Leonardo S. Andrade

Electrocatalysis in wastewater treatment: recent mechanism advances

Over 50 years, several scientists and industries have developed new alternatives for wastewater treatment and remediation. Recently, electrochemical technology has been largely developed mainly because of its versatility and environmental compatibility. Scientific contributions about role of the electrode material have allowed determining that the influence of material in the selectivity is an important parameter. However, to interpret this behavior, comprehensive physical chemistry models for organics destruction, related to electrochemical phenomena and material surfaces, were proposed in the last decades. So, this paper presents a critical and comprehensive review about the principles and recent mechanism advances in electrocatalysis for wastewater treatment.

A multidimensional high performance liquid chromatography method coupled with amperometric detection using a boron-doped diamond electrode for the simultaneous determination of sulfamethoxazole and trimethoprim in bovine milk.

The development and validation of a multidimensional HPLC method using an on-line clean-up column coupled with amperometric detection employing a boron-doped diamond (BDD) electrode for the simultaneous determination of sulfamethoxazole (SMX) and trimethoprim (TMP) in bovine milk are presented. Aliquots of pre-prepared skim-milk samples were directly injected into a RAM octyl-BSA column in order to remove proteins that otherwise would interfere with milk analysis. After exclusion of the milk proteins, SMX and TMP were transferred to the analytical column (an octyl column) and the separation of the compounds from one another and from other endogenous milk components was achieved. SMX and TMP were detected amperometrically at 1.25V vs. Ag/AgCl (3.0molL(-1) KCl). Results with good linearity in the concentration ranges 50-800 and 25-400microgL(-1) for SMX and TMP, respectively, were obtained and no fouling of the BDD electrode was observed within the experimental period of several hours. The intra- and inter-assay coefficients of variation were less than 10% for both drugs and the obtained LOD values for SMX and TMP were 25.0 and 15.0microgL(-1), respectively.

Development of a HPLC method to follow the degradation of phenol by electrochemical or photoelectrochemical treatment

The development and validation of a HPLC method to follow the degradation of phenol by electrochemical or photoelectrochemical treatment are described. This method, which allows determining amounts of phenol, p-benzoquinone and cathecol in electrolyzed or photoelectrolyzed solutions, was used for analysis of reaction intermediates during electrooxidation or photoelectrooxidation of phenol using a Ti-Pt/PbO2 (obtained by thermal-electrochemical or electrodeposition methods) or Ti/TiO2 doped with Ga3+ (obtained by thermal decomposition of precursor salts) electrode.

A novel multicommutation stopped-flow system for the simultaneous determination of sulfamethoxazole and trimethoprim by differential pulse voltammetry on a boron-doped diamond electrode

A method based on a multicommutation stopped-flow system was developed and applied in the simultaneous determination of sulfamethoxazole (SMX) and trimethoprim (TMP) in pharmaceutical formulations by differential pulse voltammetry (DPV) using a cathodically pre-treated hydrogen-terminated boron-doped diamond (HT-BDD) electrode. The obtained analytical curves were linear from 1.0 to 8.0 mg L−1 and 0.20 to 1.6 mg L−1 for SMX and TMP, respectively. The calculated LOD and LOQ values for SMX were 16.5 μg L−1 and 55.1 μg L−1 (or 65.1 nmol L−1 and 218 nmol L−1), respectively; for TMP, they were 18.3 μg L−1 and 61.1 μg L−1 (or 63.0 nmol L−1 and 210 nmol L−1), respectively. The optimization and application of the multicommutation stopped-flow system in the simultaneous electrochemical determination of SMX and TMP by DPV on the HT-BDD electrode yielded an excellent sample throughput (30 h−1). Addition and recovery studies indicated that the matrix effect did not present any significant interference in the determinations. Thus, the proposed method was successfully applied in the determination of SMX and TMP in two different commercial pharmaceutical formulations with results similar (at 95% confidence level) to those obtained using the USP method (HPLC). The obtained performance allowed concluding that the proposed method is quite advantageous and that its total automation can lead to rapid, sensitive, precise, and accurate results, with an excellent sample throughput.

Estudo de efeito dos sais precursores sobre as propriedades eletrocatalíticas de eletrodos de Ti-SnO2/Sb preparados por decomposição térmica

The physical and electrochemical properties of Ti-SnO2/Sb electrodes obtained by the thermal decomposition of solutions of the precursor salts SnCl2×2H2O/SbCl3 and SnSO4/Sb2(SO4)3 were investigated. The reversibility of the cyclic voltammetric response of the Fe(CN)64-/Fe(CN)63- redox couple was assessed using the obtained electrodes. Their catalytic activity for the oxygen-evolving reaction and maximum capacity for electronic transfer were also evaluated by potential and current linear scans in 0.5 mol L-1 H2SO4. Additionally, scanning electron microscopy analyses allowed the visualization of the morphology of the oxide films obtained. The best results were presented by the electrodes obtained from the chloride salt precursors.

