Development and applications of quaternary ammonium (QA) membrane electrodes in pharmaceutical preparation and in bioavailability of Prostaglandin E1 and Deoxycholate

The two novel ion-pairs (PB-TPB and NB-TPB) of quaternary ammonium drugs; propantheline bromide (PB), N,N-Diisopropyl-N-methyl-N-[2-(xanthen-9ylcarbonyloxy)ethyl] ammonium bromide and neostigmine bromide (NB), 3-(dimethylcarbamoyloxy) phenyl]-trimethylazanium have been synthesized, respectively and incorporated in poly (vinyl chloride)-based membrane electrodes for the quantification of propantheline bromide and neostigmine bromide in different pharmaceutical preparations. The influences of membrane compositions on the potentiometric responses of membrane electrodes have been found to substantially improve the performance characteristics. The best performance was reported with membranes having composition (w/w) of PB-TPB or NB-TPB (6%): PVC (34%): o-NPOE (60%). The proposed electrodes exhibit nernstian response in the concentration ranges of 2.1 × 10⁻⁷ M to 1.0 × 10⁻² M and 4.4 × 10⁻⁷ M to 1.0 × 10⁻² M with detection limit of 1.5 × 10⁻⁷ M and 3.3 × 10⁻⁷ M, respectively. Both the membrane electrodes perform satisfactorily over pH ranges of (3.5–7.5 and 4.0–7.0) with fast response times (11 s and 13 s), respectively. These drugs (PB and NB) were further utilized as different ion-pairs of Prostaglandin E₁ (PGE₁) and Deoxycholate (DOC) in poly (vinyl chloride)-based membrane electrodes for the determination of bioavailability of Prostaglandin E₁ and Deoxycholate in plasma of different patients.     

Amperometric detection of hydrogen peroxide at nano-nickel oxide/thionine and celestine blue nanocomposite-modified glassy carbon electrodes

A simple procedure was developed to prepare a glassy carbon (GC) electrode modified with nickel oxide (NiOx) nanoparticles and water-soluble dyes. By immersing the GC/NiOx modified electrode into thionine (TH) or celestine blue (CB) solutions for a short period of time (5–120 s), a thin film of the proposed molecules was immobilized onto the electrode surface. The modified electrodes showed stable and a well-defined redox couples at a wide pH range (2–12), with surface confined characteristics. In comparison to usual methods for the immobilization of dye molecules, such as electropolymerization or adsorption on the surface of preanodized electrodes, the electrochemical reversibility and stability of these modified electrodes have been improved. The surface coverage and heterogeneous electron transfer rate constants (k_s) of thionin and celestin blue immobilized on a NiOx-GC electrode were approximately 3.5 × 10⁻¹⁰ mol cm⁻², 6.12 s⁻¹, 5.9 × 10⁻¹⁰ mol cm⁻² and 6.58 s⁻¹, respectively. The results clearly show the high loading ability of the NiOx nanoparticles and great facilitation of the electron transfer between the immobilized TH, CB and NiOx nanoparticles. The modified electrodes show excellent electrocatalytic activity toward hydrogen peroxide reduction at a reduced overpotential. The catalytic rate constants for hydrogen peroxide reduction at GC/NiOx/CB and GC/NiOx/TH were 7.96 (±0.2) × 10³ M⁻¹ s⁻¹ and 5.5 (±0.2) × 10³ M⁻¹ s⁻¹, respectively. The detection limit, sensitivity and linear concentration range for hydrogen peroxide detection were 1.67 μM, 4.14 nA μM⁻¹ nA μM⁻¹ and 5 μM to 20 mM, and 0.36 μM, 7.62 nA μM⁻¹, and 1 μM to 10 mM for the GC/NiOx/TH and GC/NiOx/CB modified electrodes, respectively. Compared to other modified electrodes, these modified electrodes have many advantages, such as remarkable catalytic activity, good reproducibility, simple preparation procedures and long-term stabilities of signal responses during hydrogen peroxide reduction.     

