Understanding the Nucleation and Growth of Iron Oxide Nanoparticle Formation by a “Heating-Up” Process: An NMR Relaxation Study

Abstract

The formation of iron oxide nanoparticles obtained by the thermal decomposition of iron–oleate complexes via a “heating-up” process was monitored by the NMR relaxation method, which allows us to track the average diameter of iron oxide nanoparticles. The analysis of dependencies of the T 1/T 2 ratio and 1/T 2 values on time at the heating of the reaction mixture demonstrated that the nucleation and nanoparticle growth processes could proceed in two ways depending on the presence of oleic acid in the solution: continuously without separation of the nucleation stage or discretely with the separation of the nucleation and growth of nanoparticles. In the case of excess of oleic acid, the nucleation process follows the well-known LaMer model, characterized by a burst of nucleation and separation of nucleation and growth under continuous monomer supply. In the absence of oleic acid in the system, the nucleation and growth of nanoparticles are not separated and proceed continuously. The presence of a sufficient amount of oleic acid is the reason why the process of nucleation and growth of nanoparticles by heating up follows the path of “burst nucleation,” which is similar to the “hot injection” method. That is, oleic acid acts as a “fuse” for the explosive “burst nucleation.” This new approach shows that the “hot injection” method can be carried out not only mechanically (by introducing a precursor into the reaction system) but also chemically, with the help of a reagent that has been in the system from the very beginning.

Surface Coordination Layer to Enhance the Stability of Plasmonic Cu Nanoparticles

“…18,34,35 The absorbance at ∼1555 cm −1 was related to the Ac − in the bidentate chelate mode. 36 Therefore, all these results verified the presence of the surface-coordinating layer of Cu@Cu 2 O in Cu@Cu 2 O/ZnO. Based on the aforementioned results, a possible mechanism for plasmonic antioxidation of the Cu@Cu 2 O/ZnO heterojunction was proposed.…”

“…As shown in Figure S11, there existed five FTIR absorption bands, which were attributed to the −OH stretching (∼3404 cm –1 ), −CH 3 asymmetric and symmetric stretching (∼2919 and ∼2851 cm –1 ), −COO – asymmetric stretching (∼1555 cm –1 ), and −CH 3 asymmetric bending (∼1404 cm –1 ) vibrations, similar to those of Cu@Cu 2 O NPs treated with Mn­(Ac) 2 (Figure S12). ,, The absorbance at ∼1555 cm –1 was related to the Ac – in the bidentate chelate mode . Therefore, all these results verified the presence of the surface-coordinating layer of Cu@Cu 2 O in Cu@Cu 2 O/ZnO.…”

Effect of the Synthetic Approach on the Formation and Magnetic Properties of Iron-Based Nanophase in Branched Polyester Polyol Matrix

“…The experimentally measured relaxation times, (T 2 )obs, were inverted into the relaxation rates, (1/T 2 )obs. The relaxation rate is the sum of the two main contributions: the relaxation of protons in the bulk solvent (1/T 2 )d (diamagnetic component) and the relaxation of the protons located in the first coordination sphere of the paramagnetic ion (1/T 2 )p (paramagnetic component): (1/T 2 )obs = (1/T 2 )d + (1/T 2 ) [ 87 ].…”

Mechanism of Nanoparticle Formation in the Liquid-Phase Thermal Decomposition Method

“…A comprehensive understanding of the formation mechanism of nanoparticles (NPs) in a homogeneous liquid medium is of significant importance to achieve controlled morphology, phase, yield, and size distribution of NPs for their use in applications spanning biomedical to sensing to data storage. , One of the important liquid-phase routes followed for the synthesis of high-quality monodispersed NPs on a large scale is the heat-up method, wherein the precursors are gradually heated in a high boiling organic solvent to actuate the decomposition reaction that generates monomers for subsequent nucleation and growth processes. , The mechanism of NP formation in this route has relied on the concepts of burst nucleation driven by the supersaturation of monomers in the solution, growth of nuclei/particles via monomeric addition, and monodispersity due to the separation of nucleation and growth events. − These concepts were consistently used to explain the formation of various semiconductor, metallic, magnetic, and metal oxide NPs; , however, still the synthesis process and the features it manifests at varying experimental conditions are unclear. For instance, the formation of monodispersed iron oxide NPs (IONPs) by the decomposition of the iron oleate complex (IOC) precursor has been reasoned with the separation of nucleation and growth events ,, that occur around 240 and 310 °C, respectively. , On the contrary, using the same precursor and the experimental conditions, iron oxide nanowhisker-shaped particles were achieved at 150 °C in the presence of oleic acid (OA)/trioctyl phosphine oxide (TOPO) ligands . Further, the existing mechanism does not account for important features like the monomeric generation pattern, the amount and rate at which heat is supplied to the system, and the dwelling (aging) time of reaction contents.…”

“…For instance, the formation of monodispersed iron oxide NPs (IONPs) by the decomposition of the iron oleate complex (IOC) precursor has been reasoned with the separation of nucleation and growth events 5,6,8 that occur around 240 and 310 °C, respectively. 5,9 On the contrary, using the same precursor and the experimental conditions, iron oxide nanowhisker-shaped particles were achieved at 150 °C in the presence of oleic acid (OA)/trioctyl phosphine oxide (TOPO) ligands. 10 Further, the existing mechanism does not account for important features like the monomeric generation pattern, the amount and rate at which heat is supplied to the system, and the dwelling (aging) time of reaction contents.…”