Layer-by-Layer Assembly of Intercalation Compounds and Heterostructures on Surfaces: Toward Molecular "Beaker" Epitaxy

Keller, Steven W.; Kim, Hyuk Nyun; Mallouk, Thomas E.

doi:10.1021/ja00098a055

Cited by 577 publications

(374 citation statements)

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“…[18][19][20] This results in a "lasagna" architecture that separates the electroactive components into welldefined layers. We showed by using fluorescent resonant energy transfer (FRET) that there was minimal layer interpenetration in such structures.…”

Section: Visible Light Water Splittingmentioning

confidence: 99%

Visible Light Water Splitting Using Dye-Sensitized Oxide Semiconductors

et al. 2009

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R esearchers are intensively investigating photochemical water splitting as a means of converting solar to chemical energy in the form of fuels. Hydrogen is a key solar fuel because it can be used directly in combustion engines or fuel cells, or combined catalytically with CO 2 to make carbon containing fuels. Different approaches to solar water splitting include semiconductor particles as photocatalysts and photoelectrodes, molecular donor-acceptor systems linked to catalysts for hydrogen and oxygen evolution, and photovoltaic cells coupled directly or indirectly to electrocatalysts.Despite several decades of research, solar hydrogen generation is efficient only in systems that use expensive photovoltaic cells to power water electrolysis. Direct photocatalytic water splitting is a challenging problem because the reaction is thermodynamically uphill. Light absorption results in the formation of energetic charge-separated states in both molecular donor-acceptor systems and semiconductor particles. Unfortunately, energetically favorable charge recombination reactions tend to be much faster than the slow multielectron processes of water oxidation and reduction. Consequently, visible light water splitting has only recently been achieved in semiconductor-based photocatalytic systems and remains an inefficient process.This Account describes our approach to two problems in solar water splitting: the organization of molecules into assemblies that promote long-lived charge separation, and catalysis of the electrolysis reactions, in particular the four-electron oxidation of water. The building blocks of our artificial photosynthetic systems are wide band gap semiconductor particles, photosensitizer and electron relay molecules, and nanoparticle catalysts. We intercalate layered metal oxide semiconductors with metal nanoparticles. These intercalation compounds, when sensitized with [Ru(bpy) 3 ] 2+ derivatives, catalyze the photoproduction of hydrogen from sacrificial electron donors (EDTA 2-) or non-sacrificial donors (I -). Through exfoliation of layered metal oxide semiconductors, we construct multilayer electron donor-acceptor thin films or sensitized colloids in which individual nanosheets mediate light-driven electron transfer reactions. When sensitizer molecules are "wired" to IrO 2 · nH 2 O nanoparticles, a dye-sensitized TiO 2 electrode becomes the photoanode of a water-splitting photoelectrochemical cell.Although this system is an interesting proof-of-concept, the performance of these cells is still poor (∼1% quantum yield) and the dye photodegrades rapidly. We can understand the quantum efficiency and degradation in terms of competing kinetic pathways for water oxidation, back electron transfer, and decomposition of the oxidized dye molecules. Laser flash photolysis experiments allow us to measure these competing rates and, in principle, to improve the performance of the cell by changing the architecture of the electron transfer chain.

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Section: Visible Light Water Splittingmentioning

confidence: 99%

Visible Light Water Splitting Using Dye-Sensitized Oxide Semiconductors

et al. 2009

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“…Such films have been designed, constructed, and in some cases tuned for photonic, electronic, and sensor applications. 5,[9][10][11][12][13][14][15][16] Much of the current understanding of these materials has resulted from bulk analysis techniques (i.e., ellipsometry, X-ray diffraction, optical spectroscopy, X-ray photoelectron spectroscopy, and NMR spectroscopy) which provide information (i.e., film thickness, interlayer spacings, structure, and elemental content, etc.) that is averaged over macroscopic distances.…”

