Metal oxides with sizes of a few nanometers show variable crystal and electronic structures depending on their dimensions, and the synthesis of metal oxide particles with a desired size is a key technology in materials science. Although discrete metal oxide particles with an average diameter (d) smaller than 2 nm are expected to show size-specific properties, such ultrasmall metal oxide particles are significantly limited in number. In nature, on the other hand, nanosized ferrihydrite (Fh), which is ferric oxyhydroxide, occurs as a result of biomineralization in ferritin, an iron storage protein cage. Here we describe the synthesis of Fh particles using a covalent molecular organic cage (MOC) derived from 8 + 12 cyclocondensation of triaminocyclohexane with a diformylphenol derivative. At the initial reaction stage, eight iron ions accumulated at the metal binding sites in the cage cavity, and Fh particles (d = 1.9 ± 0.3 nm) encapsulated within the cage (Fh@MOC) formed with a quite narrow size distribution. The formation process of the Fh particle in the organic cage resembles the biomineralization process in the natural iron storage protein, and the present method could be applicable to the synthesis of other metal oxide particles. Fh@MOC is soluble in common organic solvents and shows substantial redox activity in MeCN.
We demonstrated that the sequential structural control of nanoparticles of an open-framework coordination polymer, copper hexacyanoferrate (CuHCF). The structural control has been achieved by addin...
The local structures around Sb, Bi, and Ag dopant atoms in the environmentally friendly semiconductor Mg2Si were investigated by Sb K-edge, Bi L3-edge, and Ag K-edge x-ray absorption spectroscopy performed at 10 K. Fourier transforms (FTs) of the k3-weighted extended x-ray absorption fine structure (EXAFS) were analyzed. The experimental FTs of k3-weighted EXAFS were compared with the results of calculations using model clusters with Sb, Bi, and Ag atoms at the 8c, 4a, and 4b sites. The inverse FT of the χ(R) spectrum was calculated to refine the local structures for neighboring atoms around the Sb, Bi, and Ag atoms, and the interatomic distances and Debye–Waller factors were determined from the fit of the inverse FTs. The occupation of the 4a site by Sb and Bi atoms was demonstrated and that of the 8c site was investigated for Ag atoms. First-principles calculations were performed to clarify the characteristic change in the second-neighbor distances around the Ag atoms. The evaluation of the crystal orbital Hamilton population clarified that the change in the second-neighbor distances is caused by the bonding character formed between the Ag and Mg atoms. These results suggest that the Ag atoms mainly occupy the 8c site, while the large value of the Debye–Waller factor for the second neighboring atoms implies the possibility of the partial occupation of Ag atoms at the 4b sites. These findings provide an explanation for limiting the p-type conductivity in Mg2Si semiconductors.
The oxidization process of the Fe–Ni mixed Prussian blue analogue (Fe0.2Ni0.8)[Fe(CN)6]0.67·zH2O was investigated by means of valence-differential spectroscopy. The spectroscopy revealed that the oxidization process selectively starts from the intermediate clusters. With a further increase in the oxidization level, all intermediate clusters are oxidized, and then Fe-rich clusters begin to be oxidized. On the basis of these results, we will discuss the redox process of the Ni–Fe cyano mixed crystal.
Three-typed porphyrin derivatives with a different chain-length alkylcarboxylic acid as their peripheral anchor group have been prepared. Anodic photocurrents were observed in a simple system where the porphyrin derivatives were directly anchored on an indium tin oxide (ITO) electrode. Cathodic photocurrents and their plasmon-assisted enhancement appeared from an Ag nanoparticle (Ag NP) composite monolayer combined with the porphyrin derivatives on the ITO electrode. In the photocurrent generation mechanism, Ag NPs played both the roles as photon- and energy-transfer to the porphyrin derivatives. The plasmon-assisted enhancement was affected by the chain-lengths of the peripheral anchor groups.
Abstract Two types of silver nanoparticle (Ag NP)–dye nanocomposite layers were prepared on an indium-tin oxide (ITO) transparent electrode, where porphyrins were fixed on the Ag NPs by chemical bonding through their carboxylate moieties or by hydrophobic interactions. Stable cathodic photocurrents were generated from the nanocomposite layer structures and were specifically enhanced by the overlap of the Q-band excitation of the porphyrins between 500 and 600 nm with the gap-mode plasmon band of the Ag NPs. The photocurrent efficiency of the chemical bonding system was significantly higher than that from the hydrophobic interaction system.
Abstract Mixed-metal Prussian-blue nanoparticles, FexNiy[Fe(CN)6]2·zH2O (x + y = 3, z = 8–12), were dispersed into n-butanol by hybrid surface modification with hexacyanoferrate(II) ions, [FeII(CN)6]4−, and n-hexylamines. In their transparent dispersion solutions, a systematic bathochromic shift of charge-transfer bands due to the FeII–CN–FeIII components was observed depending on the metal composition ratios of Fe and Ni.
