Synthesis of a Hybrid Composed of Anisotropic Niobate Layers Modified with MoC Nanoparticles.

The hybrid composed of anisotropic niobate layers modified with MoC nanoparticles is synthesized by multistep reactions. The stepwise interlayer reactions for layered hexaniobate induce selective surface modification at the alternate interlayers, and the following ultrasonication leads to the formation of double-layered nanosheets. The further liquid phase MoC deposition with the double-layered nanosheets leads to the decoration of MoC nanoparticles on the surfaces of the double-layered nanosheets. The new hybrid can be regarded as a stacking of the two layers with anisotropically modified nanoparticles. The relatively high temperature in the MoC synthesis causes partial leaching of the grafted phosphonate groups. The exposed surface of the niobate nanosheets due to the partial leaching may interact with MoC to succeed in the hybridization. The hybrid after heating exhibits photocatalytic activity, indicating that this hybridization method can be useful for hybrid synthesis of semiconductor nanosheets and co-catalyst nanoparticles toward photocatalytic application.

Bridging the Gap between Zeolites and Dense Silica Polymorphs: Formation of All-Silica Zeolite with High Framework Density from Natural Layered Silicate Magadiite.

A silica zeolite (RWZ-1) with a very high framework density (FD) was synthesized from highly crystalline natural layered silicate magadiite, bridging the gap between the two research areas of zeolites and dense silica polymorphs. Magadiite was topotactically converted into a 3D framework through two-step heat treatment. The resulting structure had a 1D micropore system of channel-like cavities with an FD of 22.1 Si atoms/1000 Å3 . This value is higher than those of all other silica zeolites reported so far, approaching those of silica polymorphs (tridymite (22.6) and α-quartz (26.5)). RWZ-1 is a slight negative thermal expansion material with thermal properties approaching those of dense silica polymorphs. It contributes to the creation of a new field on microporous high-density silica/silicates. Synergistic interactions are expected between the micropores with molecular sieving properties and the dense layer-like building units with different topologies which provide thermal and mechanical stabilities.

Phase Transfer of Inorganic Nanosheets in a Water/2-Butanone Biphasic System and Lateral Size Fractionation via Stepwise Extractions.

Lateral size fractionation of niobate nanosheets derived from K4Nb6O17·3H2O was achieved via phase transfer from the aqueous phase to the 2-butanone phase in a water/2-butanone biphasic system, in which tetra-n-dodecylammonium (TDDA+) bromide was used as a phase transfer reagent. Phase transfer of the nanosheets was observed when the TDDA+/[Nb6O17]4- molar ratios were 0.6 and 1.0, and the phase transfer ratios were 41 and 97%, respectively. FT-IR and thermogravimetry results showed that the extracted nanosheets contained TDDA+ ions. These results indicate that adsorption of TDDA+ likely induced an increase in the hydrophobicity of the nanosheet surface, leading to phase transfer. In the AFM image of the original nanosheets in the aqueous phase, their lateral sizes were in the range from several hundreds of nm to several tens of µm, while those of the nanosheets after phase transfer at a molar ratio of 0.6 were in the range from several hundreds of nm up to 2 µm, indicating that nanosheets with smaller lateral sizes were preferentially extracted into the 2-butanone phase. In addition, the phase transfer ratio of the fragmentated nanosheets with a much smaller lateral size distribution compared with the original nanosheets was 79% when the TDDA+/[Nb6O17]4- molar ratio was 0.6, indicating that phase transfer for the nanosheets with smaller lateral sizes proceeded efficiently. Following this extraction cycle, the nanosheets with a TDDA+/[Nb6O17]4- molar ratio of 0.6 remaining in the aqueous phase after extraction were extracted stepwise again through dilution of the aqueous phase with water and the addition of a fresh 2-butanone solution of tetra-n-dodecylammonium bromide to form a new biphasic system. The lateral sizes of the nanosheets increased as the extraction cycles were repeated. Completion of the three extraction cycles allowed formation of the three classes of the nanosheets with different lateral size ranges of 0.68 ± 0.5, 2.8 ± 1.9, and 6.6 ± 3.1 µm.

Modulating Electronic Metal-Support Interactions to Boost Visible-Light-Driven Hydrolysis of Ammonia Borane: Nickel-Platinum Nanoparticles Supported on Phosphorus-Doped Titania.

