A General and Straightforward Route to Noble Metal-Decorated Mesoporous Transition-Metal Oxides with Enhanced Gas Sensing Performance

A Straightforward Solvent-Pair-Enabled Multicomponent Coassembly Approach toward Noble-Metal-Nanoparticle-Decorated Mesoporous Tungsten Oxide for Trace Ammonia Sensing

The straightforward synthesis of noble-metal-nanoparticle-decorated ordered mesoporous transition metal oxides remains a great challenge due to the difficulty of balancing the interactions between precursors and templates. Herein, a solvent-pair-enabled multicomponent coassembly (SPEMC) strategy is developed for straightforward synthesis of noble-metal-nanoparticle-decorated nitrogen-doped ordered mesoporous tungsten oxide (abbreviated as NM/N-mWO3, NM = Pt, Rh, Pd). The amphiphilic poly(ethylene oxide)-block-polystyrene (PEO-b-PS) copolymers coassemble with ammonium metatungstate (AMT) clusters and different kinds of hydrophilic noble metal precursors without phase separation. SPEMC synthesis requires no direct interaction between PEO-b-PS and AMT, thus the assembly equilibriums between noble metal precursors and PEO-b-PS can be readily controlled. The obtained NM/N-mWO3 nanocomposites possess ordered mesopores, abundant oxygen vacancies, and metal-metal oxide interfaces. As a result, the Pt/N-mWO3 sensors exhibit superior ammonia sensing performances with high sensitivity, an ultralow limit of detection (51.2 ppb), good selectivity, and long-term stability. Spectroscopic analysis reveals that ammonia is oxidized stepwise to NO, NO2 -, and NO3 - during the sensing process. Moreover, a portable wireless module based on Pt/N-mWO3 sensor can recognize ppm-level concentration of ammonia, which lays a solid foundation for its application in various fields.

Iridium nanoparticles supported on polyaniline nanotubes for peroxidase mimicking towards total antioxidant capacity assay of fruits and vegetables

In this study, a straightforward approach is presented for the first time to anchor Ir nanoparticles on the surface of uniform polyaniline (PANi) nanotubes (NTs), which can be used as an efficient peroxidase (POD)-like catalyst. The morphology and chemical structure of the PANi-Ir nanocomposite are characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffractometer (XRD), Raman and X-ray photoelectron spectroscopy (XPS) measurements. Owing to the strong interaction between Ir nanoparticles and PANi, a remarkable catalytic enhancement is achieved compared to the bare Ir black catalyst and individual PANi NTs, dominating withan electron transfer mechanism. Furthermore, an efficient colorimetric sensor for ascorbic acid (AA) is developed with a low detection limit of 1.0 μM (S/N = 3), and a total antioxidant capacity (TAC) sensing platform is also constructed for the rigorous detection and analysis of fruits and vegetables.

Mechanism of Interfacial Molecular Interactions Reveals the Intrinsic Factors for the Highly Enhanced Sensing Performance of Ag-Loaded Co3O4

The noble metal-loaded strategy can effectively improve the gas-sensing performances of metal oxide sensors. However, the gas-solid interfacial interactions between noble metal-loaded sensing materials and gaseous species remain unclear, posing a significant challenge in correlating the physical and chemical processes during gas sensing. In this study, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and in situ Raman spectroscopy were conducted to collaboratively investigate the interfacial interactions involved in the ethanol gas-sensing processes over Co3O4 and Ag-loaded Co3O4 sensors. In situ DRIFTS revealed differences in the compositions and quantities of sensing reaction products, as well as in the adsorption-desorption interactions of surface species, among Co3O4 and Ag-loaded Co3O4 materials. In parallel, in situ Raman spectroscopy demonstrated that the ethanol atmosphere can modulate the electron scattering of Ag-loaded Co3O4 materials but not of raw Co3O4. In situ experimental results revealed the intrinsic reason for the highly enhanced sensing performances of the Ag-loaded Co3O4 sensors toward ethanol gas, including a decreased optimal working temperature (from 250 to 150 °C), an improved gas response level (from 24 to 257), and accelerated gas recovery dynamics. This work provides an effective platform to investigate the interfacial interactions of sensing processes at the molecular level and further advances the development of high-performance gas sensors.

