Nanostructured tungsten oxide as photochromic material for smart devices,energy conversion,and environmental remediation

The reversible photochromic response of tungsten oxide (WO₃) holds promise for solar-related applications as it is capable of photo charging during illumination (color-switching) and spontaneous discharging post-illumination (self-bleaching). Advances in WO₃-based nanostructures synthesis via micro/nanofabrication techniques have created remarkable potential application opportunities. Smart windows represent a typical energy-saving technology; ultraviolet indicators can sense radiation safety limits, and the around-the-clock photocatalysts can be used for pollutant degradation and bacterial disinfection applications. These materials, their distinct properties, and the effects of their application must be comprehensively understood prior to commercialization. In this work, we first summarize the affiliation between the crystallographic properties-optical features-photochromic behavior of WO₃. Several photochromic models and kinetic equations are then presented, accompanied by the related characterization techniques and evaluation methods. The factors affecting photochromic efficiency (e.g., light absorption, surface reaction, and carrier migration) are delineated to clarify the advantages of the specific nanostructured WO₃ and the most efficient available strategies for constructing WO₃-based nanomaterials. The theory, technique, and performance associated with chromogenic applications in smart devices, energy conversion, and environmental remediation are deliberated in detail. Finally, we outline the challenges and emerging trends in this area calling for further innovation to fill various gaps.     

Chiral Side Groups Trigger Second Harmonic Generation Activity in 3D Octupolar Bipyrimidine‐Based Organic Liquid Crystals

The design of efficient noncentrosymmetric materials remains the ultimate goal in the field of organic second‐order nonlinear optics. Unlike inorganic crystals currently used in second‐order nonlinear optical applications, organic materials are an attractive alternative owing to their fast electro‐optical response and processability, but their alignment into noncentrosymmetric film remains challenging. Here, symmetry breaking by judicious functionalization of 3D organic octupoles allows the emergence of multifunctional liquid crystalline chromophores which can easily be processed into large, flexible, thin, and self‐oriented films with second harmonic generation responses competitive to the prototypical inorganic KH₂PO₄ crystals. The liquid‐crystalline nature of these chiral organic films also permits the modulation of the nonlinear optical properties owing to the sensitivity of the supramolecular organization to temperature, leading to the development of tunable macroscopic materials.     

Nanoparticles from the Vapor Phase: Synthesis and Characterization of Si, Ge, MoO3, and WO3Nanocrystals

In this paper, we present two studies of nanocrystals prepared by the pulsed laser vaporization–controlled condensation (LVCC) technique. In the first study, we present a comparison between the surface oxidation, morphology and the photoluminescence (PL) properties of Si and Ge nanocrystals. In the second study, we compare the photochromic properties of Mo and W oxides nanoparticles with the properties of the corresponding bulk materials. We also present evidence for a novel photoreduction of the white WO₃ nanoparticles into the blue W₂O₅ following the irradiation of the particles with the second harmonic of the Nd:YAG laser in air. These studies illustrate the novel properties of the nanoscale particles, which could lead to significant practical and technological applications.     

Scalable Preparation of Photochromic Composite Foils with Excellent Reversibility for Light Printing

Photochromic inks for repeatable light‐printed media have attracted increasing attention owing to the fact that they may be widely applied to reduce the consumption of papers and plastics and conserve the environment. Therefore, it is of practical significance to develop convenient photochromic inks with a low cost and on a large scale. In this study, a simple one‐step hydrothermal route was used to prepare tungsten trioxide (WO₃) nanoparticles, which were further used to make photochromic inks and transparent photochromic films. The obtained transparent photochromic film could rapidly respond to UV light within tens of seconds, then return to its initial state, with different recovery times at different temperatures, and also exhibit good reversible coloration–bleaching effect. A typical polyethylene terephthalate (PET) foil coated with the photochromic ink could also be repeatedly printed with various patterns and displayed excellent rewritable performance over tens of cycles. This study proposes a simple method for widespread applications of WO₃‐based photochromic inks.     

