Novel cellulose supported 1,2-bis(4-aminophenylthio)ethane Ni(ii) complex (NiII(BAPTE)(NO3)2-Cell) as an efficient nanocatalyst for the synthesis of spirooxindole derivatives

Cellulose was used as a support for immobilizing a Ni(ii) complex of 1,2-bis(4-aminophenylthio)ethane to prepare NiII(BAPTE)(NO3)2-Cell as a new organo-inorganic hybrid nanocatalyst. The properties of the prepared catalyst were studied using various analyses such as FT-IR, XRD, SEM, TGA and EDX. NiII(BAPTE)(NO3)2-Cell was employed as a reusable catalyst for the synthesis of spirooxindole derivatives via a three-component condensation of isatin, malononitrile and reactive methylene compounds. The nanocatalyst can be readily and quickly separated from the reaction mixture and can be reused for at least eight successive reaction cycles without a significant reduction in efficiency. The facile accessibility to the starting materials, use of green solvents and conducting the reactions in eco-friendly and cost-effective conditions have made this protocol a suitable method for preparing spirooxindole derivatives.

Conductive interface promoted bifunctional oxygen reduction/evolution activity in an ultra-low precious metal based hybrid catalyst

Ultra low PtPd alloy deposited on Ni12P5 nanostructures (PtPd/Ni12P5) exhibited enhanced ORR activity (onset: 1.003 V and E1/2:0.95 V) on par with commercial Pt/C and superior OER activity with 81% reduction of the precious metal compared to the commercial catalyst.

Studies of Buried Layers and Interfaces of Tungsten Carbide Coatings on the MWCNT Surface by XPS and NEXAFS Spectroscopy

Currently, X-ray photoelectron spectroscopy (XPS) is widely used to characterize the nanostructured material surface. The ability to determine the atom distribution and chemical state with depth without the sample destruction is important for studying the internal structure of the coating layer several nanometers thick, and makes XPS the preferable tool for the non-destructive testing of nanostructured systems. In this work, ultra-soft X-ray spectroscopy methods are used to study hidden layers and interfaces of pyrolytic tungsten carbide nanoscale coatings on the multi-walled carbon nanotube (MWCNT) surfaces. XPS measurements were performed using laboratory spectrometers with sample charge compensation, and Near Edge X-ray Absorption Fine Structure (NEXAFS) studies using the Russian–German dipole beamline (RGBL) synchrotron radiation at BESSY-II. The studied samples were tested by scanning and transmission electron microscopy, X-ray diffractometry, Raman scattering and NEXAFS spectroscopy. It was shown that the interface between MWCNT and the pyrolytic coating of tungsten carbide has a three-layer structure: (i) an interface layer consisting of the outer graphene layer carbon atoms, forming bonds with oxygen atoms from the oxides adsorbed on the MWCNT surface, and tungsten atoms from the coating layer; (ii) a non-stoichiometric tungsten carbide WC1-x nanoscale particles layer; (iii) a 3.3 nm thick non-stoichiometric tungsten oxide WO3-x layer on the WC1-x/MWCNT nanocomposite outer surface, formed in air. The tungsten carbide nanosized particle’s adhesion to the nanotube outer surface is ensured by the formation of a chemical bond between the carbon atoms from the MWCNT upper layer and the tungsten atoms from the coating layer.

Low temperature synthesis of NbC/C nano-composites as visible light photoactive catalyst

A facile carbothermal route was adopted to obtain niobium carbide nanoparticles (NPs) embedded in carbon network from Nb2O5 to study photocatalytic behavior. Optimization of synthesis parameters to obtain single phase NbC NPs has been successfully done. The phase identification, morphology and nature of carbon were determined with the help of X-ray diffraction, transmission electron microscopy (TEM) and Raman spectroscopy. X-ray photoelectron spectroscopy (XPS) suggested the presence of multiple oxidation states of Nb associated to NbC and NbCxOy centers on the surface of NPs. Due to the presence of NbCxOy on the surface of NPs, absorption under visible region of EM spectrum has been observed by UV-visible spectroscopy. Different organic dyes (RhB, MB and MO) were used to study the effect of holding time on the photocatalytic performance of as-synthesized samples. RhB dye was found to be the most sensitive organic molecule among all the considered dyes and degraded 78% in 120 min.

