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While high cost and lack of long‐term stability of Pt‐based catalysts have been impeding their practical application in oxygen reduction reaction (ORR) in fuel cell technologies, iron and nitrogen codoped carbons (Fe–N–C) are appearing to be stable but unfortunately less‐active catalysts in acidic electrolyte. Herein, an in situ surfactant‐free Pt deposition approach to fabricate Pt nanoparticles (NPs) onto well‐designed Fe–N–C nanostructures for producing highly performing Pt/Fe–N–C catalyst for ORR in acidic electrolyte is reported. Physical and electrochemical characterizations uncovered that electron transfer from Fe–N–C to their supported Pt NPs would weaken the adsorption of O2 on the Pt surface, therefore improving the intrinsic activity of Pt for ORR. On optimizing the Pt loading, the intrinsic and mass‐specific activity data of Pt in Pt/Fe–N–C are maximized at ≈0.93 mA cm−2 and 0.46 A mg−1‐Pt, respectively, much higher than those for commercial Pt/C (0.21 mA cm−2, 0.19 A mg−1‐Pt). The Pt/Fe–N–C catalyst also shows an intriguing long‐term stability during the accelerated durability test. A new avenue for taking the advantages of Pt and non‐noble metal ORR catalysts is pointed for achieving much better ones to accomplish ORR in acidic electrolyte. [ABSTRACT FROM AUTHOR]

Pyrolyzed base‐metal‐based metal–organic frameworks (MOFs) with FeNx coordination are emerging as nonprecious metal catalysts for electrochemical oxygen reduction reaction (ORR). However, surprisingly, nonpyrolyzed MOFs involving Fe−N coordination have not been explored for the ORR. This study concerns the catalytic performance of a semiconducting nonpyrolyzed iron triazolate framework (FeTa2) for ORR in alkaline electrolyte. The FeTa2 catalyst is studied as composites with different amounts of conductive Ketjenblack carbon (KB). The performance of these FeTa2‐x KB (x denotes the KB/FeTa2 weight ratio) composites by onset and half‐wave potentials of ORR appears to be superior to most previously documented nonpyrolyzed MOFs. Characterization by elemental analysis, FTIR spectroscopy, XPS, and cyclic voltammetry suggest that N−FeIII−OH− sites at the surface of FeTa2 function as the catalytic active sites. This FeTa2 also shows very stable activity during ORR, as supported by accelerated durability test of the FeTa2‐x KB sample (20 000 cycles, ca. 90 h). The framework structure of FeTa2 remains intact during the durability test, which would help to explain its excellent catalytic durability. This would be the first study demonstrating efficient and stable ORR catalysis by a nonpyrolyzed Fe−N coordination‐based MOF material. No heat needed: An iron triazolate framework (FeTa2) featuring Fe−N coordinated sites without further heat treatment is used as an efficient and very stable catalyst for oxygen reduction reaction (ORR). XRD measurements for FeTa2‐2 KB sample (KB=Ketjenblack carbon), before and after an accelerated durability test of 90 hours, unveil that the robust framework enables remarkable ORR durability. [ABSTRACT FROM AUTHOR]

Iron and nitrogen co-doped carbon (Fe-N-C) materials are among the most active non-precious metal catalysts that could replace Pt-based electrocatalysts for the oxygen reduction reaction (ORR) in fuel cells and metal-air batteries. The synthesis of the Fe-N-C catalysts often involves the use of aniline as the precursor for both N and C and ammonium peroxydisulfate (APS) as an indispensable oxidative initiator for aniline polymerization. Herein, a detailed structure and catalytic ORR performance comparison of aniline-derived Fe-N-C catalysts synthesized with and without the use of APS is reported. The APS-free preparation, which uses FeIII ions as the Fe source as well as the aniline polymerization initiator, results in a simple Fe-N-C catalyst with a high activity for the ORR. We show that APS is not necessary for the preparation and even detrimental to the performance of the catalyst. [ABSTRACT FROM AUTHOR]

The direct redox reaction (galvanic displacement) between Pd2+ and substrate Si was used to deposit Pd on Si, and the Pd–Si catalysts enabled a chemoselective hydrogenation of para-chloronitrobenzene with the selectivity for para-chloroaniline higher than 99.9% at complete conversion of para-chloronitrobenzene. [ABSTRACT FROM AUTHOR]

