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Porphyrin Nanocrystals With Photocatalytic Activity Through Microemulsion-Mediated Mesoscale Transformation Self-assembly

Posted on:2014-11-11Degree:MasterType:Thesis
Country:ChinaCandidate:Z X WangFull Text:PDF
GTID:2251330401475418Subject:Materials science
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Molecular self-assembly is a powerful method to the synthesis of nanostructured materials. Throughdesigning molecules and supramolecular entities, desired structure and function can be achieved. Theunique property of molecular assemblies has been demonstrated to depend not only on the size, shape, andcomposition of the molecule building blocks but also to a large extent on the precise control of moleculespatial arrangement within an assembly. Despite recent advances in synthesis and assembling moleculebuilding blocks into well-defined superstructures, technologies that leverage the structural advantages ofindividual molecules amenable to practical use still remain a significant challenge. The development ofmore facile and efficient methods for rationally designing and fabricating molecule assembly is criticallyimportant for the continued advancement of this area. While previous efforts have focused on controlled2Dand3D fabrication over a limited range of scales, developments of new molecular and building blockdesigns and strategies of functionalization are essential for directing structure and property control overmultiple scales. Here we extended the interfacially driven micro-emulsion (μ-emulsion) method that wedeveloped previously to initiate self-assembly and formation of hierarchical structured nanocrystals. Usingthis method, μ-emulsions were developed through dispersion of an organic solution containingnanoparticles as the building block to another immiscible aqueous solution. Subsequent removal of organicsolvent led to self-assembly nanostructured particles arrays. In-situ studies of dynamic light scattering,UV-vis spectroscopy, and TEM, as well as optical imaging suggest an evaporation-induced nucleation andgrowth self-assembly mechanism.This thesis includes the following main aspects:1,Herein, we extended this method to synthesize hierarchically structured active nanostructures byusing an optically active macrocyclic molecule, tin (IV) meso-tetraphenylporphyrin dichloride (SnTPP) asa building block. The emulsion was formed through mixing SnTPP chloroform solution with an aqueoussolution containing surfactants. By means of vigorous stirring (greater than1500rpm) or sonication, weobtained a surfactant-stabilized oil-in-water μ-emulsion in which SnTPP molecules were well-dispersedinside the μ-emulsion droplets. The low-boiling solvent (e.g. CHCl3) was subsequently evaporated from the μ-emulsion system by heating to a given temperature. As solvent evaporates from the μ-emulsion droplets,the droplets shrink and the porphyrin concentration therein rises, inducing self-assembly of porphyrinmolecules through non-covalent interactions inside the confined3D oil-emulsion droplet spaces. Throughnon-covalent interactions such as π–π stacking, hydrophobic interaction, etc. porphyrins self-assemble intoordered nanostructures. Depending on the reaction conditions, various hierarchical nanostructures such asnanosheets, octahedra, and microspheres were obtained.The size of the assembly is tuned by the changes of the concentration of surfactant. The size of theoctahedron increases with increasing concentration with the increase of the concentration of CTAB. Incontrary, when we use the anionic surfactant(SDS) as the emulsifier, the size of the nanospheres becomesmaller with the increase of surfactant concentration. In the case of SDS, The anionic headgroups SO-4ofSDS might bind with Sn in the porphyrin molecule, which prohibits the nuclei and mesoscale re-orientationof SnTPP. But, CTAB played the sole role of a surfactant to form emulsion and confined non-covalentself-assembly of SnTPP into crystalline octahedra. We control the molecular packing and morphology ofthe self-assembly by controlling the evaporation rate of the solvent and which affects the crystalline state ofthe porphyrin molecules. The reaction emulsion was poured into the hot water of different temperatures in awater bath, with the rise of the temperature of the hot water, chloroform evaporation rate acceleratedassembly morphology by octahedron transition to the nanosheet, and the chloroform evaporation faster,more easily formed nanosheet with regular morphology.2. We synthesized hierarchically structured porphyrin nanostructures and use them as both physicaland chemical templates. At the molecular level, porphyrins possess unique photo-catalytic properties,serving as a chemical template. On the nanoscale, controlled non-covalent assembly of porphyrins enablesformation of ordered nanostructures with well-defined size and shape, providing as a continuous, physicaltemplate. The photocatalytic reduction of platinum salts by the ZnTPyPs was conducted under visible lightin the presence of an electron donor (ED), ascorbic acid (AA). The ZnTPyPs photoreaction is a reductivephotocatalytic cycle. Through the photocatalytic reaction, K2PtCl4, is reduced to form Pt nanoparticles,further grew into Pt network forming the shell top of porphyrin nanostructures. The resultant Pt hollowmaterials have well-defined nanostructures that derive from the porphyrin templates and an increaseaccessible surface area, which leads to enhanced active surface area for hydrogen adsorption and improved eletrocatalytic activity for methanol oxidation. Explore the photocatalytic degradation process of differenttin-porphyrin assembly such as nano-octahedral, nanosheet and microspheres to methyl orange. The resultsshowed that: The decolorization ratio of vis/SnTPP nanospheres/MO system has almost reached100%at4h. Photocatalytic applications, tin-porphyrin has a lot of advangtage such as less the amount, gooddispersion, high activity, stability of the catalytic performance and easy recovery.3. Extended microemulsion-assisted self-assembly method by using different porphyrin and assemblyprocess. Using tetraphenyl porphyrin (NT614) as an assembled unit and adding n-hexane to the solution toform hollow structure nanospheres. Meanwhile, we discussed the formation mechanism of hollownanospheres. Hollow porphyrin microspheres have a wide range of applications in drug release andbiological imaging.Through this approach we get the hybrid materials of NT614@Au nanocrystals, NT614@Fe3O4,SnTPP@TiO2@CdSe. The "building block" strategy lays a solid foundationcan for construction andapplication of composite multi-functional nano (super) structure of the new material system and makesinorganic nanocrystals@porphyrin supramolecular assembly easy to develop. The hybrid materials getconsolidation function of multifunctional nano (ultra) structure, porphyrin nanocrystals and assembling thecollection, which have a variety of functions such as fluorescence, magnetic and photoelectric conversion,and will have an irreplaceable position in many fields such as energy conversion, catalysis, sensing and thefield of nano-devices.
Keywords/Search Tags:Controllable Porphyrin Self-Assembly, Microemulsion-Mediated, MesoscaleTransformation, Photocatalytic Activity
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