Effect of potential electron acceptors on anoxic ammonia oxidation in the presence of organic carbon

A novel route of anoxic ammonia removal in the presence of organic carbon was identified recently from ecosystems contaminated with ammonia. Sequencing batch reactor (SBR) studies were carried out in anoxic condition at oxidation–reduction potential varied from −185 to −275 mV for anoxic ammonia oxidation with adapted biomass (mixed culture). SBR studies were carried out in absence and in the presence of externally added organic carbon and/or in the presence of inorganic electron acceptors like NO₂⁻, NO₃⁻ and SO₄²⁻. The results showed anoxic ammonia oxidation to nitrate (in contrast to reported anammox process) in the presence of organic carbon available through endogenous respiration whereas anoxic ammonia oxidation was effective in the presence of externally added organic compound for nitrogen removal. The presence of externally added inorganic electron acceptors like NO₂⁻, NO₃⁻ and SO₄²⁻ was effective in anoxic ammonia oxidation, but failed to follow the reported anammox reaction's stoichiometry in nitrogen removal in the presence of organic carbon. However, the presence of NO₂⁻ affected best in total nitrogen removal compared to other electron acceptors and maximum ammonia removal rate was 100 mg NH₄⁺/g MLVSS/d. Based on the results, it is possible to suggest that rate of anoxic ammonia oxidation depends up on the respiration activities of mixed culture involving organic carbon, NO₂⁻, NO₃⁻ and SO₄²⁻. The process shows possibilities of new pathways of ammonia oxidation in organic contaminated sediments and/or wastewater in anoxic conditions.     

Geochemistry of the upper Han River basin, China: 2: Seasonal variations in major ion compositions and contribution of precipitation chemistry to the dissolved load

A total of 252 water samples were collected from 42 sites across the upper Han River basin during the time period from 2005–2006. Major ions (Cl⁻, NO₃⁻, SO₄²⁻, HCO₃⁻, Na⁺, K⁺, Ca²⁺ and Mg²⁺), Si, water temperature, pH, EC and TDS were determined and consequently correlation matrix, analysis of variance, factor analysis and principal component analysis were performed in order to identify their seasonal variations and atmospheric inputs into river solutes. The results reveal that pH, EC, TDS, Cl⁻, SO₄²⁻, HCO₃⁻, Ca²⁺ and Mg²⁺, K⁺ and Si generally tend to show the minimum compositions in months belong to the rainy season, while the dry season for NO₃⁻ and Na⁺. NO₃⁻, Mg²⁺ and Si have the maximum concentrations in months belong to the rainy season. By comparing the major ions relating to hydrological regime, NO₃⁻, contrary to other elements, has higher concentration in the rainy season. The overall water quality is non-polluted, while there are indications of enrichment of inorganic anions including NO₃⁻ causing water entrophication in the near future. The atmospheric inputs contribute to river solutes is limited with a mean inputs of approximate 1% in the basin. The understanding of the major ion dynamics would help water quality conservation in the basin for China's interbasin water transfer project.     

Photoelectrochemical characterization of p-type silicon electrodes covered with tunnelling nitride dielectric films

The photoelectrochemical behaviour of p-Si(100) single crystal electrodes in aqueous solution, covered with a very thin nitride film, was studied. The silicon surface nitridation was achieved in a N₂-H₂ plasma at floating potential. The as-grown insulating Si₃N₄ layers, with thickness inferior to 3.1 nm, allow the electrons to tunnel in the presence of an electric field by the Fowler-Nordheim tunnelling mechanism. However, the p-Si(100)/Si₃N₄-electrolyte interface generated lower photocurrent densities than those generated by naked p-Si(100) electrodes. In contrast, the nitridated silicon surface displayed a significant stability improvement in aqueous electrolyte (neutral pH). An overvoltage higher than 0.6 V for water oxidation on a p-Si(100) covered with a 2.4 nm Si₃N₄ layer was measured. The results show that silicon covered with a nitridated thin film may be useful to stabilize electrodes in photoelectrochemical applications.     

