Inverse Opal Structure Research Articles

Solid Deep Ultraviolet Diffracting Inverse Opal Photonic Crystals

We fabricated the first solid, mechanically robust inverse opal photonic crystals that diffract in the deep ultraviolet (UV) spectral region. These photonic crystals are fabricated by self-assembling <140 nm diameter monodisperse polystyrene nanoparticles into face centered cubic 3D close-packed structures on fused silica microscope slides in the presence of tetraethyl orthosilicate via a vertical deposition method. Tetraethyl orthosilicate condenses in the nanoparticle interstices during self-assembly, immobilizing the polystyrene nanoparticles in an SiO2 matrix. Removal of the polystyrene nanoparticles using piranha solution yields a stable SiO2 inverse opal structure that Bragg diffracts in the deep UV at <245 nm. We measured the UV–vis transmission, diffraction of a collimated deep UV white light source, and diffraction of 229 nm laser light in order to characterize the deep UV optical performance of these photonic crystals. We measured a maximum light attenuation of ∼98% at the Bragg condition, calcu...

Direct Synthesis and Pseudomorphic Transformation of Mixed Metal Oxide Nanostructures with Non‐Close‐Packed Hollow Sphere Arrays

AbstractWhile bottom‐up syntheses of ordered nanostructured materials at colloidal length scales have been successful at producing close‐packed materials, it is more challenging to synthesize non‐close‐packed (ncp) structures. Here, a metal oxide nanostructure with ncp hollow sphere arrays was synthesized by combining a polymeric colloidal crystal template (CCT) with a Pechini precursor. The CCT provided defined confinement through its tetrahedral (Td) and octahedral (Oh) voids where the three‐dimensionally (3D) ordered, ncp hollow sphere arrays formed as a result of a crystallization‐induced rearrangement. This nanostructure, consisting of alternating, interconnected large and small hollow spheres, is distinct from the inverse opal structures typically generated from these CCTs. The morphology of the ncp hollow sphere arrays was retained in pseudomorphic transformations involving sulfidation and reoxidation cycling despite the segregation of zinc during these steps.

Direct Synthesis and Pseudomorphic Transformation of Mixed Metal Oxide Nanostructures with Non-Close-Packed Hollow Sphere Arrays.

While bottom-up syntheses of ordered nanostructured materials at colloidal length scales have been successful at producing close-packed materials, it is more challenging to synthesize non-close-packed (ncp) structures. Here, a metal oxide nanostructure with ncp hollow sphere arrays was synthesized by combining a polymeric colloidal crystal template (CCT) with a Pechini precursor. The CCT provided defined confinement through its tetrahedral (Td ) and octahedral (Oh ) voids where the three-dimensionally (3D) ordered, ncp hollow sphere arrays formed as a result of a crystallization-induced rearrangement. This nanostructure, consisting of alternating, interconnected large and small hollow spheres, is distinct from the inverse opal structures typically generated from these CCTs. The morphology of the ncp hollow sphere arrays was retained in pseudomorphic transformations involving sulfidation and reoxidation cycling despite the segregation of zinc during these steps.

Inverse opal substrate-loaded mesenchymal stem cells contribute to decreased myocardial remodeling after transplantation into acute myocardial infarction mice.

BackgroundThe two-dimensional incubation method is now the most commonly method for mesenchymal stem cell (MSC) production. however, gene expression and secretion of growth factors are relatively low; thus, the transplanted cells cannot be effectively utilized for potential clinical applications after acute myocardial infarction (AMI).ObjectivesWe aimed to investigate whether our newly made substrates of inverse opal with specific surface microstructures for MSC culturing can increase the viability of the cells and can contributes to decreased myocardial remodeling after transplanted to AMI mice.MethodsThe inverse opal structure is fabricated by the convenient bottom-up approach of the self-assembly of colloidal nanoparticles. Mouse-derived MSCs were then cultured on the substrates when expanded at different times to investigate the cell growth status including morphology. Then the inverse opal substrates loaded MSCs were transplanted to AMI mice, cardiomyocyte apoptosis and LV remodeling were further compared. To explore the possible mechanisms of curation, the secretions and viability of MSCs on substrates were determined using mice ELISA kits and JC-1 mitochondrial membrane potential assay kits respectively at normal and hypoxic conditions.Results6 times expanded inverse opals allowed greatly the orderly growth of MSCs as compared to four (34% ± 10.6%) and two (20%±7.2%) times expanded as well as unexpanded (13%±4.1%) (P<0.001). Nearly 90% of MSCs showed orientation angle intervals of less than 30° when at the 6X expanded (89.6%±25%) compared to the percent of cells with 30°–60° (8.7%±2.6%) or ≥60° (1.7%±1.0%) orientation angle (P<0.001). After inverse opal loaded MSCs transplanted to AMI mice, greatly decreased apoptosis of cardiomyocytes (20.45%±8.64% vs.39.63%±11.71%, P<0.001) and infarction area (5.87±2.18 mm2 vs 9.31±3.11 mm2, P<0.001) were identified. In the end, the viability of inverse opal loaded MSCs determined by membrane potential (P<0.001) and the secretion of growth factors including VEGF-α, SDF-1 and Ang-1 (P<0.001) were both confirmed significantly higher than that of the conventional culture in petri dish.ConclusionThe structure of inverse opal can not only adjust the arrangement of MSCs but also contribute to its orientated growth. Inverse opal loaded MSCs transplantation extremely curbed myocardial remodeling, the underlying mechanisms might be the high viability and extremely higher secretions of growth factors of MSCs as devoted by this method.