Photodegradation of tetrahalobisphenol-A (X = Cl, Br) flame retardants and delineation of factors affecting the process

The photoassisted degradation (HPLC-UV absorption), dehalogenation (HPLC-IC) and mineralization (TOC decay) of the flame retardants tetrabromobisphenol-A (TBBPA) and tetrachlorobisphenol-A (TCBPA) were examined in UV-irradiated alkaline aqueous TiO₂ dispersions (pH 12), and for comparison the parent bisphenol-A (BPA, an endocrine disruptor) in pH 4–12 aqueous media to assess which factor impact most on the photodegradative process. Complete degradation (2.7–2.8 × 10⁻² min⁻¹) and dehalogenation (1.8 × 10⁻² min⁻¹) of TBBPA and TCBPA occurred within 2 h of UV irradiation, whereas only 45–60% mineralization (2.3–2.7 × 10⁻³ min⁻¹) was complete within 5 h for the flame retardants at pH 12 and ca. 80% for the parent BPA. Factors examined in the pH range 4–12 that impact the degradation of BPA were the point of zero charge of TiO₂ particles (pH_pzc; electrophoretic method), particle or aggregate sizes of TiO₂ (light scattering), and the relative number of OH radicals (as DMPO–OH adducts; ESR spectroscopy) produced in the UV-irradiated dispersion. Dynamics of BPA degradation (2.0–2.4 × 10⁻² min⁻¹) were pH-independent and independent of particle/aggregate size, but did correlate with the number of OH radicals, at least at pHs 4 to 8–9, after which the rates decreased somewhat at pH > 9 with decreasing adsorption owing to Coulombic repulsive forces between the very negative TiO₂ surface and the anionic forms of BPA (pK_as ca. 9.6–11.3), even though the number of OH radicals continued to increase at the higher pHs.     

Carbon nanotube-supported Pd–ZnO catalyst for hydrogenation of CO2 to methanol

A type of Pd–ZnO catalysts supported on multi-walled carbon nanotubes (MWCNTs) were developed, with excellent performance for CO₂ hydrogenation to methanol. Under reaction conditions of 3.0 MPa and 523 K, the observed turnover-frequency of CO₂ hydrogenation reached 1.15 × 10⁻² s⁻¹ over the 16%Pd_0.1Zn₁/CNTs(h-type). This value was 1.17 and 1.18 times that (0.98 × 10⁻² and 0.97 × 10⁻² s⁻¹) of the 35%Pd_0.1Zn₁/AC and 20%Pd_0.1Zn₁/γ-Al₂O₃ catalysts with the respective optimal Pd_0.1Zn₁-loading. Using the MWCNTs in place of AC or γ-Al₂O₃ as the catalyst support displayed little change in the apparent activation energy for the CO₂ hydrogenation, but led to an increase of surface concentration of the Pd⁰-species in the form of PdZn alloys, a kind of catalytically active Pd⁰-species closely associated with the methanol generation. On the other hand, the MWCNT-supported Pd–ZnO catalyst could reversibly adsorb a greater amount of hydrogen at temperatures ranging from room temperature to 623 K. This unique feature would help to generate a micro-environment with higher concentration of active H-adspecies at the surface of the functioning catalyst, thus increasing the rate of surface hydrogenation reactions. In comparison with the “Parallel-type (p-type)” MWCNTs, the “Herringbone-type (h-type)” MWCNTs possess more active surface (with more dangling bonds), and thus, higher capacity for adsorbing H₂, which make their promoting action more remarkable.     

Gasification of charcoal using supercritical CO2 at high pressures

A novel one-shell high temperature and high pressure semi-continuous reactor has been developed for the study of the Boudouard reaction at temperatures up to 820 °C and pressures up to 32.5 MPa. Semicontinuous gasification of charcoal using supercritical CO₂ has been achieved at conversions up to 90.8% (w/w) at LSHV between 20 and 30 h⁻¹ after 5–9 h. A gasification model is proposed and validated. Effective rates of gasification (1.32 ± 0.12) × 10⁻⁶ to (6.10 ± 2.03) × 10⁻⁵ s⁻¹ were obtained. The results indicated that this method is technically feasible for the on-line production of high pressures streams of CO/CO₂ in the lab for carrying out further chemistries, avoiding the use of CO high pressure bottles.     