The use of A Zr/ZrO2 electrode as an indicator electrode in the potentiometric acid-base titrations in fused KNO3

The Zr/ZrO₂ electrode was prepared by the electrolytic oxidation of molten KNO₃ on zirconium. This electrode can be used as indicator electrode in potentiometric acid-base titrations. It behaves reversibily and responds theoretically to the oxide-ion concentration in molten KNO₃. Its potential varies linearly with the logarithm of [O²⁻] and the slope of the line amounts to 67 mV at 350°C. The standard potential of Zr/ZO₂, O²⁻ electrode, i.e. the potential at [O²⁻] = 1, is computed as −1698 mV relative to the Ag/Ag(I) reference electrode.     

Electronic and optoelectronic properties of Al/coumarin doped Pr<Subscript>2</Subscript>Se<Subscript>3</Subscript>–Tl<Subscript>2</Subscript>Se/p-Si devices

In this study, coumarin-doped Pr₂Se₃–Tl₂Se (0.00, 0.05, 0.1, 0.3 wt% coumarin) were covered on the front side of a p-Si substrate by drop coating method and thus Al/coumarin doped Pr₂Se₃–Tl₂Se/p-Si diodes were fabricated. The electronic and optoelectronic properties of the prepared diodes were investigated. The highest rectification ratio (RR?=?I_F/I_R) value was found to be 2.24?×?10⁵ for the diode having 0.05 wt% coumarin doping at dark and ±?5 V. Also, the highest I_photo/I_dark photosensitivity was found to be 1327 for the diode which has 0.1 wt% coumarin doping at 100 mW/cm² and ??5 V. The photocurrent of the diodes is higher than the dark current and increases by the increase of the light intensity. These results confirm that the fabricated diodes show a strong photovoltaic behavior. The electronic parameters of the diodes, for example ideality factor and barrier height values, were calculated by the use of current–voltage characteristics. The transient measurement proves that the diodes show both photodiode and photocapacitor behaviors. The change on the conductance and capacitance by the frequency is attributed to the existence of interface states. Thus, the obtained results suggest that the prepared diodes might be used as a photosensor in the applications of optoelectronic.     

Electronic surface state of TiO2 electrode doped with transition metals, studied with cluster model and DV-Xα method

The surface electronic structure of rutile TiO₂ used for a photo-catalyst and an electrode of the dye-sensitized solar cell, was calculated by the DV-Xα method. The electrical properties of mesoporous TiO₂ electrode are dependent on the surface levels introduced by a high surface area. In this study, the electronic state of bulk TiO₂ structure was calculated using the (Ti₁₅O₅₆)⁵²⁻ model and the surface state of (1 1 0) plane was calculated using the (Ti₁₁O₃₄)²⁴⁻–O^* (O^*=surface oxygen) model, respectively. In addition to the surface state of pure TiO₂, the surface dopant levels introduced by the doping of transition metals in Ti⁴⁺ ion site were also calculated using the MTi₁₁O₃₄–O^* (M=transition metal) model. With calculated results, the variation of surface levels including dopant levels was discussed in association with electrode properties.     

Fabrication of flower-like Ni3(NO3)2(OH)4 and their electrochemical properties evaluation

Flower-like Ni₃(NO₃)₂(OH)₄ was successfully synthesized by a facile solvothermal method. The microstructure and surface morphology of prepared Ni₃(NO₃)₂(OH)₄ were physically characterized by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM) and transmission electron microscope (TEM). The electrochemical properties studies were carried out using cyclic voltammetry (CV), chronopotentiometry technology and AC impedance spectroscopy, respectively. The results indicate that the flower-like structure has a profound impact on electrode performance at high discharge capacitance. A maximum specific capacitance of 2212.5 F g^?1 at the current density of 5 mA could be achieved, suggesting its potential application in electrode material for secondary batteries and electrochemical capacitors. Furthermore, the effects of Ni(NO₃)₂·6H₂O concentration and temperature on the microstructure and specific capacitance of prepared Ni₃(NO₃)₂(OH)₄ have also been systematically studied. The results show that flower-like structure can be formed when the concentration is appropriate, while the temperature has just little effect on its electrochemical properties.     

