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The catalytic performance of light-derived CO2 reduction with H2O is strongly dependent on the separation efficiency of photogenerated carriers. Herein, the direct Z-scheme catalysts (g-C3N4/3DOM-WO3) of graphitic carbon nitride (g-C3N4) nanosheets decorated three-dimensional ordered macroporous WO3 (3DOM-WO3) were successfully fabricated by using the in-situ colloidal crystal template method. The slow light effect of 3DOM-WO3 photonic crystals expands the absorption of visible light and improves the utilization of light energy. The Z-scheme structure of g-C3N4/3DOM-WO3 catalysts is able to upgrade the separation efficiency of photogenerated electron-hole pairs. The g-C3N4/3DOM-WO3 photocatalyst, whose formation rate of CO product is 48.7 μmol g−1 h−1, exhibits the excellent catalytic activity for CO2 reduction. The transfer pathway of stimulated electrons over the g-C3N4/3DOM-WO3 photocatalyst is proposed and discussed. The present approach provides unique insights into the rational development of high-performance photochemical systems for efficient CO2 reduction into valuable carbon-containing chemicals and energy fuels.

A series of three-dimensional ordered macroporous (3DOM) W–TiO2 catalysts have been prepared through a facile colloidal crystal template method. The prepared materials characterized in detail exhibited enhanced catalytic activity in aerobic oxidative desulfurization process. The experimental results indicated that the as-prepared materials possessed excellent 3DOM structure, which is beneficial for the catalytic activity. The sample 3DOM W–TiO2-20 exhibited the highest activity in ODS process, and the sulfur removal can reach 98% in 6 h. Furthermore, the oxidative product was also analyzed in the reaction process.

High-frequency vibration proves a fundamental step towards scalable growth in colloidal crystals. Various experimentally-replicable vibration mechanisms are hereby devised and exerted on randomly generated silicoid particles to explore geometric and dynamic effects on the induced crystal at equilibrium state. The Discrete Element Method is employed, with inter-particle contact idealized by a linear mass–spring–dashpot system with Coulomb sliding friction. With the vertical (Z) direction determined by gravity, the mechanisms comprise vertical, circular, and angular oscillation, with the latter realized in the plane normal to gravity. Characterization of the generated crystal is quantified by a hybrid machine-learning algorithm developed upon direct correlation between the coordinate data, crystallinity and grain-surface parameters. Parametric analysis is carried out in terms of vibration parameters (frequency, amplitude and duration) and the square-prismatic box aspect ratio. Results manifest optimum values of box aspect ratio, vibration amplitude and frequency, with crystallinity parameters mostly saturating after 2 minutes of vibration.

Organisms that alter body color undergo color change in response to environmental variations and stimuli by combining chromatophores that develop colors by various mechanisms. Inspired by their body color changes, we can develop sensors and optical materials that change colors in response to multiple stimuli, such as mechanical and light stimuli. In this study, we report on bioinspired composite elastomers that exhibit various color changes as the pigment color, structural color, and background color change. These composite elastomers exhibit structural colors due to their fine structures in which fine silica particles form colloidal crystals, and the structural colors reversibly change as the elastomers elongate. Furthermore, photochromic dyes can reversibly change color depending on the wavelength of irradiated light when they are introduced to the composite elastomers. Since the structural color is one of the three primary colors of light and the pigment color is the color that corresponds to the three primary colors of a pigment, each color becomes vivid when the background color is black or white. Thus, we clarify that the composite elastomers exhibit various color changes due to the combination of structural color change in response to the mechanical stimulus, pigment color change in response to light irradiation, and background color change.

Colloidal self-assembly refers to a solution-processed assembly of nanometer-/micrometer-sized, well-dispersed particles into secondary structures, whose collective properties are controlled by not only nanoparticle property but also the superstructure symmetry, orientation, phase, and dimension. This combination of characteristics makes colloidal superstructures highly susceptible to remote stimuli or local environmental changes, representing a prominent platform for developing stimuli-responsive materials and smart devices. Chemists are achieving even more delicate control over their active responses to various practical stimuli, setting the stage ready for fully exploiting the potential of this unique set of materials. This review addresses the assembly of colloids into stimuli-responsive or smart nanostructured materials. We first delineate the colloidal self-assembly driven by forces of different length scales. A set of concepts and equations are outlined for controlling the colloidal crystal growth, appreciating the importance of particle connectivity in creating responsive superstructures. We then present working mechanisms and practical strategies for engineering smart colloidal assemblies. The concepts underpinning separation and connectivity control are systematically introduced, allowing active tuning and precise prediction of the colloidal crystal properties in response to external stimuli. Various exciting applications of these unique materials are summarized with a specific focus on the structure-property correlation in smart materials and functional devices. We conclude this review with a summary of existing challenges in colloidal self-assembly of smart materials and provide a perspective on their further advances to the next generation.

