Template‐Free Synthesis of Mesoporous Iron‐Nickel‐Cobalt Oxide Microspheres via Ultrasonic Spray Pyrolysis Across Temperature Gradients for Enhanced Visible Light Photocatalytic Activity

Abstract This study explores the synthesis of template‐free mesoporous FeNiCo oxide microspheres through a direct and efficient ultrasonic spray pyrolysis (USP) technique. USP method includes precise control over particle size, the formation of mesoporous structures, multimetallic compositions, and high synthesis speed, all of which can contribute to enhanced photocatalytic activity. The analysis of the resulting microspheres involved a thorough exploration of their phase structure, texture, morphology, and photocatalytic properties. This investigation employed various analytical techniques, including X‐ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and nitrogen adsorption−desorption. The microspheres displayed a well‐crystallized cubic crystal structure, as evidenced by the X‐ray diffraction pattern, with a corresponding crystallite size ranging from 6.0 to 7.4 nm. The FESEM images revealed the synthesis of uniform‐sized particles with spherical shapes. N 2 adsorption and desorption highlighted the mesoporous structure of FeNiCo oxide microspheres, indicating diverse surface areas and pore distributions, influencing catalytic performance and dye adsorption. The capability of the synthesized photocatalysts to degrade methylene blue was examined under both UV and visible light irradiation. The FeNiCo oxide microspheres exhibited a band gap of 2.34 eV. Photocatalytic evaluation revealed that the FeNiCo oxide nanoparticles achieved a 65% degradation of methylene blue within 110 min.