Preparation,photocatalytic And Adsorption Properties Of Zinc Oxide Crystals With Different Morphologies

As a multifunctional material,the properties of zinc oxide are closely related to morphology,but the effective control of morphology is always a difficult problem to be solved.In this paper,zinc oxide single crystals and their aggregates with various morphologies have been successfully prepared by hydrothermal/solvothermal method and by adjusting various experimental parameters.The influence of various factors in different reaction systems on the morphology of zinc oxide crystals and the relationship between morphology and photocatalytic and adsorption properties of zinc oxide crystals were studied.（1）By regulating the amount of raw materials,reaction temperature and time,solvent,additives and other technological parameters in different systems,various kinds of zinc oxide with different morphology were prepared,such as lotus tabular twin crystal,hexagonal column spherulite crystal,hexagonal plate/plate spherulite crystal and cauliflower spherulite crystal.（2）Different mixed solvents have obvious influence on the morphology of zinc oxide.In the mixed solvent system of water and dimethyl sulfoxide（DMSO）,the product is a lotus table zinc oxide twin-crystal with novel morphology.The products with water and acetone as solvent are spherulite crystals with radial distribution of zinc oxide.In the mixed solvent system of water and alcohol,the obtained products are spindle aggregates composed of different conical zinc oxide crystals and spherulites with incomplete morphology.（3）The influence of different solvent dosage on the morphology of zinc oxide.In the mixed solvent system of water and DMSO,with the ratio of DMSO to water decreasing from 5:1 to 2:1,the morphology of the twin crystals gradually changed from dumbbell shape to complete lotus-like shape.In water and acetone system,with the acetone and the volume of water than the 8:1 gradually reduced to 1:4,composition of spherulite crystal zinc oxide single crystal by hexagonal prism shape gradually transition to the six-party platy six-party flake,even among them,acetone and water volume ratio of 4:1,product to form perfect spheres of hexagonal prism shape zinc oxide crystal,when the volume ratio of acetone and water as when,The product is spherulite composed of hexagonal flake zinc oxide.In the mixed solvent system of water and alcohol,when the amount of alcohol is low,the product is a spindle aggregate composed of different forms of conical zinc oxide crystals.When the amount of alcohol is increased,the product is spherulite with incomplete morphology.（4）The morphologies of the products are obviously different in the solvent systems with different p H.In weakly alkaline system dominated by ammonia,the product is cauliflower spherulite,while in KOH strongly alkaline system,the product is incomplete spherulite composed of rod-like single crystal.The addition of organic acids such as glutamic acid inhibits the formation of zinc oxide and the aggregation of single crystal to a certain extent.（5）The reaction time has little effect on the morphology of the product,mainly on the size of the product.Other things being equal,the size of the product increases with the increase of reaction time.（6）The effect of different properties of solvent and additive on nucleation rate and growth rate of different crystal planes is the main reason for the formation of zinc oxide with different morphology.DMSO,acetone and glycerol not only affect crystal nucleation,but also affect the development of different crystal planes of zinc oxide.DMSO and glycerin inhibited the nucleation of zinc oxide,acetone reduced the crystal plane development of（0001）and（10（?）0）,and methanol and glycol promoted the crystal plane development of（0001）.Organic acids such as glutamic acid,salicylic acid and sorbic acid can promote the formation of zinc oxide crystal aggregates with different morphologies.（7）The photocatalytic degradation capacity and adsorption capacity of zinc oxide crystals with different morphologies are different.The photocatalytic degradation of zinc oxide to different organic dyes is obviously different: the degradation rate of methylene blue light is 99.05% when it is illuminated for 150 min,while that of rhodamine B light for180 min is 96.48% and that of methyl orange is only 68.31%.The photocatalytic degradation capacity of sparsely radiated spherulites is twice that of compact spherulites,and the photocatalytic degradation capacity of nanocrystals is twice higher than that of micron spherulites.Under the same other conditions,the adsorption capacity of different morphs from small to large is large bundle spherulite grain < compact nano baseball grain< small bundle spherulite grain < sparse uniform radiation spherulite grain.（8）Under the light condition,zinc oxide crystal is easy to produce hydroxyl radical and superoxide radical,which is the fundamental reason for its excellent photocatalytic degradation performance.The effective reaction area of zinc oxide exposed with different morphologies is different,which results in the difference of photocatalytic performance of zinc oxide with different morphologies.The adsorption of dye by zinc oxide crystal is mainly chemical adsorption,supplemented by electrostatic force of adsorption.The morphology of zinc oxide with nano-scale and low aggregation provides larger adsorption reaction area,which is beneficial to improve the adsorption performance of the product.