Colloidal supraparticles are micron-scale spherical assemblies of uniform primary particles, which exhibit emergent properties of a colloidal crystal, yet exist as a dispersible powder. A prerequisite to utilize these emergent functionalities is that the supraparticles maintain their mechanical integrity upon the mechanical impacts that are likely to occur during processing. Understanding how the internal structure relates to the resultant mechanical properties of a supraparticle is therefore of general interest. Here, we take the example of supraparticles templated from water/fluorinated oil emulsions in droplet-based microfluidics and explore the effect of surfactants on their mechanical properties. Stable emulsions can be generated by nonionic block copolymers consisting of a hydrophilic and fluorophilic block and anionic fluorosurfactants widely available under the brand name Krytox. The supraparticles formed in the presence of both types of surfactants appear structurally similar, but differ greatly in their mechanical properties. While the nonionic surfactant induces superior mechanical stability and ductile fracture behavior, the anionic Krytox surfactant leads to weak supraparticles with brittle fracture. We complement this macroscopic picture with Brillouin light spectroscopy that is very sensitive to the interparticle contacts for subnanometer-thick adsorbed layers atop of the nanoparticle. While the anionic Krytox does not significantly affect the interparticle bonds, the amphiphilic nonionic surfactant drastically strengthens these bonds to the point that individual particle vibrations are not resolved in the experimental spectrum. Our results demonstrate that seemingly subtle changes in the physicochemical properties of supraparticles can drastically impact the resultant mechanical properties.

The chemical interactions that lead to the emergence of hierarchical structures are often highly complex and difficult to program. Herein, the synthesis of a series of superlattices based upon 30 different structurally reconfigurable DNA dendrimers is reported, each of which presents a well-defined number of single-stranded oligonucleotides (i.e., sticky ends) on its surface. Such building blocks assemble with complementary DNA-functionalized gold nanoparticles (AuNPs) to yield five distinct crystal structures, depending upon choice of dendrimer and defined by phase symmetry. These DNA dendrimers can associate to form micelle-dendrimers, whereby the extent of association can be modulated based upon surfactant concentration and dendrimer length to produce a low-symmetry Ti5Ga4-type phase that has yet to be reported in the field of colloidal crystal engineering. Taken together, colloidal crystals that feature three different types of particle bonding interactions-template-dendron, dendrimer-dendrimer, and DNA-modified AuNP-dendrimer-are reported, illustrating how sequence-defined recognition and dynamic association can be combined to yield complex hierarchical materials.

In order for the colloidal crystal films to be better applied, the influence of relative humidity on the preparation of silica colloidal crystal (SCC) films was systematically studied to solve the problem of different thicknesses of SCC films prepared by different batches under the conditions with the same temperature, concentration of suspension and diameter of the particles. SCC films with 190 nm particles were prepared by static vertical deposition method under different humidity regulated by saturated salt solutions, and the thickness of the films was obtained by an interferometric method. The results showed that the increase in humidity would reduce the thickness of the prepared films, which was believed to be caused by the decrease in evaporation rate after the wetting film absorbs water vapor. A new formula for calculating film thickness was proposed and verified from a series of experiments. With the control of humidity, high-quality SCC films with controlled thickness can be repeatedly prepared.

Previous reports have shown that colloidal crystal (CC) films with visible Bragg reflection characteristics can be fabricated by the surface modification of monodisperse silica particles (SiPs) with poly(methyl methacrylate) (PMMA) chains, followed by hot-pressing at 150 °C. However, the reflection bands of the CC films were very broad due to their relative disordering of SiPs. In this report, we attempted to fabricate the CC films using SiPs surface-modified with poly(n-octyl acrylate) (POA) chains by hot-pressing. When the cast films of POA-grafted SiPs were prepared by hot-pressing at 100 °C, the reflection bands were narrow rather than those of CC films of PMMA-grafted SiPs. This can be ascribed to easy disentanglement of POA chains during the hot-pressing process, thereby enabling the formation of well-ordered CC structures. Moreover, the reflection colors of CC films could be easily tuned by controlling the molecular weight of POA chains grafted on the SiP surface.