Impedance spectroscopy measurements of charge carrier mobility in 4,4'-N,N'-dicarbazole-biphenyl thin films doped with tris(2-phenylpyridine) iridium

The charge carrier mobility of green phosphorescent emissive layers, tris(2-phenylpyridine) iridium [Ir(ppy)₃]-doped 4,4'-N,N'-dicarbazole-biphenyl (CBP) thin films, has been determined using impedance spectroscopy (IS) measurements. The theoretical basis of mobility measurement by IS rests on a theory for single-injection space-charge limited current. The hole mobilities of the Ir(ppy)₃-doped CBP thin films were measured to be 10^− 10–10^− 8 cm²V^− 1 s^− 1 in the 2–7 wt.% Ir(ppy)₃-doped CBP from the frequency dependence of both conductance and capacitance. These hole mobility values are much lower than those of the undoped CBP thin films (~ 10^− 3 cm²V^− 1 s^− 1) because the Ir(ppy)₃ molecules act as trapping centers in the CBP host matrix. These mobility measurements in the Ir(ppy)₃-doped CBP thin films provide insight into the hole injection process.     

Electrical characteristics of ZrN metallised metal-oxide-semiconductor and metal-insulator-metal devices

The electrical properties of DC reactive sputtered zirconium-nitride metallized metal-oxide-semiconductor (MOS) and metal-insulator-metal (MIM) devices on TiO₂/p-Si and TiO₂/ZrN films were studied using capacitance-voltage (C-V) and current-voltage (I-V) measurements at room temperature. Capacitances of the ZrN/TiO₂/p-Si MOS device were measured in accumulation mode and inversion mode, from which flat band capacitance was found to be 2.86pF, which corresponds to flat band voltage of −1.7 V. Fixed oxide charged density and interface state density was found to be 1.63× 10¹⁰ cm⁻² and 6.3× 10¹¹ cm⁻² eV⁻¹. I-V characteristics revealed that the leakage current density was of 0.5 mA/cm² in accumulation mode and 2 mA/cm² in inversion mode at a field of 0.12 MV/cm, respectively. Dielectric breakdown of ZrN/TiO₂/p-Si device was found to be 0.12 MV/cm in accumulation mode. Based on the C-V and I-V characteristics, the ZrN/TiO₂/ZrN structure showed no variation in the capacitance value as the bias voltage was changed.     

Preparation of Pt/multiwalled carbon nanotubes modified Au electrodes via Pt–Cu co-electrodeposition/Cu stripping protocol for high-performance electrocatalytic oxidation of methanol

Pt nanoparticles well dispersed on multiwalled carbon nanotubes (MWCNTs) were prepared for high-performance electrocatalytic oxidation of methanol in both acidic and alkaline media via the co-electrodeposition/stripping (CS) protocol, namely, co-electrodeposition of Pt and Cu followed by electrochemical stripping of Cu, as examined by cyclic voltammetry (CV), electrochemical quartz crystal microbalance (EQCM), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The Pt catalyst prepared by the CS protocol on MWCNTs (Pt_cs/MWCNTs/Au) exhibited a specific electrocatalytic activity of 519 and 2210 A g⁻¹ toward cyclic voltammetric electrooxidation (50 mV s⁻¹) of methanol in 0.5 M CH₃OH + 0.5 M H₂SO₄ and 0.5 M CH₃OH + 1.0 M NaOH media, respectively, which are larger than those prepared by conventional electrodeposition from chloroplatinic acid on Au and MWCNTs/Au, as well as that by a CS protocol on Au. The Pt_cs/MWCNTs/Au electrode also possessed the highest stability, which maintained 91% and 90% of its initial catalytic activity after 120-cycle CV in 0.5 M CH₃OH + 0.5 M H₂SO₄ and 0.5 M CH₃OH + 1.0 M NaOH, respectively. The electrode kinetics of methanol oxidation is also briefly discussed. The nanosubstrate-based CS protocol is simple, convenient and efficient, which is expected to find wide applications in film electrochemistry and electrocatalysis.     

