A solvent-compatible filter-transfer method of semi-transparent carbon-nanotube electrodes stacked with silver nanowires.

Low-density films of single-walled carbon nanotubes (SWNTs) can be used as a semi-transparent top electrode for all-solution-processed film devices; however, their semiconductor characteristics vary depending on the experimental factors in their dispersion into solvents, and the sublayers are damaged as a result of solvent incompatibility. In this study, we report a solvent-compatible filter-transfer method for SWNT films stacked with silver nanowires (AgNWs), and evaluate the semiconductor characteristics through the p/n heterojunction with a Si wafer (SWNT/Si). AgNWs and SWNTs were successively filtered through their aqueous dispersion solutions using a membrane filter. The stacked semi-transparent films (AgNW/SWNT films with controlled densities) were successfully transferred onto glass plates and Si wafers. The transmittance at 550 nm revealed a window between 60% and 80% with a narrow sheet resistance range between 11 and 23 Ω â–¡-1. The power conversion efficiency (PCE) of SWNT/Si was improved to 11.2% in a junction area of 0.031 cm2 through the use of spin-coated Nafion resins; however, the accumulated resistance of SWNTs drastically reduced the PCE to 2% as the area increased to ≥0.5 cm2. AgNWs maintained the PCE within a range of 10.7% to 8.6% for an area ranging from 0.031 cm2 to 1.13 cm2. All of the photovoltaic parameters were dependent on the junction areas, suggesting that AgNWs function as an effective current-collector layer on the semiconductor layer of SWNTs without direct contact of AgNWs with the Si surface. In addition, we report a solvent-compatible experiment for transferring AgNW/SWNT films onto a solvent-sensitive perovskite material (CH3NH3PbI3).

Effect of Static Jahn-Teller Distortion on the Li+ Transport in a Copper Hexacyanoferrate Framework.

Prussian blue (PB) and its analogues (PBAs) are potential cathode-active materials for rechargeable lithium-ion batteries. Although a body of research has assessed the performances of various PB/PBA cathodes with an eye to practical use, the underlying Li+-transport mechanism is still unclear. Focusing on copper hexacyanoferrate (CuHCF), a PBA that exhibits static Jahn-Teller (JT) distortion, we theoretically investigate how the framework's distortion affects the pathways and energetics of the Li+ transport. Density functional theory calculations of a local structure model of CuHCF reveal that the static JT distortion makes the favorable Li+-transport pathways quasi-two-dimensional, contrary to an intuitive picture of isotropic Li+ diffusion within the regular jungle-gym framework. The pathways are mutually interconnected, thereby creating an almost barrierless transport network. To better understand the distortion-induced transport anisotropy, we visually analyze the framework's electronic structure and noncovalent Li+-framework interactions. This study helps deepen the fundamental understanding of intrinsic Li+-transport properties of a distorted porous framework.

Self-Assembly and -Cross-Linking Lamellar Films by Nanophase Separation with Solvent-Induced Anisotropic Structural Changes.

In this study, we have prepared thermally and chemically stable lamellar polymer films via humid annealing. The amphiphilic polymer poly(N-dodecyl acrylamide-stat-3-(trimethoxysilyl)propyl acrylate) [p(DDA/TMSPA)] forms a self-assembled lamellar structure via annealing at 60 °C under 98% relative humidity (humid annealing) due to nanophase separation between the hydrophobic dodecyl side and main chains with the amide groups that contain adsorbed water. Moreover, a self-cross-linking reaction of TMSPA proceeds during the humid annealing. As a result, the lamellar films maintain their structure even when annealed above their glass-transition temperature. On the other hand, the films swell when immersed in toluene. The highly ordered lamellar structure collapses due to the swelling but can be re-established by subsequent humid annealing. A multilayer freestanding film can be exfoliated via sonication in toluene. The exfoliated multilayer films initially form a dome-shaped structure, which is converted to a plate-shaped structure upon humid annealing. In their entirety, these results reveal that the molecular-scale movement associated with the formation of the lamellar structure induces a macroscopic structural change. Consequently, p(DDA/TMSPA) can be considered as a new stimulus-responsive polymer.

Oxygen vacancy mediated room-temperature ferromagnetism and band gap narrowing in DyFe0.5Cr0.5O3 nanoparticles.

