Preparation Of Carbon Quantum Dots And Their Application In Photocatalysis

Carbon quantum dots（CQDs）are a new type of zero-dimensional carbon nanomaterials and have been drawing much attention in recent years owning to their unique photoluminescence（PL）,excellent electron transfer and reservoir properties,high chemical inertness,good hydrophilicity,low toxicity,good biocompatibility,environmental friendliness,and high photostability.CQDs have shown promising applications in photocatalysis,drug delivery,optoelectronic devices,bioimaging,and ion detection.In this paper,we developed a facile chemical oxidation process to prepare CQDs by acidic oxidation of activated carbon with the most affordable oxidant and etching agent,nitric acid（HNO₃）.The structure of the CQDs were characterized by TEM,SAED,XRD,XPS,Raman,and FTIR.These results seggest that the as-prepared carbon quantum dots are completely disperse without any agglomeration,amorphous in structure,nearly spherical in shape,fine in size with an average particle size of 2.7 nm,and narrow in particle size distribution from 1.5 to 4.1 nm.The as-prepared CQDs possess oxygen-containing functional groups on their surface which endow them excellent hydrophilicity and exhibit stable,excitation-dependent,pH-sensitive and up-converted PL properties.A novel CQD/Sr TiO₃ nanocomposite was prepared by combining the as-prepared CQDs with Sr TiO3 nanoparticles through a simple impregnation process.The structure of the prepared CQD/Sr TiO3 nanocomposite was analyzed by TEM,XRD,EDS,SEM mapping,and XPS.When the CQD/Sr TiO3 nanocomposite and SrTiO3 nanoparticles were used as photocatalyst,respectively.Their photocatalytic performance was evaluated by degradation of Rhodamine B（Rh B）under sunlight irradiation.Compared with pure SrTiO₃,under the same conditions,the photocatalytic rate of the CQD/Sr TiO₃ photocatalyst is about 5.5 times higher than that of pure SrTiO₃.This clearly indicates that the CQD/SrTiO₃ photocatalyst shows an excellent photocatalytic performance in the photodegradation of RhB.The enhanced performance in the degradation of Rhodamine B may be attributed to the interfacial transfer of photogenerated electrons from SrTiO₃to CQDs,leading to effective electrons and holes separation in SrTiO₃.So the as-prepared CQDs exhibit potential applications in high-efficiency photocatalyst design.This work may open a door to the development of new CQD-based photocatalytic nanocomposites.