Structural and electrochemical characterization of a cobalt phthalocyanine bulk-modified SiO2/SnO2 carbon ceramic electrode

A cobalt phthalocyanine bulk-modified carbon ceramic composite has been prepared by using sol-gel processing, and characterized by BET surface area, X-ray photoelectron spectroscopy, scanning electron microscopy and atomic force microscopy. A water-soluble 3-n-propylpyridinium chloride silsesquioxane (SiPyCl), an ion exchanger polymer, was employed to attach cobalt(II) tetrasulfophthalocyanine (CoTsPc) and prevent its leakage, as well as, to ensure adequate dispersion in the sol-gel network. The modified electrode built in a rigid disk-format displayed good electrocatalytic behavior towards the oxidation of oxalic acid at 0.84 V (SCE), as evidenced by the enhancement of the anodic current peak intensity when the concentration of oxalic acid was increased. A linear response was found in the range of 1.6 × 10⁻⁵ to 1.5 × 10⁻³ mol l⁻¹ with a detection limit of 7.1 × 10⁻⁶ mol l⁻¹.     

Electrocatalytic reduction of NO2: Platinum modified glassy carbon electrode

Platinum particles were electrochemically deposited over glassy carbon (GC) to prepare GC-Pt electrodes. The electrocatalytic behaviors of this electrode have been compared with that of an ordinary polycrystalline(OPC) Pt and GC electrode in reducing NO₂⁻ at neutral medium. The as prepared GC-Pt electrode reduced NO₂⁻, exhibiting double-peak reduction waves. The reduction performance of this electrode was noticed at least 7.8 times higher than that of an OPC Pt electrode. The sensitivity of the GC-Pt electrode was found to be enhanced by the temperature rise. A consecutive mechanism, NO₂⁻ → NO → NH₄⁺, over the as prepared GC-Pt electrode has been investigated.     

Al2O3-coated SnO2/TiO2 composite electrode for the dye-sensitized solar cell

A novel Al₂O₃-coated SnO₂/TiO₂ composite electrode has been applied to the dye-sensitized solar cell. In such an electrode, two kinds of energy barriers (SnO₂/TiO₂ and TiO₂/Al₂O₃) were designed to suppress the recombination processes of the photo-generated electrons and holes. After the SnO₂ was modified by colloid TiO₂, the photoelectric conversion efficiency of the SnO₂/TiO₂ composite cell increased to 2.08% by a factor of 2.8 comparing with that of the SnO₂ cell. The Al₂O₃ layer on the SnO₂/TiO₂ composite electrode further suppressed the generation of the dark current, resulting in 37% improvement in device performance comparing with the SnO₂/TiO₂ cell.     

Highly stable carbon-coated Fe/SiO2 composites: Synthesis, structure and magnetic properties

A new method to coat Fe nanoparticles with carbon by pyrolysis of acetylene is reported. The Fe nanoparticles were beforehand coated with silica layers by sol-gel combined hydrogen method. The antioxidation capability of Fe/SiO₂ composites has enhanced greatly after coated with amorphous carbon shells. By the introduction of only 7.5 wt.% nonmagnetic silica and carbon, these composites have relatively high specific magnetization of 200.27 emu/g. The insulating amorphous silica and carbon shells prove effective to reduce the eddy current at high frequency.     

Direct synthesis of acetic acid from CH4 and CO2 by a step-wise route over Pd/SiO2 and Rh/SiO2 catalysts

The theoretical and experimental feasibility of direct conversion of CH₄ and CO₂ to acetic acid by an isothermal step-wise route over Pd/SiO₂ and Rh/SiO₂ catalysts was investigated. The methyl radical formation from CH₄ dissociation and CO₂ inserting into the intermediate are regarded as two limiting steps. Preliminary experimental results have shown that the following step-wise route can circumvent the thermodynamic limitation of this direct synthesis at low temperatures. Pd catalysts are more active than Rh catalysts at 170 °C and 200 °C, while formic acid is only produced on Pd catalysts. The optimum contact time of CH₄ and CO₂ with catalysts is 1 min under the experimental conditions. And there is no apparent deactivation resulting from carbon deposition for catalysts during the successive reaction cycles.     