Preparation and Characterization of Epoxy/Inorganic Anti‐electrostatic Nanocomposites Using Submicrometer Al(OH)3 and Colloid Al2O3

New organic‐inorganic hybrid materials and their anti‐electrostatic hybrid membranes are prepared via sol‐gel process. The polycondensation of epoxy oligomers and AEAPS/Al₂O₃ complexes which are organically surface modified submicrometer aluminum trihydroxide inorganic fillers with an active aminoterminal silane coupling agent, N‐(2‐aminoethyl)‐3‐aminopropyltrimethoxysilane (AEAPS), are performed. AEAPS enhances the interfacial interactions between the inorganic fillers and epoxy polymers. Meanwhile, this coupling agent maintains well dispersion of fillers in these composites. To improve the mechanical strength and thermal stability, pyromellitic dianhydride (PMDA) is used as curing agent. These hybrid films prepared from this method have excellent physical properties, such as UV‐shielding, high transmission in visible resign (> 85%), high hardness (7～8H) , high adhesive force (7～8) and low relative surface resistance (9.71 × 10¹¹～1.26 × 10¹⁰ Ω/cm²) with anti‐electrostatic characters. For thermal resistance, the best Td value of epoxy/PMDA/AEAPS/Al₂O₃ is 378.6 °C which is 85.4 °C higher than that of neat epoxy resin. Physical properties of these materials are almost the same as those of the nanocomposites prepared from expensive colloid Al₂O₃. Evidences from TEM micrograph show that the inorganic additives are dispersed evenly in organic matrix with nanometer scale.     

Highly Ordered Mesoporous Tungsten Oxides with a Large Pore Size and Crystalline Framework for H2S Sensing

An ordered mesoporous WO₃ material with a highly crystalline framework was synthesized by using amphiphilic poly(ethylene oxide)‐b‐polystyrene (PEO‐b‐PS) diblock copolymers as a structure‐directing agent through a solvent‐evaporation‐induced self‐assembly method combined with a simple template‐carbonization strategy. The obtained mesoporous WO₃ materials have a large uniform mesopore size (ca. 10.9 nm) and a high surface area (ca. 121 m² g^?1). The mesoporous WO₃‐based H₂S gas sensor shows an excellent performance for H₂S sensing at low concentration (0.25 ppm) with fast response (2 s) and recovery (38 s). The high mesoporosity and continuous crystalline framework are responsible for the excellent performance in H₂S sensing.     

The use of poly(alkylene oxide)s to achieve fast and controlled photochromic switching in rigid matrices

We report a conjugation system for the enhancement of photochromic dye performance in rigid matrices using widely available, cheap, chemically robust and compatible polymeric starting materials, namely poly(propylene oxide) (PPO) and poly(1,2‐butylene oxide). Conjugation of these soft (low T_g) polymers to an indeno‐fused naphthopyran photochromic dye, in a telechelic geometry, gives access to a wide range of accelerated and tuned fade speeds (decoloration) via variation in molecular weight. The t_1/2 and t_3/4 fade speeds for PPO conjugates (polymer molecular weights ranging between ca. 425 and 2000) are accelerated by 35–58 and 51–76%, respectively, compared with the nonconjugated control dye. Longer oligomers provide faster decoloration approaching that obtained in solution. The stability of the polyethers allows functionalization using a wide variety of chemistries, including harsh acid catalyzed transformations, providing an overall facile synthesis of photochromic dye‐polymer conjugates in high yield and purity. In addition, these polymers give easy access to conjugates with star‐type architectures, which provide an even further improvement in performance compared with their linear counterparts with less conjugated polymer needed per dye to achieve a given fade speed. © 2012 Commonwealth of Australia. J Polym Sci Part A: Polym Chem, 2012     

Polypyrrolones for membrane gas separations. I. Structural comparison of gas transport and sorption properties

Despite efforts by the membrane community to develop polymeric materials with improved O₂/N₂ separation performance, limited progress has occurred for almost a decade. Molecular sieving media, which can exhibit gas separation properties superior to polymers, tend to be brittle and uneconomical to produce for large‐scale membrane separation processes. Considering this, the polymer structures investigated in this work were designed to mimic aspects of the structure of molecular sieving media such as zeolites and carbon molecular sieves while maintaining the processability associated with polymers. Significantly attractive gas separation material properties were obtained using hyper rigid polypyrrolone copolymers with controlled packing disruptions between flat, packable segments. The gas transport properties in the materials changed dramatically as a result of different average interchain spacing. Moreover, all of the polypyrrolones studied in this work exhibited performance lying on or above the existing O₂/N₂ upper bound trade‐off line between permselectivity and permeability. These results, therefore, may point the way to a new cycle of membrane materials improvements for gas separations. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1235–1249, 1999     

