Facile preparation of carbon quantum dots/TiO2 composites at room temperature with improved visible-light photocatalytic activity

Carbon quantum dots (CQDs) have demonstrated tremendous potential in enhancing the photocatalytic performance of TiO2; however, the fabrication of CQDs/TiO2 composite photocatalysts typically involves harsh reagents/conditions, cumbersome purification procedures and external energy supplies. In this work, we present a facile and energy-efficient impregnation method for the preparation of effective CQDs/TiO2 composite photocatalysts at room temperature employing coal tar pitch (CTP) as “natural CQDs”. The characterization results indicate that TiO2 and CQDs can be successfully coupled together by forming Ti‒O‒C bonds. The fabricated CQDs/TiO2 composites show remarkably improved photodegradation performances of rhodamine B (RhB) under visible-light irradiation, which are far higher than pure TiO2. At the optimum CQDs content (6 wt%), the degradation rate constant is 43.7-fold higher than that of pure TiO2. The marked ameliorated photocatalytic performance is attributed to the fact that the successful coupling between TiO2 and CQDs can ameliorate the absorption ability of visible light, accelerate the separation/transfer of charge carriers and restrain the recombination of photogenerated electron–hole (e−–h+) pairs. This research provides a facile method for large-scale preparation of CQDs modified semiconductor photocatalysts that can potentially be used in environmental and energy applications.