Study Of Morphologically Controllable Synthesis And Their Optical Properties And Photocatalytic Performance Of ZnO Nanocrystals By Hydrothermal Method

Zinc oxide?ZnO?is a new wide band gap semiconductor material with excellent optical and electrical properties,owning a wide direct band gap of 3.37 eV and a large excition binding energy of 60 meV at room temperature.Due to its favourable structural,optical and catalytic properties,zinc oxide has been widely used as gas sensors,antireflective coatings,photo catalyst,field-emission device and in solar cells.Such performances depend not only on the compose structure of the material,but also on its dimensionality and configuration.As a result,designing ZnO material's capability and selective assembly are of practical significance for multiple applications.This work was the starting point for different forms by the hydrothermal synthesis of ZnO microstructures,the typical morphology controllable preparation,focusing on further study the relationship between the microstructure and macroscopic properties.At the same time,structures and properties of these materials were also characterized and analyzed.The main conclusions are summarized as following:?1?Different flower-like ZnO hierarchical architectures were prepared by tartaric acid assisted hydrothermal synthesis,especially four flower-like ZnO nanostructures were obtained simultaneously under the samereaction condition.The cauliflower-like ZnO is assembled by spherical shaped nanoparticles,and the chrysanthemum-like and other flower-like ZnO nanostructures are assembled by hexagonal rods/prisms with from planar to semi-pyramid,and to pyramid tips.TA acts as a capping agent and structure-directingagent during the synthesis.All ZnO possess the hexagonal wurtzite structure.The PL spectra can be tuned by changing TA concentration.XRD,PL and Raman spectra confirmed that oxygen vacancies mainly come from the ZnO surface.The flower-like samples of 1:4.5 and 1:3 with the largest aspect ratios have highest photocatalytic performance.They decompose 85%MB within 60 min.The enhanced photo-catalytic performance is mainly induced by oxygen vacancy of ZnO.?2?Different flower-like ZnO hierarchical architectures with wurtzite structure have been prepared by a facile salicylic acid?SA?assisted hydrothermal method,especially four flower-like ZnO nanostructures can be obtained simultaneously by using 18.00mmol of SA.The petals of the flower-like ZnO architectures are mainly assembled by many of single nanorods,a mixture of single nanorods and bundle?cluster?of nanorods,or bundle of nanorods respectively.The nanorod exhibits the taper-like,hexagonal prism-like,tower-like or bamboo shoot shaped body and the pyramid-like or pencil-like tip.Photoluminescence?PL?study shows two tunable wavelengths?542 nm and 565 nm?.With increasing the amount of SA,the peak at 441 cm-1 increases.The activity of photocatalysts is significantly affected by the concentration of SA.With the increase of SA,the number of nanorods of the flower-like ZnO nanostructures increases,and leads to the improvement of photocatalytic performance.?3?Different flower-like ZnO nanoarchitectures were synthesized by a facile hydrothermal method using CO?NH₂?₂ and N₂H₄ as alkali sources simultaneously.A novel ultralarge ZnO macroflower was constructed by the ultrathin leaf-like nanobelts,hollow semisphere-like,sphere-like and apple-shaped nanoparticles simultaneously.The diameter of anindividual flower can reach 90?m.Meanwhile,three or five flower like ZnO nanostructures with different diameters,lengths and tips?Planar,semi-pyramid,and/or pyramid tips?were formed simultaneously under the same reaction condition.XRD shows that all the ZnO crystals possess the hexagonal wurtzite structure.When the samples range from S1 to S5,the crystallinity is improved.FTIR indicates that S4 and S5 are pure.However,the surface of S1,S2 and S3 adsorbs the CO₃^2-group.S1 and S5 exhibit the highest photocataly tic performance and decompose 65%and 70%of MB with in 50min respectively.