Removal of toxic metals from wastewater by Brazilian natural scolecite

The cation-exchange capacity of Brazilian natural zeolite, identified as scolecite, was studied with the aim of evaluating its applications in wastewater control. We investigated the process of sorption of chromium(III), nickel(II), cadmium(II), and manganese(II) in synthetic aqueous effluents, including sorption isotherms of single-metal solutions at 298, 313, and 333 K, by batch experiments, and the influence of pH on the process. The results have demonstrated that removal of metals from specific metal solutions is best described by a Freundlich isotherm, in which the values obtained for the Kf constants were in the following order: Cr > Mn > Cd > Ni. A Lagergren pseudo-second-order was the model that best described the sorption mechanism. The retention of metals was shown to be a function of the pH; the maximum binding capacity occurring at pH values around 6.0. Thermodynamic data indicate the spontaneity of the endothermic cation-exchange process. The values of Delta G0 suggest the following selectivity series at 298 K: Ni > Cr > Cd > Mn. The desorption process reaches equilibrium during the first 60 min of binding, suggesting that the mechanism involves specific sites located in the external surface of the scolecite.     

Estimation of the pK a of the amine groups of benzhydrylamine resin and its lysyl derivative by measurement of swelling

Summary For better evaluation of the potential of benzhydrylamine resin (BHAR), used as a solid support for peptide synthesis, as a novel anion-exchange resin, the pK _a of its amine group was estimated by microscopic measurement of the sizes of the dry and swollen beads. Using the volume of the bead occupied by the solvent (as a percentage) as the swelling parameter, a plot of the degree of swelling of BHAR loaded with 2.4 mmol g^–1 amine groups against the pH of the medium produced a decreasing sigmoidal-type curve with increasing pH. By considering the point of inflection of the curve, a pK _a value of approximately 7.5 was estimated for the amine group of the BHAR. The same approach was also applied to the lysyl derivative of the BHAR (Lys-BHAR) and pK _a values around 6.5 and 10.0 were obtained for the and amine groups, respectively.     

Lanthanoid and yttrium tellurates

Preparation in aqueous medium of all the lanthanoid (except Ce and Pm) and yttrium tellurates is described. Chemical analyses, solubilities at 25°C in water and thermograms of all the products prepared were determined. X-ray diffractograms and DTA and DTG curves of La, Gd and Yb tellurates were obtained and commented. Partial volatilization of lanthanoid is observed in the thermal analysis of tellurates.     

The Cα?C internal rotation in α-alkyl substituted carbonyls and thiocarbonyls: CH(CH3)2C(X)YH (X,Y O or S)

The C_α? C internal rotation in 2-methylpropionic, 2-methylthiopropionic (thiol and thion forms) and 2-methyldithiopropionic acids was studied by the ab initio SCF-MO method using 3-21G and 3-21G + d(0.65S) basis sets. Energies and structures of several conformations of these molecules, determined by gradient geometry refinement, are reported and used to assess the effects of oxygen-by-sulphur substitution on molecular properties. The nature and relative importance of intramolecular interactions involving both the α-methyl substituents and the C(?X)Y (X, Y? O or S) fragment are also discussed.     

Investigation of Organic-Inorganic Hybrid Materials Prepared by Irradiation

New silica-based hybrid materials have been produced by gamma irradiation of the precursors using a ⁶⁰Co source. An inorganic mixture of tetraethylorthosilicate with addition of Zirconium propoxide (PrZr) (x = 0, 5 and 10 mol%) was used together with polydimethylsiloxane (PDMS) silanol terminated. Samples with volume ratios organic/inorganic of 4/1, 3/2, 1/1, 2/3 and 1/4 were prepared. The irradiation dose for gel point was observed to depend on the PDMS/ INORG. volume ratio, as expected. That dose increases with decreasing volume ratio. Samples with PDMS/ INORG = 2/3 were irradiated to several irradiation doses above that corresponding to the gel point, which becomes higher for higher fraction of PrZr added. The resulting samples are homogeneous, transparent and flexible being able of swelling in a good solvent of the polymer. The microstructure of the samples was investigated by Small Angle Neutron Scattering. Samples were measured as prepared, and immersed in deuterated cyclohexane. Results indicate the presence of oxide dense clusters interconnected by polymer structures. The addition of PrZr in the preparation stage increases the density of the clusters and decreases their size.     

