Determinação de fósforo em aços por espectrometria de absorção atômica no forno de grafite

A method for the determination of phosphorus in steel samples by graphite furnace atomic absorption spectrometry, using the Zeeman effect background correction and the STPF conditions is proposed. The effect of iron (III) on the phosphorus signal was studied. It was verified, through the pyrolysis temperature curves, that iron (III) is an efficient chemical modifier, thermically stabilizing phosphorus up to 1400ºC. The phosphorus signal increases with the iron (III) concentration, but in the range, which corresponds to the usual concentrations of iron in the sample solutions, the increase is small. Phosphorus was determined in three standard reference materials, after its dissolution in a mixture of hydrochloric and perchloric acids in a PTFE bomb. The agreement with the certified concentration values was excellent. Iron (III) was added to the reference analytical solutions prepared in the blank of the dissolution, while the sample solutions were measured directly, since they already contained the modifier. The detection limit (k = 2) was 0.0042% of phosphorus in the steel sample.

Modelo teórico quântico para o processo de adsorção física

This article introduces a simplified model for the theoretical study of the physical adsorption process of gaseous He on the planes (100) and (111) of the solid Xe matrix, whose crystalline structure is face centered cubic (fcc). The Ab initio calculations were carried out at the MP2 level of theory employing basis sets obtained through the Generator Coordinate Method, where the core electrons were represented by a pseudopotential. The calculated adsorption energies for the (100) and (111) faces are 5,39 and 4,18 kJ/mol, respectively. This simplified model is expected to be suitable for treating complex systems of applied interest.

Análise das isotermas de adsorção de Cu(II), Cd(II), Ni(II) e Zn(II) pela N-(3,4-dihidroxibenzil) quitosana empregando o método da regressão não linear

Adsorption of Cu(II), Ni(II), Pb(II) and Zn(II) ions from aqueous solutions by N-(3,4-dihydroxybenzyl) chitosan have been carried out. The Langmuir (L), Freundlich (F), Langmuir - Freundlich (LF), Redlich-Peterson (RP) and Tóth (T) adsorption isotherms models have been applied to fit the experimental data. Nonlinear regression computational program "Enzefitte", which is a library of the more commonly used adsorption isotherm equations for obtaining tabular outuput suitable for plotting theoretical of fitted isotherms, has been used to estimate the adsorption parameters. These parameters were used to calculate the amount adsorbed q calc., a function of concentration (C).

Determinação de fósforo orgânico em águas de produção petrolífera por ICP- AES e ICP- MS após pré-concentração em coluna de sílica-C18

Results on the optimization of analytical methods for the determination of phosphorus in phosphino-polycarboxylate (PPCA), used frequently as scale inhibitor during oil production, by ICP-AES and ICP-MS are presented. Due to the complex matrix of production waters (brines) and their high concentration in inorganic phosphorus, the separation of organic phosphorus prior to its determination is necessary. In this work, minicolumns of silica immobilized C18 were used. Optimization of the separation step resulted in the following working conditions: (1) prewashing of the column with methanol (80% v/v); (2) use of a flow rate of 5 mL/min and 10 mL/min, respectively, for the preconditioning step and for percolation of the water sample; (3) final elution of organic phosphorus with 7 mL of buffer of H3BO3/NaOH (0.05 M, pH 9) with a flow rate of 1 mL/min. Sample detection limits (3s) for different combinations of nebulizers and spectrometric methods, based on 10 mL water aliquots, are: ICP-AES -Cross flow (47 mg/L) and Ultrasonic (18 mug/L); ICP-MS -Cross flow (1.2 mug/L), Cyclonic (0.7 mug/L) and Ultrasonic (0.5 mug/L). Typical recoveries of organic phosphorus are between 90 and 95% and the repeatability of the whole procedure is better than 10%. The developed methodology was applied successfully to samples from the oil-well NA 46, platform PNA 2, Campos basin, Brazil. Assessment of the PPCA inhibitor was possible at lower concentrations than achieved by current analytical methods, resulting in benefits such as reduced cost of chemicals, postponed oil production and lower environmental impacts.

