Crystal Growth and Color Tuning of Large Mn(PO3OH)·3H2O Crystals via an Evaporation-Assisted Aqueous Route at Room Temperature.

Large Mn(PO3OH)·3H2O crystals have been prepared from aqueous solutions containing MnCl2 and (NH4)2HPO4 by an evaporation-induced crystal growth technique. The slow solvent evaporation at room temperature maintained the supersaturation of the precursor solution for a long time, resulting in the continuous growth of Mn(PO3OH)·3H2O crystals. The addition of citric acid as a chelating agent and increasing the total volume of the precursor solutions helped to maintain the mild supersaturation conditions for a longer time period, and transparent, unbranched Mn(PO3OH)·3H2O crystals above 2 mm in size were produced by aging for 8 weeks. The large Mn(PO3OH)·3H2O single crystals exhibited a pink color, and the color became stronger by doping with Co2+ ions.

Aqueous Synthesis of Manganese Phosphate Hydrate Crystals for Creating Inorganic Pigment Materials.

Manganese phosphate hydrate crystals were prepared from aqueous solutions containing MnCl2, (NH4)2HPO4, and citric acid. Switzerite [Mn3(PO4)2·7H2O] and niahite (NH4MnPO4·H2O) phases were produced at room temperature, and then, hureaulite [Mn5(PO3OH)2(PO4)2·4H2O] particles were obtained by aging at 80 °C or by hydrothermal treatment at 100-180 °C. The lower aging temperature (80 °C) and the chelation of Mn2+ ions by citric acid provided a slower crystal growth, resulting in large hexagonal prism blocks of ca. 500 µm in size. These were found to be single crystals of hureaulite by powder and single-crystal X-ray diffraction analysis. Diffuse reflectance spectroscopy and evaluation using L*a*b* color parameters indicated that the large single crystals present a vivid pink color and high transparency.

Single-Source Alkoxide Precursor Approach to Titanium Molybdate, TiMoO5, and Its Structure, Electrochemical Properties, and Potential as an Anode Material for Alkali Metal Ion Batteries.

Transition-metal oxide nanostructured materials are potentially attractive alternatives as anodes for Li ion batteries and as photocatalysts. Combining the structural and thermal stability of titanium oxides with the relatively high oxidation potential and charge capacity of molybdenum(VI) oxides was the motivation for a search for approaches to mixed oxides of these two metals. Challenges in traditional synthetic methods for such materials made development of a soft chemistry single-source precursor pathway our priority. A series of bimetallic Ti-Mo alkoxides were produced by reactions of homometallic species in a 1:1 ratio. Thermal solution reduction with subsequent reoxidation by dry air offered in minor yields Ti2Mo2O4(OMe)6(OiPr)6 (1) by the interaction of Ti(OiPr)4 with MoO(OMe)4 and Ti6Mo6O22(OiPr)16(iPrOH)2 (2) by the reaction of Ti(OiPr)4 with MoO(OiPr)4. An attempt to improve the yield of 2 by microhydrolysis, using the addition of stoichiometric amounts of water, resulted in the formation with high yield of a different complex, Mo7Ti7+xO31+x(OiPr)8+2x (3). Controlled thermal decomposition of 1-3 in air resulted in their transformation into the phase TiMoO5 (4) with an orthorhombic structure in space group Pnma, as determined by a Rietveld refinement. The electrochemical characteristics of 4 and its chemical transformation on Li insertion were investigated, showing its potential as a promising anode material for Li ion batteries for the first time. A lower charge capacity and lower stability were observed for its application as an anode for a Na ion battery.

Evaporation-Driven Deposition of ITO Thin Films from Aqueous Solutions with Low-Speed Dip-Coating Technique.

We suggest a novel wet coating process for preparing indium tin oxide (ITO) films from simple solutions containing only metal salts and water via evaporation-driven film deposition during low-speed dip coating. Homogeneous ITO precursor films were deposited on silica glass substrates from the aqueous solutions containing In(NO3)3·3H2O and SnCl4·5H2O by dip coating at substrate withdrawal speeds of 0.20-0.50 cm min-1 and then crystallized by the heat treatment at 500-800 °C for 10-60 min under N2 gas flow of 0.5 L min-1. The ITO films heated at 600 °C for 30 min had a high optical transparency in the visible range and a good electrical conductivity. Multiple-coating ITO films obtained with five-times dip coating exhibited the lowest sheet (ρS) and volume (ρV) resistivities of 188 Ω sq-1 and 4.23 × 10-3 Ω cm, respectively.

Transferability and Adhesion of Sol-Gel-Derived Crystalline TiO2 Thin Films to Different Types of Plastic Substrates.

