Papers by Jarem Raul Garcia Garcia
Journal of Molecular Liquids
This work was supported by the Paraná State Research Funding Agency (Araucária Foundation – proje... more This work was supported by the Paraná State Research Funding Agency (Araucária Foundation – project # FA-SESA 073/2016 - CP 04/2016) and by the Federal Agencies CAPES and CNPq (project # CNPq PVE 401271/2014-5)
The author would like to thank the Brazilian Agency Funding: CNPq, CAPES and Fundaçăo Araucária
Journal of Solid State Electrochemistry, 2003
The potential-induced changes in thymine coordination on polycrystalline silver electrodes are st... more The potential-induced changes in thymine coordination on polycrystalline silver electrodes are studied by surface enhanced Raman spectroscopy (SERS) for potentials positive to the potential of zero charge up to the end of the double layer range. Two distinct sets of spectra could be obtained in the range of potentials studied. Both states correspond to chemisorbed phases of thymine on silver, where a distinct heteroatom is deemed responsible for the bond with the surface. At less positive potentials, one of the ring oxygen atoms is responsible for the chemical bond and the molecule assumes a tilted position. At more positive potentials, one of the ring nitrogen atoms, possibly deprotonated, establishes a new bond with the surface, aligning the molecule's axis closer to the surface normal.
Modern Surface Engineering Treatments, 2013
Publicatio UEPG - Ciencias Exatas e da Terra Agrarias e Engenharias, 2012
This paper describes the synthesis and characterization of silver nanoparticles (AgNps), using th... more This paper describes the synthesis and characterization of silver nanoparticles (AgNps), using the polyelectrolyte 3-n-propylpyridinium silsesquioxane chloride (SiPy + Cl-) as a nanoreactor and the application of these nanoparticles for incorporation into textile materials. The AgNps syntheses were performed by the precipitation method, using AgNO 3 as the precursor, SiPy + Clas the stabilizer and NaBH 4 as reducing agent. The synthesis was performed using different ratios between Ag/ SiPy + Cl-(1%, 2%, 5% and 10% w/v) and the formation, stability and size of the nanoparticles were analyzed by UV-Vis spectroscopy and Zeta Potential. It was observed that in the presence of SiPy + Cl-, the plasmon band of AgNps, in the region of 350-450 nm, shifted to longer wavelengths, which may be associated with the interaction between SiPy + Cland AgNps or the difference in size of the stabilized nanoparticles in relation to the free AgNps. The nanoparticles obtained using the proportions 5% and 10% w/v were more stable, with average sizes of approximately 25 to 45 nm. From the Fourier transform infrared spectra (FTIR), a decrease in the intensity of the bands at 1634 and 1484 cm-1 could be observed, which was related to the vibrations of the pyridinium ring, after incorporation of AgNps, which is evidence of the interaction between them. The average crystallite size, calculated by the Scherer equation, was 42 nm and 48 nm for the samples with 10% and 5% of silver, respectively. The antimicrobial activity of the AgNps impregnated in cotton was evaluated and gave promising results in the inhibition of bacterial and fungal growth.
Descreve-se um método eletroquímico para a preparação do copolímero poli(2-bromo-5-metoxi-p-fenil... more Descreve-se um método eletroquímico para a preparação do copolímero poli(2-bromo-5-metoxi-p-fenilenovinileno/2,5-diciano-p-fenilenovinileno) (cop-MB-PPV/DCN-PPV). Este copolímero foi proposto por apresentar uma estrutura D-A, produzida pela presença do grupo elétron-doador metoxi e do grupo elétron-retirador diciano. O copolímero foi sintetizado eletroquimicamente por redução catódica dos materiais de partida convenientes dissolvidos em DMF/LiClO4 usando um poço de mercúrio como eletrodo de trabalho. O copolímero foi caracterizado por medidas de espectroscopia no infravermelho (IR), no UV-Vis e de fluorescência (FL) e por medidas de voltametria cíclica (CV). Todos os resultados foram comparados com o homopolímero MB-PPV. A análise dos resultados indica que o cop-MB-PPV/DCN-PPV foi obtido através da formação de blocos contendo unidades de DCN-PPV ligadas por blocos contendo unidades de MB-PPV. A caracterização da estrutura eletrônica, obtida por meio de medidas de CV, UV-Vis e FL mos...
Journal of Solid State Electrochemistry, 2015
In the present work, the photoelectrochemical characterization of ITO/TiO 2 electrodes electrosyn... more In the present work, the photoelectrochemical characterization of ITO/TiO 2 electrodes electrosynthesized at two distinct TiO 2 film charges (0.35 and 1.00 C) was performed. Scanning electron microscopy presented a globular-like nanostructure and a typical morphology that are dependent on the growing charge, where the photoelectrode synthesized at 0.35 C presented a more homogeneous morphology. Such dependence was also observed at the photoelectrochemical response, once the photoactivity for the photoelectrode synthesized at 0.35 C was better than the photoelectrode synthesized at 1.00 C, which was explained by the surface recombination process and the electron lifetime. In order to explore the charge-transfer process and the displacement of the quasi-Fermi level upon illumination, electrochemical impedance spectroscopy (EIS) was performed at distinct applied potentials. EIS results corroborate the previous results, presenting a higher charge-transfer resistance and a lower chemical capacitance for the 1.00 C electrode film, the last one in accordance with the open-circuit voltage decay.
