Zênis Novais da Rocha
@ufba.br
Department of General and Inorganic Chemistry
Universidade Federal da Bahia
RESEARCH INTERESTS
Inorganic chemistry
Bioinorganic
Metallocenes
Composting organic matter
Scopus Publications
Scopus Publications
Yuri H. L. Ribeiro, Denis G. F. David, Marcus V. S. da Silva, and Zênis N. da Rocha
Springer Science and Business Media LLC
Arthur A. Bernardes, Guilherme L. Scheffler, Claudio Radtke, Dirce Pozebon, João H.Z. dos Santos, and Zênis N. da Rocha
Elsevier BV
Abstract The immobilization of Cp2ZrCl2 was performed by entrapment within the binary oxides SiO2-CrO3, SiO2-MoO3 and SiO2-WO3 using a non-hydrolytic sol-gel route. Catalyst performance was evaluated in ethylene polymerization. The highest catalyst activity was found with a lower metal chloride:Si ratio and catalyst bearing W moieties. The catalyst and oxide matrices were characterized by complementary techniques (nitrogen porosimetry, small angle X-ray scattering, Fourier Transform infrared spectroscopy, X-ray photoelectron spectroscopy, and differential pulse voltammetry). The interaction between the binary oxide support and the immobilized metallocene reduced the electron density on the Zr centers, enabling the activation reaction to occur with lower concentrations of the methylaluminoxane (MAO) co-catalyst (Al/Zr = 500). The catalytic activity showed a direct relationship with the size and shape of the mass fractal. The results demonstrate that the entrapping method allows for the generation of a catalyst system in which part of the activation process may be attributed to the support.
Alan dos Santos da Silva, Zenis Novais da Rocha, Marcelo Luis Mignoni, and João Henrique Z. dos Santos
Elsevier BV
Abstract The use of hybrid silicas as the silica source in solvent-free zeolite synthesis was investigated as an alternative approach to obtain hybrid aluminosilicates without postsynthetic modification. Hybrid silicas bearing alkyl, amino and mercapto groups were produced by acid catalysis, base catalysis, two-step and silicate sol-gel routes. The influence of the structure and chemical nature of the hybrid silica source on zeolite formation under solvent-free conditions was evaluated. Zeolites based on the silicas synthesized by acid catalysis, base catalysis, two-step, and silicate sol-gel routes showed 51, 100, 18 and zero percent crystallinity, respectively. Furthermore, increasing the alkyl chain from a methyl to an octyl or octadecyl loaded onto the hybrid silica increased the time needed to obtain a crystalline structure from 24 h to 48 or 72 h, respectively. For all the systems, a zeolite sodalite was obtained. Thus, the results show the influence of the structural and chemical nature of the silica source on the crystallization process while keeping the sodalite arrangement for all of the conditions.
Larissa Brentano Capeletti, Cristiane dos Santos, Zenis Novais da Rocha, Mateus Borba Cardoso, and João Henrique Zimnoch dos Santos
Elsevier BV
Abstract The use of organosilanes to produce hybrid materials, also known as ORMOSILs (organically modified silicas) can be a good strategy to tune a material’s properties, enabling, for example, the optimization of important features of chemical sensors such as specificity, sensitivity and response time. Thus, different hybrid silicas were prepared by the sol-gel method to be employed as a colorimetric sensor. The investigated organic groups for producing hybrid materials included methyl, octyl, octadecyl, vinyl, phenyl, aminopropyl, isocyanatopropyl, mercaptopropyl, chloropropyl, iodopropyl and glycidoxypropyl groups, and the pH indicator alizarin red was used as the encapsulated receptor element. The sensors were characterized using a set of complementary techniques such as UV–vis spectroscopy, cyclic and differential pulse voltammetry, nuclear magnetic resonance, nitrogen porosimetry, small-angle X-ray scattering and transmission electronic microscopy. The performance was evaluated according to the color change (ΔE*ab) by conducting a colorimetric analysis and measuring the response time after ammonia exposure, with results varying from 48 to 95 s. Additionally, other characteristics of the hybrid materials, such as their surface area, reticulation degree, texture and morphologic properties, were altered depending on the organic modification present in the silica network. The potentiality for material optimization, to achieve better sensor performance, depends on the employed organosilane.
