Controllable Assembly And Formation Mechanism Of Zinc Oxide And Its Hybrid Nanomaterials

Since the 1990 s,the rise of nanotechnology has promoted the research upsurge and vigorous development of nanomaterials,while semiconductor nanomaterials have gotten extensive attention due to their unique physical and chemical properties.The properties of semiconductor nanomaterials are not only closely related to their size and shape,but also influenced by their assembly morphology because of the interaction between nanostructured building blocks.The “bottom-up” assembly method achieves both the subtle control for the assembly behavior of a single component,and the performance optimization by introducing other components to form hybrid structures.The understanding on the assembly mechanism of semiconductor nanomaterials and the analyze on the multiple forces in the scale of molecular and nano,are the keys to realize the synergistic enhancement effect in multi-particle and multi-component assembly structure by using assembly technology.In this paper,Zinc oxide(ZnO)was taken as the research object.A series of assembly structures of ZnO and its hybrid nanomaterials were realized by controllable assembly,and the formation mechanisms of its assembly structure were revealed by combining theory and experiment.Besides,the according application performances were studied.This paper aims to provide theoretical support for the controllable assembly of nanomaterials,and lay a foundation for further performance research and practical application.The main research contents are included as:Considering the self-assembly of nanoparticles(NPs)is a general method to obtain the ordered superstructures,the perfect self-assembly mechanism is conducive to the precise control of the complex interaction among NPs.The high-yield formation of ZnO nanoparticle chains with micrometer length were spontaneously achieved through dispersing ZnO NPs in water.Spectroscopic studies confirmed the solvent effect on the surface properties of ZnO nanoparticles.Based on the experimental results and multi-scale theoretical simulation,the formation mechanism of self-assembly was proposed,which was dominated by both hydrogen bond and dipole-dipole interaction among NPs in water.Furthermore,the importance of solvent-NPs interactions for promoting one-dimensional self-assembly was pointed out.The variation of visible light emission confirmed Forster resonance energy transfer(FRET)between nanoparticles.The high efficiency of FRET quenching can be ascribed to the presence of multiple energy transfer channels and the stronger coupling effect of NPs in the chain networks.Benefit from the higher FRET efficiency in the chain network,the ZnO NP chains network had better photocatalytic effect.The chemical synthesis toward superstructures could be more attractive than self-assembly because it allows an in-situ one-step assembly.However,the complexity of forming process makes it hard to be controlled.Two patterns of ZnO nanorod superstructures were obtained directly by thermal decomposition in methanol and n-pentanol.Time-dependent observa-tions indicated that the transition of quasi spherical structure to different NRs superstructures with different solvent types.The crossed fan-shaped structures of NRs were formed in methanol,and the parallel sideby-side structures of NRs were formed in n-pentanol.The DLVO theory was used to calculate the interaction potentials between two spatial arranged NRs.The results showed that solvents had significant effect on the system energy by changing the electrostatic repulsion among NRs,and further determined the final morphology of the NR superstructures.Compared with the parallel structure,the fan-shaped structure with larger specific surface area showed better photocatalytic performance.The hybrid materials can further expand the application of NPs,and the directional assembly among different materials is significant for performance enhancement.The size-controlled synthesis of ZnO hexagonal pyramids(HPs)was achieved in a methanol-water cosolvent system,and the size dependent property of HPs was studied by photocatalytic activity test.The ZnO HPs with the smallest size showed the superior photocatalytic properties.The directional assembly of gold(Au)on the surface of ZnO HPs with minimum size was realized by in-situ one-step assembly.It was found that most of Au NPs were combined at the apexes of the basal plane of ZnO HPs,while a few were at the top of HPs.The quantum chemical calculation indicated that the directional assembly of Au NPs on ZnO HPs was mainly related to the electrostatic potential distribution and LUMOs position of HPs.Benefit from the higher efficiency of carrier separation,the photocatalytic performance of Au/ZnO HPs was about 1.6 and 2 times higher than that of ZnO HPs under UV and visible light,respectively.The specific recognition function of biomolecules enables them to hybridize with NPs through surface orientation connection,so as to realize controllable assembly.The combination of BSA and ZnO NPs was assembled by solution mixing,and the BSA/ZnO spherical structures were obtained.Through the single variable method,the effect of BSA on the assembly structure was researched.The size control of BSA/ZnO was realized by changing the concentration of precursor.Based on the first principle and density functional theory(DFT),the adsorption energy of amino acids(aspartic acid and glutamic acid)with more carboxyl groups in BSA and different crystal faces of hexagonal ZnO was calculated.According to the combination of theoretical and experimental research,the formation of BSA/ZnO assembly structures was mainly attributed to the synergistic effect of electrostatic attraction and chemical adsorption.The results of drug release test showed the sustained-release effect of BSA/ZnO was about 2 times higher than that of BSA.