Hasil untuk "Physical and theoretical chemistry"

Yu KATAYAMA

The quest to design active and stable electrochemical interface hinges on unequivocally identifying the active site(s) and reaction mechanism under realistic operating conditions. This comprehensive paper summarizes the most recent understanding of the electrochemical interface during energy conversion and storage reactions probed by operando surface-enhanced infrared spectroscopy (SEIRAS), operando attenuated total reflection infrared spectroscopy (ATR-IR), and operando synchrotron surface X-ray scattering, coupled with density functional theory (DFT) calculations. The paper also demonstrates that the holistic information about the complex interaction in the electrochemical interface can alter the reaction energetics/kinetics in a way incapable of electrode-centered design strategy. This work shed light on the significance of advanced operando techniques to accelerate the design of electrochemical interfaces by providing additional knobs to tune the reaction energetics/kinetics, leading further improvements in electrocatalytic activity for energy conversion and storage reactions.

C. Xue, C. Xue, C. Ye et al.

<p>A comprehensive field campaign, with measurements of HONO and related parameters, was conducted in summer 2018 at the foot (150 m a.s.l.) and the summit (1534 m a.s.l.) of Mt. Tai (Shandong province, China). At the summit station, high HONO mixing ratios were observed (mean <span class="inline-formula">±</span> 1<span class="inline-formula"><i>σ</i></span>: 133 <span class="inline-formula">±</span> 106 pptv, maximum: 880 pptv), with a diurnal noontime peak (mean <span class="inline-formula">±</span> 1<span class="inline-formula"><i>σ</i></span>: 133 <span class="inline-formula">±</span> 72 pptv at 12:30 local time). Constraints on the kinetics of aerosol-derived HONO sources (NO<span class="inline-formula">₂</span> uptake on the aerosol surface and particulate nitrate photolysis) were performed and discussed, which enables a better understanding of the interaction of HONO and aerosols, especially in the polluted North China Plain. Various evidence of air mass transport from the ground to the summit level was provided. Furthermore, daytime HONO formation from different paths and its role in radical production were quantified and discussed.</p> <p>We found that the homogeneous reaction NO <span class="inline-formula">+</span> OH could only explain 8.0 % of the daytime HONO formation, resulting in strong unknown sources (<span class="inline-formula"><i>P</i>_un</span>). Campaigned-averaged <span class="inline-formula"><i>P</i>_un</span> was about 290 <span class="inline-formula">±</span> 280 pptv h<span class="inline-formula">⁻¹</span>, with a maximum of about 1800 pptv h<span class="inline-formula">⁻¹</span>. Aerosol-derived HONO formation mechanisms were not the major sources of <span class="inline-formula"><i>P</i>_un</span> at the summit station. Their contributions to daytime HONO formation varied from negligible to moderate (similar to NO <span class="inline-formula">+</span> OH), depending on the chemical kinetic parameters used. Coupled with sensitivity tests on the kinetic parameters used, the NO<span class="inline-formula">₂</span> uptake on the aerosol surface and particulate nitrate photolysis contributed 1.5 %–19 % and 0.6 %–9.6 % of the observed <span class="inline-formula"><i>P</i>_un</span>, respectively. Based on synchronous measurements at the foot and the summit station, an amount of field evidence was proposed to support the finding that the remaining majority (70 %–98 %) of <span class="inline-formula"><i>P</i>_un</span> was dominated by the rapid vertical transport from the ground to the summit level and heterogeneous formation on the mountain surfaces during transport.</p> <p>HONO photolysis at the summit level initialized daytime photochemistry and still represented an essential OH source in the daytime, with a contribution of about one-quarter of O<span class="inline-formula">₃</span>. We provided evidence that ground-derived HONO played a significant role in the oxidizing capacity of the upper boundary layer through the enhanced vertical air mass exchange driven by mountain winds. The follow-up impacts should be considered in regional chemistry transport models.</p>

Alexander N VTYURIN, Alexander S. Krylov, Svetlana N. Krylova et al.

