Kinetics and Mechanism of Aniline and Chloroanilines Degradation Photocatalyzed by Halloysite-TiO2 and Halloysite-Fe2O3 Nanocomposites

The kinetics of photocatalytic degradation of aniline, 2-chloroaniline, and 2,6-dichloroaniline in the presence of halloysite-TiO2 and halloysite-Fe2O3 nanocomposites, halloysite containing naturally dispersed TiO2, Fe2O3, commercial TiO2, P25, and α-Fe2O3 photocatalysts, were investigated with two approaches: the Langmuir–Hinshelwood and first-order equations. Adsorption equilibrium constants and adsorption enthalpies, photodegradation rate constants, and activation energies for photocatalytic degradation were calculated for all studied amines photodegradation. The photodegradation mechanism was proposed according to organic intermediates identified by mass spectrometry and electrophoresis methods. Based on experimental results, it can be concluded that after 300 min of irradiation, aniline, 2-chloro-, and 2,6-dichloroaniline were completely degraded in the presence of used photocatalysts. Research results allowed us to conclude that higher adsorption capacity and immobilization of TiO2 and Fe2O3 on the halloysite surface in the case of halloysite-TiO2 and halloysite-Fe2O3 nanocomposites significantly increases photocatalytic activity of these materials in comparison to the commercial photocatalyst: TiO2, Fe2O3, and P25.

pH-metric method for determining the solubility and solubility products of slightly soluble hydroxides and acids

In this paper, original methods for determining such thermodynamic characteristics as solubility K S0 product (KS) or the activity product ( )of slightly soluble hydroxides and acids are communicated. Developed methods for determining KS and solubility S are based only on the pH values of the saturated aqueous solution for a known initial composition of the heterogeneous mixture and the equilibrium constants of an arbitrary set of possible side reactions in the aqueous natural systems. The determination of solubility S and solubility product KS is also possible in the presence of other hydroxides or acids of known concentrations. Deduced equations allow the calculation of such characteristics, as the equilibrium concentrations of the components of slightly soluble compounds in aqueous phase and the degree of precipitation γ of the solid phase for various initial concentrations of the components of the heterogeneous mixture which are known in the process of preparing the mixture, requiring only experimental pH values of a saturated solution. From the known experimental pH data, S and KS were calculated for a series of hydroxides and acids of arbitrary composition. The obtained results correlated well with the known tabular values. Analysis of a number of real systems illustrated the deduced expressions, including calculations and theoretical explanations.

Allosteric mechanism of signal transduction in the two-component system histidine kinase PhoQ

Transmembrane signaling proteins couple extracytosolic sensors to cytosolic effectors. Here, we examine how binding of Mg2+ to the sensor domain of an E. coli two component histidine kinase (HK), PhoQ, modulates its cytoplasmic kinase domain. We use cysteine-crosslinking and reporter-gene assays to simultaneously and independently probe the signaling state of PhoQ's sensor and autokinase domains in a set of over 30 mutants. Strikingly, conservative single-site mutations distant from the sensor or catalytic site strongly influence PhoQ's ligand-sensitivity as well as the magnitude and direction of the signal. Data from 35 mutants are explained by a semi-empirical three-domain model in which the sensor, intervening HAMP, and catalytic domains can adopt kinase-promoting or inhibiting conformations that are in allosteric communication. The catalytic and sensor domains intrinsically favor a constitutively 'kinase-on' conformation, while the HAMP domain favors the 'off' state; when coupled, they create a bistable system responsive to physiological concentrations of Mg2+. Mutations alter signaling by locally modulating domain intrinsic equilibrium constants and interdomain couplings. Our model suggests signals transmit via interdomain allostery rather than propagation of a single concerted conformational change, explaining the diversity of signaling structural transitions observed in individual HK domains.

Density, pH, and Boron Species in the Ternary System NaBO2–Na2SO4–H2O at 298.15 K and 323.15 K

The densities and pH values in the system NaBO2–Na2SO4–H2O at 298.15 K and 323.15 K were investigated. Combining the equilibrium constants for different boron species, the distributions of six boron species in the mixed solution were calculated with total boron concentration and pH values. The molar fractions of the six boron species are mainly affected by the total boron concentration and temperature, but rarely affected by the concentration of SO42–. The dominant boron species in the mixed solution at the two temperatures is B(OH)4‒. The mole fraction of B(OH)3, B5O6(OH)4‒, and B3O3(OH)4‒ can be neglected. The polyborate ions are easier to form as the temperature increases. The results of distribution for boron species in this study and those with the Pitzer model can both be used to describe the distribution of boron species in the mixed solution.

Electrochemical Modeling of Iodide Oxidation in Metal-Halide Molten Salts

The oxidation of iodide in NaI-AlBr3, NaI-AlCl3, and NaI-GaCl3 molten salts was analyzed using simulation software to extract relevant kinetic parameters. The experimental oxidation potentials were ordered AlCl3 < AlBr3 < GaCl3, with higher oxidation potentials correlating with softer Lewis acidity of the metal halide. An iodide oxidation and metal halide speciation model was developed and simulated to fit the electrochemical response, enabling determination of electrochemical charge transfer parameters and chemical equilibrium constants. NaI-AlBr3 displayed the fastest electron transfer rates yet showed the lowest current densities. All salts revealed smaller than expected current densities, explained by equilibrium between various species, where some are not electrochemically active at the studied potentials. These equilibrium reactions are due to the various metal halide species, controlling the reactant concentration of iodide and the resultant current. We hypothesize the electrochemically active iodide species, present as a metal halide monomer (MX3I−), is decreased dramatically from the expected concentration, sequestered as a more stable metal halide dimer species (M2X6I−) with a higher oxidation potential. Traditional Tafel analysis of the experimental data supports the validity of the simulations. These results increase understanding of iodide oxidation in low-temperature Lewis acidic molten salts and inform task-specific molten salt design.

