Direct Probing of Fe₃O₄ Nanoparticle Surface Temperatures during Magnetic Heating: Implications for Induction Catalysis

Abstract

The presence of a temperature gradient between the magnetic nanoparticle (NP) surface and the bulk medium during induction heating has been observed across several fields. While no noticeable increase in bulk temperature is observed, biological (DNA denaturation, tumor apoptosis) and chemical (bond cleavage) evidence indicates high temperatures near/at the NP surface. Unfortunately, current methods for temperature probing rely on bulk temperature measurements (fiber-optic IR probes) or are limited by thermal stability and spatial resolution (organic molecules). To further the understanding of magnetic heating as a driving force in catalysis, as well as drug delivery/hyperthermia treatments, a more accurate description of the nanoparticle surface temperature is needed. This work uses inorganic luminescent probes in direct contact with the particle surface, entailing the deposition of YVO4:Eu3+ around a Fe3O4|SiO2 structure, to measure the local temperature. The luminescent response is calibrated in situ via a controlled temperature stage to extract the field-dependent heating. The luminescent probe results in a high spatial resolution (<5.5 nm) with temperatures up to 64 °C higher than standard fiber-optic probes. The direct contact between the photoluminescence (PL) probe and Fe3O4 allows for ballistic transport and improved temporal resolution, mimicking an adiabatic system (negligible long-range heat dissipation). Other advantages include avoiding measurements in liquid media, where the distance between the heat source and the probe cannot be controlled, adding to the uncertainty of the temperature measurement due to changes in colloidal anisotropy (which changes with the heating profile) of the magnetic cores and surface quenching of the luminescent signal.

Catalytic Reaction Triggered by Magnetic Induction Heating Mechanistically Distinguishes Itself from the Standard Thermal Reaction

“…Similarly, we confirmed negligible differences in temperature measurements by the optic fiber probe and the conventional metal-based thermocouple in the thermal reaction mode, the latter of which cannot be used under MIH conditions due to self-heating. Further, MIH, by its heating mechanism, will indeed bring temperature gradients (Δ T film ) between the catalyst particle as the origin and its surrounding bulk medium, − but the question is whether the Δ T film in our typical plug flow reactor setup is significant enough to distort steady-state catalytic kinetics. The significance of the Δ T film would depend on the magnetic field parameters, reaction conditions, and the capacity of the fluids around the catalyst particles to transport the dissipated heat. , For example, whereas a temperature difference up to 64 °C was reported for a temperature measurement program executed on Fe 3 O 4 in the absence of carrier fluid, other researchers found negligible temperature difference (≤5 °C) as a consequence of the experimental conditions they adopted. , Our reaction–diffusion–heat transfer analyses for our specific reaction conditions are described in detail (see Notes S1 in Supporting Information), where the MIH-generated heat, reaction heat, heat absorbance by the quartz sand and reaction stream, heat loss to the environment, mass transfer in the surface film, and simultaneous reaction and diffusion inside the catalyst pores were all factored in.…”

“…The significance of the ΔT film would depend on the magnetic field parameters, reaction conditions, and the capacity of the fluids around the catalyst particles to transport the dissipated heat. 29,30 For example, whereas a temperature difference up to 64 °C was reported for a temperature measurement program executed on Fe 3 O 4 in the absence of carrier fluid, 31 other researchers found negligible temperature difference (≤5 °C) as a consequence of the experimental conditions they adopted. 15,26 Our reaction−diffusion−heat transfer analyses for our specific reaction conditions are described in detail (see Notes S1 in Supporting Information), where the MIH-generated heat, reaction heat, heat absorbance by the quartz sand and reaction stream, heat loss to the environment, mass transfer in the surface film, and simultaneous reaction and diffusion inside the catalyst pores were all factored in.…”

Local Temperature Increments and Induced Cell Death in Intracellular Magnetic Hyperthermia

“…According to theoretical thermodynamic calculations of heat transfer, 2,14−16 it was predicted that the heat generated in a single MNP would be dissipated to the rest of the cell before reaching any significant temperature difference with its surroundings. However, contrary to the theoretical predictions, experiments involving magnetic hyperthermia in MNPs in water suspensions 17−20 and powder suspensions, 21 both ex vivo 22 and in vivo, 23 found relevant local temperature increases in MNPs with respect to the bulk water temperature. The occurrence of these temperature gradients in cells would support the local hyperthermia hypothesis.…”

Luminescence Thermometry Beyond the Biological Realm

“…Many magnetic induction heating studies have been driven by therapeutic hyperthermia applications, although additional motivating applications include catalysis and water purification. 233 Shen et al 234 dispersed microwave-transparent thermochromic zinc-based MOFs in an ethanolic solution that was distributed in a 10 × 10 × 1 cm 3 matrix consisting of 100 individual plastic cells (Figure 8c). When heated in a microwave cavity, temperature variations attributed to the nonuniform electric field were observed across the matrix.…”

“…Luminescence thermometry has also been used to monitor the temperature rise of liquids heated by magnetic induction and by microwave irradiation, the latter of which has applications in areas including chemical synthesis, separations, and catalysis. Many magnetic induction heating studies have been driven by therapeutic hyperthermia applications, although additional motivating applications include catalysis and water purification . Shen et al dispersed microwave-transparent thermochromic zinc-based MOFs in an ethanolic solution that was distributed in a 10 × 10 × 1 cm 3 matrix consisting of 100 individual plastic cells (Figure c).…”