M. Elisa Silva Serra, Dina Murtinho, Zênis N. da Rocha, Ana Salomé Pires, João Gabriel Baptista, Ana Margarida Abrantes, Mafalda Laranjo, João Eduardo Casalta-Lopes, Maria Filomena Botelho, Alberto A.C.C. Pais,et al.
Elsevier BV
Abstract Novel brominated salen metal complexes from (1R,3S)-N,N′-bis[5-bromosalicylidene]-1,3-diamino-1,2,2-trimethylcyclopentane and Cu(II), Fe(III) and Mn(III) were synthesized and screened for their in vitro cytotoxic activity against two breast cancer cell lines, HCC1806 and MCF7, and two colon cancer cells lines, LS1034 and WiDr. Results show that the copper complex exhibits the highest cytotoxic activity towards all cell lines studied, presenting IC50 values of 0.95–2.32 μM. The anti-proliferative effect observed with the copper complex constitutes a marked improvement relative to current conventional chemotherapy. A relationship between the biological activity of the most efficient Cu(II) complex and its structure is established using theoretical calculations and electrochemical studies.
William Leonardo da Silva, Marla Azário Lansarin, João Henrique Z. dos Santos, Zenis N. Da Rocha, and Iuri Muniz Pepe
Springer Science and Business Media LLC
Dexamethasone and guaifenesin were comparatively degraded under UV and visible radiation in the presence of a supported photocatalyst generated from petrochemical residue. For comparative reasons, photochemical tests were also conducted in the presence of commercial titania (P25). The photoelectrochemical behavior of the supported photocatalyst was examined using cyclic voltammetry and differential pulse voltammetry in the dark and under LED irradiation. This photodegradation study indicates the highest drug degradation values were observed for guaifenesin under UV (48.6 %) and visible (45.2 %) radiation with the synthesized photocatalyst. Under the same conditions, the commercial P25 catalyst achieved 66.3 and 50.2 % of the degradation under UV and visible radiation, respectively. Exploratory tests with tap water samples revealed that the system may be sensitive to other analytes present in these environmental samples.
Fabio Gorzoni Doro, Kleber Queiroz Ferreira, Zênis Novais da Rocha, Giovanni Finoto Caramori, Anderson Jesus Gomes, and Elia Tfouni
Elsevier BV
Abstract Macrocyclic ligands are relevant because of the properties they impart to transition metal complexes, such as enhanced thermodynamic stability and slowed substitution kinetic behavior. Here, we address issues not previously reviewed, revisit others, present new results, and review and discuss the results obtained in the last decade for ruthenium(II/III) complexes with tetraazamacrocycles (mac) such as cyclam (1,4,8,11-tetraazacyclotetradecane), [RuL1L2(mac)]q+ with emphasis on nitrosyls. Topics include synthesis, macrocycle functionalization, structure, spectroscopy, photochemistry, reactivity, density functional theory calculations, and biological properties. [RuL1L2(mac)]q+ complexes exhibit a rich chemistry, sometimes unusual, which depends on macrocycle ring size, the presence of N- or C-pendant groups, metal oxidation state, electronic structure, and the nature of L1 and L2. These same features can be used to tune the properties of the complexes leading to potential applications in diverse fields.
