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In this work, Pt nanoparticles were deposited onto the surface of Magneli phase titanium suboxide (TiOx) nanoparticles using a microwave-assisted deposition method. The effect of different concentrations of Pt nanoparticles was investigated to evaluate the strong metal-support interactions (SMSIs) between Pt and TiOx based on their performance for the degradation of organic pollutant molecules. The adsorption and catalytic performance of the as-synthesized Pt/TiOx nanoparticles were evaluated with respect to the degradation of rhodamine B (RhB) molecules without any external energy source. The Pt/TiOx nanoparticles with Pt loading at 10 wt% (10%Pt/TiOx) exhibited a remarkable performance. The XPS, CV, and FTIR analyses confirmed the presence of RhB degradation reactions under dark condition. This remarkable performance of the Pt/TiOx nanoparticles was attributed to the SMSIs between Pt and Ti3+ atoms, which improves their performance compared with Pt/TiO2 nanoparticles, and high density of active sites due to their nanometer size, which results in better performance compared with that of Pt/TiOx submicron particles.

Carbon dots (CDs) have attracted great attention because of their unique luminescence properties, chemical inertness, thermal stability, high water solubility, low toxicity, and ease of functionalization. Here, the kinetics of nitrogen-doped CD (N-CD) formation by hydrothermal synthesis were evaluated in an attempt to realize the rapid and efficient production of N-CDs. A series of N-CDs was synthesized using various heating rates, reaction times, reaction temperatures, and precursor concentrations. Characterization of the series of N-CDs indicated that N-CD formation is a first-order reaction with a reaction rate constant of 0.634 min−1. In addition, systematic investigation revealed that synthesis temperature is a more important factor to obtain highly fluorescent N-CDs than reaction time. Citric acid amides are formed by the reaction between citric acid and urea at 130 °C and N-CDs consisting of two or three citric acid amide molecules are formed through dehydration, deammoniation and dehydrogenation of citric acid at 150 °C. By adjusting the operating conditions, N-CDs with a highest quantum yield of 39.7% could be produced at a production rate of 50 g h−1 with a reaction time of 16 min. The N-CDs were then embedded in polyvinyl alcohol (PVA) nanofibers. The luminescence intensity of the N-CD–PVA composite nanofibers was more than twice that of the N-CDs in solution.

The surfaces of carbon nanotubes (CNTs) were covered with thin silica layers through the application of 3-aminopropyltriethoxysilane (APTES) in order to enhance the deposition of precious metal and transition metal oxide nanoparticles. Pt metal particles smaller than 2 nm in diameter could be deposited, using a conventional impregnation method, on CNTs coated with silica layers, whereas Pt particles supported on bare CNT surfaces were approximately 3 nm in diameter. Thus, coating CNTs with thin silica layers enhanced the catalytic activity of the Pt catalysts. In addition, CNTs with thin silica layers could be uniformly covered with transition metal oxide layers (ZrO 2 , Nb 2 O 5 and Ta 2 O 5 ) by hydrolysis of the corresponding metal alkoxides. In contrast, metal oxides were very difficult to deposit on bare CNTs. The thin silica layers produced on the CNTs via the use of APTES evidently function as adsorption sites for precursor metals and metal oxides, as well as nucleation sites for metals and metal oxides, allowing the formation of precious metal-CNT and transition metal oxide-CNT composites.

The catalytic performance of Pt metal at the tips of carbon nanotubes (CNT@Pt), which was prepared by ethylene decomposition over Pt/MgO, was compared with that of Pt metal on the outer surface of CNT (Pt/CNT). CNT@Pt showed excellent catalytic performance toward the hydrogenation of α, β-unsaturated aldehydes to unsaturated alcohols, which was similar to that of Pt/CNT and resulted from a strong interaction between Pt metal and the CNT. Pt metal particles at the tips of CNTs showed excellent activity for the selective hydrogenation of α, β-unsaturated aldehydes to unsaturated alcohols similarly to Pt metal particles supported on the outer surface of CNTs.

