Direct electron transfer and biosensing of glucose oxidase immobilized at multiwalled carbon nanotube-alumina-coated silica modified electrode

Investigations are reported regarding the direct electrochemical performance of glucose oxidase (GOD) immobilized on a film of multiwalled carbon nanotube-alumina-coated silica (MWCNT-ACS). The surface morphology of the GOD/MWCNT-ACS nanobiocomposite is characterized by scanning electron microscopy. In cyclic voltammetric response, the immobilized GOD displays a pair of well-defined redox peaks, with a formal potential (E°′) of ? 0.466 V versus Ag/AgCl in a 0.1 M phosphate buffer solution (pH 7.5) at a scan rate of 0.05 V s^? 1; also the electrochemical response indicates a surface-controlled electrode process. The dependence of formal potential on solution pH indicates that the direct electron transfer reaction of GOD is a reversible two-electron coupled with a two-proton electrochemical reaction process. The glucose biosensor based on the GOD/MWCNT-ACS nanobiocomposite shows a sensitivity of 0.127 A M^? 1 cm^? 2 and an apparent Michaelis–Menten constant of 0.5 mM. Furthermore, the prepared biosensor exhibits excellent anti-interference ability to the commonly co-existed uric acid and ascorbic acid.     

Electrochemical oxidation of adenosine-5′-triphosphate on a chitosan–graphene composite modified carbon ionic liquid electrode and its determination

In this paper a new electrochemical method was proposed for the determination of adenosine-5′-triphosphate (ATP) based on a chitosan (CTS) and graphene (GR) composite film modified carbon ionic liquid electrode (CTS–GR/CILE). CILE was fabricated by using ionic liquid 1-butyl-3-methylimidazolium dihydrogen phosphate ([BMIM]H₂PO₄) as the binder, which was further modified by GR and CTS composite. The modified electrode exhibited an excellent electrocatalytic activity toward the oxidation of ATP with the increase of the oxidation peak current and the decrease of the oxidation peak potential. The electrochemical parameters of ATP on CTS–GR/CILE were calculated with the electron transfer coefficient (α) as 0.329, the electron transfer number (n) as 2.15, the apparent heterogeneous electron transfer rate constant (ks) as 3.705 × 10^? 5 s^? 1 and the surface coverage (Γ_T) as 9.33 × 10^? 10 mol cm^? 2. Under the optimal conditions the oxidation peak current was proportional to ATP concentration in the range from 1.0 × 10^? 6 to 1.0 × 10^? 3 M with the detection limit of 0.311 μM (S/N = 3). The proposed electrode showed excellent reproducibility, stability, anti-interference ability and further successfully applied to the ATP injection sample detection.     

Synthesis and electrochemical properties of nanosized LiFeO2 particles with a layered rocksalt structure for lithium batteries

Layered rocksalt-type LiFeO₂ particles (O3-LiFeO₂) with average particle sizes of ca. 40 and 400 nm were synthesized by an ion exchange reaction from α-NaFeO₂ precursors. X-ray diffraction (XRD) patterns and scanning electron microscopy (SEM) images confirmed the formation of nanosized O3-LiFeO₂. 40-nm LiFeO₂ exhibited a higher discharge capacity (115 mAh g^?1) than 400-nm LiFeO₂ (80 mAh g^?1), and also had better rate characteristics. The downsizing effect and cation disorder between the lithium and iron layers may have improved the electrochemical activity of the LiFeO₂ particles. Transmission electron microscopy (TEM) observation indicated a phase transition from O3-LiFeO₂ to a cubic lattice system during the electrochemical process. The cubic lithium iron oxide exhibited stable electrochemical reactions based on the Fe²⁺/Fe³⁺ and Fe²⁺/Fe⁰ redox couples at voltages between 4.5 and 1.0 V. The discharge capacities of 40-nm LiFeO₂ were ca. 115, 210, and 390 mAh g^?1 under cutoff voltages of 4.5–2.0 V, 4.5–1.5 V, and 4.5–1.0 V, respectively.     