Reações de Cp'(CO)2MnPPH2H com CH3COCl e CH3S(O)2Cl em THF/trietilamina: evidências da primeira estabilização por complexação de um fósforo-homólogo das sulfonamidas

Cp'Mn(CO)3 (Cp'=h5-C5H4-CH 3) reacts with P(C6H5)2H in THF to give Cp'(CO)2MnPPh2H (Ph = Phenyl) (1), by substitution of one CO ligand. The reaction of 1 with CH3COCl and CH3S(O)2Cl in the presence of triethylamine occurs under electrophilic substitution on the diphenylphosphan ligand to yield the acetyl- and sulfonylphosphane complexes of manganese(I) Cp'(CO)2MnPPh2COCH3 (2) and Cp'(CO)2MnPPh2S(O)2 CH3 (3). The complex stabilisation of these molecules, wich are hitherto unknown in the free state, is only accomplished by blocking the free electron pair on phosphorus by coordination. The new complexes 1, 2 and 3 were analysed by IR, ¹H-NMR and 31P-MNR spectroscopy and their similar structures are discusssed.

Estudo da adsorção/dessorção do ácido 2,4 diclorofenoxiacético (2,4d) em solo na ausência e presença de matéria orgânica

The herbicides are being used in huge quantities for various porpouses. Once the herbicide finds its way into the environment, a major part of it comes in contact with soil. Humic substances are major organic constituents of soil. These substances may interact with herbicides in different modes and adsorption is probably the most important one. Adsorption will control the quantity of herbicide in the soil solution, and determines its persistence, leaching, mobility and bioavailability. In this work we studied the interaction between the herbicide 2,4D and soil in the presence and absence of organic matter. The methodology utilized for the determination of 2,4D was gas chromatography with eletron capture detector. The behavior of 2,4D was evaluated through Freundlich isotherms. It was verified that the herbicide 2,4D has a large adsorption in the humic acid .

Adsorção do complexo H[Ru(III)Cl2(H2EDTA)] sobre a superfície da sílica gel modificada com [3-(2-aminoetil) aminopropil]trimetoxissilano em soluções etanólicas

Silica gel was functionalized with [3-(2-aminoethyl)aminopropyl]trimethoxysilane group (SF-AEATS) and the characterization by chemical analysis (N) and infrared spectroscopy confirmed the functionalization. The capacity of the modified silica to adsorb the complex Ru(III)-EDTA from ethanolic solution was studied. The selectivity coefficients of the complex formed on the support obtained was (Gñ), 2,07 x 10(4) L/mol and the average number of ligand bonded by one metal ion on the support (ñ) was ~ 1.

Estudo por espectroscopia no infravermelho da interação metal-suporte em Pt/TiO2. A influência da adsorção de hidrogênio

The influence of the presence of hydrogen on Pt/TiO2 catalysts submitted to reduction treatment has been studied by FT-IR at room temperature. After submitting to LTR treatment, the hydrogen spillover has been detected and the presence of hydrogen at the bulk is shown to produce a strong absorption in the infrared spectral region. After HTR treatment, the hydrogen is strongly chemissorbed.

Adsorção de íons Cu2+ em latossolo vermelho-amarelo húmico

In environmental studies it is necessary to know the adsorption behavior of metals by soils, since the unfavorable effects of heavy metals and even the micronutrients at high concentrations in the environment are related to these adsorbents' ability to immobilize them. A sample of a humic yellow red oxisol from Araponga region in the State of Minas Gerais, Brazil, was used to verify the adsorption behavior of Cu2+ ions in this substrate. The mathematical model described by Langmuir's adsorption equation in its linearized form was applied and the values of the maximum capacity b and those of the constant related to the bonding energy a were obtained. Aliquots of copper nitrate solutions containing several concentrations of this metal were added to soil samples, the pH being predetermined for developing the adsorption experiments. The chemical and physical characterization of soil sample were performed by determining the organic carbon, nitrogen and phosphorus concentrations, cation exchange capacity (CEC), pH, concentration of metals (Al, Fe, K, Mg, Ca, Zn, Cu, Ni, Cr, Co, Pb, and Cd), granulometric analysis and X-ray diffraction. Langmuir isotherms presented two distinct adsorption regions at both pH 4 and pH 5, showing that the adsorptive phenomenon occurs in two distinct stages. The adsorption sites for the lower part presented greater bonding energy and low adsorption capacity compared with the adsorption sites of the part of the curve corresponding to higher Cu concentrations in the equilibrating solution.

