Research progress on surface modifications for phosphors used in light-emitting diodes (LEDs).

Stable and efficient phosphors are highly important for light-emitting diodes (LEDs) with respect to their application in solid-state lighting, instead of conventional lamps for general lighting. However, some problems, like low stability, low photoluminescence (PL) efficiency, and serious thermal degradation, are commonly encountered in phosphors, limiting their applications in LEDs. Surface modifications for some phosphors commonly used in LED lighting, including fluoride, sulphide, silicate, oxide, nitride, and oxynitride phosphors, are presented in this review. By forming a protective surface layer, the stabilities against moisture and high temperature of fluoride- and sulphide-based phosphors were strengthened; by coating inorganic and organic materials around the particle surface, the PL efficiencies of silicate- and oxide-based phosphors were improved; by passivation treatment upon the phosphor surface, the thermal degradation of nitride- and oxynitride-based phosphors was reduced. Various technologies for surface modification are described in detail; moreover, the mechanisms of stability strengthening, PL efficiency improvement, and thermal degradation reduction are explained. In addition, embedding of phosphors in inorganic glass matrix, especially for quantum dots, is also introduced as an effective method to improve phosphor stability for LED applications. Finally, future developments of surface modification of phosphors are proposed.

Enhanced NH3 Sensing Performance of Mo Cluster-MoS2 Nanocomposite Thin Films via the Sulfurization of Mo6 Cluster Iodides Precursor.

The high-performance defect-rich MoS2 dominated by sulfur vacancies as well as Mo-rich environments have been extensively studied in many fields, such as nitrogen reduction reactions, hydrogen evolution reactions, as well as sensing devices for NH3, which are attributed to the under-coordinated Mo atoms playing a significant role as catalytic sites in the defect area. In this study, the Mo cluster-MoS2 composite was creatively synthesized through a one-step sulfurization process via H2/H2S gas flow. The Mo6 cluster iodides (MIs) coated on the fluorine-doped tin oxide (FTO) glass substrate via the electrophoretic deposition method (i.e., MI@FTO) were used as a precursor to form a thin-film nanocomposite. Investigations into the structure, reaction mechanism, and NH3 gas sensing performance were carried out in detail. The results indicated that during the gas flowing, the decomposed Mo6 cluster iodides played the role of template and precursor, forming complicated Mo cluster compounds and eventually producing MoS2. These Mo cluster-MoS2 thin-film nanocomposites were fabricated and applied as gas sensors for the first time. It turns out that after the sulfurization process, the response of MI@FTO for NH3 gas increased three times while showing conversion from p-type to n-type semiconductor, which enhances their possibilities for future device applications.

Preparation of Oriented ZnO Rod Arrays Using Hexagonal Plate-Like Particles as a Seed Layer.

ZnO rod film is a promising material for electrodes and sensors due to its large surface area and high electrical conductivity. One of the drawbacks of conventional ZnO rod film is the random orientation of rods. In this study, an oriented ZnO seed layer composed of hexagonal plate-like ZnO particles was prepared by dip-coating. An oriented ZnO rod film was then synthesized by growing this seed layer using a hydrothermal synthesis method. We optimized the concentration of the precursor and the hydrothermal treatment time to synthesize homogeneous ZnO rod arrays. The uniformity of the rod arrays was improved by applying a strong magnetic field (12 T) during hydrothermal treatment.

A review on functional nanoarchitectonics nanocomposites based on octahedral metal atom clusters (Nb6, Mo6, Ta6, W6, Re6): inorganic 0D and 2D powders and films.

This review is dedicated to various functional nanoarchitectonic nanocomposites based on molecular octahedral metal atom clusters (Nb6, Mo6, Ta6, W6, Re6). Powder and film nanocomposites with two-dimensional, one-dimensional and zero-dimensional morphologies are presented, as well as film matrices from organic polymers to inorganic layered oxides. The high potential and synergetic effects of these nanocomposites for biotechnology applications, photovoltaic, solar control, catalytic, photonic and sensor applications are demonstrated. This review also provides a basic level of understanding how nanocomposites are characterized and processed using different techniques and methods. The main objective of this review would be to provide guiding significance for the design of new high-performance nanocomposites based on transition metal atom clusters.

