Co2(OH)3Cl nanoparticles as new-type electrode material with high electrochemical performance for application in supercapacitor

In this work, we report the preparation of Co₂(OH)₃Cl nanoparticles with average size of ～20 nm and well-defined cubic shape at room temperature by an epoxide precipitation route. It was found that the as-prepared Co₂(OH)₃Cl nanoparticles could be used as a promising new electrode material for application in redox supercapacitors due to its high electrochemical performance. It presented superior specific capacitance of 783 F g^?1 at low current density of 2.8 A g^?1, while it had a high value of 604 F g^?1 at high current density of 56.6 A g^?1, proving its excellent high rate performance. Its 75% capacitance retention after 10,000 cycles of charge–discharge demonstrated its long-life span. According to characterization results, the possible mechanism for the electrochemical process that Co₂(OH)₃Cl nanoparticles underwent was proposed as a process of Co₂(OH)₃Cl → β-Co(OH)₂ → CoOOH ? Co₃O₄.     

Microstructure correlated electrical conductivity of Manganese alloyed nanocrystalline cubic zirconia synthesized by mechanical alloying

Fully stabilized cubic (c) ZrO₂ phase has been synthesized by mechanical alloying (MA) the stoichiometric powder mixture of elemental Mn (5–20 mol%) and monoclinic (m) ZrO₂ at room temperature. XPS study reveals that major part of metallic Mn is ionized to Mn²⁺ oxidation state during MA. Mn-alloyed c-ZrO₂ nanoparticles with ～18 nm particle size have been synthesized within 10 h of MA. Microstructures of the compounds have been precisely evaluated by analyzing the X-ray powder diffraction patterns employing Rietveld refinement and transmission electron microscopy images. A decrease in lattice parameter from 5.11 Å to 5.09 Å is correlated with an increase in oxygen vacancy from 14% to 26% with increasing Mn concentrations. Elemental compositions in the compounds are obtained from electron probe microanalysis. The role of Mn alloying in the polymorphic phase transformation (m → c) has been established with changes in structure and microstructure parameters. Electrical conductivities of all c-ZrO₂ compounds are measured in the temperature range 350–550 °C. Grain and grain boundary contributions to total conductivity are calculated from frequency dependent real and imaginary impedance. Conductivity of Mn alloyed c-ZrO₂ increases with increasing temperature and Mn concentrations. Electrical transport mechanism in the compound is studied by impedance and modulus spectroscopy. The relaxation frequency is found to be temperature, microstructure and composition dependent.     

Nanoporous Cu wide ribbons with good mechanical integrity

In this work we report the fabrication of nanoporous Cu wide ribbon samples by electrochemical dealloying the minor Si alloyed γ-Cu₃₀Mn₇₀ solid solution alloys. The γ-Cu₃₀Mn₇₀ structure was found to be capable of trapping a minor amount of Si as solute by liquid quenching. Ribbon samples of 10 mm wide with tunable thickness were made at the Cu₂₈Mn₇₀Si₂ composition. The γ-Cu₂₈Mn₇₀Si₂ alloy can be turned into wide ribbon nanoporous Cu with the pore size of ～30–50 nm and with good mechanical integrity. A thin layer of Si-enriched glue structure with ～50 nm thickness was formed continuously along the grain boundaries to play the role of reinforcement for the dealloyed structure.     

Synthesis and characterization of novel magnetically separable NiFe2O4@AlMCM-41-Cu2O core-shell and its performance in removal of dye

