Porphyrin-based nanomaterials and their applications for photocatalysis

La, D 2017, Porphyrin-based nanomaterials and their applications for photocatalysis, Doctor of Philosophy (PhD), Science, RMIT University.

Document type: Thesis
Collection: Theses

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Title Porphyrin-based nanomaterials and their applications for photocatalysis
Author(s) La, D
Year 2017
Abstract The design and fabrication of organic-based supramolecular nanoassemblies is a powerful method for the fabrication of nanostructured materials with tunable morphologies. The resulting materials often have unique optical and electronic properties, which can be used for potential applications including but not limited to, optoelectronic nanodevices, energy storage, catalysis, sensors, and photonics. Among the numerous organic-based supramolecular nanoassemblies described in the literature, -conjugated porphyrins have attracted great attention as organic building blocks for the construction of soft materials. Porphyrin-based nanomaterials in particular have been extensively studied for visible-light photocatalysis due to their intrinsic optical properties. This thesis describes the synthesis of Porphyrin derived nanostructures, and reports on their properties, using a variety of methods. A particular focus is the design and fabrication of composite materials, which combine the properties of self assembled porphyrins with other materials.

Firstly, a facile synthetic protocol to grow thin films of Cu(II) tetrakis(4-carboxyphenyl)porphyrin (CuTCPP) metal-organic frameworks (MOF) from a tetrakis(4-carboxyphenyl)porphyrin (H2TCPP) solution and a Cu(OH)2 nanoneedle array formed on a Cu substrate at room temperature is described. The formation of Cu-centered TCPP ligands and crystalline platelet-like Cu MOFs were characterised by SEM, XRD, FTIR, UV-vis, and XPS. The formation process from Cu(OH)2 was monitored by using SEM images obtained at different reaction times during the first 24 h, allowing the proposal of a possible reaction pathway involving Cu(OH)2 dissolution followed by the reprecipitation of CuTCPP MOFs at the near surface. By using self-assembly with the assistance of Arginine porphyrin, (TCPP)-based supramolecular nanobelts are produced that show enhanced photocatalytic activity for the photodegradation of pollutant Rhodamine B under simulated visible-light.

Graphene has received considerable attention as a platform for studies concerning photocatalytic activity due to favorable properties imparted by its 2D geometry and large surface area. Graphene-based materials have shown excellent charge transfer properties, and have also been used as a scaffold for enhancement the photocatalytic activity of semiconductors. Hence, in this thesis, graphene is used as a substrate for porphyrin nanomaterials for enhanced photocatalytic performance. An industrial-scale method of mass production of graphene nanoplatelets is developed by chemical exfoliation of natural graphite flakes in a single step using sodium persulfate and sulphuric acid at room temperature followed by washing with dry acetone. The produced GNPs (~100%) are tens of microns in diameter with a thickness of around 10-20 nm. The structure of the so-formed GNPs was confirmed by SEM, TEM, and AFM microscopy. Using these good quality graphene nanoplates, well-dispersed porphyrin nanorods were assembled of the GNPs by surfactant-assisted self-assembly of tetrakis (4-carboxyphenyl) porphyrin (TCPP). The assembled TCPP nanorods, with a 50 nm diameter and 200 nm in length were well-distributed on the GNPs and thoroughly characterised by SEM and TEM. The resulting hybrid material showed enhanced visible-light photocatalytic activity compared to free standing TCPP nanorods for the degradation of Rhodamine B (RhB). In addition, the photodegradation mechanism of RhB when using GNPs-supported TCPP nanorods catalyst was proposed. A GNPs@porphyrin nanofibre composite was also fabricated via arginine-mediated self-assembly of tetrakis(4-carboxyphenyl) porphyrin (TCPP) on graphene nanoplates (GNPs). The visible-light photocatalytic activity for the degradation of Rhodamine B (RhB) and methyl orange (MO) was studied, which indicated that GNPs@porphyrin nanofibre composite can be used as a photocatalyst for highly efficient degradation of dyes

Anatase (TiO2) has emerged as a promising material for applications in environmental pollutant degradation via oxidative or reductive methods in the presence of UV light, due to its photoactivity, non-toxicity, high stability and low cost. The mechanistic pathways for pollutant degradation have been discussed in the literature. In this thesis, the synergistic photocatalytic activities of porphyrin aggregates in visible light and TiO2 particles in the UV region was investigated. A TiO2@porphyrin hybrid material was synthesized by surfactant-assisted co-assembly of monomeric porphyrin molecules with TiO2 nanoparticles. The obtained TiO2@porphyrin composite showed the excellent integration of TiO2 particles with diameters of 15-30 nm into aggregated porphyrin nanofibers, which have a width of 70-90 nm and are several µm long. This material exhibited efficient photocatalytic performance under simulated sunlight. A plausible mechanism for photocatalytic degradation was also proposed and discussed.

Finally, the combination of graphene, porphyrin, and TiO2 as one composite for enhanced photocatalytic efficiency was studied. The composite was fabricated via self-assembly of TCPP porphyrin on the graphene surface in the presence of TiO2 with the assistance of a CTAB surfactant. The photocatalytic performance of the graphene@TiO2@porphyrin composite under sunlight conditions was investigated. TiO2 and porphyrin aggregates are shown to be active for UV and visible light, respectively, resulting in a high performing composite. The possible photocatalytic mechanism of RhB degradation by graphene@TiO2@porphyrins composite was discussed.

This thesis has thus provided a comprehensive understanding of the fabrication of porphyrin-based nanomaterials and composites via self-assembly, as well as the mechanism for photocatalysis of selected new materials. The composites of porphyrin with graphene and/or TiO2 have been studied in some detail to increase our knowledge in this area and opened up new strategies for using the unique properties of porphyrins in materials science.
Degree Doctor of Philosophy (PhD)
Institution RMIT University
School, Department or Centre Science
Subjects Synthesis of Materials
Catalysis and Mechanisms of Reactions
Inorganic Green Chemistry
Keyword(s) porphyrin-based nanomaterials
hybrid nanomaterials
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Created: Wed, 03 Jan 2018, 10:37:15 EST by Keely Chapman
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