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.

Challenges and breakthroughs in recent research on self-assembly

“…Other examples not mentioned above include monolayers and LB films of unusual amphiphiles [735][736][737][738][739][740][741], quantum dots [742], clay plates [743], and carbon nanotubes [744] and will be described in later sections of this review. Advanced functions such as electroactive properties [745,746], photo-induced electron transfer [747], logic gate [748], photo-switched wettability control [749], protonation-induced rearrangement [750], and vectorial electron transfer [751] were reported as well as more fundamental science related to phase boundary [752], domain formation [753], acid-base dissociation [754,755], elasticity [756], basic characterization [757][758][759].…”

Soft Langmuir–Blodgett Technique for Hard Nanomaterials

“…Carbon nanotubes have also been used as components of Langmuir monolayers. [114] Qian and coworkers prepared composite monolayers of carbon nanotubes and hydrogenase [115] and carbon nanotubes and cytochrome c. [116] Electrochemical properties of their LB films were analyzed. Doyle and coworkers reported the preparation of Langmuir monolayers of zeolite Beta.…”

Photoelectrocatalytic oxidation of GMP on an ITO electrode modified with clay/[Ru(phen)2(dC18bpy)]2+ hybrid film

“…The other was an LB film containing pure [Ru(dC18bpy)(phen) 2 ] (ClO 4 ) 2 , which was used as a reference for the electrochemical oxidation of GMP. The π-A isotherms were obtained as reported previously [28] . The lift-off areas for the floating films on the clay suspension at 0, 5, 10 and 20 ppm were ca.…”