Novel coated graphite electrode for the selective determination of Gd(III) in rocks and waste water samples

A novel gadolinium selective coated graphite electrode based on 2,6-bis-[1-{N-cyanopropyl,N-(2-methylpridyl)}aminoethyl]pyridine [P] is described. The best performance was exhibited by the electrode having membrane composition P:NaTPB:PVC:NPOE as 8:4:30:58 (%, w/w). The electrode demonstrates excellent potentiometric characteristics towards gadolinium ion over several interfering ions. The electrode exhibited a Nernstian response to Gd³⁺ ion over a wide concentration range 2.8 × 10⁻⁷ to 5.0 × 10⁻² M with a detection limit (6.3 ± 0.1) × 10⁻⁸ M and slope 19.6 ± 0.1 mV decade⁻¹ of a_Gd³⁺. Furthermore, it showed a fast response time (12 s) and can be used for 2.5 months without significant divergence in its characteristics. Noticeably, the electrode can tolerate the concentration of different surfactants up to 1.0 × 10⁻⁴ M and can be used successfully in 30% (v/v) ethanol media and 10% (v/v) methanol and acetonitrile water mixture. The useful pH range of this sensor is 2.0 to 8.0. It is sufficiently selective and can be used for the determination of Gd³⁺ ions in waste water and rock samples. It also serves as a good indicator in the potentiometric titration of GdCl₃ with EDTA.     

Electrical properties of V2O5–WO3/TiO2 EUROCAT catalysts evidence for redox process in selective catalytic reduction (SCR) deNOx reaction

Electrical conductivity measurements on EUROCAT V₂O₅–WO₃/TiO₂ catalyst and on its precursor without vanadia were performed at 300°C under pure oxygen to characterize the samples, under NO and under NH₃ to determine the mode of reactivity of these reactants and under two reaction mixtures ((i) 2000 ppm NO + 2000 ppm NH₃ without O₂, and (ii) 2000 ppm NO + 2000 ppm NH₃ + 500 ppm O₂) to put in evidence redox processes in SCR deNO_x reaction.It was first demonstrated that titania support contains certain amounts of dissolved W⁶⁺ and V⁵⁺ ions, whose dissolution in the lattice of titania creates an n-type doping effect. Electrical conductivity revealed that the so-called reference pure titania monolith was highly doped by heterovalent cations whose valency was higher than +4. Subsequent chemical analyses revealed that so-called pure titania reference catalyst was actually the WO₃/TiO₂ precursor of V₂O₅–WO₃/TiO₂ EUROCAT catalyst. It contained an average amount of 0.37 at.% W⁶⁺dissolved in titania, i.e. 1.07 × 10²⁰ W⁶⁺ cations dissolved/cm³ of titania. For the fresh catalyst, the mean amounts of W⁶⁺ and V⁵⁺ ions dissolved in titania were found to be equal to 1.07 × 10²⁰ and 4.47 × 10²⁰ cm⁻³, respectively. For the used catalyst, the mean amounts of W⁶⁺ and V⁵⁺ ions dissolved were found to be equal to 1.07 × 10²⁰ and 7.42 × 10²⁰ cm⁻³, respectively. Since fresh and used catalysts have similar compositions and similar catalytic behaviours, the only manifestation of ageing was a supplementary progressive dissolution of 2.9 × 10²⁰ additional V⁵⁺ cations in titania.After a prompt removal of oxygen, it appeared that NO alone has an electron acceptor character, linked to its possible ionosorption as NO⁻ and to the filling of anionic vacancies, mostly present on vanadia. Ammonia had a strong reducing behaviour with the formation of singly ionized vacancies. A subsequent introduction of NO indicated a donor character of this molecule, in opposition to its first adsorption. This was ascribed to its reaction with previously adsorbed ammonia strongly bound to acidic sites. Under NO + NH₃ reaction mixture in the absence of oxygen, the increase of electrical conductivity was ascribed to the formation of anionic vacancies, mainly on vanadia, created by dehydroxylation and dehydration of the surface. These anionic vacancies were initially subsequently filled by the oxygen atom of NO. N^o atoms, resulting from the dissociation of NO and from ammonia dehydrogenation, recombined into dinitrogen molecules. The reaction corresponded to

