Borohydride-Assisted Surface Activation of Co₃O₄/CoFe₂O₄ Composite and Its Catalytic Activity for 4-Nitrophenol...

Surface activation of catalysts is known to be an efficient process to enhance their activity in catalytic processes. The activation process includes the generation of oxygen vacancies, changing the nature of the catalyst surface from acidic to basic and vice versa, and the reduction of catalyst surface by H₂. On the other hand, magnetically separable catalysts are highly beneficial for their utilization in water or biological fluid-based catalytic processes, as they can be easily guided to the target site and recovered. Here, we present the fabrication of CoFe₂O₄ and composites of Co₃O₄/CoFe₂O₄/α-Fe₂O₃ and Co/CoFe₂O₄/α-Fe₂O₃ through solution combustion process to utilize them as catalysts for 4-nitrophenol (4-NP) reduction. Although none of the as-prepared CoFe₂O₄ and Co₃O₄/CoFe₂O₄ was seen to be active in 4-NP reduction reaction, the surface of the composite gets activated by borohydride (NaBH₄) treatment to act as a highly active catalyst for 4-NP reduction. X-ray photoelectron spectroscopy of the composite revealed the formation of metal-hydroxide (M-O-H) species of both Co and Fe at its surface due to borohydride treatment. The mechanism of the surface activation and the dynamics of 4-NP reduction of the surface-activated composite have been studied, proposing a possible pathway for the reduction of 4-NP.