Synthesis of Fe3O4@SiO2@Ption–TiO2 hybrid composites with high efficient UV–visible light photoactivity

Platinum ion doped magnetic TiO₂ (Fe₃O₄@SiO₂@Pt_ion–TiO₂) hybrid microspheres with uniform magnetic cores were synthesized and characterized in this work. The results indicate that the photoactivity of Fe₃O₄@SiO₂@Pt_ion–TiO₂ is much higher than Fe₃O₄@SiO₂@TiO₂ for the decolorization of acid orange 20 under UV–visible light irradiation. The trend for the final degradation ratio with Fe₃O₄@SiO₂@Pt_ion–TiO₂ is quite small, even after seven repetitive experiments. These data indicate that the magnetic microspheres possess the potential to be effective and stable catalysts. The results demonstrate that the Pt ion doped magnetic catalyst meets the needs for both immobilization and high photoactivity.     

Porous Fe3O4/C microspheres for efficient broadband electromagnetic wave absorption

Porous Fe₃O₄/C microspheres, which were Fe₃O₄ nanocrystals (～8?nm) embedded in an open nanostructured carbon network, were successfully synthesized via a facile hydrothermal process. The porous Fe₃O₄/C microspheres possessed many distinct attributes that facilitate efficient broadband electromagnetic wave absorption (EMWA). EMWs were attenuated through multiple reflections and absorption in the 3D interconnected porous structure of the microspheres; these processes collectively improved the interaction between the EMWs and the absorber. Additionally, the carbon network and embedded Fe₃O₄ nanoparticles caused significant dielectric losses and magnetic losses, respectively, which also enhanced EMWA. The EMWA characteristics of the microspheres could be precisely tuned via changing the carbon content to achieve optimized impedance matching. Porous Fe₃O₄/C microspheres with a 71.5?wt% carbon content displayed particularly impressive EMWA properties: a maximum reflection loss (RL) value of ??31.75 across broad band frequencies in the range of 7.76–12.88?GHz (RL < ?10?dB) at an absorber thickness of 3.0?mm. These excellent EMWA properties may be attributed to both dielectric loss (carbon) and magnetic loss (Fe₃O₄). Additionally, the 3D interconnected porous structure of the Fe₃O₄/C microspheres is especially favorable for impedance matching.     

Preparation of high-magnetization Fe3O4–NH2–Pd (0) catalyst for Heck reaction

A magnetically separable Fe₃O₄–NH₂–Pd (0) catalyst was easily synthesized by immobilizing Pd nanoparticles on the surface of magnetic Fe₃O₄–NH₂ microspheres. It was found that the combination of Fe₃O₄ and triethylene tetramine (TETA) could give rise to structurally stable catalytic sites. Furthermore, the high-magnetization Fe₃O₄–NH₂–Pd(0) catalyst can be recovered by magnet and reused for six runs for Heck reaction without significant loss in catalytic activity.     

Optically active,magnetic microspheres: Constructed by helical substituted polyacetylene with pendent prolineamide groups and applied as catalyst for Aldol reaction

This article reports on the preparation of a novel category of optically active magnetic microspheres (OAMMPs) consisting of Fe₃O₄ nanoparticles and helical substituted polyacetylene bearing pendent prolineamide groups and the use of them for asymmetric direct Aldol reactions. The microspheres (200–300 μm in diameter) were prepared by using chiral acetylenic monomer and alkynyl-Fe₃O₄ nanoparticles via suspension polymerization approach. They were obtained in high yield (> 99%) with regular spheric morphology and exhibited noticeable optical activity, according to circular dichroism spectra and specific optical rotation measurements. The microspheres further served as chiral catalyst for performing direct Aldol reactions between acetone and p-nitrobenzaldehyde, providing the product in moderate yield (68%) and ee (75%). The magnetic microspheres can be easily recycled and reused. Mechanism for the asymmetric catalysis of Aldol reaction was further proposed.     

Trace precious metal Pt doped plate-type anodic alumina Ni catalysts for methane reforming reaction

A novel plate-type anodic alumina supported 17.9 wt% Ni/Al₂O₃/alloy showed a quick deactivation in daily start-up and shut down (DSS) steam reforming of methane (SRM) at 700 °C, because of the Ni oxidation reaction with steam. When 0.078 wt% Pt was doped, the catalyst exhibited self-activation and self-regeneration ability, while 3000 h continual and 500-time DSS stability was testified. Further, this Pt–Ni catalyst also showed excellent reactivity during carbon dioxide reforming of methane (CMR) and partial oxidation of methane reaction (POM). According to the TPR and XRD analyses, the H₂ spillover effect and the formation of Pt–Ni alloy were believed to be the main reason for the reactivity improvement of this catalyst.     

