Nonradical activation of periodate by nano-TiO2 embedded multi-walled carbon nanotubes for effective decolorization of selected organic dyes

Abstract

The catalytic activation of periodate (PI) via heterogeneous systems employing carbon nanotubes (CNTs) has demonstrated efficacy in degrading aquatic recalcitrant contaminants. However, the underlying reaction mechanisms remain controversial, and structural modifications to optimize electron transfer efficiency are underexplored. This study investigates the removal of four organic dyes (Acid Blue 80, Crystal Violet, Methylene Blue (MB), and Reactive Black 5) through periodate activation via multi-walled carbon nanotubes (MWCNT) incorporating nanoparticulate TiO2 within their internal channels (TiO2@MWCNT, TCNT). Within a 60-min reaction, the system achieved over 90 % decolorization of MB (10 mg/L initial). A series of spectroscopic approaches, including the use of inhibitors (e.g., methanol, furfuryl alcohol, and sodium azide), electron paramagnetic resonance spectroscopy analyses, and electrochemical experiments, revealed that a nonradical mechanism (i.e., electron transfer) might be responsible for the degradation of organic dyes. Notably, TiO2 encapsulation within MWCNT channels facilitated accelerated electron transfer from organic dyes to PI, enhancing degradation kinetics by 1.4-fold compared to unmodified MWCNT. The effects of varying initial pH and the presence of chloride, bicarbonate, and humic acid on MB removal were systematically evaluated. The TCNT/PI system exhibited stable catalytic performance across five consecutive degradation cycles, with detailed analysis revealing MB degradation pathways and intermediate products. Overall, these findings suggest that introducing semiconductors into the inner channels of MWCNT may serve as a strategic catalyst design option to increase the treatment efficiency of emerging micropollutants. © 2025 Elsevier Ltd