Mesoporous ferromagnetic manganese ferrite nanoparticles for enhanced visible light mineralization of azoic dye into nontoxic by-products

In this study, a one pot facile synthesis of ferromagnetic manganese ferrite nanoparticles (MnFe2O4) was carried out using chemical co-precipitation method for mineralization of azo dye (Congo red (CR)) in aqueous solution under visible light irradiation. The synthesized MnFe2O4 nanoparticles were highly crystalline and showed face-centred cubic (FCC) structure with average particle size of 58 ± 4 nm. The BET analysis of the MnFe2O4 nanoparticles revealed the mesoporous distribution of material with high surface area can provide large electro active sites and short diffusion paths for the transport of ions which plays a vital role in the photocatalytic degradation of CR. The point of zero charge (pHPZC) was observed to be 6.7 indicating favourable condition for material-anionic dye interaction. The XPS studies revealed that the large amounts of oxygen vacancies were produced due to the defects in the lattice oxygen. The MnFe2O4 nanoparticles mineralised 98.3 ± 0.2% of 50 mg/L CR within 30 min when tested in photocatalytic reactor under 565 nm. The particles were recoverable under the influence of an external magnet after the photocatalytic reaction and were reusable. The recovered nanoparticles showed 96% of CR degradation efficiency even after five cycles of reuse. The by-product analysis with GC–MS indicated mineralization of CR into simple alcohols and acids. The aqueous solution containing mineralised CR was nontoxic to Trigonella foenumgraecum and Vigna mungo seeds and favoured increased germination, plumule and radicle length when compared to untreated CR.