Growing carbon nanotubes on patterned submicron-size SiO2 spheres

Growing carbon nanotubes (CNTs) perpendicularly to the surface of submicron-size SiO₂ spheres by pyrolyzing iron(II) phthalocyanine (FePc) is reported for the first time in this paper. The large curvature isolates the nanotubes and forms unique structures. The density, lengths and morphology of CNTs on SiO₂ spheres can be controlled by varying the experimental conditions. A method of growing CNTs on patterned SiO₂ spheres on conducting surface by photolithography is further developed based on the selective growth of CNTs. This may offer an effective way to control the density of patterned, aligned CNTs on conducting substrates for various applications, particularly for field emission.     

Preparation of a sol-gel-derived carbon nanotube ceramic electrode by microwave irradiation and its application for the determination of adenine and guanine

In this study, microwave irradiation was used for the fast preparation (min) of a sol-gel-derived carbon nanotube ceramic electrode (MW-CNCE). For confirmation of the preparation of the ceramic by MW irradiation, Fourier transform infrared, X-ray diffraction spectra and scanning electron microscopy images of the produced ceramic were compared with those of conventional ceramic (which is produced by drying the ceramic in air for 48 h). The electrochemical behavior of MW-CNCE in nicotinamide adenine dinucleotide, l-cysteine, adenine and guanine was compared with that of a conventional sol-gel-derived carbon nanotube ceramic electrode (CNCE). In all systems, similar peak potentials and lower background currents were obtained with respect to CNCE. Finally, the MW-CNCE was used for the simultaneous determination of adenine and guanine using differential pulse voltammetry. The linear ranges of 0.1-10 and 0.1-20 μM were obtained for adenine and guanine, respectively. These results are comparable with some modified electrodes that have recently been reported for the determination of adenine and guanine, with the advantage that the proposed electrode did not contain modifier. In addition, the proposed electrode was successfully used for the oxidation of adenine and guanine in DNA, and the detection limit for this measurement was 0.05 μg mL⁻¹ DNA.     

Synthesis,characterization and electrochemical performances of MoO2 and carbon co-coated LiFePO4 cathode materials

The MoO₂ and carbon co-coated LiFePO₄ cathode materials were synthesized by a combined technique of solid state synthesis and the sol–gel method. Phase compositions and microstructures of the products were characterized by X-ray powder diffraction (XRD), Raman, SEM and TEM. Results indicate that MoO₂ can sufficiently coat on the LiFePO₄ surface and does not alter LiFePO₄ crystal structure, and the existence of MoO₂ increases the graphitization degree of carbon. SEM and TEM images reveal that MoO₂ presence has little impact on LiFePO₄ particle size. The electrochemical behavior of cathode materials was analyzed using galvanostatic measurement and cyclic voltammetry (CV). The results show that the existence of MoO₂ improves electrochemical performance of LiFePO₄ cathode material in specific capability and low-temperature behavior. The apparent lithium ion diffusion coefficient increases with MoO₂ content and maximizes around the MoO₂ content of x=5 wt%. It has been had further proved that the higher electronic conductivity of MoO₂ and carbon enhances the lithium ion transport to improve the electrochemical performance of LiFePO₄ cathode materials.     

The improvement in oxidation resistance of carbon by a graded SiC/SiO2 coating

A dense functionally gradient SiC/SiO₂ coating has been developed to improve the oxidation resistance of carbon at elevated temperatures. SiC was coated on the surface of a graphite substrate by a reaction between thermally evaporated silicon and carbon at 1400 °C. The SiO₂ layer was deposited by exposing the SiC coated specimens next to a bed of Si powder in a flowing H₂–H₂O gas (P_H2O=2.6×10⁻² atm) at 1400 °C. The formed SiC/SiO₂ layers were dense and had gradient compositions with good adhesion to the carbon substrate. However, as the coating thickness increased, the coating layer became cracked and delaminated from the substrate due to thermal stress. The specimens with the continuous SiC/SiO₂ layer showed a remarkably improved oxidation resistance up to 1200 °C.     

