Designed Fabrication and Characterization of Three-Dimensionally Ordered Arrays of Core–Shell Magnetic Mesoporous Carbon Microspheres

A confined interface coassembly coating strategy based on three-dimensional (3-D) ordered macroporous silica as the nanoreactor was demonstrated for the designed fabrication of novel 3-D ordered arrays of core–shell microspheres consisting of Fe₃O₄ cores and ordered mesoporous carbon shells. The obtained 3-D ordered arrays of Fe₃O₄@mesoporous carbon materials possess two sets of periodic structures at both mesoscale and submicrometer scale, high surface area of 326 m²/g, and large mesopore size of 19 nm. Microwave absorption test reveals that the obtained materials have excellent microwave absorption performances with maximum reflection loss of up to −57 dB at 8 GHz, and large absorption bandwidth (7.3–13.7 GHz, < −10 dB), due to the combination of the large magnetic loss from iron oxides, the strong dielectric loss from carbonaceous shell, and the strong reflection and scattering of electromagnetic waves of the ordered structures of the mesopores and 3-D arrays of core–shell microspheres

Polyphenol-Mediated Synthesis of Mesoporous Au–In₂O₃ Nanospheres for Room-Temperature Detection of Triethylamine

Semiconductor metal oxide gas sensors have been frequently used for gas monitoring and detection in different applications. However, the working temperature is usually high (>150 °C), which requires an additional heater and results in high energy consumption and low stability. Herein, mesoporous Au–In2O3 spheres are prepared by direct thermal decomposition of metal–polyphenol hybrids and applied for room-temperature detection of triethylamine vapor. Plant polyphenols are used as a “molecular glue” to interact with Au and In species and mediate the synthesis process. After chemical cross-linking with formaldehyde, spherical gold–indium–polyphenol hybrids are prepared. Mesoporous Au–In2O3 spheres can be prepared by calcination in air. The obtained spheres show high specific surface area (56.8 m2/g), large pore size (∼5.8 nm), and uniform spherical morphology (∼100 nm). Mesoporous Au–In2O3 spheres show high response (54.9) toward 10 ppm of triethylamine vapor at room temperature (25 °C). The modification of Au species on the mesoporous In2O3 spheres can obviously decrease the working temperature from 200 to 25 °C and significantly increase the response toward TEA (about 9.6-fold) compared with pure mesoporous In2O3 spheres. In comparison with the traditional post-modification strategy, the one-pot modification method can further improve the sensing performance of mesoporous In2O3 spheres. This work provides a feasible synthesis strategy to prepare mesoporous noble metal–In2O3 hybrid spheres, which could be used for fabrication of the gas sensor with low energy consumption and high sensitivity

Dynamic Coassembly of Amphiphilic Block Copolymer and Polyoxometalates in Dual Solvent Systems: An Efficient Approach to Heteroatom-Doped Semiconductor Metal Oxides with Controllable Nanostructures

Dynamic coassembly of block copolymers (BCPs) with Keggin-type polyoxometalates (POMs) is developed to synthesize heteroatom-doped tungsten oxide with controllable nanostructures, including hollow hemispheres, nanoparticles, and nanowires. The versatile coassembly in dual n-hexane/THF solvent solution enables the fomation of poly­(ethylene oxide)-b-polystyrene (PEO-b-PS)/POMs (e.g., silicotungstic acid, H4SiW12O40) nanocomposites with different morphologies such as spherical vesicles, inverse spherical micelles, and inverse cylindrical micelles, which can be readily converted into diverse nanostructured metal oxides with high surface area and unique properties via in situ thermal-induced structural evolution. For example, uniform silicon-doped WO3 (Si-WO3) hollow hemispheres derived from coassembly of PEO-b-PS with H4SiW12O40 were utilized to fabricate gas sensing devices which exhibit superior gas sensing performance toward acetone, thanks to the selective gas–solid interface catalytic reaction that induces resistance changes of the devices due to the high specific surface areas, abundant oxygen vacancies, and the Si-doping induced metastable ε-phase of WO3. Furthermore, density functional theory (DFT) calculation reveals the mechanism about the high sensitivity and selectivity of the gas sensors. On the basis of the as-fabricated devices, an integrated gas sensor module was constructed, which is capable of real-time monitoring the environmental acetone concentration and displaying relevant sensing results on a smart phone via Bluetooth communication

Alkaloid Precipitant Reaction Inspired Controllable Synthesis of Mesoporous Tungsten Oxide Spheres for Biomarker Sensing