Electropolymerization of Molecular‐Sieving Polythiophene Membranes for H2 Separation

Membrane technologies that do not rely on heat for industrial gas separation would lower global energy cost. While polymeric, inorganic, and mixed‐matrix separation membranes have been rapidly developed, the bottleneck is balancing the processability, selectivity, and permeability. Reported here is a softness adjustment of rigid networks (SARs) strategy to produce flexible, stand‐alone, and molecular‐sieving membranes by electropolymerization. Here, 14 membranes were rationally designed and synthesized and their gas separation ability and mechanical performance were studied. The separation performance of the membranes for H₂/CO₂, H₂/N₂, and H₂/CH₄ can exceed the Robeson upper bound, among which, H₂/CO₂ separation selectivity reaches 50 with 626 Barrer of H₂ permeability. The long‐term and chemical stability tests demonstrate their potential for industrial applications. This simple, scalable, and cost‐effective strategy holds promise for the design other polymers for key energy‐intensive separations.     

Synthesis of WOn‐WX2 (n=2.7, 2.9; X=S,Se) Heterostructures for Highly Efficient Green Quantum Dot Light‐Emitting Diodes

Preparation of two‐dimensional (2D) heterostructures is important not only fundamentally, but also technologically for applications in electronics and optoelectronics. Herein, we report a facile colloidal method for the synthesis of WO_n ‐WX₂ (n =2.7, 2.9; X=S, Se) heterostructures by sulfurization or selenization of WO_n nanomaterials. The WO_n ‐WX₂ heterostructures are composed of WO_2.9 nanoparticles (NPs) or WO_2.7 nanowires (NWs) grown together with single‐ or few‐layer WX₂ nanosheets (NSs). As a proof‐of‐concept application, the WO_n ‐WX₂ heterostructures are used as the anode interfacial buffer layer for green quantum dot light‐emitting diodes (QLEDs). The QLED prepared with WO_2.9 NP‐WSe₂ NS heterostructures achieves external quantum efficiency (EQE) of 8.53 %. To our knowledge, this is the highest efficiency in the reported green QLEDs using inorganic materials as the hole injection layer.     

Synthesis of WOn‐WX2 (n=2.7, 2.9; X=S,Se) Heterostructures for Highly Efficient Green Quantum Dot Light‐Emitting Diodes

Preparation of two‐dimensional (2D) heterostructures is important not only fundamentally, but also technologically for applications in electronics and optoelectronics. Herein, we report a facile colloidal method for the synthesis of WO_n ‐WX₂ (n =2.7, 2.9; X=S, Se) heterostructures by sulfurization or selenization of WO_n nanomaterials. The WO_n ‐WX₂ heterostructures are composed of WO_2.9 nanoparticles (NPs) or WO_2.7 nanowires (NWs) grown together with single‐ or few‐layer WX₂ nanosheets (NSs). As a proof‐of‐concept application, the WO_n ‐WX₂ heterostructures are used as the anode interfacial buffer layer for green quantum dot light‐emitting diodes (QLEDs). The QLED prepared with WO_2.9 NP‐WSe₂ NS heterostructures achieves external quantum efficiency (EQE) of 8.53 %. To our knowledge, this is the highest efficiency in the reported green QLEDs using inorganic materials as the hole injection layer.     

Controllable Synthesis of Hexagonal WO3 Nanoplates for Efficient Visible‐Light‐Driven Photocatalytic Oxygen Production

Facilitating charge‐carrier separation and transfer is fundamentally important to improve the photocatalytic performance of semiconductor materials. Herein, two‐dimensional hexagonal WO₃ nanoplates were synthesized by a two‐step route: rapid evaporation and solid‐phase sintering. The as‐prepared WO₃ exhibits an enhanced activity of photocatalytic water oxidation compared to bulk monoclinic WO₃. The electron dynamics analysis reveals that a more efficient charge‐carrier separation in the former can be obtained, the origin of which can be attributed to an increased number of surface defects in hexagonal WO₃ nanoplates. This work not only presents a novel and simple method to produce two‐dimensional hexagonal WO₃ nanoplates, but also demonstrates that surface defects and two‐dimensional geometric structures can promote the charge separation, which may be extended to the design of other efficient photocatalysts.     