Ammonia borane (AB) is a promising material for chemical H2 storage owing to its high H2 density (up to 19.6 wt %). However, the development of an efficient catalyst for driving H2 evolution through AB hydrolysis remains challenging. Therefore, a visible-light-driven strategy for generating H2 through AB hydrolysis was implemented in this study using Ni-Pt nanoparticles supported on phosphorus-doped TiO2 (Ni-Pt/P-TiO2 ) as photocatalysts. Through surface engineering, P-TiO2 was prepared by phytic-acid-assisted phosphorization and then employed as an ideal support for immobilizing Ni-Pt nanoparticles via a facile co-reduction strategy. Under visible-light irradiation at 283 K, Ni40 Pt60 /P-TiO2 exhibited improved recyclability and a high turnover frequency of 967.8 mol H 2 ${{_{{\rm H}{_{2}}}}}$ molPt -1 min-1 . Characterization experiments and density functional theory calculations indicated that the enhanced performance of Ni40 Pt60 /P-TiO2 originated from a combination of the Ni-Pt alloying effect, the Mott-Schottky junction at the metal-semiconductor interface, and strong metal-support interactions. These findings not only underscore the benefits of utilizing multipronged effects to construct highly active AB-hydrolyzing catalysts, but also pave a path toward designing high-performance catalysts by surface engineering to modulate the electronic metal-support interactions for other visible-light-induced reactions.

Materials Space-Tectonics: Atomic-level Compositional and Spatial Control Methodologies for Synthesis of Future Materials.

Reactions occurring at surfaces and interfaces necessitate the creation of well-designed surface and interfacial structures. To achieve a combination of bulk material (i.e., framework) and void spaces, a meticulous process of "nano-architecting" of the available space is necessary. Conventional porous materials such as mesoporous silica, zeolites, and metal-organic frameworks lack advanced cooperative functionalities owing to their largely monotonous pore geometries and limited conductivities. To overcome these limitations and develop functional structures with surface-specific functions, the novel materials space-tectonics methodology has been proposed for future materials synthesis. This review summarizes recent examples of materials synthesis based on designing building blocks (i.e., tectons) and their hybridization, along with practical guidelines for implementing materials syntheses and state-of-the-art examples of practical applications. Lastly, the potential integration of materials space-tectonics with emerging technologies, such as materials informatics, is discussed.

Cerium(III) Niobate Layered Perovskites: Abnormal Optical Absorption Modulations by Tuning of B-Site Composition and Perovskite Layer Charge Control.

The cerium-introduced layered perovskite of RbCeTa2O7 has exhibited a specific optical absorption due to metal-to-metal charge transfer transitions between Ce 4f and transition metal d-orbitals to show the unique pale-green coloration, which is different from conventional coloration mechanisms. To further extend the coloring state based on the same mechanism, in this work, a series of the [Ce(Ta,Nb)2O7]- layered perovskites, Rb1-xCsx[Ce(Ta1-xNbx)2O7] (x = 0∼1), with Nb substitutions in the perovskite units have been prepared and investigated in terms of those crystal structures and optical absorption mechanism. The Rietveld analysis using the XRD profile and EXAFS analyses well refined those structures as the Dion-Jacobson-type layered perovskite. The color of solid solutions gradually changed from pale-green to dark reddish-brown with increasing amount of substituted niobium. The unique coloring state change behavior of solid solutions from pale-green to dark reddish-brown depending on the amount of the substituted niobium is not observed in the other layered perovskite analogues (e.g., La and Pr analogues). The first-principles calculation based on the density functional theory method indicated that the band structural change should be a key factor for the coloration modulation. Furthermore, the redox ability through the charge modulation of the perovskite layer, which is a specific function of the cerium-based layered perovskite, was also investigated for the niobate [CeNb2O7]- perovskite layer, resulting in the anisotropic lattice changes similar to those of a Ta analogue with different structural changes in the stacking and in-plane directions. The accompanying change in electronic structure led to a clear modulation in optical absorption, yielding a drastic change in the coloring state from dark brown to yellow.

Synthesis of NaMoO3F and Na5W3O9F5 with Morphological Controllability in Non-Aqueous Solvents.