Ferrocene‐Containing Inverse Opals by Melt‐Shear Organization of Core/Shell Particles

Inside Front Cover: In article number 1800428 by Markus Gallei and coworkers, a side-chain ferrocene-containing polymer as a matrix for a metallopolymer inverse opal structure is presented as a redox-active material. Vivid structural colors are obtained due to the well-ordered voids within the metallopolymer-containing matrix, and redox-responsiveness is also demonstrated, revealing both a change of surface wettability and structural reflection colors.

Synthesis of Silica Microspheres-Inspired by the Formation of Ice Crystals-With High Homogeneous Particle Sizes and Their Applications in Photonic Crystals.

Silica microspheres (SMs) must possess the performances of desirable monodispersity, narrow particle size distribution, and high sphericity for preparing photonic crystals (PCs) and other materials such as microspheres reference material, etc. We have adopted the techniques of increasing reactant concentration and raising the temperature to improve the synthesis rate of SMs, gaining inspiration from the formation mechanism of ice crystals. SMs with uniform particle sizes (polydispersity index less than 0.05) and good spherical features were fabricated through homogeneous nucleation. The mathematical relationship between particle sizes of SMs and reactant concentrations is further fitted. High accuracy of the regression equation is verified by an F-test and verification experiment. Highly ordered PCs (the stacking fault is about 1.5%, and the point defect is about 10−3) with dense stacked opal structures have been obtained by self-assembly of SMs. In addition, highly ordered PCs (the stacking fault is about 3%, and the point defect is about 10−3) with non-dense packed opal structure and inverse opal structure were successfully prepared. PCs of inverse opal structure were used to examine their response characteristics to identify ethanol, exhibiting good performance. Our research may provide significant inspiration for the development of other sorts of microspheres.

G-C3 N4 Inverse Opals with Isotype Heterostructure for Enhanced Visible-Light-Driven Photocatalysis.

The photocatalytic activity of g-C3 N4 is limited by the low surface area and the fast recombination of photogenerated charges. In this work, a g-C3 N4 quantum dot (CNQDs) modified g-C3 N4 inverse opal (CN IO) metal-free composite (CNQDs/CN IO) was successfully synthesized by a simple calcination method. CNQDs/CN IO exhibited outstanding photocatalytic activity in the removal of organic pollutants represented by phenol, which can be ascribed to (i) the inverse opal structure that enhances the light harvesting, facilitates mass transfer, and provides adequate surface area for photocatalytic reactions; (ii) the incorporation of CNQDs in the framework of g-C3 N4 promotes photogenerated charge separation and transfer across the interfaces between CN IO and CNQDs, leading to excellent photoelectrochemical properties. The strategy of self-modification of g-C3 N4 with special structures provides a rational design idea to fabricate highly efficient metal-free photocatalysts.

Tetrahedral framework of inverse opal photonic crystals defines the optical response and photonic band gap

By forming anatase TiO2 inverse opals by infiltration of an opal photonic crystal, we demonstrate that the optical response and angle-resolved blue-shift of the band-gap of the inverse opal structure are defined by a particular three-dimensional structure of the infilled voids. The optical structure of TiO2 inverse opals usually displays significant deviation from its physical structure and from the theoretically predicted position of the photonic band-gap. Following rigorous structural characterization of the parent opal template and TiO2 inverse opals, alternative explanations for the signature of optical transmission through inverse opals are proposed. These approaches posit that, for light-matter interaction, an inverse opal is not precisely the inverse of an opal. Accurate parameters for the structure and material properties can be obtained by invoking a Bragg FCC selection rule-forbidden (-211) plane, which is not a realistic model for diffraction in the IO. Alternatively, by assuming optical interactions with just the periodic arrangement of tetrahedral filled interstitial sites in the structure of the inverse opal, a complete reconciliation with the spectral blue-shift with the angle, photonic band gap, and material parameters is obtained when a reduced unit cell is defined based on interstitial void filling. The analysis suggests a reduced interplanar spacing (d = 1/√3 D, for pore diameter D), based on the actual structure of an inverse opal in general, rather than a definition based on the inverse of an FCC packed opal. This approach provides an accurate and general description for predicting the spectral response and material parameters of ordered inverse opal photonic crystal materials.

