Stepwise Formation of Multilayered Nanostructural Films from Macromolecular Precursors

Kleinfeld, Elaine R.; Ferguson, Gregory S.

doi:10.1126/science.265.5170.370

Cited by 565 publications

(391 citation statements)

References 28 publications

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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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“…Although clustering prevented us from identifying single sheets, even at very high magnification (Fig. 3b), the average feature size did correspond to the ~30 nm 2 reported for Laponite RD (Alcover et al 2000, Kleinfeld and Ferguson 1994, Nicolai and Cocard 2000, Rosta and von Gunten 1990, Thompson and Butterworth 1992.…”

Section: Microscopy Of Laponite Rdmentioning

confidence: 99%

“…The ability to determine the size and shape of clay platelets accurately is of fundamental importance in understanding the structure of polyelectrolyte/clay multilayer films (Kleinfeld andFerguson 1994, Rouse et al 2000), the behavior of clay suspensions (Avery and Ramsay 1986, Bonn et al 1999, Kroon et al 1998, Mourchid et al 1998, Nicolai and Cocard 2000, Rosta and von Gunten 1990 and clay/polymer composites (Balazs et al 1999, Gilman 1999, Kawasumi et al 1997, Kornmann et al 2001, Sonobe et al 1999, Tyan et al 1999, Vaia et al 19961999). Although scattering techniques (e.g., visible light, x-ray, neutron) have proven useful for characterizing clay suspensions, the ability to differentiate between scattering from single particles and aggregates has proven difficult (Nicolai andCocard 2000, Rosta andvon Guten 1990).…”

Section: Introductionmentioning

confidence: 99%

“…Use of graphite, a substrate with a low atomic number, is advantageous for SEM imaging because of the small number of secondary electrons produced upon electron beam exposure -low background noise (Goldstein et al 1992). Instead of Cytochrome C, we first adsorbed a layer of the simpler commercially available polyelectrolyte, poly(diallyldimethylammonium chloride) (PDDA), from an aqueous solution to provide a positively charged substrate appropriate for adsorption of anionic clay platelets (Kleinfeld and Ferguson 1994). It was thus possible to adsorb predominately single clay sheets, with adsorption of additional platelets inhibited by Coulombic repulsion.…”

Section: Introductionmentioning

confidence: 99%

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A method for imaging single clay platelets by scanning electron microscopy

2004

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Summary:A method for preparing and observing clay platelets for size and shape analysis using scanning electron microscopy (SEM) was developed. Samples of the clay platelets were prepared by polyelectrolyte-assisted adsorption onto a pyrolytic graphite surface. The use of graphite as a substrate was advantageous because of the low number of secondary electrons emitted from it during imaging by SEM. The resulting low background noise allowed the emission from the ~1 nm thick clay sheets to be clearly visualized. Images of centrifuged montmorillonite showed large exfoliated platelets with lateral dimensions between 200 and 600 nm. In contrast, uncentrifuged montmorillonite appeared to contain a large amount of unexfoliated clusters. Although it was not possible to obtain high-quality images of the smaller sheets of Laponite RD, the images of this material did contain size features comparable to the ~30 nm 2 size reported previously using light scattering, as well as transmission electron and atomic force microscopies.

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“…The flexibility of the LbL assembly process enables the incorporation of clay platelets into LbL-assembled films [51][52][53] , but there is a gap in the scientific literature concerning the use of LbL to generate nanostructured clay composite selective layers for RO membranes.…”

Section: Introductionmentioning

confidence: 99%

Spray Layer-by-Layer Assembled Clay Composite Thin Films as Selective Layers in Reverse Osmosis Membranes

Kovacs

Liu

Hammond

2015

ACS Appl. Mater. Interfaces

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Spray layer-by-layer assembled thin films containing laponite (LAP) clay exhibit effective salt barrier and water permeability properties when applied as selective layers in reverse osmosis (RO) membranes. Negatively-charged LAP platelets were layered with poly(diallyldimethylammonium) (PDAC), poly(allylamine) (PAH), and poly(acrylic acid) (PAA) in bilayer and tetralayer film architectures to generate uniform films on the order of 100 nm thick that bridge a porous polyethersulfone support to form novel RO membranes. Nanostructures were formed of clay layers intercalated in a polymeric matrix that introduced size-exclusion transport mechanisms into the selective layer. Thermal cross-linking of the polymeric matrix can 2 be used to increase the mechanical stability of the films and improve salt rejection by constraining swelling during operation. Maximum salt rejection of 89% was observed for the tetralayer film architecture, with an order of magnitude increase in water permeability compared to commercially available TFC-HR membranes. These clay composite thin films could serve as a high-flux alternative to current polymeric RO membranes for wastewater and brackish water treatment as well as potentially for forward osmosis applications. In general, we illustrate that by investigating the composite systems accessed using alternating layer-by-layer assembly in conjunction with complementary covalent crosslinking, it is possible to design thin film membranes with tunable transport properties for water purification applications.

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Stepwise Formation of Multilayered Nanostructural Films from Macromolecular Precursors

Cited by 565 publications

References 28 publications

Visible Light Water Splitting Using Dye-Sensitized Oxide Semiconductors

Visible Light Water Splitting Using Dye-Sensitized Oxide Semiconductors

A method for imaging single clay platelets by scanning electron microscopy

Spray Layer-by-Layer Assembled Clay Composite Thin Films as Selective Layers in Reverse Osmosis Membranes

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