Pd metal supported on carbon nanotubes (Pd/CNT) for use as a cathode catalyst in polymer electrolyte fuel cells was covered with silica layers a few nanometers thick to improve the durability of the catalyst under severe cathode conditions. The silica-coated Pd/CNT cathode catalyst showed similar activity for the oxygen reduction to Pd/CNT despite coverage of the Pd metal with a silica insulator. In addition, the silica-coated Pd/CNT was highly durable during potential cycling between 0.05 and 1.20 V (vs. reversible hydrogen electrode) in aqueous HClO4 while Pd/CNT suffered serious deactivation under the same conditions. The silica layers in the silica-coated Pd/CNT prevent the diffusion of dissolved Pd species from the Pd metal out of the layers. Therefore, silica-coated Pd/CNT was highly durable under the cathode conditions. Furthermore, coverage of Pd/CNT with silica layers inhibited the two-electron reduction of oxygen to H2O2.

Ethylene decomposition was performed over supported Pt catalysts to fabricate composites of Pt metal nanoparticles and carbon nanotubes (CNTs). All supported Pt catalysts (Pt/carbon black, Pt/CNT, Pt/MgO, Pt/Al2O3 and Pt/SiO2) showed catalytic activity for ethylene decomposition at 973 K to form CNTs. Pt metal particles were found at tips of CNTs. These results indicate that Pt metal particles have catalytic activity for growth of CNTs through hydrocarbon decomposition. A broad range (5–50 nm) of CNT diameters were formed from the use of supported Pt metal catalysts although Pt metal particles in the catalysts before ethylene decomposition were relatively uniform in size (2–5 nm). These results imply that Pt metal particles in the catalysts aggregated during ethylene decomposition at 973 K. Aggregation of Pt metal particles in catalysts during ethylene decomposition could be suppressed by covering catalysts with silica layers that were a few nanometers thick. Silica-coated Pt catalysts showed high activity for ethylene decomposition to form CNTs with uniform diameters (8–10 nm) despite the uniform coverage of Pt metal particles with silica layers.

High luminance Y 3 Al 5 O 12 :Ce 3+ (YAG:Ce) nanoparticles were prepared from urea-added nitrate aqueous precursor by flame-assisted spray pyrolysis (FASP). The addition of urea into nitrate precursor plays an important role in YAG:Ce nanoparticle formation and in improving its optical performance. The decomposition and combustion of urea in the flame zone provides additional heat to the particles, which coupled with the evolution of large volumes of gasses, contributes to nanoparticle formation. The as-prepared nanoparticles are hexagonal YAlO 3 , that are nearly spherical, rough on the surface and dense—and they can be converted to YAG:Ce after being annealed at 1200 °C for 4 h. The heat-treated particles are single crystalline, smooth in surface and dense with an average size around 50 nm. The optimum cerium-doping concentration of YAG:Ce nanoparticles is 4.0 at.%, which exhibits quantum efficiency of 45.0%. This quantum efficiency is comparable with that of YAG:Ce nanoparticles produced from other processes. The efficient emission of YAG:Ce nanoparticles also originates from a relatively good distribution of Ce ions incorporated into the host material of YAG as evidenced from the elemental mapping analysis.

Carbon nanotube (CNT)-supported Pt metal nanoparticles were covered with silica layers by utilizing the successive hydrolysis of 3-aminopropyl-triethoxysilane and tetraethoxysilane on CNTs with Pt hydroxide. The CNT-supported Pt metal particles covered with silica layers (denoted as SiO2/Pt/CNT) were used as the electrocatalysts. SiO2/Pt/CNT electrocatalysts showed a high stability for the repeated potential cycling experiment, whereas Pt/CNT electrocatalysts were deactivated seriously for the experiment because of the growth of Pt metal particles in size. The silica layers in SiO2/Pt/CNT prevent the dissolution of Pt metal particles as well as the migration and agglomeration of Pt metal particles on the supports, which results in the improvement of the stability of Pt/CNT electrocatalysts.

