One-pot synthesis of graphene–cuprous oxide composite with enhanced photocatalytic activity

In this paper, graphene–cuprous oxide (G–Cu₂O) composites were synthesized at room temperature using graphene oxide (GO) as two-dimensional support. From Zeta potential analysis, the surface charge of G–Cu₂O composites altered from positive to negative, which favors the adsorption and photodegradation of positively charged dyes. Compared with Cu₂O under similar synthesis condition, the G–Cu₂O composites demonstrated improved photodegradation activity for methylene blue (MB) dye under visible light. Controlled experiments indicated that the G–Cu₂O composite synthesized with 80 mg GO in the reaction system possessed more negative Zeta potential, highest specific surface area and thus presented the highest photocatalytic activity. Electrons mechanism for the improved photocatalytic performance of G–Cu₂O composite was proposed in the degradation of MB.     

Quantum-dots containing Fe/SBA-15 silica as “green” catalysts for the selective photocatalytic oxidation of alcohol (methanol,under visible light)

Fe/SBA-15 catalysts containing iron oxide nanoparticles confined inside silica pores (replicated, internal, poorly crystalline) and grown outside silica grains (external, mainly crystalline hematite) in different proportions are prepared using a single silica support. Fe-species are deposited by the two-solvent technique with two iron salts precursors (Fe(NO₃)₃·9H₂O, FeCl₃·6H₂O) and two solvents (cyclohexane, hexane) for 11 wt% of iron. Calcination is performed in reproducible conditions (700 °C, 2 °C/min, thin bed, in air). SAXS measurements are used to show that the 2D hexagonal structure of the used silica is maintained after Fe-loading and calcination. Ar sorption measurements show that the pores are partially plugged. The oxidation of pure methanol is used as a test reaction to compare photocatalytic properties. H₂O₂ and visible light both activate the reaction. More active catalysts are formed with hexane associated with FeCl₃·6H₂O than with Fe(NO₃)₃·9H₂O. A reversed situation is observed with cyclohexane. Iron leaching (after 1 h 30 of test, up to 3 mg of Fe by mL) is important. These results are expected to be of interest in the exploration of size and shape “nanocatalysis” and to provide a further understanding for the reactions that take place when porous silicas are used as supports.     

Porous cuprous oxide microcubes for non-enzymatic amperometric hydrogen peroxide and glucose sensing

Using porous cuprous oxide (Cu₂O) microcubes, a simple non-enzymatic amperometric sensor for the detection of H₂O₂ and glucose has been fabricated. Cyclic voltammetry (CV) revealed that porous Cu₂O microcubes exhibited a direct electrocatalytic activity for the reduction of H₂O₂ in phosphate buffer solution and the oxidation of glucose in an alkaline medium. The non-enzymatic amperometric sensor used in the detection of H₂O₂ with detection limit of 1.5 × 10^?6 M over wide linear detection ranges up to 1.5 mM and with a high sensitivity of 50.6 μA/mM. This non-enzymatic voltammetric sensor was further utilized in detection of glucose with a detection limit of 8.0 × 10^?7 M, a linear detection range up to 500 μM and with a sensitivity of ?70.8 μA/mM.     

Phase transfer catalysis: Synthesis of monodispersed FePt nanoparticles and its electrocatalytic activity

Using dibenzo-24-crown-8-ether (DB24C8) as phase transfer catalyst, the monodispersed iron–platinum (FePt) alloy nanoparticles with size of ∼17 nm were synthesized by reduction of H₂PtCl₆·6H₂O and FeCl₂·4H₂O in the solvothermal system. The structure, magnetic property and electrocatalytic activity of FePt nanoparticles were characterized by transmission electron microscopy (TEM), X-ray diffraction system (XRD), vibration sample magnetometer (VSM) and CHI 820 electrochemical analyser (three electrodes system, the reference electrode is saturated calomel electrode (SCE), the counter electrode is platinum electrode and the glassy carbon electrode is used as working electrode (GCE)), respectively. The results show that the as-synthesized FePt nanoparticles have a chemically disordered fcc structure and can be transformed into chemically ordered fct structure after annealing treatment above 400 °C, simultaneously accompanying with the coercivity changed from 5 to 2400 Oe. CVs of 0.5 M H₂SO₄/0.5 M CH₃OH on GCE modified with FePt nanoparticles monolayer illustrate that the as-synthesized FePt nanoparticles have strong electrocatalytic activity toward the oxidation of CH₃OH in aqueous solution.     

