Mn_0.5Zn_0.5Fe₂O₄ ferrite nanoparticles with tunable Curie temperature and saturation magnetization are synthesized using hydrothermal co-precipitation method. Particle size is controlled in the range of 54 to 135 Å by pH and incubation time of the reaction. All the particles exhibit super-paramagnetic behaviour at room temperature. Langevin’s theory incorporating the interparticle interaction was used to fit the virgin curve of particle magnetization. The low-temperature magnetization follows Bloch spin wave theory. Curie temperature derived from magnetic thermogravimetric analysis shows that Curie temperature increases with increasing particle size. Using these particles magnetic fluid is synthesized and magnetic characterization is reported. The monolayer coating of surfactant on particle surface is confirmed using thermogravimetric measurement. The same technique can be extended to study the magnetic phase transition. The Curie temperature derived using this measurement complies with the low-temperature magnetic measurement. The room-temperature and high-temperature magnetization measurements are also studied for magnetic fluid systems. The magnetic parameters derived for fluid are in good agreement with those obtained for the particle system

Physicochemical adsorption and degradation of the azo dye, methylene blue (MB), when irradiated by visible and UV light in aqueous ZnO suspension have been investigated. The novelty of this work is to investigate the effect of dye concentration up to 200 mg/l, keeping the nanocatalysts’ concentration invariant as 1 g/l. The nanocatalysts before and after degradation process have been analysed to understand the mechanism of dye removal using X-ray diffractometer (XRD), Fourier-transform infrared spectroscopy (FTIR) and thermal gravimetric analyser(TGA). The results show that UV light degrades the dye to its intermediates through chemi-adsorption, whereas the visible light induces physisorption of dye molecules on ZnO nanocatalysts. The XRD pattern of the ZnO nanocatalysts revealed no changes in the internal structure of ZnO after the degradation process, confirming thereuse of catalysts.

The influence of metal ion to hydroxide ion ($\rm{Me^{2+} /OH^{−}}$) ratio on the synthesis of $\rm{Mn_{0.5}Zn_{0.5}Fe_{2}O_{4}}$ (MZ5) ferrite nanoparticles is reported. The aim of this low-temperature co-precipitation technique is to produce MZ5 nanoparticles with different sizes in single domain range. The variation in $\rm{Me^{2+} /OH^{−}}$ ratio affects the growth and shape of the particles. The mechanism of nucleation and growth of the particles is discussed. EDX and XPS measurements show the change in stoichiometry of the composition when $\rm{Me^{2+} /OH^{−}}$ ratio changes. When the ratio is 0.52, Zn ion was found to be absent and the structure resembles $\rm{Mn_{x}Fe_{3−x}O_{4}}$. The defect in the composition changes magnetic properties such as saturation magnetisation and Curie temperature of the samples. 119 nm crystalline size with highest magnetisation ($\rm{80 Am^{2}/kg}$) is obtained which shows quite good response to induction heating (specific absorption rate (SAR) = 78 W/g). Moreover, SAR and intrinsic loss power (ILP) are higher for MZ5 ferrite than that are reported earlier. This shows the potential of magnetic induction heating in the treatment of cancer.