Facile fabrication of stable metal-free CQDs/g-C3N4 heterojunctions with efficiently enhanced visible-light photocatalytic activity

Novel carbon quantum dots (CQDs)/graphitic-like carbon nitride (g-C 3 N 4 ) metal-free heterojunctions were firstly synthesized via a facile low temperature process. Multiple physicochemical techniques were carried out to characterize the samples. The CQDs with the average size of about 5   nm are attached to the surfaces of g-C 3 N 4 nanosheets. The photocatalytic activity of as-prepared samples was carefully evaluated by the degradation of rhodamine B (RhB) and tetracycline hydrochloride (TC-HCl) under visible light irradiation. Photocatalysis result displayed that the CQDs/g-C 3 N 4 heterojunctions can significantly enhance visible-light photocatalytic activity in compared to that of pristine g-C 3 N 4 . The reaction rate constant of the optimum active C0.50%/CN heterojunction for the photodegradation of RhB and TC-HCl were about 3.7-fold and 1.9-fold higher than that of bare g-C 3 N 4 , respectively. The efficiently enhanced photoactivity was attributed to the CQDs not only can improve the photogenerated electron–hole pair’s separation, but also can increase light harvesting by the up-conversion photoluminescence behavior. Moreover, the as-prepared C0.50%/CN sample also exhibited excellent photostability and recyclability for both photodegradation of RhB and TC-HCl. In addition, the possible enhanced photocatalytic mechanism was proposed and analyzed by the active species trapping experiments. This work will bring about potential for application in environmental purification and useful for designing other CQDs-based photocatalyst in energy conversion.