Highly porous sensitive materials with well-defined structures and morphologies are extremely desirable for developing high-performance chemiresistive gas sensors. Herein, inspired by the classical alkaloid precipitant reaction, a robust and reliable active mesoporous nitrogen polymer sphere-directed synthesis method was demonstrated for the controllable construction of heteroatom-doped mesoporous tungsten oxide spheres. In the typical synthesis, P-doped mesoporous WO3 monodisperse spheres with radially oriented channels (P-mWO3-R) were obtained with a diameter of ∼180 nm, high specific surface area, and crystalline skeleton. The in situ-introduced P atoms could effectively adjust the coordination environment of W atoms (Wδ+-Ov), giving rise to dramatically enhanced active surface-adsorbed oxygen species and unusual metastable ε-WO3 crystallites. The P-mWO3-R spheres were applied for the sensing of 3-hydroxy-2-butanone (3H2B), a biomarker of foodborne pathogenic bacteria Listeria monocytogenes (LM). The sensor exhibited high sensitivity (Ra/Rg = 29 to 3 ppm), fast response dynamics (26/7 s), outstanding selectivity, and good long-term stability. Furthermore, the device was integrated into a wireless sensing module to realize remote real-time and precise detection of LM in practical applications, making it possible to evaluate food quality using gas sensors conveniently

Alkaloid Precipitant Reaction Inspired Controllable Synthesis of Mesoporous Tungsten Oxide Spheres for Biomarker Sensing

Highly porous sensitive materials with well-defined structures and morphologies are extremely desirable for developing high-performance chemiresistive gas sensors. Herein, inspired by the classical alkaloid precipitant reaction, a robust and reliable active mesoporous nitrogen polymer sphere-directed synthesis method was demonstrated for the controllable construction of heteroatom-doped mesoporous tungsten oxide spheres. In the typical synthesis, P-doped mesoporous WO3 monodisperse spheres with radially oriented channels (P-mWO3-R) were obtained with a diameter of ∼180 nm, high specific surface area, and crystalline skeleton. The in situ-introduced P atoms could effectively adjust the coordination environment of W atoms (Wδ+-Ov), giving rise to dramatically enhanced active surface-adsorbed oxygen species and unusual metastable ε-WO3 crystallites. The P-mWO3-R spheres were applied for the sensing of 3-hydroxy-2-butanone (3H2B), a biomarker of foodborne pathogenic bacteria Listeria monocytogenes (LM). The sensor exhibited high sensitivity (Ra/Rg = 29 to 3 ppm), fast response dynamics (26/7 s), outstanding selectivity, and good long-term stability. Furthermore, the device was integrated into a wireless sensing module to realize remote real-time and precise detection of LM in practical applications, making it possible to evaluate food quality using gas sensors conveniently

Porous Au–Ag Alloy Particles Inlaid AgCl Membranes As Versatile Plasmonic Catalytic Interfaces with Simultaneous, in Situ SERS Monitoring

We present a novel porous Au–Ag alloy particles inlaid AgCl membrane as plasmonic catalytic interfaces with real-time, in situ surface-enhanced Raman spectroscopy (SERS) monitoring. The Au–Ag alloy particles inlaid AgCl membranes were obtained via a facile two-step, air-exposed, and room-temperature immersion reaction with appropriate annealing process. Owing to the designed integration of semiconductor component AgCl and noble metal Au–Ag particles, both the catalytic reduction and visible-light-driven photocatalytic activities toward organic contaminants were attained. Specifically, the efficiencies of about 94% of 4-nitrophenol (4-NP, 5 × 10^–5 M) reduction after 8 min of reaction, and degradation of rhodamine 6G (R6G, 10^–5 M) after 12 min of visible light irradiation were demonstrated. Moreover, efficiencies of above 85% of conversion of 4-NP to 4-aminophenol (4-AP) and 90% of R6G degradation were achieved as well after 6 cycles of reactions, by which robust recyclability was confirmed. Further, with distinct SERS signals generated simultaneously from the surfaces of Au–Ag particles under laser excitation, in situ SERS monitoring of the process of catalytic reactions with superior sensitivity and linearity has been realized. Overall, the capability of the Au–Ag particles inlaid AgCl membranes to provide SERS monitored catalytic and visible-light-driven photocatalytic conversion of organic pollutants, along with their mild and cost-effective fabrication method, would make sense for in-depth understanding of the mechanisms of (photo)­catalytic reactions, and also future development of potable, multifunctional and integrated catalytic and sensing devices

Engineering Pore Walls of Mesoporous Tungsten Oxides via Ce Doping for the Development of High-Performance Smart Gas Sensors