Ana Paula Graebin, Leila Bonnaud, Olivier Persenaire, Oltea Murariu, Philippe Dubois, Zenis Novais da Rocha, and Nara Regina de Souza Basso
FapUNIFESP (SciELO)
The difficult processability of polyaniline (PAni) can be overcome by preparing composites with high density polyethylene (HDPE), resulting in a conducting material with improved mechanical properties. PAni nanofibers were synthesized in this research using a rapid mixing method, while HDPE/PAni composites were prepared by in situ polymerization using Cp2ZrCl2/MAO as a catalyst system. Different experimental conditions for polymerization and an electrochemical study were performed. The findings confirmed that the addition of small amounts of Pani (up to 7%) and longer impregnation (120 min) with methylaluminoxane (MAO) before polymerization are important factors contributing to increased catalytic activity. Analysis by cyclic and differential pulse voltammetry indicates that MAO reacts with the PAni in the ethylene polymerization process, and forms active species in the presence of the catalyst. Changes in catalytic activity may be due to the kinetic consumption of the active species, which become less important in the presence of PAni.
Dina Murtinho, Zênis N. da Rocha, Ana Salomé Pires, Roberto P. Jiménez, Ana Margarida Abrantes, Mafalda Laranjo, Ana Catarina Mamede, João Eduardo Casalta-Lopes, Maria Filomena Botelho, Alberto A. C. C. Pais,et al.
Wiley
Novel Cu(II), Fe(III) and Mn(III) salen-type metal complexes from (1R,3S)-N,N′-bis[salicylidene]-1,3-diamino-1,2,2-trimethylcyclopentane were synthesized and screened for their in vitro cytotoxic activity against three human cancer cell lines: melanoma, colorectal and breast. In vitro experiments carried out with the three metal complexes show that the copper complex exhibits the highest cytotoxic activity towards all cell lines studied, presenting IC50 values of 3.32–6.71 μM. A significant improvement in the anti-proliferative effect, by 20-fold, is observed with this complex when compared with conventional chemotherapy. The relationship between structure, redox characteristics and biological activity in human cancer cell lines was evaluated for the most efficient Cu(II) complex and associated with theoretical calculations. Copyright © 2015 John Wiley & Sons, Ltd.
Emanoel Igor da Silva Oliveira, Fernando Silveira, Adelaide Maria Vieira Viveiros, Nara R. S. Basso, Zênis Novais da Rocha, and João H. Z. dos Santos
GN1 Genesis Network
Taking into account the relevance of polyethylene for modern society and the role of catalysts for the production of this material, in the present work, we carried out a review of the main catalytic systems used in industry and academia. Most systems consist of coordination compounds, whose structural versatility allows the tuning of the characteristics of polyethylene for different applications. The structural aspects and chemical reactivity of such systems are discussed based on the existing literature and experimental data.
Grasiela Gheno, Nara Regina de Souza Basso, Marco Antônio Ceschi, Paolo R. Livotto, Alanjone Azevedo Nascimento, Zênis N. da Rocha, and Griselda Barrera Galland
Elsevier BV
Abstract Two new complexes of Ti and Zr were synthesized with 3-hydroxyflavone bidentate ligand and investigated in homogeneous ethylene polymerization. Both complexes were characterized by UV–VIS, 1H and 13C NMR, and electrochemical studies. The geometries and energies of all possible isomeric species were studied by full unconstrained optimizations performed at Density Functional Theory (DFT) level. The polymerization reactions were performed at different experimental conditions with methylaluminoxane (MAO), as the cocatalyst. Both complexes were active in ethylene polymerization in all the conditions used. However, zirconium complex showed the best activity comparing to the titanium complex at 2500 Al/M ratio. The polymers obtained were high density polyethylene with ultra high molecular weights.
