Electron transfer through clay monolayer films fabricated by the Langmuir- Blodgett technique
ABSTRACT Hybrid films composed of amphiphilic molecules and clay particles were constructed by the modified Langmuir-Blodgett (LB) method. Clays used were sodium montmorillonite (denoted as mont) and synthetic smectite containing Co(II) ions in the octahedral sites (denoted as Co). Two kinds of amphiphilic molecules were used-[Ru(dC(18)bpy)(phen)2](ClO4)2 (dC(18)bpy = 4,4'-dioctadecyl-2,2'-bipyridyl and phen = 1,10-phenanthroline) (denoted as Ru) and octadecylammonium choloride (ODAH+Cl- or denoted as ODAH). Three kinds of hybrid films (denoted as Ru-mont, Ru-Co, and ODAH-Co films) were prepared by spreading an amphiphilic molecule onto an aqueous suspension of a clay. Atomic force microscopy (AFM) analyses of the films deposited on silicon wafers indicated that closely packed films were obtained at 20 ppm for all the above three cases. Cyclic voltammetry (CV) was measured on an ITO electrode modified with a hybrid film or a monolayer film of pure Ru(II) complex salt (denoted as Ru film). The Ru(II) complexes incorporated in the Ru-mont film lost their redox activity, indicating that montmorillonite layers acted as a barrier against electron transfer. In contrast, the same complexes in the Ru-Co film were electrochemically active with the simultaneous appearance of the redox peaks due to the Co(II)/Co(III) (or Co(II)/Co(IV)) couple. The results implied that electron transfer through cobalt clay layers was possible via mediation by Co(II) ions in a clay sheet. For an aqueous solution containing nitrite ions (NO2-) at pH 3.0, a large catalytic oxidation current was observed for both the electrodes modified with the Ru-mont and Ru-Co films. The results were interpreted in terms of the mechanisms that the charge separation of an incorporated Ru(II) complex took place to produce a pair of a Ru(III) complex and an electron and that the generated Ru(III) complex was reduced by a nitrite ion before it recombined with the electron.
SourceAvailable from: Muhammad Kamran[Show abstract] [Hide abstract]
ABSTRACT: Photosynthetic compounds have been paradigm for biosolarcells and biosensors and for application in photovoltaic and photocatalytic devices. However, the interconnection of proteins and protein complexes with electrodes, in terms of electronic contact, structure, alignment and orientation, remains a challenge. Here we report on a deposition method that relies on the self organizing properties of these biological protein complexes to produce a densely packed and uniformly oriented monolayer by using Langmuir-Blodgett technology. The monolayer is deposited onto a gold electrode with defined orientation and produces the highest light induced photocurrents per protein complex to date, 45 µA/cm2 (with illumination power of 23 mW/cm2 at 880 nm) under ambient conditions. Our work shows for the first time that a significant portion of the intrinsic quantum efficiency of primary photosynthesis can be retained outside the biological cell, leading to an internal quantum efficiency (absorbed photon to electron injected into the electrode) of the metal electrode-protein complex system of 32%.Biomacromolecules 06/2014; 15(8). DOI:10.1021/bm500585s · 5.79 Impact Factor
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ABSTRACT: Three derivatives of tris(bipyridyl)–ruthenium(II) complexes with different alkyl-chain lengths (nC18H37 (1), nC14H29 (2) and nC10H21 (3)) were synthesised. All these complexes behaved as an amphiphile and their surface properties were studied at the air–water interface by measuring surface pressure–area (P–A) isotherms. The surface morphology of the resulting films at the air–water interface was also studied by using Brewster angle microscopy. Mean molecular areas of these complexes were measured from the P–A isotherms, which were approximately 200 �2, thereby indicating a parallel arrangement of the Ru–bipyridyl moiety of the complexes. Mono- and multilayer Langmuir– Blodgett (LB) films were formed on different solid surfaces with transfer ratios close to one. Similarities in the absorption and fluorescence spectra of these amphiphiles in solution as well as in LB films deposited on a quartz surface confirmed the successful transfer of these films onto the substrates. The latter provided information about the arrangements of metallosurfactant molecules within the LB films. The two-dimensional concentrations of these films were calculated from the Lambert– Beer law as well as from the P–A isotherm, which confirmed regular and reproducible transfer of the complex monolayers from the air–water interface onto the quartz surface. The surface morphology of these films on various substrates was characterised by atomic force microscopy. Furthermore, by oxidising the monolayer of complex 3, a one-input sequential logic gate was constructed.
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ABSTRACT: Attempts at optical resolution and asymmetric syntheses using smectite clay minerals are described. Use of the method was prompted by the discovery that the saturated adsorption of a tris(chelated) metal complex, [Ru(1,10-phenanthroline)3 ]2+, by Na-montmorillonite depended heavily on the stereochemical properties. The pure enantiomer was adsorbed by cation exchange at negative surface sites of the clay mineral, while the racemic mixture was adsorbed to two times excess of the cation exchange capacity. The chelate takes a uniform orientation on a clay mineral surface due to the matching between the molecular symmetry and the two-dimensional network of a phyllosilicate layer. On a clay mineral surface covered with the enantiomeric chelates, a vacant space capable of chiral discrimination was generated. Based on this, an ion-exchange adduct of smectite and the chiral chelate was used as an adsorbent for separating racemic mixtures or selectively producing either one of the optical isomers.Clays and Clay Minerals 08/2012; 60(4). DOI:10.1346/CCMN.2012.0600407 · 1.40 Impact Factor