Oscar Giraldo

Bio: Oscar Giraldo is an academic researcher from National University of Colombia. The author has contributed to research in topics: Manganese & Zinc hydroxide. The author has an hindex of 19, co-authored 56 publications receiving 2067 citations. Previous affiliations of Oscar Giraldo include Facultad de Ciencias Exactas y Naturales & University of Connecticut.

A Review of Porous Manganese Oxide Materials

Abstract: This review concerns the synthesis, characterization, and applications of porous manganese oxides during the last two years The synthesis of porous tunnel structures, layered structures, and related materials is discussed Both microporous and mesoporous systems materials are covered here Characterization discussed here focuses around structural studies The focus of the application sections include electrochemical and catalytic studies

Fuel ethanol production from sugarcane and corn: Comparative analysis for a Colombian case

Abstract: The Colombian government has defined the use of bioethanol as a gasoline enhancer to reduce greenhouse gases, gasoline imports, and to boost the rural economy. To meet the projected fuel ethanol demand needed to oxygenate the gasoline in the whole country, the construction of about five additional ethanol production plants is required. For this, a comparative analysis of the technological options using different feedstocks should be performed. In this work, a comparison of the economical and environmental performance of the ethanol production process from sugarcane and corn under Colombian conditions has been carried out. Net present value and total output rate of potential environmental impact were used as the economical and environmental indicators, respectively. Through the integration of these indicators into one index by using the analytical hierarchy process (AHP) approach, sugarcane ethanol process was determined as the best choice for Colombian ethanol production facilities. AHP scores obtained in this study for sugarcane and corn ethanol were 0.571 and 0.429, respectively. However, starchy crops like corn, cassava or potatoes used as feedstock for ethanol production could potentially cause a higher impact on the rural communities and boost their economies if social matters are considered.

Films of Manganese Oxide Nanoparticles with Polycations or Myoglobin from Alternate-Layer Adsorption†

Abstract: Alternate adsorption of manganese oxide nanoparticles with polycations poly(dimethyldiallylammonium) (PDDA) or myoglobin (Mb) onto silver, quartz, and rough pyrolytic graphite gave stable, porous, ultrathin films. Quartz crystal microbalance (QCM) and UV−vis absorbance revealed regular film growth at each adsorption step for MnO2 and PDDA and for SiO2 nanoparticles and Mb. Scanning electron microscopy of MnO2/PDDA films showed smooth surfaces on the 20 nm scale and cross sections consistent with individual nanoparticles. QCM during growth of films of Mb and MnO2 reflected a competition for adsorption of the protein by the film surface and dispersed MnO2 nanoparticles. Nevertheless, films of Mb and MnO2 up to 30 nm thick on rough pyrolytic graphite electrodes could be constructed. These novel films featured reversible interconversion of the protein's heme FeIII/FeII redox couple with 10 electroactive layers of protein, considerably more than for polyion−Mb films on smooth gold (ca. 1.3 electroactive layers...

Preparation of Nanometer-Sized Manganese Oxides by Intercalation of Organic Ammonium Ions in Synthetic Birnessite OL-1

Abstract: Potassium manganese oxide materials having the synthetic birnessite structure K-OL-1 were synthesized by reduction methods. K-OL-1 has been ion-exchanged with H+ to produce H-OL-1, which was utilized in further intercalating reactions. The tetraalkylammonium hydroxides including tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide and diamines such as ethylenediamine, 1,6-diaminohexane, and 1,10-diaminooctane were used to intercalate H-OL-1. Elemental analyses, X-ray diffraction, FT-IR spectroscopy, scanning electron microscopy and energy-dispersive X-ray analysis, UV−vis spectroscopy, and transmission electron microscopy have been used to characterize the samples. Structural models of both wet and dry samples are given. The intercalation and deaquation processes of TAA and DA-OL-1 were studied. Their particle sizes were determined and nanometer-sized TAA-OL-1 samples were prepared in TAA systems.

Novel chitosan membranes as support for lipases immobilization: Characterization aspects

Abstract: Membranes of chitosan (QS), chitosan treated with glutaraldehyde (QGA) and chitosan crown ether (QCE) were utilized as carriers for immobilization of Candida antarctica and Candida rugosa lipases. Membrane supports were characterized by several techniques (Raman spectroscopy, elemental analysis by CHN determination and Energy Dispersive X-ray (EDX), water sorption isotherms, and surface area from nitrogen sorption data). To verify the presence of enzymes, some of these techniques were also used for lipase on chitosan biocatalytic systems. Measurements of protein load from Biuret assays and catalytic activity in esterification in nonaqueous media were also made for the immobilized enzymes. Sorption isotherms at 20, 30, 40 and 50 °C for QS, QGA and QCE supports were fitted to the Guggenheim, Anderson and Boer model. GAB monolayer moisture parameter, Xm, varied between 0.029 and 0.051 for QS, 0.039 and 0.058 for QGA and 0.039–0.075 g of water g −1 s.s. for QCE membranes. Elemental analysis and Raman spectra measurements of the lipase, supports and immobilized lipase systems gave evidence of the presence of enzymes on supports. Chitosan supports with internal surface area (m2 g −1 ) among 3.31 and 1.26 were obtained. Regardless of these low values, acceptable protein load (0.61 to 3.21%) and esterification initial rates were achieved (0.88–2.75 mmol min −1 g of protein −1 ).

