Electrosynthesis of hydrogen peroxide sustained by anodic oxygen evolution in a flow-through reactor

Boosting the O2-to-H2O2 Selectivity Using Sn-Doped Carbon Electrocatalysts: Towards Highly Efficient Cathodes for Actual Water Decontamination

The high cost and often complex synthesis procedure of new highly selective electrocatalysts (particularly those based on noble metals) for H2O2 production are daunting obstacles to penetration of this technology into the wastewater treatment market. In this work, a simple direct thermal method has been employed to synthesize Sn-doped carbon electrocatalysts, which showed an electron transfer number of 2.04 and outstanding two-electron oxygen reduction reaction (ORR) selectivity of up to 98.0 %. Physicochemical characterization revealed that this material contains 1.53 % pyrrolic nitrogen, which is beneficial for the production of H2O2, and -C≡N functional group, which is advantageous for H+ transport. Moreover, the high volume ratio of mesopores to micropores is known to favor the quick escape of H2O2 from the electrode surface, thus minimizing its further oxidation. A purpose-made gas-diffusion electrode (GDE) was prepared, yielding 20.4 mM H2O2 under optimal electrolysis conditions. The drug diphenhydramine was selected for the first time as model organic pollutant to evaluate the performance of an electrochemical advanced oxidation process. In conventional electro-Fenton process (pH 3), complete degradation was achieved in only 15 min at 10 mA cm-2, whereas at natural pH 5.9 and 33.3 mA cm-2, almost overall drug removal was reached in 120 min.

Performance investigation of electrochemical assisted HClO/Fe2+ process for the treatment of landfill leachate

The feasibility of removal of chemical oxygen demand (COD) and ammonia nitrogen (NH4+-N) from landfill leachate by an electrochemical assisted HClO/Fe2+ process is demonstrated for the first time. The performance of active chlorine generation at the anode was evaluated in Na2SO4/NaCl media, and a higher amount of active chlorine was produced at greater chloride concentration and higher current density. The probe experiments confirmed the coexistence of hydroxyl radical (•OH) and Fe(IV)-oxo complex (FeIVO2+) in the HClO/Fe2+ system. The influence of initial pH, Fe2+ concentration, and applied current density on COD and NH4+-N abatement was elaborately investigated. The optimum pH was found to be 3.0, and the proper increase in Fe2+ dosage and current density resulted in higher COD removal due to the accelerated accumulation of •OH and FeIVO2+ in the bulk liquid phase, whereas, the NH4+-N oxidation was significantly affected by the applied current density because of the effective active chlorine generation at higher current but was nearly independent of Fe2+ concentration. The reaction mechanism of electrochemical assisted HClO/Fe2+ treatment of landfill leachate was finally proposed. The powerful •OH and FeIVO2+, in concomitance with active chlorine and M(•OH), were responsible for COD abatement, and active chlorine played a key role in NH4+-N oxidation. The proposed electrochemical assisted HClO/Fe2+ process is a promising alternative for the treatment of refractory landfill leachate.

A novel UV-LED hydrogen peroxide electrochemical photoreactor for point-of-use organic contaminant degradation

The degradation of organic contaminants is typically achieved by exposure of hydrogen peroxide (H₂O₂) containing influent to ultraviolet (UV) lamps as the source of radiation that can convert H₂O₂ to hydroxyl radicals (·OH), which oxidize organic pollutants. However, two factors prevent this process from being scaled down: the need to introduce H₂O₂, which requires special handling, and the use of bulky UV lamps, which have a high electric power consumption. In this work, an electrochemical cell was developed for the efficient in situ generation of H₂O₂ from water and atmospheric oxygen in a process called a two-electron oxygen reduction reaction (2e-ORR), so that the external addition of H₂O₂ is no longer needed. Moreover, the electrochemical cell was equipped with ultraviolet light-emitting diodes (UV-LEDs) to convert H₂O₂ to ·OH. The reactor exhibited a current efficiency of ∼90% for the H₂O₂ production at a flow rate of 50 mL min^-1. The degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) was studied at 277 nm based on different operational parameters, such as UV fluence rate, initial concentration, and initial pH. A high degradation of >70% was obtained at a UV output of 900 mW. Our approach, the first of its kind, has novel features applied, including: optimal radiation distribution in the reactor by applying a new UV source, UV-LEDs that offer much more control for the radiation profile in the reaction system compared to traditional UV lamps, controlled hydrodynamics by implementing special flow channels to provide a more uniform residence time and offer enhanced mixing, and integrating UV reactor and electrochemical cell in a single unit which could lead to superior performance and space efficiency of the device. These features make the device very suitable for point-of-use (POU) water treatment applications to eliminate both microbial and chemical contaminants.