Tunable Omnidirectional Antireflection Coatings Inspired by Inclined Irregular Nanostructures on Transparent Blue-Tailed Forest Hawk Dragonfly Wings.

Randomly arranged inclined irregular nanostructure-covered blue-tailed forest hawk dragonfly wings are highly transparent for wide viewing angles. Inspired by the dragonfly wings, monolayer silica colloids are self-assembled on shape memory polymer-coated substrates and utilized as plasma etching masks to pattern disorderly arranged inclined irregular conical structures. The structures build gradual refractive index transitions at various angles of incidences, resulting in omnidirectional antireflection performance over the whole visible wavelength region. In comparison with a bare substrate, the optimized structure-covered substrate presents 10% higher optical transmission at 0° and even 41% higher optical transmission at an angle of incidence of 75°. Importantly, by manipulating the structural configuration of the shape memory polymer-based structures, the corresponding antireflection characteristics can be instantaneously and reversibly eliminated and recovered after drying out of common household liquids or applying contact pressures in ambient environments. The tunable omnidirectional antireflection coatings are prospective candidates for realizing optical modulation, which exhibits an enormous application value in smart windows, intelligent display screens, optical components, and novel optoelectronic devices.

Clairvoyant Melon Maturity Detection Enabled by Doctor-Blade-Coated Photonic Crystals.

Climacteric fruits are harvested before they are ripened to avoid adverse damages during transport. The unripe fruits can undergo ripening processes associated with rind color changes on exposure to ethanol vapors. Although rind coloration is a common indicator showing fruit maturity, the attribute does not provide reliable assessment of maturity especially for melons. Herein, we report the achievement of sensitive and reversible melon maturity detection using macroporous hydrogel photonic crystals self-assembled by a roll-to-roll compatible doctor-blade-coating technology. The consumption of applied ethanol vapor during melon ripening results in less condensation of ethanol vapor in the pores (250 nm in diameter), leading to a distinct blue-shift of the optical stop band from 572 to 501 nm and an obvious visual colorimetric readout from yellow green to blue. Moreover, the dependence of the color change on Brix value within the melon has also been evaluated in the study.

Leafhopper Wing-Inspired Broadband Omnidirectional Antireflective Embroidered Ball-Like Structure Arrays Using a Nonlithography-Based Methodology.

Leafhoppers (Thaia rubiginosa) actively coat their wings with embroidered ball-like secretory brochosomes, which act as antireflective structures to enhance camouflage against predators. Inspired by the leafhoppers, we report a scalable nonlithographic approach for self-assembling nonclose-packed embroidered ball-like hierarchical structure arrays. The resulting structures create a gradual refractive index transition at the air/substrate interface, thereby suppressing the optical reflection for wide viewing angles. Compared with a bare substrate, the average reflectance of the structured substrate in the whole visible spectral region is reduced from 9 to 3% at normal incidence, and the average reflectance of that is even reduced by ca. 22% as the incident angle reaches 75°. Moreover, the dependence of the height and the shape of the hierarchical structure on the omnidirectional antireflection performance is systemically evaluated in this research.

Water-Soluble Chemical Vapor Detection Enabled by Doctor-Blade-Coated Macroporous Photonic Crystals.

Water-soluble chemicals, involving a wide range of toxic chemicals in aqueous solutions, remain essential in both daily living or industrial uses. However, most toxicants are evaporated with water through their use and thus cause deleterious effects on the domestic environment and health in humans. Unfortunately, most current low-dose chemical vapor detection technologies are restricted by the use of sophisticated instruments and unable to promptly detect the quantity of diverse toxicants in a single analysis. To address these issues, this study reports the development of simple and fast chemical vapor detection using doctor-blade-coated macroporous poly(2-hydroxyethyl methacrylate)/poly(ethoxylated trimethylolpropane triacrylate) photonic crystals, in which the poly(2-hydroxyethyl methacrylate) has strong affinity to insecticide vapor owing to a favorable Gibbs free energy change for their mixing. The condensation of water-soluble chemical vapor therefore results in a significant reflection peak shift and an obvious color change. The visual colorimetric readout can be further improved by increasing the lattice spacing of the macroporous photonic crystals. Furthermore, the dependence of the reflection peak position on vapor pressure under actual conditions and the reproducibility of vapor detecting are also evaluated in this study.