Influence of Mg Addition on the Catalytic Activity of Alumina Supported Ag for C3H6-SCR of NO

The influence of different magnesium (Mg) weight percentages (1, 2.5, 5, 7.5 and 10) over silver (3 wt%) impregnated alumina (SA) catalyst was investigated for the reduction of NO by C₃H₆. Mg doped SA catalysts were prepared by conventional impregnation method and characterized by XRD, BET-SA, ICP-MS, XPS, SEM, UV-DRS, H₂-TPR and O₂-TPD. The existence of MgO and MgAl₂O₄ phases on Mg doped SA catalysts were observed from XRD and XPS analyses. Existence of high percentage MgAl₂O₄ phase on 5% Mg doped SA catalyst (Mg (5) SA) enhances the dispersion and stabilization of silver phases (Ag₂O). Mg (5) SA catalyst shows a 51% of high selectivity (NO to N₂) in presence of SO₂ (80 ppm) at low temperatures (350 °C) and maintained high selectivity’s with a wide temperature window (350–500 °C). An optimal high surface availability of Ag⁰ and Ag⁺ species were observed from XPS analysis over Mg (5) SA catalyst. H₂-TPR analysis shows high temperature reduction peak over Mg (5) SA compared to SA catalyst. XPS analysis confirms the high percent availability of MgAl₂O₄ species over Mg (5) SA catalyst. DRIFTS study reveals the molecular evidences for the evolution of enolic species during NO reduction over the highly active Mg (5) SA catalyst at low temperatures. It also confirms further transformation of enolic species into –NCO species with NO + O₂ and finally into N₂ and CO₂.     

Mechanistic Study of Carbon Oxidation with NO2 and O2 in the Presence of a Ru/Na‐Y Catalyst

The oxidation of model soot by NO₂ and O₂ in the presence of a Ru/Na‐Y catalyst under conditions close to automotive exhaust gas after‐treatment systems is investigated. Isothermal oxidation experiments of a physical mixture of carbon black and catalyst were performed in a temperature range of 300–400 °C. A remarkable increase of the oxidation rate by NO₂ and O₂ in the presence of the Ru/Na‐Y catalyst was observed. An overall mechanism involving oxygen transfer from the Ru catalyst to the carbon surface leading to an increase of C(O) complexes is proposed. These C(O) complexes are destabilized in the presence of NO₂ increasing the carbon oxidation rate.     

Catalytic effect of platinum on the kinetics of carbon oxidation by NO2 and O2

The effect of a commercial Pt/Al₂O₃ catalyst on the oxidation by NO₂ and O₂ of a model soot (carbon black) in conditions close to automotive exhaust gas aftertreatment is investigated. Isothermal oxidations of a physical mixture of carbon black and catalyst in a fixed bed reactor were performed in the temperature range 300–450 °C. The experimental results indicate that no significant effect of the Pt catalyst on the direct oxidation of carbon by O₂ and NO₂ is observed. However, in presence of NO₂–O₂ mixture, it is found that besides the well established catalytic reoxidation of NO into NO₂, Pt also exerts a catalytic effect on the cooperative carbon–NO₂–O₂ oxidation reaction. An overall mechanism involving the formation of atomic oxygen over Pt sites followed by its transfer to the carbon surface is established. Thus, the presence of Pt catalyst increases the surface concentration of –C(O) complexes which then react with NO₂ leading to an enhanced carbon consumption. The resulting kinetic equation allows to model more precisely the catalytic regeneration of soot traps for automotive applications.     

Phase Transition and Large Electrostrain in Lead‐Free Li‐Doped (Ba,Ca)(Ti,Zr)O3 Ceramics

Large piezoelectric effect is achieved in Li‐doped Ba_0.85Ca_0.15Ti_0.90Zr_0.10O₃(BCTZ) ceramics by use of tuning the phase boundaries. Rhombohedral–orthorhombic (R–O) and orthorhombic–tetragonal (O–T) multiphase coexistence is constructed in the ceramics by changing Li contents. The high piezoelectric constant d₃₃ (493 pC/N) and large electrostrain (dS_max/dE_max = 931 pm/V) have been observed in the Li‐doped (Ba, Ca)(Ti, Zr)O₃ ceramics at low sintering temperature (1350°C/2 h). The significant enhancement in materials properties is ascribed to the multiphase region around room temperature induced by Li‐doped effect.     