The synthesis of magnetic NiFe₂O₄@AlMCM-41-Cu₂O core-shell as a new class of visible light driven photocatalyst was suggested. The magnetic NiFe₂O₄ core was prepared by solvothermal method. The intermediate AlMCM-41 shell was prepared by the method of liquid crystal templating mechanism and subsequently cuprous oxide (Cu₂O) nanoparticles (NPs) were synthesized in NiFe₂O₄@AlMCM-41core-shell via colloidal chemistry approach. The properties of prepared magnetic core-shell were characterized by scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), nitrogen adsorption–desorption measurement and vibration sample magnetometer (VSM). Based on EDX results, the weight percentage (wt%) of NiFe₂O₄ core, MCM-41 shell and Cu₂O NPs were calculated to be 68.89, 30.55 and 0.56%, respectively. It consisted of mesoporous structure with a surface area of 687.00 m² g^?1, an average pore size of 2.95 nm and possessed excellent magnetic properties of 4.74 emu g^?1. The TEM results indicated that the NiFe₂O₄ as core were regular spheres with diameter of 68 nm, and the average thickness of AlMCM-41 shells was ～35 nm. The particles size of Cu₂O incorporated in core-shell was less than 5 nm. The photocatalytic activity was evaluated under visible light irradiation using the removal of methylene blue (MB) dye as a model reaction. The removal rate of MB achieved up to 90% after 60 min under visible light irradiation, and the NiFe₂O₄@AlMCM-41-Cu₂O can be recycled and reused.     

Highly dispersible and uniform size Cu2ZnSnS4 nanoparticles for photocatalytic application

Highly dispersible, uniform size (～7 nm) single-phase Cu₂ZnSnS₄ nanoparticles have been synthesized by hydrothermal method using non-toxic surfactant (oleic acid). High resolution transmission electron microscopy image indicates good crystallinity of the Cu₂ZnSnS₄ nanoparticles with the growth along (1 1 2) plane. X-ray photoelectron spectroscopy analyses suggested that the formation of with Cu, Zn, and Sn in +1, +2 and +4 oxidation states. The optical absorption spectrum of Cu₂ZnSnS₄ nanoparticles exhibits an absorption in the visible region and its optical band gap was found to be ～1.72 eV, which could be much more appropriate for photocatalytic application under visible light irradiation. These Cu₂ZnSnS₄ nanoparticles have been shown high photocatalytic degradation activity of methylene blue (MB) dye in the presence of visible light irradiation. The rate constant (k) value of Cu₂ZnSnS₄ nanoparticles is found to be 0.0144 min^?1. We have discussed the mechanism of dye degradation process that drives the photocatalytic degradation process. The reusability of the Cu₂ZnSnS₄ nanoparticles for the dye degradation is also demonstrated.     

Hydrolytic dehydrogenation of ammonia borane catalyzed by poly(amidoamine) dendrimers-modified reduced graphene oxide nanosheets supported Ag0.3Co0.7 nanoparticles

Poly(amidoamine) dendrimers-modified reduced graphene oxide nanosheets (PAMAM/rGO) composite was selected as a carrier of heterogeneous Ag_0.3Co_0.7 nanoparticles in order to obtain an excellent catalyst for ammonia borane (AB) hydrolysis. During the synthetic processes, GO could easily assembled with PAMAM by the electrostatic and hydrogen-bonding interactions. Structural characterization revealed that Ag_0.3Co_0.7 bimetallic nanoparticles with uniform size distribution of 5 nm are well dispersed on PAMAM/rGO composite architecture. Ag_0.3Co_0.7@PAMAM/rGO was found to be a highly active and reusable catalyst in hydrogen generation from the hydrolysis of AB with a turnover frequency value (TOF) of 19.79 mol_H2 min^–1 mol_M^–1 at 25.0 ± 0.1 °C and retained 75.4% of their initial activity with a complete release of hydrogen in five runs. The relatively high TOF value and low apparent activation energy (34.21 kJ mol^–1) make these Ag_0.3Co_0.7@PAMAM/rGO NPs as a high-efficient catalyst for catalytic dehydrogenation of AB facilitating the development of practically applicable energy storage materials.     

