New Synthesis of Ferrite–Silica Nanocomposites by a Sol–Gel Auto-Combustion

Abstract

A sol-gel autocombustion method was used to synthesize nanometric metal-oxide powders, and was extended for the first time to prepare ferrite-silica nanocomposites. The gels obtained by mixing suitable amounts of citric acid, metal nitrates, ammonia (pure phases) and tetraethylortosilicate (nanocomposites) were converted directly to ferrite (either c-Fe 2 O 3 or CoFe 2 O 4 ) or ferrite-silica composites through a rapid autocombustion reaction. The combustion involves a thermally induced autocatalytic oxidation-reduction reaction between the nitrate and the citrate ions. The sample characterization by X-ray diffraction, transmission electron microscopy and N 2 physisorption measurements revealed nanosized pure phase powders and nanocomposites in which small spherical nanoparticles (mean size 3.5 and 5.0 nm, respectively for the c-Fe 2 O 3 and CoFe 2 O 4 ) are homogeneously dispersed over a mesoporous silica matrix.

Studying the effect of Zn-substitution on the magnetic and hyperthermic properties of cobalt ferrite nanoparticles

“…Moreover, it shows excellent chemical and thermal stabilities, good mechanical properties 1 and is also easily synthesised with different approaches. [25][26][27][28][29] Despite its potential toxicity, cobalt-containing materials have been proposed as promising heat mediators due to their high anisotropy. 23,[30][31][32][33][34][35][36][37] The partial substitution of Co 2+ with less toxic divalent ions such as Zn 2+ (Zn x Co 1−x Fe 2 O 4 ) has been proposed in order to increase the saturation magnetisation and to lower the toxicity.…”

The Role of Nitrate on the Sol-Gel Spread Self-Combustion Process and Its Effect on the NH3-SCR Activity of Magnetic Iron-Based Catalyst

“…Due to the non-toxicity, low cost, environment, and the outstanding redox ability between Fe III and Fe II , a series of iron-based mixed oxide catalysts prepared through co-precipitation, sol-gel, and impregnation methods have been developed by many researchers [17][18][19][20]. However, the sol-gel spread self-combustion method, also called low-temperature combustion synthesis (LCS), which takes advantage of organics (citric acid, glucose, urea, and so on) as reactants and nitrates from metal nitrates as oxidants, has been widely used to obtain nano-particles, ultrafine powders, and metal oxide catalysts [21][22][23][24][25][26]. In our precious studies, a novel Fe-Ce-W mixed oxide catalyst synthesized via the citric acid sol-gel spread self-combustion method exhibited high catalytic activity of NO x reduction with high-dispersive γ-Fe 2 O 3 crystallite formed in it [27].…”

Tunable single-phase magnetic behavior in chemically synthesized AFeO3–MFe2O4 (A = Bi or La, M = Co or Ni) nanocomposites

“…The details of the self-combustion process and thermogravimetric analysis have been published elsewhere. 42,43 Briefly, 6.7 mmol of Fe(NO 3 ) 3 •9H 2 O and 3.4 mmol of Co (NO 3 ) 2 •6H 2 O (Sigma-Aldrich) were mixed in a beaker containing 10 ml of an aqueous solution of 1 M citric acid (1 : 1 molar ratio of total metals to citric acid). The solution was kept under agitation to dissolve the nitrates at room temperature and NH 3 (30%) was added dropwise to adjust the pH to 7.…”