Zr-Metal Organic Framework and Derivatives for Adsorptive and Photocatalytic Removal of Acid Dyes.

To investigate effects of modification of MOFs on removal of acid dyes via adsorption and photodegradation, zirconium-based MOF, UiO-66, and its derivatives were synthesized. UiO-66 derivatives were prepared by using amine (NH2)-containing ligand and incorporating carbon nanotubes (CNTs) and reduced graphene oxide (RGO). During the synthesis UiO-66-NH2, UiO-66-CNT and UiO-66-RGO, were obtained, respectively. While UiO-66-NH2 showed the enhanced adsorption capacity for acid dyes owing to the electrostatic attraction, CNTs were found to be the most effective addition to enhance the adsorption of acid dyes. However, the addition of RGO in UiO-66 (to form UiO-66-RGO) exhibited the highest removal efficiency via photodegradation compared to UiO-66 and other derivatives probably attributed to its unique layered morphology. The presence of NH2, CNTs and RGO not only significantly improved the adsorption capacity for acid dyes but also enabled these UiO-66 derivatives to exhibit photocatalytic activity under visible light irradiation.

Self-Assembled Hierarchical Arrays for Colored Retroreflective Coatings.

This study reports a self-assembly technology for fabricating retroreflection coatings with hierarchical nano-/microstructures, which are inspired by the binary periodic structures found in the compound eyes of insects. Silica colloidal crystals of adjustable thicknesses are assembled on encountering glass microbeads using a Langmuir-Blodgett-like approach in a layer-by-layer manner. The as-assembled hierarchical structures exhibit a brilliant color caused by Bragg diffraction from the crystalline lattice of silica colloidal crystals on glass microbeads. The resultant coating is capable of reflecting light in the opposite direction of the incident light. Moreover, the dependence of the silica particle size, the colloidal crystal thickness, and the incident angle on the retroreflective properties are investigated in this study.

Iron Sulfide Microspheres Supported on Cellulose-Carbon Nanotube Conductive Flexible Film as an Electrode Material for Aqueous-Based Symmetric Supercapacitors with High Voltage.

Nanostructured iron disulfide (FeS2) was uniformly deposited on regenerated cellulose (RC) and oxidized carbon nanotube (CNT)-based composite films using a simple chemical bath deposition method to form RC/CNT/FeS2 composite films. The RC/CNT composite film served as an ideal substrate for the homogeneous deposition of FeS2 microspheres due to its unique porous architecture, large specific surface area, and high conductivity. Polypyrrole (PPy), a conductive polymer, was coated on the RC/CNT/FeS2 composite to improve its conductivity and cycling stability. Due to the synergistic effect of FeS2 with high redox activity and PPy with high stability and conductivity, the RC/CNT/FeS2/PPy composite electrode exhibited excellent electrochemical performance. The RC/CNT/0.3FeS2/PPy-60 composite electrode tested with Na2SO4 aqueous electrolyte could achieve an excellent areal capacitance of 6543.8 mF cm-2 at a current density of 1 mA cm-2. The electrode retained 91.1% of its original capacitance after 10,000 charge/discharge cycles. Scanning electron microscopy (SEM) images showed that the ion transfer channels with a pore diameter of 5-30 µm were formed in the RC/CNT/0.3FeS2/PPy-60 film after a 10,000 cycle test. A symmetrical supercapacitor device composed of two identical pieces of RC/CNT/0.3FeS2/PPy-60 composite electrodes provided a high areal capacitance of 1280 mF cm-2, a maximum energy density of 329 µWh cm-2, a maximum power density of 24.9 mW cm-2, and 86.2% of capacitance retention after 10,000 cycles at 40 mA cm-2 when tested at a wide voltage window of 1.4 V. These results demonstrate the greatest potential of RC/CNT/FeS2/PPy composite electrodes for the fabrication of high-performance symmetric supercapacitors with high operating voltages.

