Microemulsion mediated sol-gel synthesis of nano-scaled MAl2O4 (M=Co, Ni, Cu) spinels from single-source heterobimetallic alkoxide precursors

Abstract

Nanocrystalline aluminate spinels with cobalt, nickel or copper as bivalent cations have been prepared in different particle sizes using single-source heterometal alkoxides of the type [M{Al(OR) 4} 2 ] (MII=Co, Ni, Cu; R=Pri, But) in a microemulsion assisted sol-gel process. The compatibility of the metal stoichiometry in the precursor molecules with respect to the spinel requirement was established by elemental, spectroscopic and single crystal X-ray diffraction analyses. Synthesis of CoAl 2 O 4 using both single-and multi-component routes gave different results: whereas the single-source precursor approach yielded monophasic high purity spinels, phase contamination was evident in the diffractograms of ceramics obtained using a mixture of individual components. The alkoxide precursors were hydrolysed in a homogeneous dispersion of colloidal water droplets in a non-aqueous phase. The diameter of water droplets in the microemulsion can be tuned, inter alia, by varying the hydrophilic chain length of the surfactant molecules which influences the size distribution of nanoparticles in the MAl 2 O 4 ceramics. This parameter is used to obtain nano-spinels with particle sizes in the range 5-45 nm and reveals a qualitative correlation between the initial droplet size and the crystallite size of the resulting spinels. The TG-DTA measurements showed the thermal decomposition to be a three step process with crystallisation of the spinel phase occurring around 900 °C. 27Al MAS NMR spectra reveal the inverse nature of the obtained spinels. XRD, TEM, SEM, EDX, FTIR and UV-VIS spectral studies were used for characterisation of the powders. the synthesis and characterisation of nano-spinels MAl 2 O 4

A Simple Preparation Process of Pure Mn3-Xcoxo4 (X= 1, 1.5 and 2) Desert Rose-Like Nanoparticles and Their Optical Properties

“…In order to prepare pure oxide nanoparticles with tailored morphology and size, often limited to one or a small range of composition, experimental methods usually involve a few complex stages of reaction process and organics as coordinating and/or dispersing agents. For instance, nanocrystalline spinel oxide powders and ceramics were obtained with the use of microemulsions and a sol-gel type synthesis based on the principle of controlled hydrolysis of alkoxide precursors in water droplets (Meyer, Hempelmann, Mathur, & Veith, 1999). Sun et al (2004) prepared iron-rich cobalt or manganese spinel oxide nanoparticles by mixing iron acetates with surfactants using airless procedures.…”

Applications and Preparation Methods of Copper Chromite Catalysts: A Review

“…The sol-gel synthesis of mixed oxides from alkoxide mixture usually suffers from the different hydrolysis susceptibilities of the individual components and the benefits of improved homogeneity can be lost during the hydrolysis of the alkoxides, which may ultimately lead to component segregation and mixed phases in the final materials. To achieve homogeneous mixed oxides with predetermined compositions, the difference in reactivity has been minimized by controlled prehydrolysis of the less reactive precursor [365], by chemical modification of the precursors [366], by using single-source , 6 (2), 2011, 97 heterobimetallic alkoxide precursors [367], or by non-hydrolytic sol-gel processes [368].…”

Síntese, por reação de combustão em forno de microondas, de nanoferritas de níquel dopadas com cromo

“…Apesar do método de mistura de óxido cerâmico ser relativamente simples e o mais utilizado industrialmente, ele apresenta desvantagens inerentes, como: impurezas acrescidas durante o processo de moagem; baixo controle da composição; baixa homogeneidade química; tamanhos excessivamente grosseiros das partículas, comprometendo a microestrutura e propriedades finais desses materiais [3][4][5][6][7][8]. Para contornar os problemas advindos do método de mistura de óxidos, métodos químicos em escala de laboratório, tais como: sol-gel [9], co-precipitação [10], hidrotérmica [11], microemulsão [12], reação por combustão [13,14], entre outros, foram desenvolvidos, visando obter principalmente o controle da homogeneidade química, morfológica e granulométrica dos pós, garantindo, assim, o controle da microestrutura e propriedades finais do material. O método de reação por combustão vem se destacando nos últimos anos, devido principalmente á facilidade de sua aplicação, ao custo relativamente baixo, ao controle da homogeneidade química, por requerer poucas etapas e curto tempo de duração [3][4][5][6][7][8].…”