Size-dependent photocatalytic activity of carbon dots with surface-state determined photoluminescence

• Published in: Applied catalysis. B, Environmental Environmental, 2019-07, Vol.248, p.157-166
• Main Authors: Zhou, Yiqun, Zahran, Elsayed M., Quiroga, Bruno A., Perez, Jennifer, Mintz, Keenan J., Peng, Zhili, Liyanage, Piumi Y., Pandey, Raja R., Chusuei, Charles C., Leblanc, Roger M.
• Format: Article
• Language: English
• Subjects: Absorption; Carbon; Carbon dots; Catalysis; Catalytic activity; Contaminants; Dyes; Electromagnetic absorption; Environmental degradation; Irradiation; Luminescence; Methylene blue; Nitrophenol; Organic compound degradation; p-Nitrophenol; Photocatalysis; Photodegradation; Photoluminescence; Photons; Reflectance; Rhodamine; ROS; Size exclusion chromatography; Superoxide; Surface chemistry
• ISSN: 0926-3373; 1873-3883
• DOI: 10.1016/j.apcatb.2019.02.019

[Display omitted] •Bare CDs were first studied for the size-dependent photocatalytic degradation of dyes.•CDs in the smallest size exhibits a narrow band gap of 2.04 eV, the best photocatalytic capability and excellent stability.•2-nm CDs showed promising application of bare CDs in the photocatalytic degradation of p-nitrophenol (70% within 150 min).•The photocatalytic degradation of organic compounds is mainly due to the hole in valence bands and the generated O2–.•The photocatalytic degradation of organic compounds is mainly due to the hole in valence bands and the generated O2–. Carbon dots (CDs) were synthesized by a microwave-mediated method and separated by size exclusion chromatography into three different size fractions. There was no correlation of CD size with photoluminescence (PL) emission wavelength, showing that the PL mechanism is not quantum-size dependent. UV/vis absorption and diffuse reflectance spectroscopies showed that the light absorption properties as well as the band gap of the CDs changed with the size of the particle. The combination of FTIR and XPS measurements revealed the composition on the surface of each fraction. The three CDs fractions were separately used in the photocatalytic degradation of organic dyes under simulated sunlight irradiation. The catalytic activity of the as-prepared CDs was found to increase as the size of the particles decreased. Complete degradation of both rhodamine B (RhB) and methylene blue (MB) was achieved in 150 min by the 2-nm CDs. The scavenger studies showed that the holes and superoxide radicals are the main species involved in the photocatalytic degradation of the dye by the 2-nm CDs. These CDs displayed high stability in the degradation of organic dyes for multiple cycles. The 2-nm CDs displayed promising photocatalytic degradation of p-nitrophenol (PNP). These results demonstrate for the first time the application of bare carbon dots in the degradation of environmental contaminants.