Co2SnO4/activated carbon composite electrode for supercapacitor

A new kind of Co₂SnO₄-based electrode materials for supercapacitor was synthesized by co-precipitation method. The microstructure and surface morphology of Co₂SnO₄ were characterized by X-ray diffraction and scanning electron microscopy, respectively. Cyclic voltammetry, chronopotentiometry and electrochemical impedance spectroscopy were employed for the determination of specific capacitance and the equivalent series resistance of Co₂SnO₄/activated carbon composite electrode in KCl solution. It was shown that the composite electrode with 25 wt% Co₂SnO₄ had excellent specific capacitance up to 285.3 F g⁻¹ at the current density of 5 mA cm⁻². In addition, the composite electrode exhibited excellent long-term stability and, after 1000 cycles, 70.6% of initial capacitance was retained. Regarding the low cost, easy preparation, steady performance and environment friendliness, Co₂SnO₄/activated carbon composite electrode could have potentially promising application for supercapacitor.     

Effect of Ti defects on electrochemical properties of highly-ordered titania nanotube arrays

In this paper, highly-ordered TiO₂ nanotube (TNT) electrodes fabricated by anodization at 20 V in 0.1 M F⁻-based solution were annealed in O₂, N₂ and CO respectively. The surface properties of the TiO₂ electrodes after annealing treatment by different gases were studied by means of photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrochemical properties of the TNT electrodes were investigated by cyclic voltammetry, steady-state polarization and photocurrent response measurements. The results showed that Tiⁿ⁺ (n = 0-3) cations and oxygen vacancies existed in the TNT electrode after annealing in CO, leading to a very efficient electron transfer rate of 1.34 × 10^− 3 cm/s. Steady-state polarization measurement and photocurrent response demonstrated that the electrode potential of oxygen evolution reaction (OER) reduced by 20% and the photocurrent response increased by 50% for CO-annealed TNT electrode compared with O₂-annealed TNT electrode.     

Biosensor enhanced by glucose oxidase biomimetic membrane containing the platinum and silica nanoparticles

In this paper, glucose biosensor is fabricated with immobilization of glucose oxidase (GOx) in platinum and silica sol. The glucose biosensor combined with Pt and SiO₂ nanoparticles could make full use of the properties of nanoparticles. A set of experimental results indicates that the current response for the enzyme electrode containing platinum and silica nanoparticles increases from 0.32 µA cm^− 2 to 33 µA cm^− 2 in the solution of 10 mM β-D-glucose. The linear range is 3 × 10^− 5 to 3.8 × 10^− 3 M with a detection limit of 2 × 10^− 5 M at 3σ. The effects of the various volume ratios of Pt and SiO₂ sols with respect to the current response and the stability of the enzyme electrodes are studied.     

Effect of preparation conditions on the physical and hydrophobic properties of two step processed ambient pressure dried silica aerogels

The experimental results on the physical and hydrophobic properties of the ambient pressure dried silica aerogels as a function of sol-gel and drying conditions, are reported.The aerogels have been produced by a two stage (acidic and basic) catalytic sol-gel process using tetraethylorthosilicate (TEOS) precursor, oxalic acid (OXA) and ammonium hydroxide (NH₄OH) catalysts, ethanol (EtOH) solvent and hexamethyldisilazane (HMDZ) silylating agent at 200^∘C.The molar ratios of HMDZ/TEOS (M), OXA/TEOS (A) NH₄OH/TEOS (B), acidic H₂O/TEOS (Wa) basic H₂O/TEOS (Wb), EtOH/TEOS (S) were varied from 0.09 to 0.9, 3.115 × 10^{− 5} to 3.115 × 10⁻³, 4 × 10^{− 3} to 8 × 10^{− 2}, 2 to 9, 1.25 to 5 and 1 to 16 respectively. The physical properties such as the percentage (%) of volume shrinkage, density, thermal conductivity, percentage of porosity, the percentage of optical transmission and contact angle have been found to be strongly dependent on the sol-gel parameters. It was found from the FTIR spectra of the aerogels that with the increase of M, the bands at 3500 and 1600 cm^{− 1} corresponding to H-OH and Si-OH respectively decreased and the bands at 840 and 1250 cm^{− 1} due to Si-C and 2900 and 1450 cm⁻¹ due to C-H increased. The best quality silica aerogels in terms of low density, low volume shrinkage, low thermal conductivity, high hydrophobicity and high optical transmission have been obtained with the molar ratio of TEOS:EtOH:acidicH₂O:basicH₂O:OXA:NH₄OH:HMDZ at 1:8:3.75:2.25:6.23 × 10^{− 5}: 4 × 10^{− 2}:0.36 respectively, by ambient pressure dried method.     