Larissa Brentano Capeletti, João Henrique Z. Dos Santos, Edwin Moncada, Zenis N. Da Rocha, and Iuri Muniz Pepe
Elsevier BV
Abstract Solid acid–base sensors were prepared by encapsulating alizarin red pH indicator within a silica matrix using the sol–gel method with four different routes: (1) non-hydrolytic, (2) acid catalyzed, (3) basic catalyzed and (4) without catalyst hydrolytic. The silica–indicator interactions in the resulting materials were investigated by cyclic and differential pulse voltammetry. Ultraviolet–visible photoacoustic spectroscopy was also employed in the characterization. The absorption band shift (49 to 72 nm, depending on the route) between neat alizarin and alizarin encapsulated within the silica network was observed. The electrochemical behavior and the pH indicator interactions with the silica network were dependent on the nature of the employed sol–gel route. For the sensors prepared by the acid and hydrolytic (without catalyst) routes, the interactions with the silica network occurred through alizarin red hydroxyl groups. For the basic route, different cathodic and anodic peaks were observed depending on the pH, suggesting different phenomena during preparation or analysis. In the non-hydrolytic route, it is possible that the quinone form of alizarin red was consumed during the process. The voltammetric results were related to the sensor performance, whereby the acid route produced a solid sensor with the shortest response time, probably because alizarin structure was preserved after the synthetic process.
Katia J. Ciuffi, Emerson H. de Faria, Liziane Marçal, Lucas A. Rocha, Paulo S. Calefi, Eduardo J. Nassar, Iuri Pepe, Zênis N. da Rocha, Miguel A. Vicente, Raquel Trujillano,et al.
American Chemical Society (ACS)
The catalytic efficiency of takovite-aluminosilicate-chromium catalysts obtained by adsorption of Cr(3+) ions from aqueous solutions by a takovite-aluminosilicate nanocomposite adsorbent is reported. The adsorbent was synthesized by the coprecipitation method. The catalytic activity of the final Cr-catalysts depended on the amount of adsorbed chromium. (Z)-cyclooctene conversion up to 90% with total selectivity for the epoxide was achieved when the oxidation was carried out with hydrogen peroxide, at room temperature. After five consecutive runs, the catalysts maintained high activity, although after the sixth reuse, the epoxide yields strongly decreased to 35%. The catalysts were also efficient for cyclohexane oxidation, reaching up to 18% conversion, with cyclohexanone/cyclohexanol selectivity close to 1.2. On the whole, their use as catalysts gives a very interesting application for the solids obtained by adsorption of a contaminant cation such as Cr(3+).
Robson da Silva Vidal, Fábio Gorzoni Doro, Kleber Queiroz Ferreira, Zênis Novais da Rocha, Eduardo Ernesto Castellano, Sofia Nikolaou, and Elia Tfouni
Elsevier BV
Abstract The cis to trans isomerizations during the syntheses of trans-[Ru(NO)(OH)(cyclam)](PF6)2, from cis-[RuCl2(cyclam)]Cl, and [Ru(NO)Cl(cyclam)] (PF6)2, from cis-[RuCl2(dmso)4], are reported. The novel trans-[Ru(NO)(OH)(cyclam)](PF6)2 complex was characterized by X-ray crystallography and vibrational infrared and nuclear magnetic resonance spectroscopies. The Ru–N–O bond angle (176.75o) and ν(NO) (1835 cm− 1) suggest a nitrosonium character for this hydroxo complex. The crystal and molecular structure of trans-[Ru(NO)Cl(cyclam)](ClO4)2·2 H2O is also reported. Results presented here support the cis–trans isomerization observed for the first time with ruthenium cyclam complexes.