Phase transitions in crystals of fluorine-containing elpasolites are investigated by Raman scattering spectroscopy. It was found that lattice instabilities in these crystals are induced by soft mode condensations, while restorations of these modes in the distorted phases have not been observed due to their strong interactions with low-frequency noncritical lattice vibrations. Increasing the mass of a rare-earth ions shifts down frequencies of noncritical modes, that enhances these interactions and leads to a narrowing of the range of existence of intermediate phase and then to its disappearance.

Hongmei Zhang, Yuqing Gui, Yan Cao et al.

Molecularly imprinted electrochemical sensor for the detection of sulfamethoxazole was prepared by electropolymerization with sulfamethoxazole as template molecule and o-phenylenediamine as functional monomer. Electrochemical performance of molecularly imprinted sensor was studied by cyclic voltammetry in 0.1 mol/L KCl solution containing 5 μM K3Fe(CN)6. On the optimal experimental conditions, square wave voltammetry was used to detect sulfamethoxazole. The square wave voltammetric peak current difference of the sensor has a good linear relationship with the concentration of sulfamethoxazole in the range of 0.2to 1.4 μM, and the detection limit is 0.05 μM. The molecularly imprinted sensor has good selectivity, repeatability and stability.

Ye Liu, Guowei Gao, Jingfang Hu et al.

A facile two-step electrochemical deposition of gold nanoparticles (AuNPs)/reduced graphene oxide (rGO) (AuNPs/rGO) nanocomposite was developed for Cr(VI) determination in water. First, electrodeposition of rGO on GCE by electroreduction of GO using cyclic voltammetry (CV), and then AuNPs were electrodeposited on rGO sheets using CV to obtain as AuNPs/rGO/GCE. The AuNPs/rGO nanocomposite was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive X-Ray spectroscopy (EDS) analysis. The deposition time, and concentration of HCl supporting electrolyte were respectively optimized for Cr(VI) determination. Square wave voltammetry (SWV) was applied for the detection of Cr(VI). The experimental results demonstrated the AuNPs/rGO/GCE has excellent electrocatalytic ability for Cr(VI) reduction, and a linear range of 0.1 μM-30 μM, with a high sensitivity of 0.79915 μA/μmolL-1, and a detection limit of 0.046 μM (S / N = 3) for Cr(VI) determination. The signal remained 92.98% after 12 h measurement suggested that the AuNPs/rGO nanocomposite has good stability for Cr(VI) determination. The common interfering irons of Mg2+, Zn2+, Cu2+, Mn2+ and Cr3+ were separately investigated, and less than 2% deviation values were obtained, indicating that the proposed AuNPs/rGO nanocomposite has good selectivity for Cr(VI) determination.

Kubiczek Artur, Kamiński Władysław

Room-temperature ionic liquids (RTILs) are a moderately new class of liquid substances that are characterized by a great variety of possible anion-cation combinations giving each of them different properties. For this reason, they have been termed as designer solvents and, as such, they are particularly promising for liquid-liquid extraction, which has been quite intensely studied over the last decade. This paper concentrates on the recent liquid-liquid extraction studies involving ionic liquids, yet focusing strictly on the separation of n-butanol from model aqueous solutions. Such research is undertaken mainly with the intention of facilitating biological butanol production, which is usually carried out through the ABE fermentation process. So far, various sorts of RTILs have been tested for this purpose while mostly ternary liquid-liquid systems have been investigated. The industrial design of liquid-liquid extraction requires prior knowledge of the state of thermodynamic equilibrium and its relation to the process parameters. Such knowledge can be obtained by performing a series of extraction experiments and employing a certain mathematical model to approximate the equilibrium. There are at least a few models available but this paper concentrates primarily on the NRTL equation, which has proven to be one of the most accurate tools for correlating experimental equilibrium data. Thus, all the presented studies have been selected based on the accepted modeling method. The reader is also shown how the NRTL equation can be used to model liquid-liquid systems containing more than three components as it has been the authors’ recent area of expertise.