White Roman Goose Feather-Inspired Unidirectionally Inclined Conical Structure Arrays for Switchable Anisotropic Self-Cleaning.

White Roman goose (Anser anser domesticus) feathers, comprised of oriented conical barbules, are coated with gland-secreted preening oils to maintain a long-term nonwetting performance for surface swimming. The geese are accustomed to combing their plumages with flat bills in case they are contaminated with oleophilic substances, during which the amphiphilic saliva spread over the barbules greatly impairs their surface hydrophobicities and allows the trapped contaminants to be anisotropically self-cleaned by water flows. Particularly, the superhydrophobic behaviors of the goose feathers are recovered as well. Bioinspired by the switchable anisotropic self-cleaning functionality of white Roman geese, superhydrophobic unidirectionally inclined conical structures are engineered through the integration of a scalable colloidal self-assembly technology and a colloidal lithographic approach. The dependence of directional sliding properties on the shape, inclination angle, and size of conical structures is systematically investigated in this research. Moreover, their switchable anisotropic self-cleaning functionalities are demonstrated by Sudan blue II/water (0.01%) separation performances. The white Roman goose feather-inspired coatings undoubtedly offer a new concept for developing innovative applications that require directional transportation and the collection of liquids.

Overcoming Microstructural Defects at the Buried Interface of Formamidinium-Based Perovskite Solar Cells.

Since the advent of formamidinium (FA)-based perovskite photovoltaics (PVs), significant performance enhancements have been achieved. However, a critical challenge persists: the propensity for void formation in the perovskite film at the buried perovskite-interlayer interface has a deleterious effect on device performance. With most emerging perovskite PVs adopting the p-i-n architecture, the specific challenge lies at the perovskite-hole transport layer (HTL) interface, with previous strategies to overcome this limitation being limited to specific perovskite-HTL combinations; thus, the lack of universal approaches represents a bottleneck. Here, we present a novel strategy that overcomes the formation of such voids (microstructural defects) through a film treatment with methylammonium chloride (MACl). Specifically, our work introduces MACl via a sequential deposition method, having a profound impact on the microstructural defect density at the critical buried interface. Our technique is independent of both the HTL and the perovskite film thickness, highlighting the universal nature of this approach. By employing device photoluminescence measurements and conductive atomic force microscopy, we reveal that when present, such voids impede charge extraction, thereby diminishing device short-circuit current. Through comprehensive steady-state and transient photoluminescence spectroscopy analysis, we demonstrate that by implementing our MACl treatment to remedy these voids, devices with reduced defect states, suppressed nonradiative recombination, and extended carrier lifetimes of up to 2.3 µs can be prepared. Furthermore, our novel treatment reduces the stringent constraints around antisolvent choice and dripping time, significantly extending the processing window for the perovskite absorber layer and offering significantly greater flexibility for device fabrication.

Generalized fabrication of monolayer nonclose-packed colloidal crystals with tunable lattice spacing.

Here, we report a simple colloidal transfer technology that enables scalable fabrication of monolayer nonclose-packed silica colloidal crystals on a large variety of substrates. Two-dimensional colloidal crystals with an unusual nonclose-packed structure are first assembled on silicon wafers by a spin-coating technique. A poly(vinyl alcohol) (PVA) film cast upon the spin-coated colloidal crystal is used to transfer the nonclose-packed particle arrays onto various substrates. The lattice spacing of the transferred monolayer colloidal crystal can easily be adjusted by thermally treating the PVA-silica spheres composite film for varied durations. We also have demonstrated the templating fabrication of periodic arrays of gold nanodots using a transferred monolayer nonclose-packed colloidal crystal as a structural template. The resultant plasmonic array exhibits high surface-enhanced Raman scattering enhancement factor (~3.8 × 10(7)) for adsorbed benzenethiol molecules.