High performance {Nb5TaX12}@PVP (X = Cl, Br) cluster-based nanocomposites coatings for solar glazing applications.

The development of highly ultraviolet (UV) and near-infrared (NIR) absorbent transparent coatings is an important enabling technology and area of research for environmental sustainability and energy conservation. Different amounts of K4[{Nb5TaXi 12}Xa 6] cluster compounds (X = Cl, Br) dispersed into polyvinylpyrrolidone matrices were prepared by a simple, nontoxic and low-cost wet chemical method. The resulting solutions were used to fabricate visibly transparent, highly UV and NIR absorbent coatings by drop casting. The properties of the solution and films were investigated by complementary techniques (optical absorption, electrospray ionization mass spectrometry and Raman spectroscopy). The UV and NIR absorption of such samples strongly depended on the concentration, dispersion and oxidation state of the [{Nb5TaXi 12}Xa 6] nanocluster-based units. By varying and controlling these parameters, a remarkable improvement of the figures of merit TL/TE and SNIR for solar-glazing applications was achieved compared to the previous results on nanocomposite coatings based on metal atom clusters.

Humidity Sensitivity of Chemically Synthesized ZnAl2O4/Al.

Humidity sensitivity is evaluated for chemically synthesized ZnAl2O4/Al devices. We succeeded in synthesizing the ZnAl2O4/Al device by applying chemical techniques only. Hydrothermal treatment for the anodized aluminum (AlOx/Al) gives us the device of the ZnAl2O4/Al structure. All fabrication processes were conducted under 400 °C. The key was focusing on ZnAl2O4 as the sensing material instead of MgAl2O4, which is generally investigated as the humidity sensor. The evaluation of this ZnAl2O4/Al device clarified its effectiveness as a sensor. Both electrical capacitance, Cp, and the resistivity, Rp, measured by an LCR meter, obviously responded to the humidity with good sensitivity and appreciable repeatability. Our synthesis technique is possible in principle to improve on the process for the device with a complex structure providing a large surface area. These characteristics are believed to expand the application study of spinel aluminate devices as the sensor.

Hafnium Oxide Nanostructured Thin Films: Electrophoretic Deposition Process and DUV Photolithography Patterning.

In the frame of the nanoarchitectonic concept, the objective of this study was to develop simple and easy methods to ensure the preparation of polymorphic HfO2 thin film materials (<200 nm) having the best balance of patterning potential, reproducibility and stability to be used in optical, sensing or electronic fields. The nanostructured HfO2 thin films with micropatterns or continuous morphologies were synthesized by two different methods, i.e., the micropatterning of sol-gel solutions by deep ultraviolet (DUV) photolithography or the electrophoretic deposition (EPD) of HfO2 nanoparticles (HfO2-NPs). Amorphous and monoclinic HfO2 micropatterned nanostructured thin films (HfO2-DUV) were prepared by using a sol-gel solution precursor (HfO2-SG) and spin-coating process following by DUV photolithography, whereas continuous and dense monoclinic HfO2 nanostructured thin films (HfO2-EPD) were prepared by the direct EPD of HfO2-NPs. The HfO2-NPs were prepared by a hydrothermal route and studied through the changing aging temperature, pH and reaction time parameters to produce nanocrystalline particles. Subsequently, based on the colloidal stability study, suspensions of the monoclinic HfO2-NPs with morphologies near spherical, spindle- and rice-like shapes were used to prepare HfO2-EPD thin films on conductive indium-tin oxide-coated glass substrates. Morphology, composition and crystallinity of the HfO2-NPs and thin films were investigated by powder and grazing incidence X-ray diffraction, scanning electron microscopy, transmission electron microscopy and UV-visible spectrophotometry. The EPD and DUV photolithography performances were explored and, in this study, it was clearly demonstrated that these two complementary methods are suitable, simple and effective processes to prepare controllable and tunable HfO2 nanostructures as with homogeneous, dense or micropatterned structures.

