Green synthesis of hausmannite nanocrystals and their photocatalytic dye degradation and antimicrobial studies

A simple and green route to synthesize hausmannite nanocrystals using tannic acid was presented in this work. Formation mechanism of Mn3O4 nanoparticles (NP’s) was illustrated. The Mn3O4 NP’s were characterized by X-ray powder diffraction studies (XRPD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, Fourier transformed infrared spectroscopy (FT-IR), and high-resolution transmission electron microscopy. XRPD confirms the formation of Mn3O4 NP’s and the observation of peak at 632.81 cm−1 in Raman spectroscopy confirms the same. Mixed valency of Mn3O4 was evidenced from XPS. Also surface functionalization was evidenced by FT-IR and XPS measurements. The obtained NP’s are effective in degradation of tested organic pollutants methyl orange and bromophenol blue. About 90 % degradation in methyl orange and 80 % degradation in bromophenol blue were observed within 10 min using Mn3O4 NP’s. These NP’s show good antimicrobial activity against both tested gram-positive (Bacillus subtilis 168) and gram-negative (Escherichia coli K12) bacterias. The antibacterial activity of obtained Mn3O4 Np’s was found high in E. coli K12 than in B. subtilis 168.