Wren 2018

Abstract: Due to high energy demand that was enacted worldwide in recent years, the study of materials to improve devices of storage and energy generation as supercapacitors is of pronounced interest. Materials such as transition metal hydroxides and carbonaceous materials have been studied for this purpose. The composites formed of both materials showed optimal solution to the problem. Thus, by simple synthesis of α-Ni(OH)2 and composites containing graphite, carbon black (CB) and carbon nanotubes (CNTs) with different concentrations were prepared.2 Using different techniques such as MEV, XRD, CV, among others, these materials were characterized. From MEV, it is noticed that there is very little difference between the morphologies of the synthesized materials. These consist mainly of granulated aggregates, in addition to having empty spaces in their structure. Moreover from DRX, it can be seen that the basic characteristic of the materials is non-crystalline, due to the wide and unimplemented peak diffractograms. In cyclic voltammetry, the α-Ni(OH)2 shows bigger anodic and cathodic peaks, the composites with carbonaceous materials showed be more reversible due the minor difference between the redox peaks. α-Ni(OH)2 exhibited a capacitance equal 173.83 F g-1 and had the profile of its cyclic voltammetry close to the rectangular one, but with a certain inclination, that is, with light resistance of the material. The CB/α-Ni(OH)2 presented the higher specific capacitance however displayed had a high resistance to the flow of electrons relative to other materials.

SEMINAR 9:

STUDY OF A SMALL STEAM TURBINE APPLIED TO ELECTRICAL ENERGY GENERATION

SPEAKER: Jerson R. PINHEIRO Vaz

Abstract:  The use of renewable energy sources available in the Amazon region is an alternative that should be considered for isolated communities, due to their great availability of natural resources. However, it is important for developing small system projects of easy deployment and operation to adopt a model of local self-management. In this case, the proposed system consists of a cyclonic boiler that has good thermal efficiency already studied and thermodynamic results generated (CARNEIRO et al., 2017; CARNEIRO et al., 2015) with a steam turbine coupled with a permanent magnet generator of 1.0 kW (AZEVEDO et al., 2017). Thus, the present project aims to carry out a study on the steam turbine applied to electric power generation. Therefore, it is concluded that this turbine can achieve a maximum shaft power of approximately 16.5 kW, obtaining favorable results to generate electric energy with a maximum power of 10.5537 kW, and average consumption of 1.07 kWh (Tab. 1), being a good characteristic to be applied to a small group of isolated rural families commonly found in Amazon region (MACEDO et al., (2016).

Abstract: Recently, the growing population has led to the increase of world food production and the intense use of pesticides in agriculture. This current outlook is still aggravated because organophousphorus (OP) compounds, which are potent EPSP synthase inhibitors, are the most widely used pesticides. Accordingly, their persistent overuse worldwide has caused accumulation of their compounds in food, fertile land or wasterwater runoff. Thus, it is also important to mention that the action of OP compounds, as toxic compounds and acetylcholinesterase (AChE) inhibitors, is very popular. In fact, those compounds are able to stop the hydrolysis of the neurotransmitter acetylcholine and can lead to an irreversible inhibition of the AChE enzyme (aging), thus causing the cholinergic syndrome. In this line, the high frequency of contamination by pesticides suggests the need for more active and selective agrochemicals. As such, molecular modeling studies using molecular dynamics simulations and DFT techniques were performed to understand the interaction and the action mechanism of OP compounds with the wild type enzyme and Gly96Ala mutant EPSP synthase. In addition, we investigated the reaction mechanism of the natural substrate.

Abstract: Nanostructured materials are promising systems for energy storage and conversion. These systems potentially can be design to have their catalytic, adsorption, kinetic properties enhanced. In this talk, we will highlight insights based on the computational materials design studies at IFUSP of nanostructured materials for i) hydrogen production and water splitting, ii) ethanol catalysis for alcohol direct fuel cells and iii) solar fuels conversion. To explore the stability and characterize the nanostructures, we perform first principles calculations based on Density Functional Theory with dispersion corrections. We study the catalytic and adsorption of ethanol and hydrogen on metallic (M) core-shell based nanoparticles, with M=Pt, Pd, Au, Ag and Ni. Interestingly, there is no significant energy barrier for H2 dissociation at the surface of Au@Pd NP, and the H2 molecule can spontaneously dissociates. The relationship between the geometrical details, electronic structure and adsorption energies were also explored and indicate favorable properties regarding the ethanol oxidation, which can be used for a rational design of nanostructured based materials for ethanol catalysis. Moreover, low cost Sn based metallic and oxide nanoparticles have been investigated to selectively convert CO2 to organic feedstocks, particularly the formic acid production. In this direction, the results based on first principles calculations clarifies details on the possible mechanisms involved in the conversion of CO2 into formic acid due to the catalytic activity of Sn based nanostructures.

