Macroporous Structures of Nb-SnO2 Particles as a Catalyst Support Induce High Porosity and Performance in Polymer Electrolyte Fuel Cell Catalyst Layers.

Macroporous niobium-doped tin oxide (NTO) is introduced as a robust alternative to conventional carbon-based catalyst supports to improve the durability and performance of polymer electrolyte fuel cells (PEFCs). Metal oxides like NTO are more stable than carbon under PEFC operational conditions, but they can compromise gas diffusion and water management because of their denser structures. To address this tradeoff, we synthesized macroporous NTO particles using a flame-assisted spray-drying technique employing poly(methyl methacrylate) as a templating agent. X-ray diffraction analysis and scanning electron microscopy confirmed the preservation of crystallinity and revealed a macroporous morphology with larger pore volumes and diameters than those in flame-made NTO nanoparticles, as revealed by mercury porosimetry. The macroporous NTO particles exhibited enhanced maximum current density and reduced gas diffusion resistance relative to commercial carbon supports. Our findings establish a foundation for integrating macroporous NTO structures into PEFCs to optimize durability and performance.

Controllable Synthesis of Porous and Hollow Nanostructured Catalyst Particles and Their Soot Oxidation.

The introduction of macroporous structures into three-way catalysts (TWCs) through polymer template-assisted spray drying has attracted attention because of its enhanced gas diffusion and catalytic performance. However, the surface charge effect of polymeric template components has not been investigated to control the structure of the TWC particles during synthesis. Thus, this study investigated the effect of template surface charges on the self-assembly behavior of TWC nanoparticles (NPs) during drying. The self-assembly of TWC NPs and polymer particles with different charges produced a hollow structure, whereas using the same charges generated a porous one. Consequently, the mechanism of particle self-assembly during drying and final structure particle formation is proposed in this study. Here, porous TWC particles demonstrated a faster oxidation of soot particles than that of hollow-structured particles. This occurred as a result of the larger contact area between the catalyst surface and the solid reactant. Our findings propose a fundamental self-assembly mechanism for the formation of different TWC structures, thereby enhancing soot oxidation performance using macroporous structures.

Designing the Macroporous Structure of Three-Way Catalyst Particles: The Influence of Template Concentration on Framework Thickness and Mass Transfer.

Mass transfer is an essential process that can extend the performance and utilization of nanoporous materials in various applications. Therefore, improving mass transfer in nanoporous materials has always attracted much interest, and macroporous structures are currently being studied to enhance mass transfer performance. The introduction of macroporous structures into three-way catalysts (TWC), which are widely utilized to control the emission of polluted gases from vehicles, provides the potential to enhance their mass transfer property and catalytic performance. However, the formation mechanism of macroporous TWC particles has not yet been investigated. On the other hand, the influence of the framework thickness of the macroporous structure on the mass transfer enhancement is still unclear. Therefore, this report investigates the particle formation and framework thickness of the macroporous TWC particles synthesized using the template-assisted aerosol process. The formation of macroporous TWC particles was precisely controlled and investigated by altering the size and concentration of the template particles. The template concentration played a crucial role in maintaining the macroporous structure and controlling the framework thickness between the macropores. Based on these results, a theoretical calculation showing the influence of template concentration on the particle morphology and framework thickness was developed. The final results showed that increasing the template concentration can positively affect the nanoporous material's framework thickness reduction and mass transfer coefficient improvement.

Synthesis of Submicron-Sized Spherical Silica-Coated Iron Nickel Particles with Adjustable Shell Thickness via Swirler Connector-Assisted Spray Pyrolysis.

