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Dimensionally Stable Anodes (DSA) of Sb2O5-doped Ti/RuO2-ZrO2 are prepared by the Pechini method to perform the degradation of indigo carmine (IC) under conditions similar to textile ...wastewater effluents. XRD results along with Rietveld refinement reveal that the co-deposited phases on the DSA exhibit a tetragonal crystal structure (P4/mmm) for RuO2 and monoclinic structure (P2/m) for ZrO2. Degradation tests conducted in solutions containing 0.64mM IC and 0.05M NaCl using a filter-press reactor (FM01-LC) show that the degradation rate is faster and more efficient at 200Am−2 with a flow rate of 5Lmin−1, although the energy consumption is moderately higher. Under this condition, the pollutant is efficiently removed, and converted to aliphatic acid compounds of low molecular weight, as indicated by 90 % Chemical Oxygen Demand (COD), 22 % Total Organic Carbon (TOC) elimination, along with an Average Oxidation State (AOS) value equal to 3.0. The energy consumptions revealed that it is feasible to carry out the IC degradation under reasonable operating costs. Topological and Natural Bond Orbital (NBO) analyses are computed using density functional theory (DFT), and combined with experimental results to propose a reaction pathway for IC abatement.
Evidence to what it is identified in the literature as “active chlorine” in indirect oxidation processes occurring on Ti/ZrO2-RuO2-Sb2O3 anodes is provided in this study. To discriminate such ...behavior, different catalysts are prepared using the Pechini method varying ZrO2 content, at different Zr/Ru molar ratios: 1, 0.5 and 0.3. The characterization of the materials using X-ray photoelectron spectroscopy (XPS) reveals that no solid solution (Ru-Zr) or any doping that affects the crystalline phase of Zr are obtained, while Sb2O3 was surface-segregated from the bulk to the anode surface affecting the outmost 3–5 nm surface layers. There are enormous impacts on the catalytic activity and adsorption properties of the structures as ZrO2 content is increased. The presence of ZrO2 and Sb2O3 shrink the number of favorable oxygen adsorption sites in Ti/ZrO2-RuO2-Sb2O3 catalysts, whence the adsorption energies for oxygen-metal interactions became lower than for Ti/RuO2. Differential electrochemical mass spectroscopy (DEMS) and electrochemical experiments qualitatively indicate that a lower amount of ZrO2 in the ternary electrode induce a better catalysis towards the oxygen evolution reaction (OER, O2 production), while the ionic currents for ClO− and HClO species drop. This behavior suggests that chloride oxidation needs to encompass the mitigation of the OER as the percentage of ZrO2 is increased in the anode. Active chlorine could stem from HClOads species since it was produced in larger amounts than ClOads− according to the pH of the electrolyte, and in adequate levels to generate the degradation of organic compounds.
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•Impacts on the catalytic activity and adsorption properties due to ZrO2.•Adsorption energies for O2-metal interactions became lower due to ZrO2 and Sb2O3.•Active chlorine could stem from HOClads according to the electrolyte pH.•Chloride oxidation involves the inhibition of the oxygen evolution reaction.•A higher amount of ZrO2 in Ru-Zr material catalyzes the active chlorine production.
Three FTO-BiVO4 photoelectrodes are fabricated modifying the BiVO4 thickness, and systematically evaluating the influence of FTO substrate on the optical, electrical properties, and ...photoelectrochemical performance of BiVO4 semiconductor. The catalysts are characterized using two light sources with back-side or front-side irradiations, to investigate the impacts of different energy sources and configuration illumination on the FTO-BiVO4 photoactivity. This analysis reveals the existence of an additional charge transfer resistance increasing with thickness film subjected to front-side illumination, while the resistance remarkably diminishes when this interface is directly irradiated under back-side illumination. The highest photocurrent is achieved with the LED lamp under back-side illumination, condition selected to compare the degradation of 20 mg L−1 ciprofloxacin (CIP) in 0.05 M NaCl through electrocatalysis, photocatalysis, and photoelectrocatalysis using front-side or back-side illuminations. In these evaluations, modified FTO contributes to the photogeneration of reactive chlorine species, whence it cannot be considered as a simple substrate. Back-side illumination presents a higher CIP elimination in comparison with front-irradiation. A schematic energy band diagram relying on Tauc and Mott-Schottky plots, and incorporating FTO as a photoactive semiconductor is established to rationalize the formation of oxidant species in the system. A degradation mechanism is established based on HPLC measurements of the different treatment methods.
