Raman spectroscopy investigation of magnetite nanoparticles in ferrofluids

Abstract

a b s t r a c tRaman spectroscopy is used to investigate magnetite nanoparticles dispersed in two types of bcyclodextrin suspensions. An approach is presented for characterization of the magnetic core in liquid surrounding at room temperature and atmospheric pressure. The effect of elevating laser power on the structural stability and chemical composition of magnetite in the ferrofluids is discussed. The data are compared with data from dry by-products from the fluids. Powder samples undergo total phase transition from magnetite to hematite at laser power of 1.95 mW. The same nanoparticles in the fluid undergo transformation at 9 mW, but no hematite positions appear throughout that investigation. The Raman spectra revealed that the main phase of the magnetic core in the fluids is magnetite. That is indicated by a strong and non-diminishing in intensity peak at 670 cm. A second phase is present at the nanoparticle's surface with Raman spectroscopy unveiling maghemite-like and small fractions of goethite-like structures. The Fourier transform infrared spectroscopy investigations confirm deviations in the surface structure and also point to the fact that the oxidation process starts at an early stage after formation of the nanoparticles. The analyses of the infrared data also show that b-cyclodextrin molecules retain their cyclic character and the coating does not affect the oxidation process once the particles are evicted from the fluids. A Mössbauer spectroscopy measurement on a ferrofluidic sample is also presented.

Influence of constant magnetic field on aggregation processes in magnetite colloids

“…So local heating over 500ºC caused by 1 µm mean diameter laser spot may be supposed that can be proved by microphotographs containing SiO 2 melted areas. The characteristic band of maghemite is observed at 390 cm -1 [12]. When a laser power exceeds a threshold value, the intensities of bands at 390 cm -1…”

“…[12]. The bands at ~220 cm -1 and ~280 cm -1 are usually assigned to α-Fe 2 O 3 lattice vibrations [12]. The analysis of Raman spectra (figure 2) revealed laser induced phase transition of magnetite to hematite via an intermediate maghemite phase at a laser power exceeding a threshold value (~1 mW).…”

“…The halo background at low angles is due to the amorphous phases. [12]. The bands at ~220 cm -1 and ~280 cm -1 are usually assigned to α-Fe 2 O 3 lattice vibrations [12].…”

“…Raman spectroscopy can be used for the analysis of chemical composition of magnetic nanoparticles. This technique enables one to locally observe coexisting phases and phase transitions between magnetite (Fe 3 O 4 ), maghemite (γ-Fe 2 O 3 ) and hematite (α-Fe 2 O 3 ) [12].…”

Applications of Magnetite Nanoparticles for Heavy Metal Removal from Wastewater

“…XPS is used for the analysis of the surface chemistry. Raman and Fourier transform infrared (FTIR) spectroscopy have been used to characterize the phase of the magnetic core of magnetite nanoparticles [28][29]. FTIR spectra yield information on the chemical bonds between the Fe 3 O 4 core and the organic surface coverage [30].…”