Synthesis of Fe/Ti oxides from a single source alkoxide precursor under inert atmosphere

Abstract

O alcóxido heterometálico [FeCl{Ti 2 (OPr i ) 9 }] (1) foi utilizado como um precursor de fonte única para a preparação de óxidos de Fe/Ti sob atmosfera inerte. Três procedimentos sintéticos distintos foram adotados no processamento de 1, com o emprego de soluções aquosas ácidas (HNO 3 ou HCl), ou na ausência de ácido mineral. Os produtos foram caracterizados por difratometria de raios X (pó), microscopia eletrônica de varredura combinada com espectroscopia de dispersão de raios X (MEV/EDS) e espectroscopias Raman, de ressonância paramagnética eletrônica (RPE) e Mössbauer. Os óxidos produzidos contêm titânio(IV) e ferro(III) (ou ferro(II)), dependendo das condições de reação e das temperaturas de tratamento térmico. Uma interessante redução de ferro(III) a ferro(II), que levou à obtenção de ilmenita (FeTiO 3 ), foi observada a 1000 o C no sistema contendo HNO 3 . Estudos por MEV/EDS revelaram uma distribuição altamente heterogênea dos metais em todos os produtos, possivelmente relacionada com a presença de um conteúdo significativo de carbono e de defeitos estruturais (vacâncias de oxigênio) nos sólidos.The heterometal alkoxide [FeCl{Ti 2 (OPr i ) 9 }] (1) was employed as a single source precursor for the preparation of Fe/Ti oxides under inert atmosphere. Three different synthetic procedures were adopted in the processing of 1, either employing aqueous HNO 3 or HCl solutions, or in the absence of mineral acids. Products were characterised by powder X-ray diffractometry, scanning electron microscopy combined with energy dispersive X-ray spectroscopy (SEM/EDS) and Raman, electron paramagnetic resonance (EPR) and Mössbauer spectroscopies. Oxide products contained titanium(IV) and either iron(III) or iron(II), depending on reaction conditions and thermal treatment temperatures. An interesting iron(III)→iron(II) reduction was observed at 1000 o C in the HNO 3 -containing system, leading to the detection of ilmenite (FeTiO 3 ). SEM/EDS studies revealed a highly heterogeneous metal distribution in all products, possibly related to the presence of a significant content of carbon and of structural defects (oxygen vacancies) in the solids.Keywords: oxides, sol-gel, single source precursor, inert atmosphere, electron microscopy IntroductionMultimetal oxide systems play an important role in materials science. They have been extensively investigated for the development of high performance ceramics and (nano)composites, aiming at applications in optics, electronics, magnetism and catalysis. The development of structural components, energy conversion devices, sensors and MRI contrast agents has also benefited from heterometal oxide research. [1][2][3][4] Nowadays, the preparation of these oxides is often performed by chemical methods. 3,[5][6][7] In particular, the sol-gel process, either hydrolytic or non-hydrolytic, has been widely employed due to its advantages over conventional solid state methods. These advantages include lower processing temperatures and better control over microstructure, uniformity and stoichiometry o...

Nanoparticle Self-Assembly Mechanisms in the Colloidal Synthesis of Iron Titanate Nanocomposite Photocatalysts for Environmental Applications

“…At 700 °C, along with the anatase phase, the rutile phase emerges in the composition of the material with a reflection at 2θ = 27.4°. It should be noted that the data presented in refs − and indicate that the formation of Fe 2 Ti 2 O 7 and Fe 2 TiO 5 phases visible in XRD patterns in the products of sol–gel synthesis occurs usually upon annealing at 700 °C. The synthesis in boiling water with removal of the organic ligands by evaporation offered, however, the Fe 2 TiO 5 phase distinguishable in the XRD pattern directly, without any additional thermal treatment …”

Photo induced reductive leaching of iron from ilmenite in hydrochloric acid solutions

“…Furthermore, lattice defects in oxide structures play a major role in a number of properties such as diffusion of ions and conductivity. It has been reported (Camargo et al, 2008) Experiments performed allowing only the HCl solution to expose to the UV light and blocking UV light falling to the ilmenite particles, showed similar rates for the iron dissolution. This confirms that there is no influence arising from ilmenite band gap excitation and the rate of dissolution enhancement is due to the degradation of polymeric species in the solution phase.…”

“…Furthermore, lattice defects in oxide structures play a major role in a number of properties such as diffusion of ions and conductivity. It has been reported (Camargo et al, 2008) that oxygen vacancies affect the mobility of iron and titanium cations on a crystal lattice, such as FeTiO 3 . Therefore, it is clear that titanium and iron show different mobilities in areas with different concentrations of defects.…”

Synthesis, Characterization, and Electrochemical Properties of a Series of Sterically Varied Iron(II) Alkoxide Precursors and Their Resultant Nanoparticles

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