Silica-supported Co catalysts were prepared by using microemulsion. The structure and state of the Co species in the catalysts were characterized by TEM, XRD, Co K-edge XANES/EXAFS, and diffuse reflectance UV−vis spectroscopy. Co species in the catalysts prepared using microemulsion were atomically dispersed as Co2+ with tetrahedral symmetry (CoO4), even after reduction of the catalysts with hydrogen at 773 K, while Co metal particles were supported on the silica surface for the catalysts prepared by a conventional impregnation method. The Co catalysts prepared using microemulsion selectively formed multi-walled carbon nanotubes with a uniform diameter by the decomposition of ethylene at 973 K, whereas silica-supported Co catalysts prepared by the impregnation method formed carbon nanofibers with various diameters. In addition, the Co catalysts prepared using microemulsion formed bundles of single- or double-walled carbon nanotubes by methane decomposition at 1073 K. Contact of the Co catalysts with hydro...

Silica-supported Ni catalysts were prepared by using water-in-oil typed microemulsion. By preparation using the microemulsion, Ni metal particles with diameters < ca. 5 nm were covered uniformly with silica layers with thickness of ca. 10 nm, whereas Ni metal particles were supported on the outer surface of silica by a conventional impregnation method. The Ni metal covered with silica (coat-Ni) showed excellent catalytic performance for the partial oxidation of methane into synthesis gas. Coat-Ni showed a high activity and a long life for the partial oxidation of methane at temperatures above 973 K to form CO and hydrogen, whereas Ni metal catalyst supported on silica was rapidly deactivated for the reaction. Ni K-edge XANES/EXAFS and temperature-programmed reduction for these catalysts showed that Ni metal particles in coat-Ni strongly interacted with silica. The strong interaction of Ni metal particles with silica would improve their catalytic performance for the partial oxidation of methane into synthesis gas.

Highly concentrated hydrogen and carbon nanofibers were produced through methane decomposition in a temperature range of 973–1123 K. Pd-based alloys containing Ni, Co, Rh, or Fe showed high catalytic activity and long life for methane decomposition at 973 K. In particular, Pd–Co/Al2O3 and Pd–Ni/Al2O3 showed the highest hydrogen yield at reaction temperatures above 973 K among all the catalysts tested. Highly concentrated hydrogen ( > 94 vol% ) was formed by methane decomposition over Pd–Co/Al2O3 at 1123 K. SEM images of catalysts [M/Al2O3 (M = Fe, Co, Ni, and Pd) and Pd–M/Al2O3 (M = Fe, Co, Ni, Cu, Ag, and Rh)] after methane decomposition showed the formation of carbons with fibrous structure. In addition, TEM images of Pd–Co/Al2O3 at the initial stage of reaction showed that Pd–Co alloy particles formed carbons from several facets, whereas Co or Pd metal particles formed carbon nanofibers from one facet. This would be one reason why Pd–Co alloy catalysts showed high activity and long life for methane decomposition at high temperatures.

Catalytic performance of Co catalysts supported on different supports (MgO, Al2O3, SiO2, and TiO2) for the formation of carbon nanofibers through methane decomposition was investigated. Catalytic activity and the life of supported Co catalysts for methane decomposition at 773 K strongly depended on the type of catalytic supports; i.e., the catalytic performances of Co/Al2O3 and Co/MgO were superior to those of Co/TiO2 and Co/SiO2. All the Co catalysts produced carbon nanofibers with relatively uniform diameters (10−30 nm) through the reaction at 773 K irrespective of the kind of catalytic supports, although an average crystallite size of Co metal was different for these catalysts. These results implied that Co metal particles with diameters from 10 to 30 nm grew carbon nanofibers from methane preferentially, while ones larger than 30 nm were inactive for the reaction. The structures of carbons formed by methane decomposition over Co/Al2O3 depended on the reaction temperatures. Multiwalled carbon nanotubes...