Photocatalytic activity of TiO2 nanotube layers loaded with Ag and Au nanoparticles

Ag and Au nanoparticles were found to significantly enhance the photocatalytic activity of self-organized TiO₂ nanotubular structures. The catalyst systems are demonstrated to be highly efficient for the UV-light induced photocatalytic decomposition of a model organic pollutant – Acid Orange 7. The metallic nanoparticles with a diameter of ∼10 ± 2 nm (Ag) and ∼28 ± 3 nm (Au) were attached to a nanotubular TiO₂ layer that consists of individual tubes of ∼100 nm of diameter, ∼2 μm in length and approx. 15 nm of wall thickness. Both metal particle catalyst systems enhance the photocatalytic decomposition significantly more on the nanotubes support than placed on a compact TiO₂ surface.     

Improved electrochemical performances of core-shell Cu2O/Cu composite prepared by a simple one-step method

Core-shell Cu₂O/Cu composites were successfully prepared by over-reduction of aqueous CuSO₄ with hydrazine hydrate as reductant. Field emission scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM) clearly illuminate that the core is Cu₂O with 400 nm in diameter, and the shell is Cu with about 50 nm in thickness. The core-shell Cu₂O/Cu exhibited weaker polarization and higher coulombic efficiency than pure octahedral Cu₂O, especially in the initial stage of cycles. After 50 cycles, the reversible capacity of Cu₂O/Cu (360 mAh g^?1) was much higher than that of pure Cu₂O (160 mAh g^?1). The improvement of electrochemical properties is attributed to the core-shell structure of Cu₂O/Cu and the catalytic effect of Cu on the decomposition of Li₂O during the charging process.     

Formation of out of plane oxime metallacycles in [Cu2] and [Cu4] complexes

The reaction of Cu(ClO₄)₂·6H₂O with dimethylglyoxime (H₂dmg) in a 1:1 mole ratio in aqueous methanol at room temperature affords the dinuclear complex [Cu₂(μ-Hdmg)₄] (1). Reaction of 1 with [Cu(bpy)(H₂O)₂](ClO₄)₂ (bpy = 2,2′-bipyridine) in a 1:1 mole ratio in aqueous methanol at room temperature yields the tetranuclear complex [Cu₄(μ-Hdmg)₂(μ-dmg)₂(bpy)₂(H₂O)₂](ClO₄)₂ (2). The direct reaction of Cu(ClO₄)₂·6H₂O with H₂dmg and bpy in a 2:2:1 mole ratio in aqueous methanol at room temperature also yields 2 quantitatively. The complexes 1 and 2 were structurally characterized by X-ray crystallography. Unlike the binding in Ni/Co-dmg, two different types of N?O bridging modes during the oxime based metallacycle formation and stacking of square planar units have been identified in these complexes. The neutral dinuclear complex 1 has CuN₄O coordination spheres and complex 2 consists of a dicationic [Cu₄(μ-Hdmg)₂(μ-dmg)₂(bpy)₂(H₂O)₂]²⁺ unit and two uncoordinated ClO₄^? anions having CuN₄O and CuN₂O₃ coordination spheres. The two copper(II) ions are at a distance of 3.846(8) Å in 1 for the trans out of plane link and at 3.419(10) and 3.684(10) Å in 2 for the trans out of plane and cis in plane arrangements, respectively. The average Cu–N_oxime distances are 1.953 and 1.935 Å, respectively. The average basal and apical Cu?O_oxime distances are 1.945, 2.295 and 2.429 Å. The UV–Vis spectra of 2 is similar to the spectrum of the reaction mixture of 1 and [Cu(bpy)(H₂O)₂]²⁺. Variable temperature magnetic properties measurement shows that the interaction between the paramagnetic copper centers in complex 1 is antiferromagnetic in nature. The EPR spectra of frozen solution of the complexes at 77 K consist of axially symmetric fine-structure transitions (ΔM_S = 1) and half-field signals (ΔM_S = 2) at ca. 1600 G, suggesting the presence of appreciable Cu–Cu interactions.     

