Sérgio Toshio Fujiwara

Adsorption of FeCl3, CuCl2 and ZnCl2 on silsesquioxane 3-n-propylpyridiniumchloride polymer film adsorbed on Al2O3 coated silica gel

Abstract Silsesquioxane 3- n -propylpyridiniumchloride polymer (abbreviated as SiPyCl), was used to coat SiO 2 /Al 2 O 3 substrate surface to form the chemically modified solid SiO 2 /Al 2 O 3 /SiPyCl having the specific surface area S BET = 233 m 2 g −1 . The resulting polymer film was strongly adhered to the surface by means of ≡Al–O–Si bonding (where ≡Al stands for Al 2 O 3 grafted on SiO 2 surface) and presented an ion exchange capacity of 1.04 mmol g −1 . The metal halides, M Cl z [M= Fe(III), Cu(II) and Zn(II)], were adsorbed by the modified solid from ethanol solutions as neutral species by forming the surface anionic complexes described by the equation: m SiO 2 /Al 2 O 3 /SiPyCl+MCl z ⇆(SiO 2 /Al 2 O 3 /SiPy + ) m [MCl z + m ] m − , where FeCl 4 − , ZnCl 4 2− have tetrahedral and CuCl 4 2- distorted tetrahedral symmetries. The equilibrium coefficients, K , determined for each complex species showed that SiO 2 /Al 2 O 3 /SiPyCl has a high affinity for the metal ions. The following values expressed as log K were found: Cu=3.0, Zn=3.5 and Fe=3.0. The material could efficiently preconcentrate these metal ions from an ethanol solutions and release them in aqueous solution.

Methylene blue immobilized on cellulose surfaces modified with titanium dioxide and titanium phosphate: factorial design optimization of redox properties

The electrochemical properties of methylene blue immobilized on cellulose surfaces modified with titanium dioxide and titanium phosphate were investigated by cyclic voltammetry. The materials synthesized were incorporated into carbon paste electrodes. The electron mediator property of the methylene blue was optimized using a factorial design, consisting of two levels and three factors. The factorial analysis was carried out by searching for better reversibility of the redox process, i.e. the lowest separation between positive and negative peak potentials and a current ratio near unity. The pH does not appear to influence the reversibility of electron transfer but electrolyte concentration and type of modified cellulose surface are important for this chemically modified electrode system. The experimental observations and data analyses indicate that a 0.5 mol l−1 NaCl solution and the cellulose surface modified with titanium phosphate at either a pH of 4.0 or 7.0 are optimal conditions for this system.

Adsorption of metal halides from ethanol solutions by a 3-n-propylpyridiniumsilsesquioxane chloride-coated silica gel surface

3-n-propylpyridiniumsilsesquioxane chloride polymer, abbreviated as SiPy+Cl-, was used to coat a porous silica gel, SiO2, surface to form the chemically modified solid SiO2/SiPy+Cl-. The resulting polymer film was well adhered to the surface and presented an ion exchange capacity of 0.74 mmol g(-1). Metal halides, MClz [M=Fe(III), Cu(II), and Zn(II)], were adsorbed by the modified solid from ethanol solutions as neutral species by forming the surface anionic complexes described by the equation: mSiO2/SiPy+Cl-+ MClz <=> (SiO2/SiPy+)m[MCl(z+m)]m-, where the [MCl(z+m)]m- species adsorbed on the surface are FeCl4-, ZnCl4(2-), and CuCl4(2-). Accurate estimates of the specific sorption capacities and the heterogeneous stability constants of the immobilized metal complexes were determined with the aid of computational procedures.

