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This paper describes the structural and textural characteristics of silicon oxycarbide ceramics obtained from three different hybrid polymers by varying pyrolysis temperature. The first polymer was prepared by hydrosilylation between poly(hydromethylsiloxane) and divinylbenzene in stoichiometric proportions; the second was similarly obtained, but with excess of divinylbenzene (60 wt.%) and the third was also synthesized with 60 wt.% divinylbenzene, involving simultaneously hydrosilylation and radical reactions. Precursors were pyrolysed under argon at 1000, 1200 and 1500°C to produce silicon oxycarbide-based ceramics. Silicon carbide phase development and devitrification resistance were influenced by the disordered and ordered residual carbon fraction, which was directly related to the polymer structure. High specific surface area and pore volume values were obtained in C-richer ceramics at 1500°C derived from poly(divinylbenzene) network-containing precursor. Silicon oxycarbide matrices, derived from hybrid polymers containing graphitic carbon and silicon carbide phases together with different amount of porosity, revealed desirable features for electrochemical applications and adsorbent systems.

A new screen-printed electrode (SPE) modified with carbon black and ternary oxide (SiO2/TiO2/Nb2O5), denominated SPE/CB/SiTiNb and was developed for the direct detection of triclosan in tap water and mouthwash samples. The morphological characterization and electrochemical behavior of the sensors were performed by scanning electron microscopy, energy dispersive spectroscopy, and cyclic voltammetry. Differential pulse voltammetry was used to evaluate the proposed sensor in Britton–Robinson buffer 0.1 mol L−1 and showed a limit detection of 1.23 nmol L−1 in a linear range from 0.025 to 57.01 µmol L−1. Studies with possible interferents were performed demonstrating a significant selectivity of the sensor to the triclosan oxidation reaction. The sensor was applied in tap water and mouthwash real sample analyses, whose recoveries ranged from 93.4 to 98.8%, demonstrating that the sensor shows promise in the detection of triclosan in different matrices allied to high sensitivity, selectivity, low-cost, portability, disposability, and low sample volume, without pre-treatment, per analysis. [ABSTRACT FROM AUTHOR]

The study aimed to develop an electrochemical sensor based on glassy carbon, mixed oxide (SiO2/TiO2/Sb2O5), and carbon black. The material was synthesized, characterized, and used to determine thiamethoxam in raw honey and water. The morphologic structure and electrochemical performance of the sensor was characterized by scanning electron microscopy and cyclic voltammetry. Differential pulse voltammetry with a concentration of 0.1 mol L−1 of Britton-Robinson buffer at pH 7.0 allowed the generation of a method to determine thiamethoxam in a linear range of 0.25 to 100.5 μmol L−1 and with a limit of detection of 0.012 μmol L−1. The system efficiently quantified traces of thiamethoxam in raw honey and tap water samples. The modified sensor did not present interferences of K+, Na+, Ca2+, Mg2+, glyphosate, imidacloprid, and carbendazim. In addition, the device showed good recovery values for thiamethoxam when applied directly to honey and water samples without any treatment, presenting an electrochemical sensor to monitor real-time hazardous substances in environmental and food matrices. [ABSTRACT FROM AUTHOR]

The present paper describes a new analytical method exploiting a SiO2/WO3 mixed oxide as an adsorbent synthesized via sol-gel process for the preconcentration of Ni2+. This material was characterized by energy dispersive X-ray fluorescence spectroscopy, powder X-ray diffraction, Fourier transform infrared spectroscopy, analysis of the specific surface area by Brauner, Emmett and Telle multipoint method, the average pore size and pore volume by Barrett-Joyner-Halenda method, scanning electron microscopy, and electron dispersive spectroscopy. The mixed oxide presented high surface area (710.9 m2 g−1), average pore size of 35.1 Å, and average pore volume of 0.128 cm−3 g−1. This material was used as the an adsorbent in an on-line procedure for pre-concentration of solid phase extraction, based on the adsorption of Ni2+ ions at pH 10.5 followed by elution with 1.0 mol L−1 HNO3 and determination by flame atomic absorption spectrometry. Under optimized conditions, a linear range from 10.0 to 170.0 µg L−1, an enrichment factor of 38.8-fold, and limits of detection and quantification of 4.23 µg L−1 and 14.11 µg L−1 were obtained. The precision of method, estimated as percentage of relative standard deviation of ten replicates of 30.0, 90.0 and 150.0 µg L−1 Ni2+ solutions, was lower than 4.10%. The method was employed for analysis of water samples and the accuracy was attested by addiction and recovery tests, with satisfactory recoveries (98.4–109.2%). Thus, the developed material can be successfully applied to water samples for monitoring of Ni2+ at very low levels without matrix influence. [ABSTRACT FROM AUTHOR]