Chemical bonding and electronic properties along Group 13 metal oxides

CONTEXT

The present work provides a systematic theoretical analysis of the nature of the chemical bond in Al2O3, Ga2O3, and In2O3 group 13 cubic crystal structure metal oxides. The influence of the functional in the resulting band gap is assessed. The topological analysis of the electron density provides unambiguous information about the degree of ionicity along the group which is linearly correlated with the band gap values and with the cost of forming a single oxygen vacancy. Overall, this study offers a comprehensive insight into the electronic structure of metal oxides and their interrelations. This will help researchers to harness information effectively, boosting the development of novel metal oxide catalysts or innovative methodologies for their preparation.

METHODS

Periodic density functional theory was used to predict the atomic structure of the materials of interest. Structure optimization was carried out using the PBE functional, using a plane wave basis set and the PAW representation of the atomic cores, using the VASP code. Next, the electronic properties were computed by carrying out single point calculations employing PBE, PBE + U functionals using VASP and also with PBE and the hybrid HSE06 functionals using the FHI-AIMS software. For the hybrid HSE06, the impact of the screening parameter, ω, and mixing parameter, α, on the calculated band gap has also been assessed.

Wafer-Level Manufacturing of MEMS H2 Sensing Chips Based on Pd Nanoparticles Modified SnO2 Film Patterns

In this manuscript, a simple method combining atomic layer deposition and magnetron sputtering is developed to fabricate high-performance Pd/SnO2 film patterns applied for micro-electro-mechanical systems (MEMS) H2 sensing chips. SnO2 film is first accurately deposited in the central areas of MEMS micro hotplate arrays by a mask-assistant method, leading the patterns with wafer-level high consistency in thickness. The grain size and density of Pd nanoparticles modified on the surface of the SnO2 film are further regulated to obtain an optimized sensing performance. The resulting MEMS H2 sensing chips show a wide detection range from 0.5 to 500 ppm, high resolution, and good repeatability. Based on the experiments and density functional theory calculations, a sensing enhancement mechanism is also proposed: a certain amount of Pd nanoparticles modified on the SnO2 surface could bring stronger H2 adsorption followed by dissociation, diffusion, and reaction with surface adsorbed oxygen species. Obviously, the method provided here is quite simple and effective for the manufacturing of MEMS H2 sensing chips with high consistency and optimized performance, which may also find broad applications in other MEMS chip technologies.

Novel ultrasensitive Raman assay method based on enzyme mimetics for ultra trace of H2O2

Enzyme mimetics have been widely applied on H₂O₂ assay, but it is still challenging and interesting to realize the sensitive detection for ultra-trace H₂O₂. Here, an ultrasensitive Raman assay method based on novel WO₃@IP6-Fe³⁺ enzyme mimetics with peroxidase-like activity was established. WO₃ microspheres (MSs) were found to have weak peroxidase-like activity, and the combination of IP6-Fe³⁺ and WO₃ can produce stronger activity. WO₃@IP6-Fe³⁺ MSs showed polyhedron-like structure, uniform size, and smooth surface. Although WO₃@IP6-Fe³⁺ enzyme mimetics have low catalytic efficiency and high absorbance background, the proposed Raman method can bypass the above problems. In Raman method, high concentration of WO₃@IP6-Fe³⁺ can be used to overcome low catalytic efficiency without high absorbance background. Moreover, 3,3',5,5'-tetramethylbenzidine oxide has prominent characteristic Raman peak at 1608 cm^-1, greatly improving the sensitivity and eliminating interference of impurities. Due to the high sensitivity and low background, Raman assay showed the ultra-low limit of detection (5.49 × 10^-15 M), which was 4-7 orders of magnitude lower than other detection methods. The ultrasensitive Raman assay not only provided the possibility for the enzyme mimetics-based detection of ultra-trace H₂O₂, but also enable the enzyme mimetics with low activity to be applied.