We report on the magnetic and optical properties of DyFe0.5Cr0.5O3 nanoparticles synthesized by a sol-gel method. Rietveld refinement of a powder X-ray diffraction (XRD) pattern confirms the formation of an orthorhombic disordered phase with the Pnma space group. The formation of nano-sized particles, with an average size of 42(±12) nm, was approximated by the transmission electron microscopy (TEM) image analysis. X-ray photoelectron spectroscopy (XPS) of this compound reveals the presence of Fe2+/Fe3+ and Cr2+/Cr3+ mixed-valence states as a consequence of oxygen vacancies present at the surface of nanoparticles. The temperature-dependent magnetization (M-T) shows a finite non-zero magnetization up to 300 K and the field-dependent magnetization (M-H) curve exhibits a weak ferromagnetic (WFM) nature at 300 K with a clear hysteresis loop, which is quite appealing compared to that of the previously reported micron-sized DyFe0.5Cr0.5O3. These observations indicate that the large concentration of uncompensated surface spin of nanoparticles could be responsible for the observed room-temperature ferromagnetism. Moreover, DyFe0.5Cr0.5O3 nanoparticles show a significantly narrow band gap (Eg ∼ 2.0 eV). Meanwhile, the oxygen vacancies may generate shallow trap energy levels within the band gap as observed from photoluminescence (PL) spectroscopy. The observed band gap narrowing by Fe doping and the effect of oxygen vacancies on the band gap are consistent with the predictions of density functional theory (DFT) calculations. The evidence of room-temperature ferromagnetism in DyFe0.5Cr0.5O3 nanoparticles compared to their bulk counterparts and the significantly narrow band gap in the visible range manifest the potential of this material in spintronic and optical applications.

Ion transportation by Prussian blue nanoparticles embedded in a giant liposome.

A new type of artificial giant liposome incorporating ion transport channels and using nanoparticles of metal organic frameworks was demonstrated. The micropores of Prussian blue nanoparticles served as ion transport channels between the outer and inner phases of liposomes.

Interpretation of the Role of Composition on the Inclusion Efficiency of Monovalent Cations into Cobalt Hexacyanoferrate.

Cobalt hexacyanoferrate of various compositions was prepared in flow mode and the role of the vacancy on the structure, thermogravimetric (TG) properties, and the adsorption efficiency was studied. The material, Nay Co[Fe(CN)6 ]1-x ⋅z H2 O, with a minimum vacancy of x=0.014 to the highest x=0.47, was obtained. The TG-differential scanning calorimetry (DSC) profile showed a distinct influence of the vacancy on the water release temperature. Materials with x>0.35 showed a smooth release of water at a relatively lower temperature. However, for the materials with x<0.35, water release took place in multiple steps, suggesting the existence of various forms of water. The FTIR profiles supported the existence of free and bonded water molecules. However, the materials with multiple water peaks in the FTIR spectra showed a shift of the major XRD peaks when heated at 285 °C in N2 atmosphere. Regarding the effect of the vacancy on the adsorption behavior, for NH4 , the adsorption was found to be proportional to the number of Na atoms in the material, confirming the ion-exchange process. On the contrary, the materials with low vacancy and high Na content showed nominal Cs adsorption capacity. Interestingly, the K adsorption capacity was found to be in between that of the other two ions. This means the ionic size decides the rate of placement into the interstitial sites. For larger ions like Cs, the ease of percolation via the vacancy decides the overall adsorption efficiency.

Ferrihydrite Particle Encapsulated within a Molecular Organic Cage.

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.

Improvement of the Heat Resistance of Prussian Blue Nanoparticles in a Clay Film Composed of Smectite Clay and ε-Caprolactam.

Prussian blue (PB) is limited in its application by its breakdown at elevated temperatures. To improve the heat resistance of PB, we prepared a composite film comprising PB nanoparticles (NPs), smectite clay, and an organic compound. The composite film had a microstructure in which PB NPs were intercalated between smectite/organic compound layers. The predominant oxidation temperature of the PB NPs in the composite film was around 500 °C in air, higher than the oxidation temperature of bulk PB in air (250 °C). This improvement in the oxidation temperature may be due to the composite film acting as a barrier to oxygen gas. These results indicate the effectiveness of clay materials for the improvement of heat resistance for low-temperature decomposition compounds, not only PB but also other porous coordination polymers.

Solvent-free synthesis of monodisperse Cu nanoparticles by thermal decomposition of an oleylamine-coordinated Cu oxalate complex.

Cu nanoparticles (NPs) are widely used in numerous applications because of their unique optical, catalytic, and electrical properties. However, the synthesis of monodisperse Cu NPs often involves harmful reducing agents under an inert atmosphere in a solution with low Cu ion concentrations. In this study, monodisperse Cu NPs were synthesized by the thermal decomposition of an oleylamine-coordinated Cu oxalate (Cu(ox)) complex (OA-Cu(ox)) in oleylamine in air with no reducing agent. The structure of OA-Cu(ox) was analyzed using Fourier-transform infrared spectroscopy. The decomposition temperature of the oxalate ion was reduced to 130 °C from that of Cu(ox) (300 °C) because of the coordination of the primary amino group of oleylamine with the Cu ion of Cu(ox). Furthermore, the decomposition temperature of OA-Cu(ox) strongly affected the size distribution of the synthesized Cu NPs. Monodisperse Cu NPs were successfully synthesized by the thermal decomposition of OA-Cu(ox) at temperatures higher than 240 °C with high yield (∼90%). The synthesized Cu NPs were readily dispersed in toluene.

Wisely Designed Phthalocyanine Derivative for Convenient Molecular Fabrication on a Substrate.