Controlling the Deposition Process of Nanoarchitectonic Nanocomposites Based on {Nb6-xTaxXi12}n+ Octahedral Cluster-Based Building Blocks (Xi = Cl, Br; 0 ≤ x ≤ 6, n = 2, 3, 4) for UV-NIR Blockers Coating Applications.

The antagonism between global energy needs and the obligation to slow global warming is a current challenge. In order to ensure sufficient thermal comfort, the automotive, housing and agricultural building sectors are major energy consumers. Solar control materials and more particularly, selective glazing are part of the solutions proposed to reduce global energy consumption and tackle global warming. In this context, these works are focused on developing new highly ultraviolet (UV) and near-infrared (NIR) absorbent nanocomposite coatings based on K4[{Nb6-xTaxXi12}Xa6]. (X = Cl, Br, 0 ≤ x ≤ 6) transition metal cluster compounds. These compounds contain cluster-based active species that are characterized by their strong absorption of UV and NIR radiations as well as their good transparency in the visible range, which makes them particularly attractive for window applications. Their integration, by solution processes, into a silica-polyethylene glycol or polyvinylpyrrolidone matrices is discussed. Of particular interest is the control and the tuning of their optical properties during the integration and shaping processes. The properties of the solutions and films were investigated by complementary techniques (UV-Vis-NIR spectrometry, ESI-MS, SEM, HRTEM, etc.). Results of these works have led to the development of versatile solar control coatings whose optical properties are competitive with commercialized material.

Nanoarchitectonics of Glass Coatings for Near-Infrared Shielding: From Solid-State Cluster-Based Niobium Chlorides to the Shaping of Nanocomposite Films.

The high potential of [{Nb6Cli12}La6] cluster-based building blocks as near-infrared radiation blockers for energy saving applications is exposed in the present paper (i = inner edge-bridging ligand, a = apical ligand of the Nb6; L = H2O and/or Cl). To do so, a combined experimental and theoretical investigation of edge-bridged [{Nb6Cli12}Cla6-x(H2O)x]m+/0/n- cluster unit series (x = 0, 4, 6; m = 2, 3, 4; n = 2, 3, 4) has been carried out. By using the K4[{Nb6Cli12}Cla6] starting solid-state precursor, we explored the behavior of the [{Nb6Cli12}Cla6]4- cluster unit during the different steps of its integration as a building block into a polyvinylpyrrolidone (PVP) matrix to form a glass coating composite denoted {Nb6Cli12}m+@PVP (m = 2 or 3). The optical, vibrational and redox properties [{Nb6Cli12}Cla6-x(H2O)x]m+/0/n- building blocks have been interpreted with the support of electronic structure calculations and simulation of properties. The chemical modifications and oxidation properties have been identified and studied thanks to various techniques in solution. Combining Raman and ultraviolet-visible spectroscopies, electrochemistry, and quantum chemical simulations, we bring new knowledge to the understanding of the evolution of the properties of the [{Nb6Cli12}Cla6-x(H2O)x]m+/0/n- cluster units as a function of the number of valence electron per cluster (VEC) and the nature of terminal ligands (x = 0, n = 4; x = 4, charge = 0; x = 6, m = 4). The fine understanding of the physical properties and vibrational fingerprints depending on the VEC and chemical modifications in solution are mandatory to master the processing of cluster-based building blocks for the controlled design and shaping of glass coating nanocomposites. On the basis of this acquired knowledge, [{Nb6Cli12}Cla6-x(H2O)x]m+/0/n- building blocks were embedded in a PVP matrix. The resulting {Nb6Cli12}2+@PVP nanocomposite film shows excellent ultraviolet (UV, 280-380 nm) and near-infrared (NIR, 780-1080 nm) blocking ability (>90%) and a highly visible light transmittance thanks to the controlled integration of the {Nb6Cli12}2+ cluster core. The figures of merit (FOM) value of Tvis/Tsol (Tvis = visible transmittance and Tsol = solar transmittance) as well as the haze, clarity, and the NIR shielding values (SNIR) were measured. After optimization of the integration process, a {Nb6Cli12}2+@PVP nanocomposite on glass substrate has been obtained with a high FOM equal to 1.29. This high value places the transparent green olive {Nb6Cli12}2+@PVP nanocomposites at the top system in the benchmark in the field of glass coating composites for energy-saving applications.