Silica-coated iron nickel (FeNi@SiO2) particles have attracted significant attention because of their potential applications in electronic devices. In this work, submicron-sized spherical FeNi@SiO2 particles with precisely controllable shell thickness were successfully synthesized for the first time using a swirler connector-assisted spray pyrolysis system, comprising a preheater, specific connector, and main heater. The results indicated that the thickness of the SiO2 shell can be tuned from 3 to 23 nm by adjusting the parameter conditions (i.e., preheater temperature, SiO2 supplied amount). Furthermore, our fabrication method consistently yielded a high coating ratio of more than 94%, indicating an excellent quality of the synthesized particles. Especially, to gain an in-depth understanding of the particle formation process of the FeNi@SiO2 particles, a plausible mechanism was also investigated. These findings highlight the importance of controlling the preheater and SiO2 supplied amount to obtain FeNi@SiO2 particles with desirable morphology and high coating quality.

A 3.06 µm Single-Photon Avalanche Diode Pixel with Embedded Metal Contact and Power Grid on Deep Trench Pixel Isolation for High-Resolution Photon Counting.

In this study, a 3.06 µm pitch single-photon avalanche diode (SPAD) pixel with an embedded metal contact and power grid on two-step deep trench isolation in the pixel is presented. The embedded metal contact can suppress edge breakdown and reduce the dark count rate to 15.8 cps with the optimized potential design. The embedded metal for the contact is also used as an optical shield and a low crosstalk probability of 0.4% is achieved, while the photon detection efficiency is as high as 57%. In addition, the integration of a power grid and the polysilicon resistor on SPAD pixels can help to reduce the voltage drop in anode power supply and reduce the power consumption with SPAD multiplication, respectively, in a large SPAD pixel array for a high-resolution photon-counting image sensor.

Innovative surfactant-free synthesis of core-shell SiO2/ZnO particles: rapid ultrasonication and photocatalytic inhibition.

This study demonstrates the preparation of SiO2/ZnO core-shell nanoparticles with controllable shell size and their optical properties. A facile ultrasonication method was utilized to prepare the core-shell particles in the absence of surfactant materials. The synthesis duration was 75% shorter than that required for the common sol-gel method, which favours its potential applicability in the future for mass production. Tetraethyl orthosilicate (TEOS) was used as the silica source, while the core material was prepared using zinc acetate dihydrate. The outer shell size could easily be controlled by changing the molar ratio of silica from 0.25 to 1.00. The experimental results show that increasing the silica ratio was effective in suppressing the self-agglomeration of ZnO and, further, in obtaining agglomeration-free particles. The investigation of the photoluminescence (PL) properties of nanometre-sized ZnO revealed several emission peaks in the ultraviolet (UV) wavelength range, indicating variations in bandgap energy. This did not appear in the spectrum of micrometre-sized ZnO particles. The core-shell particles produced with higher amounts of silica showed higher UV-A and UV-B absorption. In addition, the presence of silica reduced the photocatalytic activity of ZnO by 65% and reduced the PL intensity. The obtained emission peaks, intensity changes, and spectral characteristics open new avenues for further research on tailoring the properties of SiO2/ZnO core-shell structures for specific technological advancements. These advancements hold promising applications in UV attenuation materials, LED technologies, lenses, and solar cells within the realm of optical devices.

Nanostructuring silica-iron core-shell particles in a one-step aerosol process.

Silica-coated iron (Fe@SiO2) particles have attracted considerable interest as a potential powder core material due to their distinctive advantages, including higher magnetic saturation and enhanced electrical resistance. In this study, the submicron-sized core-shell Fe@SiO2 particles were successfully synthesized in a single step via an aerosol process using a spray pyrolysis method assisted by a swirler connector for the first time. Changing the reducing agent concentration (supplied H2) and tuning the number of core (Fe) particles were investigated to achieve the desired Fe@SiO2 particles. The results indicated that an excessive number of cores led to the appearance of FeO crystals due to insufficient reduction. Conversely, an insufficient number of cores resulted in a thicker SiO2 shell, which hindered the penetration of the supplied H2 gas. Furthermore, the produced Fe@SiO2 particles exhibited soft-ferromagnetic characteristics with an excellent magnetic saturation value of 2.04 T, which is close to the standard theoretical value of 2.15 T. This work contributes new insights into the production of core-shell Fe@SiO2 particles, expanding their applicability to advanced soft-magnetic materials.