Controllable Synthesis of Ordered Mesoporous Mo2C@Graphitic Carbon Core-Shell Nanowire Arrays for Efficient Electrocatalytic Hydrogen Evolution

Mo₂C is a possible substitute to Pt-group metals for electrocatalytic hydrogen evolution reaction (HER). Both support-free and carbon-supported Mo₂C nanomaterials with improved HER performance have been developed. Herein, distinct from prior research, novel ordered mesoporous core-shell nanowires with Mo₂C cores and ultrathin graphitic carbon (GC) shells are rationally synthesized and demonstrated to be excellent for HER. The synthesis is fulfilled via a hard-templating approach combining in situ carburization and localized carbon deposition. Phosphomolybdic acid confined in the SBA-15 template is first converted to MoO₂, which is then in situ carburized to Mo₂C nanowires with abundant surface defects. Simultaneously, GC layer (the thickness is down to ∼1.0 nm in most areas) is controlled to be locally deposited on the Mo₂C surface because of its strong affinity with carbon and catalytic effect on graphitization. Removal of the template results in the Mo₂C@GC core-shell nanowire arrays with the structural properties well-characterized. They exhibit excellent performance for HER with a low overpotential of 125 mV at 10 mA cm^-2, a small Tafel slope of 66 mV dec^-1, and an excellent stability in acidic electrolytes. The influences of several factors, especially the spatial configuration and relative contents of the GC and Mo₂C components, on HER performance are elucidated with control experiments. The excellent HER performance of the mesoporous Mo₂C@GC core-shell nanowire arrays originates from the rough Mo₂C nanowires with diverse active sites and short charge-transfer paths and the ultrathin GC shells with improved surface area, electronic conductivity, and stabilizing effect on Mo₂C.

Ni2P Entwined by Graphite Layers as a Low-Pt Electrocatalyst in Acidic Media for Oxygen Reduction

A simple and feasible strategy was reported to construct Ni₂P nanostructures entwined by graphite layers (Ni₂P/GC). In this process, a commercial amino phosphonic acid chelating resin was adopted as both the phosphorus and carbon resources. Then, Ni²⁺ was introduced into the resin framework via ionic exchange and chelation to form a resin-Ni²⁺ precursor. After carbonization, the highly dispersed Ni₂P particles, coupled with thin graphite layers, were simultaneously synthesized in situ. A ternary 7.5% Pt-Ni₂P/GC catalyst was further obtained by loading 7.5 wt % Pt on Ni₂P/GC. For the oxygen reduction reaction in acidic media, the 7.5% Pt-Ni₂P/GC catalyst exhibited even more positive onset (1.03 V) and half-wave (0.93 V) potentials, as well as a rather higher mass activity of 565.3 mA mg_Pt^-1 and a better long-term stability than those of the commercial 20% Pt/C (JM) electrocatalyst. The improved reaction kinetics is mainly attributed to the synergistic effect between Pt and Ni₂P/GC. This work not only provides a method for the synthesis of phosphides but also gives insight into the synergy between Pt and Ni₂P, which is helpful for the development of more low-Pt catalysts in acidic media.

