UV light and Fe2+ catalysed COD removal of AO 8 using NaOCl as oxidant

The present study aims to establish NaOCl as a potential oxidant in the COD removal of Acid Orange 8 using UVC light (λ = 254 nm) and Fe2+ as catalysts. The different systems used in this study are NaOCl, Fe2+/NaOCl, UV/NaOCl, and Fe2+/NaOCl/UV. All these process were found to be operative in acidic, neutral and basic medium. The initial decolorisation and COD removal efficiency (CODeff) for different systems follow the order: Fe2+/NaOCl/UV > UV/NaOCl > Fe2+/NaOCl > NaOCl. Nevertheless, NaOCl can alone be used in the treatment process considering its CODeff to the extent of 95% in 90 min. The change in pH of the solutions after treatment is an important observation - for non-UV systems it remained around 11.0 and 7.0 in other systems. Thus, UV systems are environmental benign. The effect of various anions on CODeff was tested in Fe2+ systems. Presence of F- ions were found to accelerate CODeff in both the systems. However, the effect is more pronounced in Fe2+/ NaOCl/UV, where complete CODeff was observed in the presence of 9.0 gl-1 of F-. The COD removal kinetics for all systems was studied using zero-order, first-order, second-order, and BMG kinetic models. BMG model was found to be more suitable among all and is in good agreement with CODeff of all systems. It is, therefore, established that NaOCl can serve as a powerful oxidant in the advanced oxidation process.

Aqueous Zinc-Chlorine Battery Modulated by a MnO2 Redox Adsorbent

Aqueous zinc-chlorine battery with high discharge voltage and attractive theoretical energy density is expected to become an important technology for large-scale energy storage. However, the practical application of Zn-Cl₂ batteries has been restricted due to the Cl₂ cathode with sluggish kinetics and low Coulombic efficiency (CE). Here, an aqueous Zn-Cl₂ battery using an inexpensive and effective MnO₂ redox adsorbent (referred to Zn-Cl₂ @MnO₂ battery) to modulate the electrochemical performance of the Cl₂ cathode is developed. Density functional theory calculations reveal that the existence of the intermediate state Cl_ads free radical catalyzed by MnO₂ on the Cl₂ cathode contributes to the charge storage capacity, which is the key to modulate the electrode and improve the electrochemical performance. Further analysis of the Cl₂ cathode kinetics discloses the adsorption and catalytic roles of the MnO₂ redox adsorbent. The Zn-Cl₂ @MnO₂ battery displays an enhanced discharge voltage of 2.0 V at a current density of 2.5 mA cm^-2 , and stable 1000 cycles with an average CE of 91.6%, much superior to the conventional Zn-Cl₂ battery with an average CE of only 66.8%. The regulation strategy to the Cl₂ cathode provides opportunities for the future development of aqueous Zn-Cl₂ batteries.

Rethinking electrochemical oxidation of bisphenol A in chloride medium: Formation of toxic chlorinated oligomers

Using boron-doped diamond (BDD) anodes to degrade bisphenol A (BPA) had been an active area of research interest within the past 20 years. A major concern about the process lie in the formation of toxic chlorinated aromatic by-products when chloride electrolytes were present in the reaction system. In this contribution, we highlighted the formation of complex poly-chlorinated oligomer by-products in electrochemical oxidation processes, which had often been overlooked in previous studies. Moreover, the distribution and complexity of the chlorinated oligomers were found to be strongly linked to the adopted initial chloride concentration. Formation of simple chlorinated by-products was ascribed to the electrophilic substitution reactions mediated by active chlorine species, while the oligomer by-products (including chlorinated dimers, trimers and tetramers) were generated through the coupling reactions between various chlorinated phenoxy radicals. The possible mechanisms describing the formation of these by-products were also proposed. The obtained results shed light on the possible risk of BDD technology in the treatment of phenolic wastewater containing chloride electrolytes.

UV-irradiation and BDD-based photoelectrolysis for the treatment of halosulfuron-methyl herbicide

This paper reports the development of a novel photoelectrochemical (PEC) oxidation technique based on UV-C irradiation and boron-doped diamond (BDD) anode and its application for the effective removal of the commercial herbicide halosulfuron-methyl (HSM). The study evaluated the influence of the following key operating variables in the photoelectrochemical process: current density, pH, temperature, and initial HSM concentration. With regard to HSM degradation/mineralization, the application of high current densities was found to be more advantageous once it promoted a more rapid degradation and mineralization, with 96% of total organic carbon removal, though the process became more energy-demanding over time. The initial concentration of HSM did not modify the relative degradation rate, though the degradation process became more efficient as expected in a mass-transfer controlled process. The use of acidic pH (pH 3) was found to be more suitable than neutral conditions; this is probably because an anionic resonant form of HSM may be formed in neutral conditions. The temperature level was also found to affect the rate of HSM removal and the degradation efficiency. Finally, the substitution of Na₂SO₄ by NaCl promoted a more rapid and effective degradation; this is attributed to high production of powerful oxidants. However, only 70% mineralization was reached after 3 h of treatment; this is probably related to the formation of recalcitrant chlorinated sub-products.

High performance direct hydrazine–hydrogen peroxide fuel cell using reduced graphene oxide supported Ni@M (M = Pt, Pd, Ru) nanoparticles as novel anodic electrocatalysts

Ni@Pd/rGO shows excellent catalytic activity and power density toward hydrazine oxidation in comparison with Ni@Pt/rGO and Ni@Ru/rGO.

Electroactive Polyhydroquinone Coatings for Marine Fouling Prevention-A Rejected Dynamic pH Hypothesis and a Deceiving Artifact in Electrochemical Antifouling Testing

Nanometer-thin coatings of polyhydroquinone (PHQ), which release and absorb protons upon oxidation and reduction, respectively, were tested for electrochemically induced anti-biofouling activity under the hypothesis that a dynamic pH environment would discourage fouling. Antifouling tests in artificial seawater using the marine, biofilm-forming bacterium Vibrio alginolyticus proved the coatings to be ineffective in fouling prevention but revealed a deceiving artifact from the reactive species generated at the counter electrode (CE), even for electrochemical bias potentials as low as |400| mV versus Ag|AgCl. These findings provide valuable information on the preparation of nanothin PHQ coatings and their electrochemical behavior in artificial seawater. The results further demonstrate that it is critical to isolate the CE in electrochemical anti-biofouling testing.

Parameters Affecting Adsorption and Photocatalytic Degradation Behavior of Gentian Violet under UV Irradiation with Several Kinds of TiO2 as a Photocatalyst

The photocatalytic decolorization of Gentian violet (GV) from an aqueous solution was studied by focusing on comparison of the photoactivity of different type of TiO2 catalyst. The process was carried out under a variety of conditions. The efficiency of P25-Degussa and PC50-Millennium photocatalysts were compared. The effect of different parameters such as pH, initial dye concentration, catalyst loading and the presence of some anions on both adsorption in the absence of light and the degradation under UV irradiation have been studied. 365 nm UV-A lamp was employed as irradiation source. The kinetic study showed that no correlation was observed between the adsorption capacity of the catalyst and its photoactivity, despite of this the effect of various parameters on adsorption and photocatalytic kinetic behavior was practically similar on various catalysts. The photocatalytic degradation of GV followed first-order reaction kinetics and the higher adsorption and photocatalytic degradation were obtained at the alkaline medium (pH = 10 for P25 and pH = 8 for PC50). However, the reaction at the acidic medium was gradually delayed due to the effect of charge repulsion. The presence of some anions (Cl−, SO42−, NO3−) in the medium at higher concentration was found to reduce the adsorption and to inhibit the degradation.