Application of TiO2–RuO2/Ti electrodes modified with transition metal oxides in photoelectrochemical degradation of H-acid - synergetic effect

A novel electrocatalyst from TOCN/CGG hydrogel-supported Fe-rich sludge and its performance in treating azo dyes-contaminated water

Monolithic electrocatalysts are desired for the electro-Fenton oxidation system. We used a hydrogel consisting of TEMPO-oxidized cellulose nanofibers (TOCN) and cationic guar gum (CGG) to disperse and support Fe-rich sludge and finally obtained a Fe-doped biochar (denoted as C-Sludge@TOCN/CGG) after the freeze-drying and carbonization. This C-Sludge@TOCN/CGG exhibited a porous structure with evenly-distributed Fe due to the inherently three-dimensional porous structure of TOCN/CGG hydrogel and the abundant carbon content. Importantly, Fe and FeO existed in C-Sludge@TOCN/CGG due to the presence of TOCN and CGG during the pyrolysis. The electrochemical properties of C-Sludge@TOCN/CGG demonstrated its good electrocatalytic activity and stability with few side reactions. It had good performance in the electrocatalytic degradation of various azo dyes, attributed to the synergistic integration of TOCN/CGG-derived carbon matrix and carbonized Fe-rich sludge particles. Specifically, two transient radicals (i.e. ·OH and ·O2-) primarily improved the electrocatalytic degradation performance of C-Sludge@TOCN/CGG. This C-Sludge@TOCN/CGG also efficiently degraded a papermill-sourced wastewater containing direct red 23, direct yellow 11, direct black 19 and toner, in which the COD value decreased from 365.12 to 179.13 mg/L within 9 h. This work provides an example of utilizing renewable materials and solid waste to design electrocatalysts to address the wastewater issue.

Enhanced dehalogenation of brominated DBPs by catalyzed electrolysis using Vitamin B12 modified electrodes: Kinetics, mechanisms, and mass balances

Vitamin B₁₂ (VB₁₂) modified electrodes were prepared for the electrocatalytic reductive debromination of tribromoacetic acid (TBAA). Under galvanostatic conditions set as 5 mmol/L VB₁₂ loading, 20 mmol/L Na₂SO₄ as electrolyte, 10.0 mA/cm² current density, pH 3, and 298 K, the degradation efficiency of 200 μg/L TBAA at the VB₁₂ modified electrode could reach 99.9 % after 6 h. The debromination of TBAA followed the first-order kinetic model. The masses of carbon and bromine elements were conserved before and after the reaction, together with the qualitative analysis of the degradation products showed the likely degradation pathways as TBAA→dibromoacetic acid (DBAA)→monobromoacetic acid (MBAA)→acetic acid (AA). ESR detection and quenching experiments confirmed the role of atomic H* in TBAA debromination. In-situ Raman spectroscopy showed that the Co-Br bond was strongly enriched to the electrode surface, accelerating the electron transfer. The H₂O dissociation performance and transition states searching catalyzed by VB₁₂ were calculated by Density Functional Theory (DFT) and proved that the composite electrode can effectively promote atomic H* generation. Material characterization and electrochemical performance tests showed that the VB₁₂ modified electrode had excellent stability and atomic H* catalytic activity. The electrocatalytic debromination of TBAA at VB₁₂ modified electrodes mainly involves two mechanisms, direct reduction by electron transfer and indirect reduction by the strongly reducing atom H*. The results provide an efficient way to achieve safe removal of brominated DBPs from drinking water after chlorination and before human consumption.

Photoelectrochemical sewage treatment by a multifunctional g-C3N4/Ag/AgCl/BiVO4 photoanode for the simultaneous degradation of emerging pollutants and hydrogen production, and the disinfection of E. coli

This study describes the photoelectrochemical (PEC) treatment of authentic sewage from Hong Kong for H₂ production and degradation of emerging pollutants (EP's) simultaneously, and disinfection of E. coli. The g-C₃N₄/Ag/AgCl/BiVO₄ (CAB-1) coated thin film acted as the photoanode in a three-electrode configuration PEC cell and real sewage as the electrolyte. Electrochemical studies revealed the near reversible, diffusion-controlled and high electron transfer reaction at the electrode-electrolyte surface. For CAB-1, the achieved photocurrent density was 0.1-0.2 mA cm^-2 at 1.23 V vs. RHE exhibiting the highest PEC degradation efficiency (11.15% h^-1 cm^-2) compared to other base materials like g-C₃N₄/BiVO₄ (6.88% h^-1 cm^-2) or Ag/AgCl/BiVO₄ (4.06% h^-1 cm^-2). During the same reaction, the evolved 118 μmol of H₂ gas corresponds to a Faradic efficiency of 69.38%. The composition of sewage was found to influence the overall PEC efficiency. The higher amount of total suspended solids, turbidity, and anionic species decreased the efficiency while as the other parameters like alkaline pH increased the PEC efficiency. Photo-electrochemically, the CAB-1 also effectively disinfected the E. coli present in the sewage with a final discharge of ≤1000 CFU/mL which is within the permissible discharge limits (≤1500 CFU/mL), in Hong Kong.