Solid-State Dispersions of Platinum in the SnO2 and Fe2O3 Nanomaterials

The dispersion of platinum (Pt) on metal oxide supports is important for catalytic and gas sensing applications. In this work, we used mechanochemical dispersion and compatible Fe(II) acetate, Sn(II) acetate and Pt(II) acetylacetonate powders to better disperse Pt in Fe₂O₃ and SnO₂. The dispersion of platinum in SnO₂ is significantly different from the dispersion of Pt over Fe₂O₃. Electron microscopy has shown that the elements Sn, O and Pt are homogeneously dispersed in α-SnO₂ (cassiterite), indicating the formation of a (Pt,Sn)O₂ solid solution. In contrast, platinum is dispersed in α-Fe₂O₃ (hematite) mainly in the form of isolated Pt nanoparticles despite the oxidative conditions during annealing. The size of the dispersed Pt nanoparticles over α-Fe₂O₃ can be controlled by changing the experimental conditions and is set to 2.2, 1.2 and 0.8 nm. The rather different Pt dispersion in α-SnO₂ and α-Fe₂O₃ is due to the fact that Pt⁴⁺ can be stabilized in the α-SnO₂ structure by replacing Sn⁴⁺ with Pt⁴⁺ in the crystal lattice, while the substitution of Fe³⁺ with Pt⁴⁺ is unfavorable and Pt⁴⁺ is mainly expelled from the lattice at the surface of α-Fe₂O₃ to form isolated platinum nanoparticles.

The Effect of Noble Metals on Co Gas Sensing Properties of In2O3 Nanoparticles

Three types of In2O3 nanoparticles decorated with Au, Pd and Pt nanoparticles, respectively, were synthesized by thermal decomposition method, and the effects of metal nanoparticles on their phase, microstructure, chemical state, carrier types were investigated with XRD, SEM/TEM, and XPS. Additionally, sensing properties to CO gas, such as sensitivity, etc., were examined with sensing apparatus. Au-decorated In2O3 nanoparticles exhibited the highest sensitivity to CO gas, with S = 5.59 at a 10 ppm CO gas concentration at 50 °C compared to Pd or Pt-decorated In2O3 nanoparticles. This can be interpreted as a much higher adsorption of oxygen molecules on the In2O3 surface due to the high oxygen vacancies in the In2O3 lattice, which generates an electron depletion region in the outer layer of In2O3 to sharply increase the resistance or the spill-over effect due to Au nanoparticles on In2O3. Au nanoparticles were observed in the TEM images and confirmed by XPS analysis.

A photoelectrochemical enzyme biosensor based on functionalized hematite microcubes for rutin determination by square-wave voltammetry

A photoelectrochemical biosensing strategy for the highly sensitive detection of the flavonoid rutin was developed by synergizing the photoelectrocatalytic properties of hematite (α-Fe₂O₃) decorated with palladium nanoparticles (PdNPs) and the biocatalysis towards laccase-based reactions. The integration of α-Fe₂O₃.PdNPs with a polyphenol oxidase as a biorecognition element yields a novel biosensing platform. Under visible light irradiation, the photoactive biocomposite can generate a stable photocurrent, which was found to be directly dependent upon the concentration of rutin. Under the optimal experimental conditions, the cathodic photocurrent, measured at 0.33 V vs. Ag/AgCl, from the square-wave voltammograms presented a linear dependence on the rutin concentration within the range of 0.008-30.0 × 10^-8 mol L^-1 (sensitivity: 1.7 μA·(× 10^-8 M^-1)·cm^-2), with an experimental detection limit (S/N = 3) of 8.4 × 10^-11 mol L^-1. The proposed biosensor device presented good selectivity towards rutin in the presence of various organic compounds and inorganic ions, demonstrating the potential application of this biosensing platform in complex matrices. This bioanalytical device also exhibited excellent operational and analytical properties, such as intra-day (standard deviation, SD = 0.21%) and inter-day (SD = 1.30%) repeatability, and long storage stability (SD = 2.80% over 30 days).Graphical abstract.

Slow and Sustained Release of Carbonate Ions from Amino Acids for Controlled Hydrothermal Growth of Alkaline-Earth Carbonate Single Crystals

Alkaline-earth metal carbonate materials have attracted wide interest because of their high value in many applications. Various sources of carbonate ions (CO₃ ^2-), such as CO₂ gas, alkaline-metal carbonate salts, and urea, have been reported for the synthesis of metal carbonate crystals, yet a slow and sustained CO₃ ^2- release approach for controlled crystal growth is much desired. In this paper, we demonstrate a new chemical approach toward slow and sustained CO₃ ^2- release for hydrothermal growth of large alkaline-earth metal carbonate single crystals. Such an approach is enabled by the multiple hydrolysis of a small basic amino acid (arginine, Arg). Namely, the amino groups of Arg hydrolyze to form OH^- ions, making the solution basic, and the hydrolysis of the guanidyl group of Arg is hydrothermally triggered to produce urea and ammonia, followed by the hydrolysis of urea to produce CO₂ and ammonia and then the release of CO₃ ^2- because of the reaction between CO₂ and the OH^- ions hydrolyzed from ammonia. Such a CO₃ ^2- release behavior enables the slow and controlled growth of various carbonate single crystals over a wide range of pH values. The growth of uniform rhombohedron MgCO₃ single crystals with variable morphologies and crystal sizes is studied in detail. The influences of reaction temperature, solution pH, precursor type, and concentration on the morphology and size of the resulting MgCO₃ crystals are elucidated. The crystal evolution mechanism is also proposed and discussed with various supportive data.