Fabrication of carbon-doped ZnCo2O4 yolk-shell microspheres compounded with magnetic graphene for enhanced electromagnetic wave absorption performance

Carbon-doped ZnCo₂O₄ (ZnCo₂O₄/C) yolk-shell microspheres are synthesized by a method of thermally decomposing precursor and then successfully compounded with magnetic graphene (MG) via co-precipitation in combination with a reduction pathway. The fabrication processes and characterizations (XRD, XPS, TEM, EDS and SEM) are described and explained in detail. It is confirmed that amorphous carbon (in situ decomposition from PVP) is uniformly doped into ZnCo₂O₄ yolk-shell microspheres. In addition, the reflection loss (RL) and electromagnetic (EM) wave absorption mechanisms of as-prepared ZnCo₂O₄/C/MG composites are calculated and analyzed exhaustively. The results show that absorption bandwidth with RL exceeding −10 dB reaches up to 4.48 GHz with a matching thickness of 3.5 mm while the maximum RL is up to −52.9 dB at 7.52 GHz with a matching thickness of 3.9 mm. Enhanced EM wave absorption performance can be attributed to good dielectric and magnetic loss, excellent impedance matching, diverse interfacial polarization and multiple reflections caused by special structures.     

Significant Improvement of Superconducting Properties in Nano‐NiFe2O4‐Doped Y–Ba–Cu–O Single‐Grain Superconductor

Introduction of refined second‐phase particles in superconducting YBa₂Cu₃O_7?x (Y‐123) matrix is known to be an effective route to improve the δl‐type pinning and the performance of Y–Ba–Cu–O (YBCO) single‐grain superconductors, while the δT_c‐type pinning induced by spatial fluctuations in matrix composition is also important and contributes to the in‐field J_c performance and high‐field applications of bulk superconductors. In this communication, chemical doping of nano‐sized NiFe₂O₄ (mean size 50 nm) in single‐grain YBCO superconductor is performed using a novel top‐seeded infiltration growth (TSIG) technique based on a solid source pellet (SSP) of nano‐Y₂O₃ + BaCuO₂. The results indicate that, significant improvement of bulk performances including levitation force (33.93 N) and trapped field (0.3628 T) has been observed in the 0.2 wt% nano‐NiFe₂O₄‐doped sample, which are much higher than the undoped sample (28.81 N and 0.2754 T). T_c measurement indicates that, a decreased onset T_c of about 87.5 K and a broadened transition width of about 5 K are observed in the NiFe₂O₄‐doped sample, indicating appearance of weak superconducting regions in superconducting matrix caused by Ni and Fe substitutions in Y‐123 crystal lattice. This study supplies a practical approach to increase the YBCO bulk performance significantly.     

Dependence of n-Butane Activation on Active Site of Vanadium Phosphate Catalysts

The nature and the role of oxygen species and vanadium oxidation states on the activation of n-butane for selective oxidation to maleic anhydride were investigated. Bi–Fe doped and undoped vanadium phosphate catalysts were used a model catalyst. XRD revealed that Bi–Fe mixture dopants led to formation of α_II-VOPO₄ phase together with (VO)₂P₂O₇ as a dominant phase when the materials were heated in n-butane/air to form the final catalysts. TPR analysis showed that the reduction behaviour of Bi–Fe doped catalysts was dominated by the reduction peak assigned to the reduction of V⁵⁺ species as compared to the undoped catalyst, which gave the reduction of V⁴⁺ as the major feature. An excess of the oxygen species (O^2?) associated with V⁵⁺ in Bi–Fe doped catalysts improved the maleic anhydride selectivity but significantly lowering the rate of n-butane conversion. The reactive pairing of V⁴⁺-O^? was shown to be the centre for n-butane activation. It is proposed that the availability and appearance of active oxygen species (O^?) on the surface of vanadium phosphate catalyst is the rate determining step of the overall reaction.     