An axial-substituted silicon phthalocyanine derivative, SiPc(OR)2 (R = C4H9), that is soluble in organic solvent is conveniently synthesized. This silicon phthalocyanine derivative reacts with a hydroxyl group on a substrate and then with another phthalocyanine derivative under mild conditions. The accumulation number of the phthalocyanine molecules on the substrates is easily controlled by the immersion time. On the basis of AFM (atomic force microscopy) images, the surface of the phthalocyanine-modified glass substrate has uneven structures on the nanometer scale. ITO electrodes modified with the composition of the phthalocyanine derivative and PCBM show stable cathodic photocurrent generation upon light irradiation.

Unveiling Cs-adsorption mechanism of Prussian blue analogs: Cs+-percolation via vacancies to complete dehydrated state.

Metal hexacyanoferrates (MHCF) or Prussian blue analogs are excellent Cs+-adsorbents used for radioactive Cs-decontamination. However, the adsorption mechanism is controversial. To clarify the issue, we quantitatively investigated the Cs-adsorption behaviors of potassium copper hexacyanoferrate (KCuHCF) and A y Cu[Fe(CN)6]1-x ·zH2O. To obtain samples having homogeneous chemical composition and particle size, flow systems were used for both synthesis and purification. After sufficient rinsing with water, the range of x stable in aqueous solution in time appropriate for Cs-adsorption was 0.25 < x < 0.50. The relations y = 4 - 2x and z = 10x were also found independent of x, indicating complete dehydration of K+ in the crystal. We concluded that the excellent Cs-selectivity of MHCF was not due to difference in free energy of the adsorbed state between K+ and Cs+ but because of the hydrated state in aqueous solution. We also found that the guiding principle for determining the maximum capacity depended on the chemical composition. In particular, for the range 0.25 < x < 0.35, we propose a new model to understand the suppression of the maximum capacity. In our model, we hypothesize that Cs+ could migrate in the crystal only through [Fe(CN)6]4- vacancies. The model reproduced the observed maximum capacity without fitting parameters. The model would also be applicable to other MHCFs, e.g. a little adsorption by soluble Prussian blue. The ion exchange between Cs+ and H+ occurred only when the implemented K+ was small.

Effects of the variation of metal substitution and electrolyte on the electrochemical reaction of metal hexacyanoferrates.

Metal hexacyanoferrates (MHCFs), also called Prussian blue analogs, are known as electrochemical electrodes and are ion-adsorbent. To investigate the effect of the ionic radius of the adsorbate (cations adsorbed upon reduction) and the pore size of the adsorbent (porous electrode that stores cations upon reduction), we investigated the electrochemical reactions with various alkali cations and by changing the metal sites of the MHCFs. First, we succeeded in controlling the pore sizes of the MHCFs, where the lattice constant a could be estimated as a = 0.98D sum + 7.21, where D sum represented the sum of the ionic diameters of the metal M and Fe. Concerning the electrochemical reaction, the redox potential increased when the hydration energy of the adsorbate decreased, implying that the hydration energy of the adsorbate affected the stability of the reduced state. With cadmium hexacyanoferrate, which has a large pore size, the variation of the redox potential was suppressed in comparison to that with copper hexacyanoferrate, which has a small pore size. With Fourier transform-infrared (FT-IR) analysis before and after the redox reactions, Na+ insertion accompanied by H2O was presumed in the reduced state.

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.

Stepwise fabrication of donor/acceptor thin films with a charge-transfer molecular wire motif.

Novel thin films composed of a donor (D)/acceptor (A) charge-transfer chain compound were fabricated by a layer-by-layer technique using complexation of a paddlewheel-type diruthenium(ii, ii) complex with an N,N'-dicyanoquinonediimine derivative on an ITO substrate with a pyridine-substituted phosphonate anchor. The stepwise growth of an electron-transfer D+A--chain thin film was confirmed.

Synthesis of water-dispersible silver nanoparticles by thermal decomposition of water-soluble silver oxalate precursors.

Silver oxalate, one of the coordination polymer crystals, is a promising synthetic precursor for transformation into Ag nanoparticles without any reducing chemicals via thermal decomposition of the oxalate ions. However, its insoluble nature in solvents has been a great disadvantage, especially for systematic control of crystal growth of the Ag nanoparticles, while such control of inorganic nanoparticles has been generally performed using soluble precursors in homogeneous solutions. In this paper, we document our discovery of water-soluble species from the reaction between the insoluble silver oxalate and N,N-dimethyl-1,3-diaminopropane. The water-soluble species underwent low-temperature thermal decomposition of the oxalate ions at 30 °C with evolution of CO2 to reduce Ag+ to Ag0. Water-dispersible Ag nanoparticles have been successfully synthesized from the water-soluble species in the presence of gelatin via similar thermal decomposition at 100 °C. The gelatin-protected and water-dispersible Ag nanoparticles with a mean diameter of 25.1 nm appeared. In addition, antibacterial activity of the prepared water-dispersible Ag nanoparticles has been preliminarily investigated.

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.