Vitis vinifera peel polyphenols stabilized gold nanoparticles induce cytotoxicity and apoptotic cell death in A431 skin cancer cell lines

Gold nanoparticles (AuNPs) are considered beneficial in the field of biomedicine and in the development of therapeutic nanomedicine products. In the present study, Vitis vinifera. L (grapes) peel polyphenols were utilized as reducing and stabilizing agents for the biosynthesis of gold nanoparticles, and their cytotoxicity and apoptotic effects were assessed. The synthesized gold nanoparticles were characterized using UV-Visible spectroscopy, Transmission electron microscopy (TEM), X-ray diffraction (XRD), Particle size distribution, Fourier transform infrared spectroscopy (FTIR) and zeta potential analysis. TEM analysis confirmed that the nanoparticles were spherical with ～20–40 nm in size. Particle size distribution revealed ～50 ± 5 nm nanoparticles and FTIR confirmed the presence of polyphenols capped onto the peel gold nanoparticles. The V. vinifera peel gold nanoparticles were studied for their antiproliferative activities and induction of apoptosis at the inhibitory concentration (IC₅₀) of 23.6 µM. A431 cell lines incubated with V. vinifera peel gold nanoparticles for 24 h exhibited cytotoxicity activity mediated by increased reactive oxygen species (ROS) production, apoptotic morphological changes and loss of membrane potential significantly (p < 0.01). Thus, the cytotoxicity of the gold nanoparticles could be attributed to the synergistic effects of the phenolic moieties of the V. vinifera peels and the efficiency of the bioconjugated gold nanoparticles causing apoptosis and secondary necrosis.     

Mesoporous structure and evolution mechanism of hydroxycarbonate apatite microspheres

Monodisperse mesoporous hydroxycarbonate apatite microspheres (MHAMs) were fabricated by soaking calcium carbonate microspheres (CCMs) in a cetyltrimethylammonium bromide (CTAB)/Na₂HPO₄/cyclohexane/n-butanol emulsion system. After soaking CCMs in the emulsion system at 20 °C, hydroxycarbonate apatite nanocrystals nucleate heterogeneously on the surfaces of CCMs via a dissolution–precipitation reaction. The as-formed nanocrystals aggregate to form mesopores with the pore size of ～ 3.9 nm and ～ 9.0 nm. The smaller mesopores are derived from the direct aggregation of the nanocrystals, which do not change obviously with the reaction time. In contrast, the larger mesopores are formed by using CTAB micelles as templates, and their pore size decreases from ～ 9.0 nm to ～ 7.4 nm with increasing the reaction time from 6 h to 1 day. After reaction for 3 or 5 days, the larger mesopores disappear because of unstability of the CTAB micelles. If reaction temperature is kept at 50 °C, the conversion rate of CCMs to MHAMs is greater than that at 20 °C, and the corresponding mesoporous structure is unimodal with the pore size of ～ 3.9 nm. Simulated body fluid immersion tests reveal that MHAMs have a great in vitro bioactivity, which is attributed to the mesoporous structure and B-type CO₃^2? substitution of MHAMs.     

Structural and functional properties of ZnO thin films grown on Si substrates by air assisted USP method from non-aqueous solutions at low-temperature

In this work, we deals with the processing and characterization of transparent conducting ZnO thin films on p-type Silicon substrates (1 0 0) by air assisted Ultrasonic Spray Pyrolysis (USP) method. The thin films from different Zn acetate precursor solution concentrations (0.1, 0.2, 0.3 and 0.4 M) were deposited at several temperatures (400, 450 and 500 °C) with thickness from ～100 to ～500 nm. The effects of precursor solution concentration, deposition time and temperature on the structural, morphological, optical, and electrical properties of ZnO films were studied by X-ray Diffraction (XRD), Atomic Force Microscopy (AFM), UV–Vis-NIR spectroscopy, and Hall Effect techniques, respectively. It has been shown that on the ZnO film surface, the preferred orientation, the average crystallite size, the electrical resistivity and the RMS surface roughness depend on the substrate temperature. The grown films have showed a good adhesion and an excellent optical transmission of about 80–95% within the visible range (400–800 nm) and a direct band gap from 3.35 to 3.23 eV with the increase of the substrate temperature and the deposition time. All the PL spectra have exhibited a typical green-yellow emission band. Additionally photovoltaic (PV) activities of n-ZnO/p-Si heterostructures fabricated are investigated.     