Abstract: There has been growing interest in utilizing small (simple) organic molecules, as alternative fuels to hydrogen, in electrochemical energy conversion systems. In addition to ethanol (biofuel), that can be ideally oxidized to carbon dioxide thus delivering twelve electrons, recent important systems include dimethyl ether as well. But realistically the respective reaction is rather slow at ambient conditions. Obviously, there is a need to develop novel electrocatalytic materials. Platinum has been recognized as the most active catalytic metal towards oxidation of ethanol at low and moderate temperatures. But Pt anodes are readily poisoned by the strongly adsorbed intermediates, namely by CO-type species, requiring fairly high overpotentials for their removal. To enhance activity of Pt catalysts towards methanol and ethanol oxidation, additional metals including ruthenium, tin, molybdenum, tungsten or rhodium are usually introduced as the alloying component. More recently it has been demonstrated that catalytic activity of platinum-based nanoparticles towards electrooxidation of ethanol has been significantly enhanced through interfacial modification with ultra-thin monolayer-type films of metal oxo species of tungsten, titanium or zirconium. We pursue a concept of utilization of mixed metal (e.g. zirconium/tungsten or titanium/tungsten) oxide matrices for supporting and activating noble metal nanoparticles (e.g. PtRu) during electrooxidation of methanol and ethanol. Among important issues is incorporation of Rh nanostructures capable of weakening, or even breaking, the C-C bond in the ethanol molecules. On the other hand, rhodium itself is not directly electrocatalytic toward oxidation of ethanol. The oxides and noble metal nanoparticles have been deposited in a controlled manner using the layer-by-layer method. Remarkable increases of electrocatalytic currents measured under voltammetric and chronoamperometric conditions have been observed. The most likely explanation takes into account possibility of specific interactions of noble metals with transition metal oxide species as well as existence of active hydroxyl groups in the vicinity of catalytic noble metal sites. In addition, formation of “nanoreactors” where ethanol is partitioned (at Rh) to methanolic residues further oxidized at PtRu cannot be excluded.

Abstract: Electric dipoles are everywhere. While they provide potentially important paradigms for controlling charge transfer (CT), dipole effects on CT still remain largely unexplored. CT is among the most fundamental processes responsible for sustaining life on earth and for ensuring the functionality of a range of energy and electronic devices that are an intricate part of everyday life. Therefore, we pioneer the concept of molecular electrets that, in addition to possessing large macrodipoles, also can mediate long-range CT.  (Electrets are systems with ordered electric dipoles, i.e., they are the electrostatic analogies of magnets.) Our electret designs are based on polypeptides composed of non-native aromatic beta-amino acids. We observe that even a single electret residue induces rectification of CT that surpasses what is reported for similar systems utilizing polypeptide helices composed of native amino acids. While dipoles generate enormous fields around them, the strength of these localized fields significantly decays with distance. Therefore, we incorporate the dipoles within the participants in the CT steps. It allows us to observe unprecedentedly large dipole effects on the CT kinetics. A decrease in solvent polarity increases the rates of CT. It appears counterintuitive and it should be the other way around: polar media stabilizes the formed charged CT states and thus increases the rates of CT in the normal region. Concurrently, polar media also screens the dipole-generated fields and suppresses the dipole effects on CT. For non-polar solvents, changing the dipole orientation can alter the reduction potentials of the photosensitizers with more than half a volt. Therefore, a careful balance between the two opposing polarity effects allows us to demonstrate CT in lipophilic media, such as toluene. For non-polar solvent, we observe enhancement of electron-transfer (ET) rates along the dipole, while ET against the dipole is completely suppressed. By modifying the semi-classical CT theory, we quantify such experimentally observed dipole effect for the first time. Our findings set an important foundation for designs and development of energy materials and devices.

Abstract: Molecular-level control of charge transfer is paramount for organic electronics and solar-energy conversion. Electromagnetic interactions, originating from the second strongest fundamental force in the universe, occur between charged particles. As electrostatic analogues of magnets, molecular electrets are dielectrics that contain ordered electric dipoles. We have demonstrated the utility of anthranilamides as suitable candidates for the bioinspired approach in the design of molecular electrets. Much like protein helices, anthranilamides, composed of non-native beta amino acids, possess intrinsic dipole moments originating from ordered amide and hydrogen bonds. Unlike the protein helices, however, anthranilamides have a backbone of directly linked aromatic moieties comprising pathways for highly efficient electron and hole transfer. The distal sites, i.e., the fourth and fifth position in the aromatic rings, provide a means for tuning the electronic properties of the electrets via chemical modifications. The dipole-generated local fields of the bioinspired molecular electrets rectify the kinetics of charge separation and charge recombination. That is, the rates of electron transfer along the dipole are different from the rates against the dipole. Because our focus is on hole-transfer electrets, we need a suitable electron acceptor for photoinitiating long-range charge transfer, providing the motivation for the design and development of such light sensitizers. To be able to harvest the energy from the sun, we choose sensitizers that absorb in the red, green and blue region of the spectrum, i.e., corroles, diketopyrrolopyrrolo and fluorescent nitropyrenes. Such broad use of the light across the visible region of the electromagnetic spectrum will open avenues toward tandem light harvesting devices. In this presentation I will focus on our newly discovered fluorescence from nitropyrenes. Pyrenes are the most used organic photoprobes. Upon nitration, pyrene exhibits a shift in its absorption to the visible spectral region. While the nitro group makes it a better electron acceptor, the nitropyrene is non-fluorescent due to efficient triplet formation. Amidating the nitropyrene to produce NO2-Py -C(O)-NH-R did not eliminate the intersystem crossing. Recently, we discovered that inversion of the amides suppresses triplet formation and makes nitropyrene fluorescent. Reorienting the amide bond with the nitrogen adjacent to the pyrene (NO2-Py-NH-C(O)-R) elevates the energy levels of the T2 and T3 states above that of the S1 state, resulting in the suppression of intersystem crossing. Double nitration of the pyrene further enhances the photophysical properties of the nitropyrene resulting in fluorescence quantum yields as high as 0.44 and lifetimes of 5.2 ns. This approach for modifying energy levels of excited states via relatively straight forward chemical changes sets an important precedent not only for energy science, but also for organic electronics and photonics.