Larissa Brentano Capeletti, Claudio Radtke, João Henrique Z. Dos Santos, Edwin Moncada, Zenis N. Da Rocha, and Iuri Muniz Pepe
Elsevier BV
Solid acid–base sensors were prepared by encapsulating two pH indicators (brilliant yellow or acridine) within a silica matrix by the sol–gel method using three different routes: (1) non-hydrolytic, (2) acid catalyzed and (3) base catalyzed. The interactions of the silica-indicator with the resulting materials were then investigated by cyclic and differential pulse voltammetry. Complementary, ultraviolet–visible, photoacoustic spectroscopy was employed for the characterization of the interactions by monitoring the band shifts (bathochromic or hypsochromic, depending on the sol–gel route) between the neat pH indicators and those encapsulated within the silica network. Furthermore, X-ray photoelectron spectroscopy showed that the N 1s binding energy in brilliant yellow was shifted for the material resulting from the acid route. The electrochemical behavior and the pH indicator interactions with the silica network were dependent on the nature of the employed sol–gel route. For the sensors prepared with acridine, the interactions with the silica network took place through the nitrogen group from the pyridinic ring. For the brilliant yellow indicator, different behaviors were observed depending on the route, suggesting different processes during preparation or analysis. For the basic catalyzed and non-hydrolytic routes, it was not possible to assign a specific interaction. Nevertheless, it seemed that interactions might have taken place through the hydroxyl and/or sulphonic groups. Furthermore, for the brilliant yellow sensor prepared through the acid route, it was possible to show that the interaction probably or partially occurred through the azo groups.
Zumira Aparecida Carneiro, Juliana Cristina Biazzotto de Moraes, Fernando Postalli Rodrigues, Renata Galvão de Lima, Carlos Curti, Zênis Novaes da Rocha, Michele Paulo, Lusiane Maria Bendhack, Antonio Claudio Tedesco, André Luiz Barboza Formiga,et al.
Elsevier BV
The synthesis, structural aspects, pharmacological assays, and in vitro photoinduced cytotoxic properties of [Ru(NO)(ONO)(pc)] (pc=phthalocyanine) are described. Its biological effect on the B16F10 cell line was studied in the presence and absence of visible light irradiation. At comparable irradiation levels, [Ru(NO)(ONO)(pc)] was more effective than [Ru(pc)] at inhibiting cell growth, suggesting that occurrence of nitric oxide release following singlet oxygen production upon light irradiation may be an important mechanism by which the nitrosyl ruthenium complex exhibits enhanced biological activity in cells. Following visible light activation, the [Ru(NO)(ONO)(pc)] complex displayed increased potency in B16F10 cells upon modifications to the photoinduced dose; indeed, enhanced potency was detected when the nitrosyl ruthenium complex was encapsulated in a drug delivery system. The liposome containing the [Ru(NO)(ONO)(pc)] complex was over 25% more active than the corresponding ruthenium complex in phosphate buffer solution. The activity of the complex was directly proportional to the ruthenium amount present inside the cell, as determined by inductively coupled plasma mass spectroscopy. Flow cytometry analysis revealed that the photocytotoxic activity was mainly due to apoptosis. Furthermore, the vasorelaxation induced by [Ru(NO)(ONO)(pc)], proposed as NO carrier, was studied in rat isolated aorta. The observed vasodilation was concentration-dependent. Taken together, the present findings demonstrate that the [Ru(NO)(ONO)(pc)] complex induces vascular relaxation and could be a potent anti-tumor agent. Nitric oxide release following singlet oxygen production upon visible light irradiation on a nitrosyl ruthenium complex produces two radicals and may elicit phototoxic responses that may find useful applications in photodynamic therapy.