Jiajun Huang

Magnesium phosphate-doped hydroxyapatite and magnesium hydrogen phosphate-doped dicalcium phosphate dihydrate superhydrophobic coatings were electrolytically deposited on an AZ91D alloy. The contact angles of water/oil were 155°/141°, respectively. In comparison with the bare substrate, electrochemical measurements of the superamphiphobic surfaces, including both EIS measurement and potentiodynamic polarization curves, all demonstrated a dramatic enhancement in the inhibition of surface corrosion.

Dandan Xu, Yan Wang, Hui Wang et al.

Electrochemical reduction-oxidation process was used to degrade simulated paper wastewater using three-electrode diaphragm system with Pd-Fe/graphene gas-diffusion cathode. The degradation efficiency and toxicity variation assessment were analyzed during the 4-chlorophenol (4-CP) wastewater degradation process. The 4-CP wastewater was degraded effectively and the removal efficiency of chemical oxygen demand (COD) in simulated paper wastewater was 78.2% (anodic), 80.7% (cathodic 1) and 81% (cathodic 2). The toxicity inhibition effect of two cathodic and anodic almost reached 100%, 100%, and 81.0% at 120 min, respectively. The comparison showed concentration for 50% of maximal effect (EC50) of simulated paper wastewater increased with the raise of EC50 of 4-CP. The elimination of toxicity exhibited a hysteresis effect and a rise tendency within 60 min, which might be attributed to the formation of more toxic intermediates such as benzoquinone. A good kinetics model was used to predict degradation of 4-CP and two possible reaction pathways were proposed, featuring a series of steps including cleavage of C-Cl bond, hydrodechlorination, hydroxyl radical addition and oxidation. The Pd-Fe/graphene gas-diffusion cathode was promising to dechlorination and detoxication of simulated paper wastewater containing 4-CP.

Jinbin Lin, Yesheng Shang, Xiujing Lin et al.

Nitrogen doped carbon nanotubes(N-CNTs) have been synthesized on carbon felt (N-CNT/CF) with chemical vapor deposition method by utilizing decomposition of melamine in the presence of ferrocene. The as-prepared N-CNT/CF composite was investigated as positive electrodes for vanadium redox flow batteries(VRBs). The microporous nanotube networks consisting of N-CNTs with higher surface area can increase the electrochemical reactive area, which means that N-CNT/CF can generate more active sites for VO2+/VO + redox couple. The charge-discharge test of the full battery with N- CNT/CF as positive electrode showed that the N-CNT/CF electrode gave better battery performance in terms of rate capability and polarization.

Delville Marie-Hélène

Zagorskis Alvydas, Vaiškūnaitė Rasa

Recent studies in the area of biological air treatment in filters have addressed fundamental key issues, such as a biofilter bed of different origin composed of natural zeolite granules, foam cubes and wood chips. When foam and zeolite are mixed with wood chips to remove volatile organic compounds from the air, not only biological but also adsorption air purification methods are accomplished. The use of complex purification technologies helps to improve the efficiency of a filter as well as the bed service life of the filter bed. Investigations revealed that microorganisms prevailing in biological purification, can also reproduce themselves in biofilter beds of inorganic and synthetic origin composed of natural zeolite and foam. By cultivating associations of spontaneous microorganisms in the filter bed the dependencies of the purification efficiency of filter on the origin, concentration and filtration time of injected pollutants were determined. The highest purification efficiency was obtained when air polluted with acetone vapour was supplied to the equipment at 0.1 m/s of superficial gas velocity. When cleaning air from volatile organic compounds (acetone, toluene and butanol), under the initial pollutant concentration of ~100 mg/m3, the filter efficiency reached 95 %.