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. In the presence of oxygen, NO did not exhibit anymore its electron acceptor character, since the filling of anionic vacancies was performed by oxygen from the gas phase. NO reacted directly with ammonia strongly bound on acidic sites. A tentative redox mechanism was proposed for both cases.     

PTFE-F-PbO2 电极在H2SO4溶液中的析氧行为

F-PbO2 electrode and polytetrafluoroethylene （PTFE） doped F-PbO2 electrode （PTFE-F-PbO2） were prepared on a plexiglas sheet substrate by a series of procedure including chemical and electrochemical depositions. The electrochemical activities of these two electrodes for oxygen evolution （OE） reaction were examined by electrochemical tests. In comparison with F-PbO2, PTFE-F-PbO2 electrode exhibited larger active surface area and higher oxygen vacancy deficiency, which resulted in its higher electrocatalytic activity for OE. In addition, both exchange current density and activation energy of the electrodes for OE were calculated in terms of active surface area. The values of exchange current density and activation energy in 0.5 mol·L^-1 H2SO4 aqueous solution were 1.125×10^ -3 mA·cm^-2 and 18.62 kJ·mol^-1 for PTFE-F-PbO2, and 8.384×10^-4 mA·cm^- 2 and 28.98 kJ·mol^-1 for F-PbO2, respectively. Because these values are calculated on the basis of the active surface areas of the electrodes, the enhanced activity of PTFE-F-PbO2 can be attributed to an increase in oxygen vacancy deficiency of PbO2 due to doping by PTFE. The influence of PTFE adulteration on the activity of PbO2 film electrode for OE was investigated in detail in this study.     

Electrochemical performance of Li3V2(PO4)3/C cathode material using a novel carbon source

Polyethylene glycol (PEG, mean molecular weight of 10,000) has been used to prepare a Li₃V₂(PO₄)₃/C cathode material by a simple solid-state reaction. The Raman spectra shows that the coating carbon has a good structure with a low I_D/I_G ratio. The images of SEM and TEM show that the carbon is dispersed between the Li₃V₂(PO₄)₃ particles, which improves the electrical contact between the corresponding particles. The electronic conductivity of Li₃V₂(PO₄)₃/C composite is 7.0 × 10⁻¹ S/cm, increased by seven orders of magnitude compared with the pristine Li₃V₂(PO₄)₃ (2.3 × 10⁻⁸ S/cm). At a low discharge rate of 0.28C, the sample presents a high discharge capacity of 131.2 mAh/g, almost achieving the theoretical capacity (132 mAh/g) for the reversible cycling of two lithium. After 500 cycles, the discharge capacity is 123.9 mAh/g with only 5.6% fading of the initial specific capacity. The Li₃V₂(PO₄)₃/C material also exhibits an excellent rate capability with high discharge capacities of 115.2 mAh/g at 1C and 106.4 mAh/g at 5C.     