SiO/TiO/SbO ternary oxide was prepared by the sol-gel method in two different proportions, and were characterized by X-ray fluorescence (XRF), analysis of the specific surface area by BET and the average pore size and pore volume by BJH method, thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and electron dispersive spectroscopy (EDS) analyses, powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and other spectroscopic technics (FT-Raman, FT-IR, UV-Vis-NIR and DRS). The ternary oxides showed high surface area 758 and 529 m g for SiTiSb-A and SiTiSb-B, respectively. The binding energy values for the Sb 3d and Ti 2p levels show the insertion of Sb and Ti atoms in the silica matrix, confirming the high dispersion of the metals presented in SEM, both in the bulk and on the surface. The thermogravimetric analysis (TGA) showed weight loss of 23% for both ternary oxides. The crystallographic data showed an increase of the crystalline order with the increase of the temperature of the thermal treatment. The anatase phase as well as a small content of the rutile phase of TiO were identified by FT-Raman. The Raman spectrum corroborated with the DTA and XRD of the SiTiSb-B which showed a slight decrease in the degree of crystallinity. Optical band gap values are dependent on the content of oxides. The pyridine adsorption studies showed the presence of Lewis and Brønsted acid sites on the SiTiSb ternary oxide surface, where the SiTiSb-B presented more acid sites on the surface. [ABSTRACT FROM AUTHOR]

In the present paper an amperometric sensor based on graphite-SiO2/Al2O3/Nb2O5- methylene blue (GRP-SiAlNb-MB) composite has been successfully prepared for dopamine (DA) determination in real samples. The electrochemical behavior of DA at the GRP-SiAlNb-MB has been evaluated by employing cyclic voltammetry. The best ratio (m/m) of GRP-SiAlNb-MB composite was found to be 1:0.54. Under optimized conditions (pH 7.5 in 0.15 mol L-1 phosphate buffer) the amperometry method responds linearly to DA from 5.0 up to 500.0 lmol L-1 (r= 0.995) with limits of detection and quantification of 1.49 and 4.97 lmol L-1, respectively. The developed method was successfully applied for DA determination in real samples of pharmaceutical formulations and can be used for routine quality control analysis of pharmaceutical formulations containing DA. The use of inorganic matrix SiAlNb was found to be very useful to adsorb MB in the composite material with further improvement of the anodic peak current of DA. [ABSTRACT FROM AUTHOR]

A SiO2/Al2O3/Sb2O5mixed oxide was synthesized via a sol-gel method and applied to the on-line preconcentration of Ni(II) with determination by flame atomic absorption spectrometry. The mixed oxide was characterized by infrared spectroscopy, scanning electron microscopy, energy dispersive X-ray fluorescence, thermogravimetric analysis, and the specific surface area. Analysis was performed by percolating 20.0 mL of sample at pH 7.1 through 100 mg of SiO2/Al2O3/Sb2O5packed into a mini-column at 9.5 mL min−1. Under the optimum conditions, a preconcentration factor of 77.5-fold, linear dynamic range from 5.0 to 270.0 µg L−1, and limits of detection and quantification of 0.48 and 1.61 µg L−1were obtained. The effects of several concomitant ions were evaluated and no interferences were observed. The method was employed for the analysis of water with good recoveries (92.9–100.6%) and the accuracy was verified by using a marine sediment certified reference material (MESS-3). [ABSTRACT FROM AUTHOR]