A simple ZVI-Fenton pre-oxidation using steel-nails for NOM degradation in water treatment

The feasibility of a heterogeneous Fenton Process (ZVI/H2O2) using commercial low-carbon-steel nails as the Zero-Valent Iron (ZVI) source was evaluated for the first time for the removal of natural organic matter (NOM) from natural surface waters with distinct physico-chemical characteristics. The synergistic effect of ZVI nails and H2O2 on the process was confirmed. Results showed similar removal efficiencies of NOM in water samples from Thames river and Regent's Park lake (both in London, UK) (under initial pH 3.5 and 100% excess of H2O2 dosage), reaching dissolved organic carbon (DOC) removals of 61.6% ± 3.0 and 59.6% ± 4.7, and UV254 removals of 79.9% ± 0.6 and 77.3 ± 6.2, respectively with 60 min of batch reaction time. ZVI nail surface characterization by scanning electron microscopy (SEM), X-ray energy-dispersive spectroscopy (EDS), and X-ray photoemission spectroscopy (XPS) revealed the formation of a passivating oxide-hydroxide layer on the nail during the reaction, which reduces its surface activity with 20% in continuous use. Results indicate that ZVI/H2O2 process using commercial iron nails is a promising pre-oxidation step for drinking water treatment. The low cost of commercial nails together with the facility of separating them from the water are the main advantages for the application of this process in remote regions with limitations in infrastructure and/or finance

Esterase-D and chromosome patterns in Central Amazon piranha (Serrasalmus rhombeus Linnaeus, 1766) from Lake Catalão

This study presents additional genetic data on piranha (Serrasalmus rhombeus Linnaeus, 1766) complex previously diagnosed due to the presence of distinct cytotypes 2n = 58 and 2n = 60. Three esterase-D enzyme loci (Est-D1, Est-D2 and Est-D3) were examined and complemented with chromosomal data from 66 piranha specimens collected from Lake Catalão. For all specimens the Est-D1 and Est-D2 loci were monomorphic. In contrast, the Est-D3 locus was polymorphic with genotypes and alleles being differentially distributed in the previously described cytotypes and served as the basis for detecting a new cytotype (2n = 60 B). In cytotype 2n = 58 the Est-D3 locus was also polymorphic and presented Mendelian allelic segregation with four genotypes (Est-D311, Est-D312, Est-D322 and Est-D333) out of six theoretically possible genotypes, presumably encoded by alleles Est-D31 (frequency = 0.237), EsT-D32 (0.710) and Est-D33 (0.053). A Chi-squared (χ2) test for Hardy-Weinberg equilibrium was applied to the Est-D3locus and revealed a genetic unbalance in cytotype 2n = 58, indicating the probable existence in the surveyed area of different stocks for that karyotypic structure. A silent null allele (Est-D30 with a high frequency (0.959) occurred exclusively in the 2n = 60 cytotype. On the other hand, the new cytotype 2n = 60 B described here for the first time was monomorphic for the presumably fixed Est-D33 allele. The data as a whole should contribute to the better understanding the rhombeus complex taxonomic status definitíon in the Central Amazon. © 2006 Sociedade Brasileira de Genética

Isothermal calorimetric investigation of the interaction of poly(N-isopropylacrylamide) and ionic surfactants

The interaction of poly(N-isopropylacrylamide) (PNIPAM) with an anionic (SDS) and three cationic (dodecyl and hexadecyltrimethylammonium bromides, DTAB and CTAB, and dodecylammonium chloride, DAC) surfactants has been studied using isothermal titration calorimetry between 17 and 29 degreesC. The high sensitivity of this technique allows precise determination of the parameters that characterize polymer-surfactant interactions. Based on these results, it is possible to conclude that the interaction of PNIPAM with ionic surfactants is significantly affected by temperature. This is attributed to changes in polymer hydration, which become more important near the lower critical solution temperature (approximate to32 degreesC). Interaction of PNIPAM with SDS is more favorable than with cationic surfactants. Surfactant hydrophobicity is also an important factor for this interaction, with CTAB displaying a more intense interaction than DTAB. The contribution from the size of the headgroup was also investigated: DAC interacts more strongly than DTAB with PNIPAM. Thus, for the same degree of hydrophobicity, a smaller headgroup favors interaction.108103196320

An algebraic method for solving Hartree-Fock equations. II. Open-shell molecular systems

This paper is the follow-up of an earlier one. It presents (i) the system of nonlinear algebraic equations of the Algebraic Method corresponding to the Hartree-Fock-Pople-Nesbet Approach; and (ii) a systematic study of the variations of the energy of an Unrestricted-Hartree-Fock (UHF) type wave-function as a function of molecular orbitals, for some molecular systems. The results show explicitly for NH, OH and CH the existence of two Hartree-Fock (HF) minimum points with the same spatial symmetry and satisfying the aufbau occupancy rule