Navegando por Autor "Monteiro, Douglas Santos"
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Item d-FeOOH : a superparamagnetic material for controlled heat release under AC magnetic field.(2013) Chagas, Poliane; Silva, Adilson Cândido da; Passamani, Edson Caetano; Ardisson, José Domingos; Oliveira, Luiz Carlos Alves de; Fabris, José Domingos; Paniago, Roberto Magalhães; Monteiro, Douglas Santos; Pereira, Márcio CésarExperimental evidences on its in vitro use reveal that d-FeOOH is a material that release-controlled amount of heat if placed under an AC magnetic field. d-FeOOH nanoparticles were prepared by precipitating Fe(OH)2 in alkaline solution followed by fast oxidation with H2O2. XRD and 57Fe Mo¨ssbauer spectroscopy data confirmed that d-FeOOH is indeed the only iron-bearing compound in the produced sample. TEM images evidence that the averaged particle sizes for this d-FeOOH sample is 23 nm.Magnetization measurements indicate that these d-FeOOH particles behave superparamagnetically at 300 K; its saturationmagnetization was found to be 13.2 emu g-1; the coercivity and the remnant magnetization were zero at 300 K. The specific absorption rate values at 225 kHz were 2.1, 6.2, and 34.2 W g-1, under 38, 64, and 112 mT, respectively. The release rate of heat can be directly controlled by changing the mass of d-FeOOHnanoparticles. In view of these findings, the so-preparedd-FeOOHis a real alternative tobe further tested as amaterial formedicalpractices in therapies involving magnetic hyperthermia as in clinical oncology.Item Enhanced photocatalytic hydrogen generation from water by Ni(OH)2 loaded on Ni-doped d-FeOOH nanoparticles obtained by one-step synthesis.(2013) Rocha, Thomás da Silva; Nascimento, Eliandro Silva; Silva, Adilson Cândido da; Oliveira, Henrique dos Santos; Garcia, Eric Marsalha; Oliveira, Luiz Carlos Alves de; Monteiro, Douglas Santos; Rodriguez, Mariandry del Valle Rodriguez; Pereira, Márcio CésarNi(OH)2 loaded on Ni-doped d-FeOOH photocatalysts were prepared by a simple and low-cost one-step precipitation method. The effect of Ni(OH)2 nanoparticles and Ni2+ doping on the photocatalytic hydrogen production rates by d-FeOOH in aqueous suspension was investigated. The results showed that the photocatalytic H2-production activity of d-FeOOH was significantly enhanced by doping with Ni2+ ions and by loading Ni(OH)2 on its surface. The maximum H2-production was obtained for the sample with 20 wt% Ni, which provided 5746 mmol h 1 g 1. This high photocatalytic H2-production is due to the combined effects of Ni2+ doping and Ni(OH)2 loaded on the d-FeOOH surface. The Ni2+ doping increased the conductivity and charge transfer in d-FeOOH, whereas the Ni(OH)2 improved the charge separation in the d-FeOOH and, consequently, the photocatalytic H2-production activity.Item Production of reduced graphene oxide platelets from graphite flakes using the Fenton reaction as an alternative to harmful oxidizing agents.(2019) Velásquez Piñas, Jean Agustin; Andrade, Tatiana Santos; Oliveira, Andreia Teixeira de; Salomão, Pedro Emílio Amador; Rodriguez, Mariandry del Valle Rodriguez; Silva, Adilson Cândido da; Oliveira, Henrique dos Santos; Monteiro, Douglas Santos; Pereira, Márcio CésarThe conventional chemical methods to produce graphene using strong oxidizing agents produce toxic gases during synthesis; therefore, these methods do not meet the principles of green chemistry. In this work, an alternative top-down method for the synthesis of a few layers of graphene sheets has been produced by a Fenton reaction- (a mixture of Fe2+/H2O2) assisted exfoliation process in water using graphite flakes as a starting material. Based on X-ray diffraction data and Fourier transform infrared (FTIR), Raman spectroscopy, and transmission electron microscopy measurements, it is proposed that the oxidation of graphite by Fenton chemistry facilitates the exfoliation of graphene sheets under mild sonication. Subsequent chemical reduction with ascorbic acid produced a few layers of reduced graphene oxide. Compared to Hummers’ method, the Fenton reagent has similar exfoliation efficiency, but due to the Fenton reagent’s preference to react with the edges of graphite, the chemical reduction can lead to the formation of less defective reduced graphene oxides. Moreover, since Fe and H2O2 are cheap and environmentally innocuous, their use in large-scale graphene production is environmentally friendlier than conventional methods that use toxic oxidizing agents.