Controlling the Magnetic Responsiveness of Cellulose Nanofiber Particles Embedded with Iron Oxide Nanoparticles.

2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanofiber (TOCN) particles, an innovative biobased material derived from wood biomass, have garnered significant interest, particularly in the biomedical field, for their distinctive properties as biocompatible particle adsorbents. However, their microscopic size complicates their separation in liquid media, thereby impeding their application in various domains. In this study, superparamagnetic magnetite nanoparticles (NPs), specifically iron oxide Fe3O4 NPs with an average size of 15 nm, were used to enhance the collection efficiency of TOCN-Fe3O4 composite particles synthesized through spray drying. These composite particles exhibited a remarkable ζ-potential (approximately -50 mV), indicating their high stability in water, as well as impressive magnetization properties (up to 47 emu/g), and rapid magnetic responsiveness within 60 s in water (3 wt % Fe3O4 to TOCN, 1 T magnet). Furthermore, the influence of Fe3O4 NP concentrations on the measurement of the speed of magnetic separation was quantitatively discussed. Additionally, the binding affinity of the synthesized particles for proteins was assessed on a streptavidin-biotin binding system, offering crucial insights into their binding capabilities with specific proteins and underscoring their significant potential as functionalized biomedical materials.

Rapid Indomethacin Release from Porous Pectin Particles as a Colon-Targeted Drug Delivery System.

The conventional pectin delivery systems in the colon are often impaired by a slow release rate. Nanostructured particles, especially porous ones, have gained popularity as drug delivery systems owing to their high mass transfer efficiency. In this research, porous pectin particles were synthesized as drug carriers (using indomethacin as a model drug) via template-assisted spray drying. Specific surface areas of the porous pectin particles have been improved by up to 203 m2 g-1 compared with nonporous particles (1 m2 g-1). The porous structure shortened the diffusion path and improved the release rate of drug molecules. Additionally, the predominant drug release mechanism from porous pectin particles is Fickian diffusion, which is different from the combination of erosion and diffusion mechanism observed for nonporous particles. As a result, these porous drug-loaded pectin particles demonstrated rapid drug release rates of up to three times faster than nonporous particles. Control of the release rate could be achieved by changing the porous structure of the particles. This strategy is an efficient means to synthesize porous particles allowing rapid drug release into the colonic target.

Macropore-Size Engineering toward Enhancing the Catalytic Performance of CO Oxidation over Three-Way Catalyst Particles.

In recent years, transportation-related air pollution has escalated into a global concern, necessitating the development of a three-way catalyst (TWC) technology to address harmful emissions. However, the efficiency of TWC's performance in mitigating these emissions has been hindered because of limited mass transfer efficiency within their structures. Thus, this study attempted to overcome the existing issue by synthesizing a series of macroporous TWC particles exhibiting various macropore sizes via a template-assisted spray process, aiming to achieve optimal mass transfer efficiency and catalytic performance. The synthesis incorporated various template particles (size of 67-381 nm) to obtain various macroporous structures. Thereafter, these macroporous particles were assessed for their carbon monoxide (CO) oxidation performance, revealing a substantial influence of the macropore size on the catalytic performance of TWC structures. Interestingly, among the investigated samples, those containing the smallest and largest macropores demonstrated the highest CO oxidation performances. Based on these results, a plausible reactant diffusion mechanism was proposed to explain the effect of the macropore size on the diffusion efficiency within the macroporous structures. This work may have significant implications in optimizing the macroporous structure to enhance catalytic performance in the gas purification process.

Tuning of water resistance and protein adsorption capacity of porous cellulose nanofiber particles prepared by spray drying with cross-linking reaction.