ZnBO-doped (Ba, Sr)TiO3 ceramics for the low-temperature sintering process

ZnBO-doped (Ba, Sr)TiO₃ ceramics were investigated for low-temperature co-fired ceramics (LTCCs) applications. Until now, B₂O₃ and Li₂CO₃ dopants have been commonly employed as the low-temperature sintering aids. In this paper, we suggest ZnBO as an alternative dopant to the B₂O₃ and Li₂CO₃. To reduce the sintering temperature of (Ba, Sr)TiO₃, we have added 1–5 wt.% of ZnBO to (Ba, Sr)TiO₃. ZnBO-doped (Ba, Sr)TiO₃ ceramics were respectively sintered from 750 to 1350 °C by 50 °C to confirm the sintering temperature with different dopant contents. By adding 5 wt.% of ZnBO to the (Ba, Sr)TiO₃ ceramics, the sintering temperature of (Ba, Sr)TiO₃ ceramics can be reduced to 1100 °C. From the XRD analysis, ZnBO-doped (Ba, Sr)TiO₃ has no pyro phase. By adding ZnBO dopants to (Ba, Sr)TiO₃ ceramics, both of relative dielectric permittivity and loss tangent were decreased. From the frequency dispersion of dielectric properties, the relative dielectric permittivity and loss tangent of 5 wt.% ZnBO-doped (Ba, Sr)TiO₃ were 1180 and 3.3 × 10⁻³, while those of BST were 1585 and 4.8 × 10⁻³, respectively.     

Preparation and electrochemical properties of functionalized ionic liquid self-assembled modified graphite electrode

A modified graphite electrode with functionalized ionic liquid (IL) pyridinium derivative of β-cyclodextrin ([CDbPy]BF₄) was prepared by layer-by-layer self-assembly technique. With ferrocene as probe, the characterization of the (CDIL/PDDA)_n/GE SAMs in the solution of phosphate (PBS, pH 7.0) was investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronocoulometry. The electrochemical behavior of p-chloronitrobenzene (p-CNB) at the modified electrode was studied. It was found that the modified electrode could catalyze the reduction of p-CNB and made the cathode peak move about 100 mV in positive direction in the solution of 0.1 mol/L PBS (pH 7.0). Differential pulse voltammetry (DPV) was applied to the determination of p-CNB in waste water with satisfactory results. The detection limit and the linear range of the concentration of p-CNB to the reduction peak current were 8.0 × 10⁻⁸ mol/L and 3.0 × 10⁻⁷–1.0 × 10⁻⁵ mol/L, respectively.     

Decomposition of ozone on Ag/SiO2 catalyst for abatement of waste gases emissions

A silica-supported Ag system made by the incipient wetness impregnation method was investigated in the reaction of heterogeneous catalytic decomposition of ozone. It was established that the catalytic ozone decomposition on Ag/SiO₂ proceeded in the temperature interval −40 °C to 25 °C as a first order reaction with activation energy of 65 kJ/mol (pre-exponential factor 5.0 × 10¹⁴ s⁻¹). Based on the results from the instrumental methods (SEM, XRD, XPS, EPR, TPD) it can be concluded that in presence of ozone the silver is oxidized to a complicated mixture of Ag₂O₃ and AgO. Due to the high activity and stability of the Ag/SiO₂ catalyst, it is promising for neutralization of waste gases containing ozone.     

Solubilities of actinides in a domestic groundwater and a bentonite porewater calculated by using PHREEQC

This study presents the solubilities and speciations of actinides, calculated by the PHREEQC (V.2) code in a granitic groundwater and a Ca-bentonite porewater under a reducing condition. The respective solubilities for the amorphous U, Am, Th, Np and Pu compounds in the groundwater were 2.2 × 10⁻⁵, 1.2 × 10⁻⁷, 3.1 × 10⁻⁹, 3.4 × 10⁻⁹ and 6.3 × 10⁻¹¹ mole/L, and these values are comparable to the results calculated by the MUGREM and EQ3/6 codes. The major dissolved species for U, Am, Th, Np and Pu were UO₂(OH)₃⁻, Am(OH)₂⁺, Th(OH)₄(aq), Np(OH)₃CO₃⁻ and Pu(OH)₃CO₃⁻, respectively. However, carbonate complex ions were anticipated as the major species in the porewater except for thorium due to an increase of the carbonate concentration and a decrease of the pH.     

