RESUMO
A new protocol for the analysis of the azo-dye carmoisine (CMS) is presented by coupling differential pulse voltammetry (DPV) with a cathodically pretreated boron-doped diamond electrode (CPT-BDDE), in phosphate buffer solution (pH 2.0). The CMS presented diffusion-controlled oxidation and reduction peaks at +0.88 and -0.15 V vs Ag/AgCl, respectively. The effect of the pretreatment conditions, pH, and supporting electrolytes were evaluated to the voltammetric determination of CMS. Under optimized conditions, the differential pulse voltammetric signals for CMS were linear over the concentration range of 0.059-1.31 µmol L-1 and 0.010-0.079 µmol L-1 with limits of detection of 7.0 and 3.0 nmol L-1, for the anodic and cathodic processes respectively. The method was precise for CMS determination (RSD < 5.0%) and selective against other dyes. The developed protocol was successfully applied in the analysis of CMS in surface water and foodstuffs with accurate results in comparison with those obtained using a validated spectrophotometric method.
Assuntos
Boro , Diamante , Compostos Azo , Eletrodos , NaftalenossulfonatosRESUMO
In the last decades, the demand for lithium-ion batteries (LIBs) has been growing fast to attend the markets of electric and hybrid vehicles and of electric portable devices. As scarce metals like cobalt and lithium are employed in their manufacturing the recycling of spent LIBs is a strategic solution for the sustainability of these minerals and also the maintenance of the LIBs production. Therefore, efforts should be driven to produce low cost, environment-friendly and industrially scalable recycling processes. In this study, a closed-loop process with these characteristics was developed to recover cobalt and lithium compounds from LiCoO2 cathodes of spent cell phone lithium-ion batteries. The process employs citric acid as green leaching agent to recover cobalt as CoC2O4.2H2O and Co3O4 and lithium as Li2CO3. Lithium compound was recovered from a proposed new and original method based on simple chemical procedures as evaporation-calcination and water dissolution. The developed process also allows the resynthesis of LiCoO2 as a stoichiometric, well crystallized and structurally ordered compound from the recovered Co and Li compounds, in a closed-loop recycling process. The obtained results indicate that the developed process has great potential to be scaled up to a recycling industrial plant of spent lithium-ion batteries.
RESUMO
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 Fenton's 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.