This paper proposed a novel fragile image watermarking scheme for tampering detection and content recovery. The watermark information for each image block consist of the authentication bits and the recovery bits. It generated the authentication bits by the information of the parity and average intensity, and generated the recovery bits from the encoded DCT coefficients, which embedded into the mapped block according to the chaotic mapping and secure embedding mechanism. On the receiver side, it used the hierarchical tampering detection, which could effectively decrease the missing and misjudgments for tampered blocks. Experimental results show that the proposed scheme can achieve better recovery performance than the reported schemes in both small and large tampered area. [ABSTRACT FROM AUTHOR]

This work reveals an ordered mesoporous carbon material co-doped with nitrogen and iron (Fe-N-C) for ORR catalysis in an alkaline electrolyte, whose ORR performance surpasses most of the previous metal-free heteroatom-containing carbon materials and is comparable to that of conventional Pt/C in terms of half-wave potential, limiting current density and kinetic current density. A procedure for preparing this Fe-N-C catalyst is described. [ABSTRACT FROM AUTHOR]

Gas-phase dehydration of lactic acid (LA) to acrylic acid (AA) was investigated over alkali-exchanged β zeolite (M xNa1− xβ, M=Li+, K+, Rb+, or Cs+) of different exchange degrees ( x). The reaction was conducted under varying conditions to understand the catalyst selectivity for AA production and trends of byproduct formation. The nature and exchange degree of M+ were found to be critical for the acid-base properties and catalytic performance of the exchanged zeolite. K xNa1− xβ of x=0.94 appeared to be the best performing catalyst whereas Li xNa1− xβ and Naβ were the poorest in terms of AA selectivity and yield. The AA yield as high as 61 mol % (selectivity: 64 mol %) could be obtained under optimized reaction conditions for up to 8 h over the best performing K0.94Na0.06β. The acid and base properties of the catalysts were probed, respectively by temperature-programmed desorption (TPD) of adsorbed NH3 and CO2, and were related to the electrostatic potentials of the alkali ions in the zeolite, which provided a basis for the discussion of the acid-base catalysis for sustainable AA formation from LA. [ABSTRACT FROM AUTHOR]

Using chitooligosaccharides (COS) as the backbones and polycaprolactones (PCL) as the branches, a novel type of amphiphilic graft copolymers with a large amount of free OH and NH2 groups remained on the COS backbones was synthesized. The obtained Chitooligosaccharide-graft-poly( ε-caprolactone)(COS- g-PCL) was self-assembled into giant vesicles which served as templates for the preparation of hollow spheres of a series of metals(Au, Ag, Cu, Pt, and Pd). The method involved the initial mixing of COS- g-PCL and metal-containing groups or metal ions to generate corresponding complex, followed by adding the selective solvent of water to induce the self-assembly of the graft copolymers into giant vesicles; Metal ions were reduced and crosslinked by a subsequent calcination procedure to form metal hollow spheres. In addition, hybrid hollow spheres with fluorescent quantum dots and silica hollow spheres were also prepared by slightly modified procedures. A preliminary study on the trinitrotoluene sensor of CdS/vesicle hybrid hollow spheres revealed a considerable sensitivity, which exemplifies the distinct properties imparted by the hybrid hollow structure. All of the results demonstrate that the giant vesicles self-assembled from COS- g-PCL could be utilized as effective templates for the synthesis of various hollow spheres. Using Chitooligosaccharide-graft-poly( ε-caprolactone) vesicles as general templates, the hollow spheres of a series of metals such as Au, Ag, Cu, and Pt were produced. The method involved the initial absorption of metal ions from solution into the functional surface layer of the graft copolymer giant vesicles. Metal ions were reduced and crosslinked by a subsequent calcination procedure to form metal hollow spheres. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 [ABSTRACT FROM AUTHOR]