Chemiresistive gas sensors are widely used in environmental monitoring and industry production; however, their selectivity and sensitivity are yet to be improved and their working temperature is usually too high (around 250 °C), which limit their applications in detecting trace gases at low temperatures due to the low activity of sensitive layers. Herein, novel Ce-doped mesoporous WO3 with high specific surface areas of 59–72 m2/g, a stable crystalline framework, and finely tailored pore walls was synthesized via a facile in situ cooperative assembly method combined with a carbon-supported crystallization strategy. The doping of Ce atoms in the mesoporous WO3 pore wall can effectively adjust the coordination environment of W atoms, giving rise to dramatically enhanced oxygen vacancy (Ov) and forming Wδ+-Ov sites. As a result, the obtained Ce-doped mesoporous WO3 showed excellent H2S sensing performance at a low working temperature (150 °C) with an ultrahigh response value (381 vs 50 ppm), fast response dynamics (6 s), outstanding selectivity, and antihumidity property as well as good long-term stability. The superior gas sensing performance is attributed to the increased Ov density and enhanced conversion of surface-adsorbed H2S into SOx and SOx2– during the surface adsorption-catalysis reaction in the sensitive layer. Density functional theory (DFT) calculations reveal that Ce4+ is embedded into the crystal lattice of WO3 to form an optimal structure rather than atom substitution, and Ce-doped WO3 shows a higher H2S adsorption energy and a larger charge transfer than that in pure WO3, accounting for the better H2S sensing response of Ce4+-doped WO3. Furthermore, a novel gas sensing module and smart portable sensor device based on Ce-doped mesoporous WO3 was developed for efficient real-time monitoring of H2S concentration on a smartphone via Bluetooth communication

Significant Improvement on Electrochemical Performance of LiMn₂O₄ at Elevated Temperature by Atomic Layer Deposition of TiO₂ Nanocoating

The spinel LiMn₂O₄ cathode is considered a promising cathode material for lithium ion batteries. Unfortunately, the poor capacity stability, especially at elevated temperature, hinders its practical utilization. In this study, the atomic layer deposition (ALD) technique is employed to deposit a TiO₂ nanocoating on a LiMn₂O₄ electrode. To maintain electrical conductivity, this amorphous coating layer with high uniformity, conformity, and completeness is directly coated on cathode electrodes instead of LiMn₂O₄ particles. Among all the samples studied, the TiO₂-coated sample with 15 ALD cycles exhibits the best cyclability at both room temperature of 25 °C and elevated temperature of 55 °C and has the higher specific capacity of 136.4 mAh g^–1 at 0.1 C that is nearly close to the theoretical capacity of LiMn₂O₄. Meanwhile, this sample realizes lower polarization and less self-discharge. The improved electrochemical performance is ascribed to the high conformal and ultrathin TiO₂ coating, which enhances the kinetics of Li⁺ diffusion and stabilizes the electrode/electrolyte interface. Also, the deconvolution of Ti 2p X-ray photoelectron spectroscopy shows a weaker peak of Ti–O–F after cycling, which indicates that the coexistence of TiO₂ and TiO_<i>x</i>F_<i>y</i> layers can inhibit Mn dissolution and electrolyte decomposition

Mesoporous TiO₂ Mesocrystals: Remarkable Defects-Induced Crystallite-Interface Reactivity and Their in Situ Conversion to Single Crystals

Oriented self-assembly between inorganic nanocrystals and surfactants is emerging as a route for obtaining new mesocrystalline semiconductors. However, the actual synthesis of mesoporous semiconductor mesocrystals with abundant surface sites is extremely difficult, and the corresponding new physical and chemical properties arising from such an intrinsic porous mesocrystalline nature, which is of fundamental importance for designing high-efficiency nanostructured devices, have been rarely explored and poorly understood. Herein, we report a simple evaporation-driven oriented assembly method to grow unprecedented olive-shaped mesoporous TiO₂ mesocrystals (FDU-19) self-organized by ultrathin flake-like anatase nanocrystals (∼8 nm in thickness). The mesoporous mesocrystals FDU-19 exhibit an ultrahigh surface area (∼189 m²/g), large internal pore volume (0.56 cm³/g), and abundant defects (oxygen vacancies or unsaturated Ti³⁺ sites), inducing remarkable crystallite-interface reactivity. It is found that the mesocrystals FDU-19 can be easily fused in situ into mesoporous anatase single crystals (SC-FDU-19) by annealing in air. More significantly, by annealing in a vacuum (∼4.0 × 10^–5 Pa), the mesocrystals experience an abrupt three-dimensional to two-dimensional structural transformation to form ultrathin anatase single-crystal nanosheets (NS-FDU-19, ∼8 nm in thickness) dominated by nearly 90% exposed reactive (001) facets. The balance between attraction and electrostatic repulsion is proposed to determine the resulting geometry and dimensionality. Dye-sensitized solar cells based on FDU-19 and SC-FDU-19 samples show ultrahigh photoconversion efficiencies of up to 11.6% and 11.3%, respectively, which are largely attributed to their intrinsic single-crystal nature as well as high porosity. This work gives new understanding of physical and chemical properties of mesoporous semiconductor mesocrystals and opens up a new pathway for designing various single-crystal semiconductors with desired mesostructures for applications in catalysis, sensors, drug delivery, optical devices, etc