Anatase thin films were prepared on various plastic substrates by our recently developed sol-gel transfer technique. Polycarbonate (PC), poly(methyl methacrylate) (PMMA), polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polyether ether ketone (PEEK), and polyvinylidene chloride (PVDC) were employed as plastic substrates. A Si(100) substrate was first coated with a polyimide (PI)/polyvinylpyrrolidone (PVP) mixture layer, and an alkoxide-derived titania gel film was deposited on it by spin-coating. The resulting titania gel film was heated to 600 °C, during which the PI/PVP layer decomposed and the gel film was converted into a 60 nm thick anatase film. The anatase film was then transferred from the Si(100) substrate to the plastic substrate. This was achieved by heating the plastic/anatase/Si(100) stack in a near-infrared image furnace to 120-350 °C, depending on the type of plastic substrate, under unidirectional pressure. The anatase film cracked during transfer to PE, PP, PEEK, and PVDC substrates but did not crack during transfer to PC, PMMA, and PET substrates. The fraction of the total film area that was successfully transferred was assessed with the aid of image analysis. This fraction tended to be large for plastics with C═O and C-O groups and small for those without these groups. The film/substrate adhesion assessed by cross-cut tape tests also tended to be high for plastics with C═O and C-O groups and low for those without these groups. The adhesion to plastics without C═O or C-O groups could be enhanced and their transfer area fraction increased by oxidizing the native plastic surface by ultraviolet-ozone treatment prior to transfer.

Evaporation-Driven Deposition of WO3 Thin Films from Organic-Additive-Free Aqueous Solutions by Low-Speed Dip Coating and Their Photoelectrochemical Properties.

We prepared tungsten trioxide (WO3) photoelectrode films from organic-additive-free aqueous solutions by a low-speed dip-coating technique. The evaporation-driven deposition of the solutes occurred at the meniscus during low-speed dip coating, resulting in the formation of coating layer on the substrate. Homogeneous WO3 precursor films were obtained from (NH4)10W12O41·5H2O aqueous solutions and found to be crystallized to monoclinic WO3 films by the heat treatment at 400-700 °C. All the films showed a photoanodic response irrespective of the heat treatment temperature, where a good photoelectrochemical stability was observed for those heated over 500 °C. The highest photoanodic performance was observed for the WO3 film heated at 700 °C, where the IPCE (incident photon-to-current efficiency) was 36.2% and 4.6% at 300 and 400 nm, respectively.

Spontaneous Pattern Formation Induced by Bénard-Marangoni Convection for Sol-Gel-Derived Titania Dip-Coating Films: Effect of Co-solvents with a High Surface Tension and Low Volatility.

Evaporation-driven surface tension gradient in the liquid layer often causes the convective flow, i.e., Bénard-Marangoni convection, resulting in the formation of cell-like patterns on the surface. Here, we prepared sol-gel-derived titania films from Ti(OC3H7(i))4 solutions by dip coating and discussed the effect of the addition of co-solvents with a high surface tension and low volatility on the spontaneous pattern formation induced by Bénard-Marangoni convection. Propylene glycol (PG, with a surface tension of 38.6 mN m(-1)) and dipropylene glycol (DPG, with a surface tension of 33.9 mN m(-1)) were added to the coating solutions containing 2-propanol (2-Pr, with a surface tension of 22.9 mN m(-1)) for controlling the evaporation-driven surface tension gradient in the coating layer on a substrate. During dip coating at a substrate withdrawal speed of 50 cm min(-1) in a thermostatic oven at 60 °C, linearly arranged cell-like patterns on a micrometer scale were spontaneously formed on the titania gel films, irrespective of the composition of coating solutions. Such surface patterns remained even after the heat treatment at 200 and 600 °C, where the densification and crystallization of the titania films progressed. The width and height of the cell-like patterns increased with increasing PG and DPG contents in the coating solutions, where the addition of PG resulted in the formation of cells with a larger height than DPG.

Hydrothermal synthesis of dittmarite-group NH4(Co1-xMnx)PO4·H2O particles as inorganic violet pigments.

Dittmarite-group NH4(Co1-xMnx)PO4·H2O particles were prepared via a hydrothermal route. Single-phase platelike NH4(Co1-xMnx)PO4·H2O particles were obtained from aqueous solutions containing MnCl2·4H2O, CoCl2·6H2O, and (NH4)2HPO4, where the [Mn2+]/([Co2+] + [Mn2+]) mole ratios in the products were controlled by changing the MnCl2 and CoCl2 concentrations of the precursor solutions. The vivid violet colour of the ammonium cobalt phosphate (NH4CoPO4·H2O) particles was maintained upon substitution of Co2+ with Mn2+ ions up to x = 0.8, thus achieving an 80% saving of cobalt in the preparation of violet pigments.