An Alternative Method for the Preparation of Diphenylboron Chelates. The Crystal and Molecular Structures of (Pyridine‐2‐acetyloximato)diphenylboron and (1‐Phenylazo‐2‐naphtholato)diphenylboron

A convenient method for the preparation of diphenylboron chelates from ammonium tetraphenylborate is described. A variety of five‐ or six‐membered O,O‐, N,O‐ and N,N‐chelates were obtained in yields from 60 to 90 %. The isolated compounds were characterized by elemental analysis, IR spectroscopy and multinuclear magnetic resonance spectroscopy (¹H, ¹³C, and ¹¹B). The crystal and molecular structures of (pyridine‐2‐acetyloximato)diphenylboron and (1‐phenylazo‐2‐naphtholato)diphenylboron were determined by X‐ray diffraction on single crystals.     

Magnesium doping on brownmillerite Ca2FeAlO5

Ca₂FeAl_1−xMg_xO₅ (x=0, 0.05 and 0.1) compounds adopting the brownmillerite-type structure were prepared by a self-combustion route using two different fuels. Characterisation was performed using X-ray powder diffraction, Mössbauer spectroscopy, magnetisation measurements, chemical analysis, scanning electron microscopy and 4-point dc conductivity measurements. Global results indicate that the solubility limit was reached for x=0.1. An antiferromagnetic behaviour was detected for all studied compositions, with magnetic ordering temperatures of 340 and 290 K for x=0 and 0.05, respectively. Mg doping increases the number of iron cations in tetrahedral sites, which induces magnetisation enhancement at low temperatures through the coupling between octahedral iron cations in different octahedral planes. The compounds exhibit semiconductor behaviour and Mg²⁺ doping yields a significant enhancement of the total conductivity, which can be essentially attributed to the presence of Fe⁴⁺ ions.     

Spectrophotometric Determination of Dithionite in Household Commercial Formulations Using Naphthol Yellow S

 A rapid and quantitative procedure for the determination of dithionite based on the reduction of naphthol yellow S in ammonia containing solution and measurement of the absorbance of the product formed at 502 nm is described. The mechanism of the reaction is discussed and its analytical application is shown to be possible in a concentration range of dithionite between 16.7 and 133.1 mg l⁻¹ (1.3 × 10⁻⁴ and 1.04 × 10⁻³ mol l⁻¹). The procedure was applied to the determination of dithionite in commercial formulations used in the household. In a 0.5 g sample of decolorant, dithionite was found to be present at concentrations between 25 and 35% (w/w), which can be determined without interference of its decomposition products. The results are shown to be in good agreement with those of polarographic determinations. Received April 26, 2001. Revision August 2, 2001.     

Ellipsometry as a probe of crystallization kinetics in thin diblock copolymer films

We present results on the use of ellipsometry as a novel probe for the crystallization kinetics in thin films of a diblock copolymer. Ellipsometry makes use of the change in polarization induced upon the reflection of light from a film-covered substrate to enable the calculation of the refractive index and thickness of the film. The information obtained with these measurements can be compared with information from differential scanning calorimetry, with the additional advantages that small sample volumes and slow cooling rates can be employed and that expansion coefficients can be determined. By studying the temperature dependence of these quantities, we are able to measure the crystallization kinetics within very small volumes (∼10⁻¹⁰ L) of a poly(butadiene-b-ethylene oxide) diblock copolymer. Through a comparison of two different poly (ethylene oxide) block lengths, we demonstrate a reduction in both the crystallization and melting temperatures as the domain volume is reduced. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3448–3452, 2006     

Chaotic properties of the elliptical stadium

The elliptical stadium is a curve constructed by joining two half-ellipses, with half axesa>1 andb=1, by two straight segments of equal length 2h.Donnay [6] has shown that if 1 <a < and ifh is big enough, then the corresponding billiard map has a positive Lyapunov exponent almost everywhere; moreover,h asa In this work we prove that if , then assures the positiveness of a Lyapunov exponent. And we conclude that, for these values ofa andh, the elliptical stadium billiard mapping is ergodic and has theK-property.During this work, partially supported by Fac. de Ciencias, UruguayPartially supported by CNPq, Brasil