Pt and Pt–Ru nanoparticles decorated polypyrrole/multiwalled carbon nanotubes and their catalytic activity towards methanol oxidation

Conducting polymer composite films comprised of polypyrrole (PPy) and multiwalled carbon nanotubes (MWCNTs) [PPy–CNT] were synthesized by in situ polymerization of pyrrole on carbon nanotubes in 0.1 M HCl containing (NH₄)S₂O₈ as oxidizing agent over a temperature range of 0–5 °C. Pt nanoparticles are deposited on PPy–CNT composite films by chemical reduction of H₂PtCl₆ using HCHO as reducing agent at pH = 11 [Pt/PPy–CNT]. The presence of MWCNTs leads to higher activity, which might be due to the increase of electrochemically accessible surface areas, electronic conductivity and easier charge-transfer at polymer/electrolyte interfaces allowing higher dispersion and utilization of the deposited Pt nanoparticles. A comparative investigation was carried out using Pt–Ru nanoparticles decorated PPy–CNT composites. Cyclic voltammetry demonstrated that the synthesized Pt–Ru/PPy–CNT catalysts exhibited higher catalytic activity for methanol oxidation than Pt/PPy–CNT catalyst. Such kinds of Pt and Pt–Ru particles deposited on PPy–CNT composite polymer films exhibit excellent catalytic activity and stability towards methanol oxidation, which indicates that the composite films is more promising support material for fuel cell applications.     

Complexes derived from the copper(II) perchlorate/maleamic acid/2,2′-bipyridine and copper(II) perchlorate/maleic acid/2,2′-bipyridine reaction systems: Synthetic,reactivity, structural and spectroscopic studies

A systematic investigation of the reactions of Cu(ClO₄)₂ · 6H₂O with maleamic acid (H₂L) in the presence of 2,2′-bipyridine (bpy) has been carried out. The chemical and structural identity of the products depends on the solvent, the absence or presence of external hydroxides in the reaction mixture and the molar ratio of the reactants. Various reaction schemes have led to the isolation of the complexes [Cu₂(HL)₂(bpy)₂(H₂O)₂](ClO₄)₂ (1), [Cu₂(HL)₂(bpy)₂(H₂O)₂](ClO₄)₂ · 2H₂O (1 · 2H₂O), [Cu(L′′)(bpy)]_n · 2nH₂O (2 · 2nH₂O), [Cu₂(L′′)(bpy)₂(H₂O)₂]_n(ClO₄)_2n · 0.5nH₂O (3 · 0.5nH₂O), [Cu₂(L′′)₂(bpy)₂] · 2MeOH (5 · 2MeOH), [Cu₂(L′)₂(bpy)₂(ClO₄)₂] (6) and [Cu(ClO₄)₂(bpy)(MeCN)₂] (7b), where L′′^2? and L′^? are the maleate(?2) and monomethyl maleate(?1) ligands, respectively. The HL^? ion has been transformed to L′′^2? and L′^? in the known compounds 2 · 2nH₂O and 6, respectively, via metal ion-assisted processes involving hydrolysis (2 · 2nH₂O) and methanolysis (6) of the primary amide group. The reaction that leads to 6 takes place through the formation of the mononuclear complex [Cu(ClO₄)₂(bpy)(MeOH)₂] (7a), whose structure was assigned on the basis of its spectral similarity with the structurally characterized complex 7b. The structures of the cations in 1 and 1 · 2H₂O consists of two Cu^II atoms bridged by the carboxylate groups of the two HL^? ligands, each exhibiting the less common η² coordination mode; a chelating bpy molecule and a H₂O ligand complete square pyramidal coordination at each metal centre. The structure of the dinuclear repeating unit in the 1D coordination polymer 3 · 0.5nH₂O consists of two Cu^II atoms bridged by two syn,syn η¹:η¹:μ₂ carboxylate groups belonging to two L′′^2? ions; each ligand bridged two neighboring [Cu^II,II₂] units thus promoting the formation of a helical chain. The structure of the dinuclear molecule of complex 5 · 2MeOH consists of two Cu^II atoms bridged by two η² carboxylate groups from two L′′^2? ligands; the second carboxylate group of each maleate(?2) ligand is monodentately coordinated to Cu^II, creating a remarkable seven-membered chelating ring. The L′^? ion behaves as a carboxylate-type ligand in 6, with the carboxylate group being in the familiar syn,syn η¹:η¹:μ₂ coordination mode; a chelating bpy molecule and a coordinated ClO₄^? complete five-coordination at each Cu^II centre. The crystal structures of the complexes are stabilized by various H-bonding patterns. Characteristic IR bands of the complexes are discussed in terms of the known structures and the coordination modes of the ligands.     