A series of tantalum oxide samples (Ta2O5-T) were prepared by varying the calcination temperature T in the range of 110–700 °C of a highly hydrated precursor (Ta2O5·2.1H2O), which was obtained from a hetero-phase reaction between tantalum pentachloride and aqueous ammonia. These Ta2O5-T samples were characterized by TG/DTA, XPS, nitrogen adsorption, XRD, and UV-Raman, and were employed to catalyze the gas-phase dehydration of glycerol (GL) to produce acrolein (AC) at around 315 °C. n-Butylamine titration using Hammett indicators, NH3- and CO2-TPD, and IR of adsorbed pyridine were measured to assess the surface acid–base properties of the catalysts. The Ta2O5-350 catalyst, which was in a hydrated amorphous state and showed no basicity but a maximum strong acidity at −8.2 ＜ H0≤−3.0 (H0 being the Hammett acidity function) prior to the reaction, was identified among all Ta2O5-T samples as the best performing catalyst in terms of AC selectivity and GL consumption rate. The AC selectivity increased with increasing the fractional strong acidity at −8.2 ＜ H0≤−3.0 but the catalytic GL consumption rate increased with increasing the number of strong acid sites on the catalyst prior to the reaction. The partly (Ta2O5-600) and fully (Ta2O5-700) crystallized samples showed almost no strong acidity but they exhibited some basicity in the CO2-TPD experiments; their much lower AC selectivity (＜40 mol%) as compared with that on Ta2O5-350 (75 mol%) indicated that surface basicity was detrimental to the AC selectivity. The best performing Ta2O5-350 catalyst also showed after activation in the initial hours of the reaction a good catalytic stability in long term reactions, regardless of the reaction temperature (305–340 °C) and GHSVGL (80–400 h−1). [ABSTRACT FROM AUTHOR]

Adding a very small amount of Pt entities (0.01–0.03 wt%) onto the Au surface of a Au/TiO2 catalyst is found to be an efficient approach to improve the catalytic activity of Au for the hydrogenation of p-chloronitrobenzene (p-CNB), without loss of selectivity towards p-chloroaniline (p-CAN). The effect of catalyst amount, reaction temperature, H2 pressure and reaction time on p-CNB hydrogenation was studied with 0.02wt%Pt–0.5wt%Au/TiO2 (Pt0.0002–Au0.005/TiO2). The selectivity to p-CAN could be up to 100% at complete conversion of p-CNB with reaction temperatures at or below 333 K. The catalyst also exhibited perfect stability. The catalyst structure was characterized by TEM and XRD, and the mechanism of the high activity of the catalyst was discussed. [ABSTRACT FROM AUTHOR]

PtmAg nanostructures (mbeing the atomic Pt/Ag ratio, m= 0.1–0.6) were prepared by reflux citrate reduction of PtCl62−ions in aqueous solution containing colloidal Ag (6.3 ± 3.9 nm). A distinct alloying of Pt with Ag was detected due to an involvement of the galvanic replacement reaction between PtCl62−and metallic Ag colloids. The nanostructure transformed from a structure with an Ag-core and an alloyed PtAg-shell to a hollow PtAg alloy structure with the increase in m. Compared to a commercial E-TEK Pt/C catalyst, the catalytic performance of Pt in the PtmAg/C samples for the cathode oxygen reduction reaction (ORR) strongly correlated with the electronic structure of Pt, as a consequence of varied Pt dispersion and Pt–Ag interaction. With either H2SO4or KOH as an electrolyte, Pt in the PtmAg nanostructures with a relatively high m(≥0.4) showed significantly enhanced intrinsic activity whereas Pt in those catalysts with low m(≤0.2) appeared less active than the Pt/C catalyst. These data are used to discuss the role of electronic structure and geometric effects of Pt toward ORR. [ABSTRACT FROM AUTHOR]

We report a coprecipitation method for the preparation of solid solutions in the Zn2Ti x Sn1– x O4 (0 ≤ x ≤ 1) series. The precipitates obtained from the coprecipitation were calcined using different temperatures and then characterized with X-ray diffraction (XRD), Raman scattering (RS), scanning electron microscopy (SEM), and surface area measurements to gain insights into the solid-state reaction and phase transformation during the calcinations. Formation of the Zn2Ti x Sn1– x O4 solid solutions was observed after the calcination up to 1000 °C, which is much lower than the temperature (1300 °C) required in the conventional solid-state reaction method. The optical absorption property of the Zn2Ti x Sn1– x O4 solid solutions, measured by ultraviolet-visible diffuse reflectance spectroscopy (UV–Vis DRS), was shown to change according to the composition of the solid solutions. [ABSTRACT FROM AUTHOR]

Flexible insect wings deform passively under the periodic loading during flapping flight. The wing flexibility is considered as one of the specific mechanisms on improving insect flight performance. The constitutive relation of the insect wing material plays a key role on the wing deformation, but has not been clearly understood yet. A viscoelastic constitutive relation model was established based on the stress relaxation experiment of a dragonfly wing (in vitro). This model was examined by the finite element analysis of the dynamic deformation response for a model insect wing under the action of the periodical inertial force in flapping. It is revealed that the viscoelastic constitutive relation is rational to characterize the biomaterial property of insect wings in contrast to the elastic one. The amplitude and form of the passive viscoelastic deformation of the wing is evidently dependent on the viscous parameters in the constitutive relation. [ABSTRACT FROM AUTHOR]