Polymerization-Induced Aggregation Approach toward Uniform Pd Nanoparticle-Decorated Mesoporous SiO2/WO3 Microspheres for Hydrogen Sensing

Hydrogen as an important clean energy source with a high energy density has attracted extensive attention in fuel cell vehicles and industrial production. However, considering its flammable and explosive property, gas sensors are desperately desired to efficiently monitor H₂ concentration in practical applications. Herein, a facile polymerization-induced aggregation strategy was proposed to synthesize uniform Si-doped mesoporous WO₃ (Si-mWO₃) microspheres with tunable sizes. The polymerization of the melamine-formaldehyde resin prepolymer (MF prepolymer) in the presence of silicotungstic acid hydrate (abbreviated as H₄SiW) leads to uniform MF/H₄SiW hybrid microspheres, which can be converted into Si-mWO₃ microspheres through a simple thermal decomposition treatment process. In addition, benefiting from the pore confinement effect, monodispersed Pd-decorated Si-mWO₃ microspheres (Pd/Si-mWO₃) were subsequently synthesized and applied as sensitive materials for the sensing and detection of hydrogen. Owing to the oxygen spillover effect of Pd nanoparticles, Pd/Si-mWO₃ enables adsorption of more oxygen anions than pure mWO₃. These Pd nanoparticles dispersed on the surface of Si-mWO₃ accelerated the dissociation of hydrogen and promoted charge transfer between Pd nanoparticles and WO₃ crystal particles, which enhanced the sensing sensitivity toward H₂. As a result, the gas sensor based on Pd/Si-mWO₃ microspheres exhibited excellent selectivity and sensitivity (R_air/R_gas = 33.5) to 50 ppm H₂ at a relatively low operating temperature (210 °C), which was 30 times higher than that of the pure Si-mWO₃ sensor. To develop intelligent sensors, a portable sensor module based on Pd/Si-mWO₃ in combination with wireless Bluetooth connection was designed, which achieved real-time monitoring of H₂ concentration, opening up the possibility for use as intelligent H₂ sensors.

Synthesis of Mesoporous Ag2O/SnO2 Nanospheres for Selective Sensing of Formaldehyde at a Low Working Temperature

Formaldehyde (HCHO) is a prevalent indoor gas pollutant that has been seriously endangering human health. Developing semiconductor metal oxide (SMO) gas sensors for selective measurement of formaldehyde at low working temperatures remains a great challenge. In this work, silver/tin-polyphenol hybrid spheres are applied as a sacrificial template for the fabrication of spherical mesoporous Ag₂O/SnO₂ sensing materials. The obtained mesoporous Ag₂O/SnO₂ spheres have a uniform particle size (∼80 nm), large pore size (5.8 nm), and high specific surface area (71.3 m² g^-1). The response is 140 toward formaldehyde (10 ppm) at a low working temperature (75 °C). The detection limit reaches a low level of 23.6 ppb. Most importantly, it has excellent selectivity toward interfering gases. When the concentration of the interfering gas (e.g., ethanol) is 5 times as high as that of formaldehyde, the response is little affected. Theoretical calculations suggest that the addition of Ag₂O can significantly enhance the adsorption energy toward formaldehyde, thus improving formaldehyde sensing performance. This work demonstrates an efficient self-template synthesis strategy for noble metal catalyst-decorated mesoporous metal oxide spheres, which could boost gas sensing performance at a lower working temperature.

