Controllable Synthesis Of Novel CdS Nanostructures And In Situ Study Of Ni₂Co Oxidation

Conception of new ideas,design of new paths,exploration of new methods and use of advanced in-situ techniques are key to controllable synthesis of novel nanostructures to improve their performance.In this thesis,we conceived the new idea of synthesis of high-quality hollow nanostructures by synergistic reactions,designed the new paths for complicated nanoboxes by a millisecond pulsed laser irradiation,explored the new method for synthesis of ultra-thin single-crystal hierarchical nanowires by a laser-induced thermal field,and used advanced techniques for in situ study of bimetallic particle oxidization.We synthesized novel nanostructures under control,proposed the new formation mechanisms,and enhanced their photocatalytic performance.1.The synergic reaction synthesis strategy combining the merits of cation exchange and chemical etching generated quasi-monocrystal and smallest CdS nanoboxes with high-energy facets.We proposed the mechanism that chemical etching guided cation exchange along the inner surface of the PbS nanocube and led to the formation of a uniform CdS shell.The nanoboxes exhibited superior photodegradation efficiency of methylene blue over CdS nanoparticles synthesized by the conventional heating.We used the same strategy to prepare other nanoboxes,such as Co9S8 and Cu7.2S4.In this work,we challenged the traditional strategies of stepwise or synchronous reactions for synthesis of hollow nanostructures,and put forward to the new idea of synergistic reactions for high-quality hollow nanostructures.2.By changing millisecond pulsed laser parameters and irradiation times,we adjusted the shell thickness of the PbS@CdxPb1-xS core-shell nanostructures,the core shape of the yolk-shell nanostructures as cube,sphere,core-shell and yolk shell,and the shell layer of the CdxPb1-xS nanoboxes.In this work,we first used millisecond pulsed laser to irradiate nanoparticle target and control their chemical reactions to design structures of the final product.3.We developed a new,simple and fast approach of laser-induced thermal field to synthesize ultrathin and single-crystal CdS hierarchical nanowires.We proposed the formation mechanism.The light absorber(dye)was pyrolyzed by the laser and released a lot of heat.The solution was heated rapidly,forming tiny primary CdS nucleus nuclei.Driven by intense convection,such CdS nuclei then move to zones with lower temperatures where they assemble into nanowires.Next,the nanowires experienced a phase transformation and then branch growth,eventually grew into well-developed hierarchical nanowires.The obtained nanowires exhibited higher photocatalytic efficiency in decaying RhB when compared with their CdS nanoparticle counterparts prepared via conventional heating.4.We used environmental transmission electron microscope(TEM),mass-contrast and chemical sensitive tomography for three-dimensional visualization of Ni2 Co particle oxidation on the nanoscale.We found that both the external oxide shell and the internal oxides are porous in nature.It was observed that a graded segregation of cobalt and nickel oxides with more cobalt sit close to the surfaces that are exposed to oxygen.All these evidences strongly suggest there were infiltration of oxygen into the hollow structure to oxidize the metal in the core.