Chandrabhan Verma, M.A. Quraishi, E.E. Ebenso

The corrosion inhibition of mild steel using two new Mannich bases namely 2,2’,2”((((1,3,5-triazine-2,4,6-triyl)tris(azanediyl)tris(Methylene)tris(azanediyl)triethanol (INH-1) and 2,2’,2”,2”’,2”“((((1,3,5-triazine-2,4,6-triyl)tris(azanediyl)tris(Methylene)tris(azanediyl)hexaethanol (INH-2) has been investigated using weight loss and electrochemical methods . The INH-1and INH-2 showed maximum efficiency of 92% and 95% at 25ppm concentration respectively. Potentiodynamic polarization suggests that the inhibitors depict mixed type behavior. The Electrochemical impedance spectroscopy (EIS) measurement shows that inhibitors were adsorbed at mild steel surface and obeyed Langmuir adsorption isotherm. Various thermodynamic parameters were also determined to investigate the mechanism of corrosion inhibition. The results obtained from weight loss and electrochemical methods are in good agreements.

A.H. El-Shazly, S.S. Al-Shahrani

This work investigates the possibility of improving the corrosion resistance of rotating copper parts in a solution of NaCl and Na2S by using one of triazole derivatives namely 4-Amino-4H-1,2,4-triazole (AHT) as corrosion inhibitor. The potentiodynamic technique was used for investigation of the effect of different variables on the corrosion of rotating copper such as rotational speed, initial S-2 concentration, rotating copper diameter, solution temperature and initial AHT inhibitor concentration. The results showed that AHT inhibitor can improve the corrosion resistance of rotating copper parts by a factor ranging from1.30 to 1.66 depending on AHT inhibitor concentration and rotational speed. The results show that the activation energy for corrosion of copper in 3.5% sodium chloride solution and 10ppm S-2 without the inhibitor ranges from 0.7 to 1.07kCal/gmol while it ranges from 1.879 to 3.366kCal/gmol in the presence of 10ppm of AHT corrosion inhibitor depending on the rotational speed which indicate that the process is mainly diffusion controlled.

Raja Rizwan Hussain

This paper elaborates the electrochemical behavior and dependency of anodic current density on chloride concentration and temperature based on reverse corrosion modeling approach for steel reinforced concrete. This research presents a semi-empirical corrosion modeling approach which obeys the basic mathematical laws and is also verified by the test results involving a wide range of chloride and temperature variations. The numerical modeling task has been incorporated by the use of computer based finite element model as a computational platform on which the coupled temperature-chloride induced corrosion throughout the life of reinforced concrete structures is examined in both space and time domains. This article contains advances in the development and use of computational methods for the solution and simulation of corrosion problems in civil engineering. In this paper a back calculation mathematical model has been developed and its numerical solution along with testing verification is presented. This article makes use of computers and numerical methods to model and solve the temperature induced corrosion problems in concrete structures. The paper provides a unique combination of strong numerical experiments, mathematical analysis, and comparisons with the test data. In this paper an automatic solution of mathematical models has been developed for corroding structures presenting algorithms for optimization and simulation which will help in profound understanding of temperature controlled corrosion reactions in reinforced concrete structures based on primary scientific laws and principles for complete life cycles. Investigations revealed that in fact anodic current also varies as a function of chloride concentration and temperature. This relation has been successfully extracted in this paper from the past research. It was interesting to observe the similarity present in the profiles of anodic current at different temperature conditions of 20°C, 40°C and 60°C.

Damir Iveković, Matea Japec, Matea Solar et al.

Electrodes modified with Prussian blue containing structurally incorporated Ni2+ ions were employed as the alkaline-stable H2O2 transducers in amperometric uric acid biosensors based on urate oxidase. The employed H2O2 transducers enabled operation of the biosensor at low cathodic potentials and in mild alkaline media, near the optimal pH of urate oxidase. At the pH value of 9.0 and working potential of -0.05 V, the biosensor exhibited a linear response towards uric acid in the concentration range of 2.5 to 200 μM, with the sensitivity of 26.9± 0.4 mAM-1 cm-2 and detection limit of 0.65 μM. The biosensor was successfully applied for determination of uric acid in samples of commercial dairy products.