Modeling Interfacial Interaction between Gas Molecules and Semiconductor Metal Oxides: A New View Angle on Gas Sensing

With the development of internet of things and artificial intelligence electronics, metal oxide semiconductor (MOS)-based sensing materials have attracted increasing attention from both fundamental research and practical applications. MOS materials possess intrinsic physicochemical properties, tunable compositions, and electronic structure, and are particularly suitable for integration and miniaturization in developing chemiresistive gas sensors. During sensing processes, the dynamic gas-solid interface interactions play crucial roles in improving sensors' performance, and most studies emphasize the gas-MOS chemical reactions. Herein, from a new view angle focusing more on physical gas-solid interactions during gas sensing, basic theory overview and latest progress for the dynamic process of gas molecules including adsorption, desorption, and diffusion, are systematically summarized and elucidated. The unique electronic sensing mechanisms are also discussed from various aspects including molecular interaction models, gas diffusion mechanism, and interfacial reaction behaviors, where structure-activity relationship and diffusion behavior are overviewed in detail. Especially, the surface adsorption-desorption dynamics are discussed and evaluated, and their potential effects on sensing performance are elucidated from the gas-solid interfacial regulation perspective. Finally, the prospect for further research directions in improving gas dynamic processes in MOS gas sensors is discussed, aiming to supplement the approaches for the development of high-performance MOS gas sensors.

Controllable construction of ZnFe2O4-based micro-nano heterostructure for the rapid detection and degradation of VOCs

Micro-nano heterogeneous oxides have received extensive attention due to their distinctive physicochemical properties. However, it is a challenge to prepare the hierarchical multicomponent metal oxide nanomaterials with abundant heterogeneous interfaces in a controllable way. In this work, the effective construction of the heterogeneous structure of the material is achieved by regulating the ratio of metal salts under thermal solvent condition. Three-dimensional spheres (ZnFe₂O₄) constructed by zero-dimensional ultra-small nanoparticles, in particular three-dimensional hollow sea urchin spheres (ZnO/ZnFe₂O₄) constructed by one-dimensional nanorods and three-dimensional hydrangeas (α-Fe₂O₃/ZnFe₂O₄) assembled by two-dimensional nanosheets were obtained. The two composite materials contain a large number of heterojunctions, which enhances the sensitivity of material to volatile organic compounds gas. Among them, the α-Fe₂O₃/ZnFe₂O₄ composite shows the best sensing performance for VOCs. For example, its response to 100 ppm acetone reaches 142 at 170 °C with the response time shortened to 3 s and the detection limit falling to 10 ppb. Meanwhile, the composite material presents a degradation rate of more than 90% for VOCs at a flow rate of 20 mL/min at 170 °C. In addition, the sensing and sensitivity mechanism of the composite material are studied in detail by combining GC-MS, XPS with UV diffuse reflectance tests.

Fabrication of Zn-Cu-Ni Ternary Oxides in Nanoarrays for Photo-Enhanced Pseudocapacitive Charge Storage

To meet the increasing demands of energy consumption, sustainable energy sources such as solar energy should be better employed to promote electrochemical energy storage. Herein, we fabricated a bifunctional photoelectrode composed of copper foam (CF)-supported zinc-nickel-copper ternary oxides in nanoarrays (CF@ZnCuNiOx NAs) to promote photo-enhanced pseudocapacitive charge storage. The as-fabricated CF@ZnCuNiOx NAs have shown both photosensitive and pseudocapacitive characteristics, demonstrating a synergistic effect on efficient solar energy harvest and conversion. As a result, a high areal specific capacitance of 2741 mF cm−2 (namely 418 μAh cm−2) under light illumination can be calculated at 5 mA cm−2, which delivered photo-enhancement of 38.3% compared to that obtained without light. In addition, the photoelectric and photothermal effects of the light energy on pseudocapacitive charge storage have been preliminarily studied and compared. This work may provide some evidence on the different mechanisms of photoelectric/thermal conversion for developing solar-driven energy storage devices.