Section: Introductionmentioning

confidence: 99%

“…[15][16][17][18] This paper is focused on the morphological investigation of zirconium phosphate multilayer films prepared by self-assembly involving the sequential layer-by-layer adsorption of oppositely charged polyelectrolyte species. 9 Multilayer films in this process are formed in a simple dipping procedure in which a substrate is exposed sequentially to solutions containing oppositely charged polyelectrolytes. In principle, there are no restrictions to the substrate size and topology that can be modified with this technique, in contrast to the Langmuir-Blodgett technique which requires planar substrates.…”

Section: Introductionmentioning

confidence: 99%

NSOM Investigations of the Spectroscopy and Morphology of Self-Assembled Multilayered Thin Films

et al. 1998

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Near-field scanning optical microscopy (NSOM) and atomic force microscopy (AFM) have been employed to spatially resolve the complex nanoscale morphologies, spectroscopy, and energy-transfer efficiencies of self-assembled multilayered structures composed of alternating layers of R-zirconium phosphate [R-Zr(HPO 4 ) 2 ] (ZrP) and dye-labeled poly(allylamine hydrochloride) (dye-PAH) (where dye ) Fluorescein (FL), Rhodamine B (RhB), or Texas Red (TR)). Two types of multilayer films have been investigated, namely, glass/anchor/ ZrP/dye-PAH and glass/anchor/ZrP/dye-PAH/ZrP/dye-PAH, which were formed by the sequential layer-bylayer adsorption of the charged polyelectrolyte component layers. High-and low-coverage films were investigated. The glass/anchor/ZrP assemblies were shown to consist of a densely packed "tiled" motif of ZrP sheets which lie flat on the surface and cover more than 95% of the area, with average plate sizes of height ) 13 (7) Å, width ≈ 150 nm. The dye-labeled polymer layers in glass/anchor/ZrP/dye-PAH and glass/ anchor/ZrP/dye-PAH/ZrP/dye-PAH were shown to adhere to the surface of the ZrP sheets and fill in the cracks between the sheets to a lesser extent. The measured heights of these polymer-coated multilayer films are 26(9) and 48(15) Å, respectively. These heights are consistent with theoretical estimates of ideally packed ionic films (28 and 48 Å, respectively). Dual-wavelength fluorescence NSOM imaging at 580 nm and >610 nm and near-field photobleach experiments were used to spatially resolve nanoscopic regions that display energy transfer between the layers.

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“…Although a wide range of nano-sized elements in different dimensionalities can be used, the fascinating physical phenomena in materials at atomic layer thicknesses make two-dimensional (2D) materials such as graphene, boron nitride and transition metal dichalcogenides extremely attractive building blocks for macroscopic multilayer assemblies [9][10][11] . 3D frameworks can be built from these 2D materials by template assisted growth or self-assembly in solution by van der Waals forces or chemical cross-linking [12][13][14] .…”

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confidence: 99%

Low-density three-dimensional foam using self-reinforced hybrid two-dimensional atomic layers

et al. 2014

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Low-density nanostructured foams are often limited in applications due to their low mechanical and thermal stabilities. Here we report an approach of building the structural units of three-dimensional (3D) foams using hybrid two-dimensional (2D) atomic layers made of stacked graphene oxide layers reinforced with conformal hexagonal boron nitride (h-BN) platelets. The ultra-low density (1/400 times density of graphite) 3D porous structures are scalably synthesized using solution processing method. A layered 3D foam structure forms due to presence of h-BN and significant improvements in the mechanical properties are observed for the hybrid foam structures, over a range of temperatures, compared with pristine graphene oxide or reduced graphene oxide foams. It is found that domains of h-BN layers on the graphene oxide framework help to reinforce the 2D structural units, providing the observed improvement in mechanical integrity of the 3D foam structure.

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Layer-by-Layer Assembly of Intercalation Compounds and Heterostructures on Surfaces: Toward Molecular "Beaker" Epitaxy

Cited by 577 publications

References 0 publications

Visible Light Water Splitting Using Dye-Sensitized Oxide Semiconductors

Visible Light Water Splitting Using Dye-Sensitized Oxide Semiconductors

NSOM Investigations of the Spectroscopy and Morphology of Self-Assembled Multilayered Thin Films

Low-density three-dimensional foam using self-reinforced hybrid two-dimensional atomic layers

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