Rapid One-Pot Solvothermal Batch Synthesis of Porous Nanocrystal Assemblies Composed of Multiple Transition-Metal Elements

Solvothermal synthesis of hair-like carbon nanotubes onto sub-micron-sized spherical metal oxide catalyst cores

Long- and uniform-length, and high-density hair-like carbon nanotubes (CNTs) were produced by CNT growth on sub-micron-sized spherical catalyst supports. The nanosized catalysts (FeO _x , CoO _x , and NiO _x ) that were supported in/on the sub-micron-sized spherical metal oxides (TiO₂, ZrO₂, SnO₂, and CeO₂) were prepared via one-step solvothermal and/or two-step impregnation methods. The nanosized catalysts supported in/on the spherical metal oxide supports were converted into CNT conjugates with the CNT-hair morphology via a chemical thermal vapor deposition technique using ethyne gas as a carbon source; the CNTs grew on the central spherical metal oxide core under the base growth process conditions. Among the many types of candidate spherical catalyst materials, the combination of FeO _x as a catalyst for CNT growth and ZrO₂ as a support led to the best growth of CNT-hair under the reaction conditions, which included a temperature of 730 °C, pressure of 65 Pa, a 10 sccm ethyne gas flow, and a reaction time of 10 s. The CNTs consisted of five-to-eight-layered multi-wall structures with lengths of approximately 3 μm. The CNT-hair that was obtained using the solvothermally embedded catalyst showed higher crystallinity and was dense, thick, and straight, while the corresponding CNT-hair obtained using the impregnated catalyst was slightly sparse, thin, and curly. A unique layer structure constructed using large quantities of uniform CNT-hair, including multiple CNT yarns similar to fuzzy balls or cotton candies, was assembled. The CNT-hair conjugate, specifically constructed in a layer structure with core FeO _x /ZrO₂ catalysts and tangled CNT yarns, had an appearance similar to frog eggs. Therefore, we successfully prepared suitable catalysts for CNT-hair production and fabricated a layer structure consisting of large numbers of CNT-hair conjugates. The unique structures are expected as a new metamaterial with intriguing physical properties, including isotropic absorption of polarized light and electromagnetic waves.

One-Step Solvothermal Synthesis of Ni Nanoparticle Catalysts Embedded in ZrO2 Porous Spheres to Suppress Carbon Deposition in Low-Temperature Dry Reforming of Methane

Ni nanoparticle catalysts embedded in ZrO₂ porous spheres and ZrO₂ porous composite spheres, SiO₂-ZrO₂, MgO-ZrO₂, and Y₂O₃-ZrO₂, with 83-115 nm diameter and 167-269 m²/g specific surface area were prepared by a one-pot and one-step solvothermal reaction from precursor solutions consisting of Ni(NO₃)₂‧6H₂O, Zr(OⁿBu)₄, and acetylacetone in moist ethanol combined with either Si(OEt)₄, magnesium acetylacetate, or Y(OⁱPr)₃. The obtained Ni catalysts have high specific surface areas of 130-196 m²/g, even after high-temperature reduction by H₂ at 450 °C for 2 h. They were utilized as catalysts for low-temperature dry reforming of methane (DRM) at 550 °C to suppress carbon deposition on Ni nanoparticles. The Ni catalysts embedded in SiO₂-ZrO₂ and Y₂O₃-ZrO₂ demonstrated high catalytic activity and long stability in the reaction. Moreover, carbon deposition on Ni nanoparticles in the DRM reaction was effectively suppressed in when using the SiO₂-ZrO₂ and Y₂O₃-ZrO₂ composites.

Insights into the solvothermal reaction for synthesizing tin(iv) oxide porous spheres

Various hetero-elements were combined with porous SnO2 spheres simply by adding hetero-element sources to the precursor solutions of optimized synthetic conditions.