Preparation and Electrochemical Characterization of a Carbon Ceramic Electrode Modified with Ferrocenecarboxylic Acid

The present paper describes the characterization of a carbon ceramic electrode modified with ferrocenecarboxylic acid (designated as CCE/Fc) by electrochemical techniques and its detection ability for dopamine. From cyclic voltammetric experiments, it was observed that the CCE/Fc presented a redox pair at Epa = 405 mV and Epc = 335 mV (ΔE = 70 mV), related to the ferrocene/ferrocenium process. Studies showed a considerably increase in the redox currents at the same oxidation potential of ferrocene (Epa = 414 mV vs. Ag/AgCl) in the presence of dopamine (DA), differently from those observed when using only the unmodified CCE, in which the anodic peak increase was considerably lower. From SWV experiments, it was observed that the AA (ascorbic acid) oxidation at CCE/Fc occurred in a different potential than the DA oxidation (with a peak separation of approximately 200 mV). Moreover, CCE/Fc did not respond to different AA concentrations, indicating that it is possible to determine DA without the AA interference with this electrode.

Cobalt(II) phthalocyanine bonded to 3-n-propylimidazole immobilized on silica gel surface: preparation and electrochemical properties

A ftalocianina de cobalto(II) imobilizada sobre a silica gel (area superficial SBET = 500 m2 g-1) modificada com 3-n-propilimidazol, foi incorporada a um eletrodo de pasta de carbono e mostrou-se eficiente na eletrocatalise da oxidacao do acido oxalico. As interacoes intermoleculares do complexo, as quais podem normalmente interferir no processo redox, praticamente nao foram observadas no presente caso, devido a baixa densidade media do complexo na superficie do material sintetizado d = 4,7 x 10-13 mol cm-2 (d= Nf/SBET, onde Nf e a quantidade de Co-Ftalocianina adsorvida por grama de silica gel modificada ). A resposta linear do eletrodo para concentracoes do acido oxalico entre 6,5 x 10-4 e 3,2 x 10-3 mol L-1, associado com sua alta estabilidade quimica tornam o material com a ftalocianina de cobalto(II) ligado covalentemente muito atrativo na preparacao de uma nova classe de sensores quimicos.

Electrochemical study and complete factorial design of Toluidine Blue immobilized on SiO2/Sb2O3 binary oxide

SiO2/Sb2O3 of specific surface area SBET = 788 m2 g−1 and 4.7 wt % of Sb was prepared by the sol–gel method. Toluidine Blue (TB+) was immobilized on SiO2/Sb2O3 by ion exchange reactions and the amount of dye bonded to the substrate surface was 13.72 μmol g−1 for SiO2/Sb2O3. This material was used to modify carbon paste electrodes and the electrochemical properties of Toluidine Blue (TB+) immobilized on a silica surface modified with antimonium trioxide were investigated by cyclic voltammetry. The electron mediator property of toluidine blue was optimized using a factorial design, consisting of four factors each at two levels. Factorial analysis was carried out by searching for better reversibility of the redox process, that is, the lowest separation between anodic and cathodic peak potentials and a current ratio near unity. The aqueous phase pH does not appear to influence the peak separation, ΔE, and the |Ipa//Ipc| current ratio response. The other factors studied, the scan rate, type of electrolyte and electrolyte concentration are important for this chemically modified electrode system demonstrating significant influences on the reversibility of electron transfer. The experimental observations and data analyses on this system indicate that the smallest peak separation occurs using 20 mV s−1 and 1.0 mol L−1 KCl while values of |Ipa//Ipc| close to unity are found for 20 mV s−1 with 1.0 mol L−1 concentrations of either KCl or CH3COONa. The electrodes presented reproducible responses and were chemically stable for various oxidation-reduction cycles.