Self-Assembly of Shark Scale-Patterned Tunable Superhydrophobic/Antifouling Structures with Visual Color Response.

The stacked riblet-like shark scales, also known as dermal denticles, allow them to control the boundary layer flow over the skin and to reduce interactions with any biomaterial attached, which guide the design of antifouling coatings. Interestingly, shark scales are with a wide variation in geometry both across species and body locations, thereby displaying diversified antifouling capabilities. Inspired by the multifarious denticles, a stretchable shark scale-patterned silica hollow sphere colloidal crystal/polyperfluoroether acrylate-polyurethane acrylate composite film is engineered through a scalable self-assembly approach. Upon stretching, the patterned photonic crystals feature different short-term antibacterial and long-term anti-biofilm performances with a distinguished color response under varied elongation ratios. To gain a better understanding, the dependence of elongation ratio on antiwetting behaviors, antifouling performances, and structural color changes has also been investigated in this research.

Self-Assembly of Hemimyzon Formosanus-Inspired Crescent-Shaped Nanosucker Arrays for Reversible Adhesion.

Hemimyzon formosanus, a species of ray-finned fish, makes use of crescent-shaped abdominal suckers for adhering to irregular, rough, and slippery gravel in fast-flowing headwaters and minor tributaries. Bioinspired by the adhesion characteristics, two-dimensional non-close-packed colloidal crystals are self-assembled and serve as templates to pattern crescent-shaped shape memory polymer-based nanostructure arrays. By the manipulation of the configuration of nanosuckers through applying common solvent stimulations, the corresponding adhesion performances on glass, sandpaper, or even porcine kidney surfaces can be switched instantaneously and reversibly under ambient conditions. The biomimetic nanostructures indicate possible solutions to a variety of challenges, such as wound nursing, and so on.

Leafhopper-inspired reversibly switchable antireflection coating with sugar apple-like structure arrays.

Optical coatings with reversibly tunable antireflective characteristics hold a tremendous potential for next generation optical energy-related applications. Bioinpsired by the camouflage behavior of small yellow leafhoppers, silica hollow sphere/shape memory polymer composites are self-assembled using a non-lithography-based approach. The average visible transmittance of the as-patterned hierarchical structure array-covered substrate is increased by ca. 6.3% at normal incident, and even improved by more than 20% for an incident angle of 75°. Interestingly, the broadband omnidirectional antireflection performance can be reversibly erased and recovered by applying external stimuli under ambient conditions. To gain a better understanding, its reversibility, mechanical robustness, and the structure-shape effect on the antireflective properties are systematically investigated in this research.

Hollow-Structured N-doped carbon-embedded CoFe NanoAlloy for boosting activation of Monopersulfate: Engineered interface and heteroatom Doping-Induced enhancements.

While transition metals are useful for activating monopersulfate (MPS) to degrade contaminants, bimetallic alloys exhibit stronger catalytic activities owing to several favorable effects. Therefore, even though Co is an efficient metal for MPS activation, CoFe alloys are even more promising heterogeneous catalysts for MPS activation. Immobilization/embedment of CoFe alloy nanoparticles (NPs) onto hetero-atom-doped carbon matrices appears as a practical strategy for evenly dispersing CoFe NPs and enhancing catalytic activities via interfacial synergies between CoFe and carbon. Herein, N-doped carbon-embedded CoFe alloy (NCCF) is fabricated here to exhibit a unique hollow-engineered nanostructure and the composition of CoFe alloy by using Co-ZIF as a precursor after the facile etching and Fe doping. The Fe dopant embeds CoFe alloy NPs into the hollow-structured N-doped carbon substrate, enabling NCCF to possess the higher mesoscale porosity, active N species as well as more superior electrochemical properties than its analogue without Fe dopants, carbon matrix-supported cobalt (NCCo). Thus, NCCF exhibits a considerably larger activity than NCCo and the benchmark catalyst, Co3O4 NP, for MPS activation to degrade an environmental hormone, dihydroxydiphenyl ketone (DHPK). Besides, NCCF + MPS shows an even lower activation energy for DHPK degradation than literatures, and retains its high efficiency for eliminating DHPK in different water media. DHPK degradation pathway and ecotoxicity assessment are unraveled based on the insights from the computational chemistry, demonstrating that DHPK degradation by NCCF + MPS did not result in the formation of toxic and highly toxic by-products. These features make NCCF a promising heterogeneous catalyst for MPS activation to degrade DHPK.

