Three-dimensional Inverse Opal Research Articles

A multi-platform sensor for selective and sensitive H2S monitoring: Three-dimensional macroporous ZnO encapsulated by MOFs with small Pt nanoparticles

The high-selectivity and high-sensitivity determination of trace concentrations of toxic gases is a major challenge when using semiconductor metal oxide (SMO) gas sensors in complicated real-world environments. In this study, by strategically combining a three-dimensional inverse opal (3DIO) macroporous ZnO substrate and a ZIF-8 outer filter membrane, two series of sensors with Pt NPs loaded at different locations are developed. In the optimal 3DIO ZnO@ZIF-8/Pt sensor, the existence of small Pt NPs in ZIF-8 cavities can effectively accelerate the absorption of H2S, capture electrons from the N site of ZIF-8, and donate the electron to the S site of H2S, as indicated by density functional theory simulations, leading to a significantly increased response to H2S. Together with the molecular-sieving effect that ZIF-8 exerts on gas molecules with larger kinetic diameters, the 3DIO ZnO@ZIF-8/Pt sensor exhibits a high response to H2S (118–5.5 ppm), a detection limit of 40 ppb, and importantly, a 59-fold higher selectivity to H2S against typical interference gases. In addition, the 3DIO ZnO@ZIF-8/Pt sensor is developed as a multi-platform sensor to evaluate trace concentrations of H2S in meat quality assessment, halitosis diagnosis, and automobile exhaust assessment.

Three-dimensional mesostructured binder-free nickel-based TiO2/RGO lithium-ion battery negative electrodes with enhanced volumetric capacity

Realization of high energy density Li-ion anodes is a significant challenge due to the volume changes generally exhibited by such systems during charge and discharge. Here, three-dimensional inverse opal (3D-IO) mesostructured Ni@TiO2@RGO electrodes were fabricated by templating nickel electrodeposition with self-assembled, three dimensionally ordered polystyrene (PS) opals, followed by atomic layer deposition (ALD) of TiO2 and spray coating of reduced graphene oxide (RGO). The electrode delivers initial discharge and charge volumetric capacities of 2082 mAh cm-3 and 1873 mAh cm-3 at 0.5 C, respectively. The composite electrode exhibits volumetric discharge and charge capacities of 1508 mAh cm-3 and 1504 mAh cm-3 at 0.5 C after 200 cycles and good rate capacity up to at least 10 C. The almost unbroken 3D-IO mesostructure after 200 lithiation and delithiation cycles demonstrates the excellent structural stability of the 3D-IO electrode design concept. The enhanced volumetric capacity and structural stability originate from high active materials loading, the short and efficient ion and electron pathways, and the composite structure provided by the nickel electrodeposition, ALD, and RGO spray coating electrode preparation process, as well as that both TiO2 and RGO participate in lithium storage.

Three-Dimensional Inverse Opal TiO2 Coatings to Enable the Gliding of Viscous Oils

As a result of the increasing emphasis on accessing unconventional deposits of heavy oil and bitumen to meet global energy needs, there is an intense focus on addressing the rheological challenges ...

Au@ZnO functionalized three–dimensional macroporous WO3: A application of selective H2S gas sensor for exhaled breath biomarker detection

Sensitive and selective determination of H2S in human exhalation is essential for understanding some physiological and pathological processes. However, effective detection of H2S at ppb level remains a challenge. In this work, three-dimensional inverse opal (3DIO) WO3 structure modified with metal-organic framework (MOF) derived ZnO@Au nanoparticles (NPs) were designed and fabricated for trace H2S detection. The ordered macroporous structure of 3DIO, n-n heterojunctions between WO3 and ZnO, and effective encapsulated of small-sized Au NPs benefited to the sensing performance. Compared to pristine 3DIO WO3 sensor, the response of MOF derived 3DIO WO3/ZnO@Au sensor enhanced 6.5-folds (175 to 10 ppm H2S), the optimal working temperature dramatically decreased to 170 °C, and the actual detection limit extended to 50 ppb with a response of 8.5. The good selectivity and long-term stability of the sensor were also identified. The theoretical simulation indicated that improved conductivity, higher negative charge of O, and increased adsorption energies contributed to the excellent selectivity. Furthermore, the proposed sensor could distinguish the trace H2S concentration change in the exhaled breath environment. This work demonstrates an example of a simple and versatile method for high performance H2S gas sensor design, which is promising for exhaled breath biomarker determination.

