Preparation and characterization of Sb2O5-doped Ti/RuO2-ZrO2 for dye decolorization by means of active chlorine

Quantitative structure-activity relationship(QSAR) models for color and COD removal for some dyes subjected to electrochemical oxidation

Electrochemical oxidation is an efficient method for the destruction of dyes in wastewater streams. The experimental conditions during electrochemical oxidation (EO) and molecular structure of a dye greatly influence the extent of degradation. The extent of degradation for a variety of dyes by EO can be predicted conveniently by the use of Quantitative structure-activity Relationship (QSAR) models. An abundant amount of published data on dye degradation by EO using highly variable experimental conditions lies unutilized to prepare QSAR models. In this study, an effort is made to use published experimental data on EO of aqueous dyes after applying an easy method of normalization, to prepare QSAR models for percent color and COD removal. Normalized color and COD removal were obtained by multiplying the reported removal by volume of reactor and concentration of dye; and divided by total current passed and the time of electrolysis. More than 15 molecular descriptors were computed using Schrodinger-suit 2018-3. The multiple linear regression (MLR) approach was used to develop normalized color and COD removal models. The quantum chemical descriptors: highest occupied molecular orbital energy (HOMO) and lowest unoccupied molecular orbital energy (LUMO), polar surface area (PSA), hydrogen bond donor count (HBD), and number of atoms were found significant. The statistical indices: goodness-of-fit, R² > 0.75, and internal and external validations, Q²_LOOCV and Q²_ext, > 0.5, satisfied the criteria for predictive models and indicated that the method of normalization used in this study is adequate. Developed QSAR models are quite simple, interpretable, and transparent.

Adapted Pechini method to prepare DSA type electrodes of RuO2-ZrO2 doped with Sb2O5 over titanium plates

This paper describes a thermal method to obtain metal oxides on a titanium substrate surface. This adapted Pechini method is a versatile, easy to handle and scalable technique to obtain electrodes for industrial uses, such as Dimensionally Stable Anodes (DSA). This method has advantages over other thermal methods like dip coating or sputtering, as it needs a smaller amount of polymeric mixture than dip coating method to cover the same area and is less expensive than sputtering method. The thermal method described herein to prepare DSA type electrodes of RuO₂-ZrO₂ doped with Sb₂O₅ over titanium plates needs no sophisticated equipment as spray pyrolysis technique does; a muffle, ultrasonic equipment, and a hot plate magnetic stirrer are the principal apparatus necessary to carry out the adapted Pechini method. On the other hand, this method allows metal oxides to disperse homogeneously. The cyclic voltammograms showed the stability of DSA, and the accelerated life test allowed establishing its useful life (18.18 years) at a current density of 10 mA cm⁻².

Influence of Sb5+ as a Double Donor on Hematite (Fe3+) Photoanodes for Surface-Enhanced Photoelectrochemical Water Oxidation

To exploit the full potential of hematite (α-Fe₂O₃) as an efficient photoanode for water oxidation, the redox processes occurring at the Fe₂O₃/electrolyte interface need to be studied in greater detail. Ex situ doping is an excellent technique to introduce dopants onto the photoanode surface and to modify the photoanode/electrolyte interface. In this context, we selected antimony (Sb⁵⁺) as the ex situ dopant because it is an effective electron donor and reduces recombination effects and concurrently utilize the possibility to tuning the surface charge and wettability. In the presence of Sb⁵⁺ states in Sb-doped Fe₂O₃ photoanodes, as confirmed by X-ray photoelectron spectroscopy, we observed a 10-fold increase in carrier concentration (1.1 × 10²⁰ vs 1.3 × 10¹⁹ cm^-3) and decreased photoanode/electrolyte charge transfer resistance (∼990 vs ∼3700 Ω). Furthermore, a broad range of surface characterization techniques such as Fourier-transform infrared spectroscopy, ζ-potential, and contact angle measurements reveal that changes in the surface hydroxyl groups following the ex situ doping also have an effect on the water splitting capability. Theoretical calculations suggest that Sb⁵⁺ can activate multiple Fe³⁺ ions simultaneously, in addition to increasing the surface charge and enhancing the electron/hole transport properties. To a greater extent, the Sb⁵⁺- surface-doped determines the interfacial properties of electrochemical charge transfer, leading to an efficient water oxidation mechanism.

Electrogeneration of Active Chlorine in a Filter-Press-Type Reactor Using a New Sb2O5 Doped Ti/RuO2-ZrO2 Electrode: Indirect Indigoid Dye Oxidation

This paper presents the study on active chlorine mediated electrochemical oxidation of model solutions that simulate textile effluents containing an indigoid dye (indigo carmine) and sodium chloride (0.05 M) using a new Sb2O5-doped Ti/RuO2-ZrO2 electrode. The study was carried out in a filter-press electrochemical reactor specially designed to minimize flow deviations and provide homogeneous mass transfer flux over the electrode surface. Firstly, the mass-transfer-limited chloride oxidation reaction was studied in the absence of dye in order to understand the active chlorine formation process. Changes in pH, chloride concentration and UV-visible absorption spectra during electrolysis reveal the formation of active chlorine (mainly hypochlorite) with current efficiencies for chloride oxidation of 0.558 and 0.503 at 10 and 20 mA cm−2, respectively. Secondly, chloride oxidation was investigated in the presence of indigo carmine dye (0.5 mM) where in-situ generated active chlorine was responsible for -C=C- bond breaking and dye degradation. The solution discoloration followed a pseudo-first order kinetics where kinetic coefficient was inversely proportional to dye concentration. The oxidation with active chlorine had an average efficiency of 0.7 and a very competitive energy consumption between 49.2 and 128.5 kW h (kg COD removed)−1 depending on current density and flow rate.