Synthesis of dispersed PrBaCo0.9Cu0.1O5+δ cathode nanopowders with layered perovskite structure for intermediate temperature solid oxide fuel cells

PrBaCo_1.9Cu_0.1O_5+δ (PBCCO) nanopowders were synthesized by an EDTA-citrate complexing process using water and ethanol as solvents, and their structures and electrochemical properties were characterized. PBCCO precursor gels were highly oxidized at 450 °C, using either water (PBCCO-W) or ethanol (PBCCO-E) as the solvent. PBCCO powders calcined at 450 °C had a second phase, while those calcined at 850 °C for 4 h were obtained as single phase PBCCO with a layered perovskite structure in the P4mm space group. PBCCO-E primary particles were approximately 5–10 nm in size and were well-dispersed compared with those of the PBCCO-W powder. We hypothesized that the enhanced dispersibility of the PBCCO-E powder was caused by a decrease in bridging hydrogen bonds on the chelate surface, which prevents chelate agglomeration in sol state. It causes the larger specific surface area of PBCCO-E powders and thus a lower polarization resistance (R_p) than that of PBCCO-W powders at the measured temperature. The R_p value of PBCCO-E powder was 0.041 Ω cm² at 750 °C, which is about 1.5 times lower than that of PBCCO-W at the same temperature.     

Effect of characteristics of (Sm,Ce)O2 powder on the fabrication and performance of anode-supported solid oxide fuel cells

Effect of characteristics of Sm_0.2Ce_0.8O_1.9 (SDC) powder as a function of calcination temperature on the fabrication of dense and flat anode-supported SDC thin electrolyte cells has been studied. The results show that the calcination temperature has a significant effect on the particle size, degree of agglomeration, and sintering profiles of the SDC powder. The characteristics of SDC powders have a significant effect on the structure integrity and flatness of the SDC electrolyte film/anode substrate bilayer cells. The SDC electrolyte layer delaminates from the anode substrate for the SDC powder calcined at 600 °C and the bilayer cell concaves towards the SDC electrolyte layer for the SDC powder calcined at 800 °C. When the calcinations temperature increased to 1000 °C, strongly bonded SDC electrolyte film/anode substrate bilayer structures were achieved. An open-circuit voltage (OCV) of 0.82–0.84 V and maximum power density of ～1 W cm^?2 were obtained at 600 °C using hydrogen as fuel and stationary air as the oxidant. The results indicate that the matching of the onset sintering temperature and maximum sintering rate temperature is most critical for the development of a dense and flat Ni/SDC supported SDC thin electrolyte cells for intermediate temperature solid oxide fuel cells.     

Synthesis of three-dimensionally ordered porous perovskite type LaMnO3 for Al-air battery

LaMnO₃ catalysts with three-dimensionally ordered holes perovskite structure were prepared via close-packed SiO₂ template synthesized by Stöber-Frink method. SEM, XRD and BET were employed to characterize the microstructure, phases and specific surface area. CV method was used to the oxygen electrode behavior of catalysts. Diameter of the holes was about 330 nm, corresponding to the size of SiO₂ template. Full-cell discharge tests were performed on aluminum-air battery fabricated by porous LaMnO_3. Results showed that the discharge performance of porous LaMnO₃ were 1.54 V, 1.42 V and 1.24 V respectively when the discharge currents were set at 5 mA/cm², 10 mA/cm² and 20 mA/cm², respectively, which were higher than that of LaMnO₃ prepared by coprecipitation method (1.33 V, 1.09 V, 0.63 V, respectively).     

Synthesis of nanocrystalline LaF3 doped silica glasses by hydrofluoric acid catalyzed sol–gel process

Silica glasses doped with LaF₃ nanocrystals were prepared by HF-catalyzed sol–gel method. HF was used both as fluorine source and as catalyst of the sol–gel reaction, making it possible to shorten the processing time with reducing the concentration of SiOH groups to ～10¹⁸ cm^?3. The resultant glasses are transparent at visible spectral range, and the optical loss at the ultraviolet absorption edge is dominated by the Rayleigh scattering from LaF₃ crystallites. The size of LaF₃ crystallites increases with an increase in the sintering temperature and time, and is smaller than ～40 nm in samples showing good visible transparency. Green upconversion photoluminescence is observed in an Er³⁺-doped sample under excitation at 980 nm.     

