Manabu Ishizaki

Simple synthesis of three primary colour nanoparticle inks of Prussian blue and its analogues

Historic Prussian blue (PB) pigment is easily obtained as an insoluble precipitate in quantitative yield from an aqueous mixture of Fe3+ and [FeII(CN)6]4? (Fe2+ and [FeIII(CN)6]3?). It has been found that the PB pigment is inherently an agglomerate of 10?20?nm nanoparticles, based on powder x-ray diffraction (XRD) line broadenings and transmission electron microscopy (TEM) images. The PB pigment has been revived as both organic-solvent-soluble and water-soluble nanoparticle inks. Through crystal surface modification with aliphatic amines, the nanoparticles are stably dispersed from the insoluble agglomerate into usual organic solvents to afford a transparent blue solution. Identical modification with [Fe(CN)6]4? yields water-soluble PB nanoparticles. A similar ink preparation is applicable to Ni-PBA and Co-PBA (nickel and cobalt hexacyanoferrates). The PB (blue), Ni-PBA (yellow), and Co-PBA (red) nanoparticles function as three primary colour inks.

Electrochromic Thin Film Fabricated Using a Water-Dispersible Ink of Prussian Blue Nanoparticles

We dispersed nanoparticles of Prussian blue (PB) in water using surface modification of the PB nanoparticles. Using spin-coating method, a thin film is easily fabricated with water dispersible ink of PB nanoparticles. The PB film thickness was estimated as 40–430 nm. The PB nanoparticle film on an indium tin oxide glass substrate showed a stable electrochromic response: the color changed repeatedly between blue and colorless without any post-treatment.

Preparation of electrochromic Prussian blue nanoparticles dispersible into various solvents for realisation of printed electronics

An insoluble solid of historic Prussian blue (PB) was transformed into dispersible PB nanoparticles in water and various hydrophilic and hydrophobic organic solvents. Via hybrid surface modification using Na4[FeII(CN)6] and short-chain alkylamines, the insoluble PB was successfully dispersed in hydrophilic-and-hydrophobic boundary alcohols, such as n-butanol. The n-butanol-dispersible PB nanoparticles afforded homogeneous spin-coated thin films on various substrates. The chemisorbed shorter-chain alkylamines, n-propylamines, of the PB nanoparticles were thermally released at 100 °C from their surfaces to present stubborn electrochromic PB thin films adhering to the substrate via mutual coordination-bonding networks.

Thermodynamics and Mechanism Studies on Electrochemical Removal of Cesium Ions from Aqueous Solution Using a Nanoparticle Film of Copper Hexacyanoferrate

Nanoparticle (NPs) film of copper hexacyanoferrate (CuHCF(III)) was developed for electrochemically cesium separation from wastewater. Different form the electro- or chemical deposited films, CuHCF(III) NPs were firstly covered with ferrocyanide anions, so that they can be well dispersed in water and formed ink. Then CuHCF(III) NPs can be uniformly coated by simple wet printing methods, so it is feasible to prepare NPs film of any sizes, or any patterns at low cost. This process provided a promising technology for preparing large scale electrodes for sequential removal of Cs from wastewater in the columns. Cs separation can be controlled by an electrically switched ion exchange (ESIX) system. Effect of temperatures, and ionic strength on Cs removal was investigated. Thermodynamics results showed that Cs adsorption process was exothermic in nature and favored at low temperature. Ionic strength study indicated the CuHCF(III) film can selectively separate Cs in wide ionic strength range from 1 × 10(-4) to 1 × 10(-1) M Na(+). XPS results demonstrated that the electrochemical oxidation-reduction of Fe (II/III) made contributions to Cs separation.

Molecular Nanostamp Based on One-Dimensional Porphyrin Polymers

Surface design with unique functional molecules by a convenient one-pot treatment is an attractive project for the creation of smart molecular devices. We have employed a silane coupling reaction of porphyrin derivatives that form one-dimensional polymer wires on substrates. Our simple one-pot treatment of a substrate with porphyrin has successfully achieved the construction of nanoscale bamboo shoot structures. The nanoscale bamboo shoots on the substrates were characterized by atomic force microscopy (AFM), UV-vis spectra, and X-ray diffraction (XRD) measurements. The uneven and rigid nanoscale structure has been used as a stamp for constructing bamboo shoot structures of fullerene.