The addition of Pd into Ni/SiO2 improved the catalytic activity and life for methane decomposition into hydrogen and carbon nanofibers. Thus, Pd-added Ni/SiO2 (denoted as Pd−Ni/SiO2) was characteri...

The effect of the addition of different metals (Cu, Rh, Pd, Ir, and Pt) into supported Ni catalysts on the catalytic performance of methane decomposition into pure hydrogen and carbon was examined. The addition of Pd brought about considerable increases in the catalytic life and in the accumulated yields of hydrogen and carbon at the complete deactivation of the catalyst, while modification with the other metals decreased the yields compared to those for Ni/SiO2. For the Ni catalysts modified with Pd, the appropriate preparation conditions of the catalysts, the effect of catalytic supports, and the optimum reaction temperature on the methane decomposition were examined. The hydrogen yield attained a high value, 16,000 molH2/molPd+Ni, when Pd and Ni were of a mole ratio Pd/(Pd+Ni)=0.5 and a total loading Pd+Ni=37 wt% on carbon nanofiber support. This yield is the highest among those reported so far. Methane decomposition over Ni catalysts modified with Pd produced carbon nanofibers with unique structures, i.e., branched carbon nanofibers. XRD studies on the Ni catalysts modified with Pd indicated the formation of Pd–Ni alloys. The alloys are responsible for the increase in the catalytic life and the formation of carbon nanofibers with unique structures.

The Ni-supported catalysts have been prepared in situ by the solid phase crystallization (spc) method starting from layered double hydroxides (LDHs) as the precursor and tested for the partial oxidation of methane to synthesis gas. The spc-Ni/M–Al (M: Mg, Ca and Sr) catalysts were prepared from Ni–M/Al-LDHs as the precursors, and the activities were studied in relation to the structure of the catalysts and compared with those prepared by the impregnation method. Among the catalysts tested, spc-Ni/Ca–Al was easily reduced to form active Ni metal particles during the reaction and showed the highest activity and selectivity to synthesis gas production as well as the highest sustainability against coke formation on the catalyst. The high activity and the high sustainability against coke formation of spc-Ni/Ca–Al may be due to the stable and highly dispersed Ni metal particles in addition to the basic property of Ca–Al mixed oxide as the support.

A solid phase crystallization (spc) method was applied for the preparation of SrTiO3-supported Ni catalysts and compared to the impregnation (imp) method. spc-Ni0.2/SrTiO3 has highly dispersed and stable Ni metal particles resulting in higher activity and higher sustainability against coking than imp-Ni0.2/SrTiO3 in the partial oxidation of CH4. Both catalysts were tested for the CH4 pyrolysis in order to elucidate the catalytic nature against coking of spc-Ni0.2/SrTiO3. The amount of carbon and the rate of H2 formation were similar over both catalysts at both 773 and 1073 K. On both catalysts, CH4 continuously decomposed at 773 K, while the rate of CH4 pyrolysis quickly decreased at 1073 K. Fibrous carbons grew up with a Ni metal particle on the tip of the fiber at 773 K, while carbon balls and short carbon fibers with a Ni metal particle encapsulated inside formed and no sufficient growth of the fiber was observed at 1073 K. The carbon species formed at 773 K was hydrogenated completely to CH4 around 873 K, while the hydrogenation of that formed at 1073 K needed higher temperature around 1073 K. However, the carbon species formed on both the catalysts at either 773 or 1073 K was completely oxidized around 773 K. Thus, judging from the anti-coking nature, the behaviors in the CH4 pyrolysis are similar over both catalysts, nonetheless spc-Ni0.2/SrTiO3 was far superior to imp-Ni0.2/SrTiO3 in the CH4 oxidation. It is likely that the high sustainability against coking of spc-Ni0.2/SrTiO3 is not due to its intrinsic nature suppressing the coking but due to its high activity of reforming which can quickly eliminate the carbon formed on the catalyst surface.