Application of silica gel as an effective modifier for the voltammetric determination of dopamine in the presence of ascorbic acid and uric acid

Amorphous silica gel modified carbon paste electrode (CPE) offers substantial improvements in voltammetric sensitivity and selectivity towards determination of dopamine (DA). Cyclic voltammetry of Fe(CN)₆^3−/4− as a negatively charged probe revealed that the surface of the silica gel modified carbon paste electrode had a high density of negative charge at pH 8.0. Therefore, the modified electrode adsorbed DA (pK_a = 8.9) and enhanced its voltammetric response while repulsed ascorbic acid (AA) (pK_a = 4.2) and uric acid (UA) (pK_a = 5.4) and inhibited their interfering effects. The influence of various experimental parameters including percent of silica gel in the CPE, pH of solution, and accumulation time and potentials, on the voltammetric response of DA was investigated. At the optimum conditions, the analytical curve was linear for dopamine concentrations from 2.0 × 10⁻⁷ to 1.0 × 10⁻⁶ mol L⁻¹ and 2.0 × 10⁻⁶ to 1.5 × 10⁻⁴ mol L⁻¹ with a detection limit (3σ) of 4.8 × 10⁻⁸ mol L⁻¹. The prepared electrode was used for determination of DA spiked into DA injection and human serum samples, and very good recovery results were obtained over a wide concentration range of DA.     

Electrochemical behaviour of N-acetyl-l-cysteine on gold electrode—A tentative reaction mechanism

The electrochemical behaviour of N-acetyl-l-cysteine (NAC) has been investigated by linear and cyclic voltammetry on gold electrode at room temperature. The results showed two oxidation peaks under acid and neutral conditions and only one in basic medium. For each oxidation, as many electron was exchanged as proton. The influence of both the concentration and the potential scan rate on the peak currents highlighted a diffusion-controlled phenomenon for the first peak and an adsorption-limited reaction rate for the second one. The diffusion coefficient of NAC in solution and the surface concentration of the adsorbed species at pH 3 and 7 were close to 2 × 10⁻⁴ to 2 × 10⁻⁵ cm² s⁻¹ and 6 × 10⁻⁹ to 6 × 10⁻¹⁰ mol cm⁻², respectively. Film transfer experiments resulted in an irreversible adsorption of NAC on gold electrode, and the formation of a self-assembled monolayer (SAM).     

Electrochemical characterizations on MnO2 supercapacitors with potassium polyacrylate and potassium polyacrylate-co-polyacrylamide gel polymer electrolytes

MnO₂·nH₂O supercapacitors with potassium polyacrylate (PAAK) and potassium polyacrylate-co-polyacrylamide (PAAK-co-PAAM) gel polymer electrolytes (GPEs) having the weight compositions of polymer:KCl:H₂O = 9%:6.7%:84.3% have been characterized for their electrochemical performance. Compared with the liquid electrolyte (LE) counterpart, the GPE cells exhibit remarkable (50–130%) enhancement in specific capacitance of the oxide electrode, and the extent of the enhancement increases with increasing amount of the carboxylate groups in the polymers as well as with increasing oxide/electrolyte interfacial area. In situ X-ray absorption near-edge structure (XANES) analysis indicates that the oxide electrodes of the GPE cells possess higher Mn-ion valences and are subjected to greater extent of valence variation than that of the LE cell upon charging/discharging over the same potential range. Copolymerization of PAAK with PAAM greatly improves the cycling stability of the MnO₂·nH₂O electrode, and the improvement is attributable to the alkaline nature of the amino groups. Both GPEs exhibit ionic conductivities greater than 1.0 × 10⁻¹ S cm⁻¹ and are promising for high-rate applications.     

