Studies on high-temperature thermal transformation and dielectric property of aluminum–chromium phosphates

High-temperature thermal transformation of aluminum–chromium phosphates has been investigated by means of DSC–TG, IR, and XRD analysis. The relative dielectric constant and thermal decomposition were measured and discussed. The results show that crystallization and thermal decomposition started at about 1,273 K, only AlPO₄ and Cr₂O₃ have been found at 1,873 K due to the decomposition of PO ₃ ^? , P₂O ₇ ^2? , and PO ₄ ^3? . The relative dielectric constant is fluctuant.     

Effect of inorganic ions on the photocatalytic degradation of humic acid

The article studies on the effects of six inorganic ions (Ca²⁺, Mg²⁺, Cl^?, SO ₄ ^2? , H₂PO ₄ ^? , and HCO ₃ ^? ) on titanium dioxide (TiO₂)-based photocatalytic degradation of humic acid (HA). We focus on the effects of the inorganic ions on HA characters, adsorption of HA on TiO₂ and photocatalytic degradation of HA. The results indicate that Ca²⁺ and Mg²⁺ with HA can form complexes which can decrease the solubility of HA, and then increase the HA adsorbed on TiO₂. However, the complex is more difficult to be degraded than HA. The effects of Cl^? and SO ₄ ^2? are closely related to their influences on HA solubility. The solubility changes of HA to some extent can enhance the adsorption of HA on TiO₂, and promote the photocatalytic degradation. Nevertheless, great solubility decreasing of HA can weaken the photocatalytic degradation. HCO ₃ ^? and H₂PO ₄ ^? can inhibit the photocatalytic degradation process seriously, because HCO ₃ ^? and H₂PO ₄ ^? are the strong scavengers of hydroxyl radicals, and can weaken the adsorption of HA on TiO₂ due to adsorption competition.     

Adsorption affinity of anions on metal oxyhydroxides

The dependences of anion (phosphate, carbonate, sulfate, chromate, oxalate, tartrate, and citrate) adsorption affinity anions from geometric characteristics, acid-base properties, and complex forming ability are generalized. It is shown that adsorption depends on the nature of both the anions and the ionic medium and adsorbent. It is established that anions are generally grouped into the following series of adsorption affinity reduction: PO ₄ ^3? , CO ₃ ^2? > C₂O ₄ ^2? , C(OH)(CH₂)₂(COO) ₃ ^3? , (CHOH)₂(COO) ₂ ^2? > CrO ₄ ^2? ? SO ₄ ^2? .     

Investigations of the thermal stability and phase transformations in the system marocco phosphorite—(NH4)3H(SO4)2.NH4HSO4

Different physical chemical methods were used to study the thermochemical processes in a system involving a natural phosphate and complex acid salts of ammonium sulphate. The products of decomposition of the double ammonium salt and the products of their interactions with the phosphate were identified. The formation of ammonium and calcium polyphosphates and the disproportionation of P₃O ₁₀ ^5? and P₂O ₇ ^4? to PO ₄ ^3? and PO ₃ ^? were found to depend on the circumstances of the thermal interactions.     

Sorption of Mo(VI), W(VI), Cr(VI), and V(V) anions on a silica gel modified with immobilized polyionene

The sorption of polyionene 1,4-MePh on the silica gel surface was studied. The silica gel modified with polyionene sorbed was used for sorption preconcentration of MoO ₄ ^2? , WO ₄ ^2? , Cr₂O ₇ ^2? , and VO ₃ ^? anions from aqueous solutions. The sorption isotherms of these anions on the initial and modified silica gels were obtained and analyzed.     

The Standard Chemical-Thermodynamic Properties of Phosphorus and Some of its Key Compounds and Aqueous Species: An Evaluation of Differences between the Previous Recommendations of NBS/NIST and CODATA

The aqueous chemistry of phosphorus is dominated by P(V), which under typical environmental conditions (and depending on pH and concentration) can be present as the orthophosphate species H₃PO ₄ ⁰ (aq),H₂PO ₄ ^? (aq),HPO ₄ ^2? (aq) or PO ₄ ^3? (aq). Many divalent, trivalent and tetravalent metal ions form sparingly soluble orthophosphate phases that, depending on the solution pH and concentrations of phosphate and metal ions, can be solubility limiting phases. Geochemical and chemical engineering modeling of solubilities and speciation require comprehensive thermodynamic databases that include the standard thermodynamic properties for the aqueous species and solid compounds. The most widely used sources for standard thermodynamic properties are the NBS (now NIST) Tables (from 1982 and earlier, with a 1989 erratum) and the final CODATA evaluation (1989). However, a comparison of the reported enthalpies of formation and Gibbs energies of formation for key phosphate compounds and aqueous species, especially H₂PO ₄ ^? (aq) and HPO ₄ ^2? (aq), shows a systematic and nearly constant difference of 6.3 to 6.9 kJ?mol^?1 per phosphorus atom between these two evaluations. The existing literature contains numerous studies (including major data summaries) that are based on one or the other of these evaluations. In this report we examine and identify the origin of this difference and conclude that the CODATA evaluation is more reliable. Values of the standard entropies of the H₂PO ₄ ^? (aq) and HPO ₄ ^2? (aq) ions at 298.15 K and p?° =1 bar were re-examined in the light of more recent information and data not considered in the CODATA review, and a slightly different value of S _m ^o (H₂PO ₄ ^? , aq, 298.15 K) = (90.6±1.5) J?K^?1?mol^?1 was obtained.     

