Magnetic Nanoparticles as Smart Heating Mediator for Hyperthermia and Sorbent Regeneration

Abstract

Titanium oxide (TiO2) nanopowders can be reproducibly formed by hydroxylation of titanium organic complexes. The crystallisation to anatase and rutile can be controlled by systematic calcination and a complex range of properties optimized for specific applications. Characterisation of the powders has been undertaken using advanced physical techniques. The morphology of the TiO2 powders is determined by solution concentration and precipitation phenomena, particularly temperature and stirring regime. However the fine powders have limitations in terms of processing flexibility particularly when nanostructured and organised features are desired, due to their fine particle structure and inability to be sintered without undergoing complete phase change. Anodising titanium metal can overcome these difficulties and under appropriate conditions semi-ordered nanotubes of TiO2 have been prepared. These can be heat treated to develop the phase of choice, anatase or rutile. A mechanism for the formation of the nanotubes has been proposed which is based on the linkage of pores developed in the anodized oxidation product. The pores are driven to into alignment by the applied potential and link up to form the tubular structures. A degree of control of the tube size and wall thickness is shown possible by control of applied voltage. The nanotubes have been investigated using SEM, TEM, XRD and Raman spectroscopy to elucidate the structure and postulate the formation mechanism.

Evidence of non-stoichiometry effects in nanometric manganite perovskites: influence on the magnetic ordering temperature

“…A size of 50 nm or 500 nm was claimed to be necessary to observe in nanomanganites the same behaviour as in bulk La-Ca or La-Sr systems, respectively. 17,20 In contrast, other authors reported, for x close to 0.3 for both La-Ca and La-Sr systems, an increase of T C with cristallite size 10,22,25 that would be correlated to the lattice distortions at the grain surface, which caused a structure relaxation from the surface to the core of the grain. 10 The formation of magnetic polarons was also proposed as a possible cause for such a T C increase.…”

“…17,20 In contrast, other authors reported, for x close to 0.3 for both La-Ca and La-Sr systems, an increase of T C with cristallite size 10,22,25 that would be correlated to the lattice distortions at the grain surface, which caused a structure relaxation from the surface to the core of the grain. 10 The formation of magnetic polarons was also proposed as a possible cause for such a T C increase. Dutta et al also reported a T C increase in La 0.875 Sr 0.125 MnO 3 nanoparticles that was fully consistent with the increased symmetry observed in this case.…”

“…7 Same systems have also attracted much recent attention to act as mediators in self-controlled magnetic fluid hyperthermia applications. [8][9][10][11][12][13][14][15] The magnetic behaviour of the nanosized manganite perovskites was consequently carefully screened. Among the literature, a decrease of saturation magnetization was systematically observed, for example in nanosized La 1Àx Ca x MnO 3 and La 1Àx Sr x MnO 3 materials, 8,[16][17][18][19][20][21][22][23][24][25][26] and it was currently admitted to originate from the formation of a magnetically dead layer (MDL) at the surface of the inorganic core.…”

Manganite perovskite nanoparticles for self-controlled magnetic fluid hyperthermia: about the suitability of an aqueous combustion synthesis route

“…12 Few papers dealt with magnetic suspensions based on LSMO or unaggregated LSMO nanoparticles, and some of them were specific for MFH application. [16][17][18][19][20][21] These nanoparticles were prepared by several routes: the freeze drying technique, 13,14 coprecipitation, 15 Pechini route, [16][17][18] microwave refluxing technique, 19 and conventional solid-state reactions followed by mechanical milling. 20,21 Nevertheless, each of these techniques necessitate an extra stage of calcination at a temperature over 700 C in order to get well-crystallized compounds.…”

“…However, remnant bridges were often maintained leading to the formation of submicrometric aggregates of nanocrystallites. [13][14][15][16][17][18][19][20][21] That is why we investigated another route based on the Glycine Nitrate Process (GNP). Among self-combustion synthesis routes, GNP was firstly proposed in 1990 by Chick et al to elaborate chromite and manganite powders.…”