Fabio G. Doro, Iuri M. Pepe, Sergio E. Galembeck, Rose M. Carlos, Zenis N. da Rocha, Mauro Bertotti, and Elia Tfouni
Royal Society of Chemistry (RSC)
Chemical reactivity, photolability, and computational studies of the ruthenium nitrosyl complex with a substituted cyclam, fac-[Ru(NO)Cl(2)(κ(3)N(4),N(8),N(11)(1-carboxypropyl)cyclam)]Cl·H(2)O ((1-carboxypropyl)cyclam = 3-(1,4,8,11-tetraazacyclotetradecan-1-yl)propionic acid)), (I) are described. Chloride ligands do not undergo aquation reactions (at 25 °C, pH 3). The rate of nitric oxide (NO) dissociation (k(obs-NO)) upon reduction of I is 2.8 s(-1) at 25 ± 1 °C (in 0.5 mol L(-1) HCl), which is close to the highest value found for related complexes. The uncoordinated carboxyl of I has a pK(a) of ∼3.3, which is close to that of the carboxyl of the non coordinated (1-carboxypropyl)cyclam (pK(a) = 3.4). Two additional pK(a) values were found for I at ∼8.0 and ∼11.5. Upon electrochemical reduction or under irradiation with light (λ(irr) = 350 or 520 nm; pH 7.4), I releases NO in aqueous solution. The cyclam ring N bound to the carboxypropyl group is not coordinated, resulting in a fac configuration that affects the properties and chemical reactivities of I, especially as NO donor, compared with analogous trans complexes. Among the computational models tested, the B3LYP/ECP28MDF, cc-pVDZ resulted in smaller errors for the geometry of I. The computational data helped clarify the experimental acid-base equilibria and indicated the most favourable site for the second deprotonation, which follows that of the carboxyl group. Furthermore, it showed that by changing the pH it is possible to modulate the electron density of I with deprotonation. The calculated NO bond length and the Ru/NO charge ratio indicated that the predominant canonical structure is [Ru(III)NO], but the Ru-NO bond angles and bond index (b.i.) values were less clear; the angles suggested that [Ru(II)NO(+)] could contribute to the electronic structure of I and b.i. values indicated a contribution from [Ru(IV)NO(-)]. Considering that some experimental data are consistent with a [Ru(II)NO(+)] description, while others are in agreement with [Ru(III)NO], the best description for I would be a linear combination of the three canonical forms, with a higher weight for [Ru(II)NO(+)] and [Ru(III)NO].
C. dos S. Alfenas, G.P. Ricci, E.H. de Faria, M. Saltarelli, O.J. de Lima, Z.N. da Rocha, E.J. Nassar, Paulo S. Calefi, Lilian B. Montanari, and Carlos H. Gomes Martins
Elsevier BV
Abstract Brazil has been the largest producer of niobium (Nb 2 O 5 ) since 1980, and this material is usually applied to reduce corrosion in alloys. In addition, it has recently been evaluated for use in other technological areas, such as adsorption and catalysis. This paper presents the results of the antibacterial activity of Nb–aluminum oxide, designated MAC–Nb 5+ , prepared by the non-hydrolytic sol–gel route. The resulting material MAC–Nb 5+ was characterized by several techniques including X-ray diffraction, thermal analysis, infrared absorption spectroscopy, differential pulse voltammetry, surface area measurements, and scanning electron microscopy. The displacements of the bands due to Al–O and Al–OH in the infrared spectra of MAC–Nb 5+ in relation to alumina confirmed the coordination of Nb 5+ ions to the surface and inside the pores of the alumina matrix. The powder XRD of MAC–Nb 5+ suggested that the material is amorphous and that the niobium oxide is well-dispersed over the alumina matrix. Differential pulse voltammetry revealed the redox process that involves Nb–O–Al. Results from the biological assays for determination of the antibacterial activity of MAC–Nb 5+ were obtained by the following methodologies: determination of the minimum inhibitory concentration and antibacterial activity assay by agar diffusion. It was observed that MAC–Nb 5+ displays antibacterial activity against all the tested bacteria.