Determination of sulfamethoxazole in foods based on CeO2/chitosan nanocomposite-modified electrodes

An electrochemical immunosensor based on nanocomposite-modified glass carbon (GC) electrode has been developed. The biospecific surface was a CeO₂-chitosan (CHIT)-modified nanocomposite to which anti-sulfamethoxazole (SMX) polyclonal antibody (Ab) was immobilized. The assay was based on competition of SMX and horseradish peroxidase (HRP)–SMX to the antibody immobilized. Electrochemical voltammetry and impedance spectroscopy studies revealed that the presence of CeO₂-CHIT nanocomposite significantly enhanced conductivity of the electrode. The large electro-active surface area of nanoCeO₂-CHIT/GC electrode resulted in the high loading of anti-SMX polyclonal antibody. The electrochemical signals of the immunosensor mainly resulted from the HRP catalyzed hydrogen peroxide reduction in the presence of thionine. The immunosensor showed high sensitivity for the detection of SMX. The electrochemical response signals of the immunosensor were found to be linearly proportional to SMX concentration in the range from 5 × 10^? 7 to 5 × 10^? 4 mg mL^? 1 with a regression coefficient of 0.9935 and a detection limit of 3.25 × 10^? 7 mg mL^? 1. No cross-reactivity of antibodies with other antibiotics of sulfonamide family was found. Under optimal conditions, the immunosensor was successfully applied to the electrochemical determination of SMX in milk, honey and egg samples, showing excellent stability and anti-interference ability.     

Electrochemical horseradish peroxidase biosensor based on dextran–ionic liquid–V2O5 nanobelt composite material modified carbon ionic liquid electrode

Direct electrochemistry of horseradish peroxidase (HRP) was realized in a dextran (De), 1-ethyl-3-methylimidazolium ethylsulphate ([EMIM]EtOSO₃) and V₂O₅ nanobelt composite material modified carbon ionic liquid electrode (CILE). Spectroscopic results indicated that HRP retained its native structure in the composite. A pair of well-defined redox peaks of HRP appeared in pH 3.0 phosphate buffer solution with the formal potential of ?0.213 V (vs. SCE), which was the characteristic of HRP heme Fe(III)/Fe(II) redox couple. The result was attributed to the specific characteristics of De–IL–V₂O₅ nanocomposite and CILE, which promoted the direct electron transfer rate of HRP with electrode. The electrochemical parameters of HRP on the composite modified electrode were calculated and the electrocatalysis of HRP to the reduction of trichloroacetic acid (TCA) was examined. Under the optimal conditions the reduction peak current increased with TCA concentration in the range from 0.4 to 16.0 mmol L^?1. The proposed electrode is valuable for the third-generation electrochemical biosensor.     

Electrochemical properties of all solid state Li/S battery

All-solid-state lithium/sulfur (Li/S) battery is prepared using siloxane cross-linked network solid electrolyte at room temperature. The solid electrolytes show high ionic conductivity and good electrochemical stability with lithium and sulfur. In the first discharge curve, all-solid-state Li/S battery shows three plateau potential regions of 2.4 V, 2.12 V and 2.00 V, respectively. The battery shows the first discharge capacity of 1044 mAh g^?1-sulfur at room temperature. This first discharge capacity rapidly decreases in 4th cycle and remains at 512 mAh g^?1-sulfur after 10 cycles.     

Synthesis and characterization of V,Mo and Nb incorporated micro–mesoporous MCM-41 materials

Highly microporous metal-MCM-41 ordered mesoporous structure catalysts having different metal/Si (V, Mo, Nb) atomic ratios and combinations of metal sources were hydrothermally synthesized. The structural properties estimated using different techniques were found to be in agreement with each other. Metals were successfully incorporated into MCM-41 without deteriorating the ordered hexagonal structure. The metal ions in the synthesis solutions probably settled on the hydrophilic end of the template hence the metal incorporation resulted improvements in the micropore structure. Low loading of metals caused an increase in the surface area and pore volume values of the catalysts. The highest total (1310 m² g^?1) and micropore surface area values (1083 m² g^?1) were obtained by Nb incorporation. The micro- and mesopore dimensions of MCM-41 increased from 0.5 to 1.1 nm and from 2.5 to 2.8 nm, respectively, with metal incorporation. Low V/Si ratios and presence of Nb in the starting solution enhanced narrow mesopore size distribution. The pore dimension and wall thickness values estimated from nitrogen adsorption and X-ray diffraction methods were consistent with the corresponding values obtained using transmission electron microscopy.     

