Nerilso Bocchi

Electrochemical degradation of a real textile effluent using boron-doped diamond or β-PbO2 as anode

Constant current electrolyses are carried out in a filter-press reactor using a boron-doped diamond (Nb/BDD) or a Ti-Pt/β-PbO(2) anode, varying current density (j) and temperature. The degradation of the real textile effluent is followed by its decolorization and chemical oxygen demand (COD) abatement. The effect of adding NaCl (1.5 g L(-1)) on the degradation of the effluent is also investigated. The Nb/BDD anode yields much higher decolorization (attaining the DFZ limit) and COD-abatement rates than the Ti-Pt/β-PbO(2) anode, at any experimental condition. The best conditions are j = 5 mA cm(-2) and 55 °C, for the systems optimized hydrodynamic conditions. The addition of chloride ions significantly increases the decolorization rate; thus a decrease of more than 90% of the effluent relative absorbance is attained using an applied electric charge per unit volume of the electrolyzed effluent (Q(ap)) of only about 2 kA h m(-3). Practically total abatement of the effluent COD is attained with the Nb/BDD anode using a Q(ap) value of only 7 kA h m(-3), with an energy consumption of about 30 kW h m(-3). This result allows to conclude that the Nb/BDD electrode might be an excellent option for the remediation of textile effluents.

Voltammetric determination of L-dopa using an electrode modified with trinuclear ruthenium ammine complex (Ru-red) supported on Y-type zeolite.

The L-dopa is the immediate precursor of the neurotransmitter dopamine. Unlike dopamine, L-dopa easily enters the central nervous system and is used in the treatment of Parkinsons disease. A sensitive and selective method is presented for the voltammetric determination of L-dopa in pharmaceutical formulations using a carbon paste electrode modified with trinuclear ruthenium ammine complex [(NH(3))(5)Ru(III)ORu(IV)(NH(3))(4)ORu(III)(NH(3))(5)](6+) (Ru-red) incorporated in NaY zeolite. The parameters which influence on the electrode response (paste composition, potential scan rate, pH and interference) were also investigated. The optimum conditions were found to an electrode composition (m/m) of 25% zeolite containing 6.7% Ru, 50% graphite and 25% mineral oil in acetate buffer at pH 4.8. Voltammetric peak currents showed a linear response for L-dopa concentration in the range between 1.2x10(-4) and 1.0x10(-2)moll(-1) (r=0.9988) with a detection limit of 8.5x10(-5)moll(-1). The variation coefficient for a 1.0x10(-3)moll(-1) L-dopa (n=10) was 5.5%. The results obtained for L-dopa in pharmaceutical formulations (tablet) was in agreement with compared official method. In conclusion, this study has illustrated that the proposed electrode modified with Ru-red incorporated zeolite is suitable valuable for selective measurements of L-dopa.

Electrochemical mineralization of the azo dye Acid Red 29 (Chromotrope 2R) by photoelectro-Fenton process

The degradation of 100 mL of 244 mg L(-1) of the azo dye Acid Red 29 (AR29) has been studied by photoelectro-Fenton (PEF) using an undivided cell containing a boron-doped diamond (BDD) anode and an air-diffusion cathode under UVA irradiation. The effect of current density, concentration of catalytic Fe(2+) and pH on the process was examined. Quick decolorization and almost total mineralization were achieved due to the synergistic action of UVA light and oxidant hydroxyl radicals formed in the bulk from Fentons reaction between electrogenerated H(2)O(2) at the cathode and added Fe(2+), as well as in the BDD surface from water oxidation. Optimum PEF conditions were found for 0.5-1.0 mM Fe(2+) and pH 3.0. Comparable electro-Fenton (EF) degradations in the dark yielded much poorer mineralization. The decay kinetics of AR29 followed a pseudo-first-order reaction with similar rate for EF and PEF. The azo dye disappeared much more rapidly than solution color, suggesting the formation of colored conjugated products with λ(max) similar to that of AR29. Ion-exclusion HPLC allowed the detection and quantification of tetrahydroxy-p-benzoquinone, oxalic, oxalacetic, tartronic, tartaric, oxamic, malonic and fumaric acids as intermediates in the PEF process. Oxalic acid, accumulated in large extent, was quickly destroyed by the efficient photolysis of Fe(III)-oxalate complexes with UVA light, whereas tartronic and oxamic acids were the most persistent byproducts because of the larger stability of their Fe(III) complexes. The mineralization of the initial N of the azo dye yielded NH(4)(+) ion and NO(3)(-) ion in smaller proportion.

Lead recovery from a typical Brazilian sludge of exhausted lead-acid batteries using an electrohydrometallurgical process

Abstract Lead recovery from the nonmetallic portion of exhausted lead-acid batteries, also called sludge, was investigated using an electrohydrometallurgical process. Among 13 aqueous solutions studied in solubility tests, only the following three were chosen for the whole process (leaching and electrowinning steps): tetrafluoroboric acid (200 g/L), glycerol (92 g/L)+sodium hydroxide (120 g/L) and sodium potassium tartrate (150 g/L)+sodium hydroxide (150 g/L). The tetrafluoroboric acid showed an attractive performance as leaching electrolyte due to its low cost and reasonable leaching strength. In the electrowinning process using the solution obtained from the leaching of a desulfated sludge with this acidic electrolyte, compact, adherent and highly pure lead deposits were produced at 250 A/m2. Scanning electron micrographs (SEM) of lead deposits obtained at different current densities in the range of 250–500 A/m2 revealed a marked influence of the current density on the deposit morphology.