Structures of NO 3 − formed via glow discharge in atmospheric gases

Tandem mass spectrometry experiments using both ion-molecule reactions and collision-induced dissociation (CID) in an ion trap mass spectrometer have been performed to characterize the structures of the NO ₃ ^? ions that issue from an atmospheric sampling glow discharge ionization source. The experimental evidence suggests that significant abundances of at least two stable forms of NO ₃ ^? can be obtained from an air-sustained glow discharge. Ab initio calculations have been performed to identify the structures of the likely isomers. Rate constants have been measured for the reaction of the less thermodynamically stable isomer(s) with carbon dioxide, and evidence is given for a new reaction, (OO?NO)^? + NO ₂ ^? → NO ₂ ^? + O₂ + NO^?. The combination of em with a kinetic study is shown to be a useful approach for obtaining rate constant information when a mixture of reactive and unreactive isomers is present in the reactant population.     

Determination of nitrite, nitrate, bromide, and iodide in seawater by ion chromatography with UV detection using dilauryldimethylammonium-coated monolithic ODS columns and sodium chloride as an eluent

A method was developed for determination of inorganic anions, including nitrite (NO ₂ ^? ), nitrate (NO ₃ ^? ), bromide (Br^?), and iodide (I^?), in seawater by ion chromatography (IC). The IC system used two dilauryldimethylammonium bromide (DDAB)-coated monolithic ODS columns (50?×?4.6?mm i.d. and 100?×?4.6?mm i.d.) connected in series for separation of the ions. Aqueous NaCl (0.5?mol/L; flow rate, 3?mL/min) containing 5?mmol/L phosphate buffer (pH 5) was used as the eluent, and detection was with a UV detector at 225?nm. The monolithic ODS columns were coated and equilibrated with a 1-mmol/L DDAB solution (in H₂O/methanol, 90:10 v/v). The hydrophilic ions (NO ₂ ^? , NO ₃ ^? , and Br^?) were separated within 3?min and the retention time of I^? was 16?min. No interferences from matrix ions, such as chloride and sulfate ions, were observed in 35?‰ artificial seawater. The detection limits were 0.6?μg/L for NO ₂ ^? , 1.1?μg/L for NO ₃ ^? , 70?μg/L for Br^?, and 1.6?μg/L for I^? with a 200-μL sample injection. The performance of the coated columns was maintained without addition of DDAB in the eluent. The IC system was successfully applied to real seawater samples with recovery rates of 94–108?% for all ions.

Using epichlorohydrin for a simultaneous increase of functional group hydrophilicity and spatial separation from the matrix of anion exchangers for ion chromatography

To increase the efficiency of anion exchangers based on copolymers of styrene and divinylbenzene in ion chromatography a new method for spatial separation and hydrophilization of functional groups using epichlorohydrin is suggested. Synthesis consists of acylation of a matrix by acetic anhydride, reductive amination by methylamine hydrochloride, alkylation of the aminated phase using epichlorohydrin, amination by dimethylamine at the terminal chlorine atom, and quaternization of the terminal amino group with epichlorohydrin. The obtained anion exchangers make it possible to simultaneously determine eight anions (F^?, HCOO^?, Cl^?, NO ₂ ^? Br^?, N ₃ ^? HPO ₄ ^3? and SO ₄ ^2? ) and demonstrate high efficiency (more than 62000 N/m for HPO ₄ ^2? ) in a suppressed ion-chromatography mode.     