New Classes of Ferromagnetic Materials with Exclusively End‐on Azido Bridges: From Single‐Molecule Magnets to 2 D Molecule‐Based Magnets

A new, flexible synthetic route, which does not require the co‐presence of any organic chelating/bridging ligand but only the “key” precursor Me₃SiN₃, has been discovered and led to a new class of inorganic materials containing exclusively end‐on azido bridges; the reported 3d‐metal clusters and coordination polymers exhibit ferromagnetic, single‐molecule magnet, and long‐range magnetic ordering properties.     

Nanocomposite smart hydrogels with improved responsiveness and mechanical properties: A mini review

Responsive hydrogels have the ability to change their volume, transparency, or other properties in response to external chemical and/or physical stimuli. The responsiveness properties including responsive rate and degree, as well as mechanical properties such as Young's modulus, toughness, breaking strength, and breaking strain are crucial parameters of the smart hydrogels that determine the scope of hydrogel applications such as soft actuators, artificial muscles, and tissue engineering scaffolds. In this paper, the development of the nanocomposite smart hydrogels, which can achieve both improved responsiveness and mechanical properties, is reviewed. First, the fabrication approaches for building the nanocomposite networks by doping organic or inorganic nanomaterials via crosslinking or blending strategies are introduced. Then, the mechanisms used to improve both responsiveness and mechanical properties of nanocomposite responsive hydrogels are discussed. Finally, the perspectives as well as current challenges of such nanocomposite responsive hydrogels are addressed. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 1306–1313     

Optically Active Hybrid Materials Constructed from Helically Substituted Polyacetylenes

Functional materials derived from synthetic helical polymers are attracting increasing interest. Helically substituted polyacetylenes (HSPAs) are especially interesting as typical artificial helical polymers. In recent years, we designed and prepared a series of functional materials based on HSPAs and inorganic materials. The target is to establish some novel hybrid materials that combine the superior properties of both. The examined inorganic materials include silica, graphene, and magnetic Fe₃O₄ nanoparticles. Such new functional materials hold great promise and are expected to find practical applications, for instance, as chiral absorbents, chiral sensors, chiral selectors for inducing enantioselective crystallization, chiral catalysts towards asymmetric catalysis, and chiral carriers for enantioselective release. The Personal Account summarizes our major achievements in preparing optically active hybrid materials. We hope it will speed up progress in chiral‐related research areas.     

Synthesis of Three‐dimensionally Ordered Macroporous TiO2 and TiO2/WO3 Composites and Their Photocatalytic Performance

This work presents the characterization and preparation of three‐dimensionally ordered macroporous TiO₂ and TiO₂/WO₃ composite nanoparticles with enhanced visible‐light‐responsive properties for rhodamine B (Rh B) photodegradation. The 3DOM TiO₂ and TiO₂/WO₃ composites were prepared through a dip‐infiltrating sol‐gel process using a polystyrene (PS) colloidal crystal template. The materials were characterized by SEM, TEM, XRD, BET, XPS and UV/Vis. The 3DOM TiO₂/WO₃ composite structures ranged from well‐defined 3DOM structures, which are highly ordered and interconnected via small pore windows, to collapsed three‐dimensional structures as the WO₃ content increased. The photoresponse range and specific surface area of the composite increased with less than 0.025 g of WCl₆. The 3DOM TiO₂/WO₃ composite with less than 0.025 g of WCl₆ exhibited a higher catalytic activity than 3DOM TiO₂ for the photocatalytic degradation of Rh B under simulated sunlight illumination.     

