Superior photocatalytic performance of ancillary-oxidant-free novel starch supported nano MFe2O4 (M = Zn, Ni, and Fe) ferrites for degradation of organic dye pollutants

Abstract

This work presents the effectual degradation of MB and MO dyes in an aqueous solution under UV light irradiation on nano ZnFe2O4, NiFe2O4, and Fe3O4 without using any supplementary oxidants has been reported. Nano ZnFe2O4, NiFe2O4, and Fe3O4 are successfully prepared via a co-precipitation technique utilizing biodegradable starch as a surfactant. XRD patterns reveal a pure spinel phase for all the samples. FTIR spectra confirm the successful embedding of the starch surfactant. SEM micrographs exhibit tiny spherical particles of size 5–8 and 4–6 nm for ZnFe2O4 and NiFe2O4 but spherical particles of 8–10 nm and flake-like particles of ∼14 nm thick for Fe3O4. N2 sorption studies show type-IV isotherms typical of mesoporous structures. The direct bandgap of these ferrite nanoparticles is 2.03–2.15 eV, related to the metal D-d onsite transfers, which are permitted by spin but prohibited by parity. MB decolorization of 99% is achieved in less than 2 h for all the samples; in contrast, MO decolorization takes relatively longer irradiation. The decolorization kinetics suggests that the pseudo-second-order model is more appropriate to explain the decolorization process of MB and MO by the catalysts. The order of photocatalytic activity evaluated from rate constant (k1) per SSA values is Fe3O4 < ZnFe2O4 < NiFe2O4 for both MB and MO decolorization. NiFe2O4 photocatalyst shows the best effect on the decolorization of both dyes due to its low bandgap and high surface area. All the ferrite catalysts demonstrate high stability with no substantial deterioration of photocatalytic activity even after three cycles. The results of this study endorse that the nano ferrites prepared in this work are potential candidates for the photocatalytic degradation of aqueous solutions of MB and MO.