In situ immobilization of cobalt phthalocyanine on the mesoporous carbon ceramic SiO2/C prepared by the sol–gel process. Evaluation as an electrochemical sensor for oxalic acid

The mesoporous carbon ceramics SiO₂/20 wt% C (S_BET = 160 m² g⁻¹) and SiO₂/50 wt% C (S_BET = 170 m² g⁻¹), where C is graphite, were prepared by the sol–gel method. Scanning electron microscopy images and the respective element mapping showed that, within the magnification used, no phase segregation was detectable. The materials containing 20 and 50 wt% of C presented electric conductivities of 9.2 × 10⁻⁵ and 0.49 S cm⁻¹, respectively. These materials were used as matrices to support cobalt phthalocyanine (CoPc), prepared in situ on their surfaces, to assure homogeneous dispersion of the electroactive complex in the pores of both matrices. The surface densities of cobalt phthalocyanine on both matrix surfaces were 0.014 mol cm⁻² and 0.015 mol cm⁻² for materials containing 20 and 50 wt% of C, respectively. Pressed disk electrodes made with SiO₂/50 wt% C/CoPc and SiO₂/20 wt% C/CoPc were tested as sensors for oxalic acid. The electrode was chemically very stable and presented very high sensitivity for this analyte, with a limit of detection, LOD = 5.8 × 10⁻⁷ mol L⁻¹.     

Promoting effects of CO2 on dehydrogenation of propane over a SiO2-supported Cr2O3 catalyst

The effects of carbon dioxide on the dehydrogenation of C₃H₈ to produce C₃H₆ were investigated over several Cr₂O₃ catalysts supported on Al₂O₃, active carbon and SiO₂. Carbon dioxide exerted promoting effects only on SiO₂-supported Cr₂O₃ catalysts. The promoting effects of carbon dioxide over a Cr₂O₃/SiO₂ catalyst were to enhance the yield of C₃H₆ and to suppress the catalyst deactivation.     

Synthesis and characterization of carbon-coated Li3V2(PO4)3 cathode materials with different carbon sources

The carbon-coated monoclinic Li₃V₂(PO₄)₃ (LVP) cathode materials were synthesized by a solid-state reaction process under the same conditions using citric acid, glucose, PVDF and starch, respectively, as both reduction agents and carbon coating sources. The carbon coating can enhance the conductivity of the composite materials and hinder the growth of Li₃V₂(PO₄)₃ particles. Their structures and physicochemical properties were investigated using X-ray diffraction (XRD), thermogravimetric (TG), scanning electron microscopy (SEM) and electrochemical methods. In the voltage region of 3.0-4.3 V, the electrochemical cycling of these LVP/C electrodes all presents good rate capability and excellent cycle stability. It is found that the citric acid-derived LVP owns the largest reversible capacity of 118 mAh g⁻¹ with no capacity fading during 100 cycles at the rate of 0.2C, and the PVDF-derived LVP possesses a capacity of 95 mAh g⁻¹ even at the rate of 5C. While in the voltage region of 3.0-4.8 V, all samples exhibit a slightly poorer cycle performance with the capacity retention of about 86% after 50 cycles at the rate of 0.2C. The reasons for electrochemical performance of the carbon coated Li₃V₂(PO₄)₃ composites are also discussed. The solid-state reaction is feasible for the preparation of the carbon coated Li₃V₂(PO₄)₃ composites which can offer favorable properties for commercial applications.     

ZrO2/SiO2- and La2O3/Al2O3-supported platinum catalysts for CH4/CO2 reforming

Surface-phase ZrO₂ on SiO₂ (SZrOs) and surface-phase La₂O₃ on Al₂O₃ (SLaOs) were prepared with various loadings of ZrO₂ and La₂O₃, characterized and used as supports for preparing Pt/SZrOs and Pt/SLaOs catalysts. CH₄/CO₂ reforming over the Pt/SZrOs and Pt/SLaOs catalysts was examined and compared with Pt/Al₂O₃ and Pt/SiO₂ catalysts. CO₂ or CH₄ pulse reaction/adsorption analysis was employed to elucidate the effects of these surface-phase oxides.