Comparison of chemical effects of UV radiation from spark discharge in air and a low-pressure mercury lamp

The chemical effects of UV radiation from atmospheric-pressure spark discharge and a DBK-9 low-pressure mercury lamp in distilled water and aqueous solutions of hydrogen peroxide and tryptophan have been studied. Reactive species generated in water by the both radiation sources are HO ₂ ^· radicals, acid residue ions NO ₂ ^? and NO ₃ ^? , and ammonium ions. The yield of HO ₂ ^· radicals has appeared to be the same for both sources, (1.1–1.2) × 10^?6 mol L^?1 s^?1. This is confirmed by measurements of the degradation kinetics of tryptophan, which can be destroyed by HO ₂ ^· radicals. The pH of water monotonically decreases with time during the spark discharge treatment. In the case of the mercury lamp, the pH varies insignificantly because of the competition of NH ₄ ⁺ alkali ions with the acid residues. UV radiation plays the major role in the decomposition of hydrogen peroxide.     

The oxidation of chlorine ions under the joint action of ozone and permanganate ions

The oxidation of chlorine ions in the system O₃ + MnO ₄ ^? + H⁺ + Cl^? with the formation of Cl₂ in the gas phase was studied. The phenomenon of transfer catalysis of the reaction between O₃ and Cl^? by the MnO ₄ ^? ion was observed (the products of the reduction of MnO ₄ ^? by the chlorine ion are oxidized by ozone to recover MnO ₄ ^? ). The rate of the formation of Cl₂ in the O₃ + MnO ₄ ^? + H⁺ + Cl^? system was higher than the sum of the corresponding rates in the oxidation of Cl^? by O₃ and MnO ₄ ^? separately. A scheme explaining the trends observed experimentally for the formation of Cl₂ and changes in MnO ₄ ^? concentration was suggested. The formation of MnO ₄ ^? in the oxidation of Mn³⁺ with ozone in acid media was studied.     

Spontaneous disproportionation of NO2 (N2o4) by aromatic hydrocarbons. Formation of nitrosonium EDA complexes as chemical intermediates

Strong (orange/red) colourations resulting immediately upon the exposure of nitrogen dioxide and its equilibrium dimer (dinitrogen tetroxide) to various aromatic hydrocarbons (ArH) are shown to arise from the nitrosonium EDA or electron donor-acceptor complexes [ArH, NO⁺NO ₃ ^? ]. The latter exhibit diagnostic charge-transfer absorptions and characteristic N-O stretching bands in the UV-vis and IR spectra, respectively, that relate directly to ArH/NO⁺ interactions extant in the EDA complexes previously derived from the authentic nitrosonium salt, NO⁺PF ₆ ^- . Time-resolved picosecond spectroscopy establishes the charge-transfer excited state of [ArH, NO⁺NO ₃ ^? ] to be essentially identical to that from [ArH, NO⁺BF ₄ ^? ]. Furthermore, the same temporal decay of the spectral transients (ArH^+?) from both systems indicates minimal ion-pairing effects of the counterions (NO ₃ ^? and BF ₄ ^? ) on the kinetics of back electron transfer.     

The conformational changes of 5SrRNA from lupin seeds in presence of ClO 4 − , NO 3 − , Br−, BF 4 − , SO 4 2− , Cl−, COO− anions by adiabatic scanning calorimetry

The results of calorimetric studies of 5SrRNA solutions isolated from lupin seeds in the pressence of the ClO ₄ ^? , NO ₃ ^? , Br ₄ ^? , SO ₄ ^2? , Cl^?, COO^? (maleic and fumaric acids) anions were reported. The plots of calorimetric curves, enthalpy of conformational changes of two state transitions were presented. Using the deconvolution method proposed by Freire and Biltonen the elementary transitions were distinguished and discussed.     

Stabilization of Carbonate Hydroxyapatite by Isomorphic Substitutions of Sodium for Calcium

Carbonate hydroxyapatite (CHA) is an analogue of the mineral component of bone tissue. Synthetic CHA is thermally unstable: it readily decomposes with carbon oxide evolution when sintered to ceramics. Its thermal stability has been studied as affected by partial isomorphic substitution of sodium for calcium intended to compensate a possible charge imbalance induced by CO ₃ ^2? groups. Investigative tools were thermogravimetry and FTIR spectroscopy of the condensed vapor produced by heating CHA samples doped with 0.4 and 0.8 wt % sodium. Sodium does not improve the thermal stability of CHA: weight loss on heating increases with increasing sodium level; evolution of carbon oxides occurs at lower temperatures and more intensively. Sodium enhances the generation of B-type defects (CO ₃ ^2? → PO ₄ ^3? substitutions); these defects are thermodynamically less stable than AB-type defects (2CO ₃ ^2? → PO ₄ ^3? , OH^? substitutions), which are characteristic of sodium-free CHA.     