Omnidirectional / Unidirectional Antireflection-Switchable Structures Inspired by Dragonfly Wings.

Randomly arranged irregular inclined conical structure-covered dragonfly wings, distinguished from periodic conical structure-covered cicada wings, are with high optical transparency for wide viewing angles. Bioinspired by the antireflective structures, we develop a colloidal lithography approach for engineering randomly arranged irregular conical structures with shape memory polymer-based tips. The structures establish a gradual refractive index transition to suppresses optical reflection in the visible spectrum. By manipulating the configuration of structure tips through applying common solvent stimulations or contact pressures under ambient conditions, the resulting unidirectional antireflection and omnidirectional antireflection performances are able to be instantaneously and reversibly switched. The dependences of structure shape, structure inclination, structure arrangement, and structure composition on the switchable antireflection capability are also systematically investigated in this study.

Single-Step Fabrication of Longtail Glasswing Butterfly-Inspired Omnidirectional Antireflective Structures.

Most bio-inspired antireflective nanostructures are extremely vulnerable and suffer from complicated lithography-based fabrication procedures. To address the issues, we report a scalable and simple non-lithography-based approach to engineer robust antireflective structures, inspired by the longtail glasswing butterfly, in a single step. The resulting two-dimensional randomly arranged 80/130/180 nm silica colloids, partially embedded in a polymeric matrix, generate a gradual refractive index transition at the air/substrate interface to suppress light reflection. Importantly, the randomly arranged subwavelength silica colloids display even better antireflection performance for large incident angles than that of two-dimensional non-close-packed silica colloidal crystals. The biomimetic coating is of considerable technological importance in numerous practical applications.

Hollow porous cobalt oxide nanobox as an enhanced for activating monopersulfate to degrade 2-hydroxybenzoic acid in water.

As 2-hydroxybenzoic acid (HBA) represents a typical pharmaceutical and personal care product (PPCP), constant releasing of HBA into the environment poses threats to the ecology, and thus it is critical to develop effective techniques to remove HBA from water. Recently, sulfate radical (SO4‒)-based advanced oxidation processes involved with monopersulfate (MPS) activation are proven as effective approaches for eliminating PPCPs from water, and Co3O4 is recognized as a capable catalyst for activating MPS. Therefore, great interests have arisen to develop Co3O4-based catalysts with advantageous morphologies and characteristics for enhancing catalytic activities. Therefore, a special Co3O4-based material is proposed in this work. Through a surfactant-assisted strategy, a cubic Co-MOF is prepared and used as a precursor, which is etched to afford hollow structure, and then transformed into hollow porous Co3O4 nanobox (PCNB). PCNB can exhibit distinct reactive surface with abundant surface oxygen vacancy as well as physical properties in comparison to the commercial Co3O4 NPs (com-Co3O4 NP), thereby leading to the outstanding catalytic activity of PCNB for activating MPS to degrade HBA. The activation energy (Ea) of 46.2 kJ/mol is also calculated using PCNB + MPS system, which is much lower than most of recent reported studies for activating MPS. PCNB could be also reusable over 5 consecutive HBA degradation cycles. The activation mechanism of MPS by PCNB and HBA degradation pathway are also comprehensively elucidated via experimental evidences and the theoretical calculation to offer insightful information of development of Co3O4 for HBA degradation.