Solar photoelectro-Fenton degradation of the herbicide 4-chloro-2-methylphenoxyacetic acid optimized by response surface methodology

A central composite rotatable design and response surface methodology (RSM) were used to optimize the experimental variables of the solar photoelectro-Fenton (SPEF) treatment of the herbicide 4-chloro-2-methylphenoxyacetic acid (MCPA). The experiments were made with a flow plant containing a Pt/air-diffusion reactor coupled to a solar compound parabolic collector (CPC) under recirculation of 10 L of 186 mg L(-1) MCPA solutions in 0.05 M Na(2)SO(4) at a liquid flow rate of 180 L h(-1) with an average UV irradiation intensity of about 32 Wm(-2). The optimum variables found for the SPEF process were 5.0 A, 1.0mM Fe(2+) and pH 3.0 after 120 min of electrolysis. Under these conditions, 75% of mineralization with 71% of current efficiency and 87.7 k Wh kg(-1) TOC of energy consumption were obtained. MCPA decayed under the attack of generated hydroxyl radicals following a pseudo-first-order kinetics. Hydroxyl radicals also destroyed 4-chloro-2-methylphenol, methylhydroquinone and methyl-p-benzoquinone detected as aromatic by-products. Glycolic, maleic, fumaric, malic, succinic, tartronic, oxalic and formic acids were identified as generated carboxylic acids, which form Fe(III) complexes that are quickly photodecarboxylated by the UV irradiation of sunlight at the CPC photoreactor. A reaction sequence for the SPEF degradation of MCPA was proposed.

Catalytic Electrooxidation of 2-Mercaptoethanol on Perchlorinated Iron Phthalocyanine Adsorbed on a Graphite Electrode

In this article we show that iron perchlorinated phthalocyanine (FePcCl16), adsorbed on an OPG electrode, acts as a catalyst for the electrooxidation of 2-mercaptoethanol (R-SH), lowering the overpotential of the reaction by near 0.3 V, compared to the unmodified OPG. A Tafel slope close to 0.12 V/decade was observed, indicating that the first electron-transfer is rate determining. Chemical orders of one in R-SH and in OH− are obtained. The linearity of a plot of log I vs. log [RSH] indicates that this system could have potential applications in the amperometric detection of thiols.

Electrochemical degradation of the reactive red 141 dye on a β-PbO2 anode assessed by the response surface methodology

The electrochemical degradation of the Reactive Red 141 dye using a filter-press reactor with a β-PbO2 anode was investigated through the application of the response surface methodology. The charge required for 90% decolorization (Q90) and the chemical oxygen demand removal percentage after 30 min electrolysis (COD30) were used to model the system. The investigated independent variables were the current density, pH, NaCl concentration, and temperature. Low values of Q90 (0.2-0.3 A h L-1) were obtained at acidic conditions (pH 1-3) and high concentrations of NaCl (1.0-2.0 g L-1), when Cl2 and HOCl are the predominant oxidant species. The best values of COD30 were obtained at high current densities and acidic to neutral conditions (pH 5-7); however, the consequent energy consumption makes the process not economically feasible under these conditions. For strongly acidic solutions, specific energy consumptions associated to Q90 as low as 0.79 kW h m-3 were attained.

Studies on the stability of anodic oxides on zirconium biocompatible alloys

Studies on the stability of anodic oxides grown on zirconium and its biocompatible alloys Ti-50Zr at.% and Zr-2.5Nb wt.%, in aerated Ringer physiological solution, at 25 and 37 °C, were carried out by comparing their formation charge and their reconstruction charge after dissolution at open circuit in the physiological solution. The stability of oxides grown in the Ringer solution and in a 0.15 mol L-1 Na2SO4 solution was compared. The obtained results show that the stability of these oxides is increased by aging under potentiostatic conditions and can be decreased by the presence of chloride ions in the electrolyte during the anodization process.

An Electrochemical Sensor Based on Nanostructured Hollandite-type Manganese Oxide for Detection of Potassium Ions

The participation of cations in redox reactions of manganese oxides provides an opportunity for development of chemical sensors for non-electroactive ions. A sensor based on a nanostructured hollandite-type manganese oxide was investigated for voltammetric detection of potassium ions. The detection is based on the measurement of anodic current generated by oxidation of Mn(III) to Mn(IV) at the surface of the electrode and the subsequent extraction of the potassium ions into the hollandite structure. In this work, an amperometric procedure at an operating potential of 0.80 V (versus SCE) is exploited for amperometric monitoring. The current signals are linearly proportional to potassium ion concentration in the range 4.97 × 10−5 to 9.05 × 10−4 mol L−1, with a correlation coefficient of 0.9997.

A comparison of electrodeposited Ti/β-PbO2 and Ti-Pt/β-PbO2 anodes in the electrochemical degradation of the direct yellow 86 dye

The electrochemical performance of electrodeposited Ti/β-PbO2 and Ti-Pt/β-PbO2 anodes was galvanostatically evaluated (batch mode, 50 mA cm-2) to degrade the Direct Yellow 86 dye (100 or 200 mg L-1 in 0.1 mol L-1 Na2SO4 + 1.5 g L-1 NaCl), investigating the effect of pH and temperature. Similar results were obtained for both electrodes and the best conditions for removal of color and chemical oxygen demand are pH 7 and 40 °C, when 90% decolorization is attained by passing a charge of only ~0.13 A h L-1 and total mineralization is achieved with expenditure of ~5 kW h m-3.