Technology for production of granular calcium-ammonium nitrate

The article presents the technology for production of granular calcium-ammonium nitrate, which is suitable for implementation into the existing production of complex mineral fertilizers. The paper considers the physicochemical foundations of manufacturing calcium-ammonium nitrate and provides the calculations of the equilibrium constants of the reactions occurring at the temperatures of 25–1700С. A new process flow diagram was proposed. It was shown that the production of calcium ammonium nitrate as a valuable agrochemical fertilizer is possible by mixing of 82–84% ammonium nitrate solution with solid carbonate raw materials with further granulation and drying in a drum granulator and dryer. The work determines the conditions for the interaction of reagents making it possible to reduce the losses of nitrogen. The density of aqueous suspensions of chalk and the rate of its precipitation are established. The obtained results allow improving an industrial plant based on the existing equipment for the production of complex mineral fertilizers. The technological parameters for the preparation of the product are optimized to meet the requirements of technical conditions. During commissioning and stabilization of the technological regime, a product was obtained containing 25.9–27.8% of total nitrogen, 15.6–16.8% of CaCO3, 0.01–0.64% of Ca(NO3)2, and 0.32–0.75% of H2O with the following particle size distribution: 95.3–96.3% of 1–5 mm particle size, and 3.7–4.8% of particle size of less than 1 mm with a granule hardness of 30 N per granule.

Thermodynamic analysis of strontium deoxidizing ability in liquid iron at presence of aluminum

Phase diagram of the ternary oxide system FeO - SrO -Al2O3 was constructed for the first time. In this system, the following compounds can be formed: hercynite FeAl2O4 and five strontium aluminates - Sr4Al2O7 , Sr3Al2O6 , SrAl2O4 , SrAl4O7 , SrAl12O19 . According to the calculations performed, solid solutions of oxides are not formed in the system, as it is confirmed by the literature data. In the course of modeling, the optimal energy parameters of the theory of subregular ionic solutions were selected for the components of the oxide melt (FeO, SrO, Al2O3 ). Thermodynamic analysis of strontium deoxidizing ability in liquid iron at presence of aluminum was carried out using the technique for constructing the surface of solubility of strontium and aluminum in metal for steelmaking temperatures (1550 and 1600 °C) and carbon concentrations of 0.1 and 0.4 %. The equilibrium constants of the reactions of formation of strontium aluminates Sr3Al2O6 and SrAl2O4 from the components of the metal melt were calculated for the temperature range of 1550 - 1650 °C. It was found that the rest of strontium aluminates can be formed in liquid metal only at temperatures above 1750 °C. The base of thermodynamic data for the studied systems is given: temperature dependences of equilibrium constants for reactions occurring between components; values of interaction parameters of the first order (according to Wagner) for elements in liquid iron; values of energy parameters of the theory of subregular ionic solutions (for oxide melt). It follows from the calculations that the formation of strontium monoaluminate SrAl2O4 and corundum Al2O3 is most probable as the interaction products in Fe -Al - Sr - O and Fe -Al - Sr - C - O systems.

A Short Note Regarding the Number of Bound Molecules of Oxygen to Hemoglobin

Oxygen, a molecule essential to many biological functions in the human body, binds coop?eratively to a protein known as hemoglobin. This cooperative binding of oxygen to hemoglobin can be described by a binding polynomial of degree n = 4. In this paper, I theoretically prove that a molecule of hemoglobin must have at least one molecule of oxygen bound to its subunits at any given point in time. I remove a condition for the equilibrium constants K_R and K_T in the binding polynomial for the binding of oxygen to hemoglobin. Removing the condition partially proves the proposed statement in this paper. I then make use of the cubic formula to derive the concentration of oxygen for which the number of bound oxygen molecules tohemoglobin is zero, thus completing a comprehensive mathematical justification of the proposed theoretical statement. Through this paper, I hope to provide a further insight into the mechanisms of oxygen and hemoglobin with regards to the respiratory system.

An improved Wilson equation for phase equilibrium K values estimation

Phase equilibrium K values are either estimated with empirical correlations or rigorously calculated based on fugacity values determined from an equation of state. There have been several empirical analytical equations such as Raoult’s Law, the Hoffman Equations (Hoffman A, Crump J, Hocott C. Equilibrium constants for a gas condensate system. J Petrol Technol 1953;5:1–10) and their modifications and the well-known Wilson Equation (Wilson G. A modified Redlich–Kwong equation of state applicable to general physical data calculations. In: AIChE National Meeting Paper15C, May 4–7, Cleveland, OH; 1969). along with several modifications. This work presents a new modification of the Wilson Equation for estimating phase equilibrium K values, predominantly for light hydrocarbon mixtures. The modification is based on correlating a subset of a database of K values, established from convergence pressure data. Results show the method to accurately correlate and predict the K value data, within 10% on average. Moreover, the predicted K factors provide remarkable results for such a simple model when used in a variety of phase equilibrium calculations. The results also show that the new model compares favorably with existing empirical analytical methods. Such a model would provide excellent initial estimates for rigorous thermodynamic calculations.