Adsorção de zinco e cádmio em colunas de turfa

The aim of this work was to evaluate the adsorption conditions of zinc and cadmium ions from aqueous solutions using a comercially available peat from Balneário Arroio do Silva, Santa Catarina State, Brazil. Adsorption studies were carried out in column experiments using radiotracers of the studied metals (65Zn and 115Cd). The pH influence and the interference of other ions, such as Na+, Ca2+, Fe3+ and Al3+on the adsorption process were investigated. The results showed that peat columns are able to retain more than 99% of metal ions in solution in a range of pH from 3,7 to 6,5. Ca2+ and Al3+ ions were the main interferent on adsorption of Zn and Cd ions in solution.

Caracterização química e física de turfa litorânea e avaliação da adsorção competitiva por cobre e zinco

The chemical and physical characterization of coastal peat has been studied. It was examined the pH, organic matter content and elementary and XRD analyses, among other characteristics. The peat was then applied to the retention and competition of metal micronutrients (Cu and Zn) from metal nitrate solutions. The retention was affected by both the pH and time of adsorption, while the competitive character of these metals for the substrate was relevant to each pH examined.

Utilização de modelos físico-químicos de adsorção no estudo do comportamento do cobre em solos argilosos

It was evaluated the applicability of Langmuir, Freundlich and Temkin models to copper adsorption in three classes of soils. Fractions of each soil were added to test tubes containing growing concentrations of the metal in solution. The tubes were shaken and the copper concentrations were determined in the extracts by atomic absorption spectrometry (AAS). The models offered a good fit for the experimental data indicating that presence of silicated clay had high influence on copper sorption. The Langmuir isotherm showed high influence of the organic matter in the absorption phenomenon. It was evidenced the importance of further studies related to Temkin model.

Estudo da adsorção de hidrogênio e sulfeto na superfície de paládio: aspectos experimentais (eletroquímica) e teóricos (ab initio e Teoria do Funcional da Densidade)

The adsorption of H and S2- species on Pd (100) has been studied with ab initio, density-functional calculations and electrochemical methods. A cluster of five Pd atoms with a frozen geometry described the surface. The computational calculations were performed through the GAUSSIAN94 program, and the basis functions adapted to a pseudo-potential obtained by using the Generator Coordinate Method adapted to the this program. Using the cyclic voltammetry technique through a Model 283 Potentiostat/Galvanostat E.G.&G-PAR obtained the electrochemical results. The calculated chemisorption geometry has a Pd-H distance of 1.55Å, and the potential energy surface was calculated using the Becke3P86//(GCM/DFT/SBK) methodology. The adsorption of S2- ions on Pd surface obtained both through comparison between the experimental and theoretical results, at MP2 level, suggest a S2- absorption into the metallic cluster. The produced Pd-(S2-) system was show to be very stable under the employed experimental conditions. The paper has shows the powerful aid of computational methods to interpret adsorption experimental data.

Adsorção de xantatos sobre pirita

This paper presents a study of adsorption of xanthate with alkyl chain of two (C2XK), four (C4XK) and eight (C8XK) atoms of carbon, on pyrite from Santa Catarina, Brazil. The results showed that pyrite surface changes from hydrophilic to hydrophobic when xanthate is adsorbed increasing the contact angle to 35º for C2XK, and to 90º for C4XK and C8XK. The rate of flotation of pyrite particles after adsorption increases with the increase of the number of carbon atoms in the alkyl chain in agreement with the results of contact angle measurements.

Correlação entre a estrutura atômica superficial e o processo de adsorção-dessorção reversível de hidrogênio em eletrodos monocristalinos Pt(111), Pt(100) e Pt(110)

Platinum is widely used as electrode in electrocatalytic processes, however the use of polycrystalline electrodes introduces a series of variables in the electrochemical system due to the aleatory contribution of all the crystallographic orientations with different surface packing of atoms. Single crystal platinum electrodes of low Miller index present surface structure of high regularity and serve as model to establish a correlation among the macroscopic and microscopic properties of the electrochemical interface. Therefore, the main aim of this work is the study of the voltammetric profiles of the reversible adsorption-desorption of hydrogen on Pt(100), Pt(110) and Pt(111), in order to correlate the electrochemical properties of each different orientation with the surface atomic structure.