Electro-activated periodate for organic contaminants degradation: Insights into the pH-dependent mechanism of active species

[Display omitted] •The generation of active species in GF-PI system exhibits remarkable pH dependency.•No formation of 1O2 and low concentration of ·OH generation under acid conditions.•·OH, IO3·, and 1O2 are the main ROSs for SMX removal under initial pH=7 and 9.•The system performed remarkable stability, anti-interference capabilities, and cost-effectiveness for SMX removal.•The degradation intermediates of SMX are proposed at different initial pH. Although electro-activated periodate (PI) has demonstrated significant efficiency in degrading emerging contaminants (ECs), there has been limited research investigating the pH-dependence of active species generation and pollutant degradation. A graphite felt-based electrochemical system (GF-PI) was chosen to deeply explored. It exhibited significant differences in contaminants removal under different pH conditions. Notably, an interesting result is found that the GF-PI system at pH=3 exhibited exceptional removal performance specifically for phenolic contaminants, such as bisphenol A (BPA) and acetaminophen (ACT), whereas it displayed poor efficiency for other compounds, including sulfamethoxazole (SMX), carbamazepine (CBZ), benzoic acid (BA), and atrazine (ATZ). However, there is no selectivity for contaminants removal in pH=4, 7, and 9 system. The experiment of probe capture and quenching are conducted to thoroughly investigate the variety of reactive oxygen species (ROSs) generated. It has been proven that hypoiodous acid (HOI) is the main active species in the system with pH=3. In addition, the system with pH=4 exhibits the highest degradation efficiency and TOC removal efficiency, despite the low yield of hydroxyl radical (·OH), indicating that the iodate radical (IO3·) plays a pivotal role. Under neutral and alkaline conditions, ·OH, IO3·, and singlet oxygen (1O2) are the main active species. Moreover, the system exhibits remarkable stability, anti-interference capabilities, and cost-effectiveness, indicating the superiority for treatment of authentic wastewater. Additionally, the degradation intermediates and biotoxicity of SMX are evaluated through multiple measures. A comprehensive understanding of pH is indispensable in electro-activated PI system for treatment of emerging organic contaminants.