Ligand-assisted deposition of ultra-small Au nanodots on Fe2O3/reduced graphene oxide for flexible gas sensors

The development of flexible room-temperature gas sensors is important in environmental monitoring and protection. In this contribution, by using 1-octadecanethiol (ODT) as a surface ligand, Au nanodots (NDs) with ultra-small size of ∼1.7 nm were deposited on the surface of α-Fe₂O₃/reduced graphene oxide (rGO). The Au ND-ODT/α-Fe₂O₃/rGO composite was fabricated into flexible gas sensors, which could detect NO₂ gas down to 200 ppb at room temperature. Compared with α-Fe₂O₃/rGO, Au ND-ODT/α-Fe₂O₃/rGO showed enhanced sensing performance because of the beneficial effects of Au NDs, including facilitating the adsorption of NO₂ molecules and forming ohmic-like contact with rGO and α-Fe₂O₃. In addition, the sensing performance of the composite was also influenced by the surface ligands of the Au NDs. Ligands with less polar terminal groups were found to be beneficial to charge transfer in the sensing film. Moreover, Au ND-ODT/α-Fe₂O₃/rGO-based flexible sensors showed negligible performance deterioration under moderately bent conditions, suggesting their potential to be used in portable and wearable devices.

Electrospun ZnSnO3/ZnO Composite Nanofibers and Its Ethanol-Sensitive Properties

In this work, a novel heterojunction based on ZnSnO3/ZnO nanofibers was prepared by a simple electrospinning method. The crystal, structural, and surface compositional properties of ZnSnO3 and ZnSnO3/ZnO composite nanofibers were investigated by X-ray diffractometer (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray photoelectron spectrometer (XPS), and Brunauer–Emmett–Teller (BET). Compared to pure ZnSnO3 nanofibers, the ZnSnO3/ZnO heterostructure nanofibers had high sensitivity and selectivity response with the fast response toward ethanol gas at low operational temperature. The sensing response of the sensor based on ZnSnO3/ZnO composite nanofibers was 19.6 toward 50 ppm ethanol gas at 225 °C, which was about 1.5 times superior to that of pure ZnSnO3 nanofibers. It can be owed mainly to the oxygen vacancies and the synergistic effect between ZnSnO3 and ZnO.

A highly stable and sensitive ethanol sensor based on Ru-decorated 1D WO3 nanowires

Decorating materials with noble metal catalysts is an effective method for optimizing the sensing performance of sensors based on tungsten trioxide (WO₃) nanowires. Ruthenium (Ru) exhibits excellent catalytic activity for oxygen adsorption/desorption and chemical reactions between gases and adsorbed oxygen. Herein, small Ru nanoparticles were uniformly distributed on the surface of one-dimensional WO₃ nanowires. The nanowires were prepared by the electrospinning method through an ultraviolet (UV) irradiation process, and decoration with Ru did not change their morphology. A sensor based on 4% Ru nanowires (NWs) shows the highest response (∼120) to 100 ppm ethanol, which was increased around 47 times, and the lowest ethanol detection limit (221 ppb) at a lower temperature (200 °C) displays outstanding repeatability and stability even after 45 days or in higher-humidity conditions. Moreover, it also has faster response–recovery features. The improvement in the sensing performance was attributed to the stable morphology of the nanowires, the sensitization effect of Ru, the catalytic effect of RuO₂ and the optimal atomic utilization efficiency. This work offers an effective and promising strategy for promoting the ethanol sensing performance of WO₃.

Decorating Ru does not effect the morphology of NWs, increased the oxygen vacancies, adsorbed oxygen. This strategy results in a better sensing performance (∼120 to 100 ppm ethanol was increased around 47 times at 200 °C) and humidity resistance.

Noble Metal Nanoparticles Decorated Metal Oxide Semiconducting Nanowire Arrays Interwoven into 3D Mesoporous Superstructures for Low-Temperature Gas Sensing