Mesoporous cadmium bismuth niobate (CdBi_2Nb_2O_9) nanospheres for hydrogen generation under visible light

Herein, we report visible light active mesoporous cadmium bismuth niobate(CBN) nanospheres as a photocatalyst for hydrogen(H_2) generation from copious hydrogen sulfide(H_2S). CBN has been synthesized by solid state reaction(SSR) and also using combustion method(CM) at relatively lower temperatures.The as-synthesized materials were characterized using different techniques. X-ray diffraction analysis shows the formation of single phase orthorhombic CBN. Field emission scanning electron microscopy and high resolution-transmission electron microscopy showed the particle size in the range of ~0.5–1 μm for CBN obtained by SSR and 50–70 nm size nanospheres using CM, respectively. Interestingly, nanospheres of size 50–70 nm self assembled with 5–7 nm nanoparticles were observed in case of CBN prepared by CM.The optical properties were studied using UV–visible diffuse reflectance spectroscopy and showed band gap around ~3.0 eV for SSR and 3.1 eV for CM. The slight shift in band gap of CM is due to nanocrystalline nature of material. Considering the band gap in visible region, the photocatalytic activity of CBN for hydrogen production from H_2S has been performed under visible light. CBN prepared by CM has shown utmost hydrogen evolution i.e. 6912 μmol/h/0.5 g which is much higher than CBN prepared using SSR.The enhanced photocatalytic property can be attributed to the smaller particle size, crystalline nature,high surface area and mesoporous structure of CBN prepared by combustion method. The catalyst was found to be stable, active and can be utilized for water splitting.     

Preparation of cuprous oxides with different sizes and their behaviors of adsorption,visible-light driven photocatalysis and photocorrosion

Cuprous oxide (Cu₂O) nanoparticles and microparticles have been prepared by liquid phase chemical synthesis. The samples were characterized by means of SEM, XRD, UV/DRS and XPS. It was presented that as-prepared Cu₂O nanoparticles are substantially stable in ambient atmosphere and the Cu⁺ as main state exists on the surface of Cu₂O nanoparticles. As-prepared Cu₂O microparticles can exist stably as a Cu₂O/CuO core/shell structure; and the Cu²⁺ as main state exists on the surface of Cu₂O microparticles. The behaviors of adsorption, photocatalysis and photocorrosion of Cu₂O particles with different sizes were investigated in detail. The results show that Cu₂O nanoparticles are very easy to photocorrosion during the photocatalytic reaction, which cannot be used as photocatalyst directly to degrade organic compound, although as-prepared Cu₂O nanoparticles exhibit special property of adsorption. Cu₂O microparticles have a higher photocatalytic activity than Cu₂O nanoparticles because of its slower photocorrosion rate, although Cu₂O microparticles have much lower adsorption capacity than Cu₂O nanoparticles. The mechanisms of photocatalysis and photocorrosion for Cu₂O under visible light were also discussed.     

A novel vanadium oxide deposit for the cathode of asymmetric lithium-ion supercapacitors

Hydrous vanadium oxide (denoted as VO_x·yH₂O) deposited at 0.4 V shows promising capacitive behavior in aqueous media containing concentrated Li ions. VO_x·yH₂O annealed in air at 300 °C for 1 h shows highly reversible Li-ion intercalation/de-intercalation behavior with specific capacitance reaching ca. 737 and 606 F g^? 1 at 25 and 500 mV s^? 1 in 12 M LiCl between ?0.2 and 0.8 V. In 14 M LiCl, retention of specific capacitance is about 95% when the scan rate is increased from 25 to 500 mV s^? 1. This work is the first report showing the ultrahigh rate of Li-ion intercalation/de-intercalation in VO_x·yH₂O. A so-called Li-ion supercapacitor of the asymmetric type consisting of a VO_x^.yH₂O cathode and a WO₃^.zH₂O anode is proposed here.     