An innovative process to fabricate copper/diamond composite films for thermal management applications

Diamond dispersed copper matrix (Cu/D) composite films with strong interfacial bonding were produced by tape casting and hot pressing without carbide forming additives. The tape casting process offers an original solution to obtain laminated materials with accurate thickness control, smooth surface finish, material net-shaping, scalability, and low cost. This study presents an innovative process of copper submicronic particles deposition onto diamond reinforcements prior to densification by hot pressing. Copper particles act as chemical bonding agents between the copper matrix and the diamond reinforcements during hot pressing, thus offering an alternative solution to traditionnal carbide-forming materials in order to get efficient interfacial bonding and heat-transfer in Cu/D composites. It allows high thermal performances with low content of diamond, thus enhancing the cost-effectiveness of the materials. Microstructural study of composites by scanning electron microscopy (SEM) was correlated with thermal conductivity and thermal expansion coefficient measurements. The as-fabricated films exhibit a thermal conductivity of 455 W m^?1 K^?1 associated to a coefficient of thermal expansion of 12 × 10^?6 °C^?1 and a density of 6.6 g cm^?3 with a diamond volume fraction of 40%, which represents a strong enhancement relative to pure copper properties (λ_Cu = 400 W m^?1 K^?1, α_Cu = 17 × 10^?6 °C^?1, ρ_Cu = 8.95 g cm^?3). The as-fabricated composite films might be useful as heat-spreading layers for thermal management of power electronic modules.     

A novel fiber-reinforced polyethylene composite with added silicon nitride particles for enhanced thermal conductivity

A novel thermally conductive plastic composite was prepared from a mixture of silicon nitride (Si₃N₄) filler particles and an ultrahigh molecular weight polyethylene–linear low density polyethylene blend. The effects of Si₃N₄ particle sizes, concentration, and dispersion on the thermal conductivity and relevant dielectric properties were investigated. With proper fabrication the Si₃N₄ particles could form a continuously connected dispersion that acted as the dominant thermally conductive pathway through the plastic matrix. By adding 0–20% Si₃N₄ filler particles, the composite thermal conductivity was increased from 0.2 to ～1.0 W m^?1 K^?1. Also, the composite thermal conductivity was further enhanced to 1.8 W m^?1 K^?1 by decreasing the Si₃N₄ particle sizes from 35, 3 and 0.2 μm, and using coupling agent, for the composites with higher filler content. Alumina short fibers were then added to improve the overall composite toughness and strength. Optimum thermal, dielectric and mechanical properties were obtained for a fiber-reinforced polyethylene composite with 20% total alumina–Si₃N₄ (0.2 μm size) filler particles.     

Electrocatalytical oxidation and sensitive determination of acetaminophen on glassy carbon electrode modified with graphene–chitosan composite

The electrochemical behaviors of acetaminophen (ACOP) on a graphene–chitosan (GR–CS) nanocomposite modified glassy carbon electrode (GCE) were investigated by cyclic voltammetry (CV), chronocoulometry (CC) and differential pulse voltammetry (DPV). Electrochemical characterization showed that the GR–CS nanocomposite had excellent electrocatalytic activity and surface area effect. As compared with bare GCE, the redox signal of ACOP on GR–CS/GCE was greatly enhanced. The values of electron transfer rate constant (k_s), diffusion coefficient (D) and the surface adsorption amount (Γ^?) of ACOP on GR–CS/GCE were determined to be 0.25 s^? 1, 3.61 × 10^? 5 cm² s^? 1 and 1.09 × 10^? 9 mol cm^? 2, respectively. Additionally, a 2e^?/2H⁺ electrochemical reaction mechanism of ACOP was deduced based on the acidity experiment. Under the optimized conditions, the ACOP could be quantified in the range from 1.0 × 10^? 6 to 1.0 × 10^? 4 M with a low detection limit of 3.0 × 10^? 7 M based on 3S/N. The interference and recovery experiments further showed that the proposed method is acceptable for the determination of ACOP in real pharmaceutical preparations.     