EXAFS study of spin transition effect on the spatial and electronic structure of Fe(II) complexes with triazoles

EXAFS spectroscopy is used to investigate the characteristic features of the spatial and electronic structure of the polynuclear Fe(II) complexes Fe(ATR)₃A₂ (where A is the NO ₃ ^? , BF ₄ ^? , Br^?, or ClO ₄ ^? anion and ATR is 4-amino-1,2,4-triazole) and their magnetically diluted phases Fe_xZn_1?x(ATR)₃(NO₃)₂. The absolute distances from Fe and Zn to the surrounding atoms are determined at temperatures higher and lower than the spin transition point. In all complexes, the spin transition is accompanied by significant changes in the local environment of Fe atoms, while in the magnetically diluted phases the surrounding of zinc remains unchanged. It is shown that addition of Zn atoms distorts the triazole rings in the low-spin state of the complexes. No localized anions were revealed within 3.3 Å from the Fe and Zn atoms. It is shown that a decrease in the spin transition temperature correlates with an increase in Fe?N distances in the low-spin complexes due to magnetic dilution and substitution of anions in the series NO ₃ ^? , BF ₄ ^? , Br^?, ClO ₄ ^? of ATR-containing complexes.     

Extraction-photometric selective determination of trace perchlorates in potable waters

A method is proposed for the selective photometry determination of perchlorates in potable water with a detection limit of 2×10^?3 mg/L is proposed based on the extraction of its ion pair with the astrafloxin cation and absorbance measurements at 540 nm. The following ratios of matrix ions are acceptable (in parentheses): ClO^?, ClO ₂ ^? , ClO ₃ ^? , BrO ₃ ^? (500); I^? (1000); IO ₃ ^? (7000); HCO ₃ ^? , Cl^?,SO ₄ ^2? , NO ₃ ^? , Br^?, Na⁺, K⁺, Ca²⁺, Mg²⁺ (10000). The relative error of determination for ClO ₄ ^? is 20% in the range 4 × 10^-3-1 × 10^?2 mg/L and 10% in the range 1 × 10^-2–5 × 10^?2 mg/L.     

Studies on the equilibrium uptake of some anions on a mixed and doped hydrous oxide

A mixed hydrous Fe(III)?Zr(IV) exhibits enhanced adsorption of anions in comparison to its constituent oxides. The uptake has been observed at pH 2.0, as a function of initial salt concentration and the product shows specific affinity for Cl^?, SO ₄ ^2? and PO ₄ ^3? ions. Doping the mixed oxide with Sn(II) improves its sorption capability for halide ions, while no significant enhancement is observed in the case of polyvalent anions.     

Interpretation of experimental Mössbauer quadrupole splittings of iron pentacyanide complexes using molecular orbital theory

Semiempirical self-consistent-field molecular-orbital calculations are carried out for six iron-pentacyanide complexes and are used to interpret their experimental Mössbauer quadrupole splittings. Probable orientations are identified for the C₆H ₅ ^? and NO ₂ ^? groups in Fe(CN)₅NOC₆H ₅ ^?3 and Fe(CN)₅NO ₂ ^?4 . Calculations on Fe(CN)₅NO^?2 and Fe(CN)₅NO^?3 can simultaneously be brought into agreement with experiment by reparametrization to make the NO group more positively charged. All the calculations indicate the importance of including all the Fe 3d and 4p orbitals in the calculations and of considering neighboring-atom effects.     

Formation of O 2 − in charge transfer collisions of fast molecular hydrogen ions with O2 molecules

Cross sections for the production of O ₂ ^? in charge transfer collisions of fast molecular hydrogen ions (H ₂ ⁺ , D ₂ ⁺ , H ₃ ⁺ , and D ₃ ⁺ of 10 to 140 keV kinetic energy) with O₂ molecules have been determined by means of a time-of-flight mass spectrometer analysing the slow negative product ions from the collisions. Within the measuring accuracy equivelocity H ₂ ⁺ and D ₂ ⁺ ions have the same cross sections for the generation of O ₂ ^? . The projectile velocity dependence curve of the cross section passes through a broad maximum with a peak value of about 6.5×10^?18 cm² around the Bohr velocity (25 keV/u) before showing an asymptotic decrease still within the limited energy range under investigation that is in inverse proportion to the square of velocity. Throughout the examined energy range H ₃ ⁺ ions yield a cross section which is about 1.4 times larger than that of H ₂ ⁺ ions of the same velocity. The fragment ion O^? has been found to appear with cross sections between 10^?19 and 10^?18 cm² upon collisional excitation in the energy range under investigation, with ever decreasing intensity when the energy of the positive hydrogen ions, the proton included, was increased.     

Boric acid

pH ranges of existence of boric acid and its ionic species H₂BO ₃ ^? , HBO ₃ ^2? , BO ₃ ^3? , and B(OH) ₄ ^? in aqueous solutions are calculated using Mathcad software package.