Video Processing Electrophoretic Measurements under High Electric Fields for Sub-millimeter Particles in Oil.

Electrokinetic properties such as the mobility, surface charge, and zeta potential of sub-millimeter particles are vital parameters in various industrial applications. Their measurement and control in aqueous media have been extensively studied. However, despite their growing importance, the electrokinetic properties of organic solvents have not been studied as thoroughly as those of aqueous media. An electrophoresis cell with a microscope monitor was designed for the electrokinetic studies of sub-millimeter particles in cyclohexane, which is a solvent with very low permittivity. The movement of large particles in the range of 4 ~ 478 µm was successfully traced under a strong electric voltage up to 1100 V, even without the addition of surfactants. The particle sizes were at least 300 times larger than those reported previously. By applying electric fields up to 55 kV/m, the electrophoretic mobilities were measured to be of the order of 10-9 to 10-7 m2/V∙s through image processing of the recorded particle movement. Five organic sub-millimeter particles had charge densities in the range of -3.5 ~ 4.4 e/µm2, and polyethersulfone particles showed extremely high mobilities. The surface charge of organic and inorganic particles is mainly generated by the dissociation of hydroxide groups or by the protonation to surface Lewis base oxygen atoms.

Evidence of the Ambipolar Behavior of Mo6 Cluster Iodides in All-Inorganic Solar Cells: A New Example of Nanoarchitectonic Concept.

Ambipolar materials such as carbon nanotubes, graphene, or 2D transition metal chalcogenides are very attractive for a large range of applications, namely, light-emitting transistors, logic circuits, gas sensors, flash memories, and solar cells. In this work, it is shown that the nanoarchitectonics of inorganic Mo6 cluster-based iodides enable to form thin films exhibiting photophysical properties that enable their classification as new members of the restricted family of ambipolar materials. Thus, the electronic properties of the ternary iodide Cs2[{Mo6I8i}I6a] and those of thin films of the aqua-complex-based compound [{Mo6I8i}I4a(H2O)2a]·xH2O were investigated through an in-depth photoelectrochemical study. Once hole/electron pairs are created, the holes and electrons turn to be transported simultaneously in opposite directions, and their lifetimes exhibit similar values. The ambipolar properties were demonstrated via the integration of [{Mo6I8i}I4a(H2O)2a]·xH2O as light harvesters in an all-solid solar cell. A significant photoresponse with a typical diode characteristic clearly provides evidence of the simultaneous transfer and transport of holes and electrons within the [{Mo6I8i}I4a(H2O)2a]·xH2O layer. The ambipolar behavior results, on the one hand, from the confinement of electrons imposed by the nanometric size of the molecular metal clusters and, on the other hand, from the poor electronic interactions between clusters in the solid state. Such molecular structure-based layers lead naturally to an intrinsic semiconducting behavior.

Synthesis of novel hexamolybdenum cluster-functionalized copper hydroxide nanocomposites and its catalytic activity for organic molecule degradation.