Gustavo P. Ricci, Zênis N. Rocha, Shirley Nakagaki, Kelly A.D.F. Castro, A.E. Miller Crotti, Paulo S. Calefi, Eduardo J. Nassar, and Katia J. Ciuffi
Elsevier BV
Abstract Novel alumina materials containing Fe III ions were prepared by the non-hydrolytic sol–gel route and applied as heterogeneous catalysts in the oxidation of hydrocarbons (cyclooctene and cyclohexane) by the green oxidant hydrogen peroxide. The synthetic route followed an alkyl halide elimination pathway, via etherolysis/condensation between AlCl 3 and diisopropyl ether ( i Pr 2 O), in the presence of Fe III ions (Fe III :Al III : i Pr 2 O molar ratio ∼1:15:30). The obtained xerogel (designated FeAlO-50) was thermally treated at 400, 750, or 1100 °C (samples FeAlO-400, FeAlO-750, and FeAlO-1100, respectively), and the resulting materials were characterized by means of different techniques, such as thermal analyses (TG/DTA), ultraviolet–visible (UV–vis) and infrared (FTIR) absorption spectroscopy, X-ray powder diffraction (XRD) and electron paramagnetic resonance (EPR). The concentration of Bronsted acid sites (BAS) at the surface of the samples was also evaluated by adsorption–desorption of cyclohexylamine. The thermal treatments led to truly heterogeneous catalysts, and the FeAlO-1100 material furnished the highest substrate conversion values. The larger catalytic activity of FeAlO-1100 is probably due to the absence of BAS on its surface. Indeed, the other FeAlO samples presented high BAS concentration, and it is known that H 2 O 2 can be non-productively decomposed in the presence of strong acid sites. The catalytic efficiency of FeAlO-1100 can be considered promising (96% cyclooctene and 22% cyclohexane conversions), while the selectivity cyclohexanone/cyclohexanol achieved in the oxidation of cyclohexane was 1.2 (molar ratio). The catalytic systems obtained here are advantageous because they involve the use of H 2 O 2 , a green oxidant, and the temperature employed for the oxidation reactions (50–55 °C) is milder than those reported in the literature for other heterogeneous catalyst/H 2 O 2 systems.
Diego Ivan Petkowicz, Sibele B.C. Pergher, Carlos Daniel Silva da Silva, Zênis Novais da Rocha, and João H.Z. dos Santos
Elsevier BV
Abstract The degradation of dyes (methylene blue, direct blue 71, direct yellow 8) by a series of titania-supported catalysts generated in situ via the impregnation of TiCl4 onto a series of zeolite, which was synthesized using rice husks as the silicon source, was individually evaluated. After calcination, the resulting supported catalysts were characterized by X-ray diffraction spectrometry, ultraviolet–visible diffuse reflectance spectroscopy, diffuse reflectance and transmittance infrared Fourier transform spectroscopy, energy dispersive X-ray scanning electron microscopy, small angle X-ray scattering and differential pulse voltammetry. The titania generated is present in the anatase phase, without affecting the zeolite framework. Catalyst activity was shown to be comparable to that of the commercial P-25 catalyst after 1 h of UV light exposition. Monitoring the catalyst performance of several batches of material showed that P-25 provided the highest photodecomposition until the third cycle. On the other hand, the activity of the in situ-supported titania catalyst, in spite of showing lower catalytic activity, remained roughly constant up to the fifth cycle. This suggests that the catalyst generated in situ is more suitable for both filtering and reuse.
Silvio Cunha, Luis Fernandes P. Santos, Zênis N. Rocha, Roberto Rivelino, Jailton Ferrari, Ivo Vencato, and Carlito Lariucci
FapUNIFESP (SciELO)
This study represents an integrated approach towards understanding the electronic and structural aspects of 2-benzylamino-1,4-naphthalenedione, a representative 2-amino-napfthoquinone. To this end, theoretical calculations performed at the B3PW91/6-31+G(d) level of density functional theory, electrochemical and X-ray structural investigation were employed. Two intramolecular H-bonds and other two intermolecular H-bonds were observed, including non-classical interactions. Cyclic voltammogram (CV) and differential pulse voltammetry (DPV) show two pairs of peaks, being each one a monoelectronic process.