The dynamics of complex topological defects in ferroelectric materials is explored using automated experimentation in piezoresponse force microscopy. Specifically, a complex trigger system (i.e., "FerroBot") is employed to study metastable domain-wall dynamics in Pb0.6Sr0.4TiO3 thin films. Several regimes of superdomain wall dynamics have been identified, including smooth domain-wall motion and significant reconfiguration of the domain structures. We have further demonstrated that microscopic mechanisms of the domain-wall dynamics can be identified; i.e., domain-wall bending can be separated from irreversible domain reconfiguration regimes. In conjunction, phase-field modeling was used to corroborate the observed mechanisms. As such, the observed superdomain dynamics can provide a model system for classical ferroelectric dynamics, much like how colloidal crystals provide a model system for atomic and molecular systems.

Chemical reactions can be efficiently carried out in microfluidic devices using a small amount of solution, meaning that fewer resources are required and less liquid waste is generated, making them...

The catalytic performances for soot purification over the perovskite-type ABO3 oxides, as one of the most potential non-noble metal catalysts, are closely correlated with the substitution of A-site and B-site ions. Herein, three-dimensional ordered macroporous (3DOM) structural catalysts of double perovskite-type La2-xKxNiCoO6 were prepared by a method of colloidal crystal template. The contact efficiency between the catalyst and soot particles is significantly promoted by the 3DOM structure, and the partial substitution of A-site (La) with low-valence potassium (K) ions in La2-xKxNiCoO6 catalysts boosts the increasing surface density of coordinatively unsaturated active B-sites (Co and Ni) and active oxygen. 3DOM La2-xKxNiCoO6 catalysts exhibited superior performance during the purification of soot particles, and the 3DOM La1.80K0.20NiCoO6 catalyst exhibited the highest activity, that is, the values of T50, SCO2, and turnover frequency are 346 °C, 99.3%, and 0.204 h-1 (at 300 °C), respectively. According to the results of multiple experimental characterizations and density functional theory calculations, the mechanism of the samples during soot removal is proposed: the increase in surface oxygen density induced by the doping of K ions significantly promotes the critical step of the oxidation from NO to NO2 in catalyzing soot purification. It is one new strategy to develop the high-efficient non-noble metal catalysts for soot purification in practical application.

It is critical to assemble nanoparticles (NPs) into superlattices with controlled symmetries and spacings on substrates for metamaterials applications, where such structural parameters dictate their properties. Here, we use DNA to assemble anisotropic NPs of three shapes-cubes, octahedra, and rhombic dodecahedra-on substrates and investigate their thermally induced reorganization into two-dimensional (2D) crystalline films. We report two new low-density 2D structures, including a honeycomb lattice based on octahedral NPs. The low-density lattices favored here are not usually seen when particles are crystallized via other bottom-up assembly techniques. Furthermore, we show that, consistent with the complementary contact model, a primary driving force for crystallization is the formation of directional, face-to-face DNA bonds between neighboring NPs and between NPs and the substrate. Our results can be used to deliberately prepare crystalline NP films with novel morphologies.

The effect of the substrate surface groups on the thermal stability of colloidal crystals formed via heterogeneous nucleation was investigated by observing the melting behavior of the colloidal crystals on three types of substrate: one charged negatively by silanol groups, one with introduced amino groups, and one with introduced quaternary ammonium groups. The degree of particle binding by the substrate in the colloidal dispersion was evaluated in terms of the particle arrangement formed through a dry deposition process that involved drying the dispersion on each substrate. The particle mobility on the substrates was higher in the order of the negatively charged substrate, the substrate with introduced amino groups, and the substrate with introduced quaternary ammonium groups. The melting temperature was measured in terms of the colloidal crystals formed on each substrate and was found to be 40.5 °C on the negatively charged substrate, 46.0 °C on the substrate with introduced amino groups, and 52.4 °C on the substrate with introduced quaternary ammonium groups. The increase in melting temperature was derived from the decrease in the particle mobility on the substrates with introduced positively charging groups, which resulted in an increase in the thermal stability of the colloidal crystalline lattice in relation to the Brownian motion due to the reduction in the particle mobility through the interaction between the negatively charged particles and the substrates.

The development of appropriate methods to correlate the structure and optical properties of colloidal photonic structures is still a challenge. Structural information is mostly obtained by electron, X-ray, or optical microscopy methods and X-ray diffraction, while bulk spectroscopic methods and low resolution bright-field microscopy are used for optical characterization. Here, we describe the use of reflectance confocal microscopy as a simple and intuitive technique to provide a direct correlation between the ordered/disordered structural morphology of colloidal crystals and glasses, and their corresponding optical properties.

A novel self-assembly technique, analogous but different in essence from the conventional gas–liquid interface self-assembly method, is proposed for the first time to fabricate three-dimensional (3...

Structural colors generated by colloidal crystals offer a promising method to create large-scale nanostructures due to their stability in comparison with dyes and pigments. However, the low durabil...

