A possible formation mechanism and photocatalytic properties of CoFe2O4/PVA-SiO2 nanocomposites

Highlights: • Carboxilate precursors are formed in the hybrid matrix up to 200 °C. • CoFe₂O₄ with high photocatalytic activity is formed by using 1,2-ethanediol and 1,4-butanediol. • Nanoparticles size increases with the increase of diol chain length. • CoFe₂O₄ nanoparticles size varies in the range of 22–26 nm. - Abstract: The paper presents the synthesis of CoFe₂O₄ nanocrystallites embedded in PVA-SiO₂ hybrid matrix by a modified sol-gel method. The paper is focused on two aspects: (1) formation of cobalt and iron carboxylate-type precursors (oxalate, lactate, malonate and succinate) in the presence of tetraethylorthosilicate, polyvinylalcohol (PVA) and different diols: 1,2-ethanediol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, and (2) possible decomposition mechanism of carboxylate-type precursors into CoFe₂O₄ within the pores of PVA-SiO₂ hybrid matrix. The formation and decomposition of carboxylate-type precursors was studied by thermal analysis coupled with mass spectrometry, while the formation of CoFe₂O₄/PVA-SiO₂ nanocomposites (NCs) was investigated by X-ray diffraction and Fourier transformed infrared spectroscopy. The particle size and shape were studied by transmission electron microscopy. At 1000 °C, well-crystallized CoFe₂O₄ was evidenced as single phase in G1,2ED and G1,4BD and together with Co₂SiO₄ in G1,2 PD and G1,3 PD. Based on UV–vis absorption spectra, the band gaps of the NCs were evaluated. The photocatalytic activities of the NCs were evaluated by degrading Rhodamine B under UV–vis light irradiation. The reactive radical species produced at the solid-liquid interface were evidenced using electron spin resonance coupled with spin trapping.