Chitosan Film Containing an Iron Complex: Synthesis and Prospects for Heterocyclic Aromatic Amines (HAAs) Recognition

Hybrid organic-inorganic materials have been seen as a promising approach to produce sensors for the detection and/or recognition of heterocyclic aromatic amines (HAAs). This work shows the synthesis of a hybrid film as a result of the incorporation of [Fe(CN)₅(NH₃)]^3- into chitosan (CS); CS-[(CN)₅Fe(NH₃)]^3-. The sensitivity of CS-[(CN)₅Fe(NH₃)]^3- toward HAA-like species was evaluated by using pyrazine (pz) as probe molecule in vapor phase by means of electrochemistry and spectroscopic techniques. The crystallinity (SEM-EDS and XRD) decrease of CS-[(CN)₅Fe(NH₃)]^3- in comparison to CS was assigned to the disturbance of the hydrogen bond network within the polymer. Such conclusion was reinforced by the water contact angle measurements. The results presented in this work indicate physical and intermolecular interactions, mostly hydrogen bond, between [Fe(CN)₅(NH₃)]^3- and CS, where the complex is likely trapped in the polymer with its sixth coordination site available for substitution reactions.

Biomass-Derived Porous Fe3C/Tungsten Carbide/Graphitic Carbon Nanocomposite for Efficient Electrocatalysis of Oxygen Reduction

The oxygen-reduction reaction (ORR) draws an extensive attention in many applications, and there is a growing interest to develop effective ORR electrocatalysts. Iron carbide (Fe₃C) is a promising alternative to noble metals (e.g., platinum), but its performances need further improvement, and the real role of the Fe₃C phase remains unclear. In this study, we synthesize Fe₃C/tungsten carbide/graphitic carbon (Fe₃C/WC/GC) nanocomposites, with waste biomass (i.e., pomelo peel) serving as carbon source, using a facile, one-step carbon thermal-reduction method. The nanocomposite is characterized by a porous structure consisting of uniform Fe₃C nanoparticles encased by graphitic carbon (GC) layers with highly dispersed nanosized WC. The Fe₃C provides the active sites for ORR, while the graphitic layers and WC nanoparticles can stibilize the Fe₃C surface, preventing it from dissociation in the electrolyte. The Fe₃C/WC/GC nanocomposite is highly active, selective, and stable toward four-electron ORR in pH-neutral electrolyte, which results in a 67.82% higher power density than that of commercial Pt/C and negligible voltage decay during a long-term phase of a 33 cycle (2200 h) operation of a microbial fuel cell (MFC). The density functional theory (DFT) calculations suggest high activity for splitting the O-O bond of molecular oxygen on the surface of Fe₃C.

Fe3W3C/WC/graphitic carbon ternary nanojunction hybrids for dye-sensitized solar cells

Fe3 W3 C/WC/graphitic carbon (GC) ternary nanojunction hybrids are synthesized through a solid-state pyrolysis process for dye-sensitized solar cells (DSSCs). First-principles calculations have been first employed to investigate the adsorption energy between I3 (-) and Fe3 W3 C and WC nanoclusters. Scanning Kelvin probe images indicate that the work function changes greatly due to the formation of ternary nanojunctions, which favor fast photoelectron transfer. A photoelectrical conversion efficiency of 7.1 % is achieved based on Fe3 W3 C/WC/GC hybrid counter electrodes, which is much higher than those of pure GC (5.02 %) and WC/GC hybrids (6.11 %). It has been further revealed that Fe3 W3 C/WC/GC hybrid counter electrodes exhibit the best catalytic performances according to relevant electrochemical measurements, which can be attributed to fast photoelectron transfer due to the ternary junctions and the addition of Fe3 W3 C with more catalytic metallic atoms.

Angstrom-sized tungsten carbide promoted platinum electrocatalyst for effective oxygen reduction reaction and resource saving

Pt/WC^rod shows higher ORR efficiency and stabilization than commercial Pt/C.

Hollow tungsten carbide/carbon sphere promoted Pt electrocatalyst for efficient methanol oxidation

The surface carbon thickness and particle size of tungsten carbide (WC) are critical to its synergistic effect on noble metal based electrocatalysts.

Novel synthesis of dispersed molybdenum and nickel phosphides from thermal carbonization of metal- and phosphorus-containing resins

New (Mo,Ni),P-containing resin precursors to dispersed MoP and Ni₂P nanoparticles.

