Graphene Quantum Dots/ Bi₂O₃ Composite Photocatalysts For Dye Degradation Under Visible Light

With the development of the social economy,the destruction of the natural environment is becoming more and more serious,and the organic dye is an important factor in the water pollution.In recent years,the use of photocatalytic technology to catalyze the degradation of organic pollutants in water is an important means of water pollution control.Bismuth trioxide is a semiconductor that has a band gap of 2.8e V,it has recently drawn tremendous attentions for its excellent thermal and chemical stability.Nevertheless,the band of bismuth oxide is close to the ultraviolet region and restricts its response to visible light.It is necessary to find a method to impoving its photocatalytic activity of Bi₂O₃.Graphene quantum dot?GQD?is a kind of zero dimensional nanomaterial,its bandgap can be tunable by changing size.In this dissertation,GQDs/Bi₂O₃ composite photocatalysts were synthesized by using a hydrothermal method,and demonstrated to be better photocatalysts than Bi₂O₃.In the composite photocatalysts,the bandgap of GQDs is tuned as low as possible for harvesting more solar light by reducing the particle size.The contents of the dissertation include three parts.First,we successfully prepared graphene quantum dots by a top-down method: thermal reduction of graphene sheets in an acid media followed by the hydrothermal reduction.The morphology and structure GQDs were characterized by using SEM,HRTEM,XPS,Raman,XRD,FTIR and UV-vis methods.The results demonstrated that the obtained GQDs are well dispersed hexagon nanoparticles with a diameter around 10 nm and a lattice spacing of 0.227 nm.The stronger G peak and weaker D peak shows that the prepared GODs are with fewer defects.Second,Bi₂O₃ nanoparticles were prepared by using a hydrothermal method.SEM and HRTEM results show that the obtained Bi₂O₃ samples are nanoparticles with a lattice spacing of 0.317 nm and a diameter around 100 nm.Finally,GQDs/Bi₂O₃ composite catalysts were prepared by using a hydrothermal method.The optimum GQD content was determined to be 10 wt%.By using the GQDs?10%?/Bi₂O₃,the photodegradation of Rhodamine B Organic dye with a initial concentration of 10 mg/m L can reach 93% under 90 min of visible-light irradiation.