Z-Scheme CoFe2O4/g-C3N4/MWCNT catalyst for the degradation of organic pollutants: electrochemical evaluation and HPLC analysis of the intermediates

Abstract

In this work, a ternary CoFe₂O₄/g-C₃N₄/MWCNT (CGC4) nanocomposite (NC) was successfully produced through a sol–gel auto-combustion approach, followed by calcination. It was evaluated for its efficacy in the visible-light-driven photocatalytic decomposition of RhB. XRD, FESEM–EDS, XPS, FTIR spectroscopy, and zeta potential measurements of the structure, morphology, and surface chemistry showed that a well-integrated hetero-structured nanocomposite was formed with better crystallinity, interfacial coupling, and surface activity. The CGC4 photocatalyst showed improved photocatalytic performance, degrading 84.1% of RhB in 180 minutes and exhibiting a much higher pseudo-first-order rate constant of 1.5 × 10⁻⁴ s⁻¹ than pure CoFe₂O₄ and binary composites. The optimization studies showed that the catalyst amount, initial dye concentration, and pH significantly affected the degradation efficiency. The scavenger tests revealed that superoxide radicals and photogenerated holes were the most reactive species. High-performance liquid chromatography (HPLC) analysis showed that rhodamine B (RhB) was broken down into less harmful intermediates without creating toxic by-products. The improved photocatalytic performance is due to the Z-scheme heterojunction, the conductive multi-walled carbon nanotube (MWCNT) network, and the synergistic interaction of the components, which enhance charge separation. This study shows that CoFe₂O₄/g-C₃N₄/MWCNT NCs can serve as effective visible-light-responsive photocatalysts for wastewater treatment. Electrochemical analysis showed that CGC2 had the highest specific capacitance of 6.407 F g⁻¹. The CGC2 samples also exhibited the highest energy density and stored charge at a scan rate of 0.08 V s⁻¹. The enhanced performance was associated with the synergistic interaction between the conductive network of MWCNTs and the electroactive CoFe₂O₄ nanoparticles. The enhanced performance is also well supported by the Nyquist and Randles–Sevcik plots. Thus, in CGC2 samples, the synergistic effect enabled efficient electron transport and ion accessibility.