Large-Scale Synthesis of Colloidal Fe₃O₄ Nanoparticles Exhibiting High Heating Efficiency in Magnetic Hyperthermia

Abstract

Exceptional magnetic properties of magnetite, Fe3O4, nanoparticles make them one of the most intensively studied inorganic nanomaterials for biomedical applications. We report successful gram-scale syntheses, via hydrothermal route or controlled coprecipitation in an automated reactor, of colloidal Fe3O4 nanoparticles with sizes of 12.9 ± 5.9, 17.9 ± 4.4, and 19.8 ± 3.2 nm. To investigate structure–property relationships as a function of the synthetic procedure, we used multiple techniques to characterize the structure, phase composition, and magnetic behavior of these nanoparticles. For the iron oxide cores of these nanoparticles, powder X-ray diffraction and electron microscopy both confirm single-phase Fe3O4 composition. In addition to the core composition, the magnetic performance of nanoparticles in the 13–20 nm size range can be strongly influenced by the surface properties, which we analyzed by three complementary techniques. Raman scattering and X-ray photoelectron spectroscopy (XPS) measurements indicate overoxidation of nanoparticle surfaces, while transmission electron microscopy (TEM) shows no distinct core–shell structure. Considered together, Raman, XPS, and TEM observations suggest that our nanoparticles have a gradually varying nonstoichiometric Fe3O4+δ composition, which could be attributed to the formation of Fe3O4–γ-Fe2O3 solid solutions at their outermost surface. Detailed analyses by TEM reveal that the hydrothermally produced samples include single-domain nanocrystals coexisting with defective twinned and dimer nanoparticles, which form as a result of oriented-attachment crystal growth. All our nanoparticles exhibit superparamagnetic-like behavior with a characteristic blocking temperature above room temperature. We attribute the estimated saturation magnetization values up to 84.01 ± 0.25 emu/g at 300 K to the relatively large size of the nanoparticles (13–20 nm) coupled with the syntheses under elevated temperature; alternative explanations, such as surface-mediated effects, are not supported by our spectroscopy or microscopy measurements. For these colloids, the heating efficiency in magnetic hyperthermia correlates with their saturation magnetization, making them appealing for therapeutic and other biomedical applications that rely on high-performance nanoparticle-mediated hyperthermia.

Up-scaling the synthesis of Cu2O submicron particles with controlled morphologies for solar H2 evolution from water

“…The products were characterized by scanning electron microscopy (SEM) (Quanta 650 FEG microscope, FEI Company), energy dispersive X-ray spectroscopy (EDX) (INCA 350 spectrometer, Oxford Instruments), powder X-ray diffraction (XRD) (X'Pert PRO diffractometer, PANalytical), Raman spectroscopy (alpha300 R confocal microscope, WITec), X-ray photoelectron spectroscopy (XPS) (ESCALAB 250 Xi, Thermo Scientific) [27,28], and UV-Vis-NIR spectroscopy (Lambda 950 spectrophotometer, Perkin Elmer). For more details regarding characterization, see the Supplementary Material (SM).…”

“…Therefore, successfully adapting and further optimizing convenient and controllable synthesis protocols up-scaled from the original milligram-scale methods is not commonly achieved or reported for Cu 2 O materials. Our recent success in developing large-scale synthesis of iron oxide nanocolloids using an automated laboratory reactor [27] motivated us to study the possibility of extending this approach to the synthesis of Cu 2 O colloids. Accordingly, here we report (1) the effect of synthesis up-scaling on the properties of the resultant Cu 2 O colloids, (2) preparation of large quantities of Cu 2 O materials having different uniform shapes, (3) the mechanism of particle formation, and (4) a preliminary investigation of the PEC performance of the as-synthesized Cu 2 O materials.…”

The Atomistic Structure of Metal/Ceramic Interfaces Is the Key Issue for Developing Better Properties

“…A small diameter is best for a fast response. However, for stabilizing metallic nano-sized particles, their surfaces need to be passivated by oxide layers in order to prevent agglomeration [64,65]. Such core-shell nano-powders became popular after reasonable coating techniques were available.…”

Синтез Кластеров Оксидов Железа В Мезопорах Монодисперсных Сферических Частиц Кремнезема

“…Наночастицы магнетита (Fe 3 O 4 ), гематита (α-Fe 2 O 3 ) и маггемита (γ-Fe 2 O 3 ) благодаря низкой токсичности и биосовместимости интенсивно исследуются для приме-нения в биомедицине в качестве T 2 контрастных средств для магнитно-резонансной томографии (МРТ) [4] и маг-нитной гипертермии [5]. Намагниченность и магнитная анизотропия наноразмерных однодоменных частиц мо-гут быть заметно больше, чем у массивного материала, а отличия в температурах Кюри и Нееля достигают сотен процентов.…”