Low temperature superparamagnetic nanocomposites obtained by Fe(acac)3-SiO2-PVA hybrid xerogel thermolysis

Abstract

Fe(acac) 3 /silica/PVA hybrid xerogel nanocomposite was obtained by one pot acid catalysed sol-gel synthesis using the homogeneous mixture of iron(III) acetylacetonate (Fe(acac) 3), tetraethylorthosilicate (TEOS), and polyvinyl alcohol (PVA). Nominal composition ratio of iron oxide/silica was 15/85 (weight percent). Nitric acid was used as catalyst. Another sample of Fe(acac) 3 /silica xerogel without PVA addition was prepared in the similar processing conditions. Based on thermal analysis studies, the thermal behaviour of both xerogel samples was unveiled and it allowed choosing the optimal calcination temperatures in order to obtain iron oxide silica magnetic nanocomposite samples. The two xerogel (with and without PVA) samples were thermally treated, in air, at 220, 260 and 300°C and characterized by different techniques. XRD investigations revealed phase composition evolution with calcination temperature, from cubic spinel phase (maghemite) to hexagonal stable hematite containing nanocomposite of 10-20 nm average crystallite size. These findings were confirmed by Mössbauer spectroscopy. Up to 300°C, the surface area and total pores volume increased with temperature for all samples. By calcination at the same temperature, the hybrid xerogel containing PVA resulted in significantly higher magnetization and free volume values in comparison with the sample without PVA.

SiO2-PVA-Fe(acac)3 Hybrid Based Superparamagnetic Nanocomposites for Nanomedicine: Morpho-textural Evaluation and In Vitro Cytotoxicity Assay

“…This isotherm is a combination of Type IV(a) isotherm (H4 hysteresis) and I(b) reversible isotherm, indicating a significant percentage of microporosity when comparing to mesoporosity. At 300 • C, all of the samples exhibited the maximum values of specific surface area, total pore, and micropores volume, which was consistent with literature data and also with our previous works [57,58]. At this temperature, the volatile products were eliminated in a large amount without a significant collapse of the silica pore walls.…”

“…The nanocomposites are named as P-x, where x is the temperature of thermal treatment. The hybrid nanocomposite xerogel sample that was obtained at 120 • C had a compact nonporous structure, consisting of iron precursor and organics [58]. As a consequence, the adsorbed nitrogen amount was very small and did not allow for obtaining an isotherm plot.…”

“…At 260 • C, the specific surface area and total pore volume increased, because most of the organic phase and precursors decomposed [58]. Thus, the free volumes appear in the samples that were calcined above 260 • C. Therefore, the increases are due to the partial carbonization, oxidation, and volatilization of the organic parts (acetylacetonate and PVA).…”

Molybdate Recovery by Adsorption onto Silica Matrix and Iron Oxide Based Composites

“…These exothermic processes can be also associated with the redox reaction between iron II ions acetylacetonate. In the temperature range between 250 and 440 °C, an exothermic process associated with condensation and dihydroxylation of silica is taking place, with a mass loss of around 2%, as well as a thermal decomposition of organic compounds from matrix, and some polymer chain cleavage [ 56 ]. At temperature higher than 400 °C can be noticed the presence of another thermal decomposition plateau, associated with 5% mass loss, when the organic residues and C obtained from acetylacetonate decomposition are eliminated.…”

“…At temperature higher than 400 °C can be noticed the presence of another thermal decomposition plateau, associated with 5% mass loss, when the organic residues and C obtained from acetylacetonate decomposition are eliminated. Concomitant can take place the condensation of –OH groups into the silica matrix [ 56 , 57 , 58 , 59 ].…”