Numerous studies suggest that modification with functional nanomaterials can enhance the electrode electrocatalytic activity, sensitivity, and selectivity of the electrochemical sensors. Here, a ...highly sensitive and cost-effective disposable non-enzymatic glucose sensor based on copper(II)/reduced graphene oxide modified screen-printed carbon electrode is demonstrated. Facile fabrication of the developed sensing electrodes is carried out by the adsorption of copper(II) onto graphene oxide modified electrode, then following the electrochemical reduction. The proposed sensor illustrates good electrocatalytic activity toward glucose oxidation with a wide linear detection range from 0.10 mM to 12.5 mM, low detection limit of 65 µM, and high sensitivity of 172 μA mM
cm
along with satisfactory anti-interference ability, reproducibility, stability, and the acceptable recoveries for the detection of glucose in a human serum sample (95.6-106.4%). The copper(II)/reduced graphene oxide based sensor with the superior performances is a great potential for the quantitation of glucose in real samples.
Substitution of (Al3+, Nb5+) co–dopants into TiO6 octahedral sites of CaCu3Ti4O12 ceramics, which were prepared by a solid state reaction method and sintered at 1090°C for 18h, can cause a great ...reduction in a low–frequency loss tangent (tanδ≈0.045–0.058) compared to those of Al3+ or Nb5+ single–doped CaCu3Ti4O12. Notably, very high dielectric permittivities of 2.9−4.1×104 with good dielectric–temperature stability are achieved. The room–temperature grain boundary resistance (Rgb≈0.37–1.17×109Ω.cm) and related conduction activation energy (Egb≈0.781–0.817eV), as well as the non–Ohmic properties of the co–doped ceramics are greatly enhanced compared to single–doped ceramics (Rgb≈104–106Ωcm and Egb≈0.353–0.619eV). The results show the importance of grain boundary properties for controlling the nonlinear–electrical and giant–dielectric properties of CaCu3Ti4O12 ceramics, supporting the internal barrier layer capacitor model of Schottky barriers at grain boundaries.
Display omitted
•Decomposition of KNO3 to K2O was obtained at temperature above 500°C.•Increasing calcination temperature enlarged metal oxide crystallite size.•Increasing calcination temperature led ...to a harder reducibility of iron oxide.•CO2 conversion monotonically decreased with ascending calcination temperature.•The catalyst calcined at 700°C showed the highest olefins/paraffins ratio of 7.6.
Fe-Co/K-Al2O3 catalyst has been reported to be active and selective for olefin production from CO2 hydrogenation. However, the effect of calcination temperature on the physicochemical properties of Fe-Co/K-Al2O3 catalysts as well as their catalytic activity in CO2 hydrogenation to olefins has not yet been addressed. Here, we show that the calcination temperature (400–800°C) has significant impacts on metal oxides crystallite size, on the interaction between Fe2O3 and other metal oxides and on the transformation of potassium phases, which affect CO2 conversion, product selectivity as well as yield of olefins. The Fe-Co/K-Al2O3 catalyst calcined at 400°C achieves the highest CO2 conversion, hydrocarbons selectivity and olefins yield of 49.0%, 90.6% and 18.1%, respectively. The CO2 conversion and hydrocarbons selectivity decrease with ascending calcination temperature which is ascribed to the increase of metal oxides crystallite size, inducing stronger interactions between Fe2O3 and other metal oxides. Unlike the CO2 conversion and hydrocarbons selectivity, the olefins to paraffins (O/P) ratio followed a volcano-shaped trend as the function of calcination temperature with a maximum at 7.6 over the Fe-Co/K-Al2O3 catalyst calcined at 700°C. This volcanic trend is attributed to the interplay among the positive effect of high calcination temperature on the complete decomposition of KNO3 to K2O, a stronger interaction between Fe2O3 and K2O and the formation of KAlO2 phase, favorably suppressing the hydrogenation of olefins, and the negative effect of high calcination temperature on the increase of the particle size of the active phase and lower dispersion of mixed metal oxides due to a drastic decrease in BET surface area.
The influences of sintering temperature on the microstructure and giant dielectric properties of a new co-doped TiO2 system, i.e., V and Ta co-doped TiO2, were investigated. The grain size of ...(V1/2Ta1/2)0.01Ti0.99O2 ceramics was enlarged with increasing sintering temperature. Dense microstructure and homogeneous dispersion of dopants were achieved in the ceramics sintered at 1400–1500 °C for 5 h. The dielectric permittivity in the frequency range 40–106 Hz of the (V1/2Ta1/2)0.01Ti0.99O2 ceramics significantly increased with the mean grain size, while the dielectric loss tangent was reduced to 0.033 at 102 Hz. Furthermore, the high-temperature stability of the dielectric permittivity was improved with increasing mean grain size. The electrically heterogeneous microstructure consisting of semiconducting grains and insulating grain boundaries and/or surface layers was confirmed using impedance spectroscopy. The conduction inside the semiconducting grains was attributed to electron hopping between Ti4+ and Ti3+, which was confirmed by X-ray photoelectron spectroscopy. Very high resistivity with a large conduction activation energy of the insulating parts was suggested as the primary cause of the giant dielectric permittivity with low loss tangent.