The three-dimensional colloidal crystal materials have unique optical properties and spatial structure due to their ordered arrangement and have great potential to prepare three-dimensionally ordered microporous (3DOM) materials. This review outlines various methods for preparing three-dimensional colloidal crystals (3DCCs). The preparation methods of commonly used colloidal particles are introduced in detail, and the effects of different parameters on the assembly of 3DCCs are discussed. On this basis, using the colloidal crystal template (CCT) method to prepare 3DOM materials. After that, the common stacking methods and defects of 3DCCs were analyzed. The latter part of this review discusses the main applications of 3DCCs, namely optical materials, adsorption materials, sensors, porous electrode materials, inverse colloidal crystal (ICC) scaffolds, and other popular applications in recent years.

A thermosensitive poly(N-isopropylacrylamide) (PNIPAM) circular gel film containing single-crystalline colloidal crystals was prepared, and the circular edge was pinched with washers to restrain the in-plane shrinkage of the gel film. Upon heating, the film shrunk in the thickness direction selectively, resulting in a change in the crystal structure of colloids embedded in the anisotropic shrunken gel. This led to the manipulation of the optical stop-band wavelength of the colloidal photonic crystals with a higher thermosensitivity and over a wider range of wavelengths covering a wide margin on either side of the visible-light region. The present method for enhancement of the sensitivity is very simple, and the principle should also be applicable to the gel-immobilized colloidal crystals that respond to stimuli other than temperature changes. The present findings contribute to the progress of practical applications of gel-immobilized colloidal photonic crystals as tunable photonic crystals and biological ...

Soft photonic materials formed from nanoscale colloidal crystals are versatile platforms for sensing and signaling in biomedical, chemical, and mechanical application scenarios. A particularly leve...

We studied the influence of the surface charge of the substrate on the heat stability of electrostatic interactional colloidal silica crystals grown through heterogeneous nucleation from the substrate by relative reflection spectroscopy and optical microscopy. During the crystal growth stage on a negatively charged substrate, a large blue shift of the reflection peak was observed in the reflection spectrum. On the other hand, during crystallisation on a positively charged substrate, the blue shift occurring on the negatively charged substrate was completely suppressed. This blue shift indicates a reduction in the lattice spacing when the crystals push each other during crystal growth. The melting behaviour of the crystal was also investigated in the case of heating from the substrate side. The melting point of the crystal on the positively charged surface was higher than that on the negatively charged surface. The blue shift in the spectrum of the crystals on the positively charged substrate was suppressed in the stage before melting; however, the blue shift increased when the crystal started to melt from the substrate surface. Colloidal crystals formed from heterogeneous nuclei on a positively charged substrate were stabilised by the interaction between the negatively charged colloidal particles in the substrate’s vicinity and the positively charged substrate surface.

Folic acid is an important biological compound for human disease diagnosis. Traditional detection methods of folic acid are mostly time-consuming or dependent on analytical equipment. Here we demonstrate the rapid and colorimetric detection of folic acid using a novel colorimetric sensor enabled by molecularly imprinted photonic hydrogels, which are prepared by the polymerization of precursor solution in the interstitial voids of the polystyrene colloidal crystal and subsequent removal of colloidal crystal and folic acid molecules. As folic acid is instable under the preparation process of molecularly imprinted photonic hydrogels, we introduce folic acid (imprinted molecule) in the form of supramolecular complex with β-CD units to improve its stability and further create stable molecular recognition sites. The folic acid recognition can be directly transferred into a visually perceptible color change due to the highly ordered macroporous structure. With this novel sensory system, the highly selective, high sensitive (as low as 10–12 M), and rapid response (

The design of pore structure is the key factor for the performance of porous carbon spheres. In this work, novel micron-sized colloidal crystal microspheres consisting of fibrous silica (F-SiO2) nanoparticles are firstly prepared by water-evaporation-induced self-assembly of F-SiO2 nanoparticles in the droplets of an inverse emulsion system to be used as sacrificial templates. Acrylonitrile (AN) was infiltrated in the voids of the F-SiO2 colloidal crystal microspheres, and in-situ induced by 60Co γ-ray to polymerize into polyacrylonitrile (PAN). After the PAN-infiltrated F-SiO2 colloidal crystal microspheres were carbonized and etched with HF solution, novel micron-sized inverse-opal N-doped carbon (IO-NC) microspheres consisting of hollow carbon nanoparticles with a hierarchical macro/meso-porous inner surface were obtained. The IO-NC microspheres have a specific surface area as high as 266.4 m2/g and a molar ratio of C/N of 5. They have a good dispersibility in water, and show a high adsorption capacity towards rhodamine B (RhB) up to 137.28 mg/(g microsphere). This work offers a way to obtain novel micron-sized hierarchical macro/meso-porous N-doped carbon microspheres, which opens a new idea to prepare high-performance hierarchical porous carbon materials.