Preparation of WO3-Mica Hybrid Coatings with Electrochromic Properties and Pearl Luster.

Tungsten oxide-mica composites were prepared by adding different amounts of commercial mica (alumina silicate) in order to provide high luster to electrochromic coatings. The mechanical stability was sustained for up to 50 weight % mica for application in aqueous medium. The electrochemical properties, coloration, and luster were investigated. The luster of the composites increased roughly linearly with increased mica content and was retained after coloration. The addition of 10 weight % mica was found to be optimal with respect to the compromise between electrochromic coloration and pearlescent luster. This is, to the best of our knowledge, the first report on the preparation and characterization of WO3-mica inorganic composites with high luster in both bleached and colored states.

Spontaneous formation of linearly arranged microcraters on sol-gel-derived silica-poly(vinylpyrrolidone) hybrid films induced by Bénard-Marangoni convection.

Complex, sophisticated surface patterns on micrometer and nanometer scales are obtained when solvent evaporates from solutions containing nonvolatile solutes dropped on a solid substrate. Such evaporation-driven pattern formation has been utilized as a fabrication process of highly ordered patterns in thin films. Here, we suggested the spontaneous pattern formation induced by Bénard-Marangoni convection triggered by solvent evaporation as a novel patterning process of sol-gel-derived organic-inorganic hybrid films. Microcraters of 1.0-1.5 µm in height and of 100-200 µm in width were spontaneously formed on the surface of silica-poly(vinylpyrrolidone) hybrid films prepared via temperature-controlled dip-coating process, where the surface patterns were linearly arranged parallel to the substrate withdrawal direction. Such highly ordered micropatterns were achieved by Bénard-Marangoni convection activated at high temperatures and the unidirectional flow of the coating solution on the substrate during dip-coating.

Aqueous synthesis of tin- and indium-doped WO3 films via evaporation-driven deposition and their electrochromic properties.

M-doped WO3 (M = Sn or In) films were prepared from aqueous coating solutions via evaporation-driven deposition during low-speed dip coating. Sn- and In-doping were easily achieved by controlling the chemical composition of simple coating solutions containing only metal salts and water. The crystallinity of the WO3, Sn-doped WO3, and In-doped WO3 films varied with heating temperature, where amorphous and crystalline films were obtained by heating at 200 and 500 °C, respectively. All the amorphous and crystalline films showed an electrochromic response, but good photoelectrochemical stability was observed only for the crystalline samples heated at 500 °C. The crystalline In-WO3 films exhibited a faster electrochromic color change than the WO3 or Sn-WO3 films, and good cycle stability for the electrochromic response in the visible wavelength region.

Synthesis and applications of SnO nanosheets: parallel control of oxidation state and nanostructure through an aqueous solution route.

Tin monoxide (SnO) nanosheets 5 nm in thickness are generated on substrates through an aqueous solution process under mild conditions. Parallel control of the oxidation state and morphology is achieved by a urea-mediated approach in aqueous solution. The SnO nanosheets form a porous thin film on substrates such as indium tin oxide and carbon nanofiber (CNF). The porous thin film of SnO nanosheets shows cathodic photocurrent generation upon irradiation by UV and visible light. In contrast, the photocurrent is not observed in the bulk SnO microcrystals. Composites of the SnO nanosheets and CNF perform as the anode material of lithium-ion batteries with improved charge-discharge reversible stability.

Spontaneous formation of linear striations and cell-like patterns on dip-coating titania films prepared from alkoxide solutions.

Linear striations and cell-like patterns were spontaneously formed on the dip-coating titania films prepared titanium tetraisopropoxide (Ti(OC(3)H(7)(i))(4)) solutions. Such unique patterns on micrometer scale were arranged parallel to the substrate withdrawal direction. The values of R(Z) (10 point height of irregularities) and S (mean spacing of local peaks) of the patterns increased with increasing film thickness depending on the substrate withdrawal speed for dip-coating, the viscosity of the coating solutions, and the distance from the top edge of films. The shape of patterns changed from linear striations to cell-like patterns with increasing viscosity of the coating solutions. Although the heat treatment at 600 degrees C reduced the height (R(Z)) of stripes and cells without the change in spacing (S), the visibility of patterns was enhanced by the increase in refractive index due to the crystallization of films.

Correction: Nano- and micro-structural control of WO3 photoelectrode films through aqueous synthesis of WO3·H2O and (NH4)0.33WO3 precursors.

[This corrects the article DOI: 10.1039/D0RA01321H.].