Passivation and antireflection AZO:H layer in AZO:H/p-Si heterojunction solar cells

In this work, aluminum-doped zinc oxide (AZO)/p-Si heterojunction solar cells were prepared by sputtering of ~120 nm AZO thin films in Ar or Ar–H₂ atmosphere on textured p-Si wafers, and the effects of hydrogen incorporation on the solar cell performance were investigated. Results showed that the performance of AZO/p-Si heterojunction solar cells was improved with the increase of hydrogen volume concentration from 0 to 23 %. The AZO:H/p-Si heterojunction solar cells prepared in Ar–23 % H₂ exhibited a short-circuit current density of 29 mA/cm² and a conversion efficiency of 2.84 %. The reflectance measurement indicated that the reflectance of p-Si surface in the range of 400–1,100 nm decreased from 13 to 4 % after AZO:H films coating; and the capacitance–voltage measurement indicated that the density of defect states at AZO/p-Si interface was decreased after hydrogen incorporation. Passivation and antireflection functions can be realized in AZO:H films deposited in Ar–H₂, which opens a novel route to prepare cost-effective AZO/p-Si heterojunction solar cells.     

Electrochemical behavior and multilayer films of the sandwich-type polyoxotungstate complex {K10Co4(H2O)2(PW9O34)2}

The electrochemical behavior of the sandwich-type polyoxotungstate complex of K₁₀Co₄(H₂O)₂(PW₉O₃₄)₂ (Co₄(PW₉)₂) was investigated by cyclic voltammetry in aqueous solutions. The polyoxoanion exhibits two successive redox peaks originating from the tungsten-oxo framework. The electrochemical behavior for the Co^II species was not detected. Moreover, the multilayer films consisting of PEI and Co₄(PW₉)₂ were prepared by the layer-by-layer self-assembly method. The films were characterized by UV–vis spectroscopy, cyclic voltammetry and atomic force image. The films exhibit the electrochemical behavior of Co₄(PW₉)₂ polyoxoanion. Moreover, the films can catalyze the electrochemical reduction of NO₂⁻. Electron transfer to Fe(CN)₆^3−/4− redox probe was also investigated.     

Analyzing the ZnO and CH₃NH₃PbI₃ as Emitter Layer for Silicon Based Heterojunction Solar Cells

Today, it has become an important task to modify existing traditional silicon-based solar cell factory to produce high-efficiency silicon-based heterojunction solar cells, at a lower cost. Therefore, the aim of this paper is to analyze CH₃NH₃PbI₃ and ZnO materials as an emitter layer for p-type silicon wafer-based heterojunction solar cells. CH₃NH₃PbI₃ and ZnO can be synthesized using the cheap Sol-Gel method and can form n-type semiconductor. We propose to combine these two materials since CH₃NH₃PbI₃ is a great light absorber and ZnO has an optimal complex refractive index which can be used as antireflection material. The photoelectric parameters of n-CH₃NH₃PbI₃/p-Si, n-ZnO/p-Si, and n-Si/p-Si solar cells have been studied in the range of 20–200 nm of emitter layer thickness. It has been found that the short circuit current for CH₃NH₃PbI₃/p-Si and n-ZnO/p-Si solar cells is almost the same when the emitter layer thickness is in the range of 20–100 nm. Additionally, when the emitter layer thickness is greater than 100 nm, the short circuit current of CH₃NH₃PbI₃/p-Si exceeds that of n-ZnO/p-Si. The optimal emitter layer thickness for n-CH₃NH₃PbI₃/p-Si and n-ZnO/p-Si was found equal to 80 nm. Using this value, the short-circuit current and the fill factor were estimated around 18.27 mA/cm² and 0.77 for n-CH₃NH₃PbI₃/p-Si and 18.06 mA/cm² and 0.73 for n-ZnO/p-Si. Results show that the efficiency of n-CH₃NH₃PbI₃/p-Si and n-ZnO/p-Si solar cells with an emitter layer thickness of 80 nm are 1.314 and 1.298 times greater than efficiency of traditional n-Si/p-Si for the same sizes. These findings will help perovskites materials to be more appealing in the PV industry and accelerate their development to become a viable alternative in the renewable energy sector.     

