Research On Micro/Nanomaterials Preparation By Selective Laser Irradiation In Liquid Medium

Micro/nano materials have been attracting remarkable research interest due to their unique physicaland chemical features and have been applied in many fields.Conventional methods to synthesize micro/nano materials suffer from complicated preparation process and complex product composition,so they are not suitable for rapid and controllable preparation of micro/nano materials.As a new method for micro/nanomaterials preparation,selective laser irradiation in liquid media（SLIL）is particularly suitable for the preparation of various micro/nano materials due to its unique feathres,such as selective heating effect,simple preparation process,controllable product（morphology,size,and composition）,low cost and high efficiency.However,the research of SLIL technology has just started,and the related technology and corresponding mechanism remain to be further studied.By systematically studying this technology in this dissertation,the controllable preparation of several micro/nano materials,such as carbon dots（CDs）,titanium dioxide submicrometer-sized hollow/solid spheres and metal/semiconductor nanocomposites were prepared successfully.The detailed contents are as follows:Based on the technical characteristics of SLIL,a set of experimental devices,including optical path,airway,cooling,stirring and spectrum monitoring system was designed and manufactured.And it was successfully applied in the preparation of a variety of micro/nano materials.Because the CDs that prepared by other precursors suffer from complex composition and low fluorescence efficiency,a simple approach to preparing CDs by SLIL from toluene was presented.The as-prepared CDs were size tunable graphite dots and exhibited size-dependent PL,which can be controlled by changing laser irradiation fluence,and the emission quantum yields reached about 18%.Further research showed that graphene was generated as an intermediate before the CDs were finally produced.These results show that SLIL technology can be used for the rapid and controllable preparation of ultra-small quantum dots.The micro colloidal particles that prepared by conventional methods have the disadvantages of imperfect structure,rough surface,and difficulty in controlling size and crystal structure.Taking titanium dioxide as an example,SLIL technique was used to prepare micro colloidal spheres.The phases（rutile,amorphous and anatase）,size（100-500 nm）and hollow/solid structure of the as-prepared spheres could be easily tuned by changing experimental parameters.Mechanism exploration shows that the sphere formation includes melting and photochemical process.The formation mechanism of hollow spheres was also discussed.It was found that the air inside the agglomerates is a significant factor for the void formation,and the movement of the inside air results in the decentered void formation.This indicates that SLIL technology can be used for rapid and controllable preparation of submicron（0.1-1 μm）spheres.The preparation of nanocomposites was successfully carried out by using SLIL technology,in which the performance of each components was kept after preparation.As an example,the preparation of Ag/TiO₂ nanocomposites by SLIL technology was presented,in which a laser was used to heat the metal nanoparticles,and welded them on the TiO₂ nanoparticles.In this process,the size,morphologies and crystal structures of TiO₂ can be maintained,whilst the size and contents of Ag are adjustable.The prepared nanocomposites are well bonded and have excellent light absorption properties.In summary,SLIL technology can prepare not only CDs and micro colloidal spheres,but also nanocomposites.It indicates that the SLIL technology is a controllable and promising method for preparation of micro/nano materials.