Thionin functionalized signal amplification label derived dual-mode electrochemical immunoassay for sensitive detection of cardiac troponin I

A sensitive sandwich-type electrochemical immunosensor was established by employing Au@Pt core-shell multi-branched nanoparticles, and thionin functionalized nitrogen/sulfur co-doped graphene oxide (N/S-cGO/L-lys/Au@Pt MBs/Thi) as a double signal label to detect cardiac troponin I (cTnI). In this work, Au nanorods functionalized polydopamine (Au NR@PDA) with high adsorption capacity and superior electroconductivity can provide an efficient substrate for immobilizing primary antibodies (Ab₁). In the proposed N/S-cGO/L-lys/Au@Pt MBs/Thi, an electrochemically active molecule, Thi was covalently bonded in the N/S-cGO/L-lys/Au@Pt MBs. It presented a strong differential pulse voltammetry (DPV) current signal without electron transfer mediators, and showed a high electrocatalytic activity toward H₂O₂ reduction by using amperometric i-t (i-t). Impressively, with the synergistic effect of N/S-cGO/L-lys/Au@Pt MBs/Thi and Au NR@PDA, the developed dual-mode electrochemical immunosensor for cTnI detection showed a wide linear concentration range (50 fg/mL to 250 ng/mL, 750 fg/mL to 100 ng/mL) and a low detection limit (16.7 fg/mL, 250 fg/mL) via i-t and DPV, respectively. Furthermore, this immunosensor exhibited acceptable reproducibility, high sensitivity and good stability under optimal conditions. More importantly, the satisfactory results were obtained in detection of cTnI-spiked human serum samples, and the presented method may be a promising application in clinical bioanalysis.

Synthesis of novel cellulose- based antibacterial composites of Ag nanoparticles@ metal-organic frameworks@ carboxymethylated fibers

A novel cellulose-based antibacterial material, namely silver nanoparticles@ metal-organic frameworks@ carboxymethylated fibers composites (Ag NPs@ HKUST-1@ CFs), was synthesized. The results showed that the metal-organic frameworks (HKUST-1) were uniformly anchored on the fiber's surfaces by virtue of complexation between copper ions in HKUST-1 and carboxyl groups on the carboxymethylated fibers (CFs). The silver nanoparticles (Ag NPs) were immobilized and well-dispersed into the pores and/or onto the surfaces of HKUST-1 via in situ microwave reduction, resulting in the formation of novel Ag NPs@ HKUST-1@ CFs composites. The antibacterial assays showed that the as-prepared composites exhibited a much higher antibacterial activity than Ag NPs@ CFs or HKUST-1@ CFs samples.

Realizing Synergy between In2O3 Nanocubes and Nitrogen-Doped Reduced Graphene Oxide: An Excellent Nanocomposite for the Selective and Sensitive Detection of CO at Ambient Temperatures

Hierarchical mesoporous In₂O₃ nanocubes and nitrogen-doped reduced graphene oxide-indium oxide nanocube (In_NrGO) composites were prepared for carbon monoxide (CO) sensing. The as-synthesized materials were systematically investigated by different characterization techniques such as field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, thermogravimetic analysis, X-ray photoelectron spectroscopy, micro-Raman, Fourier transform infrared spectroscopy, and photoluminesce analysis. The obtained results are consistent with each other. The CO-sensing characteristics of the In₂O₃ nanocubes and In_NrGO composites were examined at different operating temperatures (35 °C < T_s < 300 °C) and CO concentrations (1-1000 ppm). Owing to their large surface-to-volume ratio and porosity, the In₂O₃ nanocubes exhibited a superior sensitivity with a detection limit of 1 ppm at 250 °C. Furthermore, to enhance the sensing characteristics and reduce the operating temperature, a composite of NrGO and In₂O₃ nanocubes was fabricated. The incorporation of NrGO drastically improved the sensing performance of the In₂O₃ nanocubes, showing an excellent sensitivity (S_R ∼ 3.6-5 ppm of CO at ∼35 °C) with appreciably fast response (Γ_RES ∼ 22 s) and recovery (Γ_REC ∼ 32 s) times. The sensing studies supported by the structural and morphological material characteristics lead to the plausible sensing mechanism proposed.