A novel heterogeneous catalytic nanomaterial based on a molybdenum cluster-based halide (MC) and a single-layered copper hydroxynitrate (CHN) was first prepared by colloidal processing under ambient conditions. The results of the elemental composition and crystalline pattern indicated that CHN was comprehensively synthesized with the support of the MC compound. The absorbing characteristic in the ultraviolet and near-infrared regions was promoted by both of the ingredients. The proper chemical interaction between the materials is a crucial reason to modify the structure of the MCs and only a small decrease in the magnetic susceptibility of CHN. The heterogeneous catalytic activity of the obtained MC@CHN material was found to have a high efficiency and excellent reuse when it is activated by hydrogen peroxide (H2O2) for the degrading reaction of the organic pollutant at room temperature. A reasonable catalytic mechanism was proposed to explain the distinct role of the copper compound, Mo6 compound, and H2O2 in the production of the radical hydroxyl ion. This novel nanomaterial will be an environmentally promising candidate for dye removal.

Spontaneously formed gradient chemical compositional structures of niobium doped titanium dioxide nanoparticles enhance ultraviolet- and visible-light photocatalytic performance.

Semiconductor photocatalysts showing excellent performance under irradiation of both ultraviolet (UV)- and visible (VIS)-light are highly demanded towards realization of sustainable energy systems. TiO2 is one of the most common photocatalysts and has been widely investigated as candidate showing UV/VIS responsive performance. In this study, we report synthesis of Nb doped TiO2 by environmentally benign mechanochemical reaction. Nb atoms were successfully incorporated into TiO2 lattice by applying mechanical energy. As synthesized Nb doped TiO2 were metastable phase and formed chemical compositional gradient structure of poorly Nb doped TiO2 core and highly Nb doped TiO2 surface after high temperature heat treatment. It was found that formed gradient chemical compositional heterojunctions effectively enhanced photocatalytic performance of Nb doped TiO2 under both of UV- and VIS-light irradiation, which is different trend compared with Nb doped TiO2 prepared through conventional methods. The approach shown here will be employed for versatile systems because of simple and environmentally benign process.

Revisiting properties of edge-bridged bromide tantalum clusters in the solid-state, in solution and vice versa: an intertwined experimental and modelling approach.

Edge-bridged halide tantalum clusters based on the {Ta6Br12}4+ core have been the topic of many physicostructural investigations both in solution and in the solid-state. Despite a large number of studies, the fundamental correlations between compositions, local symmetry, electronic structures of [{Ta6Bri12}La6]m+/n- cluster units (L = Br or H2O, in solution and in the solid-state), redox states, and vibrational and absorption properties are still not well established. Using K4[{Ta6Bri12}Bra6] as a starting precursor (i: inner and a: apical), we have investigated the behavior of the [{Ta6Bri12}Bra6]4- cluster unit in terms of oxidation properties and chemical modifications both in solution (water and organic solvent) and after recrystallization. A wide range of experimental techniques in combination with quantum chemical simulations afford new data that allow the puzzling behavior of the cluster units in response to changes in their environment to be revealed. Apical ligands undergo changes like modifications of interatomic distances to complete substitutions in solution that modify noticeably the cluster physical properties. Changes in the oxidation state of the cluster units also occur, which modify significantly their physical properties, including optical properties, which can thus be used as fingerprints. A subtle balance exists between the number of substituted apical ligands and the cluster oxidation state. This study provides new information about the exact nature of the species formed during the transition from the solid-state to solutions and vice versa. This shows new perspectives on optimization protocols for the design of Ta6 cluster-based materials.

Development of novel bone-like nanocomposite coating of hydroxyapatite/collagen on titanium by modified electrophoretic deposition.