Adriano G. Fisch, Nilo S.M. Cardozo, Argimiro R. Secchi, Fernanda C. Stedile, Cláudio Radtke, Denise S. De Sá, Zênis N. da Rocha, and João Henrique Z. dos Santos
Elsevier BV
Abstract The immobilization of Cp2ZrCl2 was performed by entrapment within the binary oxide SiO2–WO3 using a non-hydrolytic sol–gel route. The catalyst and oxide matrix were characterized by complementary techniques (Rutherford backscattering spectrometry, ultraviolet–visible diffuse reflectance and infrared transmission spectroscopy, differential pulse voltammetry, adsorption–desorption of N2, and X-ray diffraction). The catalyst performance in terms of catalytic activity and polymer properties was evaluated by ethylene polymerization. Catalyst characterization suggested that the entrapped complex exhibited lower Zr electronic density than the corresponding unsupported metallocene. The polymerization results also revealed that this low Zr electronic density is optimized in terms of complex activation with low MAO concentration (low [Al/Zr] ratio) and reactivity. This fine tuning results in a catalyst system that is active with a low [Al/Zr] ratio and that achieves high catalytic activity. The results demonstrate that the entrapping method allows the generation of a catalyst system in which part of the activation process is attributed to the support. In this sense, the support may partially play MAO functions by stabilizing the active catalytic species.
Ivy Calandreli, Fabiana de Souza Oliveira, Guogang Liang, Zênis Novais da Rocha, and Elia Tfouni
Elsevier BV
Abstract The trans-[RuCl2(L)4], trans-[Ru(NO)Cl (L)4](PF6)2 (L = isonicotinamide and 4-acetylpyridine) and trans-[Ru(NO)(OH)(py)4]Cl2 (py = pyridine) complexes have been prepared and characterized by elemental analysis, UV–visible, infrared, and 1H NMR spectroscopies, and cyclic voltammetry. The MLCT band energies of trans-[RuCl2(L)4] increase in the order 4-acpy
Diego Ivan Petkowicz, Rodrigo Brambilla, Cláudio Radtke, Carlos Daniel Silva da Silva, Zênis N. da Rocha, Sibele B.C. Pergher, and João H.Z. dos Santos
Elsevier BV
Abstract The degradation of methylene blue dye was evaluated for a series of in situ generated titania resulting from the impregnation of TiCl 4 into a series of NaA zeolites, which were synthesized using alternative silicon sources, namely rice husk and chrysotile, and submitted to different treatments. The resulting catalysts were characterized by X-ray diffraction spectrometry, X-ray photoelectron spectroscopy, ultraviolet–visible diffuse reflectance spectroscopy, diffuse reflectance and transmittance infrared Fourier transform spectroscopy, energy dispersive X-ray scanning electron microscopy and differential pulse voltammetry. The generated titania are present in the form of anatase phase, without alteration of the zeolite framework. Homogeneous distribution of Ti is reached for up to 10 wt.% Ti, where higher contents seem to afford isolated conglomerates. The highest catalyst activity was reached with samples having 10 wt.% Ti. Catalyst activity was shown to be comparable to that exhibited by commercial P-25 after 1 h of UV light exposition. Experiments carried out in natural sunlight reached 92% decomposition of the methylene blue dye.
Adriano G. Fisch, Nilo S.M. Cardozo, Argimiro R. Secchi, Fernanda C. Stedile, Paolo R. Livotto, Denise S. de Sá, Zênis N. da Rocha, and João H.Z. dos Santos
Elsevier BV
Abstract Bis(cyclopentadienyl)zirconium dichloride was immobilized within binary oxides of SiO 2 –TiO 2 via a non-hydrolytic sol–gel route. Different coordinatively unsaturated Ti species were identified within the oxide structure depending on the TiO 2 content, which can interact with the encapsulated metallocene complex and affect its catalystic performance in ethylene polymerization. The catalysts were shown to be active in the polymerization using MAO as the cocatalyst in a low Al/Zr ratio. High molecular weight polymer was obtained, probably due to the suppression of chain termination reactions that occur by β-elimination. Furthermore, oxide network structures are suggested from analysis of the catalysts (via Rutherford backscattering spectrometry, infrared spectroscopy, UV–vis diffuse reflectance spectroscopy, diffuse pulse voltammetry), molecular simulation and polymerization performance.