Fabrication of ultrahigh hydrogen barrier polyethyleneimine/graphene oxide films by LBL assembly fine-tuned with electric field application

In this study, layer-by-layer self-assembly of polyethyleneimine (PEI)/graphene oxide (GO) was successfully controlled by an applied electric field. The influences of the applied electric field direction, voltage, and dipping time on the hydrogen barrier properties of PEI/GO self-assembled film were investigated. Ultraviolet–visible light absorption spectroscopy, ellipsometry, atomic force microscopy, and scanning electron microscopy were used to analyze the effects of the electric field on the growth, nanostructure, and micromorphology of the self-assembled film. Results indicated that an applied electric field accelerates the adsorption rate of assembly and increases the GO adsorption quantity. Additionally, such electric field modifies the composite structure of the self-assembled film and spreads out the GO sheets uniformly on the substrate, which results in the formation of a more compact and ordered gas barrier layer with significantly improved hydrogen barrier properties. Higher applied voltage results in a more noticeable field effect. Under 25 V, the hydrogen transmission rate of the PEI/GO self-assembled 10-layer film reached 81 cm³/m² 24 h 0.1 MPa, which was 65% lower than that of standard composite films prepared without using an electric field.     

Behaviour of hybrid fibre reinforced concrete beam–column joints under reverse cyclic loads

An experimental investigation was carried out to study the effect of hybrid fibres on the strength and behaviour of High performance concrete beam column joints subjected to reverse cyclic loads. A total of 12 reinforced concrete beams column joints were cast and tested in the present investigation. High performance concrete of M60 grade was designed using the modified ACI method suggested by Aïtcin. Crimped steel fibres and polypropylene fibres were used in hybrid form. The main variables considered were the volume fraction of (i) crimped steel fibres viz. 0.5% (39.25 kg/m³) and 1.0% (78.5 kg/m³) and (ii) polypropylene fibres viz. 0.1% (0.9 kg/m³), 0.15% (1.35 kg/m³), and 0.2% (1.8 kg/m³). Addition of fibres in hybrid form improved many of the engineering properties such as the first crack load, ultimate load and ductility factor of the composite. The combination of 1% (78.5 kg/m³) volume fraction of steel fibres and 0.15% (1.35 kg/m³) volume fraction of polypropylene fibres gave better performance with respect to energy dissipation capacity and stiffness degradation than the other combinations.     

Trypsin immobilization on discs of polyvinyl alcohol glutaraldehyde/polyaniline composite

Discs of polyvinyl alcohol cross-linked with glutaraldehyde (PVAG) were synthesized and covered with polyaniline activated with glutaraldehyde (PANIG). Trypsin was covalently immobilized on this composite yielding a preparation containing 21.1 units per disc. The FT-IR spectra of the discs showed bands of PVA (3300 cm^?1, 2930 cm^?1 and 1440 cm^?1) and PANI (1594 cm^?1 and 1100 cm^?1). The best immobilization conditions were: trypsin concentration at 0.2 mg mL^?1, pH 7.6 and 60 min of incubation, similar to polyaniline–trypsin systems reported in the literature. The PVAG–PANIG–trypsin derivative showed an optimal pH and an optimal temperature of 7.0 and 35 °C, respectively. Hydrolysis of casein showed variations in the size of the products, revealing differences between the immobilized enzyme and the mechanism catalyzed by the native enzyme.     