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•Light source affects the formation of a true FTO-BiVO4 heterojunction.•FTO beyond a current collector influencing the photoelectrochemical performance.•Charge transfer resistance increasing with FTO-BiVO4 thickness at front radiation.•FTO contributes to photogenerate reactive chlorine species (non-substrate).•Back-side illumination presents higher Ciprofloxacin elimination than front one.
Dimensionally Stable Anodes (Sb2O5-doped Ti/RuO2-ZrO2) are synthesized at four different Zr/Ru molar ratios using the Pechini method to account for the effects of ZrO2 content on the active chlorine ...formation. X-ray diffraction for ternary catalysts reveal co-deposited phases consisting of a tetragonal crystalline structure (P42/mnm) for RuO2, and two phases corresponding to monoclinic (P2/m) and tetragonal (P42/mnm) crystalline structures for ZrO2. SEM micrographs show that ZrO2 alters grain growth and film morphology as its content is increased. Electrochemical tests performed in 1 mol L−1 H2SO4 and 0.1 mol L−1 NaCl demonstrate that the kinetic rate to perform the oxygen evolution reaction (OER) decreases with the simultaneous augment of ZrO2 and Sb2O5 compositions in the ternary anode, while in the ZrO2 absence, Sb2O5 catalyzes the OER (Ti/SbRu) compared to the Ti/Ru and ternary electrodes. Although the chlorine evolution reaction (CER) preferentially occurs by the suppression of OER in chloride media, the CER rate mainly increases due to the rise of the ZrO2 content. This finding is corroborated with an iodometric method using UV-Vis spectroscopy, which shows that the electro-generation capacity to form active chlorine species is significantly enhanced when ZrO2 is added, compared to Ti/RuO2 and Sb2O5 doped Ti/RuO2 materials. Accelerated life tests conducted with all catalysts indicate that all ternary anodes present failure times considerably longer than Ti/Ru, Ti/SbRu and Ti/RuZr electrodes, suggesting a stability enhancement due to the combined presence of Sb and Zr species.
The electrochemical degradation of two highly consumed analgesics, naproxen (NPX) and diclofenac (DFC), mediated by chloride ions and using a dimensionally stable anode (Ti/IrO2), is compared. In the ...first part, the ability of the system to generate reactive chlorine species was evaluated as a function of the current density (j= 1.25, 3.13, 5.00 mA cm-2) and the chloride concentration (NaCl= 0.01, 0.025, 0.05 mol L-1). Subsequently, under proper conditions, the process performance to degrade the pharmaceuticals individually and mixed, in distilled water and synthetic fresh urine, was evaluated. The electrochemical system achieved 100 % of NPX and DFC elimination in distilled water at 0.017 and 0.056 Ah L-1, respectively. A strong dependence on the chemical structure of the analgesic was evidenced in the degradation kinetics. Finally, slow elimination of the pharmaceuticals in the urine was observed, because of compounds in this complex matrix that compete for the degrading agents.
Evidence to what it is identified in the literature as “active chlorine” in indirect oxidation processes occurring on Ti/ZrO2-RuO2-Sb2O3 anodes is provided in this study. To discriminate such ...behavior, different catalysts are prepared using the Pechini method varying ZrO2 content, at different Zr/Ru molar ratios: 1, 0.5 and 0.3. The characterization of the materials using X-ray photoelectron spectroscopy (XPS) reveals that no solid solution (Ru-Zr) or any doping that affects the crystalline phase of Zr are obtained, while Sb2O3 was surface-segregated from the bulk to the anode surface affecting the outmost 3–5 nm surface layers. There are enormous impacts on the catalytic activity and adsorption properties of the structures as ZrO2 content is increased. The presence of ZrO2 and Sb2O3 shrink the number of favorable oxygen adsorption sites in Ti/ZrO2-RuO2-Sb2O3 catalysts, whence the adsorption energies for oxygen-metal interactions became lower than for Ti/RuO2. Differential electrochemical mass spectroscopy (DEMS) and electrochemical experiments qualitatively indicate that a lower amount of ZrO2 in the ternary electrode induce a better catalysis towards the oxygen evolution reaction (OER, O2 production), while the ionic currents for CIO and HCIO species drop. This behavior suggests that chloride oxidation needs to encompass the mitigation of the OER as the percentage of ZrO2 is increased in the anode. Active chlorine could stem from HCIOads species since it was produced in larger amounts than CIO-ads according to the pH of the electrolyte, and in adequate levels to generate the degradation of organic compounds.