Nanostructured Materials for Room-Temperature Gas Sensors

Sensor technology has an important effect on many aspects in our society, and has gained much progress, propelled by the development of nanoscience and nanotechnology. Current research efforts are directed toward developing high-performance gas sensors with low operating temperature at low fabrication costs. A gas sensor working at room temperature is very appealing as it provides very low power consumption and does not require a heater for high-temperature operation, and hence simplifies the fabrication of sensor devices and reduces the operating cost. Nanostructured materials are at the core of the development of any room-temperature sensing platform. The most important advances with regard to fundamental research, sensing mechanisms, and application of nanostructured materials for room-temperature conductometric sensor devices are reviewed here. Particular emphasis is given to the relation between the nanostructure and sensor properties in an attempt to address structure-property correlations. Finally, some future research perspectives and new challenges that the field of room-temperature sensors will have to address are also discussed.

Magnetite-supported palladium single-atoms do not catalyse the hydrogenation of alkenes but small clusters do

Pd clusters of low atomicity supported on magnetite nanoparticles are extremely active for the hydrogenation of styrene, overcoming the best reported TOFs.

Fabrication of porous g-C3N4/Ag/Fe2O3 composites with enhanced visible light photocatalysis performance

Porous graphitic carbon nitride (pg-C₃N₄) synthetized by pyrolysis of urea was hybridized with Ag-doped Fe₂O₃ to form a visible-light-driven photocatalyst pg-C₃N₄/Ag/Fe₂O₃via a simple chemical adsorption method.

Selective growth of TiO2 beads on Ag nanowires and their photocatalytic performance

Necklace-like Ag nanowire@TiO₂ heterostructures were fabricated by a two-step solvothermal method, which exhibited excellent photocatalytic performance.

Plate-like p-n heterogeneous NiO/WO₃ nanocomposites for high performance room temperature NO₂ sensors

Plate-like heterogeneous NiO/WO₃ nanocomposites have been successfully prepared by annealing Ni(OH)₂ and H₂WO₄ in air. These NiO/WO₃ nanocomposites have shown excellent sensitivity towards NO₂ and ultrafast response at room temperature due to their p-n heterogeneous characteristics.

Preparation of uniform magnetic recoverable catalyst microspheres with hierarchically mesoporous structure by using porous polymer microsphere template

Merging nanoparticles with different functions into a single microsphere can exhibit profound impact on various applications. However, retaining the unique properties of each component after integration has proven to be a significant challenge. Our previous research demonstrated a facile method to incorporate magnetic nanoparticles into porous silica microspheres. Here, we report the fabrication of porous silica microspheres embedded with magnetic and gold nanoparticles as magnetic recoverable catalysts. The as-prepared multifunctional composite microspheres exhibit excellent magnetic and catalytic properties and a well-defined structure such as uniform size, high surface area, and large pore volume. As a result, the very little composite microspheres show high performance in catalytic reduction of 4-nitrophenol, special convenient magnetic separability, long life, and good reusability. The unique nanostructure makes the microspheres a novel stable and highly efficient catalyst system for various catalytic industry processes.

Ruthenium oxide-based nanocomposites with high specific surface area and improved capacitance as a supercapacitor

A solvothermal approach and a mutual oxidation–reduction strategy were demonstrated for the synthesis of RuO₂-based nanocomposites for supercapacitors.

Controlled synthesis of Au–Fe3O4 hybrid hollow spheres with excellent SERS activity and catalytic properties

Here demonstrated a facile one-pot hydrothermal method for the controlled synthesis of porous Au–Fe₃O₄ hybrid hollow spheres. The obtained spheres exhibit superior SERS sensitivity and excellent catalytic activity.

Multifunctional superparamagnetic iron oxide nanoparticles: design, synthesis and biomedical photonic applications

Superparamagnetic iron oxide nanoparticles (SPIONs) have shown great promise in biomedical applications. In this review, we summarize the recent advances in the design and fabrication of core-shell and hetero-structured SPIONs and further outline some exciting developments and progresses of these multifunctional SPIONs for diagnosis, multimodality imaging, therapy, and biophotonics.

Encapsuled nanoreactors (Au@SnO₂): a new sensing material for chemical sensors

New Au@SnO2 yolk-shell nanospheres have been successfully synthesized by using Au@SiO2 nanospheres as sacrificial templates. This process is environmentally friendly and is based on hydrothermal shell-by-shell deposition of polycrystalline SnO2 on spheriform Au@SiO2 nanotemplates. Au nanoparticles can be impregnated into the SnO2 nanospheres and the nanospheres show outer diameters of 110 nm and thicknesses of 15 nm. The possible growth model of the nanospheres is proposed. The gas sensing properties of the Au@SnO2 yolk-shell nanospheres were researched and compared with that of the hollow SnO2 nanospheres. The former shows lower operating temperature (210 °C), lower detection limit (5 ppm), faster response (0.3 s) and better selectivity. These improved sensing properties were attributed to the catalytic effect of Au, and enhanced electron depletion at the surface of the Au@SnO2 yolk-shell nanospheres.

Magnetically-driven selective synthesis of Au clusters on Fe3O4 nanoparticles

A novel procedure to direct the local synthesis of gold clusters on Fe(3)O(4) nanocrystals by means of alternating magnetic fields (AMFs) is demonstrated. This process allows growing gold selectively onto the heated magnetite surface, while keeping the synthesis solution comparatively cold. Sequential AMF cycles allowed fine-tuning the amount of gold on the magnetite surfaces.