NaMoO3F and Na5W3O9F5 were synthesized by solvothermal reaction of MoO3 and WO3, respectively, with NaF in nonaqueous solvents. These reactions were realized at low temperatures (150-200 °C) without the use of HF. This synthesis method is much more facile and safe procedure compared with general synthesis methods for oxyfluorides which includes hydrothermal reaction under a presence of HF or solid-state reaction at high temperatures in vacuum sealed tube or under high pressure. In the case of the reaction of MoO3 with NaF, the kind of solvent largely affected the obtained morphologies of NaMoO3F. The morphology in the case of acetonitrile as a solvent was rodlike with a micrometer-scale size, while that in the case of ethanol was polyhedral with a size of several hundred nanometers. In addition, the solvothermal reaction of WO3 with NaF led to the formation of Na5W3O9F5. Also, the difference of solvents for the solvothermal reaction affected the obtained particle sizes. The effect of the solvents on the morphologies of the obtained oxyfluorides probably resulted from the difference of the solubility of NaF and the subsequent dissolution ratio of MoO3 or WO3 in the used solvents. Our synthesis method can expand the applicability of oxyfluorides by providing a new phase and/or unique morphology.

High yield post-thermal treatment of bulk graphitic carbon nitride with tunable band structure for enhanced deNOx photocatalysis.

The bulk graphitic carbon nitride (CN) suffers from low specific surface area, which limits its practical application for air purification. Here, we reported a facile post-thermal treatment to break bulk CN into nanosheets whose specific surface areas increased from 13.6 m2 g-1 to 68.0 m2 g-1. The yield of CN nanosheets reached up to 67%, and its photocatalytic decomposition of NOx activity was about 3.0 times higher than that of bulk CN. Moreover, the CN nanosheets obtained at 550 °C with higher specific surface area (113.9 m2 g-1) displayed lower photocatalytic activity than that obtained at 500 °C with lower specific surface area (68.0 m2 g-1), which was attributed to its lower valence band. This study illustrates that many factors including specific surface area and band structure could affect the performance of photocatalysts so that it is necessary to take account of various factors. Moreover, the facile and high yield thermal treatment provides the foundation for further large-scale industrial applications.

Supercritical temperature synthesis of fluorine-doped VO2(M) nanoparticle with improved thermochromic property.

Fluorine-doped VO2(M) nanoparticles have been successfully synthesized using the hydrothermal method at a supercritical temperature of 490 °C. The pristine VO2(M) has the critical phase transformation temperature of 64 °C. The morphology and homogeneity of the monoclinic structure VO2(M) were adopted by the fluorine-doped system. The obtained particle size of the samples is smaller at the higher concentration of anion doping. The best reduction of critical temperature was achieved by fluorine doping of 0.13% up to 48 °C. The thin films of the fluorine-doped VO2(M) showed pronounced thermochromic property and therefore are suitable for smart window applications.

Multifunctionality in coating films including Nb-doped TiO2 and Cs x WO3: near infrared shielding and photocatalytic properties.

Various types of coating films were obtained from hydrothermally synthesized Nb-doped TiO2 (NTO) and Cs x WO3 (CWO) nanoparticles. The coating films possessed multifunctionality including near infrared (NIR) absorption and photocatalysis abilities. The NTO and CWO nanoparticles were synthesized by a unique solvothermal reaction in which water induced by an esterification reaction between alcohol and carboxylic acid can act as a hydrolyzing agent for metal precursors. NTO was synthesized by the unique solvothermal reaction for the first time. The reaction accompanied by the reduction of Ti4+ to Ti3+ led to the formation of nanoparticles with both NIR absorption and photocatalytic properties. The effect of the ethanol-acetic acid ratio on the morphology of the obtained NTO was investigated, and the larger amount of acetic acid led to a larger nanoparticle size, indicating the size controllability. The two types of coating film, including CWO and NTO nanoparticles, were obtained for comparison: (1) coexistent coating film: one side of the quartz glass was coated with a dispersion, including both CWO and NTO nanoparticles, and (2) double-sided coating film: a quartz glass coated with a CWO dispersion on one side and an NTO dispersion on the other side. The double-sided coating led to higher multifunctionality. Furthermore, the optimized condition for the double-sided coating was investigated by using various NTO particles obtained using different ethanol-acetic acid ratios.

Synthesis of a Single-Crystalline Macroporous Layered Silicate from a Macroporous UTL-Type Zeolite and Its Accelerated Intercalation.

