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The rational design and synthesis of frame-like hollow structures with unique three-dimensional open architectures for their diverse applications is still challenging. We herein propose a facile anisotropic surface modification and etching strategy for the synthesis of hollow structured ZIF-67 nanoframes. Our strategy relies on the structural and compositional distinctions between each crystallographic facet of truncated rhombic dodecahedrons ZIF-67 (tZIF-67 RDs) and the moderate coordinating and etching effects of cyanuric acid (CA). Thereby, the CA can anisotropically modify and protect the {110} facets from etching, causing the six {100} facets be selectively etched via an inside-out manner, and finally forming the hollow nanoframes. Interestingly, the surface modified hollow tZIF-67 RDs can further be facet-selectively etched by metal salts via an outside-in manner to give metal-doped tZIF-67 nanoframes. After calcination in reducing atmosphere, the metal-tZIF-67 hydrids are converted into metal-Co alloy/C composite catalysts with hollow nanoframed structures. Among them, the PtCo/C catalyst with only 5.9 wt.% Pt exhibits high catalytic activities and stabilities in the hydrogen evolution reaction (HER) in acidic solutions, outperforming the commercial 20 wt.% Pt/C catalyst. Our results offer insight into the development of metal-organic frameworks with compositional and structural multiplicity, which in turn could encourages more practical catalytic applications.

Taking advantages of the high heat tolerance, large specific surface area, and rough surface morphology created by agglomeration of fine primary particles, a solvothermally prepared CeO2 aggregate, SiO2–CeO2 nanocomposite, and TiO2–CeO2 nanocomposite are proposed to be used as sintering-resistant catalyst supports in highly exothermic reactions. Well-dispersed Ru metal catalysts were deposited on support surfaces by the precipitation–deposition method. The methanation of CO2 by H2, which is a highly exothermic reaction, was selected as a probe reaction in order to evaluate the catalytic activity and sintering-resistant capability of Ru catalysts deposited on those prepared supports. As expected, the low temperature (150–200 °C) activity and CH4 production of the Ru catalysts on the prepared CeO2 aggregate and TiO2–CeO2 nanocomposites were better than those on commercial CeO2 aggregates. Moreover, long-term stability (400 °C, 24 h; 50–300 °C, 10 cycles) was also achieved in the catalysts on these prepared supports.

We propose a novel method for the fabrication of CeO2 nanoparticles (NPs) with enhanced heat tolerance. SiO2 was mixed with CeO2 at the nano-level to yield SiO2‒CeO2 NP composites by a solvothermal reaction of precursor solutions consisting of Si(OEt)4, Ce(NO3)3·6H2O, and N,N,N′,N′-tetramethylethylenediamine in methanol. SiO2 content in the SiO2‒CeO2 NP composites was freely controllable by adjusting the Si(OEt)4 mol fraction in range of 0–0.5 in the precursor solutions. With an increase of SiO2 content in the SiO2‒CeO2 NP composites, the primary particle sizes of the CeO2 NPs decreased, and the specific surface areas of the SiO2‒CeO2 NP composites increased remarkably. For SiO2‒CeO2 NP composites obtained from a precursor solution consisting of 1:1 Si(OEt)4 and Ce(NO3)3·6H2O, the specific surface area was over 300 m2/g. Excellent heat tolerance was achieved through the retention of small size of CeO2 crystallites, as well as the large specific surface areas of the SiO2‒CeO2 NP assemblies, even after calcination at 850 °C for 3 h or at 700 °C for 72 h in air.

Mesoporous spherical aggregates of Nb-doped anatase TiO2 nanoparticles were synthesized by a simple one-pot solvothermal method in supercritical methanol and were evaluated as anode materials for L...

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.

Ultrafine titania nanocrystals were synthesized using a rapid heating, one-pot solvothermal method. These nanocrystals are extremely small with a narrow size distribution (3.0 ± 0.4 nm). The detailed structural analysis by using transmission electron microscopy reveals periodic alignment of the resultant titania nanocrystals with hexagonal symmetry due to their size uniformity. The drop-casting deposition and calcination of these nanocrystals are also enable to convert into mesoporous thin layer films with nano convex-concave surface. The resultant transparent mesoporous thin layer exhibits not only anti-reflection properties but also high photocatalytic activity.

A single-step synthetic method was developed to obtain ultrafine MgO nanocrystals by ultimately simple solvothermal treatment of a precursor solution containing magnesium acetylacetonate in acetonitrile at 400 °C for 10 min. HRTEM images and calculations based on Scherer equation showed that the average size of obtained ultrafine MgO nanocrystals was ca. 7 nm.

