Micro-scaled Chemical Reactions And Material Synthesis Modified By High-energy Laser

Fabrication of nanomaterials with uniform and controllable structure, simplesynthesis process, and good performance is an important topic in materials field, andthe explorations of new methods and new concepts are critical to the synthesis ofmaterials. In this thesis, high energy laser is combined with common chemicalreactions to generate extreme synthesis conditions, resultantly, a series of novelnanostructures are obtained. The formation mechanisms of novel nanostructures arecomprehensively investigated, and the principle of laser effect is discovered.Laser ablation method is adopted to synthesize active metal nanoparticles. Theparameters of laser ablation are varied to determine their influence on the dispersionand uniformity of nanoparticles. It is found that the gas flux and flying distance ofnanoparticles are the key factors on preparing uniform and disperse product.Furthermore, active metal nanoparticles prepared under different laser ablationconditions are used for the galvanic replacement reaction, resulting in porous hollowAu nanospheres which are considered promising for bio-application.The laser synthesized Zn nanoparticles are employed as a starting material for thegalvanic replacement reaction with Cu_<sup>2+ions, and surface oxide layer of Znnanoparticles shows a remarkable impact on the reaction and products. Coppernano-dendrites were obtained in absence of the oxide layer, a large number of uniformsize monodispersed copper nanoparticles were fabricated without the oxide layer.The concept of nanoscale solvothermal reaction is proposed. The laser irradiationis introduced to heat Cu nanoparticles, which act as the heat source to induce thesolvothermal reaction and then the formation of the metal-semiconductorheterojunctions. The laser energy, irradiation time, precursors are varied to makecontrol experiments.A hydrolyzation process is proposed to synthesize uniform and controllable Cu₂Ohollow nanocubes. The formation mechanism of Cu₂O hollow nanocubes is discussed.It is found that CuCl micropowder first decomposes and then precipitates to give riseto uniform CuCl nanocubes which act as sacrificial templates to produce Cu₂O hollownanocubes by hydrolyzation. This work demonstrates for the first time thathydrolyzation is an effective way to produce hollow nanocubes. The influence of the pH value on the reaction of CuCl in aqueous solution was studied systematically,copper nanoparticles and hollow cuprous oxide nanocubes were obtained at differentpH value.The hydrolyzation of CuCl is conducted under the laser ablation, and thechemical reaction is modified by the laser energy, and Cu₂O nanocubes are obtainedunder acidic conditions, which is obviously different from the case without laserenergy. The influence of laser wavelength, laser energy and laser irradiation time onthe morphology of products is investigated, which is a meaningful attempt on thematerials synthesis by laser chemistry.