Study On The Controllable Preparation Of Silver Sulfide Quantum Dots And Its Photocatalytic Performance

As a direct narrow band gap semiconductor?1.1 eV?,silver sulfide nanomaterials have become an ideal photocatalytic and photovoltaic material due to their high chemical stability,low toxicity,wide absorption range?from UV spectrum to NIR region?and high absorption coefficient(about 10⁴ m^-1).More importantly,when the size of silver sulfide quantum dots?Ag₂S QDs?is close to its Bohr radius?2.2 nm?,quantum efficiency has been greatly improved because of the quantum confinement effect.Up to now,the synthesis of size-controllable Ag₂S QDs has become a research hotspot in recent years.At present,the reported method of synthesizing Ag₂S nanoparticles is still difficult to control the size below 10 nm.It is still a great challenge to find a quantum-level size-controllable method.According to the literatures,the size of as-prepared Ag₂S is mostly between 10-100 nm.Therefore,the purpose of this paper is to explore new synthetic methods to achieve controllable preparation of small size and uniform Ag₂S QDs.Through reading a large number of literatures,two routines were investigated for preparation of Ag₂S QDs,i.e.two-phase interface method and reverse microemulsion method.The effects of ratios of water to surfactant???,reaction temperature and surfactants on the morphology and properties of the Ag₂S QDs were explored.The as-prepared Ag₂S QDs were characterized by TEM,UV-vis,fluorescence spectroscopy,XRD,DSC,etc.The results show that the two-phase interface method is a simple,easy-to-operate and environmentally method for preparing Ag₂S QDs.The size distribution of the quantum dots is uniform,but which cannot be achieved the controllable growth.Then,based on the original traditional reverse microemulsion method,controllable synthesis of Ag₂S QDs could be realized via the new reverse nano-emulsion method assisted with phase transfer mechanism and small size and uniform monoclinic quantum dots were obtained.The particle size can be controlled at 3-8 nm and the particle size distribution is uniform.The Ag₂S QDs perform full spectrum absorption from UV to NIR region,and the emission peak is at 1140 nm under the excitation of 785 nm.The photocatalytic activity of the Ag₂S QDs was tested in the degradation of MO,and the results showed that more than 40%of MO was degraded by the Ag₂S QDs in 2h,which was significantly improved compared with the reported results.