A single-crystalline macroporous layered silicate was obtained for the first time. Firstly, UTL-type zeolite with macropores was prepared hydrothermally under the presence of acetylene black as a macropore template and the subsequent calcination to remove the template. Double four-membered ring (d4r) units in the UTL framework were selectively dissolved to yield a layered silicate with macropores. Intercalation of tetrabutylammonium ions into the macroporous layered silicate is accelerated if compared with that into the same silicate without macropores, indicating the effectiveness of macropores due to easy diffusion. The layered silicate with macropores was converted into PCR-type zeolite with macropores, a hierarchically micro- and macroporous material, through interlayer condensation.

Highly Efficient Water Oxidation Photoanode Made of Surface Modified LaTiO2 N Particles.

An improved variation of highly active/durable O2 -evolving LaTiO2 N powder-based photoelectrode has been fabricated by pre-cleaning the powder with mild polysulfonic acid and by homogeneous deposition of CoOx co-catalyst aided by microwave annealing. The treatment in aqueous solution of poly(4-styrene sulfonic acid) results in removal of surface LaTiO2 N layers, forming fine pores in the crystallites. The CoOx co-catalyst by microwave deposition in Co(NH3 )6 Cl3 /ethylene glycol homogeneously covers the particle surface. The LaTiO2 N powder is fabricated into particle-transferred electrodes on Ti thin film supported on solid substrate. The modified LaTiO2 N grains on the electrode serve as a highly active O2 -evolving photoanode achieving 8.9 mA cm-2 of the photocurrent density at 1.23 V versus reversible hydrogen electrode (RHE) in 0.1 m NaOH (pH 13) under solar-simulator irradiation Airmass 1.5 Global (AM 1.5G). The activity has been much improved, compared with conventional LaTiO2 N treated in mineral acid or with CoOx deposited by impregnation. The new electrode also exhibits better durability in fixed-potential chronoamperometric tests under AM 1.5G irradiation.

Proton tunneling in low dimensional cesium silicate LDS-1.

In low dimensional cesium silicate LDS-1 (monoclinic phase of CsHSi2O5), anomalous infrared absorption bands observed at 93, 155, 1210, and 1220 cm(-1) are assigned to the vibrational mode of protons, which contribute to the strong hydrogen bonding between terminal oxygen atoms of silicate chain (O-O distance = 2.45 Å). The integrated absorbance (oscillator strength) for those modes is drastically enhanced at low temperatures. The analysis of integrated absorbance employing two different anharmonic double-minimum potentials makes clear that proton tunneling through the potential barrier yields an energy splitting of the ground state. The absorption bands at 93 and 155 cm(-1), which correspond to the different vibrational modes of protons, are attributed to the optical transition between the splitting levels (excitation from the ground state (n = 0) to the first excited state (n = 1)). Moreover, the absorption bands at 1210 and 1220 cm(-1) are identified as the optical transition from the ground state (n = 0) to the third excited state (n = 3). Weak Coulomb interactions in between the adjacent protons generate two types of vibrational modes: symmetric mode (93 and 1210 cm(-1)) and asymmetric mode (155 and 1220 cm(-1)). The broad absorption at 100-600 cm(-1) reveals an emergence of collective mode due to the vibration of silicate chain coupled not only with the local oscillation of Cs(+) but also with the proton oscillation relevant to the second excited state (n = 2).

Topotactic conversion of ß-helix-layered silicate into AST-type zeolite through successive interlayer modifications.

AST-type zeolite with a plate morphology can be synthesized by topotactic conversion of a layered silicate (ß-helix-layered silicate; HLS) by using N,N-dimethylpropionamide (DPA) to control the layer stacking of silicate layers and the subsequent interlayer condensation. Treatment of HLS twice with 1) hydrochloric acid/ethanol and 2) dimethylsulfoxide (DMSO) are needed to remove interlayer hydrated Na ions and tetramethylammonium (TMA) ions in intralayer cup-like cavities (intracavity TMA ions), both of which are introduced during the preparation of HLS. The utilization of an amide molecule is effective for the control of the stacking sequence of silicate layers. This method could be applicable to various layered silicates that cannot be topotactically converted into three-dimensional networks by simple interlayer condensation by judicious choice of amide molecules.

Covalent Organic Framework Nanoarchitectonics: Recent Advances for Precious Metal Recovery.

