Performance-optimized N-doped CrCo2O4 nanoferrite integrated with CNTs: a high-performance photocatalyst for next-generation wastewater remediation

Abstract

Photocatalysis offers a scalable route to safeguard water security by destroying persistent dyes and drug residues under sunlight. We report a dual-strategy enhancement of spinel chromium cobaltite (CrCo₂O₄, CCO) via nitrogen doping (NCCO) and carbon-nanotube (CNT) compositing (NCCO@CNTs), synthesized by wet-chemical precipitation (urea as N source) followed by ultrasonication with CNTs. XRD/FTIR confirm phase-pure spinel formation with N-induced lattice disorder; SEM/EDX show improved dispersion and homogeneous N/Cr/Co/O/C distribution; UV-Vis/Tauc reveal band-gap narrowing from ∼3.0 eV (CCO) to ∼2.65 eV (NCCO); transient photocurrent demonstrates possible effective charge separation in NCCO@CNTs. Under natural sunlight (7 ppm, 25 mg catalyst, 75 mL), NCCO@CNTs degrades methylene blue (MB) and amoxicillin (AMX) by 90.7% and 85% in 60 min, surpassing NCCO (65.7%, 62%) and CCO (49.5%, 47.5%). Pseudo-first-order kinetics yield rate constants k(MB) = 0.037, 0.017, 0.011 min⁻¹ and k(AMX) = 0.030, 0.015, 0.010 min⁻¹ for NCCO@CNTs, NCCO, and CCO, respectively (≥3× over pristine CCO). Radical-trapping pinpoints ˙O₂⁻ and ˙OH as dominant species, aligning with a mechanism wherein N-doping broadens visible-light absorption/creates shallow states, while CNTs act as rapid electron sinks, suppressing e⁻/h⁺ recombination and adding adsorption/active sites. Benchmarking against reported spinel's indicates competitive or superior sunlight activity. By optimizing the performance of CrCo₂O₄ through dual modification (nitrogen doping and CNT compositing), this work enhances its photocatalytic activity, enabling effective degradation of a wide range of chemically distinct pollutants, and offers a scalable solution for practical wastewater remediation.