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Particle Networks from Powder Mixtures: Generation of TiO(2)-SnO(2) Heterojunctions via Surface Charge-Induced Heteroaggregation.

ABSTRACT: We explored the impact of interfacial property changes on aggregation behavior and photoinduced charge separation in mixed metal oxide nanoparticle ensembles. TiO(2) and SnO(2) nanoparticles were synthesized by metal organic chemical vapor synthesis and subsequently transformed into aqueous colloidal dispersions using formic acid for adjustment of the particles' surface charge. Surface charge-induced heteroaggregation was found to yield blended nanoparticle systems of exceptionally high mixing quality and, after vacuum annealing, to extremely high concentrations of heterojunctions between TiO(2) and SnO(2) nanoparticles with dehydroxylated surfaces. For tracking charge transfer processes across heterojunctions, the photogeneration of trapped charge carriers was measured with electron paramagnetic resonance (EPR) spectroscopy. On blended nanoparticles systems with high concentrations of SnO(2)-TiO(2) heterojunctions, we observed an enhanced cross section for interparticular charge separation. This results from an effective interfacial charge transfer across the interfaces and gives rise to substantially increased concentrations of electrons and hole centers. The here presented insights are key to the rational design of particle-based heterojunctions and mesoporous nanoparticle networks and help to engineer composite nanomaterials for photocatalysis and solar energy conversion.

SUBMITTER: Siedl N

PROVIDER: S-EPMC3558020 | biostudies-literature | 2012 Nov

REPOSITORIES: biostudies-literature

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Particle Networks from Powder Mixtures: Generation of TiO(2)-SnO(2) Heterojunctions via Surface Charge-Induced Heteroaggregation.

Siedl Nicolas N Baumann Stefan O SO Elser Michael J MJ Diwald Oliver O

The journal of physical chemistry. C, Nanomaterials and interfaces 20121004 43

We explored the impact of interfacial property changes on aggregation behavior and photoinduced charge separation in mixed metal oxide nanoparticle ensembles. TiO(2) and SnO(2) nanoparticles were synthesized by metal organic chemical vapor synthesis and subsequently transformed into aqueous colloidal dispersions using formic acid for adjustment of the particles' surface charge. Surface charge-induced heteroaggregation was found to yield blended nanoparticle systems of exceptionally high mixing q ...[more]

PMID: 23378867

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Project description:Graphitic carbon nitride (g-C₃N₄) and titanium dioxide (TiO₂) were chosen as a model system to investigate photocatalytic abilities of heterojunction system under UV and visible light conditions. The use of g-C₃N₄ has been shown to be effective in the reduction in recombination through the interaction between the two interfaces of TiO₂ and g-C₃N₄. A simple method of preparing g-C₃N₄ through the pyrolysis of melamine was employed, which was then added to undoped TiO₂ material to form the g-C₃N₄-TiO₂ system. These materials were then fully characterized by X-ray diffraction (XRD), Brunauer Emmett Teller (BET), and various spectroscopic techniques including Raman, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), diffuse absorbance, and photoluminescence analysis. Photocatalysis studies were conducted using the model dye, rhodamine 6G utilizing visible and UV light irradiation. Raman spectroscopy confirmed that a composite of the materials was formed as opposed to a mixture of the two. Using XPS analysis, a shift in the nitrogen peak to that indicative of substitutional nitrogen was detected for all doped samples. This is then mirrored in the diffuse absorbance results, which show a clear decrease in band gap values for these samples, showing the effective band gap alteration achieved through this preparation process. When g-C₃N₄-TiO₂ samples were analyzed under visible light irradiation, no significant improvement was observed compared that of pure TiO₂. However, under UV light irradiation conditions, the photocatalytic ability of the doped samples exhibited an increased reactivity when compared to the undoped TiO₂ (0.130 min-1), with 4% g-C₃N₄-TiO₂ (0.187 min-1), showing a 43.9% increase in reactivity. Further doping to 8% g-C₃N₄-TiO₂ lead to a decrease in reactivity against rhodamine 6G. BET analysis determined that the surface area of the 4% and 8% g-C₃N₄-TiO₂ samples were very similar, with values of 29.4 and 28.5 m²/g, respectively, suggesting that the actual surface area is not a contributing factor. This could be due to an overloading of the system with covering of the active sites resulting in a lower reaction rate. XPS analysis showed that surface hydroxyl radicals and oxygen vacancies are not being formed throughout this preparation. Therefore, it can be suggested that the increased photocatalytic reaction rates are due to successful interfacial interactions with the g-C₃N₄-doped TiO₂ systems.

Dataset Information

Particle Networks from Powder Mixtures: Generation of TiO(2)-SnO(2) Heterojunctions via Surface Charge-Induced Heteroaggregation.

Publications

Particle Networks from Powder Mixtures: Generation of TiO(2)-SnO(2) Heterojunctions via Surface Charge-Induced Heteroaggregation.

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