Mesoporous materials have been extensively studied for various applications due to their high specific surface areas and well-interconnected uniform nanopores. Great attention has been paid to synthesizing stable functional mesoporous metal oxides for catalysis, energy storage and conversion, chemical sensing, and so forth. Heteroatom doping and surface modification of metal oxides are typical routes to improve their performance. However, it still remains challenging to directly and conveniently synthesize mesoporous metal oxides with both a specific functionalized surface and heteroatom-doped framework. Here, we report a one-step multicomponent coassembly to synthesize Pt nanoparticle-decorated Si-doped WO₃ nanowires interwoven into 3D mesoporous superstructures (Pt/Si-WO₃ NWIMSs) by using amphiphilic poly(ethylene oxide)-block-polystyrene (PEO-b-PS), Keggin polyoxometalates (H₄SiW₁₂O₄₀) and hydrophobic (1,5-cyclooctadiene)dimethylplatinum(II) as the as structure-directing agent, tungsten precursor and platinum source, respectively. The Pt/Si-WO₃ NWIMSs exhibit a unique mesoporous structure consisting of 3D interwoven Si-doped WO₃ nanowires with surfaces homogeneously decorated by Pt nanoparticles. Because of the highly porous structure, excellent transport of carriers in nanowires, and rich WO₃/Pt active interfaces, the semiconductor gas sensors based on Pt/Si-WO₃ NWIMSs show excellent sensing properties toward ethanol at low temperature (100 °C) with high sensitivity (S = 93 vs 50 ppm), low detection limit (0.5 ppm), fast response-recovery speed (17-7 s), excellent selectivity, and long-term stability.

Exclusive and ultrasensitive detection of formaldehyde at room temperature using a flexible and monolithic chemiresistive sensor

Formaldehyde, a probable carcinogen, is a ubiquitous indoor pollutant, but its highly selective detection has been a long-standing challenge. Herein, a chemiresistive sensor that can detect ppb-level formaldehyde in an exclusive manner at room temperature is designed. The TiO₂ sensor exhibits under UV illumination highly selective detection of formaldehyde and ethanol with negligible cross-responses to other indoor pollutants. The coating of a mixed matrix membrane (MMM) composed of zeolitic imidazole framework (ZIF-7) nanoparticles and polymers on TiO₂ sensing films removed ethanol interference completely by molecular sieving, enabling an ultrahigh selectivity (response ratio > 50) and response (resistance ratio > 1,100) to 5 ppm formaldehyde at room temperature. Furthermore, a monolithic and flexible sensor is fabricated successfully using a TiO₂ film sandwiched between a flexible polyethylene terephthalate substrate and MMM overlayer. Our work provides a strategy to achieve exclusive selectivity and high response to formaldehyde, demonstrating the promising potential of flexible gas sensors for indoor air monitoring.

Formaldehyde, a probable carcinogen, is a ubiquitous indoor pollutant, but its ultraselective detection has been a long-standing challenge. Here, the authors develop a chemiresistive sensor that can detect ppb-level formaldehyde in an exclusive manner at room temperature.

Design of highly sensitive and selective ethanol sensor based on α-Fe2O3/Nb2O5 heterostructure

The introduction of heterostructures is a new approach in gas sensing due to their easy and quick transport of charges. Herein, facile hydrothermal and solid-state techniques are employed to synthesize an α-Fe₂O₃/Nb₂O₅ heterostructure. The morphology, microstructure, crystallinity and surface composition of the synthesized heterostructures are investigated by scanning electron microscope, transmission electron microscope, x-ray diffraction, x-ray photoelectron spectroscopy and Brunauer-Emmett-Teller analyses. The successful fabrication of the heterostructures was achieved via the mutual incorporation of α-Fe₂O₃ nanorods with Nb₂O₅ interconnected nanoparticles (INPs). A sensor based on the α-Fe₂O₃(0.09)/Nb₂O₅ heterostructure with a high surface area exhibited enhanced gas-sensing features, maintaining high selectivity and sensitivity, and a considerable recovery percentage towards ethanol gas. The sensing response of the α-Fe₂O₃(0.09)/Nb₂O₅ heterostructure at lower operating temperature (160 °C) is around nine times higher than a pure Nb₂O₅ (INP) sensor at 180 °C with the flow of 100 ppm ethanol gas. The sensors also show excellent selectivity, good long-term stability and a rapid response/recovery time (8s/2s, respectively) to ethanol. The superior electronic conductivity and upgraded sensitivity performance of gas sensors based on the α-Fe₂O₃(0.09)/Nb₂O₅ heterostructure are attributed due to its unique structural features, high specific surface area and the synergic effect of the n-n heterojunction. The promising results demonstrate the potential application of the α-Fe₂O₃(0.09)/Nb₂O₅ heterostructure as a good sensing material for the fabrication of ethanol sensors.