The recovery of precious metals (PMs) from secondary resources has garnered significant attention due to environmental and economic considerations. Covalent organic frameworks (COFs) have emerged as promising adsorbents for this purpose, owing to their tunable pore size, facile functionalization, exceptional chemical stability, and large specific surface area. This review provides an overview of the latest research progress in utilizing COFs to recover PMs. Firstly, the design and synthesis strategies of chemically stable COF-based materials, including pristine COFs, functionalized COFs, and COF-based composites, are delineated. Furthermore, the application of COFs in the recovery of gold, silver, and platinum group elements is delved into, emphasizing their high adsorption capacity and selectivity as well as recycling ability. Additionally, various interaction mechanisms between COFs and PM ions are analyzed. Finally, the current challenges faced by COFs in the field of PM recovery are discussed, and potential directions for future development are proposed, including enhancing the recyclability and reusability of COF materials and realizing the high recovery of PMs from actual acidic wastewater. With the targeted development of COF-based materials, the recovery of PMs can be realized more economically and efficiently in the future.

Effect of salinity on arsenic uptake, biotransformation, and time-dependent speciation pattern by Sargassum species.

The arsenic (As) content of seaweed has been extensively studied due to its toxicological concerns. As a primary producer, seaweed plays a vital role in the biochemical cycling of As in marine environments. Several studies have focused on the growth and behavior of seaweed under a salinity gradient; however, information related to the impact of salinity on As uptake, biotransformation mechanism, and time-dependent speciation patterns of these plants is limited. This study aimed to investigate the temporal effects of salinity on these factors in seaweed. Three seaweed species, Sargassum fusiforme, Sargassum thunbergii, and Sargassum horneri, were maintained in a 1% Provasoli-enriched seawater medium for 14 d under 5‰, 15‰, 25‰, and 34‰ salinities. The results revealed that the high salinity media promoted a rapid uptake of As by all three species. Arsenic accumulation inside the cell approached 100% within seven days of culture for S. thunbergii, irrespective of the salinity content of the media. In addition, As(V) biotransformation and release by S. fusiforme and S. thunbergii were time-dependent, while S. horneri released dimethylarsinic acid (DMAA) from day 3 of the culture. All seaweed species showed methylation of As(V) to DMAA during the culture period. Furthermore, S. thunbergii released DMAA when As(V) was completely depleted from the culture media, whereas the release by S. fusiforme and S. horneri was relatively earlier than that of S. thunbergii. S. horneri showed minimal tolerance to low salinity, as the cells revealed significant damage. Based on the results of this study, a conceptual model was developed that demonstrated the effects of salinity on As uptake and the biotransformation mechanism of seaweed.

Nanoarchitectonics of Hollow Covalent Organic Frameworks: Synthesis and Applications.

Hollow covalent organic frameworks (COFs) have gained significant attention because of their specific properties, including enhanced surface-to-volume ratio, large surface area, hierarchical structure, highly ordered nanostructures, and excellent chemical stability. These intrinsic characteristics endow hollow COFs with fascinating physicochemical properties and make them highly attractive for widespread applications, such as catalysis, energy storage, drug delivery, therapy, sensing, and environmental remediation. This review focuses on the recent developments in the synthesis of hollow COFs and their derivatives. In addition, their practical applications in various fields are summarized. Finally, challenges and future opportunities in terms of their synthetic methodologies and practical applications are discussed. Hollow COFs are expected to play an important role in the future of materials science.

Water Activation in Solar-Powered Vapor Generation.

Solar-powered vapor evaporation (SVG), based on the liquid-gas phase conversion concept using solar energy, has been given close attention as a promising technology to address the global water shortage. At molecular level, water molecules escaping from liquid water should overcome the attraction of the molecules on the liquid surface layer to evaporate. For this reason, it is better to reduce the energy required for evaporation by breaking a smaller number of hydrogen bonds or forming weak hydrogen bonds to ensure efficient and convenient vapor production. Many novel evaporator materials and effective water activation strategies have been proposed to stimulate rapid steam production and surpass the theoretical thermal limit. However, an in-depth understanding of the phase/enthalpy change process of water evaporation is unclear. In this review, a summary of theoretical analyses of vaporization enthalpy, general calculations, and characterization methods is provided. Various water activation mechanisms are also outlined to reduce evaporation enthalpy in evaporators. Moreover, unsolved issues associated with water activation are critically discussed to provide a direction for future research. Meanwhile, significant pioneering developments made in SVG are highlighted, hoping to provide a relatively entire chain for more scholars who are just stepping into this field.