Patchy particles, defined as particles with one or more well-defined patches, have attracted much attention due to their anisotropic and directional interactions. The anisotropic nature of the patchy particle surface enables a certain degree of control over the assembly process. Enormous efforts have been carried out to design and explore the properties of patchy particles and their collective behaviour. However, the techniques to fabricate patchy particles are still limited in terms of tunability and scalability. In this work, an effective method of fabricating patchy particles with tunable spatial topology and chemical composition of patches is presented. The number, distribution and size of the patches can be tailored by adjusting the packing of the colloidal particles and the processing condition. The active secondary reaction on the polydopamine (PDA)-coated surface and silica surface could functionalize the obtained patchy particles with desired properties to meet different requirements. As a proof of principle, the PDA-coated patches were modified with thiol-based dye via the Michael reaction and the silica surfaces were functionalized with amine-terminated alkoxysilanes via the silane coupling reaction have been demonstrated. Furthermore, the unique properties of PDA, such as reductive ability, powerful adhesive capability and carbonizable feature, have also been proven to fabricate metallic nanoparticle-decorated patchy particles and anisotropic carbon nanocapsules. The well-defined patchy particles are templated from colloidal crystal and their gram-scale fabrication is easily achieved. These results indicate that our strategy will help access the transformative potential of patchy particles in the rational design and large-scale production of functional materials.

Colloidal photonic crystals show structural colors yet are generally opaque due to multiple scattering. To address this problem, composite colloidal crystals with a low index mismatch were prepared...

Sublattice melting is the loss of order of one lattice component in binary or ternary ionic crystals upon increase in temperature. A related transition has been predicted in colloidal crystals. To understand the nature of this transition, we study delocalization in self-assembled, size asymmetric binary colloidal crystals using a generalized molecular dynamics model. Focusing on BCC lattices, we observe a smooth change from localized-to-delocalized interstitial particles for a variety of interaction strengths. Thermodynamic arguments, mainly the absence of a discontinuity in the heat capacity, suggest that the passage from localization-to-delocalization is continuous and not a phase transition. This change is enhanced by lattice vibrations, and the temperature of the onset of delocalization can be tuned by the strength of the interaction between the colloid species. Therefore, the localized and delocalized regimes of the sublattice are dominated by enthalpic and entropic driving forces, respectively. This work sets the stage for future studies of sublattice melting in colloidal systems with different stoichiometries and lattice types, and it provides insights into superionic materials, which have potential for application in energy storage technologies., Hector Lopez-Rios and Ali Ehlen contributed equally

International audience; Over the last three decades, photonic crystals (PhCs) have attracted intense interests thanks to their broad potential applications in optics and photonics. Generally, these structures can be fabricated via either ‘‘top-down’’ lithographic or ‘‘bottom-up’’ self-assembly approaches. The self-assembly approaches have attracted particular attention due to their low cost, simple fabrication processes, relative convenience of scaling up, and the ease of creating complex structures with nanometer precision. The self-assembled colloidal crystals (CCs), which are good candidates for PhCs, have offered unprecedented opportunities for photonics, optics, optoelectronics, sensing, energy harvesting, environmental remediation, pigments, and many other applications. The creation of high-quality CCs and their mass fabrication over large areas are the critical limiting factors for real-world applications. This paper reviews the state-of-the-art techniques in the self-assembly of colloidal particles for the fabrication of large-area high-quality CCs and CCs with unique symmetries. The first part of this review summarizes the types of defects commonly encountered in the fabrication process and their effects on the optical properties of the resultant CCs. Next, the mechanisms of the formation of cracks/defects are discussed, and a range of versatile fabrication methods to create large-area crack/defect-free twodimensional and three-dimensional CCs are described. Meanwhile, we also shed light on both the advantages and limitations of these advanced approaches developed to fabricate high-quality CCs. The self-assembly routes and achievements in the fabrication of CCs with the ability to open a complete photonic bandgap, such as cubic diamond and pyrochlore structure CCs, are discussed as well. Then emerging applications of large-area high-quality CCs and unique photonic structures enabled by the advanced self-assembly methods are illustrated. At the end of this review, we outlook the future approaches in the fabrication of perfect CCs and highlight their novel real-world applications.