Highly sensitive and selective acetone sensor based on three-dimensional ordered WO3/Au nanocomposite with enhanced performance

With the development of medical science, analyzing the concentration of the volatile organic compounds (VOCs) in expiration has been considered as a rapid, convenient and noninvasive method for medical diagnosis. The detection of diabetes with acetone as a marker has received extensive attention, but the development of a highly sensitive acetone sensor remains various challenges to improve the sensing performance with nanostructure-controllable novel materials. In this work, an acetone sensor based on three-dimensional inverse opal (3DIO) tungsten oxide (WO3) composite modified with Au (WO3/Au) was obtained through a simple sacrificial template synthesis, which provided more active sites with macropore architecture. Moreover, with modification of Au nanoparticles (NPs), it is obvious that gas sensing property with “spillover effects” and catalytic action was obtained. The 3DIO WO3/Au gas sensor exhibited good selectivity to acetone, and showed great test performance from 100 ppb to 100 ppm. A corresponding actual detection limit of 100 ppb at 410 °C was realized, which could allow real-time and reliable diagnosis of diabetic by acetone monitoring. Furthermore, it also showed good stability and faster response and recovery times compared with pure WO3 sensors. The 3DIO WO3/Au gas sensor shows great potential in practical application of a noninvasive and more accurate monitoring and detection of diabetes.

ZnO@ZIF-8 inverse opal structure photoanode for efficient CdS/CdSe co-sensitized quantum dot solar cells

Photoanodes in quantum-dot-sensitized solar cells are essential to the process of light collection and charge transfer. In this paper, three-dimensional inverse opal (ZnO@ZIF-8 3D IO) photoanode is fabricated via a self-assembled opal template method. The synthesized photoanode has completely connected pores with extended diameter, thus promoting the permeability of QDs and electrolyte. Meanwhile, the light trapping ability and charge transfer process can be enhanced due to the slow photon and multi-scattering effect of the regularly interconnected macroporous array structure. ZIF-8 shell coated on the surface of ZnO IO not only provides high porosity but also serves as a protective passivation layer to reduce the carriers recombination occurred at the interfacial. In order to investigate the charge transport mechanism of ZnO @ ZIF-8 IO, cascaded CdS/CdSe quantum dots were used as sensitizers. Benefiting from the IO structure and ZIF-8 modification, the photoelectric conversion efficiency of solar cells based on ZnO@ZIF-8 IO can reach 1.75% (1.71 ± 0.04%), almost twice of that of the solar cells based on ZnO IO photoanode (0.81 ± 0.05%).

Highly dispersed Metal–Organic-Framework-Derived Pt nanoparticles on three-dimensional macroporous ZnO for trace-level H2S sensing

The effective detection of trace-level H2S gas is not only necessary for personal safety but is also important for understanding various physical and pathological processes in human biological systems. In this work, three-dimensional inverse opal (3DIO) ZnO sensors modified with small and well-dispersed Pt nanoparticles (NPs) are presented for ultra-low concentration H2S detection. The 3DIO ZnO skeleton, which is prepared through a simple self-assembly template method, provides fast diffusion pathways for H2S molecules and a large surface area for surface-related reactions. The optimal metal–organic framework (MOF)-derived 3DIO Pt/ZnO sensor exhibits an excellent response to trace H2S (11.2 at 1 ppm), a low detection limit (25 ppb), superior selectivity, and stability. The enhanced gas sensing performance can be attributed to the size effect of the Pt NPs and the rational design of the MOF-derived 3DIO Pt/ZnO nanomaterial. These results indicate that the strategy of combining the MOF-derived small and well-dispersed noble metal NPs with the 3DIO structure can efficiently improve the gas sensing properties for trace-level target gas determination. This method can likely be extended to similar systems based on 3DIO materials.

Three-Dimensional Inverse Opal Photonic Crystal Substrates toward Efficient Capture of Circulating Tumor Cells.

Artificial fractal structures have attracted considerable scientific interest in circulating tumor cells (CTCs) detection and capture, which plays a pivotal role in the diagnosis and prognosis of cancer. Herein, we designed a bionic TiO2 inverse opal photonic crystal (IOPC) structure for highly efficient immunocapture of CTCs by combination of a magnetic Fe3O4@C6@silane nanoparticles with anti-EpCAM (antiepithelial cell adhesion molecule) and microchannel structure. Porous structure and dimension of IOPC TiO2 can be precisely controlled for mimicking cellular components, and anti-EpCAM antibody was further modified on IOPC interface by conjugating with polydopamine (PDA). The improvement of CTCs capture efficiency reaches a surprising factor of 20 for the IOPC interface compared to that on flat glass, suggesting that the IOPCs are responsible for the dramatic enhancement of the capture efficiency of MCF-7 cells. IOPC substrate with pore size of 415 nm leads to the optimal CTCs capture efficiency of 92% with 1 mL/h. Besides the cell affinity, IOPCs also have the advantage of light scattering property which can enhance the excitation and emission light of fluorescence labels, facilitating the real-time monitoring of CTCs capture. The IOPC-based platform demonstrates excellent performance in CTCs capture, which will take an important step toward specific recognition of disease-related rare cells.