•Sintering temperature has effects on microstructure and dielectric properties.•Correlation between grain size and giant dielectric permittivity was found in VTTO.•1% VTTO exhibited very low tanδ value of ≈0.033 with high ε′≈ε′≈7.07 × 103.•Giant−dielectric response was attributed to the interfacial polarization effect.
Giant dielectric behavior and electrical properties of monovalent cation/anion (Li+, F−) co‐doped CaCu3Ti4O12 ceramics prepared by a solid‐state reaction route were systematically investigated. ...Substitution of Li+ and F− led to a significantly enlarged mean grain size. A reduced loss tangent (tanδ ~0.06) with the retainment of an ultra‐high dielectric permittivity (ε′ ~7.7‐8.8 × 104) was achieved in the co‐doped ceramics, while the breakdown electric field and nonlinear coefficient of CaCu3Ti4O12 ceramics were increased by co‐doping with (Li+, F−). The variations in nonlinear electrical properties and giant dielectric response, as well as the dielectric relaxation, were well explained by the Maxwell‐Wagner polarization model for an electrically heterogeneous microstructure, in which a Schottky barrier height at the grain boundaries (GBs) was formed. ε′ was closely correlated to the GB capacitance. Significantly decreased tanδ value and enhanced nonlinear properties were related to a significant increase in the GB resistance, which was attributed to the significantly increased potential barrier height and conduction activation energy at the GBs. The semiconducting nature of the grains was also studied using X‐ray photoelectron spectroscopy and found to originate from the presence of Cu+ and Ti3+ ions.
Display omitted
•XANES and XPS confirm the nanocomposites exhibited the magnetic behavior.•XANES and XPS confirm the chemical compositions of GO, GO doped with Fe3O4 and Fe3O4/rGO reduced by ...glucose.•The Fe3O4/rGO modified MSPE demonstrated excellent electrochemical properties and good performance for the determination of ractopamine.•This proposed sensor was capable of determining RAC amounts of the actual pork samples with high recoveries.
A new disposable electrochemical sensor for rapid determination of ractopamine (RAC) is developed based on the use of a magnetic screen-printed electrode (MSPE) modified with an iron oxide magnetic nanoparticles doping on reduced graphene oxide (Fe3O4/rGO). Morphology, structure and composition of nanocomposites were characterized by TEM, x-ray absorption spectroscopy (XANES) and x-ray photoelectron spectroscopy (XPS). XANES results indicated that the prepared nanocomposites exhibited the magnetic behavior, and the original structure of Fe3O4 NPs was displayed after being successfully doped on the rGO. XPS was used to confirm the chemical compositions of GO, GO doped with Fe3O4 and Fe3O4/rGO reduced by glucose. The electrochemical and electrocatalytic characteristics of the modified MSPE were recorded using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) and the factors that affected the performance of the sensor were also optimized. The peak currents obtained by DPV increased linearly with the increasing of the concentration of RAC and the sensor had a detection range over the concentration ranges of 0.05–10 and 10–100 μM, with a detection limit of 13 nM (S/N = 3). Due to the Fe3O4/rGO promoting the electron transfer, and raising the sensitivity of the sensor, the proposed disposable sensor displayed a good sensitivity, stability and reproducibility and robust operation in spiked real pork samples.
Display omitted
•(Al1/2Ta1/2)0.05Ti0.95O2 exhibits a very low tanδ˜0.012 and high ε′˜104.•Excellent dielectric―temperature stability (Δε′˜2.69% at 150 °C) is achieved.•(Al1/2Ta1/2)0.05Ti0.95O2 ...exhibits nonlinear current-voltage properties.•Giant dielectric and electrical properties are originated at internal interfaces.
The nonlinear current-voltage and dielectric properties of (Al3++Ta5+) co-doped TiO2 (ATTO) ceramics are represented. Microstructural analysis reveals that sintered ceramics are highly dense and nonporous. ATTO ceramics exhibit low loss tangent (tanδ<0.1) and large dielectric permittivity (ε′˜103-104). Furthermore, ATTO ceramics exhibited nonlinear current-voltage characteristics. The best dielectric properties are achieved in the (Al1/2Ta1/2)0.05Ti0.95O2 ceramic with a very low tanδ (˜0.012) and high ε′ (˜104) with excellent dielectric-temperature stability with a temperature coefficient at 150 °C as low as 2.69%. The resistivity of insulating phases decreases with increasing Al3+ and Ta5+ concentrations, which is correlated to decreased breakdown voltage. The nonlinear electrical properties and dielectric response are explained based on the electrical response of internal interfaces.
