Insights into Adsorption of Uncharged Macrocyclic Complexes into a Nafion Film:  Adsorption Characteristics and Analysis of Tetraphenylporphyrine Zinc(II)

Abstract

Tetraphenylporphine zinc(II) (ZnTPP) was found to be adsorbed from its CH2Cl2 solution into a Nafion (Nf) film. The characteristics of the adsorption of ZnTPP into the Nf film were studied using a visible absorption spectroscopic technique. The initial rate (v0, mol cm(-2) s(-1)) for uptake of ZnTPP was saturated with increasing ZnTPP concentration (c0, M) in the solution. This kinetic profile was analyzed in terms of a Michaelis-Menten model considering preequilibrium of ZnTPP adsorption between the solution and the outer layer of the Nf film, followed by diffusion to an inner bulk region, giving a maximum diffusion reflux of v(max) = (2.2 +/- 0.2) x 10(-13) mol cm(-2) s(-1). This is different from the kinetics for the Nf/phthalocyanine zinc(II) (ZnPc) film, which gives a linear plot of v(0) vs c(0). This can be explained by the relatively slow diffusion of ZnTPP in the film compared to that of ZnPc because of steric factors: ZnTPP contains bulky tetraphenyl moieties attached perpendicular to a porphyrin ring, whereas ZnPc has higher planarity. The isotherm for the adsorption of ZnTPP into the Nf film was analyzed using a Langmuir isotherm equation, yielding an equilibrium constant of (3.6 +/- 1.1) x 10(6) M(-1) and a saturated amount of adsorbed ZnTPP of (1.8 +/- 0.1) x 10(-9) mol cm(-2), suggesting monolayer adsorption of ZnTPP on the hydrophobic polymer network interfacial with hydrophilic transport channels without significant intermolecular overlap. This is in contrast to the multilayer adsorption mode suggested for the ZnPc adsorption. The tetraphenyl moieties could prevent the stacking of ZnTPP for multilayer adsorption.

Molecular catalysis of the oxygen reduction reaction by iron porphyrin catalysts tethered into Nafion layers: An electrochemical study in solution and a membrane-electrode-assembly study in fuel cells

“…6 shows the UVeVis spectral changes observed for Fe(III) TMPyP in the absence and presence of Nafion. Upon the addition of two drops of Nafion there was a red-shift of the Soret band from 396 nm to 402 nm, and this shift was accompanied by a decrease in absorbance and band broadening [58,59]. The pep* transitions in metalloporphyrins are known to be affected by the complex coordination environment or by the distortion of the ring [58,59].…”

“…Upon the addition of two drops of Nafion there was a red-shift of the Soret band from 396 nm to 402 nm, and this shift was accompanied by a decrease in absorbance and band broadening [58,59]. The pep* transitions in metalloporphyrins are known to be affected by the complex coordination environment or by the distortion of the ring [58,59]. This red-shift could therefore be explained in terms of the interaction between Nafion with the central metal ion or with the ring, though the latter is strongly accepted [58e60].…”

Self-Assembled Nanostructures of Oligopyridine Molecules

“…( 2.6) × 10 4 and (21.2 ( 0.6) × 10 4 L • mol -1 , respectively. 150 The corresponding adsorption enthalpies amount to -30.4 ( 0.1 and -32.8 ( 0.1 kJ • mol -1 , respectively, both in the expected range of physisorption. A further increase of the surface coverage is restricted by the solubility of CuPc in TCB.…”

“…This points to an equilibrium between adsorbed and dissolved species. Assuming a Langmuir adsorption isotherm allows us to determine the equilibrium constants for 55 and CuPc on HOPG to K ads = (55.9 ± 2.6) × 10 4 and (21.2 ± 0.6) × 10 4 L·mol −1 , respectively . The corresponding adsorption enthalpies amount to −30.4 ± 0.1 and −32.8 ± 0.1 kJ·mol −1 , respectively, both in the expected range of physisorption.…”

Preparation of multilayer films containing a crown heteropolyanion and an osmium functionalised pyrrole monomer

“…So far, nanoparticles, organic and inorganic components have been assembled as ordered ultrathin films with surface functionalities [1][2][3][4][5]. Polyoxometalates (POMs) are a distinctive class of inorganic metal-oxygen cluster compounds of nanometer dimension that possess diverse properties, such as catalytic activity, molecular conductivity, magnetism and optical properties [6][7][8][9][10].…”