Solvothermal synthesis of Ag/ZnO micro/nanostructures with different precursors for advanced photocatalytic applications

Micro/nanostructured systems based on metallic oxide (ZnO) with noble metal (Ag) on the surface (Ag/ZnO) are synthesized by solvothermal method from zinc nitrate hexahydrate (Zn(NO₃)₂·6H₂O), zinc acetate dehydrate (Zn(CH₃COO)₂·2H₂O), zinc acetylacetonate hydrate (Zn(C₅H₇O₂)₂·xH₂O) and silver nitrate (Ag(NO₃)) as precursors. In these systems, polyvinylpyrrolidone (PVP) is used as surfactant for controlling particle morphology, size and dispersion. The obtained materials are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), UV–vis diffuse reflectance spectroscopy (DRS), N₂ gas adsorption–desorption (BET) and Raman spectroscopy (RS). By XRD results, all major peaks are indexed to the hexagonal wurtzite-type structure of the ZnO and samples with noble metal, extra diffraction peaks are detected which correspond to the face-centered-cubic (fcc) structure of the metallic Ag. Depending on used precursor, different morphologies have been obtained. Mainly, ZnO prims-like rods – NRs (with 0.8 ? aspect ratio ? 3.4) – have been observed. Quasi-spherical particles of metallic Ag (with diameters between 558 ± 111 μm and 22 ± 1 nm) have been detected on the ZnO surface. Photocatalytic results (all samples studied >30% MB degradation) verify the important effect of surfactant and the viability of synthesized Ag/ZnO micro/nanocomposites for environmental applications.     

A Novel near white light emitting nanocrystalline Zn2P2O7:Sm3+ derived using citrate precursor route: Photoluminescence spectroscopy

Nanocrystalline Zn₂P₂O₇:Sm³⁺ was synthesized using citrate precursor route. Rietveld refined XRD shown the formation of pure phase at 900 °C. Based on scanning electron microscopy, size distribution of the pyrophosphate particle was found to be in the range of 50–100 nm. Upon near UV light excitation (403 nm), Zn₂P₂O₇:Sm³⁺exhibits host emission at 450 nm along with characteristic emission lines of Sm³⁺. Based on PL decay measurement, it was inferred that two different types of Sm³⁺ ions were present in the zinc pyrophosphate. The first type was a short lived species (∼τ = 100 μs) present at less symmetric ‘5-coordinated Zn’ sites, while the second was a long lived species (∼τ = 1.9 ms) present at symmetric ‘6-coordinated Zn’ sites. The color coordinates of the system were evaluated using CIE index diagram to be 0.36 and 0.37, which suggest that the prepared material is a potential near white light emitting phosphor.     

Self-nitrogen-doped porous biochar derived from kapok (Ceiba insignis) fibers: Effect of pyrolysis temperature and high electrochemical performance

Self-nitrogen-doped porous biochar derived from kapok fibers possesses unique structure and excellent electrochemical performance. In this study, one-step pyrolysis method was introduced to prepare porous biochar from kapok fibers, and effect of pyrolysis temperature on structure and electrochemical performance of the porous biochar was investigated. It was found that pyrolysis temperature played an important role in determining microstructure of the biochar. At the pyrolysis temperature of 750 °C, the as-prepared biochar (C_KF-750) represented a largest specific surface area of 1125.7 m² g^?1 and pore volume of 0.7130 m³ g^?1, and hence brings C_KF-750 a highest specific capacitance of 283 F g^?1 at a current density of 1 A g^?1 in a 6 mol L^?1 KOH electrolyte. Furthermore, the cycle stability of C_KF-750 was wonderful, and the specific capacitance retained almost constant after 10000 cycles. Therefore, the pyrolysis temperature of 750 °C is optimal for the preparation of porous biochar as an outstanding electrode material for supercapacitor.     