COPPER (II) TETRASULPHO-PHTHALOCYANINE ENTRAPPED IN A PROPYLPYRIDINIUMSILSESQUIOXANE POLYMER IMMOBILIZED ON A SiO2/Al2O3 SURFACE: USE FOR ELECTROCHEMICAL OXIDATION OF ASCORBIC ACID

ABSTRACT Copper (II) tetrasulphophthalocyanine, CuPc4−, was encapsulated in a n-propylpyridinium silsesquioxane polymer, SiPy+Cl−, immobilized on the SiO2/Al2O3 surface. The material obtained incorporated in a carbon paste electrode, presented the property of electrocatalysing the oxidation of ascorbic acid at 0.18 vs SCE. It was observed that the anodic peak potential at different solution pH remained practically constant between pH 5 and 8 and shifted to more positive potentials below pH 5. The electrode showed a very reproducible response and was chemically stable under various oxidation-reduction cycles. By amperometric measurements, a linear response was obtained in the range of 1 × 10−4–1.4 × 10−3 mol l−1 of ascorbic acid. The modified electrode was used to determine ascorbic acid (vitamin C) in tablets. The results were validated by comparison with the results obtained by using the standard 2,6-dichlorophenolindophenol titration method.

Otimizaçâo das condições de preparação de eletrodos à base de carbono cerâmico utilizando-se planejamento fatorial

Different parameters of carbon ceramic electrodes (CCE) preparation, such as type of precursor, carbon material, catalyst amount, among others, significantly influence the morphological properties and consequently their electrochemical responses. This paper describes a 23 factorial design (2 factors and 3 levels with central point replicates), which the factors analyzed were catalyst amount (HCl 12 mol L-1), graphite/precursor ratio, and precursor type (TEOS - tetraethoxysilane and MTMOS - methyltrimetoxysilane). The design resulted in a significant third order interaction for peak current values (Ipa) and a second order interaction for potential difference (ΔE), between thefactors studied, which could not be observed when using an univariated study.

Photocatalytic degradation of camphor by suspended and immobilized photocatalysts

In this work, the degradation of aqueous solution of camphor by heterogeneous photocatalysis was study using suspended and supported TiO2 and ZnO. The supported catalysts (TiO2/borosilicate reaching ring, TiO2/calcium alginate and ZnO/calcium alginate) were characterized by scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM/EDX), X-ray diffractometry (XRD), energy dispersive X-ray fluorescence (EDXRF) and Raman spectroscopy, techniques that permitted to confirm the porosity of the material as well as the characteristic crystalline forms (anatase and wurtzite). The degradation efficiency of the supported photocatalysts was compared with the performance of free TiO2 and ZnO, observing comparable results between conventional Degussa P25 TiO2 and TiO2 immobilized in glass-rings. On the other hand, the use of calcium alginate beads leads to lower degradation efficiency probably due to the significant area reduction observed in immobilized systems.

Sol gel synthesis of 3- n -propyl(4-aminomethyl)pyridinium silsesquioxane chloride and the enhanced electrocatalytic activity of LbL films

AbstractA silsesquioxane based on a silica matrix and 4-(aminomethyl)pyridine group was successfully synthesized using the sol–gel process with the proposal of two different carbonic chain arrangments in the structure of the silica polymer, observed employing NMR techniques. The silsesquioxane proposed succeeds an improvement of the adsorption of monomer electroactive species on the surface of the electrode obtained through films assembly, this fact was attributed to the presence of two coordinating nitrogen in new silsesquioxane. In this study, the Layer-by-Layer (LbL) technique was shown suitable to be used to produce electroactive electrodes with indium tin oxide electrode (ITO) coated by tetrasulfonated nickel phthalocyanine (NiTsPc) alternated with the silsesquioxane. Voltammetric techniques were used to investigate the electrochemical behavior of the nitrite oxidation, which exhibited an enhanced current response at the modified electrode. The proposed electroddisplayed a current response which varied linearly with the concentration of nitrite in the range 0.113 to 0.860 mmol L−1 with a detection limit of 0.026 mmol L−1, a sensitivity of 32.06 µA (mmol L−1) and relative standard deviation of approximately 3%. HighlightsSynthesis of hybrid containing both ammoniummethyl pyridine and aminomethyl pyridinium groups.The new material allows a greater adsorption of metal phthalocyanine monomers.The electrode obtained allows the detection of 0.026 mmol L−1 nitrite.