Ordered CdSe-sensitized TiO2 inverse opal film as multifunctional surface-enhanced Raman scattering substrate

The surface-enhanced Raman scattering (SERS) study on semiconductor material has attracted much attention, but the traditional semiconductor materials possess low SERS sensitivity and single function, which cannot meet the need of people very well. Here, the ordered three-dimensional CdSe-sensitized TiO2 (CdSe-TiO2) composite film with inverse opal structure (IOS) and multifunction was synthesized successfully. The as-prepared CdSe-TiO2 IOS film was first used as the excellent SERS substrate and photoelectrochemical material. The synergistic effect of slow photons, multiple scattering and CdSe sensitization make the SERS substrate more sensitive. The detection limit of the methylene blue (MB) on CdSe-TiO2 IOS film can be as low as 7 × 10−9 M. In addition, CdSe-TiO2 IOS exhibits excellent photoelectric converting performance, the photocurrent density of CdSe-TiO2 IOS can achieve 0.924 mA/cm2 under chopped light illumination at a fixed bias of 0 V versus Ag/AgCl. The above performance enhancement of CdSe-TiO2 IOS film makes it becoming a promising multifunctional material to be used in SERS detection and photoelectrochemical field.

Reliable and General Route to Inverse Opal Structured Nanohybrids of Carbon‐Confined Transition Metal Sulfides Quantum Dots for High‐Performance Sodium Storage

AbstractSodium‐ion batteries (SIBs) have recently attracted increasing attention as the promising alternative to lithium‐ion batteries due to their multiple advantages of abundant reserves and low cost. However, the development of highly desirable anode materials suitable for SIBs is still hampered by a rather low capacity, poor rate capability, and cycling stability. Herein, a deliberate design to implement reliable and simple fabrication of an inverse opal structured nanohybrid of carbon‐confined various transition metal sulfides quantum dots (QDs) is presented. Comprehensive characterizations demonstrate that the hybrids hold a 3D architecture with uniform dispersion of QDs in a conductive carbon matrix that in turn encapsulates these quantum dots. With Co9S8 as an example, such a unique architecture, when applied as the anode of SIBs, endows the hybrids with multiple advantages including a high reversible specific capacity, extraordinary high rate capability, and excellent durability over 2000 cycles charging–discharging process.

Effects of Surface Passivation on Trap States, Band Bending, and Photoinduced Charge Transfer in P3HT/TiO2 Hybrid Inverse Opals

We investigate the effect of a common TiO2 passivation reagent, TiCl4, on the photoinduced charge transfer of poly(3-hexylthiophene) (P3HT) to TiO2 in the inverse opal structure. Treating the inorganic oxide framework with TiCl4 leads to an increase in the size of the TiO2 nanoparticles, a thickening of the inverse opal framework, and a decrease in the trap-state photoluminescence. These changes lead to different energy alignments at the interface. In comparison to the unpassivated P3HT/TiO2 inverse opal, we measured a larger polaron yield, by as high as ninefold, and significantly shorter and more uniformly distributed polaron lifetimes in TiCl4-treated samples. We show that downward band bending in the polymer can be circumvented by tuning the trap states on the metal oxide using TiCl4, thereby eliminating the energetic barrier for photoelectron injection from the polymer to the metal oxide. The findings suggest a way to overcome a potential factor that has plagued the performance of metal oxide–polymer...

Assembly and optical properties of SiO2 three-dimensional ordered porous materials

ABSTRACTBy constantly trying to change the amount of sodium dodecyl benzene sulfonate (SDBS), monodispersed P(St-MMA-AA) colloids with diameters about 211 nm and 221 nm was synthesized successfully using emulsion polymerization. The colloidal crystal template was prepared by co-assembly of P(St-MMA-AA) microspheres and SiO2 sol. Finally, the P(St-MMA-AA) microspheres were calcined by the calcination method to prepare the macroporous ordered inverse opal structure materials.

Folic Acid-Functionalized Hybrid Photonic Barcodes for Capture and Release of Circulating Tumor Cells.