The zirconia can be homogeneously dispersed on SiO₂ to form a stable surface-phase oxide. The lanthana cannot be spread well on Al₂O₃, but it forms a stable amorphous oxide with Al₂O₃. The Pt/SZrOs and Pt/SLaOs catalysts showed higher steady activity than did Pt/SiO₂ and Pt/Al₂O₃ by a factor of three to four. The Pt/SZrOs and Pt/SLaOs catalysts were also much more stable than the Pt/SiO₂ and Pt/Al₂O₃ catalysts for long stream time and for reforming temperatures above 700 °C. These findings were attributed to the activation of CO₂ adsorbed on the basic sites of SZrOs and SLaOs.     

Synthesis of nanocrystalline SnO2 powder from SnCl4 by mechanochemical processing

The rapid synthesis of nanocrystalline SnO₂ powder using a mechanochemical reaction of SnCl₄ (instead of the widely used tin (II) compounds) with (NH₄)₂CO₃ and the subsequent annealing of the product in air and under an H₂O/NH₃ atmosphere has been investigated using X-ray powder diffraction, TG and TEM. The reaction was complete within 5 min. Additional milling of the product at a higher milling intensity for 120 min led to the crystallisation of tetragonal SnO₂. The NH₄Cl salt matrix was removed by annealing at 300 °C. The average crystallite size of tetragonal SnO₂ was in the range of 2-48 nm and it can be controlled by variation heating temperatures and annealing atmospheres in the range of 300-700 °C.     

Fabrication and characterization of ZrB2–SiC ceramic electrodes coated with a proton conducting, SiO2-rich glass layer

3.5 μm thin layers of dense, crack-free, proton conducting, SiO₂-rich glass have been developed on ZrB₂–SiC ceramic composites, by thermal oxidation at 1400 °C for 30 min in air. A conductivity of 2 mS cm⁻¹ at 25 °C was found, as measured by AC impedance and steady-state voltammetry, and was estimated at ca. 2 × 10⁻² S cm⁻¹ at 80 °C. A striking behaviour of the oxidized ZrB₂–SiC composites is also pointed out: underneath the glass layer, there is a porous layer rich in electronic conductive ZrB₂, without well-defined interface between them, i.e., exhibiting a composition gradient in oxygen. In other words, protonic half-fuel cells could be fabricated under such conditions, for future use in hydrogen or direct alcohol fuel cells.     

Synthesis of single-crystal SnO2 nanowires for NOx gas sensors application

Single-crystal SnO₂ nanowires (NWs) were successfully synthesized and characterized as sensing materials for long-term NO_x stability detection in environmental monitoring. Reproducible and selective growths of the SnO₂ NWs on a patterned, 5 nm-thick gold catalyst coated on a SiO₂/Si wafer as substrate were conducted by evaporating SnO powder source at 960 °C in a mixture of argon/oxygen ambient gas (Ar: 50 sccm/O₂: 0.5 sccm). The as-obtained products were characterized by field-emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Raman scattering, and photoluminescence (PL). The SEM and HRTEM images revealed that the products are single-crystal SnO₂ NWs with diameter and length ranges of 70 nm–150 nm and 10 μm–100 μm, respectively. The three observed Raman peaks at 476, 633, and 774 cm⁻¹ indicated the typical rutile phase, which is in agreement with the XRD results. The NWs showed stable PL with an emission peak centered at around 620 nm at room-temperature, indicating the existence of oxygen vacancies in the NW samples. The electrical properties of synthesized SnO₂ NWs sensor were also investigated and it exhibited a negative temperature coefficient of resistance in the measured range (300–525 K). The calculated activation energy E_c of SnO₂ NWs was 0.186 eV. Moreover, the SnO₂ NW sensors exhibited good response to NO_x gas. The response of the sensors to 5 ppm NO_x reached 105% at an operating temperature of 200 °C.     