This study investigated the combined effects of commercial electroplating additives on the proper... more This study investigated the combined effects of commercial electroplating additives on the properties of nickel electrodeposits. Pieces of carbon steel were electroplated in a Hull cell, using the Watt’s bath with different concentrations of additives and different times of deposition according a 25-1 fractional factorial design. Three response variables, namely brightness, roughness and charge transfer resistance were studied. Several synergistic and antagonistic interactions between the studied factors were found and briefly discussed on a physical basis. Principal Component Analysis (PCA) revealed that clustering in PC-space can be associated with morphological characteristics of the coatings.
The electrochemical behavior of the herbicide paraquat was studied for an electrode modified with... more The electrochemical behavior of the herbicide paraquat was studied for an electrode modified with a PANI/CaraiaGum composite by means of square wave voltammetry. It was obtained an analytical curve in the range of 1x10 -7 to 3x10 -4 molL -1 using the following parameters: frequency of 20 Hz, wave amplitude of 80 mV, scan increment of 5 mV, an acetate buffer (pH=10) as electrolyte solution and paraquat pre-concentration of 4 minutes at the open circuit potential. The detection limit obtained was 2x10 -6 molL -1 . The results showed that the modifiers act synergistically with each other, forming a composite with properties not observed when both modifiers are separated in the respective electrodes. The paraquat or 1,1 '-dimethyl-4, 4'-bipiridina-dichloride is a contact herbicide, non-selective and is an important target molecule due to its the large volume of commercialization and due to its specific toxicity (highly toxic). It acts in the body causing oxidative stress by the ...
Synthesis, 2018
Experimental and theoretical studies showed the differences observed in the benzylic tetrabromina... more Experimental and theoretical studies showed the differences observed in the benzylic tetrabromination reactions in 2,5-dimethylterephthalonitrile compared to 1,4-dimethylbenzene. It was observed that the compound containing the nitrile substituent underwent a slower bromination reaction, with the formation of four intermediate compounds, while for the compound without substituents, the reaction was faster and only two intermediate compounds were observed.
Bulletin of Materials Science
Design and production of α-MnO 2 structures over carbonaceous material is considered as potential... more Design and production of α-MnO 2 structures over carbonaceous material is considered as potential strategy for improving electrochemical performance of supercapacitors. This study describes the development of a simple method for hydrothermal synthesis of a composite material with directly anchoring α-MnO 2 over a nanographite matrix. The nanographite matrix was obtained by electrochemical exfoliation of graphite rods (from depleted Leclanché batteries) and characterized by X-ray diffraction (XRD), Raman spectroscopy and field emission gun-scanning electron microscopy (FEG-SEM). The obtained results indicated that nanographite produced presented low levels of defects with a mild oxidized surface. This nanographite was used as anchoring base for producing MnO 2 particles, using the developed hydrothermal procedure. For paralleling, pure MnO 2 particles were also produced in same conditions. The prepared materials were characterized by XRD, Raman spectroscopy and FEG-SEM. XRD patterns proved formation of α-MnO 2 for pure and composite materials. Morphological characterization indicated the formation of nanoneedles in both situations; however, in the composite the α-MnO 2 was produced as smaller nanoneedles homogeneously spread over the nanographite surface. Raman spectra showed that the desired composition was achieved. Electrochemical characterization showed that the adopted strategy was successful in producing materials with improved pseudocapacitive performance, high reversibility, presenting specific capacitance of 279.8 F g −1 and coulombic efficiency of 99.7%.
