspheres were successfully obtained by the facile hydrothermal method. The CDs, bare ZnO and CDs/ZnO composites were characterized in detail by integrated investigations of XRD, FTIR, XPS, FESEM, TEM, BET, UV–Vis, PL, PC and EIS. The surface of CDs possessed a large number of C–OH, C=C, C=O and C–N hydrophilic groups, the abundant surface states resulted in the multistage absorption in the visible light range from 370 to 600 nm. Considering the PL spectra of CDs displaying with different wavelengths from 250 to 500 nm, the maximum emission peak positioned at 610 nm were virtually independent of the excitation wavelength, suggests that the CDs behaved actively and stably as an excellent modifier with ZnO. Moreover, porous ZnO microspheres consisted of multitudinous hollow nano-cylinders with high specific surface area (30.078 m2/g), together with the advantageous optical and photoelectrical properties, made the CDs/ZnO-30 achieve superior photocatalytic activity (98%) and exhibit obvious absorption in visible light comparing to bare ZnO. Therefore, the modification of CDs can not only broaden the visible light response, but also enhance the separation efficiency of the photo-generated electrons and holes subjected to the accelerated electron transfer.