Largely enhanced photocurrent via gap-mode plasmon resonance by a nanocomposite layer of silver nanoparticles and porphyrin derivatives fabricated on an electrode

Photocurrent generation efficiency via the photoactive dyes, porphyrins, was strongly enhanced by construction of a nanocomposite structure, which consists of an undercoat layer of (3-mercaptopropyl)trimethoxysilane and densely and homogeneously attached silver nanoparticles on an electrode. The employed 5 -(4-carboxyphenyl)-10,15,20-triphenylporphyrins, 1, were embedded on the silver nanoparticle surface through their carboxylate moiety. The photo-absorption of 1 was significantly influenced by normal and gap-mode plasmon bands. The photocurrent of the nanocomposite structure was more strongly enhanced via the Q band excitation of 1, overlapped with the gap-mode plasmon band in the absorption wavelength range, and also showed stable photocurrent.

Column study on electrochemical separation of cesium ions from wastewater using copper hexacyanoferrate film

Nanoparticle film of copper hexacyanoferrate (CuHCFIII) was developed and coated on the rolled sheet electrodes for column cesium separation from wastewater. Results indicated well balance of Cs adsorption and desorption can be achieved switching the potentials between anodes and cathodes. XPS and isotherm studies indicated the electrochemical oxidation–reduction of Fe(II/III) on the monolayer of the CuHCFIII film made contributions to reversible Cs separation. Minimization of secondary waste, simple regeneration and uniformly coating for any size, suggest a promising column technology for sequential removal of Cs from actual wastewater.

Synthesis of Water-Dispersible Copper Hexacyanoferrate Nanoparticles and Electrochromism of the Thin Films

A Prussian blue analog (PBA), copper hexacyanoferrate (Cu-PBA) has been synthesized as an insoluble aggregated solid of nanoparticles (NPs). The Cu-PBA NPs bore negative surface-charge via their surface modification using [FeII(CN)6]4− and were stably dispersed into water from the insoluble solid. Spin-coated thin films consisting of the Cu-PBA NPs on ITO glass substrates showed reversible electrochromism of red (reduced form) and yellow (oxidized form). The spectroscopic investigation revealed that the reduced form of Cu-PBA was a mixed valence form included Cu(I).

Energy location of Ce3+ 4f level and majority carrier type in Gd3Al2Ga3O12:Ce crystals studied by surface photovoltage spectroscopy

Gd3Al2Ga3O12:Ce (GAGG:Ce) was studied by surface photovoltage spectroscopy using the ultraviolet photoelectron spectroscopy technique with synchrotron radiation and a laser source. The lowest Ce3+ 4f level is located below the conduction band minimum by 3.02 eV. This result is supported by the excitation spectrum for photo-stimulated luminescence and is compatible with the value predicted by the vacuum-referred binding energy scheme for GAGG:Ce. It is also found that GAGG:Ce is of the p-type. The information on the energy location of the Ce3+ 4f level and majority carrier type provides us with hints on how to improve the optical properties of GAGG:Ce for photonic device applications.

Grain-Boundary-Free Super-Proton Conduction of a Solution-Processed Prussian-Blue Nanoparticle Film

A porous crystal family has been explored as alternatives of Nafion films exhibiting super-proton conductivities of ≥10-2  S cm-1 . Here, the proton-conduction natures of a solution-processed film of nanoparticles (NPs) have been studied and compared to those of a Nafion film. A mono-particle film of Prussian-blue NPs is spontaneously formed on a self-assembled monolayer substrate by a one-step solution process. A low-temperature heating process of the densely packed, pinhole-free mono-particle NP film enables a maximum 105 -fold enhancement of proton conductivity, reaching ca. 10-1  S cm-1 . The apparent highest conductivity, compared to previously reported data of the porous crystal family, remains constant against humidity changes by an improved water-retention ability of the film. In our proposed mechanism, the high-performing solution-processed NP film suggests that heating leads to the self-restoration of hydrogen-bonding networks throughout their innumerable grain boundaries.