Fabrication and characterization of a zirconia/multi-walled carbon nanotube mesoporous composite

A zirconia/multi-walled carbon nanotube (ZrO₂/MWCNT) mesoporous composite was fabricated via a simple method using a hydrothermal process with the aid of the cationic surfactant cetyltrimethylammonium bromide (CTAB). Transmission electron microscopy (TEM), N₂ adsorption–desorption, Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) techniques were used to characterize the as-made samples. The cubic ZrO₂ nanocrystallites were observed to overlay the surface of MWCNTs, which resulted in the formation of a novel mesoporous–nanotube composite. On the basis of a TEM analysis of the products from controlled experiment, the role of the acid-treated MWCNTs and CTAB was proposed to explain the formation of the mesoporous–nanotube structure. The as-made composite possessed novel properties, such as a high surface area (312 m² · g^? 1) and a bimodal mesoporous structure (3.18 nm and 12.4 nm). It was concluded that this composite has important application value due to its one-dimensional hollow structure, excellent electric conductivity and large surface area.     

Polyaniline–MWCNT nanocomposites for microwave absorption and EMI shielding

Highly conducting polyaniline (PANI)–multi-walled carbon nanotube (MWCNT) nanocomposites were prepared by in situ polymerization. The FTIR and XRD show systematic shifting of the characteristic bands and peaks of PANI, with the increase in MWCNT phase, suggesting significant interaction between the phases. The SEM and TEM pictures show thick and uniform coating of PANI over surface of individual MWCNT. Based on observed morphological features in SEM, the probable formation mechanism of these composites has been proposed. The electrical conductivity of PANI–MWCNT composite (19.7 S cm^?1) was even better than MWCNT (19.1 S cm^?1) or PANI (2.0 S cm^?1). This can be ascribed to the synergistic effect of two complementing phases (i.e. PANI and MWCNT). The absorption dominated total shielding effectiveness (SE) of ?27.5 to ?39.2 dB of these composites indicates the usefulness of these materials for microwave shielding in the Ku-band (12.4–18.0 GHz). These PANI coated MWCNTs with large aspect ratio are also proposed as hybrid conductive fillers in various thermoplastic matrices, for making structurally strong microwave shields.     

Hydrogen production from water splitting of real-time industry effluent using novel photocatalyst

The simultaneous degradation of real-time industrial effluent and hydrogen production was carried out in this study, taking into account the global clean energy demand. A novel photocatalyst based on a metal–organic framework and spindle-shaped titanium dioxide nanoparticles was synthesized to perform photocatalytic water splitting reactions. The resulting composite (MIL-53@TiO_2, MIL: Matériaux de l′Institut Lavoisier) was characterized by standard analytical methods. The photocatalytically active MIL-53@TiO₂ composite produced hydrogen without using any sacrificial agents. The hydrogen production was observed to be 0.26 mmol in the presence of TiO₂ which increased to 7.9 mmol in the presence of MIL-53@TiO₂ composite after 180 min of irradiation. The corresponding hydrogen evolution rate was 26.33 mmol h^-1g^?1, which was observed 30 times higher than the pristine materials. The remarkable photoactivity was due the superior charge separation property and less recombination of the charge carrier pair in the MIL-53@TiO₂ composite. Furthermore, the photocatalyst exhibited excellent reusability for hydrogen production up to 4 cycles. The results shown in the present work may be extended for large-scale applications.     

Novel Ag@TiO2 nanocomposite synthesized by electrochemically active biofilm for nonenzymatic hydrogen peroxide sensor

A novel nonenzymatic sensor for H₂O₂ was developed based on an Ag@TiO₂ nanocomposite synthesized using a simple and cost effective approach with an electrochemically active biofilm. The optical, structural, morphological and electrochemical properties of the as-prepared Ag@TiO₂ nanocomposite were examined by UV–vis spectroscopy, X-ray diffraction, transmission electron microscopy and cyclic voltammetry (CV). The Ag@TiO₂ nanocomposite was fabricated on a glassy carbon electrode (GCE) and their electrochemical performance was analyzed by CV, differential pulse voltammetry and electrochemical impedance spectroscopy. The Ag@TiO₂ nanocomposite modified GCE (Ag@TiO₂/GCE) displayed excellent performance towards H₂O₂ sensing at ? 0.73 V in the linear response range from 0.83 μM to 43.3 μM, within a detection limit and sensitivity of 0.83 μM and ~ 65.2328 ± 0.01 μAμM^? 1 cm^? 2, respectively. In addition, Ag@TiO₂/GCE exhibited good operational reproducibility and long term stability.     

