Binding Studies of Molecular Linkers to ZnO and MgZnO Nanotip Films

Abstract

Two bifunctional linkers, a rigid-rod p-ethynyl-isophthalic acid capped with a Ru(II)-polypyridyl complex and 3-mercaptopropionic acid, were covalently bound to ZnO nanotip films grown by metal-organic chemical vapor deposition (MOCVD) technology. This highly vertically aligned, crystalline form of ZnO had not been functionalized before. The binding was studied by Fourier transform (FT) IR and UV spectroscopies and probed, in the case of the Ru complex, by static and dynamic fluorescence quenching. The molecules did bind through the carboxylic acid groups, and the FT-IR attenuated total reflectance spectra are indicative of a bidentate carboxylate binding mode. Other molecules (heptanoic acid, isophthalic acid, and trimethoxy(2-phenylethyl)silane) were also bound to the ZnO nanotips. A comparison was made with epitaxial ZnO films grown by MOCVD and ZnO mesoporous films prepared from colloidal solutions to investigate the effect of the ZnO morphology. The ZnO nanotips were excellent binding substrates, particularly for the rigid-rod linker. Since ZnO films are etched at low pH (< 4), novel nanotip films made of ternary MgxZn1-xO, which is formed by alloying ZnO with MgO and is more resistant to acids, were developed. The MgxZn1-xO nanotip films were employed to use linkers with acidic groups and to study the effect of pH pretreatment of the surface on the binding.

Arsenate removal with 3-mercaptopropanoic acid-coated superparamagnetic iron oxide nanoparticles

“…In the FTIR spectrum of the 3-MPA coated SPION (Fig. 3c), there are also new bands at 1521 cm -1 and 1386 cm -1 , which are assigned to asymmetric and symmetric stretching vibrations of COO -group and the band attributed to C=O for the carboxyl group and S-H groups of MPA lose intensity [34]. A reasonable conclusion would therefore be that the binding of 3-MPA to SPION occurs primarily through the carboxylic group rather than through the SH group.…”

“…The vibration of the -SH group present two peaks at 2664 and 2571 cm -1 (slightly observed in 3-MPA-coated SPION). The -COOH group has a stretching vibration of C=O at 1714 cm -1 and the stretching vibration for C-O at 1267 cm -1 [34,35]. Finally, a band at 951 cm -1 is attributed to O-H out of plane wagging [36].…”

Zinc oxide modified with benzylphosphonic acids as transparent electrodes in regular and inverted organic solar cell structures

“…SAM modifications have already been applied to other transparent metal oxides such as indium tin oxide (ITO); [15][16][17] however, deposition of these mostly acidic molecules onto ZnO is well-known to cause etching of the chemically less stable ZnO surface. 18,19 Therefore, recent attempts drastically reduced the exposure time to the acidic environment simply by spin coating the solution of the SAM forming molecules onto ZnO. 20,21 However, given the short time for molecular assembly, the quality of the so-formed monolayer might be ill defined.…”

First principles investigations on the electronic structure of anchor groups on ZnO nanowires and surfaces

“…3 Several molecules have been investigated to determine the most appropriate anchor groups for the functionalization of ZnO. Compounds that has been employed as ligands include carboxylic acids, 4-12 amines, [13][14][15] silanes, 4,[16][17][18] phosphonic acids, 19 and thiols. 14,[19][20][21][22] Aside from a required covalent binding between the anchor group and the substrate, the electronic structure of the adduct determines the suitability of the ligand for a desired function of the modified nanostructure.…”