Direct Utilization of Photoinduced Charge Carriers to Promote Electrochemical Energy Storage

Electrochemical energy storage has been regarded as one of the most promising strategies for next-generation energy consumption. To meet the increasing demands of urban electric vehicles, development of green and efficient charging technologies by exploitation of solar energy should be considered for outdoor charging in the future. Herein, a light-sensitive material (copper foam-supported copper oxide/nickel copper oxides nanosheets arrays, namely CF@CuO_x @NiCuO_x NAs) with hierarchical nanostructures to promote electrochemical charge storage is specifically fabricated. The as-fabricated NAs have demonstrated a high areal specific capacity of 1.452 C cm^-2 under light irradiation with a light power of 1.76 W, which is 44.8% higher than the capacity obtained without light. Such areal specific capacity (1.452 C cm^-2 ) is much higher than that of the conventional supercapacitor structure using a similar active redox component reported recently (NiO nanosheets array@Co₃ O₄ -NiO FTNs: maximum areal capacity of 623.5 mF cm^-2 at 2 mA cm^-2 ). This photo-enhancement for charge storage can be attributed to the combination of photo-sensitive Cu₂ O and pseudo-active NiO components. Hence, this work may provide new possibilities for direct utilization of sustainable solar energy to realize enhanced capability for energy storage devices.

Structure Engineering of Yolk-Shell Magnetic Mesoporous Silica Microspheres with Broccoli-Like Morphology for Efficient Catalysis and Enhanced Cellular Uptake

Yolk-shell magnetic mesoporous microspheres exhibit potential applications in biomedicine, bioseparation, and catalysis. Most previous reports focus on establishing various interface assembly strategies to construct yolk-shell mesoporous structures, while little work has been done to control their surface topology and study their relevant applications. Herein, a unique kind of broccoli-like yolk-shell magnetic mesoporous silica (YS-BMM) microsphere is fabricated through a surfactant-free kinetic controlled interface assembly strategy. The obtained YS-BMM microspheres possess a well-defined structure consisting of a magnetic core, middle void, mesoporous silica shell with tunable surface roughness, large superparamagnetism (36.4 emu g^-1 ), high specific surface area (174 m² g^-1 ), and large mesopores of 10.9 nm. Thanks to these merits and properties, the YS-BMM microspheres are demonstrated to be an ideal support for immobilization of ultrafine Pt nanoparticles (≈3.7 nm) and serve as superior nanocatalysts for hydrogenation of 4-nitrophenol with yield of over 90% and good magnetic recyclability. Furthermore, YS-BMM microspheres show excellent biocompatibility and can be easily phagocytosed by osteoclasts, revealing a potential candidate in sustained drug release in orthopedic disease therapy.

High-Sensitive MEMS Hydrogen Sulfide Sensor made from PdRh Bimetal Hollow Nanoframe Decorated Metal Oxides and Sensitization Mechanism Study

Here we report the fabrication of a high performance metal oxide semiconductor (MOS) sensor for the detection of hydrogen sulfide (H₂S) using PdRh bimetal hollow nanocube (HC) with Rh-rich hollow frame and Pd-rich core frame as sensitizing materials. PdRh bimetal HC with the edge-length about 10 nm was prepared by chemical etching PdRh bimetal solid nanocube (SC) in HNO₃ aqueous solution. The results of gas-sensing tests indicate that the response value order of the MEMS gas sensors based on MOSs (including ZnO, MoO₃ and SnO₂) is as follows: R_PdRh HC/MOS > R_PdRh SC/MOS > R_MOS. First, in the system of ZnO, gas sensor modified by PdRh (PdRh SC/ZnO and PdRh HC/ZnO) possess enhanced H₂S sensing performance with a better response and excellent low-concentration detection capability (down to 15 ppb) comparing to pure ZnO. The improved H₂S sensing performance could be attributed to the good conductivity of Rh-rich frame, the high catalytic activity of PdRh bimetal and formation of Schottky barrier-type junctions and defect. Second, PdRh HC/ZnO sensor shows better response (185-1 ppm of H₂S) compared to PdRh SC/ZnO sensor (108-1 ppm of H₂S), which is due to the higher specific surface area of PdRh HC/ZnO and good gas diffusion of the hollow structure. This work indicate that the sensitization characteristics of PdRh bimetal HC will provide new paradigms for the future development of the high performance sensor.