Preparation and characterization of copper nanoparticles/zinc oxide composite modified electrode and its application to glucose sensing

We report a new method for selective detection of d(+)-glucose using a copper nanoparticles (Cu-NPs) attached zinc oxide (ZnO) film coated electrode. The ZnO and Cu-NPs were electrochemically deposited onto indium tin oxide (ITO) coated glass electrode and glassy carbon electrode (GCE) by layer-by-layer. In result, Cu-NPs/ZnO composite film topography was characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM), respectively. SEM and AFM confirmed the presence of nanometer sized Cu-NPs/ZnO composite particles on the electrode surface. In addition, X-ray diffraction pattern revealed that Cu-NPs and ZnO films were attached onto the electrode surface. Indeed, the Cu-NPs/ZnO composite modified electrode showed excellent electrocatalytic activity for glucose oxidation in alkaline (0.1 M NaOH) solution. Further, we utilized the Cu-NPs/ZnO composite modified electrode as an electrochemical sensor for detection of glucose. This glucose sensor showed a linear relationship in the range from 1 × 10^? 6 M to 1.53 × 10^? 3 M and the detection limit (S/N = 3) was found to be 2 × 10^? 7 M. The Cu-NPs/ZnO composite as a non-enzymatic glucose sensor presents a number of attractive features such as high sensitivity, stability, reproducibility, selectivity and fast response. The applicability of the proposed method to the determination of glucose in human urine samples was demonstrated with satisfactory results.     

Electroanalytical properties and application of anthraquinone derivative-functionalized multiwalled carbon nanotubes nanowires modified glassy carbon electrode in the determination of dissolved oxygen

We herein report a simple, low cost and green preparation of nanowires of (anthraquinone-2-carboxylic acid/amino functionalized) multiwalled carbon nanotubes (HOOC-2-AQ/AMWCNTs) which has been further employed for the development of highly sensitive oxygen sensor. The prepared composite has been characterized by TEM and electrochemical studies. The glassy carbon electrode modified with composite shows an irreversible and good electrocatalytic activity for the reduction of oxygen. The reduction potential of the oxygen was shifted 460 mV towards the positive potential with this modified electrode as compared to bare glassy carbon electrode. The prepared material was stable with no leaching observed of the mediator. A linear response range of 0.2–6.8 mg L^?1, with a sensitivity of 5.0 μA L mg^?1 and a detection limit of 0.02 mg L^?1 were obtained with this sensor.     

Measuring the eco-efficiency of cement use

At present, the cement industry generates approximately 5% of the world’s anthropogenic CO₂ emissions. This share is expected to increase since demand for cement based products is forecast to multiply by a factor of 2.5 within the next 40 years and the traditional strategies to mitigate emissions, focused on the production of cement, will not be capable of compensating such growth. Therefore, additional mitigation strategies are needed, including an increase in the efficiency of cement use. This paper proposes indicators for measuring cement use efficiency, presents a benchmark based on literature data and discusses potential gains in efficiency. The binder intensity (bi) index measures the amount of binder (kg m^?3) necessary to deliver 1 MPa of mechanical strength, and consequently express the efficiency of using binder materials. The CO₂ intensity index (ci) allows estimating the global warming potential of concrete formulations. Research benchmarks show that bi ～5 kg m^?3 MPa^?1 are feasible and have already been achieved for concretes >50 MPa. However, concretes with lower compressive strengths have binder intensities varying between 10 and 20 kg m^?3 MPa^?1. These values can be a result of the minimum cement content established in many standards and reveal a significant potential for performance gains. In addition, combinations of low bi and ci are shown to be feasible.