Carbon nanodots as efficient photosensitizers to enhance visible-light driven photocatalytic activity

Obtaining photochemically stable, efficient, and earth abundant visible-light photocatalyst is still one of the challenging tasks in the photocatalysis area. In the present paper, a new type of nitrogen-doped carbon nanodots, CDs, have been prepared and used as a photosensitizer for a well-known wide-band gap photocatalyst to enhance visible-light driven photocatalytic degradation of an environmental organic pollutant. Blue emitters of nitrogen-doped carbon nanodots (CDs) have been prepared in an aqueous solution via hydrothermal method. ZnO-CDs nanocomposites were prepared via loading of CDs on ZnO in a low temperature mode, in order to modify the optical, electronic, and surface properties of ZnO nanoparticles. The nanocomposites were characterized by UV vis absorption spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, X-ray diffraction, Raman spectra, and Fourier transform infrared spectroscopy. Photocatalytic degradation of methylene blue (MB) showed that the nanocomposites of ZnO-CDs enhanced the photodegradation efficiency (95% for 100 min) comparing to the pure ZnO in the UV region (365 nm). Interestingly, ZnO-CDs showed enhanced visible light photodegradation comparing with pure ZnO. Such enhancement is attributed to the increase of charge separation rate, photoluminescence up-conversion properties in CDs, and high absorptivity of the ZnO-CDs nanocomposites. Tailoring various CDs with different chemical reactivities and optical properties will eventually lead to harnessing sufficient portion of the solar spectrum in order to obtain high efficient photocatalysts.