Synthesis,growth mechanism,photoluminescence and field emission properties of metal–semiconductor Zn–ZnO core–shell microcactuses

Metal–semiconductor Zn–ZnO core–shell microcactuses have been synthesized on Si substrate by simple thermal evaporation and condensation route using NH₃ as carrier gas at 600 °C under ambient pressure. Microcactuses with average size of 65–75 μm are composed of hollow microspheres with high density single crystalline ZnO rods. The structure, composition and morphology of the product were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), scanning electron microscope (SEM), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). A vapor–liquid–solid (VLS) based growth mechanism was proposed for the formation of Zn–ZnO core–shell microcactuses. Room temperature photoluminescence (PL) investigations revealed a strong and broad blue emission band at 441 nm associated with a weak ultraviolet (UV) peak at 374 nm. This blue emission (BE) is different from usually reported green/yellow-green emission from Zn–ZnO or ZnO structures. The field emission (FE) measurements exhibited moderate values of turn-on and threshold fields compared with reported large field emissions for other materials. These studies indicate the promise of Zn–ZnO core–shell microcactuses for the applications in UV-blue light display and field emission microelectronic devices.     

Mixture of fuels approach for the solution combustion synthesis of LaAlO3 nanopowders

A modified solution combustion approach was used in the preparation of nanosize LaAlO₃ (～23.6 nm) using mixture of citric acid and oxalic acid as fuels with corresponding metal nitrates. The synthesized and calcined powders were characterized by Fourier transform infra red spectrometry (FTIR), Differential thermal analysis-Thermogravimetry analysis (DTA–TGA), X-ray diffractometry (XRD) and Transmission electron microscopy (TEM). The FTIR spectra show the lower frequency bands at 656 and 442 cm^?1corresponds to metal–oxygen bonds (possible La–O and Al–O stretching frequencies) vibrations for the perovskite structure compound. DTA confirms the formation temperature of LaAlO₃ varies between 830–835 °C. XRD results show that mixture of fuels ratio is influential on the crystallite size of the resultant powders. The average particle size of LaAlO₃-1 as determined from TEM was about 41 nm, whereas for LaAlO₃-2 and LaAlO₃-3 samples, particles are seriously aggregated.     

Preparation of smooth zinc oxide thin film via liquid phase reaction with aluminum ion additives

ZnO thin films were formed in a solution with Zn(NO₃)₂ and Dimethylaminoborane at 70 °C. The effects of the aluminum ion concentration in the aqueous solution on the surface morphology, crystallographic structure and growth rate were investigated. By adding 10^? 4 mol/l of Al, the growth rate was enhanced from 0.13 to 0.35 μm/h. In addition, the surface morphology became flat when the appropriate amount of Al(NO₃)₃, i.e., 10^? 4 mol/l, was added. The R_a and R_z decreased from 20–32 nm and 115–145 nm to 1–11 nm and 7–60 nm, respectively.     

Nanocrystalline cobalt-oxide powders by solution-combustion synthesis and their application in chemical sensors

The present study demonstrates the relationship between the combustion reaction mechanism induced by the exothermicity of the cobalt nitrate-glycine solution-combustion reactions and morphological details of the nanocrystalline Co₃O₄. The thermal decomposition pathway and the amount of the heat liberated in combustion are defined by the exothermic reaction between gaseous NH₃ and N₂O species. A direct evidence that the exothermicity of the combustion reaction plays an important role in formation of the powders with different morphology was obtained from the scanning and transmission electron microscopies. In contrast to stoichiometric reaction, where the short-string Co₃O₄ particles form hard agglomerates, the energetically softer 50% fuel lean reaction is responsible for weak bonds between Co₃O₄ particles and formation of the loose cauliflower-like agglomerates. The latter powder with the specific surface area of 64.4 m²/g and the average crystallite size of ～11 nm was used for the processing of drop-coated sensors, which showed a superior sensor response toward 20 ppm of acetone in 25% r.h. humidity and at low operating temperature of 150 °C.