Synthesis of nanofibrous chitosan/Fe3O4/TiO2@TiO2 microspheres with enhanced biocompatibility and antibacterial property

Multifunctional materials have received considerable attention as they could integrate different functional components in one-single platform. In this study, novel chitosan/Fe₃O₄/TiO₂@TiO₂ nanowire (NW) microspheres having extracellular matrix-like fibrous surface and photothermal antibacterial property were synthesized through in situ hydrothermal growth of TiO₂ NWs on chitosan/Fe₃O₄/TiO₂ microspheres. It is found that the microspheres were spherical in morphology with a diameter of 100–300 µm and exhibited a hierarchical and nanofibrous feature. Their surface was mainly constructed by numerous TiO₂ NWs with a diameter of 20– 30nm. In vitro biological evaluation indicates that the chitosan/Fe₃O₄/TiO₂@TiO₂ NW microspheres significantly enhanced attachment and proliferation of human umbilical vein endothelial cells compared with chitosan/Fe₃O₄/TiO₂ nanocomposite microspheres due to the presence of nanofibrous surface. Moreover, the microspheres showed photothermal antibacterial property to inhibit the growth of bacteria due to the presence of Fe₃O₄ component.     

Formation mechanism of β-Sialon with different morphologies based on DFT calculation and its effect on the performance of refractory composites

β-Sialon with whisker-like, columnar, and plate-shaped structures was successfully synthesized with Al₂O₃–C refractory compositions. In the presence of a catalyst, the preferential growth face of columnar β-Sialon was (100), whereas plate-like β-Sialon preferred (101) and (111). DFT calculations demonstrated that the SiO adsorption energy on the (100), (101), and (111) faces of β-Sialon crystal were –34.95, –52.88, and –45.08 eV, respectively. Therefore, the (101) and (111) faces were more stable in Al-rich β-Sialon. With the increase in catalyst content, the Si-rich Si–Al–O–N liquid phases, which contributed to the generation of columnar β-Sialon, were converted into the Al-rich Al–Si–O–N system that was conducive to the formation of plate-like β-Sialon. Compared to the sample without the catalyst, the CMOR and HMOR of the specimen were increased by 45.07% and 60.47%, respectively, with the addition of Fe₂O₃. This was attributed to the formation of β-Sialon with a one- or two- dimensional shape.     

Magnetite (Fe3O4) Nanoparticles‐Catalyzed Sonogashira– Hagihara Reactions in Ethylene Glycol under Ligand‐Free Conditions

A novel application of nanoparticles of paramagnetic magnetite (Fe₃O₄) as an efficient catalyst for carbon‐carbon bond formation via the Sonogashira–Hagihara reaction under heterogeneous ligand‐free conditions in ethylene glycol (EG) is described. By using this catalyst, arylalkynes are produced from the reaction of aryl iodides and activated heteroaryl bromides with alkynes. The results are reproducible using the catalyst, which was prepared from different sources. The catalyst is easily separated by an external magnetic field from the reaction mixture. The separated catalyst can be recycled for several consecutive runs without appreciable loss of its catalytic activity.     

Effects of carbon on the sulfidation and hydrodesulfurization of CoMo hydrating catalysts

The effects of carbon addition on CoMo catalyst performance for sulfidation and hydrodesulfurization (HDS) were investigated. The carbon-containing catalyst was prepared by impregnation of γ-Al₂O₃ support with NH₃ aqueous solution containing Co(NO₃)₂·6H₂O, (NH₄)₆Mo₇O₂₄·4H₂O and ethylenediamine. The results indicated that the incorporation of proper carbon on CoMo catalyst can improve its HDS performance. The carbon species on the catalyst were characterized by temperature-programmed oxidation and reduction, temperature-programmed desorption of ammonia and ultraviolet-visible diffuse reflectance spectra. Two forms of carbon species were differentiated: one is spread over the catalyst surface, similar to coke formed from reaction; the other interacts with active phase as an intermediate support. The carbon species acting as intermediate support may decrease the interaction of active metals with support, which enhances the sulfidation and HDS activities of CoMo catalyst. This work was presented at the 7th China-Korea Workshop on Clean Energy Technology held at Taiyuan, Shanxi, China, June 26–28, 2008.     

Hybrid organic-inorganic Cu(II) iminoisonicotine@TiO2@Fe3O4 heterostructure as efficient catalyst for cross-couplings

