Síntese, caracterização e estudo das propriedades catalíticas e magnéticas de nanopartículas de Ni dispersas em matriz mesoporosa de SiO2

Nickel nanoparticles supported on amorphous silica ceramic matrix were synthesized by the polymeric precursor method. The nanostructure was characterized by NMR, BET, XRD, SEM, TEM, and flame atomic absorption spectrometry techniques. It was observed a dependence of the crystallite size on the thermal annealing, under a N2 atmosphere. The materials presented a high catalytic activity and selectivity upon the beta-pinene hydrogenation reaction. The magnetic hystereses were also correlated with the morphology of the processed material.

Procedimentos para recuperação de Ag de resíduos líquidos e sólidos

A simple procedure for recovering Ag, generated as residual solutions, from three different analytical methods, is presented. Based on the rate of the total Ag mass recovered, to the initial one in the initial residual solutions, efficiency as high as 97,9 ± 2,9% was obtained in the process. The purity of Ag, as Ag2O, was verified by employing this reagent in the determination of S in plant tissue. This leads to the generation of a solid metallic Ag as waste. In this situation, an 88,7 ± 0,6% Ag recovery was acquired, when a HNO3 solution was employed as solvent.

Gerenciamento de resíduos laboratoriais: recuperação de elementos e preparo para descarte final

This work shows some laboratory waste management developed in order to recover some elements or to prepare the waste for a correct final disposal. The 25 elements chosen cover basically all chemical behaviors found for the metals in the Periodic Table. The treatments adopted were based on the classical behavior in aqueous solution (wet chemistry) but an important condition for a full success was the previous knowledge of the qualitative composition of the wastes treated. Some general trends were found: the final liquid waste was always saline and normally presented a higher volume than the original waste; most original wastes were acid in nature; steps such as solid-liquid separation, washing, evaporating and calcining were currently performed. This work was also a very good experience in chemistry in solution for students and showed them the need of treating wastes for a better environment.

Aplicações eletroanalíticas com eletrodos de prata confeccionados a partir de CDs graváveis

This paper presents a new way for the construction of silver electrodes utilizing recordable CDs. The new electrodes were explored for the quantification of chloride (by potentiometry/FIA), cyanide (by amperometry/FIA) and for lead analysis (by square wave voltammetry). For the flowing measurements, a digital multimeter, connected to a microcomputer (via RS 232 interface) was used to collect directly the potential signal (for Cl- measurements) or to take the output signal from a potentiostat (for CN- measurements). The square wave voltammetry analysis was performed in a commercial instrument. The results shown good performance of the new electrodes and the detection limit (s/n = 3) attained for these three analytes were: 0.2, 50, and 200 µg L-1 for Pb2+, Cl-, and CN- respectively.

Recuperação de metais de catalisadores mássicos e monometálicos

This work presents a study on the dissolution of some commercial monometallic and non-supported deactivated catalysts in HF + H2O2 mixtures (and, eventually, other media) under mild experimental conditions, after a previous oxidation step. The samples were neither crushed nor grinded. The best experimental conditions were dependent on the nature of the support and of the active phase. For example, the Pt/Al2O3 catalyst was dissolved in about 10 minutes, without agitation and heating; however, dissolution of the Pd/Al2O3, Ni/Al2O3, Ni/SiO2, Cu/Al2O3 and V2O5 samples required a temperature of 60 ºC and an agitation of 400 rpm. A careful addition of a NaOH solution allowed a quantitative precipitation of aluminium as criolite (Na3AlF6) or precipitation of Si as Na2SiF6; NaF was obtained as a by-product. As expected, processing of Pd/C, V2O5 and CuO.Cr2O3 samples was relatively simple. Metals recovery from catalysts reached a quantitative level in all samples studied; it is particularly interesting that platinum and palladium could be easily recovered in a single step process, thus separing them from aluminium.

Recuperação de sílica-gel utilizando processos oxidativos avançados: uma alternativa simples e de baixo custo

Silica gel is widely used as adsorbent for isolating and purifying natural compounds. Intensive use and high cost make this process expensive and generate solid residues contaminated with many different organic compounds. In the present work a simple method for recycling silica was investigated, by using Advanced Oxidative Processes. Silica gel was treated with H2O2/solar light and compared with a sample treated by conventional methods (high temperature and oxidation with KMnO4). High temperature treatment changes the structure of the silica and, consequently, the separation efficiency. Oxidation by using KMnO4 requires multiple steps and produces residues, including manganese and oxalic acid. The method using H2O2/solar light to recuperate silica gel does not modify its separation efficiency and is less expensive than the traditional methods. Additionally, HPLC and GC-MS analysis indicate that H2O2/solar light eliminates all residues of the silica gel.

Recuperação de bromo em soluções aquosas residuais

A laboratory procedure was devised to recover bromine from waste alkaline aqueous solutions used in the isotopic determination of N-15. The laboratory apparatus comprises two round bottom flasks (1 and 2 L), a dropping funnel, a gas bubbler, a gas regulator and glass fittings. The waste solution is acidified with sulfuric acid forming molecular bromine that is stripped out by a flow of nitrogen gas bubbled through the solution. This gas is then bubbled through a solution of lithium hydroxide generating lithium bromide and lithium hypobromite. The efficiency of bromine recovery was estimated to be 82±2%. This resulting solution was successfully reused in the isotopic determination of N-15. The procedure can recycle most of the bromine used in the laboratory saving resources and preserving the environment. The procedure can be adapted to recover bromine of other laboratory waste streams.