Particle-based delivery systems have emerged as a powerful platform in controlled drug release. In the present study, we developed a new inverse opal hydrogel microcarrier system composed of gold nanorods (AuNRs) for near-infrared light (NIR) activated drug delivery. AuNRs with a desired aspect ratio were prepared by a seed-mediated growth method. The inverse opal hydrogel microcarriers composited with AuNRs were synthesized by negatively replicating silica colloidal crystal beads (SCCBs). The NIR-thermo response of the microcarriers was due to the NIR photothermal heating effect of AuNRs and the thermo responsive volume transition of poly(N-isopropylacrylamide) (pNIPAM) hydrogel. It was found that the NIR-controlled reversible shrinking response of the microcarriers was ideal for the controllable drug release with real-time self-reporting color indication.

Monodisperse black carbon nanoparticles (average diameters: 272 and 511 nm) are prepared by the carbonization of monodisperse spherical π-conjugated polymer particles. Meanwhile, silica nanoparticles of different sizes are prepared by a conventional sol–gel process on the basis of the Stober method. The cast films fabricated from aqueous dispersion of silica nanoparticles show size-dependent iridescent structural colours of blue (212 nm), green (240 nm), yellow (261 nm), and red (270 nm). Remarkably, these structural colours show enhanced saturation when black carbon nanoparticles are mixed with a low ratio, such as 1 wt%. The reflection UV-vis spectra indicate that adding carbon particles causes an extreme reduction of reflectance in the visible wavelength region, while the peaks of the structural colours become enhanced in height with almost no shift. Scanning electron microscopy observations suggest that the carbon nanoparticles are well dispersed in the colloidal crystal films of silica nanoparticles but do not disturb the array arrangement. Hence, the iridescence of structural colour is retained. The angle-dependent reflectance spectra of the carbon nanoparticle-doped colloidal crystals mostly agree with theoretical predictions. Since the maverick carbon nanoparticles are thermally stable, the highly saturated structural colours persist up to 350 °C.

In this study, colloidal crystals were immobilized in a linear thermosensitive copolymer hydrogel film that was simultaneously bound on a glass substrate using a silane coupling agent via photopolymerization. Due to the suppression of the in-plane shrinkage of the gel, the thermosensitivity increased 1.6-fold, while the linear sensitivity was maintained.

Metal–organic frameworks (MOFs) are potential sensing materials with inherent sensitivity for molecule detection. However, reliable and reproducible MOF-based optical sensors with well-defined selectivity suitable for practical application have not been reported, which is partly due to the lack of control over film textures, crystalline orientations and exposed crystal facets. Herein, we report on versatile MOF optical sensors based on the self-assembly of polyhedral ZIF-8 crystals into monolayer colloidal crystals (MCCs) with precisely controlled particle sizes, crystalline orientations and specific crystal facets. By eliminating grain boundaries and randomly exposed crystal surfaces, the fabricated polyhedral ZIF-8 MCCs exhibited ‘sharpened’ selectivity for organic vapors compared with in situ grown ZIF-8 films. The selectivity of polyhedral ZIF-8 MCCs was also found to depend on the exposed crystal facets. Among three polyhedral ZIF-8 MCCs, namely rhombic dodecahedral (RD), truncated rhombic dodecahedral (TRD) and slightly truncated cubic (TC) ZIF-8 MCCs, RD ZIF-8 MCCs exclusively exposing the (110) facets allow the detection of C5–C8 linear alkane, C6–C8 linear alkenes and C1–C8 linear alcohols according to the sequence of the carbon number, while all branched isomers were excluded through size sieving. Combining fast kinetics, wide linear range and excellent reversibility and stability, RD ZIF-8 MCCs were successfully applied for detecting gasoline octane number and achieving colorimetric sensing.

To improve solar light harvesting and charge separation efficiency, we develop a facile strategy for synthesizing defect-engineered three-dimensionally ordered macroporous (3DOM) WO3 photonic crystals via the colloidal crystal template method and subsequent H2/N2 atmosphere thermal treatment. The oxygen evolution rate of the obtained defect-engineered 3DOM WO3 (W270–400) is 40.1 μmol h−1, which is much higher than that of the untreated 3DOM WO3 and the defect-engineered WO3 nanoparticles. The enhanced performance is due to the good light harvesting and excellent charge transportion properties. The results show that the slow photon effect and bulk oxygen vacancy (VO) induced narrowed band gap greatly improve the light harvesting efficiency, while abundant surface VO can lower the valence band to increase the driving force for water oxidation, and thus significantly promote electron–hole separation. Our work can guide further design and preparation of high-efficiency defect-engineered 3DOM semiconductors for solar energy conversion.

