Cezar Augusto Bizzi

In this work, a sample preparation method based on ultrasound-assisted extraction (UAE) for the determination of Al, Ba, Ca, Fe, K, Mg, Mn, Na, P, Sr, and Zn in lignocellulosic biomasses (sugarcane bagasse, eucalyptus wood residues, and pine wood residues) was evaluated. Reference values were achieved following the EN ISO 16967, which was based on a microwave-assisted wet digestion sample preparation method for further element determination by inductively coupled plasma optical emission spectrometry (ICP OES). The optimizations for the proposed UAE method were performed using 250 mg of sugarcane bagasse sample, where the ultrasonic bath frequency (25, 35, 37, 45, 80, and 130 kHz), and acoustic amplitude (50, 70 and 100%) were evaluated. After selecting the most efficient extractant solvent (20 mL of 1 mol L-1 of H2O2, HNO3, H2SO4, H2O, or CH2O2), the extraction temperature (20, 50, or 70 ºC) and time (15, 30, or 40 min) were evaluated. The most efficient extraction condition using the UAE method employed 45 kHz (70% amplitude), 20 mL of 1 mol L-1 of H2SO4, and 50 °C for 30 min. The optimized UAE was used for extraction and subsequent element determination in residues of pine wood and eucalyptus wood. Although poor recoveries were observed for Al, Ba, and Fe (lower than 75%), the results for Ca, K, Mg, Mn, Na, P, Sr, and Zn were in agreement (Student t-test, 95% confidence level) with those obtained by EN ISO 16967. Therefore, the proposed UAE method proved to be efficient for the determination of most of the evaluated elements in lignocellulosic biomasses with different matrix complexity, employing milder extraction conditions and diluted reagents.

Lignocellulosic materials have been considered as an alternative source from which liquid biofuel and fine chemicals can be produced with a moderate environmental impact. However, they can be contaminated with metals, soil, and ash, owing incrustation and corrosion of industrial reactors and pipelines. In this work, the use of ultrasound energy was applied for the removal of metals and nonmetals (Ba, Ca, Mg, Mn, P, S, Si, and Sr) from sugarcane straw. Ultrasound-assisted demineralization (UAD) experiments were carried out in ultrasonic baths in several frequencies (from 25 up to 130 kHz). The following experimental conditions were evaluated: demineralization solution (HNO₃, HCl, H₂SO₄, H₂O₂, and H₂O), H₂O₂ concentration (from 5 to 30% v v⁻¹), extraction temperature (from 30 to 70 °C), sonication time (from 5 to 45 min), and ultrasound amplitude (from 10 to 70%). Better demineralization efficiencies (66%) were obtained employing an ultrasound bath operating at 25 kHz for 30 min, ultrasound amplitude of 60%, and using a diluted H₂O₂ solution (15% v v⁻¹) at 70 °C. When the obtained results were compared with those obtained by mechanical stirring (MS, 500 rpm), it was observed that the use of ultrasound energy increased the demineralization efficiency up to 16%. Furthermore, acid hydrolysis was performed to evaluate the influence of US and mechanical stirring in fermentable sugars’ production. The total sugars’ yield (glucose, xylose, and arabinose) increased around 55% for both systems (US and MS). To prove the applicability of the proposed process, some experiments for scaling up were performed using several reaction loads (0.5 to 3 L). An attempt for scaling the proposed process up was well succeeded up to a 3 L load. Therefore, the proposed ultrasound-assisted procedure can be considered as a suitable alternative for high-efficiency demineralization from sugarcane straw.

Microwave-assisted solid sampling analysis coupled to flame furnace atomic absorption spectrometry (MW-SS-FF-AAS) was used for Cd and Pb determination in food-contact polymer samples, with the aim of minimizing reagents and laboratory waste. Operational parameters, such as the FF tube design, the oxygen flow rate, the flame stoichiometry, the sample mass, among others, were evaluated and optimized. Calibration was performed using only reference solutions, and the limits of quantification were 1.7 and 4.6 μg g⁻¹ for Cd and Pb, respectively. Accuracy was assessed by the analysis of certified reference materials (CRMs), and by comparison with the results obtained by inductively coupled plasma mass spectrometry after microwave-assisted wet digestion. The MW-SS-FF-AAS results for the CRMs showed no statistical difference with the certified values, and good agreement was observed with the results of the digestion method. The MW-SS-FF-AAS method was considered suitable for Cd and Pb determination in food-contact polymers. The concentrations of Cd and Pb in the analyzed samples varied from −1, and from −1, respectively. As sample digestion is not necessary, the use of concentrated acids can be avoided by using the proposed MW-SS-FF-AAS method, greatly reducing waste generation.

A single reaction chamber microwave-assisted wet digestion system using O ₂ as an auxiliary reagent and diluted HNO ₃ for multisample digestion and metal determination.

This study aimed to determine the antioxidant activity of red onion peel extract using ultrasound extraction. Antioxidant activity was evaluated using DPPH, inhibition of β-carotene, ABTS and FRAP. The results indicated that the 130 W ultrasound power, in pulsed mode, and with 60% solvent favored flavonoids and total anthocyanins, FRAP and β-carotene. The highest levels of total phenolics were found using 60% solvent, at 130 W, and in continuous extraction mode. DPPH was influenced only by the 60% solvent, and the ABTS values were higher with the 80% solvent, in pulsed mode, and at 130 W of power.