High photocatalytic performance of carbon quantum dots/TNTs composites for enhanced photogenerated charges separation under visible light

Abstract

A novel high-efficiency composite photocatalyst, carbon quantum dots (CQDs) are embedded onto out-surface surface of the TiO2 nanotubes (TNTs) with high percentage of photocatalytic reactive facets, was fabricated through an improved hydrothermal method. The characterization results showed that the CQDs was chemically adhered to out-surface of the TNTs through the CO and/or CO bonds formed between the CQDs and TNTs. The photocatalytic performance of as-prepared photocatalysts was evaluated to degrade methylene blue (MB) solution under the visible light. The as-prepared photocatalysts had a marvelous photocatalytic performance and the CQDs/TNTs-0.2 sample had the best photocatalytic performance with a decolorization rate of 91.3% and approximately 2 times more than that of pure TNTs for the high initial concentration of MB solution (30 mg/l) within 50 min under visible-light irradiation. The CQDs with excellent Up-Conversion Photoluminescence(UCPL)properties as co-catalysts can covert long wavelength light (>600 nm) absorbed from infrared light into visible light (<600 nm), which activates the TNTs to produce electron-hole pairs. Moreover, the CQDs also can capture the photoexcited electrons and prolong the lifetime of the photoexcited charges. In addition, the stacking interaction of the π-π bonds between the CQDs and the dyes of the benzene ring structure would be beneficial for enhancing the absorption performance of the CQDs/TNTs photocatalysts. The photocatalytic mechanism and process have also been discussed in detail according to the characterization and photodegradation results. This work is of great interest to introduce a new visible-light photocatalyst for the treatment of organic wastewater and protect environment.