Fernanda Gomes de Mendonça

Selective Oxidation of Amorphous Carbon by CO2 to Produce Fe@C Nanoparticles from Bulky Fe/C Matrices

In this work, a bulky Fe0/carbon matrix obtained by a low cost and simple reduction/carbonization of Fe3+ salt with sucrose was treated with CO2 to selectively oxidize the amorphous carbon to release the graphite like carbon coated magnetic Fe0 particles. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman, X-ray diffraction (XRD), BET, thermogravimetric analysis (TG) (in CO2) and particle size analyses showed that the treatment with CO2 of the Fe/carbon bulky composite led to the selective oxidation of the more amorphous carbon with the formation of 125-132 nm Fe@C nanoparticles with surface areas of 217 m2 g−1.

Tuning the surface properties of biochar by thermal treatment

In this work, the effect of controlled thermal treatment to tune biochar surface properties such as area/porosity, functionalities and reactivity was investigated. TG-MS, CHN, Raman, IR, BET, Zeta and SEM analyses suggested that thermal treatment led to the decomposition of an organic complex/amorphous phase to produce micropores based on graphene nanostructures and a strong increase on surface area from 3m2g-1 for biochar to 30, 408 and 590m2g-1, at 400, 600 and 800°C, respectively. The treatment also led to a gradual decrease on oxygen content from 27 to 14wt% at 800°C due to decomposition of surface functionalities changing surface properties such as zeta potential, adsorption of anionic and cationic species and an increase on the activity for sulfide oxidation which is discussed in terms of increase in surface area and the presence of surface redox quinone groups.

Micromesoporous Activated Carbons as Catalysts for the Efficient Oxidation of Aqueous Sulfide

KOH activation of a mesophase pitch produces very efficient carbons for the removal of sulfide in aqueous solution, increasing the sulfur oxidation rate with the degree of activation of the carbon. These carbons are characterized by their graphitic structures, with domains of sizes of around 20 nm, and a moderate concentration of surface oxygen groups (0.2-0.5 mmol·g-1) dominating the basic groups. Because the activation leads first to a strong development of the micropores and later to a development of the mesopores, the surface area values are always high, reaching values of as high as 3250 m2·g-1 in the most activated carbon, with a volume of mesopores of as high as 44% of the total pore volume. In the presence of this carbon, the sulfide oxidation rate is 100 times higher than that found for a commercial activated carbon, the results indicating that the porosity of the carbon, especially mesoporosity, plays a role more important than the structure or the chemical nature of the carbon in the kinetics of sulfide oxidation to different polysulfides.

Surface modified mesoporous nanocast carbon as a catalyst for aqueous sulfide oxidation and adsorption of the produced polysulfides

In this work, a mesoporous nanocast carbon prepared using SBA-15 as a template was modified by surface oxidation to produce unique catalysts for sulfide oxidation/elimination from an aqueous medium. Different characterization techniques (BET, SEM, Raman, FTIR, potentiometric titration, elemental analyses, cyclic voltammetry) showed that treatment with concentrated HNO3 at 80 °C for 5, 15 and 30 min attacks the carbon structure creating different oxygen surface functionalities in concentrations varying from 0.4–1.1 mmol g−1 with a small effect on the surface area (1080–1148 m2 g−1) and pore volumes (micropore 0.17–0.20 cm3 g−1 and mesopores 0.36–0.50 cm3 g−1). These materials showed high activities for the oxidation of sulfide in an aqueous medium forming polysulfides, e.g., S22−, S32− and S42−, which are rapidly eliminated from the aqueous medium. These results are discussed regarding efficient sulfide oxidation at redox surface oxygen sites leading to the formation of higher polysulfides followed by adsorption of these relatively large and more hydrophobic molecules into the mesopores.

Human Hair as Adsorbent of Palladium(II) in Solution: A Precursor of Well-Dispersed Size-Controlled Pd Nanoparticles

This work describes, for the first time, the preparation of palladium nanoparticles supported in thermally-treated human hair. Human hair showed to be an efficient adsorbent of Pd in aqueous media, reaching nearly 100% of adsorption from a 100 ppm solution. The thermal treatment of hair containing Pd at 200 °C under nitrogen atmosphere led to the formation of an N, S-containing material presenting 0.5 wt.% of palladium. The material was extensively characterized by elemental analysis (CHN and inductively coupled plasma optical emission spectroscopy (ICP OES)), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) and Raman spectroscopies, and by thermogravimetry (TG), thermogravimetry coupled to mass spectrometry (TG-MS), scanning electron miscroscopy (SEM), transmission electron microscopy (TEM) and dispersive X-ray spectroscopy (EDS) analyses. It was possible to observe that the surface structure of hair was preserved during thermal treatment, presenting palladium nanoparticles with particle sizes of approximately 4 nm. This material was used as heterogeneous catalyst in a preliminary application in nitrobenzene reduction to aniline in aqueous medium using sodium borohydride.

Rejeitos de Biomassas Oriundas da Cadeia de Biocombustíveis no Brasil: Produção de Bio-óleo e Sub-produtos

Neste trabalho e descrito o potencial de utilizacao da pirolise rapida como rota para a obtencao de diferentes produtos a partir de quatro rejeitos de biomassa oriundas das cadeias de biocombustiveis no Brasil, i.e. tortas de tucuma e mamona(biodiesel) e palha/bagaco de cana (producao de etanol).Atraves de dados de analise elementar, TG,CGEM,balancos de massa, analise imediata e poder calorifico, observou-se que as tortas de biodiesel produzem de 17-25% de um gas composto de CO x , H 2 e hidrocarbonetos C 1 -C 2 , 33-38% biocarvao e 42-45% de liquidos, composta de 18-23% de uma fracao aquosa altamente acida e elevada carga orgânica e 22-23% de uma fracao oleosa constituida de uma complexa mistura de compostos orgânicos. A pirolise rapida da palha e do bagaco de cana produziu 6% de gas composto basicamente de COx, 6-18% biocarvao e 25-75% de liquidos. Com base nasinformacoes obtidas, diferentes possibilidades de usos sao discutidas para as fracoes obtidas.