Non-thermal helium atmospheric pressure plasma jet treatment is applied to the surface activation of porous TiO2 nanoparticle assemblies. Treatment conditions such as the working distance of the plasma discharge, helium gas flow rate, and treatment time are optimized for effective removal of contaminants from the assembly surface. Laser desorption/ionization time-of-flight mass spectrometry (LDI-TOF MS) is applied to detect trace amounts of contaminants on assembly surfaces. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations confirm that the nanoparticle assemblies retain their original perfect spherical structures as well as their ultra-fine convex-concave nano-surfaces even after the plasma jet treatment. N2 adsorption/desorption and X-ray diffraction (XRD) measurements show no significant changes in their BET specific surface areas and crystal structures, respectively. The plasma jet-treated TiO2 nanoparticle assemblies show a 3.8 fold improvement in their reaction rate constants for methylene blue degradation and a 2 fold enhancement of their photocurrents under UV irradiation when compared with untreated TiO2.

The characteristics of nano-fillers in a polymer matrix have a significant influence on the microstructural, thermo-mechanical, optical, and conductivity properties of organic-inorganic nanocomposites. In this study, we investigated the influence of inorganic component – ZnO nanoparticles (NPs) on the characteristics and properties of PVA-ZnO nanocomposites which have been applied as an insulation layer in a resistive switching (RS) device. Three nanocomposites originating from three different types of ZnO NPs exhibit different RS characteristics: Abnormal volatile RS is observed with the ∼20-nm-sized spherical-like NPs (Z1) and 15–20-nm-sized mixed shaped NPs (Z2), whereas normal nonvolatile bipolar RS is observed with the 50–150-nm-sized hexagonal rod-like NPs (Z3). The concentration and size of the intrinsic defects of the ZnO NPs as well as the thickness of the PVA-ZnO interface are responsible for the different charge transport paths, operating voltage ranges, and ON/OFF switching ratios of the memory devices. Simultaneously, the distinct sizes and morphologies of the ZnO NPs can affect the nanoholes among the PVA chains and induce various fractional free volumes in the nanocomposites. It may modify the conductivity of the nanocomposite layer or the resistance ratio of the memory devices. Understanding the influence of ZnO NPs size, morphology, and defects on the characteristics of RS of PVA-ZnO nanocomposites can help in the selection and management of functional applications, especially in the data storage field.

Nanofiber bundles of TiO2 with a unique cheek-brush morphology were prepared by simple, rapid, one-pot, single-step, and template-free solvothermal treatment of a titanium alkoxide and aromatic ester in methanol. The solvothermal reaction was performed by heating a mixture of titanium tetraisopropoxide and dimethyl phthalate in methanol to 300 °C. The precursor solution had to be kept at room temperature for 20 min before heating the solution to obtain a cheek-brush morphology. The heating rate (5–6 °C/min), final reaction temperature (300 °C), and holding time at the final temperature (10 min) were also crucial for formation of the cheek-brush morphology. A systematic study of additives in the precursor solution showed that aromatic esters such as diethyl phthalate and methyl benzoate gave cheek-brush morphologies. The cheek-brush TiO2 assemblies were used to crosslink a poly(N-isopropylacrylamide) hydrogel; the brushes enhanced the physical adhesion properties of the hydrogel. The hydrogel prepared from a 20wt% polymer containing 0.02wt% of the cheek-brush TiO2 assemblies had an 11 % and 9.1 % higher ultimate tensile strength and elongation ability, respectively, compared with a prototype hydrogel without a crosslinker. A hydrogel prepared using TiO2 spheres of a similar size had an 11 % and 18 % lower ultimate tensile strength and elongation ability, respectively, compared with the prototype hydrogels.

Five novel surfactants were prepared by modifying the three hydroxy groups of sodium cholate with triethylene glycol chains endcapped with an amide (SC-C1 , SC-n C4 , and SC-n C5 ) or a carbamoyl group (SC-On C4 and SC-Ot C4 ). The phase behavior of aqueous mixtures of these surfactants with 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine (DMPC) was systematically studied by 31 P NMR spectroscopy. The surfactants endcapped with carbamate groups (SC-On C4 and SC-Ot C4 ) formed magnetically alignable bicelles over unprecedentedly wide ranges of conditions, in terms of temperature (from 21-23 to >90 °C), lipid/surfactant ratio (from 5 to 8), total lipid content (5-20 wt %), and lipid type [DMPC, 1,2-dilauroyl-sn-glycero-3-phosphatidylcholine (DLPC), or 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine (POPC)]. In conjunction with appropriate phospholipids, the carbamate-endcapped surfactants afforded unique bicelles, characterized by exceptional thermal stabilities (from 0 to >90 °C), biomimetic lipid compositions (DMPC/POPC=25:75 to 50:50), and extremely large 2 H quadrupole splittings (up to 71 Hz).