Synthesis,physico-chemical and spectral investigations of novel homo-bimetallic mixed-ligand complexes: 57Fe Mössbauer parameters of [Fe2(imda)2(H2O)3Cl]

The newly prepared homo-bimetallic complexes [M₂(imda)₂(H₂O)₄], [M₂(imda)₂(Bipy)₂] (M = Co, Ni or Cu) and [Fe₂(imda)₂(H₂O)₃Cl] (H₂imda = iminodiacetic acid and Bipy = 2,2′-bipyridine) have been studied employing IR, FAB-mass, ¹H and ¹³C NMR, EPR and ligand field spectra, which indicated a high-spin state of metal ion with hexa-coordinate environment. ⁵⁷Fe Mössbauer data of the homo-bimetallic complex [Fe₂(imda)₂(H₂O)₃Cl] confirm a high-spin configuration with Fe (±3/2 → 1/2) nuclear transitions and the presence of Kramer's double degeneracy. At RT, the spin–spin interactions of the neighbouring nuclei (Fe³⁺–Fe³⁺ = S_5/2–S_5/2) are anti-ferromagnetically coupled. However, at LNT, the complex acquires a mixed-valent [Fe^III–Fe^II] composition corroborated from the X-band EPR data. CV studies indicated the presence of quasi-reversible redox Cu^II/I, Cu^II/III, Fe^III/II, Fe^III/I and Fe^II/I couples.     

Highly stable PtRuTiOx/C anode electrocatalyst for direct methanol fuel cells

In the present investigation, PtRuTiO_x/C electrocatalyst was prepared by a modified polyol synthesis method and the as-prepared electrocatalyst was treated under the reductive atmosphere (30 vol% H₂ in Ar) at 500 °C for 2 h (denoted as PtRuTiO_x/C-500) to enhance the interaction between the metal particles and the support. For comparison, the commercial PtRu/C electrocatalyst was also treated by the same procedure as PtRuTiO_x/C (denoted as PtRu/C-500). Transmission electron microscopy results indicated that PtRuTiO_x/C electrocatalyst exhibited not only a uniform dispersion and narrow size distribution with a smaller particle size, but also excellent stability during the thermal treatment. In contrast, the commercial PtRu/C electrocatalyst is not stable during the thermal treatment and the metal particles greatly agglomerated. The results of CO-stripping voltammetry, single direct methanol fuel cell tests and life-time test jointly showed that PtRuTiO_x/C-500 had better durability than commercial PtRu/C while keeping a desirable activity toward methanol electro-oxidation, which may be attributed to the addition of titanium oxide that improved the interaction between noble metal particles and the support.     

Magnetic properties of hybrid organo-inorganic copper(II) oxovanadate(V) phosphate and phosphonate bridged systems

The hybrid organo-inorganic compounds [Cu₄(bipy)₄V₄O₁₁(PO₄)₂]nH₂O (n ∼ 5) (1), [Cu₂(phen)₂(PO₄)(H₂PO₄)₂(VO₂) · 2H₂O] (2) and [Cu₂(phen)₂(O₃PCH₂PO₃)(V₂O₅) (H₂O)]H₂O (3) which present different bridging forms of the phosphate/phosphonate group, show different bulk magnetic properties. We herein analyze the magnetic behaviour of these compounds in terms of their structural parameters. We also report a theoretical study for compound (1) assuming four different magnetic exchange pathways between the copper centres present in the tetranuclear unit. For compound (1) the following J values were obtained J₁ = +3.29; J₂ = −0.63; J₃ = −2.23; J₄ = −46.14 cm⁻¹. Compound (2) presents a Curie–Weiss behaviour in the whole range of temperature (3–300 K), and compound (3) shows a maximum for the magnetic susceptibility at 64 K, typical for antiferromagnetic interactions. These data where fitted using a model previously reported in the literature, assuming two different magnetic exchange pathways between the four copper(II) centres, with J₁ = −30.0 and J₂ = −8.5 cm⁻¹.     