Pd cathode catalysts for polymer electrolyte fuel cells have been covered with silica layers a few nanometres thick. The silica-coated Pd catalysts showed high activity and excellent durability for the oxygen reduction under the severe cathode conditions of PEFCs, while Pd catalysts without silica-coating were seriously deactivated under the same conditions. The coverage of Pd metal with silica prevents the diffusion of Pd species out of the silica layers.

Supported Pd or Rh catalysts were prepared by the solid-phase crystallization method starting from hydrotalcite anionic clay minerals based on [Mg6Al2(OH)16CO 2 2− ]·4H2O as the precursors. The precursors were prepared by a coprecipitation method from the raw materials containing Pd2+ and various trivalent metal ions which can replace each site of Mg2+ and Al3+ in the hydrotalcite. Rh3+ was also used for preparing the catalyst as comparison. The precursors were then thermally decomposed and reduced to form supported Pd or Rh catalysts and used for the methanol decomposition to synthesis gas. Among the precursors tested, use of Mg–Cr hydrotalcite containing Pd2+ resulted in the formation of efficient Pd supported catalysts for the production of synthesis gas by selective decomposition of methanol at low temperature. Although Pd2+ cannot well replace the Mg2+ site in the hydrotalcite, the Pd supported catalyst (Pd/Mg–Cr) prepared by the solid-phase crystallization method formed highly dispersed Pd metal particles and showed much higher activity than that prepared by the conventional impregnation method. When the precursor was prepared under mild conditions, more fine particles of Pd metal were formed over the catalyst, resulting in high activity. It is likely that the high activity may be due to the highly dispersed and stable Pd metal particles assisted by the role of Cr as the co-catalyst.

Ni-supported catalysts on perovskite-type oxides, i.e. , Ni 0.2 /ATiO 3 (A: Ca, Sr or Ba) have been prepared by solid phase crystallization (spc) method and tested for partial oxidation of CH 4 into synthesis gas. Ni 0.2 /SrTiO 3 catalyst showed the highest activity as well as the highest sustainability among the catalysts tested, followed by Ni 0.2 /BaTiO 3 and then Ni 0.2 /CaTiO 3 . The high and stable activity may be due to highly dispersed and stable Ni metal particles (diameter

Pt metal particles supported on carriers such as MgO and SiO2 showed high activity for the formation of carbon nanotubes (CNTs) through ethylene decomposition at 973 K. However, these CNTs were not...

A facile, economic and environmentally friendly one-step approach for the preparation of highly luminescent graphene quantum dots (GQDs) was developed using a hydrothermal reaction between citric acid and urea. Unlike previous reports, we focused on the effect of the transient nature of GQD formation on the photoluminescence (PL) properties and molecular structure changes of the products. We found that the GQDs have an optimum reaction time and require an effective precursor to achieve excellent luminescent properties. The PL, ultraviolet-visible (UV-vis) absorption, zeta potential, and nuclear magnetic resonance (NMR) analyses of the GQDs prepared at various reaction times revealed that the molecular structures responsible for the luminescence of the GQDs are aggregates or condensation products of citric acid amides. We found that urea addition to the precursor drastically enhances the PL intensity of the GQDs, and it is 40 times higher than those prepared using the pure citric acid precursor. Additionally, a GQDs–polyvinyl alcohol composite achieved an excellent quantum yield (QY) of 43.6%., This work was supported by JSPS KAKENHI Grant numbers 26709061 and 24656413. We thank Dr Eishi Tanabe from the Hiroshima Prefectural Institute of Industrial Science and Technology for helping with TEM analyses, and Drs Naoya Tochio and Junichi Kakimura from Hiroshima University for NMR analyses.