Guar Gum-Assisted Synthesis of Vanadium-Doped Mesoporous Cobalt Ferrites for H2O2 Activation and 4-Nitrophenol Fenton-like Oxidation

Vanadium-doped cobalt ferrite nanoparticles, Co1−xVxFe2O4 (x = 0.0–0.04), were synthesized via a guar gum-assisted alkaline co-precipitation. Guar gum biopolymer proved to be a stabilizing and templating agent that improves vanadium incorporation and porous structure development. Both the as-synthesized and annealed Co-V catalysts are monophasic spinel ferrites, as determined by XRD. XRF and EDS confirmed the presence of Co, Fe, V, and O and allowed assessment of the elemental composition of the synthesized samples. The BET isotherms are of type IV, indicating that a mesoporous surface was formed. Vanadium doping increased the specific surface area approximately threefold, from 29.6 m2/g for CoFe2O4 to 86.24 m2/g for Co0.97V0.03Fe2O4. The vanadium-substituted cobalt ferrites were found to be effective catalysts in the decomposition of hydrogen peroxide and degradation of 4-nitrophenol. After annealing at 500 °C, the catalytic efficiency decreased by about half, indicating that the pristine surface of the as-synthesized ferrites has specific sites for H2O2 activation. The incorporation of vanadium atoms had a non-linear effect on catalytic performance. The optimal vanadium ion content for catalytic activity is x(V) = 0.03, as determined from the rate constants of H2O2 decomposition and 4-nitrophenol oxidation. The maximum degradation of 4-nitrophenol was recorded at 93% after 120 min. Measurements of ortho-phenylenediamine oxidation showed that CoV-0.03 is the most active radical-generating catalyst, confirming the close relationship between H2O2 decomposition and radical formation. XPS results confirm the catalytic redox cycling of Fe and Co ions, while subsurface V ions likely act as structural and electronic promoters. The obtained results identify Co0.97V0.03Fe2O4 as an effective magnetic catalyst for Fenton-like water treatment applications.