Catalytic activity of Ni/MgO-AN prepared from alcogel derived MgO was studied for the dry reforming of methane under atmospheric as well as high pressure (1.5 MPa). Different catalytic performances are observed in the atmospheric and high-pressure reactions; while the catalyst was highly active and extremely stable under atmospheric pressure it shows a self-stabilization process under high pressure. The self-stabilization process was characterized initially by a decrease in deactivation rate with increasing the reaction time-on-stream (TOS) up to ca. 12 h and then by a thereafter stabilization during the reaction. Characterizations of the coked catalyst with TPO, TEM, SEM, TPH and XRD techniques detected very little carbon deposits (ca. 0.2 wt% of the catalyst charge) on the used catalyst under atmospheric pressure. In contrast, large amount of whisker carbon deposit (ca. 100 wt% of the catalyst charge) were formed on the used catalyst under high pressure. In the high-pressure reaction, the activity decline during the initial stage was closely related to the amount of carbon deposits on the catalyst, which also became stabilized after the catalyst had served the reaction for ca. 12 h. The carbon deposits on the used catalyst in the high-pressure reaction contained two different components (a-carbon and ß-carbon) while the carbon deposits in the atmospheric pressure reaction were in the form of a-carbon. No notable sintering of metallic nickel was detected by XRD on the used catalyst in the reaction under atmospheric pressure whereas unavoidable sintering of metallic Ni particles happened within the very first hours of the high-pressure reaction. [ABSTRACT FROM AUTHOR]

A systematic study of the “size effect” of zirconia nanocrystals on nickel-catalyzed reforming of methane with CO2 shows that extremely stable Ni/ZrO2 catalysts are obtainable by hydrogen reduction of impregnated nickel nitrate on zirconia particles with sizes less than 25 nm. The same preparation method with larger particles of zirconia results in catalyst samples that deactivate rapidly in the reforming reaction. Comprehensive characterization with XRD, TPR/TPD, and TEM shows that the stable Ni/ZrO2 catalysts are better described as nanocomposites of size comparable to Ni metal (9-15 nm) and zirconia (7-25 nm) nanoparticles. The high percentage of the Ni-zirconia boundary or perimeter in the nanocomposite catalysts is believed to be crucial for the extremely stable catalytic activity. [ABSTRACT FROM AUTHOR]

By the international certification, OECE (School of Optical-Electrical and Computer Engineering) has improved the whole school education quality. At the same time, OECE is actively renewing its education concept, focusing the cultivation of students' engineering practice ability, and promoting the construction of the experiment center through the international certification. The school integrated the experiment resources, maximized the resources sharing; offered innovation, comprehensive experiments, to encourage the students' practical ability and innovation; The school introduced an open management mode that allows the students to do experiments more flexible and effective; and also strengthened the cultivation of the experiment center teachers to improve the quality of the teachers. These measures provide students with an optimized practice platform. [ABSTRACT FROM AUTHOR]

Adding a small amount of fully dispersed Pt entities onto the Au surface in Au/SiO2catalyst is found to be an efficient approach to improve the catalytic activity of Au (up to 70-fold) for the hydrogenation of α,β-unsaturated carbonyl compounds, without alternating its selectivity towards CO or CC bond hydrogenation. [ABSTRACT FROM AUTHOR]

Nearly monodisperse Au nanorods (NRs) with different aspect ratios were separated from home-synthesized polydisperse samples using a gradient centrifugation method. The morphology, size and its distribution, and photo-absorption property were analyzed by transmission electron microscopy, atomic force microscopy and UV–visible spectroscopy. Subsequently, using colloidal Au NRs (36.2 nm ×10.7 nm) with 97.4% yield after centrifugation and Au nanospheres (NSs) (22.9 ± 1.0 nm in diameter) with 97.6% yield as Au substrates, surface-enhanced Raman scattering (SERS) spectra of 2,4-dichlorophenoxyacetic acid (2,4-D) were recorded using laser excitation at 632.8 nm. Results show that surface enhancement factors (EF) for Au NRs and NSs are 6.2 × 105 and 5.7 × 104 using 1.0 × 10−6 M 2,4-D, respectively, illustrating that EF value is a factor of ∼10 greater for Au NRs substrates than for Au NSs substrates. As a result, large EF are a mainly result of chemical enhancement mechanisms. Thus, it is expected that Au NPs can find a comprehensive SERS application in the trace detection of pesticide residues. [ABSTRACT FROM AUTHOR]