Chemical strategies to design textured materials: from microporous and mesoporous oxides to nanonetworks and hierarchical structures.

Abstract: 3.

Trends in biotechnological production of fuel ethanol from different feedstocks.

Abstract: Present work deals with the biotechnological production of fuel ethanol from different raw materials. The different technologies for producing fuel ethanol from sucrose-containing feedstocks (mainly sugar cane), starchy materials and lignocellulosic biomass are described along with the major research trends for improving them. The complexity of the biomass processing is recognized through the analysis of the different stages involved in the conversion of lignocellulosic complex into fermentable sugars. The features of fermentation processes for the three groups of studied feedstocks are discussed. Comparative indexes for the three major types of feedstocks for fuel ethanol production are presented. Finally, some concluding considerations on current research and future tendencies in the production of fuel ethanol regarding the pretreatment and biological conversion of the feedstocks are presented.

Oxidation of Alcohols with Molecular Oxygen on Solid Catalysts

Abstract: ion from a primary OH group of glyc-erol. 223,231 A similar mechanism was proposed manyyears ago for alcohol oxidation on Pt/C, involving asecond step, the transfer of a hydride ion to the Ptsurface (Scheme 11). 8,87,237 We consider it more feasible that the rate-deter-mining step is the cleavage of the C-H bond at theR-carbon atom. A similar mechanism is now generallyaccepted for Au electrodes (Scheme 12). 238 Despite thestructural differences between Au nanoparticles andan extended Au electrode surface, there are alsosimilarities, such as the critical role of aqueousalkaline medium and the absence of deactivation dueto decomposition products (CO and C x H y frag-ments). 239,240 An important question is the nature of active siteson Au nanoparticles. Electrooxidation of ethanol onAu nanoparticles supported on glassy carbon re-quired the partial coverage of Au surface by oxides. 241 Another analogy might be the model proposed for COoxidation. 219,242,243 According to this suggestion, theactive site consists of an ensemble of metallic Auatoms and a cationic Au

Asymmetric Supercapacitors Based on Graphene/MnO2 and Activated Carbon Nanofiber Electrodes with High Power and Energy Density

Abstract: Asymmetric supercapacitor with high energy density has been developed successfully using graphene/MnO2 composite as positive electrode and activated carbon nanofibers (ACN) as negative electrode in a neutral aqueous Na2SO4 electrolyte. Due to the high capacitances and excellent rate performances of graphene/MnO2 and ACN, as well as the synergistic effects of the two electrodes, such asymmetric cell exhibits superior electrochemical performances. An optimized asymmetric supercapacitor can be cycled reversibly in the voltage range of 0–1.8 V, and exhibits maximum energy density of 51.1 Wh kg−1, which is much higher than that of MnO2//DWNT cell (29.1 Wh kg−1). Additionally, graphene/MnO2//ACN asymmetric supercapacitor exhibits excellent cycling durability, with 97% specific capacitance retained even after 1000 cycles. These encouraging results show great potential in developing energy storage devices with high energy and power densities for practical applications.

The biorefinery concept: Using biomass instead of oil for producing energy and chemicals

Abstract: A great fraction of worldwide energy carriers and material products come from fossil fuel refinery. Because of the on-going price increase of fossil resources, their uncertain availability, and their environmental concerns, the feasibility of oil exploitation is predicted to decrease in the near future. Therefore, alternative solutions able to mitigate climate change and reduce the consumption of fossil fuels should be promoted. The replacement of oil with biomass as raw material for fuel and chemical production is an interesting option and is the driving force for the development of biorefinery complexes. In biorefinery, almost all the types of biomass feedstocks can be converted to different classes of biofuels and biochemicals through jointly applied conversion technologies. This paper provides a description of the emerging biorefinery concept, in comparison with the current oil refinery. The focus is on the state of the art in biofuel and biochemical production, as well as discussion of the most important biomass feedstocks, conversion technologies and final products. Through the integration of green chemistry into biorefineries, and the use of low environmental impact technologies, future sustainable production chains of biofuels and high value chemicals from biomass can be established. The aim of this bio-industry is to be competitive in the market and lead to the progressive replacement of oil refinery products.