Nano- and micro-structural control of WO3 photoelectrode films through aqueous synthesis of WO3·H2O and (NH4)0.33WO3 precursors.

Nano- and micro-structured tungsten trioxide (WO3) photoelectrode films were prepared through an aqueous solution route. WO3 precursor layers were deposited on glass substrates through heterogeneous nucleation from (NH4)10W12O41 aqueous solutions at 50-60 °C. The crystal phase of the precursors changed from WO3·H2O to (NH4)0.33WO3 with increasing (NH4)10W12O41 concentration (x), which involved a morphological change from micron-scale plates to nano-scale fine particles. The WO3·H2O and (NH4)0.33WO3 layers were thermally converted to the monoclinic WO3 phase. The fine-particle WO3 films obtained from (NH4)0.33WO3 layers showed a better photoanodic performance in the UV range below 350 nm, which was attributed to the larger surface area arising from the porous structure. On the other hand, platy-particle WO3 films were obtained from WO3·H2O layers, which exhibited strong light scattering in the visible range, and resulted in an enhanced photoanodic response at wavelengths above 375 nm.

Biomimetic synthesis of nanostructured WO3 · H2O particles and subsequent thermal conversion to WO3.

Nanostructured tungsten oxide (WO3) particles were prepared in aqueous solution by mimicking biomineralization. Precursor WO3 · H2O particles were generated by ageing a 60°C (NH4)10W12O41 · 5H2O solution containing gelatin. This was followed by heating to 600°C in air for thermal conversion to WO3. The addition of gelatin led to the formation of layered structures consisting of WO3 · H2O platy particles, which contained segmented, block-like nanoscale units. The macroscopic layered structure was preserved after thermal conversion to WO3, while the morphology of the block-like units changed to orthogonally crossed nanorods.

Crystal growth of metastable rutile-type TixSn1-xO2 solid solutions in an aqueous system.

Nanoscale grains of crystalline TixSn1-xO2 were directly grown over the whole range of [Ti]/([Ti] + [Sn]) ratio (x = 0.00-1.00) in aqueous solutions at near room temperature.

Superior properties of silica thin films prepared from perhydropolysilazane solutions at room temperature in comparison with conventional alkoxide-derived silica gel films.

Preparation of silica thin films from perhydropolysilazane (PHPS) at room temperature has attracted much attention because it provides a new way to realize silica thin films in a variety of technologies where any high temperature processes should be avoided. Although silica gel films can also be prepared from alkoxides at room temperature by conventional sol-gel method, they are believed to have low mechanical and chemical durability. However, even such alkoxide-derived silica gel films have possibilities to become more durable via condensation reaction and densification when aged at room temperature. In order to clarify whether or not PHPS-derived silica thin films have critical superiority on properties, the hardness and chemical durability were compared between PHPS- and alkoxide-derived silica thin films, where PHPS films were exposed to the vapor from aqueous ammonia at room temperature for PHPS-to-silica conversion. Alkoxide-derived silica gel films were found to be densified and hardened when stored in air at room temperature, which resulted in pencil hardness even higher than 9H on Si(100) substrates. However, the ultra-microindentation tests demonstrated that the PHPS-derived films are definitely harder than the alkoxide-derived ones. The PHPS-derived films were also found to have higher chemical durability in water and in aqueous ammonia. Such higher mechanical and chemical durability of the PHPS-derived films was ascribed to their higher density, i.e., more highly condensed states, which was evidenced in infrared absorption spectra. Hard coating performance on plastic substrates was also studied, and the PHPS-derived films were demonstrated to have much higher adhesive strength on polymethylmethacrylate substrates. The in-plane stress measurement demonstrated that the PHPS-derived films have much lower or even negligible tensile stress, which may be one of the causes for such higher adhesive strength.

Ceramic thin films on plastics: a versatile transfer process for large area as well as patterned coating.

A versatile technique for fabricating ceramic thin films on plastics has been proposed. The technique comprises (i) the deposition of a gel film by spin- or dip-coating on a silicon substrate coated beforehand with a release layer, (ii) the firing of the gel film into a ceramic film, and (iii) its transfer onto plastics by melting or softening the plastics surface. Reflective anatase and electrically conductive indium-tin-oxide (ITO) thin films were prepared on acrylic resin and polycarbonate substrates. Patterned ITO thin films could also be fabricated on plastics by using a mother silicon substrate with periodic grooves.

Biomimetic synthesis of metal ion-doped hierarchical crystals using a gel matrix: formation of cobalt-doped LiMn(2)O(4) with improved electrochemical properties through a cobalt-doped MnCO(3) precursor.

We have synthesized spinel type cobalt-doped LiMn(2)O(4) (LiMn(2-y)Co(y)O(4), 0