Two novel mononuclear copper (II) complex catalysts were synthesized from a new tridentate iminoisonicotine ligand (HL) by coordination with Cu(II) ion, with (CuL@TiO₂@Fe₃O₄) and without (CuL) immobilization on TiO₂-coated nanoparticles of Fe₃O₄. The ester moiety on the back of the ligand was utilized for immobilization on nanoparticles of Fe₃O₄. Both ligand and CuL complex were fully characterized by using alternative spectral techniques (nuclear magnetic resonance, infrared, ultraviolet-visible and mass spectroscopy, and elemental analyses). Different analytical techniques were used to identify the structural feature and morphology of the immobilized copper catalyst (CuL@TiO₂@Fe₃O₄) shell-shell-core system. The structural analysis revealed that the catalyst system is composed of both agglomerated nanospheres and deformed nanorods. Both copper catalysts, immobilized CuL@TiO₂@Fe₃O₄ and un-immobilized CuL were studied in heterogeneous and homogeneous catalysis, respectively, for Suzuki-Miyaura (C–C) and Buchwald-Hartwig (C–N) cross-coupling reactions of various heteroaryl halides. Both catalysts showed good catalytic potential under the controlled optimal reaction conditions. In contrast to the homogeneous catalyst (CuL), the heterogeneous catalyst (CuL@TiO₂@Fe₃O₄) showed slightly better catalytic performance. The characteristic obtains supported the catalytic potential of the current samples. Reusability/recycling of both catalysts was also investigated in C–C cross-coupling reactions. It was found that the homogeneous catalyst (CuL) could be only recycled up to three times, whereas the heterogeneous one (CuL@TiO₂@Fe₃O₄) could be reused up to seven times with good efficiency.     

Gold catalysts on Co-doped ceria for complete benzene oxidation: Relationship between reducibility and catalytic activity

Very high catalytic activity in complete benzene oxidation (CBO) was observed over gold catalyst on prepared by mechanochemical mixing CeO₂–Co₃O₄ (10 wt.% of dopant). It was significantly higher compared with gold catalysts supported on ceria doped with 5 wt.% or 15 wt.% Co₃O₄. The presence of Co₃O₄ phase and Co-modified ceria was observed by XRD data. The HRTEM/HAADF results revealed that the doping with 10 wt.% Co₃O₄ was favorable for the higher gold dispersion. The highest reducibility, i. e. ability of oxygen supplying of gold catalyst on ceria doped with 10 wt.% Co₃O₄ correlates with the highest oxidation activity in CBO.     

Investigation of the conditions required for the formation of V(C,N) during carburization of vanadium or carbothermal reduction of V2O5 under nitrogen

Phase stability diagrams of V–C–N and V–O–C–N systems were constructed as a function of carbon activity, nitrogen partial pressure, oxygen partial pressure, and solution formation characteristics to determine the conditions for the formation of V(C,N) via the carburization of vanadium or carbothermal reduction of V₂O₅ under nitrogen. The diagram showed that only V, V₂C, and V(C,N) phases would be stable in the V–C–N system. From the diagram, it was also observed that only V(C,N) exists after the carburization of vanadium under nitrogen atmosphere more than 10^?5 atm. The diagram of V–O–C–N system suggests that V₂O₅ can be reduced to V(C,N) without forming VO, owing to the high stability of the V(C,N) phase. Using these stability diagrams, the conditions for preparing V(C,N) from vanadium or V₂O₅ were deduced and the validity of the diagrams was verified using the experimental results.     

Design of magnetic triple-shell hollow structural Fe3O4/FeCo/C composite microspheres with broad bandwidth and excellent electromagnetic wave absorption performance

A three-step strategy combining solvothermal and liquid phase reduction method had been developed for preparation of magnetic triple-shell hollow structural Fe₃O₄/FeCo/C (TSH–Fe₃O₄/FeCo/C) composite microspheres. FeCo was used to enhance electromagnetic (EM) wave absorption in different frequency band and broaden effective absorbing bandwidth, while carbon was used to improve impedance matching. Triple-shell hollow structure was designed to enrich the multiple interfaces to favor the interfacial polarization, increase the multiple reflections and scattering, and provide physicochemical protection to Fe₃O₄ core from oxidation. The microstructure and morphology of TSH-Fe₃O₄/FeCo/C composite microspheres were characterized by TEM, XRD and Raman in detail. The results indicated that magnetic Fe₃O₄ was completely covered by FeCo and carbon via layer by layer. As an EM wave absorber, the maximum reflection loss of TSH-Fe₃O₄/FeCo/C composite microspheres was up to -37.4 dB due to better normalized characteristic impedance at a thickness of 2.2 mm and the bandwidth less than -10 dB even reached up to 5.9 GHz. The excellent EM wave absorption performance was attributed to the combination of shell materials (Fe₃O₄, FeCo and carbon) and unique triple-shell hollow structure, which lead to multiple relaxation processes and good impedance matching. Consequently, this work would contribute to the design and preparation of high performance EM wave absorbent with outstanding absorbing property and wider absorption range.