Porous particles composed of 2,2,6,6-tetramethylpiperidinyl-1-oxyl-oxidized cellulose nanofiber (TOCN) as building block, i.e., porous TOCN particles, are attracting attention due to their environmental friendliness, superior properties, such as easy handling, large surface area, and high adsorption capacity. However, the instability of TOCNs in aqueous environments limits their applications. An effective solution to improve water resistance of TOCN particles is to reduce the hydrophilicity of TOCNs by forming chemical bonds with a cross-linker. In this study, Carbodilite, a common, easy-to-use, commercially available cross-linker with carbodiimide groups, was used to investigate a chemical cross-linking strategy for porous TOCN particles prepared by spray drying. The water resistance of cross-linked TOCN particles was evaluated through morphological observation by SEM images. The presence of polycarbodiimide significantly increased water resistance of cross-linked TOCN particles up to 24 h. This study demonstrates the trade-off between water resistance and adsorption efficiency according to cross-linker concentrations. These data are useful for interface science of TOCNs in liquids, assisting in controlling specific properties of porous TOCN particles for particular applications in adsorption and separation.

Spherical submicron YAG:Ce particles with controllable particle outer diameters and crystallite sizes and their photoluminescence properties.

The purpose of this study was to demonstrate the preparation of spherical submicron YAG:Ce particles with controllable particle outer diameters and crystallite sizes and their photoluminescence (PL) properties, which were produced using a flame-assisted spray-pyrolysis method followed by the annealing process. The correlation of particle outer diameter, crystallite size, and PL performance of the prepared particles was also investigated. Experimental results showed that the increases in the particle outer diameters have an impact on the obtainment of higher PL performance. Large particle outer diameters permitted the crystallites to grow more, whereas this is in contrast to the condition for small particle outer diameter having limitations in crystallite growth. This study also found that too large outer diameter (>557 nm) was not effective since crystallites cannot grow anymore and it permits possible scattering problems. This study provides significant information for optimizing synthesis parameters for controlling particle outer diameters and crystallite sizes, which could be relevant to other functional properties, especially for lens, solar cell, and LED applications.

Correlations between Reduction Degree and Catalytic Properties of WO x Nanoparticles.

Degrading organic dyes via catalytic processes for waste water purification is an important research topic from the environmental conservation point of view. Herein, the catalytic performance of tungsten blue oxide (WO x ) nanoparticles was investigated systematically by varying the reduction temperature. The optimum reduction temperature to obtain the most stable WO x phase was obtained when plasma-synthesized WO3 nanoparticles were thermally reduced at 425 °C. The as-synthesized nanoparticles had an average diameter of 10 nm and a calculated band gap of 2.37 eV, which is lower than that of the WO3 nanoparticles (2.61 eV). The WO x nanoparticles exhibited an excellent performance in degrading rhodamine B under dark conditions and visible light irradiation, with a reaction rate constant 93 times higher than that of the WO3 nanoparticles.

IR sensitivity enhancement of CMOS Image Sensor with diffractive light trapping pixels.

We report on the IR sensitivity enhancement of back-illuminated CMOS Image Sensor (BI-CIS) with 2-dimensional diffractive inverted pyramid array structure (IPA) on crystalline silicon (c-Si) and deep trench isolation (DTI). FDTD simulations of semi-infinite thick c-Si having 2D IPAs on its surface whose pitches over 400 nm shows more than 30% improvement of light absorption at λ = 850 nm and the maximum enhancement of 43% with the 540 nm pitch at the wavelength is confirmed. A prototype BI-CIS sample with pixel size of 1.2 µm square containing 400 nm pitch IPAs shows 80% sensitivity enhancement at λ = 850 nm compared to the reference sample with flat surface. This is due to diffraction with the IPA and total reflection at the pixel boundary. The NIR images taken by the demo camera equip with a C-mount lens show 75% sensitivity enhancement in the λ = 700-1200 nm wavelength range with negligible spatial resolution degradation. Light trapping CIS pixel technology promises to improve NIR sensitivity and appears to be applicable to many different image sensor applications including security camera, personal authentication, and range finding Time-of-Flight camera with IR illuminations.