Synthesis and electrochemical performance of Li2FeSiO4/carbon/carbon nano-tubes for lithium ion battery

Li₂FeSiO₄/carbon/carbon nano-tubes (Li₂FeSiO₄/C/CNTs) and Li₂FeSiO₄/carbon (Li₂FeSiO₄/C) composites were synthesized by a traditional solid-state reaction method and characterized comparatively by X-ray diffraction, scanning electron microscopy, BET surface area measurement, galvanostatic charge-discharge and AC impedance spectroscopy, respectively. The results revealed that the Li₂FeSiO₄/C/CNT composite exhibited much better rate performance in comparison with the Li₂FeSiO₄/C composite. At 0.2 C, 5 C and 10 C, the former composite electrode delivered a discharge capacity of 142 mAh g⁻¹, 95 mAh g⁻¹, 80 mAh g⁻¹, respectively, and after 100 cycles at 1 C, the discharge capacity remained 95.1% of its initial value.     

Flow injection amperometric determination of pyridoxine at a Prussian blue nanoparticle-modified carbon ceramic electrode

This work describes the electrocatalytic properties of a carbon composite electrode (CCE) modified with Prussian blue (PB) nanoparticles (NPs) for the electrocatalytic oxidation of pyridoxine (PN). The morphology of the PBNP-modified CCE was characterized by scanning electron microscopy (SEM). The mechanism and kinetics of the catalytic oxidation reaction of PN were monitored by cyclic voltammetry and chronoamperometry. The rate-limiting step of the charge transfer reaction was found to be a one-electron abstraction. The value of α, k, and D were calculated as 0.66, 6.7 × 10⁴ M⁻¹ s⁻¹, and 1.88 × 10⁻⁵ cm² s⁻¹, respectively. The modified electrode showed electrocatalytic activity toward the oxidation of PN and was used as an amperometric sensor. The sensor exhibited good linear response for PN over the concentration ranges 5-69 and 1-80 μM with detection limits of 0.51 and 0.87 μM, and sensitivities of 0.97 and 0.673 A M⁻¹ cm⁻² in batch and flow conditions, respectively. Some important advantages such as simple preparation, fast response, good stability, and reproducibility of the sensor for the amperometric determination of PN were achieved.     

Meldola blue immobilized on a new SiO2/TiO2/graphite composite for electrocatalytic oxidation of NADH

Meldola blue immobilized on a new SiO₂/TiO₂/graphite composite was applied in the electrocatalytic oxidation of NADH. The materials were prepared by the sol-gel processing method and characterized by several techniques including scanning electronic microscopy coupled to energy dispersive spectroscopy (SEM-EDS), X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electronic microscopy (HRTEM). Si and Ti mapping profiles on the surface showed a homogeneous distribution of the components. Ti2p binding energy peaks indicate that the formation of Si-O-Ti linkage is presumably the responsible for the high rigidity of the matrices. The good electrical conductivity presented by the composites (5 and 11 S cm⁻¹) can be related to a homogeneous distribution of graphite particles observed by TEM. After the materials characterization, a SiO₂/TiO₂/graphite electrode was prepared and some chemical modifications were performed on its surface to promote the adsorption of meldola blue. The resulting system presented electrocatalytic properties toward the oxidation of NADH, decreasing the oxidation potential to −120 mV. The proposed sensor showed a wide linear response range from 0.018 to 7.29 mmol l⁻¹ and limit of detection of 0.008 mmol l⁻¹. SiO₂/TiO₂/graphite has shown to be a promising material to be used as a suitable support in the construction of new electrochemical sensors.     

微波合成SnO2/活性炭粒子电极及降解4-氯酚

以甘蔗渣为原料,KOH为活化剂,SnCl₄·5H₂O为修饰剂,采用微波法制备了SnO₂/活性炭粒子电极,对其进行了表征,使用线性伏安法和循环伏安法分析了粒子电极的电化学性能,以4-氯酚为目标污染物进行电化学降解实验,对降解机理进行了探讨。结果表明,SnO2成功地负载于粒子电极表面。在微波功率640 W、微波时间15 min、质量分数10%的KOH、质量浓度200 g/L的SnCl₄·5H₂O条件下制备所得粒子电极显示出最高的电子传导系数和最大的电化学活性面积。在以DSA板作阳极,钛板作阴极的三维电极反应器中,电解4-氯酚的质量浓度500 mg/L的模拟废水150 min,4-氯酚去除率达到96.15%。