A millimeter-long metal–organic framework fiber has been successfully constructed. The fiber structure was unexpectedly found via the solvent vaporization process of a dispersion of a Zn-based MOF crystal. Detailed experiments and structural analysis indicate that a humid environment is a key to the growth of the fiber structure, inducing drastic transformation of the MOF crystal morphology from the nanoscopic to macroscopic scale. Synchrotron X-ray single-crystal diffraction analysis reveals that the complete crystal transformation from the Zn-MOF sheet to Zn-MOF fiber is accompanied by water coordination and ligand rearrangement. The highly anisotropic MOF fiber is easily converted to an electro-conductive fiber while maintaining the long-fiber morphology.

In this study, a novel hydrothermal route has been developed for the synthesis of MoS2/graphene composite with controllable structures, in which ammonium molybdatetetrahydrate, as-prepared graphene oxide (GO), and thioacetamide were used as staring materials. Effects of Mo4+-to-C precursor ratios and crystalline time on the structures, components and morphologies of MoS2/graphene were investigated. MoS2/graphene samples were characterized using XRD, FESEM, HRTEM, FTIR, Raman spectroscopy, HAADF-STEM/EDS, HXPES and electrical measurements. The results show that petal-like MoS2 nanostructures with ultrathin petals (~1–10 layers) and coexistence of 1T- and 2H-MoS2 phases can be synthesized on graphene surface in a short time (~2 h). Comparison of crystallization conditions, we found that the crystallization time had a significant effect on the size of the MoS2 nanopetals. The shorter the reaction time is, the thinner the petal-like MoS2 nanoscale is. On the other hand, by adjusting the ratios of Mo4+to C (denoted as: MoS2/C (1:2), MoS2/C (3:2), MoS2/C (2.5:1) and MoS2/C (3:1)), different MoS2/graphene architectures including “sandwich-liked”, “layer–by–layer” and “anchored” can be obtained. On the basis of these results, a possible growth mechanism of MoS2nanopetals on GO was proposed. Interestingly, the as-synthesized material depicts its memristive behavior through the Volt-Ampere characteristics, suggesting a potential application in logic memory devices.

The ability of a rapid-heating solvothermal process to synthesize porous nanocrystal assemblies composed of the multiple transition metals was demonstrated. The rapid heating facilitated the quick formation of nascent nanocrystals to generate homogeneous mixed transition-metal oxides. Systematic studies of the synthesis of mixed-metal oxides under various experimental conditions indicated that the present simple method is suitable to develop a wide variety of binary and ternary transition-metal systems such as Co/Mn, Ni/Mn, and Co/Mn/Fe mixed-metal oxides. The products obtained from the rapid heating process were hierarchically assembled porous nanospheres composed of sub-10 nm nanocrystals, which had an extraordinarily high surface area and nano/mesopores. Electrochemical tests revealed the high catalytic ability of the porous nanocrystal assemblies in water oxidation.

SiO2–TiO2 composite nanoparticle assemblies with or without alkyl surface modification and bearing a higher-order hollow spherical morphology were successfully synthesized by a simple, rapid, one-pot, and single-step solvothermal method using a precursor solution consisting of n-octyl-Si(OMe)3 or Si(OEt)4, Ti(OiPr)4, o-phthalic acid, and acetic acid in methanol. The addition of acetic acid is essential for a high yield of nanoparticle assemblies with hollow spherical morphology and a high content of Si. The Si/Ti atomic ratio in the SiO2–TiO2 composite nanoparticle assemblies was easily controlled by changing the Si/Ti atomic ratio in the precursor solutions. The TiO2 nanoparticles exhibited good dispersibility in a polar solvent (methanol), while the n-octyl-modified SiO2–TiO2 composite nanoparticle assemblies were readily dispersed in a nonpolar solvent (toluene). Thus, the hydrophilic–lipophilic balance of the SiO2–TiO2 nanoparticle assemblies with hollow spherical morphology was directly controlled by the one-pot and single-step solvothermal method.