Corrosion behavior of AZ91 magnesium alloy in dilute NaCl solutions

The corrosion behavior of AZ91 magnesium alloy in dilute NaCl solutions was studied using electrochemical measurements, whereby a corrosion map in terms of electrode potential and chloride concentration [Cl⁻] was obtained. AZ91 alloy exhibited the corrosion and passivation zones in dilute NaCl solutions. The passivation zone became narrow with increasing [Cl⁻]. The values of open-circuit potential were in the passivation zone when the [Cl⁻] was less than 0.5 mol/L. XRD patterns showed the presence of the Mg(OH)₂, Mg₅(CO₃)₄(OH)₂·8H₂O and MgO phases in the corrosion product, whereas the latter two phases found in the passive film.     

Electrical and optical properties of 12CaO·7Al2O3 electride doped indium tin oxide thin film deposited by RF magnetron co-sputtering

12CaO·7Al₂O₃ electride (C12A7:e⁻) doped indium tin oxide (ITO) (ITO:C12A7:e⁻) thin films were fabricated on a glass substrate by an RF magnetron co-sputtering system with increasing number of C12A7:e⁻ chips (from 1 to 7) and at various oxygen partial pressure ratios. The optical transmittance of the ITO:C12A7:e⁻ thin film was higher than 70% in the visible wavelength region. In the electrical properties of the thin film, a decrease of the carrier concentration from 2.6 × 10²⁰ cm^− 3 to 2.1 × 10¹⁸ cm^− 3 and increase of the resistivity from 1.4 × 10^− 3 Ω cm to 4.1 × 10^− 1 Ω cm were observed with increasing number of C12A7:e⁻ chips and oxygen partial pressure ratios. It was also observed that the Hall mobility was decreased from 17.27 cm²·V^− 1·s^− 1 to 5.13 cm²·V^− 1·s^− 1. The work function of the ITO thin film was reduced by doping it with C12A7:e⁻.     

A new coral structure TiO2/Ti film electrode applied to photoelectrocatalytic degradation of Reactive Brilliant Red

A novel structure TiO₂/Ti film was prepared on a titanium matrix using anodic oxidation technique and applied to degrade Reactive Brilliant Red (RBR) dye in simulative textile effluents. The film was characterized by Field-Emission Scanning Electron Microscope (FE-SEM), Laser Micro-Raman Spectrometer (LMRS), UV–vis spectrophotometer (UVS) and Photoelectrocatalytic (PEC) experiment. The results show that the surface morphology of the film is coral structure, and the crystal structure of the film is anatase. The absorbency of the coral structure TiO₂/Ti film is 87–93% in the UV light region, and 77–87% in the visible light region. PEC experiment indicates that the photocurrent density of the coral structure TiO₂/Ti film electrode achieves 160 μA/cm². The color and Chemical Oxygen Demand (COD) removal efficiencies of RBR achieve 73% and 60% in 1 h, respectively. These are 16% and 58% higher than those of nanotube TiO₂/Ti film electrode. These were attributed to that these electrodes with different surface morphologies exhibit distinct surface areas and light absorption rate.