Ce3+-enriched spherical porous ceria with an enhanced oxygen storage capacity

Porous ceria was obtained using a unique solvothermal reaction in acetonitrile, applying high temperature and pressure. The resulting material comprised homogeneous and monodisperse spheres and exhibited an extremely large surface area of 152 m2 g-1. From catalytic performance evaluation by vapor- and liquid-phase reactions, the synthesized porous ceria showed superior and different reaction activity compared with commercial CeO2. To examine the origin of the reaction activity of the present porous ceria, synchrotron hard X-ray photoelectron spectroscopy (HAXPES) measurements were carried out. The systematic study of HAXPES measurements revealed that the obtained porous ceria with the present solvothermal method contained a very high concentration of Ce3+. Moreover, O2-pulse adsorption analyses demonstrated a significant oxygen adsorption capacity exceeding 268 μmol-O g-1 at 400 °C owing to its high contents of Ce3+ species.

A novel electrochemical biosensor based on peptidoglycan and platinum-nickel-copper nano-cube for rapid detection of Gram-positive bacteria

A novel non-enzyme electrochemical biosensor for the rapid detection of Gram-positive bacteria has been constructed that relys on a stable and efficient combination between the peptidoglycan layer and platinum-nickel-copper nanocubes (Pt-Ni-Cu NCs). Briefly, bacteria were first captured by a specific antibody. Then, the electrochemical signal materials (Pt-Ni-Cu NCs) were bound to the bacteria peptidoglycan layer using specific structural and surface features. The rapid and sensitive bacterial detection was then achieved using intrinsic electrochemical characteristics and superoxidase-like activity of the Pt-Ni-Cu NCs. Moreover, the nature of peptidoglycan covering the whole bacteria provided the premise for signal amplification. Under optimal conditions, the electrochemical signal variation was proportional to the concentration of bacteria ranging from 1.5 × 10² to 1.5 × 10⁸ CFU/mL with a detection limit of 42 CFU/mL using a working potential of - 0.4 V. This electrochemical biosensor has been successfully applied to detect bacteria concentrations in urine samples, and the recoveries range from 90.4 to 107%. The proposed biosensor could be applied for broad-spectrum detection of Gram-positive bacteria since most Gram-positive bacteria possess a thick peptidoglycan layer. The developed electrochemical biosensing strategy might be used as a potential tool for clinical pathogenic bacteria detection and point-of-care testing (POCT).

Porous niobia spheres with large surface area: alcothermal synthesis and controlling of their composition and phase transition behaviour

Submicron-sized niobia (Nb2O5) porous spheres with a high specific surface area (300 m2 g-1) and nano concave-convex surfaces were synthesized via a rapid one-pot single-step alcothermal reaction. Prolonged reaction time or high reaction temperatures resulted in a morphology change of Nb2O5 from amorphous sphere to rod crystals with hexagonal crystal phase. A similar alcothermal reaction yielded TiO2-Nb2O5 composite porous spheres, whose Ti : Nb molar ratio was controlled by changing the precursor solution component ratios. A simple thermal treatment of amorphous TiO2-Nb2O5 porous spheres consisting of 1 : 2 (molar ratio) Ti : Nb at 600 °C for 2 h induced crystal phase transfer from amorphous to a monoclinic crystal phase of submicron-sized TiNb2O7 porous spheres with a specific surface area of 50 m2 g-1.

Nanoscale Effect of Zirconia Filler Surface on Mechanical Tensile Strength of Polymer Composites

A characteristic effect of a nano-concave-convex structure of a zirconia nanoparticle assembly with an inherent porous structure and huge surface area enabled us to introduce systematic surface modification by thermal treatment to smooth surface and polymer impregnation to mask the nano-concave-convex structure of the zirconia nanoparticle assembly. A polymer composite prepared from 30 wt% poly(N-isopropylacrylamide) containing 0.02 wt% zirconia nanoparticle assembly with the inherent nano-concave-convex surface structure showed the highest tensile strength in mechanical tensile testing. However, both sintered zirconia nanoparticle assembly with smooth surface and zirconia nanoparticle assemblies with polymer masked surface showed lower strength with longer elongation at break in mechanical tensile testing.