The ability to generate rotation in ellipsoidal catalytic micro swimming devices by catalyst deposition at glancing angles allows reliable access to circling trajectories. This behaviour could enable propulsive ellipsoids to gather cargo and enhance mixing at small scales. Catalytically propelled colloidal rotation has been previously achieved in spherical swimming devices by means of neighbour shadowing during catalyst deposition leading to non-symmetrical coatings. However in this work shadowing effects arise due to the ellipsoid's inherent anisotropy, removing the requirement for a closely packed colloidal crystal monolayer. We use geometric analysis of the catalyst deposition process, and mechanistic understanding to propose a link between the observed trajectories and the catalyst distribution and suggest further routes to improve control of rotation rates.

Recent advances in high-performance flexible electronic devices have increased the demand for more diverse and complex nanofabrication methods; high-resolution, high-efficiency, and low-cost patterning strategies for next-generation devices are therefore required. In this study, we demonstrate the formation of dewetting-induced hierarchical patterns using two self-assembled materials: block copolymers (BCPs) and colloidal crystals. The combination of the two self-assembly methods successfully generates multiscale hierarchical patterns because the length scales of the periodic colloidal crystal structures are suitable for templating the BCP patterns. Various concentric ring patterns were observed on the templated BCP films, and a free energy model of the polymer chain was applied to explain the formation of these patterns relative to the template width. Frequently occurring spiral-defective features were also examined and found to be promoted by Y-junction defects.

We show that both the optical stopband wavelength and effective bandwidth of films of gel-immobilized loosely packed colloidal photonic crystals can be controlled over a wide range. When the gelation reagent of the charge-stabilized colloidal crystals was photopolymerized under ultraviolet light using different upper- and bottom-light intensities, it resulted in a gel-immobilized colloidal crystal film with a broadened Bragg reflection peak. Moreover, the width of the Bragg peak increased from 30 to 190 nm as the difference between the light intensities increased. Films with wider Bragg peaks exhibited a brighter reflection color because of the superposition of the shifted Bragg reflections. Furthermore, the Bragg wavelength could be varied over a wide range (500–650 nm) while maintaining the same broadened effective bandwidth by varying the swelling solvent concentration. These findings will expand the applicability of colloidal crystals for use in photonic devices and color pigments.

Self-assembly at the air/water interface (AWI) has proven to be an efficient strategy for fabricating two-dimensional (2D) colloidal monolayers, which was widely used as the template for nanosphere lithography in nanophononics, optofluidics, and solar cell studies. However, the monolayers fabricated at the AWI usually suffer from a small domain area and quasi-double layer structure caused by submerged particles. To overcome this, we proposed an improved protocol to prepare 2D colloidal monolayers free of overlapping nanospheres at the AWI. Utilizing the stable suspension infusion to the water surface, a convex meniscus, whose height is related to viscous force, was formed adjoining the three-phase boundary. As a result of the resistance of the convex meniscus, the polystyrene nanospheres in the initial suspension directly self-assembled into a preliminary monolayer, which proved effective in preventing nanospheres' sinking and increasing the colloidal crystal domain size. An optimal parameter for transferring the monolayer was also developed based on the numerical simulation results. Finally, a wafer-scale monolayer, covered with less than one nanosphere per 100 μm × 100 μm area, was achieved on the desired substrate with an average domain size attaining centimeter scale. The high-quality 2D colloidal crystal may further promote the application of nanosphere lithography, especially in the fields that require a defect-free template.

Cristobalite with ordered interstitial dual-sized mesopores was synthesized through the crystallization of silica colloidal crystals composed of monodispersed amorphous silica nanoparticles. An aqueous solution containing both a flux (Na2 O) and a carbon precursor (an aqueous low-molecular weight phenolic resin) was infiltrated into the interstices of silica colloidal crystals. The organic fraction in the nanocomposite was further polymerized and subsequently carbonized in an Ar flow at 750 °C to reinforce the colloidal crystal structure. The thermal treatment resulted in the crystallization of the colloidal crystals into cristobalite while retaining the porous structure. The cristobalite-carbon nanocomposite was calcined in air to remove the carbon and create interstitial ordered mesopores in the cristobalite. The surfaces of crystalline mesoporous silica are quite different from those of various ordered mesoporous silica with amorphous frameworks; thus, the present findings will be useful for a precise understanding and control of the interfaces between the mesopores and silica networks.

The combination of microstructures and nanostructures has broad application prospects. However, most existing methods are oriented to fabricating microstructures and nanostructures separately, and the fabrication of nanostructures on a microstructured surface at the wafer level is rarely studied. In this work, a new method of fabricating large-area high aspect ratio nano-cylinders on micro-pillars based on a colloidal crystal mask is proposed. An experimental device for stripping and draining was designed to create a polystyrene colloidal crystal mask. Together with reactive-ion etching and metal-assisted chemical etching, high aspect ratio nano-cylinders on micro-pillars with controllable size were obtained on a 4-inch silicon wafer. Wetting tests were performed on four groups of fabricated structures of different sizes, and the results showed that all samples were superhydrophobic. Thus, a method for fabricating uniform, size-controllable, large-area high aspect ratio nano-cylinders on micro-pillars with great potential as a superhydrophobic engineering material is proposed.

