Diffusivities of Tris(2,2′-bipyridyl)ruthenium inside Silica- Nanochannels Modified with Alkylsilanes

Abstract

The apparent diffusion coefficients of tris(2,2′-bipyridyl)ruthenium ([Ru(bpy3)] 2+ ) are estimated in silica-nanochannels which are assembled inside columnar alumina pores in an anodic alumina membrane, and are modified with alkylsilanes such as trimethylchlorosilane (C1), butyldimethylchlorosilane (C4), and dodecyldimethylchlorosilane (C12). The estimation is performed by observing the lag-time, which is defined as the time required for [Ru(bpy)3] 2+ to diffuse through alkylsilane-modified silica-nanochannels in the alumina membrane. When ethanol is used as a solvent, the apparent diffusion coefficients of [Ru(bpy)3] 2+ are estimated as 2.1 × 10 -10 and 3.2 × 10 -10 cm 2 s -1 in the C1-and C4-modified silica-nanochannels, respectively. These values are about 10 4 times smaller than that obtained in bulk ethanol. Based on the experimental results on the solvent dependency of the lag-time, the hydrogen-bonding interaction between ethanol molecules is considered to be stronger in the C1-and C4-modified silica-nanochannels than in bulk ethanol, and the hydrogen-bonding interaction plays a critical role for the slow diffusivity in those nanochannels. In contrast, the apparent diffusion coefficient in the C12-modified silica-nanochannel is at least two orders of magnitude larger than those in the C1-and C4-modified silica-nanochannels. This relatively fast diffusion is most likely explained by the presence of a long alkyl chain of C12, which reduces a hindrance effect that is originates in the hydrogen-bonding interaction.

Mesoporous Structures Confined in Anodic Alumina Membranes

“…They offer a largely independent control of pore size, pore topology, pore orientation, molecular functionalization and pore wall composition. Potential functionality and applications include molecular separators,82, 85, 127, 128, 132, 133 or host materials for the inclusion of conducting or semiconducting nanostructures 78, 81, 94, 122, 124. For example, such composite membranes were found to exhibit superior permselectivity than commercially available membrane systems in gas permeation experiments 85.…”

“…Furthermore, permeation measurements of tris(2,2’‐bipyridyl)ruthenium through a composite membrane after the one‐step extraction of the ionic surfactant and simultaneous modification of the silica with alkylsilanes131 were carried out 132. The transport of the ruthenium complex through the membrane was recorded by time‐dependent absorption spectroscopy of a feed and a permeate solution.…”

Solvation Dynamics of Coumarin 153 in Alcohols Confined in Silica Nanochannels

“…The carbon content derived from the elemental analysis is used for the estimation of the surface density of the TMS group immobilized on the inner surface of the silica nanochannels. The details of the estimation procedure were described in our previous paper, 22 and the estimated value is 2.1 molecules/ nm 2 . The surface density of the TMS group has been studied by many researchers and is reported as 2.1-2.7 molecules/nm 2 at the maximum density.…”

“…For example, in our previous study, the apparent diffusion coefficient of tris(2,2′-bipyridyl)ruthenium(II) in ethanol confined in mesoporous silica whose pore surface had been modified by alkylsilanes ((CH 3 ) 3 -Si and C 4 H 9 (CH 3 ) 2 -Si) was found to be on the order of 10 -10 cm 2 s -1 . 22 Since the diffusion coefficient was smaller for protic solvents (methanol and ethanol) than for aprotic solvents (acetonitrile and dimethyl sulfoxide (DMSO)), it was inferred that the hydrogen bonding interaction between alcohol molecules confined in the pores was responsible for the slow diffusivity of tris(2,2′-bipyridyl)ruthenium(II). Takahashi et al 20 examined the diffusion coefficients of ketones in alkanes with different chain lengths confined in porous sol-gel glasses with different pore sizes and found the diffusivity of ketones in mesopores (4.0 and 10.5 nm) decreased with increasing molecular size of solvents, and the diffusivity in small mesopores (4.0 nm) was larger for solvents with an odd number of carbon atoms than for those with an even number of carbon atoms.…”

Adsorption and Desorption Dynamics of Sodium Dodecyl Sulfate at the Octadecylsilane Layer on the Pore Surface of a Mesoporous Silica Film Observed in-situ by Optical Waveguide Spectroscopy

“…During the above modification and drying procedures, the template surfactants were replaced by ODS and trimethylsilyl (TMS) groups using the reported modification methods. 27,28 For the characterization of the optical properties of the ODS-MS layer, a reference substrate was prepared by forming ODS-MS layers on a glass substrate without the Al layer. Formation of MS layers and modification with ODS and TMS groups were performed by the same manner as described above.…”