The giant dielectric behavior of CaCu
3
Ti
4
O
12
(CCTO) has been widely investigated owing to its potential applications in electronics; however, the loss tangent (tan
δ
) of this material is too ...large for many applications. A partial substitution of CCTO ceramics with either Al
3+
or Ta
5+
ions generally results in poorer nonlinear properties and an associated increase in tan
δ
(to ~0.29–1.15). However, first-principles calculations showed that self-charge compensation occurs between these two dopant ions when co-doped into Ti
4+
sites, which can improve the electrical properties of the grain boundary (GB). Surprisingly, in this study, a greatly enhanced breakdown electric field (~200–6588 V/cm) and nonlinear coefficient (~4.8–15.2) with a significantly reduced tan
δ
(~0.010–0.036) were obtained by simultaneous partial substitution of CCTO with acceptor-donor (Al
3+
, Ta
5+
) dopants to produce (Al
3+
, Ta
5+
)-CCTO ceramics. The reduced tan
δ
and improved nonlinear properties were attributed to the synergistic effects of the co-dopants in the doped CCTO structure. The significant reduction in the mean grain size of the (Al
3+
, Ta
5+
)-CCTO ceramics compared to pure CCTO was mainly because of the Ta
5+
ions. Accordingly, the increased GB density due to the reduced grain size and the larger Schottky barrier height (
Φ
b
) at the GBs of the co-doped CCTO ceramics were the main reasons for the greatly increased GB resistance, improved nonlinear properties, and reduced tan
δ
values compared to pure and single-doped CCTO. In addition, high dielectric constant values (
ε
′ ≈ (0.52–2.7) × 10
4
) were obtained. A fine-grained microstructure with highly insulating GBs was obtained by Ta
5+
doping, while co-doping with Ta
5+
and Al
3+
resulted in a high
Φ
b
. The obtained results are expected to provide useful guidelines for developing new giant dielectric ceramics with excellent dielectric properties.
(Co, Nb) co-doped rutile TiO2 (CoNTO) nanoparticles with low dopant concentrations were prepared using a wet chemistry method. A pure rutile TiO2 phase with a dense microstructure and homogeneous ...dispersion of the dopants was obtained. By co-doping rutile TiO2 with 0.5 at.% (Co, Nb), a very high dielectric permittivity of ε′ ≈ 36,105 and a low loss tangent of tanδ ≈ 0.04 were achieved. The sample–electrode contact and resistive outer-surface layer (surface barrier layer capacitor) have a significant impact on the dielectric response in the CoNTO ceramics. The density functional theory calculation shows that the 2Co atoms are located near the oxygen vacancy, creating a triangle-shaped 2CoVoTi complex defect. On the other hand, the substitution of TiO2 with Nb atoms can form a diamond-shaped 2Nb2Ti complex defect. These two types of complex defects are far away from each other. Therefore, the electron-pinned defect dipoles cannot be considered the primary origins of the dielectric response in the CoNTO ceramics. Impedance spectroscopy shows that the CoNTO ceramics are electrically heterogeneous, comprised of insulating and semiconducting regions. Thus, the dielectric properties of the CoNTO ceramics are attributed to the interfacial polarization at the internal insulating layers with very high resistivity, giving rise to a low loss tangent.
In order to bridge the gap between academia and industry in the development of cathode active material for high-energy lithium-ion batteries (LIBs), several experimental factors reflecting commercial ...use need to be considered. Herein, based on a thick commercial level NMC811 electrode, we simply demonstrated the effect of charging protocols on the rate performance, cycling stability, and Li storage mechanism. A constant current charge/discharge, typically used in most publications, was found to exhibit worse rate capability and cycling stability compared to the constant current constant voltage (CCCV) mode of charge, used in commercial LIB cells due to the less uniform Li concentration gradient between the surface and bulk of the material. In operando XRD also revealed that there was no negative impact from the rapid change in lattice parameters towards cycling performance. We also found that the major degradation mechanism of Ni-rich NMC811 showing poor cycling performance across literature, can be mainly ascribed to the thick cathode electrolyte interphase (CEI) resistive layer, hindering Li intercalation at high rate and also lead to lower accessible capacity in each cycle. This work illustrates a simple example of the gaps between research in academic and industry that need to be narrowed for the development of practical high energy materials.
PDF