The high demand for H2 gas sensors is not just limited to industrial process control and leak detection applications but also extends to the food and medical industry to determine the presence of v...

A material that can capture changes in environmental stimuli as a color change can be used to develop sensors and displays. By producing an ordered structure in a polymer gel that reflects particular wavelengths of light, we can express the volume change that occurs based on the environment as the change in the wavelength of reflected light, i.e., structural color. To date, many systems have been developed to change the hue of the structural color as a function of temperature, pH, substance, applied force, and so on. However, as is expected from the principle of optical interference, the gel usually shows a red-shift with increasing volume. In this study, we propose a method for preparing structurally colored stimuli-responsive polymer gels that display appropriate color changes according to changes in environmental stimuli. For this purpose, we employ the photonic balls, which are spherical colloidal crystals consisting of monodisperse silica particles, as templates. By combining the wavelength-selective reflection generated from different photonic band gaps of the photonic balls, we succeeded in developing porous stimuli-responsive polymer gels that exhibited various types of color change, which are not observed in conventional systems.

The performance of photovoltaic devices can be improved and sustained when their surfaces are designed to increase light absorption of photoactive layers and minimize contaminant adsorption. Pyrami...

Icosahedral colloidal clusters are a new class of spherical colloidal crystals. This cluster allows for potentially superior optical properties in comparison to conventional onion-like colloidal su...

Optical metamaterials, engineered to exhibit electromagnetic properties not found in natural materials, may enable new light-based applications including cloaking and optical computing. While there have been significant advances in the fabrication of two-dimensional metasurfaces, planar structures create nontrivial angular and polarization sensitivities, making omnidirectional operation impossible. Although three-dimensional (3D) metamaterials have been proposed, their fabrication remains challenging. Here, we use colloidal crystal engineering with DNA to prepare isotropic 3D metacrystals from Au nanocubes. We show that such structures can exhibit refractive indices as large as ∼8 in the mid-infrared, far greater than that of common high-index dielectrics. Additionally, we report the first observation of multipolar Mie resonances in metacrystals with well-formed habits, occurring in the mid-infrared for submicrometer metacrystals, which we measured using synchrotron infrared microspectroscopy. Finally, we predict that arrays of metacrystals could exhibit negative refraction. The results present a promising platform for engineering devices with unnatural optical properties.

The electrochemical reduction of CO2 is a promising solution for sustainable energy research and carbon emissions. However, this solution has been challenged by the lack of active and selective catalysts. Here, we report a two-step synthesis of 3D ordered mesoporous Cu sphere arrays, which is fabricated by a dual template method using a poly methyl methacrylate (PMMA) inverse opal and the nonionic surfactant Brij 58 to template the mesostructure within the regular voids of a colloidal crystal. Therefore, the well-ordered 3D interconnected bi-continuous mesopores structure has advantages of abundant exposed catalytically active sites, efficient mass transport, and high electrical conductivity, which result in excellent electrocatalytic CO2RR performance. The prepared 3D ordered mesoporous Cu sphere array (3D-OMCuSA) exhibits a low onset potential of -0.4 V at a 1 mA cm−2 electrode current density, a low Tafel slope of 109.6 mV per decade and a long-term durability in 0.1 M potassium bicarbonate. These distinct features of 3D-OMCuSA render it a promising method for the further development of advanced electrocatalytic materials for CO2 reduction.

An ordered nanoporous silicone-based material with an inverse opal structure consisting of interconnected spherical pores was prepared by the thiol-ene reaction of linear and cyclic organosiloxanes...

Using a combination of fluorescence and bright-field optical imaging, the solid-state packing structures of semi-confined two-layer spherical colloidal crystals were observed during modulation of an external AC electric field. Upon increasing field strength, the bottom layer of colloids (layer 1) transitioned from the entropically favored hexagonal packing structure with p6m symmetry to a square-packing structure with p4m symmetry. The packing structure of layer 2 was determined by the packing structure of layer 1, with layer 2 particles resting in, and moving in registry with, the low-energy interstitial sites of layer 1. Modulation of the field strength thus resulted in a reversible transition between a face-centered cubic crystal structure and a body-centered cubic crystal structure at low and high field strengths, respectively. These structures were found to be sensitive to the particle density in the wells, with vacancies and insertions leading to the formation of mixed crystal phases at high field strengths.