R. Vijayalakshmi Puranik, Prakash Kumar, B.M. Chandrashekara et al.

Three nanoporous adsorbent materials, viz. beta zeolite, porous clay hetero-structure (PCH) and hexadecyltrimethylammonium cation-intercalated montmorillonite (Mont-2), having different pore architectures were used in the investigation. The adsorption of benzene, C 1 –C 4 alkyl-substituted benzenes, C 6 –C 9 straight-chain alkenes and isomeric hexenes was studied using a McBain–Bakr gravimetric balance. Interesting observations were made with respect to the adsorption uptake of the different probe molecules for exploring the pore architecture. Beta zeolite is a large pore zeolite (7.5 Å) which allows three-dimensional access to molecules, whereas PCH is known to have large pores allowing two-dimensional access for molecular entry. Irrespective of the number of attached –CH 2 side-chain groups attached, the rate of diffusion of the molecules inside the beta zeolite pore channels was less constrained. However, in the case of Mont-2, where the pores were blocked by the surfactant molecules, adsorption was apparently due to the diffusion of molecules through the interlayer packed with a bilayer of surfactant molecules. The packing density of the adsorbate molecules in the channels of the adsorbent was determined by the space-filling characteristics of the molecules which, in turn, depended on various factors such as the effective molecular volume, steric factors, the positioning of the double bonds, and the attractive and repulsive forces.

Farnoush Faridbod, Mohammad Reza Ganjali, Parviz Norouzi

A Ho3+ microelectrode, an asymmetric PVC membrane sensor was prepared based on N-(1-thien-2-ylmethylene)-1,3-benzothiazol-2-amine (TBA) for the first time. TBA shows a good selectivity and sensitivity towards Ho3+ ions, in respect with other tested cations. The log Kf of complexation between Ho3+ and TBA which was calculated by spectroscopic method was 5.23±0.27. The proposed Ho3+ microsensor exhibits a nice Nernstian response of 19.4±0.2 mV/decade of holmium concentration in a wide linear range of 1.0×10-8-1.0×10-3 M and a detection limit of 1.0×10-8 M. It can be used in the pH range of 3.0-8.0.

Lian-Sheng Duan, Qiao Xu, Fen Xie et al.

Myoglobin/multi-walled carbon nanotubes/chitosan film (Mb/MWNTs/Cs) electrodes were fabricated based on cross-linking myoglobin (Mb) with multi-walled carbon nanotubes/chitosan (MWNTs/Cs) composite film coated on a glassy carbon electrode (GCE). Direct electrochemistry and electrocatalysis of Mb on the Mb/MWNTs/Cs/GCE were studied. The Mb/MWNTs/Cs/GCE exhibited excellent electrocatalytic activity and rapid response for H2O2 in the absence of a mediator. The linear range of detection towards H2O2 was from 3.79×10−5 to 5.50×10−4 mol L-1 by the method of amperometric i-t curve. The Mb/MWNTs/Cs/GCE had good repeatability and stability for the determination of H2O2.

Pavel S. Yaremov, Oleksiy V. Shvets, Vladimir G. Ilyin

The characteristics of the dehydration, thermal desorption and thermal decomposition of organic templates in zeolite-like aluminophosphates and silica aluminophosphates of different structural types have been elucidated. The influence of the pore size and acidic centres on the composition of the thermal decomposition products, including the secondary syntheses of normal, cyclic and aromatic hydrocarbons, has been established. The possibility of dehydration, oligomerization, cyclization, cracking, aromatization and alkylation of hydrocarbons in zeolite-like phosphates has been shown.