Recovery of circulating tumor cells (CTCs) from cancer patients by an efficient CTCs capture and release method can greatly increase their application in diagnostics and treatment of cancers. In this paper, we presented a folic acid (FA)-functionalized hybrid photonic barcode for capture and release of CTCs. The hybrid photonic barcodes were formed by two nano-ordered parts, poly(ethylene glycol) diacrylate (PEGDA) inverse opal structure for sustaining integrity and methacrylated gelatin (GelMA) gel filler for conjugating FA molecules to mediate cell capture. The nano-ordered structures of the hybrid photonic barcodes not only increased contact area, but also decreased steric hindrance among FA molecules. Thus, the topographic interaction between the barcodes and CTCs was greatly enhanced. In addition, GelMA gel was soft and extracellular matrix (ECM) alike, which was beneficial to decrease impairment to CTCs during the CTCs-barcode interaction as well as preserving their viability. Demonstrated by four CTCs types, Hela (epithelial tissue, folate receptor positive, FR+), A02 (bone marrow, FR+), Raji (lymphoid tissue, FR+), and A549 (epithelial tissue, folate receptor negative, FR-), FR+ CTCs could be captured efficiently with reliability and specificity. The captured cells could be controllably released with high viability just by quick trypsinization. The whole processes were simple and efficient. These features indicated that the FA-functionalized hybrid photonic barcodes were promising for full recovery of CTCs from cancer patients, which was important for diagnosis and treatment of cancer.

Au-Au composites with inverse opal structure for surface-enhanced Raman spectroscopy

Golden inverse opals additionally decorated with 15.5 ± 1.5 nm gold nanoparticles are proposed as reusable substrates for surface-enhanced Raman spectroscopy (SERS). Gold nanoparticles are found to be uniformly distributed making an input of enhancement ability of spectral characteristics with the colloidal system by ten times. This technique is demonstrated to be efficient in spectral features tuning via a combination of different gold derivatives. Two lasers served for resonant, pre-resonance, and non-resonance signal analyses. Reusability of the Au-Au composite films is demonstrated for methylene blue as a stable dye deposited onto the SERS chips using a 632.8-nm resonant laser for exciting. The enhancement factor for methylene blue achieved 108 and for rohodamine 6G was of about 105. It was observed that rinsing of Au-Au nanocomposite SERS films with distilled water and heating up to 100 °C followed by dropping on a new portion of Au colloids onto the platform regenerates the substrates.

Controlling the size of connecting windows in three-dimensionally ordered macroporous TiO2 for enhanced photocatalytic activity

Herein, for the first time, three-dimensionally ordered macroporous TiO2 (3DOM-TiO2) with well-tuned sizes of connecting windows were synthesized by regulation the driving force of the self-assembly process. 3DOM-TiO2 materials exhibit a clear relationship between photocatalytic activities and connecting window sizes, which provides a new perspective on the connecting window size effect. The possible mechanism of 3DOM-TiO2 with window-size dependent effect is also proposed, and it would guide further design and synthesis of highly efficient photocatalysts with controllable inverse opal structures.

Enhanced electrochromic properties of nanorod based WO3 thin films with inverse opal structure

Tungsten trioxide (WO3) is a typical electrochromic material that exhibits reversible optical property changes depending on the applied voltage. Previously, studies for its application in smart windows and various technologies have been made. However, improvements to the WO3-specific low color change rate are needed. The above problem can be solved by fabricating a color change layer with a large specific surface area through physical/chemical modification of the WO3 layer and structural control for smooth electrolyte injection. In this study, three dimensional porous WO3 nanostructures were prepared using polystyrene nanospheres. Inverse opal structured WO3 thin films with high porosity showed excellent electrochromic properties. The change in transmittance was 86% at a wavelength of 700 nm; the response time was 5.55 s; and the coloration efficiency was calculated at 154.94 cm2/C. The response time was about 3 times faster and the coloration efficiency was about 2 times higher than that of the flat thin film. As a result, the WO3 thin film with an inverted opal structure exhibited excellent electro reversibility and enhanced properties.

Egg Component-Composited Inverse Opal Particles for Synergistic Drug Delivery.