Carbon encapsulated magnetic nanoparticles produced by hydrothermal reaction

Carbon encapsulated magnetic nanoparticles(CEMNs)were synthesized by heating an aqueous glucose solution containing Fe-Au(Au coated Fe nanoparticles)nanoparticles at 160-180℃ for 2 h.This novel hydrothermal approach is not only simple but alsoprovides the surface of CEMNs with functional groups like-OH.The formation of carbon encapsulated magnetic nanoparticles wasnot favored when using pure Fe nanoparticles as cores because of the oxidation of Fe nanoparticles by H2O during the reaction and,therefore,the surfaces of the naked Fe nanoparticles had to be coated by Au shell in advance.TEM,XRD,XPS and VSMmeasurments characterized that they were uniform carbon spheres containing some embedded Fe-Au nanoparticles,with asaturation of 14.6 emu/g and the size of the typical product is$350 nm.     

Cu2O-catalyzed Ullmann-type reaction of vinyl bromides with imidazole and benzimidazole

Cu₂O was found to be an efficient and economical metal catalyst in the Ullmann cross-coupling reaction of vinyl bromides with imidazole or benzimidazole. The system Cu₂O/ethyl 2-oxocyclohexanecarboxylate showed high catalytic activity in MeCN at 80–90 °C. The reaction gave the corresponding coupling products in good to excellent yields.     

Hydrogen-bond transition from the vibration mode of ordinary water to the (H,Na)I hydration states: Molecular interactions and solution viscosity

With the aid of differential phonon spectrometrics (DPS) and surface stress detection, we show that HI and NaI solvation transforms different fractions of the HO stretching phonons from the mode of ordinary water centred at ∼3200 to the mode of hydration shell at ∼3500 cm⁻¹. Observations suggest that an addition of the H ↔ H anti-hydrogen-bond to the Zundel notion, [H(H₂O)₂]⁺, would be necessary as the HO bond due H₃O⁺ has a 4.0 eV energy, and the H ↔ H fragilization disrupts the solution network and the surface stress. The I⁻ and Na⁺ ions form each a charge centre that aligns, stretches, and polarize the O:HO bond, resulting in shortening the HO bond and its phonon blue shift in the hydration shell or at the solute-solvent interface. The solute capabilities of bond-number-fraction transition follow: f_H = 0, f_Na ∝ C, and f_I ∝ 1 − exp(−C/C₀) toward saturation, with C being the solute molar concentration and C₀ the decay constant. The f_H = 0 evidences the non-polarizability of the H⁺ because of the H ↔ H formation. The linear f_Na(C) suggests the invariance of the Na⁺ hydration shell size because of the fully-screened cationic potential by the H₂O dipoles in the hydration shell but the nonlinear f_I(C) fingerprints the I⁻ ↔ I⁻ interactions at higher concentrations. Concentration trend consistency between Jones–Dole’s viscosity and the f_NaI(C) coefficient may evidence the same polarization origin of the solution viscosity and surface stress.     

Ultrafine molybdenum carbide nanoparticles supported on nitrogen doped carbon nanosheets for hydrogen evolution reaction

Nitrogen doped carbon nanosheets supported molybdenum carbides nanoparticles (Mo_xC/NCS) have been synthesized by tuning the mass ratio of melamine and ammonia molybdate. The Mo₂C/NCS-10 exhibits superior electrocatalytic performance and stability for HER, which was attributed to N-doped carbon nanosheets, small particle size, mesoporous structure, and large electrochemical active surface area.     

Novel method for the preparation of carbon supported nano-sized amorphous ruthenium oxides for supercapacitors

Nanostructured amorphous RuO₂ · xH₂O/C composite materials are prepared via a modified sol–gel process using glycolic acid. The glycolate anion, which dissociates from glycolic acid at pH 7, behaves as a stabilizer by adsorbing onto the RuO₂ · xH₂O surface, thus resulting in particles with a size of about 2 nm. As evidenced by zeta potential measurements, the surface charge of RuO₂ · xH₂O becomes more electronegative as the amount of glycolic acid increases. After heat treatment at 160 ^oC to remove the stabilizer, RuO₂ · xH₂O/C is found to exhibit an amorphous structure. The specific capacitance of RuO₂ · xH₂O/C particles (40 wt% Ru) prepared in the presence of glycolic acid (0.3 g L⁻¹) is 462 F g⁻¹, which is 30% higher than that of the material prepared in the absence of glycolic acid. Both the nanosized particles and the amorphous structure mainly contribute to this increase in the specific capacitance.