Comportamento da atomização eletrotérmica de ouro, prata, bismuto, cádmio, chumbo e estanho em soluções aquosas e em etanol, a partir de diferentes superfícies atomizadoras

The atomization behavior of Au, Ag, Bi, Cd, Pb, and Sn from pyrolitic graphite coating (L'vov platform) with the use Pd and Mg solutions, and zirconium coated platform with the analytes in nitric acid 0.2% v/v and in ethanol was investigated. In ethanol medium, the sensitivity gain was three-fold for Bi and Cd using Zr as modifier. Without modifier, the ethanol medium is appropriate only for Au and Cd. In nitric acid medium, the Zr coated platform elevates sensitivity at least two-fold for Bi and Cd. The method was applied to the determination of Ag, Au and Bi of certified steel samples, after on-line preconcentration, sorption on a minicolumn filled with C-18 bonded to silica gel and elution with ethanol. The concentrations obtained agreed with the recommended values.

Métodos de preparação de nanopartículas metálicas suportadas em carbono de alta área superficial, como eletrocatalisadores em células a combustível com membrana trocadora de prótons

Fuel cells are attracting much interest as efficient and clean energy conversion devices. The main components of low temperature fuel cells are the electrocatalysts used to promote the anodic and cathodic reactions, which are based on platinum and platinum alloys. These electrocatalysts are normally prepared in the form of metal nanoparticles supported on a conductive material, usually high surface area carbon, to improve catalyst utilization and reduce cost. This work presents and comments some methods used presently to produce these electrocatalysts. The performances of the produced electrocatalysts are compared to that of state-of-the-art commercial E-TEK electrocatalysts.

Fotoluminescência e adsorção de CO2 em nanopartículas de CaTiO3 dopadas com lantânio

Ca1-xLa xTiO3 powders were prepared by the polymeric precursor method. X-ray diffraction (XRD), FT-Raman spectroscopy, transmission electron microscopy (TEM), and N2 and CO2 adsorption were used for the microstructural and surface characterization of the powders. Room temperature photoluminescence (PL) was observed in Ca1-xLa xTiO3 amorphous particles. The PL intensity of these powders was found to be dependent on the lanthanum molar concentration.

Síntese de sulfadiazina e sulfadiazina de prata em escala semi-micro: prática experimental em síntese de fármacos

The total synthesis of sulfadiazine and silver sulfadiazine from readily available starting materials was adapted to semi-micro laboratory scale and is proposed as an experiment in drug synthesis for undergraduate courses.

Aplicação da tecnologia de eletrofloculação na recuperação do corante índigo blue a partir de efluentes industriais

The indigo blue dye is widely used in the textile industry. When discarded, besides polluting the environment, it affects the appearance and transparency of aquatic bodies, causing damage to flora and fauna. The removal of this dye from industrial effluents is difficult due to its resistance towards degradation. This work proposes the recovery of indigo blue by electroflocculation, as a subsidy for the treatment of effluents from the jeans industry.

Determinação turbidimétrica de dipirona em fluxo utilizando um reator contendo cloreto de prata imobilizado em resina poliéster

A simple flow injection procedure was developed for determining dipyrone (1-phenyl-2,3-dimethyl-4-methylaminomethano-5-pyrazolone sodium, metamizol, analgin) in pharmaceutical formulations. The determination is based on the reduction of Ag+ ions to Ag0 by dipyrone. A colloidal suspension of Ag0 produced was transported by carrier solution (0.01 mol L-1 NaOH) and turbidimetrically detected at 425 nm. The analytical curve for dipyrone was linear in the range from 5.0 x 10-4 to 2.5 x 10-3 mol L-1 with a correlation coefficient of 0.9990. The detection limit was 1.3 x 10-4 mol L-1 (3sigmaB/slope). The relative standard deviation for ten successive measurements was 1.8% and an analytical frequency of 45 h-1 was obtained. The recovery values from three samples ranged from 96.0 to 102%.

Recuperação de metais de catalisadores de hidrorrefino usados via fusão com KHSO4

This work describes a process for metal recovery from spent NiMo and CoMo/Al2O3 commercial hydrorefining catalysts. The samples were treated by fusion with potassium hydrogen sulfate (5 h, 600 ºC) with a KHSO4/catalyst mass ratio of 10:1. After fusion the solid was solubilized in water (100 ºC), leaving silicon compounds as residue. Losses of nickel and cobalt may reach 16 wt% of the amount present in the sample, depending on the silicon content. Soluble metals were isolated by selective precipitation techniques (nickel, cobalt, aluminum) or by solvent extraction with methyl-isobutyl ketone (molybdenum) in a hydrochloric acid medium. All metals were recovered in very good yields except for nickel and cobalt in the presence of considerable amounts of silicon. Soluble wastes consist of potassium/sodium sulfates/chlorides. Solid wastes correspond to about 4 wt% of the catalyst and can be discarded in industrial dumps.

Estudo de recuperação de glifosato e AMPA derivados em solo utilizando-se resinas nacionais

In the present paper we studied the recoveries of glyphosate, N-(phosphonomethyl)glycine (GLY) and its major metabolite, (aminomethyl)phosphonic acid (AMPA) in soil using national (Brazilian) ion-exchange resins, derivatization by a mixture of trifluoroacetic anhydride and trifluoroethanol and analyses by GC-MS. The quantification limits were 12 ng.g-1 for both compounds and the methodology showed a range of recuperation from 85 to 94% with coefficients of variation (CV) ranging from 4.07 to 6.91% for GLY. For AMPA, the mean recoveries ranged from 87 to 102% with CVs ranging from 5.81 to 6.99%. Additional studies showed that, due to the instability of the derivatized compounds, they must be analysed keeping constant time between derivatization and analysis, preferably less than 24 h.