Electrophoretic deposition (EPD) is a simple, rapid, and inexpensive technique to accomplish uniform coatings with controlled thicknesses. The EPD using binders that do not require a thermal degreasing process, which also eliminates the polymer components of the composite, are required for coating polymer-ceramic composites. This study demonstrated the application of a modified EPD technique utilizing Mg2+ ions to coat a bone-like hydroxyapatite/collagen nanocomposite (HAp/Col) on a titanium (Ti) substrate. The coating thickness was successfully controlled by varying the applied voltage and/or the treatment time. The adhesive strength of the modified EPD coating, evaluated by the tape test, showed class 0 (coating was not peeled off) and drastically increased in comparison to that of the non-Mg2+ EPD coating, class 5 (coating was completely peeled off). The MG63 cells on the HAp/Col-coated Ti demonstrated similar proliferation to and superior alkaline phosphatase activity to that on the bare Ti. Thus, the HAp/Col-coated Ti is expected to facilitate the surrounding bone formation than the bare-Ti. The results of the study indicated the HAp/Col-coated Ti prepared by the modified EPD is effective for applications in novel instruments, such as, subperiosteal temporary anchorage devices, which strongly requires rapid osseointegration at the bone-implant surface.

Electrophoretically Deposited Layers of Octahedral Molybdenum Cluster Complexes: A Promising Coating for Mitigation of Pathogenic Bacterial Biofilms under Blue Light.

The fight against infective microorganisms is becoming a worldwide priority due to serious concerns about the rising numbers of drug-resistant pathogenic bacteria. In this context, the inactivation of pathogens by singlet oxygen, O2(1Δg), produced by photosensitizers upon light irradiation has become an attractive strategy to combat drug-resistant microbes. To achieve this goal, we electrophoretically deposited O2(1Δg)-photosensitizing octahedral molybdenum cluster complexes on indium-tin oxide-coated glass plates. This procedure led to the first example of molecular photosensitizer layers able to photoinactivate bacterial biofilms. We delineated the morphology, composition, luminescence, and singlet oxygen formation of these layers and correlated these features with their antibacterial activity. Clearly, continuous 460 nm light irradiation imparted the layers with strong antibacterial properties, and the activity of these layers inhibited the biofilm formation and eradicated mature biofilms of Gram-positive Staphylococcus aureus and Enterococcus faecalis, as well as, Gram-negative Pseudomonas aeruginosa and Escherichia coli bacterial strains. Overall, the microstructure-related oxygen diffusivity of the layers and the water stability of the complexes were the most critical parameters for the efficient and durable use. These photoactive layers are attractive for the design of antibacterial surfaces activated by visible light and include additional functionalities such as the conversion of harmful UV/blue light to red light or oxygen sensing.

Zn-Al Layered Double Hydroxide Film Functionalized by a Luminescent Octahedral Molybdenum Cluster: Ultraviolet-Visible Photoconductivity Response.

A novel UV-Vis photodetector consisting of an octahedral molybdenum cluster-functionalized Zn2Al layered double hydroxide (LDH) has been successfully synthesized by co-precipitation and delamination methods under ambient conditions. The electrophoretic deposition process has been used as a low-cost, fast, and effective method to fabricate thin and transparent nanocomposite films containing a dense and regular layered structure. The study provided evidence that the presence of the Mo6 cluster units between the LDH does not affect the ionic conduction mechanism of the LDH, which linearly depends on the relative humidity and temperature. Moreover, the photocurrent response is remarkably extended to the visible domain. The reproducibility and stabilization of the photocurrent response caused by the Mo6 cluster-functionalized LDH have been verified upon light excitation at 540 nm. Additionally, it was demonstrated that the films show advantageously strong adherence properties for application requirements.

Robust Structurally Colored Coatings Composed of Colloidal Arrays Prepared by the Cathodic Electrophoretic Deposition Method with Metal Cation Additives.