Nanocage-Shaped Co3- x Zrx O4 Solid-Solution Supports Loaded with Pt Nanoparticles as Effective Catalysts for the Enhancement of Toluene Oxidation

Nanocage-shaped Co_{3- x} Zr_x O₄ solid-solution supports and the corresponding platinum loaded nanocomposites, yPt/Co_{3- x} Zr_x O₄ (x =0.27, 0.50, 0.69; y = 0.5, 1.0, 2.0 wt.%), are successfully fabricated via a Cu₂ O nanocube hard template method and a glycol reduction method, respectively. The hollow nanocage structures obviously improve surface areas; moreover, the Zr doping forms the Co_{3- x} Zr_x O₄ solid-solution supports, and the corresponding yPt/Co_{3- x} Zr_x O₄ catalysts promote the enhancement of catalytic performance. Catalytic activity toward toluene combustion is enhanced for the 2.0 wt% Pt/Co_2.73 Zr_0.27 O₄ catalyst. The catalysts are characterized using multiple techniques. Pt nanoparticles are uniformly dispersed across the Co_2.73 Zr_0.27 O₄ nanocage surface. The 2.0 wt% Pt/Co_2.73 Zr_0.27 O₄ catalyst exhibits the highest catalytic activity among all the samples and demonstrates good stability, with 90% toluene conversion obtained at a temperature of 165 °C. The same catalyst accomplishes full toluene oxidation at 180 °C, at a weight hourly space velocity of 36 000 mL h^-1 g^-1 . The apparent activation energy (E_a ) over the yPt/Co_2.73 Zr_0.27 O₄ samples are significantly lower than those over the Co_{3- x} Zr_x O₄ supports, with the 2.0 wt% Pt/Co_2.73 Zr_0.27 O₄ catalyst exhibiting the lowest E_a value. These findings demonstrate the potential of the 2.0 wt% Pt/Co_2.73 Zr_0.27 O₄ catalyst as a promising catalyst toward atmospheric toluene removal.

Pd-Decorated PdO Hollow Shells: A H2-Sensing System in Which Catalyst Nanoparticle and Semiconductor Support are Interconvertible

Developing a simple strategy to fabricate high-performance hydrogen sensors with long-term stability remains quite challenging. Here, we report the H₂-sensing performance of Pd-decorated PdO hollow shells (Pd/PdO HSs). In this novel system, the catalyst nanoparticles (Pd NPs) and semiconductor support (PdO) are interconvertible, which is different from traditional hydrogen-sensing systems such as Pd/TiO₂ and Pd/ZnO. This Pd/PdO system exhibits multiple unique properties. First, well-distributed Pd NPs with controllable density can be decorated on PdO support through a one-step NaBH₄ treatment during which PdO is partially reduced into Pd. Second, the decorated Pd NPs are physically inlaid in the PdO support, which not only prevents the agglomeration or detachment of Pd NPs but also enhances the electron transfer between Pd NPs and PdO. Third, Pd/PdO HSs can be reoxidized into PdO HSs once their sensing performance degrades, which repeatedly manipulates Pd/PdO HSs under the initial reduction process, leading to the reactivation of the sensing performance. With all these advantages, Pd/PdO HSs demonstrate a detection limit lower than 1 ppm, a response/recovery time to 1% H₂ of 5 s/32 s at room temperature, and a repeatable reactivation ability. The strategy presented here is convenient and time saving and has no need to prefunctionalize the PdO surface for the decoration of catalyst NPs. Moreover, the unique reactivation ability of Pd/PdO system opens a new strategy toward extending the lifetime of H₂ sensors.