Journal of Electroanalytical Chemistry
Journal of The Electrochemical Society
Journal of Polymer Science Part B: Polymer Physics
Journal of Materials Science
The interaction of surfactants and hydrophobic polymers in solution has attracted substantial int... more The interaction of surfactants and hydrophobic polymers in solution has attracted substantial interest due to the broad application in industry. In this study, the interactions of the nonionic surfactant polyethylene glycol-p-(1,1,3,3 tetramethylbutyl)-phenyl ether (Triton X) and anionic surfactant sodium dodecyl sulfate (SDS) with a cationic polymer 3-chloride-n-propylpyridinium silsesquioxane (SiPy+Cl−) and their effects on the layer-by-layer (LbL) film assembly with nickel tetrasulfonated phthalocyanine (NiTsPc) have been analyzed by surface tension, viscosity, and Brewster angle microscopy. As Triton X and SDS surfactants are inserted in the solution containing the polycation SiPy+Cl−, they are immediately incorporated in the hydrophobic nanodomains present in the silsesquioxane skeleton. The association between polyelectrolytes and oppositely charged surfactants starts at very low surfactant concentrations far below the critical micelle concentration, named critical aggregation concentration (cac), which was determined for both surfactants in the presence of SiPy+Cl− (cac Triton X = 2.4 × 10−6 and SDS = 8.2 × 10−7 mol L−1). The coexistence of mixed and pure micelles containing only Triton X and SDS also occurs in higher surfactant concentrations. The implication of these aggregates adsorption on the surface was analyzed in thin films by using the LbL technique. Multilayered films were obtained in presence of surfactants, (T-SiPy/NiTsPc)n or (S-SiPy/NiTsPc)n to compare with LbL films in absence of surfactant (SiPy/NiTsPc)n, and these films were characterized by UV–Vis, FTIR, and Raman spectroscopies to analyze the molecular interactions and to investigate the presence of specific interactions between the polyelectrolytes. The formation of LbL film in the architectures (T-SiPy/NiTsPc)n or (S-SiPy/NiTsPc)n is more efficient in relation to (SiPy/NiTsPc)n LbL films since the presence of the surfactants causes a greater amount of material to be deposited on each bilayer formed. The results of UV–Vis indicate that the film in the presence of SDS has a higher amount of material added to each bilayer. The electrochemical studies of (S-SiPy/NiTsPc)3 film show that the charge transfer resistance is lower than the one observed for the other architectures. Thus, the characteristic hopping electron effect of LbL film may be responsible for lower capacitance and lower resistance of the films. When the surfactant SDS is present, a higher oxidation peak current of dopamine is seen.
Applied Surface Science
Abstract In this manuscript, we describe the synthesis and electrochemical characterization of po... more Abstract In this manuscript, we describe the synthesis and electrochemical characterization of polyaniline—gum arabic nanocomposites and graphene oxide (PANI-GA/GO) modified electrodes with a detailed study concerning their supercapacitive properties. The electrode modification was carried out by using the Layer-by-Layer technique (LbL), where the PANI-GA nanocomposite dispersion was used as polycation and the GO colloidal dispersion as polyanion. The bilayer growth was followed by both UV–vis spectroscopy and cyclic voltammetry, and an increase in the characteristic PANI absorption and in the electrochemical signal was verified, confirming the electrode build up. Galvanostatic charge-discharge curves (GCDC) were performed to evaluate the supercapacitive properties of the modified electrodes, these results showed the dependence of the specific capacitance with the number of bilayers, where values of CS around 15 mF cm−2 (i = 0.1 mA cm−2) were found. Electrochemical impedance spectroscopy confirmed the pseudocapacitive properties of the modified electrodes, showing an increase in the low-frequency capacitance with the number of bilayers. Hereby the (PANI-GA/GO)-LbL electrodes were shown to be good candidates for active materials in supercapacitors.
Organic Electronics
Abstract Although research in the field of organic photovoltaics (OPV) still merely focuses on ef... more Abstract Although research in the field of organic photovoltaics (OPV) still merely focuses on efficiency, efforts to increase the sustainability of the production process and the materials encompassing the device stack are of equally crucial importance to fulfil the promises of a truly renewable source of energy. In this study, a number of steps in this direction are taken. The photoactive polymers all contain an electron-deficient building block inspired on the natural indigo dye, bay-annulated indigo, combined with electron-rich thiophene and 4 H -dithieno[3,2- b :2′,3′- d ]pyrrole units. The synthetic protocol (starting from indigo) is optimized and the final materials are thoroughly analyzed. MALDI-TOF mass spectrometry provides detailed information on the structural composition of the polymers. Best solar cell efficiencies are obtained for polymer:fullerene blends spin-coated from a pristine non-halogenated solvent ( o -xylene), which is highly recommended to reduce the ecological footprint of OPV and is imperative for large scale production and commercialization.
Journal of Solid State Electrochemistry, 2016
A method to obtain poly(2,5-dicyano-p-phenylene-vinylene)-co-(p-phenylene-vinylene) (DCN-PPV/PPV)... more A method to obtain poly(2,5-dicyano-p-phenylene-vinylene)-co-(p-phenylene-vinylene) (DCN-PPV/PPV) block copolymer was developed. The structural characteristics of the copolymer and its capability to generate a photocurrent were evaluated. IR spectra indicate the complete conversion of precursor copolymer into DCN-PPV/PPV at 250 °C under low-pressure conditions. The DCN-PPV/PPV polymer optical band gap was determined based on the observed UV-Vis spectral data by using Tauc’s equation. The two linear regions in the Tauc curve (Eg = 2.63 eV and 2.02) revealed the formation of a block copolymer. Thermal analysis showed that DCN-PPV/PPV has a higher stability than PPV and starts to degrade at 317 °C in air. The electronic parameters of DCN-PPV/PPV (IP = 5.25 eV, EA = 3.30 eV, and Eg = 1.95 eV) indicate that the cyano groups reduce the LUMO energy level without affecting the HOMO energy by much. DCN-PPV/PPV photoactivity measurements show higher photocurrent values compared to those for PPV.
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Papers by Jarem Raul Garcia Garcia