Structural, magnetic and antibacterial properties of manganese substituted magnetite ferrofluids

Manganese substituted magnetite ferrofluids Mn_xFe_1-xFe₂O₄ (x=0 to 0.8) are prepared in this work by chemical co-precipitation reaction. The controlled growth of ferrofluids nanomaterials for antibacterial activities is challenging and therefore very few reports are available on the topic. This research focus on stabilizing the aqueous ferrofluids with tetramethylammonium hydroxide (TMAH) surfactant for high homogeneity. Morphological characterization reveals nanoparticles of 5-11 nm formed by the chemical reaction and the nanocrystalline nature as evident from the structural investigation. Mn-substituted magnetic ferrofluids are analyzed for their structural, functional and antibacterial performance according to the concentration of Mn-substituent concentration. Optical studies showed higher blue shift for Mn²⁺ substituted Mn_xFe_1−xFe₂O₄ with theoretical correlation of optical band gaps with Mn-concentration. Super paramagnetic nature of substituted ferrofluids causes zero coercivity and remanance, and this influence the particle size, cation distribution and spin canting. The structural and functional performance of the ferrofluids are correlated with the antibacterial activity finally demonstrating the highest inhibition zone formation for Mn_xFe_1-xFe₂O₄ ferrofluids.