Microparticles have a demonstrated value in drug delivery systems. The attempts to develop this technology focus on the generation of functional microparticles by using innovative but accessible materials. Here, we present egg component-composited microparticles with a hybrid inverse opal structure for synergistic drug delivery. The egg component inverse opal particles were produced by using egg yolk to negatively replicate colloid crystal bead templates. Because of their huge specific surface areas, abundant nanopores, and complex nanochannels of the inverse opal structure, the resultant egg yolk particles could be loaded with different kinds of drugs, such as hydrophobic camptothecin (CPT), by simply immersing them into the corresponding drug solutions. Attractively, additional drugs, such as the hydrophilic doxorubicin (DOX), could also be encapsulated into the particles through the secondary filling of the drug-doped egg white hydrogel into the egg yolk inverse opal scaffolds, which realized the synergistic drug delivery for the particles. It was demonstrated that the egg-derived inverse opal particles were with large quantity and lasting releasing for the CPT and DOX codelivery, and thus could significantly reduce cell viability, and enhance therapeutic efficacy in treating cancer cells. These features of the egg component-composited inverse opal microparticles indicated that they are ideal microcarriers for drug delivery.

Z-Scheme Pt@CdS/3DOM-SrTiO3 composite with enhanced photocatalytic hydrogen evolution from water splitting

The core-shell shaped Pt@CdS nanoparticles were successful anchored onto the surface of three-dimensionally ordered macroporous (3DOM) SrTiO3 with different pore sizes through a two-step photo-deposition method, to form a series of promising Z-scheme Pt@CdS/3DOM-SrTiO3 composites for photocatalytic hydrogen evolution from water splitting. The well-ordered inverse opal and ternary heterojunction structure of Pt@CdS/3DOM-SrTiO3 composites were well illustrated through SEM and HRTEM characterizations. The Pt@CdS/3DOM-SrTiO3 composites exhibited excellent efficiency for hydrogen evolution (57.9 mmol/g h) under UV–vis light irradiation. Through a series of controlled experiments and related characterizations, the notably enhanced catalytic performance of Pt@CdS/3DOM-SrTiO3 composites can be mainly attributed to the synergistic effect of the slow photon enhancement of 3DOM-SrTiO3, which significantly promotes the light harvesting efficiency of photocatalysts, and the enhanced separation of photogenerated carriers because of the Z-scheme charge transfer mechanism. In addition, the ternary Pt@CdS/3DOM-SrTiO3 catalysts are very stable and can be recycled five times without any decrease in photocatalytic activity.

3D FTO/FTO-Nanocrystal/TiO2 Composite Inverse Opal Photoanode for Efficient Photoelectrochemical Water Splitting.

A 3D fluorine-doped SnO2 (FTO)/FTO-nanocrystal (NC)/TiO2 inverse opal (IO) structure is designed and fabricated as a new "host and guest" type of composite photoanode for efficient photoelectrochemical (PEC) water splitting. In this novel photoanode design, the highly conductive and porous FTO/FTO-NC IO acts as the "host" skeleton, which provides direct pathways for faster electron transport, while the conformally coated TiO2 layer acts as the "guest" absorber layer. The unique composite IO structure is fabricated through self-assembly of colloidal spheres template, a hydrothermal method and atomic layer deposition (ALD). Owing to its large surface area and efficient charge collection, the FTO/FTO-NC/TiO2 composite IO photoanode shows excellent photocatalytic properties for PEC water splitting. With optimized dimensions of the SnO2 nanocrystals and the thickness of the ALD TiO2 absorber layers, the 3D FTO/FTO-NC/TiO2 composite IO photoanode yields a photocurrent density of 1.0 mA cm-2 at 1.23 V versus reversible hydrogen electrode (RHE) under AM 1.5 illumination, which is four times higher than that of the FTO/TiO2 IO reference photoanode.

Investigation of Nanoporous Carbon Scaffold with Ordered Pore Structure As Microporous Layer for PEM Fuel Cells

The microporous layer (MPL) is a key component of the membrane electrode assembly (MEA) of a polymer electrolyte membrane fuel cell (PEMFC). Historically, the MPL has been prepared by applying a slurry of carbon particles and Teflon onto the carbon paper. Together, the carbon paper with the MPL on it is known as the gas diffusion layer. The MPL fabricated by the aforementioned method results in a random pore structure varying both in pore size (ranging 20-200 nm) and wettability (hydrophobic and hydrophilic). Although the primary role of the MPL is thought to improve water management, delineation of the effect of pore size from wettability becomes difficult in a physically and chemically heterogenous porous structure of a conventional MPL. Recently, the Birss group has developed nanoporous carbon scaffolds (NCS) with an inverse opal structure that has well-defined and tunable pore sizes. The wettability of the internal surface of the NCS films can also be altered by functionalization, from highly hydrophilic to hydrophobic. We have successfully integrated the NCS as an MPL in PEMFCs and evaluated its performance under low and high RH operations. The effect of pore size and wettability of NCS-based MPLs on the performance of PEMFCs will be presented in this talk.