Three-dimensional ordered ZnO–Fe3O4 inverse opal gas sensor toward trace concentration acetone detection

Three-dimensional inverse opal (3DIO) ZnO-Fe3O4 composite structure was prepared by a template method and the gas sensing property was investigated toward trace acetone which is an important biomarker of diabetes. The prepared 3DIO composite sensors have large surface area due to both macropores (larger than 100nm) and mesoporous structure in skeleton, which make the inner surface accessible and provide more active sites to adsorb more oxygen species and target molecules. 3DIO ZnO-Fe3O4 composite sensor exhibits much higher response toward acetone relative to pure ZnO sensor. The optimal 3DIO sensor exhibited a detection limit as low as 100ppb acetone and showed 40% response increase from 0.9ppm (healthy humans) to 1.8ppm (diabetics) which allow reliable diagnosis of diabetic patients by acetone monitoring.

Gas Sensor Based on 3-D WO₃ Inverse Opal: Design and Applications.

A three-dimensional inverse opal (3DIO) WO3 architecture has been synthesized via a simple sacrificial template method. Morphology features of the 3DIO were characterized by scanning electron microscope (SEM) and its structure was characterized by X-ray diffraction (XRD). The shrinking ratio of the PMMA spheres was ~28.2% through measuring the distribution of the PMMA spheres and 3DIO WO3 center-to-center distance between the spheres and macropores, respectively. Beyond that, the 3DIO gas sensing properties were investigated systematically and the sensing mechanism of 3DIO WO3 was proposed. The results indicated that the response of the 3DIO sensor possessed excellent sensitivity to acetone gas, especially at trace levels. The 3DIO gas sensor response was ~7 to 5 ppm of acetone and could detect acetone low to 0.2 ppm effectively, which was in close proximity to the theoretical low detection limit of 0.14 ppm when Ra/Rg ≥ 1.2 was used as the criterion for reliable gas sensing. All in all, the obvious satisfaction of the gas-sensing properties was ascribed to the structure of the 3DIO, and the sensor could be a promising novel device in the future.

Three-dimensional In2O3–CuO inverse opals: synthesis and improved gas sensing properties towards acetone

Specific three-dimensional inverse opal (3DIO) In2O3–CuO architecture with additional via-holes was first prepared by a simple sacrificial template method.

Layer-by-Layer Assembly of Polyelectrolyte Multilayers in Three-Dimensional Inverse Opal Structured Templates

A novel means of layer-by-layer deposition (LbL) of polyelectrolyte multilayers on three-dimensionally porous inverse opal (3D-IO) structures is presented. The 3D-IO structures comprising UV-curable polymer are highly flexible and can be readily demonstrated as free-standing films with double-sided open porosity over a large scale. A conflict between the intrinsically hydrophobic polymeric structures and waterborne characteristics of the LbL deposition process is overcome by employing a mixed solvent system of water and alcohol. The deposition pH of the LbL assembly can strongly affect the charge density and the degree of entanglement of polyelectrolyte chains, resulting in contrastingly different film deposition and growth behaviors. Since this method utilizes a three-dimensionally structured surface as a deposition substrate, 3D-IO films with a thickness of tens of micrometers can be uniformly and completely deposited with polyelectrolyte multilayers using only several tens of bilayer depositions, which can offer a new pathway of fabricating functionalized polymeric films. Finally, the LbL treated 3D-IO films are applied to nanofiltration membranes for removing multivalent metallic cations. Due to the enhanced Donnan exclusion effect as a result of multiple interfaces formed inside the 3D-IO structures and the relatively large volumetric ratio of water-permeable polyelectrolyte complexes, outstanding membrane performance was observed. Specifically, a good rejection rate of metal ions was achieved even under highly diluted feed conditions without sacrificing the high permeation flux.

The Electrodeposition of Zinc Oxide Two-Dimensional Nanomesh and Three-Dimensional Inverse Opal Complex Connected Structures

The fabrication of the periodic ordered structures with complex shapes or heterostructures are important for many potential applications. In this paper, zinc oxide two-dimensional (2D) nanomesh and three-dimensional (3D) inverse opal complex connected structures were fabricated by the electrochemical deposition method. 2D ZnO nanosheets or sheet-like porous structures standing on the 3D ZnO inverse opals were synthesized. Two different methods: the co-deposition method and the two-step deposition method were employed for the preparation of the complex structures. The deposition process of complex structures is discussed. The photonic band gap of the complex macroporous structure was calculated using the Translight software and characterized by the micro-region reflection and transmission spectra. The exciton luminescence of ZnO can be inhibited by the inverse opal structure when the photonic band gap superposes with the luminescent band.