Structurally colored coatings composed of colloidal arrays of monodisperse spherical particles have attracted great attention owing to their versatile advantages, such as low cost, resistance to fading, and low impacts on the environment and human health. However, the weak mechanical stability is considered to be a major obstacle for their practical applications as colorants. Although several approaches based on the addition of polymer additives to enhance the adhesion of particles have been reported, the challenge remains to develop a strategy for the preparation of structurally colored coatings with extremely high robustness using a simple process. Here, we have developed a novel approach to fabricate robust structurally colored coatings by cathodic electrophoretic deposition. The addition of a metal salt, i.e., Mg(NO3)2, to the coating dispersion allows SiO2 particles to have a positive charge, which enables the electrophoresis of SiO2 particles toward the cathode. At the cathode, Mg(OH)2 codeposits with SiO2 particles because OH- ions are generated by the decomposition of dissolved oxygen and NO3- ions. The mechanical stability of the colloidal arrays obtained by this process is remarkably improved because Mg(OH)2 facilitates the adhesion of the particles and substrates. The brilliant structural color is maintained even after several cycles of the sandpaper abrasion test. We have also demonstrated the coating on a stainless steel fork. This demonstration reveals that our approach enables a homogeneous coating on a complicated surface. Furthermore, the high durability of the coating is clarified because the coating did not peel off even when the fork was stuck into a plastic eraser. Therefore, the coating technique developed here will provide an effective method for the pervasive application of the structural color as a colorant.

Rapid Growth of Colloidal Crystal Films from the Concentrated Aqueous Ethanol Suspension.

Developing a rapid fabrication of colloidal crystal film is one of the technical issues to apply to wide and various fields. We have been investigating a drying process of colloidal aqueous ethanol (EtOH) suspension formed by electrophoretic deposition (EPD). Here, the detailed formation mechanism of the colloidal crystal films with the closest packing structure was investigated by optical microscope and spectroscopy. The growth mechanism from the colloidal suspension to the colloidal crystal film was found to consist of four stages. In the first stage, concentrated colloidal suspension changed to order structure, i.e., nonclosely packed colloidal crystal by Alder phase transition. After this crystallization, we observed Bragg's diffraction peak and structural color. In the second stage, the diffraction peak shifts toward the shorter-wavelength direction (blue shift) due to the reduction of the interparticle distance of the nonclosely packed colloidal crystal. Finally, this peak shift continued until the closely packed colloidal crystal film was formed. In the third stage, the diffraction peak kept almost a similar wavelength due to the liquid film of aqueous EtOH covering on the colloidal crystal film. In the fourth stage, the colloidal crystal film changed from wet to dry condition. The structural color changes from green to blue by the evaporation of the solvent from the interspace of the colloidal crystal film. This color change is explained by the change in the refractive index of the interparticle medium from solvent to air. One of the key findings in our process is a rapid crystal growth using concentrated colloid aqueous EtOH suspension. Drying the concentrated suspension formed a closely packed colloidal crystal film within 55 s. This process has the potential for high-speed deposition of the colloidal crystalline thin films.

Enhanced visible-light photocatalytic activity of anatase-rutile mixed-phase nano-size powder given by high-temperature heat treatment.

Nano-size EVONIK AEROXIDE® P25 titanium dioxide, TiO2, powder was heat-treated at temperatures, 700-900°C, in air. An X-ray diffraction study showed that the P25 powder is composed of approximately 20 and approximately 80 mass% of rutile and anatase phases, respectively. It was also shown that the transformation from anatase to rutile induced by high-temperature heat treatment was almost completed at 750°C, whereas a small amount (less than 3 mass%) of anatase phase was still left even in the powder heat-treated at 900°C. The transformation behaviour was consistent with results obtained by Raman scattering spectroscopy. Raman experiments also indicated that high-temperature heating induced the formation of oxide ion vacancies. Powders were dispersed in methyl orange (MO) aqueous solution, and the bleach rate of MO was measured to evaluate photocatalytic activity under ultraviolet (UV)- and visible-light irradiation. After the heat treatment, the UV-light photocatalytic performance sharply deteriorated. Interestingly, visible-light photocatalytic activity was enhanced by high-temperature heating and reached the highest performance for an 800°C-heated sample, indicating that the P25 powder obtained high visible-light photocatalytic performance after heat treatment. Even after 900°C heat treatment, the photocatalytic performance was higher than that of as-received powder. Enhancement of photocatalytic activities was discussed in relation to visible light absorption and charge carrier transfer.