Enhanced degradation of ultra-violet stabilizer Bis(4-hydroxy)benzophenone using oxone catalyzed by hexagonal nanoplate-assembled CoS 3-dimensional cluster.

As UV-light stabilizers, Bis(4-hydroxy)benzophenone (BBP), are extensively consumed to quench radicals from photooxidation, continuous release of BPs into the environment poses serious threats to the ecology in view of their xenohormone toxicities, and BBP shall be eliminated from water to avoid its adverse effect. Since sulfate radical (SR)-based chemical oxidation techniques have been proven as effective procedures for eliminating organic emerging contaminants, this study aims to develop useful SR-based procedures through activating Oxone for degrading BBP in water. In contrast to the conventional Co3O4, cobalt sulfide (CoS) is particularly proposed as an alternative heterogeneous catalyst for activating Oxone to degrade BBP because CoS exhibits more reactive redox characteristics. As structures of catalysts predominantly control their catalytic activities, in this study, a unique nanoplate-assembled CoS (NPCS) 3D cluster is fabricated via a convenient one-step process to serve as a promising heterogeneous catalyst for activating Oxone to degrade BBP. With NPCS = 100 mg/L and Oxone = 200 mg/L, 5 mg/L of BBP can be completely eliminated in 60 min. The catalytic activity of NPCS towards Oxone activation also significantly surpasses the reference material, Co3O4, to enhance degradation of BBP. Ea of BBP degradation by NPCS-activated Oxone is also determined as a relatively low value of 42.7 kJ/mol. The activation mechanism as well as degradation pathway of BBP degradation by NPCS-activated Oxone was investigated and validated through experimental evidences and density functional theory (DFT) calculation to offer valuable insights into degradation behaviors for developing SR-based processes of BBP degradation using CoS catalysts.

Reversible embroidered ball-like antireflective structure arrays inspired by leafhopper wings.

Highly transparent leafhopper (Thaia rubiginosa) wings are self-decorated with embroidered ball-shaped proteinaceous brochosmoes as distinct anti-predator defenses. The non-sticky brochosomal coating serves as antireflective structures for camouflage in vegetated environments. Inspired by the leafhopper wings, this study reports a new type of reversible antireflection coating enabled by integrating self-assembly methodologies using a shape memory polymer. The resulting embroidered ball-like structure array establishes a refractive index transition on surface, and thereby behaves omnidirectional antireflective characteristics in a broadband visible light region. Interestingly, the highly transparent appearance can be instantly erased and recovered by submerging in common liquids, such as water and ethanol, or by applying contact pressures at ambient conditions. Furthermore, the reversibility and structure-shape effect on the antireflective characteristics are systematically evaluated in this study.

Large-scale colloidal self-assembly by doctor blade coating.

This article reports a simple, roll-to-roll compatible coating technology for producing 3D highly ordered colloidal crystal-polymer nanocomposites, colloidal crystals, and macroporous polymer membranes. A vertically beveled doctor blade is utilized to shear align silica microsphere-monomer suspensions to form large-area nanocomposites in a single step. The polymer matrix and the silica microspheres can be selectively removed to create colloidal crystals and self-standing macroporous polymer membranes. The thickness of the shear-aligned crystal is correlated with the viscosity of the colloidal suspension, and the coating speed and the correlations can be qualitatively explained by adapting the mechanisms developed for conventional doctor blade coating. We further demonstrate that the doctor blade coating speed can be significantly increased by using a dual-blade setup. The optical properties of the self-assembled structures are evaluated by normal-incidence reflection measurements, and the experimental results agree well with the theoretical predictions using Bragg's law and a scalar wave approximation model. We have also demonstrated that the templated macroporous polymers with interconnected voids and uniform interconnecting nanopores can be directly used as filtration membranes to achieve size-exclusive separation of particles.