Biomimetic Preparation And Morphological Control Of Zinc And Copper Oxides

Micro/nano-inorganic materials with particular morphologies and sizes have extensivelypromising applications in many fields, such as chemistry, electron, and biology. Conventionalphysical and chemical synthetic methods for these materials need harsh reaction conditions,including high temperature and pressure, and strongly acid and basic solution. However, livingorganisms generate various biomaterials in biomineralization, which are synthesized throughmildly reaction utilizing many biomolecules as templates or agents during inorganic crystalgrowth. This phenomenon provides an important route for the inorganic materials. Therefore，biomimetic synthesis or biologically-inspired synthesis of inorganic materials have beengenerated. This novel method generally process under gentle conditions （ambient temperature andpressure） and often in aqueous environments, so it has been a quickly expanding area of researchdue to it offers a lower cost, more efficient, and “green” approach. In this article, we use manybiomolecules as crystal modifier to control the morphologies of ZnO and Cu₂O. The contents arelined as follows:（1） β-cyclodextrin （β-CD） has been chosen as a crystal modifier for the synthesis ofhierarchical ZnO with unusual surface morphology and textures at a relatively mild reactioncondition. The crystalline of the products were characterized by X-ray diffraction （XRD）. Theresults showed that the diffraction peaks were well assigned to hexagonal wurtzite phase ZnOwith the high purity and good crystalline. The morphologies of ZnO were seriously affected bymany reaction parameters including β-CD concentration and reaction time. When the β-CDconcentration was increased, the shape of flower-like ZnO changed to be sphere-like; At70°C,within the initial time for10min, no visible precipitates were observed. From time of10min to10h, the products evolved from irregularly shaped polycrystalline aggregates toward flower-likestructures; the temperature had not affected the shapes of the products evidently. Finally, we haveproposed a growth mechanism for the morphological evolution of the as-synthesized ZnO crystals,in which the adsorption and coating effect of β-CD were underlined.（2） Novel flower-like ZnO mesocrystals have been synthesized in water/glycerol system,using a biomimetic method in the presence of DNA. The morphologies and strutcures, constitute elements, and surface properties of the as-prepared products were characterized by manytechniques, such as field-emission scanning electron microscope （FESEM）, transmission electronmicroscopy （TEM）, XRD. The as-prepared ZnO morphologies were affected by a number ofreaction parameters such as DNA concentration, reaction time and constitutes of solvent. DNAserved as a crystal modifier and influenced the formation and growth of ZnO crystal nuclei. Thetiny ZnO building units crystallographically aligned along a mutual order and finally formed theflower-like mesocrystal structures. This result was explained by oriented attachment （OA）.Theconstitutes of the solvent severely impacted the morphologies of ZnO mesocrystals. When thepure water or alcohol/water mixed solvent was used, the as-synthesized products did not appearthe flower-like mesocrystal. XRD analysis showed that the as-prepared ZnO mesocrytsals hadhigh crystallization. The FESEM overviews revealed that the as-produced mesocrystals had roughsurfaces and consisted of a large number of nanoparticles, which were further identified by TEMimages. The selected electron diffraction （SAED） pattern disclosed that the as-synthesized ZnOmesocrystals diffracted like a single crystal, indicating that DNA led the whole assembly of thebuilding units to highly orient and align along with the mutual order. Moreover, the Oswaldripening （OR） could also play an important role, which resulted in the generation of the productswith larger diameters. The antibacterial experiments show that ZnO mesocrystals had evidentantibacterial effect on E.coli and S.aureus; its antibacterial activity was obviously higher thancommercial ZnO nanoparticles.（3） DNA was used as a crystal growth modifier to prepare hierarchical flower-like ZnOsuperstructures. In this paper, we studied the effects of many reaction paremeters, including DNAconcentration, reaction time, reaction temperature, NaOH concentration, and kind of zinc salts, onthe morphologies of the final products. The results shows that the addition of DNA was necessaryin fabrication of the as-synthesized products; the temperature did not have the evident impact onthe ZnO morphologies, while NaOH concentration and the select of zinc salts played animportant role in the synthetic system. Studying on the change of the morphology of the productswith reaction time, we proposed a growth model of the as-produced ZnO crystals. Thephotocatalytic performance of the three as-synthesized products was evaluated by using NBB as arepresentative dye pollutant. The result demonstrates that as-prepared products had high photocatalystic activities. The antibaterial experiments are also carried out. The results show thatthe products exhibit high antibacterial ability against E. coli and S. aureus, with more effectiveactivity against the former one. Importantly, the products had higher photocatalytic andantibacterial activities than commercial ZnO NPs.（4） Cu-Cu₂O composite materials with various morphologies were synthesized by usinggelatin as a crystal modifier. With Adjustment of the reaction parameters, the as-preparedproducts appeared various shapes such as solid sphere-like, hollow sphere-like, andcore-shell-like. The results showed that gelatin concentration and temperature had importanteffect on the morphologies of the products. In addition, the growth of the as-synthesized materialswas affected by the Oswald ripening process. With increasing reaction time, the size of theproducts became larger, and a dissolution-recrystallization process occurred in interior of thecrystals and formed a shell structure. The obtained Cu-Cu₂O crystals all show higher antibacterialeffect on the gram-negative bacteria E.coli than the gram-positive S.aureus. In addition, increaseof the content of Cu improved the antibacterial activity of the products.（5） Ag-Cu₂O and TiO₂-Cu₂O composite materials were prepared in the presence of thedopamine and lysozyme （Lys）. The structures and morphologies of the as-synthesized productswere determined by XRD and XPS, and FESEM and TEM, respectively. In this paper, Cu₂Ocrystals were firstly prepared serving as the core in the composites. The surfaces of Cu₂O werethen decorated with dompamine. The following contents of research were divided into two parts:（a） by using the adhesion and redox characteristic of dopamine, Ag nanoparticles （Ag NPs） wereformed in the surfaces of the Cu₂O core. XRD patterns showed that the dopamine did not reactwith Cu₂O, and only coated on the surfaces of the core material. Moreover, effect of the AgNO₃concentration on the shape of the products was also studied. The results displayed that yield of AgNPs were reduced with the AgNO₃concentration. EDS energy spectrum also testified that AgNPs indeed existed in the surfaces of the composites, whith was in accordance with the results ofXRD. Finally, the Fourier transform infrared （FTIR） spectroscopy was employed. The resultsconfirmed that the dopamine adsorbed on the surfaces of the products and the adsorption peaks ofthe dopamine shifted after the synthesis of Ag NPs.（b） Lys was adsorbed beforehand on thesurfaces of the Cu₂O core, duo to the adhesion of dopamine. Then, Lys was used to condense the TiO₂precursor to synthesize nanocrystalline titanium dioxide under the room temperature. XPSresults confirmed the presence of the TiO₂.The as-prepared Ag-Cu₂O have higher antibaterialeffects on the bacteria E.coli than the S.aureus. In addition, increase of the content of Agnanoparticles enhanced the antibacterial activity of the products.（6） Apple-like Cu₂O was synthesized in the presence of DNA. DNA originated from herringsperm was selected as a crystal modifier to control the morphologies of Cu₂O, in the roomtemperature. This method presented an easy, facile and environment-friendly approach togenerate Cu₂O. The results showed that the condensation of DNA using CTAB was necessary forpreparing the as-synthesized products with the peculiar shape. This paper indirectly demonstratedthat the genetic materials might act in biomineralization.