Co2Nx/nitrogen-doped reduced graphene oxide for enzymeless glucose detection

Co₂N_x/nitrogen-doped reduced graphene oxide (Co₂N_x/NG) is synthesized by electrostatic co-precipitation of Co and rGO followed by high-temperature nitridation, which can serve as an efficient catalyst for sensitive glucose detection due to the unique electrocatalytic property of Co₂N_xand synergistic effect between Co₂N_xand N-doped rGO.

Synergistic effect of tungsten carbide and palladium on graphene for promoted ethanol electrooxidation

The synergistic effect of WC and Pd has large benefit for ethanol electrooxidation. The small-sized Pd nanoparticles (NPs) decorated tungsten carbide on graphene (Pd-WC/GN) will be a promising anode catalyst for the direct ethanol fuel cells. The density functional theory (DFT) calculations reveal that the strong interaction exists at the interface between Pd and WC, which induces the electron transfer from WC to Pd. Fortunately, the nanoscale architecture of Pd-WC/GN has been successfully fabricated in our experiments. X-ray photoelectron spectrum further confirms the existence of electron transfer from WC to Pd in a Pd-WC/GN nanohybrid. Notably, electrochemical tests show that the Pd-WC/GN catalyst exhibits low onset potential, a large electrochemical surface area, high activity, and stability for ethanol electrooxidation in alkaline solution compared with Pd/graphene and Pd/commercial Vulcan 72R carbon catalysts. The enhancement can be attributed to the synergistic effect of Pd and WC on graphene. At the interface between Pd and WC, the electron transfer from WC to Pd leads to the increased electron densities of surface Pd, which is available for weakening adsorption of intermediate oxygen-containing species such as CO and activating catalyst. Meanwhile, the increased tungsten oxide induced by electron transfer can facilitate the effective removal of intermediate species adsorbed on the Pd surface through a bifunctional mechanism or hydrogen spillover effect.

A universal method to synthesize nanoscale carbides as electrocatalyst supports towards oxygen reduction reaction

We have developed a general ion-exchange method of preparing a composite of low nanometre size carbide particles with controllable size less than 10 nm on carbon foams. The nanoarchitectures of the carbide nanoparticles on carbon foam are used to load Pt nanoparticles as electrocatalysts which show enhanced activity for the oxygen reduction reaction.

Chitosan: a green carbon source for the synthesis of graphitic nanocarbon, tungsten carbide and graphitic nanocarbon/tungsten carbide composites

In this paper, a simple approach was proposed to fabricate graphitic carbon nanocapsules, tungsten carbide and tungsten carbides/graphitic carbon composites by using chitosan, a green and renewable biopolymer, as a carbon source. The route includes, first, fabrication of the precursors that consist of chitosan coordinated with a certain metal ion (or metal complex anion) followed by carbonizing the precursors under N(2) atmosphere. The composition of the final products could be regulated by changing the type and ratio of the metal source (cations or complex anions) combined with the chitosan in the precursors. The experimental results showed that uniform carbon nanocapsules could be obtained when Ni(2+) was introducing in the precursors, while incorporating [PW(12)O(40)](3-) (PW(12)) with chitosan led to the formation of WC nanoparticles. As the Ni(2+) and PW(12) are simultaneously coordinated with chitosan, the composites of tungsten carbide/graphitic carbon were successfully produced. Transmission electron microscopy (TEM) analysis revealed that the graphitic carbon nanocapsules are about 45 nm in diameter; uniform WC nanoparticles with a average size of 40 nm are observed. Moreover, the particle size of WC in the tungsten carbide/graphitic carbon composite is about 10 nm, which is smaller than that of the pure WC particles. Furthermore, the performance of the sample-loaded Pt nanoparticles for methanol electro-oxidation was studied in detail. The results indicated that the samples could act as good carriers for Pt in the methanol electro-oxidation reaction with high effectivity and improved stability.