Optimizing the self-assembly of conjugated polymers and small molecules through structurally programmed non-covalent control

Organic conjugated polymers and oligomers are key electronic materials for applications such as transistors, photovoltaics, and light emitting devices due to their potential for solution processability, mechanical flexibility, and precise structure-based tuning compared to inorganic materials. In dilute environments, the optoelectronic properties of conjugated polymers are largely governed by their constitutional structure and, to a lesser degree, their solution-state intramolecular configuration. In the solid state, intramolecular conformation and intermolecular electronic coupling impact these properties substantially, especially in relation to device performance. Therefore, an increasingly important area of research concerning conjugated materials is developing design strategies aimed at optimizing the solid-state packing for electronic applications. Programming solid-state packing arrangements through discrete non-covalent interactions is an emerging strategy within the context of conjugated polymers. This review focuses on the use of the two most prevalent discrete and directional interactions used to dictate the self-assembly of conjugated polymers and oligomers—hydrogen bonds and chalcogen bonds. We also discuss how these design motifs can imbue conjugated materials with appealing physical properties while simultaneously retaining or improving electronic capabilities.     

Facile preparation of Ag/Ag2WO4/g‐C3N4 ternary plasmonic photocatalyst and its visible‐light photocatalytic activity

Introducing plasmonic metals into semiconductor materials has been proven to be an attractive strategy for enhancing photocatalytic activity in the visible region. In this work, a novel and efficient Ag/Ag₂WO₄/g‐C₃N₄ (AACN) ternary plasmonic photocatalyst was successfully synthesized using a facile one‐step in situ hydrothermal method. The composition, structure, morphology and optical absorption properties of AACN were investigated using X‐ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and UV–visible diffuse reflectance spectroscopy, respectively. Photocatalytic performance of AACN was evaluated via rhodamine B and tetracycline degradation. The results indicated that AACN had excellent photocatalytic performance for rhodamine B degradation with a rate constant of 0.0125 min^?1, which was higher than those of Ag₂WO₄ and Ag/Ag₂WO₄. Characterization and photocatalytic tests showed that the strong coupling effect between the Ag/Ag₂WO₄ nanoparticles and the exfoliated ultrathin g‐C₃N₄ nanosheets was superior for visible‐light responsivity and reduced the recombination rate of photogenerated electrons and holes. A proposed mechanism is also discussed according to the band energy structure and the experimental results.     

Synthesis,Photochromic, and Computational Studies of Dithienylethene‐Containing β‐Diketonate Derivatives and Their Near‐Infrared Photochromic Behavior Upon Coordination of a Boron(III) Center

A series of dithienylethene‐containing 1‐thienyl‐3‐aryl‐propane‐1,3‐diones (aryl=phenyl (Ph), thienyl (Th), and 4,5‐bis(2,5‐dimethylthiophen‐3‐yl)thiophen‐2‐yl (DTE‐Th)) and the corresponding boron(III) diketonates, (O^O)BR₂ (R=F, C₆F₅, and Ph), have been designed and synthesized. Their photophysical, electrochemical, and photochromic properties have been studied. Upon coordination of a boron(III) center, the closed forms of the dithienylethene‐containing β‐diketonates show near‐infrared response and the photochromic behavior was also found to be affected by the aryl substituents at the 3‐position of the β‐diketonates. Moreover, computational studies have been performed that help to provide an understanding of the effect of substituents on the photophysical and photochromic properties.     

Synthesis,Characterization and Photochromic Properties of Novel Naphthopyrans with Hydrazone Unit Residue

A series of naphthopyrans with hydrazone unit ( 8a – 8m ), were synthesized and characterized by ¹H NMR, ¹³C NMR, IR and HRMS. The photochromic properties were investigated under continuous irradiation, in particular regard to the fatigue resistance and the lifetime of the colored open form in solution and polymers. The results showed that these compounds had both good photochromic properties and high fatigue resistance. Detailed studies showed that representative compound 8d (3,3‐di‐4‐methoxybenzoic acid methylenehydrazino‐[3H]‐naphtho [2,1‐b]pyran) had good photochromic properties in THF solution, in solid state, and in polymers, and exhibited a significant bathochromic shift in the spectra of the open forms compared to known naphthopyrans 9 (3,3‐diphenyl‐[3H]‐naphtho[2,1‐b]pyran). On the other hand, the higher melting points of target compounds are promising for the polymer film preparation through hot‐melt method.