Synthesis of carbon-encapsulated iron nanoparticles by pyrolysis of iron citrate and poly(vinyl alcohol): a critical evaluation of yield and selectivity

Abstract

Carbon-encapsulated iron nanoparticles were synthesized by pyrolysis at 1000 °C of two solid precursors: poly(vinyl alcohol) and iron citrate. The weight ratio between the precursors controlled the reaction yield, crystallinity, morphological features and magnetic properties of the products. The encapsulation yield of iron nanoparticles in carbon shells was strongly influenced by the iron-to-carbon ratio and depended on the iron citrate content in the initial reactant mixtures. Despite the inherent simplicity of the process and the use of low cost starting materials the demonstrated route possesses limited selectivity, especially at high iron-to-carbon ratios. At these experimental conditions the as-obtained products contained non-encapsulated Fe particles and graphite in addition to magnetic carbon encapsulates. These by-products were effectively removed by a one-pot purification procedure that included acid treatment.

Temperature and Copper Concentration Effects on the Formation of Graphene-Encapsulated Copper Nanoparticles from Kraft Lignin

“…This is the same trend as reported previously [23]. The reason was that more copper enabled a higher amount of lignin to be oxidized into carbonaceous gases vaporizing during the redox process of reducing copper ions to atoms and rendering the loss of carbon material.…”

“…The particle size decreased significantly when the weight ratio increased from 1:2 to 1:1, while the particle diameter increased significantly when the weight ratio increased from 1:4 to 1:2. The particle size’s downward trend was similar to the observation from the study of mixing poly (vinyl alcohol) with iron citrate, with an iron-to-carbon weight ratio increasing up to 7:9 [23], and from another study wherein ferrocene and aromatic heavy oil was mixed with a ferrocene-to-oil weight ratio increasing up to 7:20 [26]. However, the extent of size decline was lower than the one with copper because iron has a carbon solubility much higher than copper, which can prevent carbon from effectively acting as a barrier to prevent the agglomeration of iron nanoparticles [27].…”

Carbon-Based Nanomaterials from Biopolymer Lignin via Catalytic Thermal Treatment at 700 to 1000 °C

“…In general, as the temperature increased from 700 to 900 • C, the diffraction intensity of α-Fe decreased while the γ-Fe increased, and as the temperature further increased to 1000 • C, the γ-Fe diffraction intensity (2θ = 43.6 • ) decreased, while the Fe 3 C intensity appeared. The existence of γ-Fe starting at 700 • C indicated that the γ-Fe was somehow shielded or blocked in the carbon matrix, preventing the phase transformation of γ-Fe to α-Fe and Fe 3 C [25,26] at ambient conditions, because at ambient conditions γ-Fe is thermodynamically unstable and normally transforms to α-Fe and Fe 3 C spontaneously [17]. The iron phase shifting from α-Fe to γ-Fe started at 700 • C, which is lower than the bulk iron phase transformation (α-Fe to γ-Fe) temperature of 727 • C [27].…”

“…During this process, polymers first decompose to amorphous carbon (AC), after which AC, as the solid carbon source, dissolves in and precipitates out of the catalyst [16][17][18][19][20][21]. The dissolution and precipitation of AC is affected by the thermal treatment temperatures.…”

Synthesis and characterization of Fe/C core–shell nanoparticles

“…It is known that for each fabrication method of magnetic carbon nanoparticles there are more or less some metallic nanoparticles which are nonencapsulated or encapsulated in defective carbon coatings. We did acid treatment to our product (4 M HCl for 24 h) [23], VSM pattern of the acid-treated product was shown in Fig. 3(c), where the contribution of paramagnetism signals of the sample was deducted.…”