Coal tar pitch as natural carbon quantum dots decorated on TiO2 for visible light photodegradation of rhodamine B

Carbon quantum dots (CQDs) modified semiconductor photocatalysts for visible light photodegradation of organic contaminant has attracted increasing attention, but the tedious preparation procedure of CQDs hinders their large-scale application. Coal tar pitch (CTP) is a rich by-product isolated from the coke industry. The molecule of CTP consists of polycyclic aromatic hydrocarbon nucleus and alkyl side chains or heteroatom functional groups attached to the edge of the nucleus, which is similar in structure to CQDs and should be considered as natural CQDs. Based on this perception, we first propose the use of CTP as a natural alternative for CQDs, and prepare effective CTP/TiO2 composite photocatalysts by a simple green one-step solvothermal method. With Rhodamine B (RhB) as target pollutant, the as-prepared CTP/TiO2 composite photocatalysts have higher photocatalytic activity than pure TiO2 under visible light irradiation. The apparent degradation rate constant of the CTP/TiO2 composite photocatalyst with optimum CTP content is 23 times higher than that of pure TiO2. The main active species involved in the photocatalytic degradation of RhB are holes (h+) and hydroxyl radicals (·OH). The usage of cheap raw materials and facile synthesis method paves the way for the large-scale preparation of effective CTP/TiO2 composite photocatalysts.