Effect of reaction temperature on properties of carbon nanodots and their visible-light photocatalytic degradation of tetracyline

Abstract

Water-soluble carbon nanodots (CND_t) with diverse sizes, crystal structures, surface properties, and characteristic fluorescence spectra were synthesized by the hydrothermal carbonization of larch at different temperatures. The effects of reaction temperature on the diameter distribution, structural components, and fluorescence properties of the CND_t were investigated systematically. The synthesized CND_t were found to be monodispersed spherical polymer nanodots with a low degree of aromatization and abundant oxygen-containing groups on their surface. Increasing the reaction temperature decreased the average size of the nanodots from 20.35 to 6.48 nm, while their quantum yield increased from 13% to 18%. Broader and weaker UV characteristic peaks were detected when the reaction temperature was increased from 200 to 260 °C. All the CND_t samples exhibited excitation and emission-independent properties, and obvious blue shift of the excitation and emission peaks occurred at higher reaction temperatures owing to the smaller size and different surface properties obtained. The CND_t were used as a photosensitizer in a CND/TiO₂ system to effectively degrade tetracycline hydrochloride (TCH) under visible-light irradiation. The obvious blue shift exhibited by the smaller CND_t allowed the light to be fully used by the TiO₂, resulting in nearly 100% TCH degradation for CND₂₆₀/TiO₂.