Dielectric properties and microstructures of CaSiO3 ceramics with B2O3 addition

The effects of B₂O₃ additives on the sintering behavior, microstructure and dielectric properties of CaSiO₃ ceramics have been investigated. The B₂O₃ addition resulted in the emergence of CaO–B₂O₃–SiO₂ glass phase, which was advantageous to lower the synthesis temperature of CaSiO₃ crystal phase, and could effectively lower the densification temperature of CaSiO₃ ceramic to as low as 1100 °C. The 6 wt% B₂O₃-doped CaSiO₃ ceramic sintered at 1100 °C possessed good dielectric properties: _r = 6.84 and tan δ = 6.9 × 10⁻⁴ (1 MHz).     

Multi-walled carbon nanotubes (MWCNTs) and room temperature ionic liquids (RTILs) carbon paste Er(III) sensor based on a new derivative of dansyl chloride

Solution studies showed the strong interaction of [5-(dimethylamino) naphthalene-1-sulfonyl 4-phenylsemicarbazide] (NSP) with Er(III) ions. NSP was used as a sensing material during construction of carbon paste Er(III) sensors. The electrodes were modified with 1-n-butyl-3-methylimidazolium tetrafluoroborate, [bmim]BF₄, as room temperature ionic liquid (RTIL) and multi-walled carbon nanotube (MWCNT). Potentiometric sensors constructed with [bmim]BF₄ and MWCNTs show better sensitivity, selectivity, response time, and response stability compared to Er(III) carbon paste sensors. The best performance for the modified sensor was obtained with an electrode composition of 20% [bmim]BF₄, 20% NSP, 45% graphite powder and 15% MWCNT. This particular sensor formulation exhibits a Nernstian response (19.8 ± 0.3 mV decade⁻¹) toward Er(III) ions in the range of 1.0 × 10⁻⁷ to 1.0 × 10⁻¹ mol L⁻¹ with a detection limit of 5.0 × 10⁻⁸ mol L⁻¹. The proposed modified Er(III) sensor can be used over the pH range from 3.5 to 9.0.     

Synthesis of nano-crystalline Ce0.9Gd0.1O1.95 electrolyte by novel sol–gel thermolysis process for IT-SOFCs

In the present work, nano-crystalline Ce_0.9Gd_0.1O_1.95 (GDC) powder has been successfully prepared by a novel sol–gel thermolysis method using a unique combination of urea and PVA. The gel precursor obtained during the process was calcined at 400 and 600 °C for 2 h. A range of analyzing techniques including XRD, TGA, BET, SEM, EDS and TEM were employed to characterize the physical and chemical properties of obtained powders. GDC gel precursors calcined at 400 and 600 °C were found to have an average crystallite size of 10 and 19 nm, respectively. From the result of XRD patterns, we found that well-crystalline cubic fluorite structure GDC was obtained by calcining the precursor gel at 400 and 600 °C. It has been also found that the sintered samples with lower temperature calcined powder showed better sinterability as well as higher ionic conductivity of 2.21 × 10⁻² S cm⁻¹ at 700 °C in air.     

Low-temperature thermionic emission from nitrogen-doped nanocrystalline diamond films on n-type Si grown by MPCVD

Temperature-dependent emission current–voltage measurements were carried out for nitrogen (N)-doped nanocrystalline diamond (NCD) films grown on n-type Si substrates by microwave plasma-assisted chemical vapor deposition (MP-CVD). Low threshold temperature (~ 260 °C) and low threshold electric field (~ 5 × 10^− 5 V/µm) were observed. Both the temperature dependence and the electric field dependence have shown that the obtained emission current was based on electron thermionic emission from N-doped NCD films. We have also studied the relation between nitrogen concentration and the saturation emission current. The saturation current obtained was as high as 1.4 mA at 5.6 × 10^− 3 V/µm at 670 °C when the nitrogen concentration was 2.4 × 10²⁰ cm^− 3. Low value of effective work function (1.99 eV) and relatively high value of Richardson constant (~ 70) were estimated by well fitting to Richardson–Dushman equation. The results of smaller φ and larger A′ suggest that N-doped NCD has great possibility of being a highly efficient thermionic emitter material.