Performance and kinetic-mechanistic aspects in the electrochemical degradation of sulfadiazine on boron-doped diamond electrode

The electrochemical performance of boron-doped diamond (BDD) electrode in the electrochemical degradation of wastewaters containing sulfadiazine (SDZ) using a filter-press reactor is presented and discussed. The electrooxidation of the SDZ (volume of 0.5 L, with a SDZ initial concentration of 250 mg L-1) obtained at optimized conditions (current density of 36 mA cm-2, pH 7.0 and volume flow rate of 5.0 L min-1) showed that at the end of only 2 h of electrolysis (corresponding to a charge passed through the cell per unit volume of the wastewater of 5.2 Ah L-1) SDZ was totally eliminated. The reduction of the wastewater organic load, monitored by its chemical oxygen demand (COD) showed that the antibiotic was virtually all mineralized. Under optimized conditions the intermediate compounds were properly identified by gas chromatography-mass spectrometry (GC-MS) and a SDZ oxidation pathway was elucidated. Clearly the BDD electrode proved to be quite efficient for both degradation and mineralization of SDZ.

Dye Degradation Enhanced by Coupling Electrochemical Process and Heterogeneous Photocatalysis

In this study, we evaluated the combination between an electrochemical process, occurring in the dark, and a heterogeneous photocatalytic process for dye degradation, using the azo dye tartrazine as model of oxidizable substrate. TiO2 P25 and an Ag-doped TiO2 were used as photocatalysts in suspensions containing 50 mg L–1 of tartrazine. The best result, 74% of dye mineralization in 120 min of reaction, was obtained using TiO2 P25 as photocatalyst and a current density of 10 mA cm–2 in the electrochemical cell, a value 30% higher than the sum of the results obtained by heterogeneous photocatalysis (44%) and electrochemical oxidation (13%). The use of Ag-doped TiO2 did not result in significant improvement on tartrazine mineralization, due to the aggregation of these nanoparticles. Our results suggest that this process can be an alternative for a complete treatment (discoloration and mineralization) of tartrazine and most likely other azo dyes.

Combined use of coagulation (M. oleifera) and electrochemical techniques in the treatment of industrial paint wastewater for reuse and/or disposal

In this work, water-based paint (WBP) wastewater was treated using a natural coagulant, Moringa oleifera aqueous extract (MOAE), fortified with Ca2+ (from nitrate and chloride salts). In order to improve the quality of the treated wastewater and render it suitable for disposal, an electrolytic flow process was associated with the wastewater treatment using a filter-press reactor with a boron doped diamond (BDD) electrode. The feasibility of the treatment was evidenced by the reuse of the treated wastewater in the production of a new paint (manufactured by the company supplying the raw wastewater), whose quality was compatible with the water used by the manufacturer. The best conditions for the coagulation-flocculation process involved the use of 80 mL of MOAE (50 g/L of MO and 0.125 mol/L of Ca2+) for every 1.0 L of wastewater at pH 6.5. The limiting current density (35 mA/cm2) and an electrolysis time of 90 min (charge passed of 3.68 A h/L) were used in the electrochemical treatment. Biotoxicity assays using the brine shrimp Artemia salina revealed that the mortality (in %) of microcrustaceans was reduced from 100% (raw wastewater) to only 11% at the end of the electrolysis process, in addition to eliminating the strong odor and 85% of the organic load. Moreover, microbiological tests showed that the number of mesophiles decreased by more than six orders of magnitude and there was no growth of thermotolerant coliforms (TC).

Development and application of a cloud point method for the extraction of natural estrogens E1 and E2 from urine samples and their simultaneous determination by HPLC-EC using a BDD electrode

The cloud point extraction (CPE) method was developed to extract and preconcentrate estrone (E1) and 17β-estradiol (E2) hormones from human urine. These hormones were detected and quantified using a combination of the techniques of high-performance liquid chromatography and electrochemical detection (HPLC-EC). A boron doped diamond (BDD) electrode was cathodically pretreated and used as the electrode material for all the electrochemical measurements. Limits of detection (S/N = 3) of 57.1 ng mL−1 and 53.4 ng mL−1 were obtained for E1 and E2 hormones, respectively. Extraction solvent volumes were changed in the 0.5–2.5 mL range, and optimum results were obtained when using 1.0 mL of nonionic Tergitol TMN-6 surfactant. A comparison was made of the efficiency of the CPE method and that of direct liquid–liquid extraction (LLE), using CCl4 as the organic solvent, which clearly indicated the superiority of the CPE method over LLE. The proposed method was validated based on fundamental parameters such as selectivity, accuracy, precision and recovery, and was successfully applied to individual urine samples collected from a man, a pregnant woman, a woman of fertile age, and a lactating woman.