The thermal stability of maghemite-silica nanocomposites: An investigation using X-ray diffraction and Raman spectroscopy

Sartoratto, P.P.C.; Caiado, Kely Lopes; Pedroza, R.C.; Silva, S. W. da; Morais, P.C.

doi:10.1016/j.jallcom.2006.08.208

Cited by 50 publications

(45 citation statements)

References 23 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…In the XRD patterns, only a few very broad peaks are recognizable (Figs. 7-9), which is consistent with other works [e.g., 65,68]. The formation of nanomaghemite results in substantial increase in magnetic susceptibility (Fig.…”

Section: Pure Ferrihydritesupporting

confidence: 92%

See 1 more Smart Citation

The influence of silicate on transformation pathways of synthetic 2-line ferrihydrite

Rzepa

Pieczara

Gaweł

et al. 2016

J Therm Anal Calorim

View full text Add to dashboard Cite

In this study, a series of synthetic ferrihydrite samples of Si/Fe molar ratios ranging from zero to 1.5 were heated up to 1000°C using simultaneous TG-DTA equipment. The XRD, FTIR, SEM-EDS and magnetic susceptibility measurements were carried out prior to and after heating. It has been found that silicate retards ferrihydrite transformation to hematite and affects crystallinity of the product. Low Si admixture in the precursor reduces hematite crystal size severely, but the increase in average crystal dimensions with increasing Si/Fe molar ratio was observed. High Si content results in the formation of hematite which exhibits a wide range of crystal habits. The conversion of pure ferrihydrite to hematite proceeds without any intermediate phase, whereas the increasing silicate content in the pristine oxyhydroxide strongly affects the transformation pathway. During annealing of high-Si ferrihydrites, the presence of two or three intermediate Fe 2 O 3 polymorphs (gamma, epsilon and beta) was demonstrated prior to the crystallization of final a-Fe 2 O 3 . The conditions favoring crystallization of intermediate phases result from progressive silica polymerization which forms separate matrix-type phase and impedes the aggregation of iron oxide nanoparticles.

show abstract

Section: Pure Ferrihydritesupporting

confidence: 92%

“…600 cm -1 at 850°C. Similar FTIR features were reported for e-Fe 2 O 3 [68]. Therefore, between 800 and 885°C, two Fe 2 O 3 polymorphs (alpha and epsilon) coexist in the sample.…”

Section: Pure Ferrihydritesupporting

confidence: 82%

The influence of silicate on transformation pathways of synthetic 2-line ferrihydrite

Rzepa

Pieczara

Gaweł

et al. 2016

J Therm Anal Calorim

View full text Add to dashboard Cite

show abstract

“…In nature, both hematite and maghemite can be found in minerals as well as in nanoparticle form, but it is generally accepted that a nanoparticle sizedependent transition from maghemite to hematite occurs around 10 nm 43 . Furthermore, the stabilization of maghemite nanoparticles has been observed at maghemite silica-based supports 44 . We believe that the N-rGOx sheets in our study have a similar role in stabilizing the maghemite nanoparticles by providing sufficient and suitable adsorption sites, thus inhibiting their transformation to hematite particles.…”

Section: Resultsmentioning

confidence: 95%

Formation of nitrogen-doped graphene nanoscrolls by adsorption of magnetic γ-Fe2O3 nanoparticles

et al. 2013

View full text Add to dashboard Cite

Graphene nanoscrolls are Archimedean-type spirals formed by rolling single-layer graphene sheets. Their unique structure makes them conceptually interesting and understanding their formation gives important information on the manipulation and characteristics of various carbon nanostructures. Here we report a 100% efficient process to transform nitrogen-doped reduced graphene oxide sheets into homogeneous nanoscrolls by decoration with magnetic g-Fe 2 O 3 nanoparticles. Through a large number of control experiments, magnetic characterization of the decorated nanoparticles, and ab initio calculations, we conclude that the rolling is initiated by the strong adsorption of maghemite nanoparticles at nitrogen defects in the graphene lattice and their mutual magnetic interaction. The nanoscroll formation is fully reversible and upon removal of the maghemite nanoparticles, the nanoscrolls return to open sheets. Besides supplying information on the rolling mechanism of graphene nanoscrolls, our results also provide important information on the stabilization of iron oxide nanoparticles.

show abstract

“…A região II, de 145 a 355 °C corresponde à zona de oxidação da matéria carbônica ligada as partículas magnéticas, sejam estas o oxalato (a), o lauril sulfato (b) e a enzima palatase (c). A região III, de 355 a 900 °C corresponde à zona de oxidação de algum carbono residual que não tenha sido oxidado na região II e nesta região a maghemita passa da fase γ-Fe 2 O 3 para α-Fe 2 O 3 (comumente ocorrem as duas fases entre 500 e 700 °C (Sartoratto et al, 2007), ou seja, não ocorre variação de massa, apenas uma mudança na estrutura cristalina do material suporte. Na Tabela 2, encontra-se o percentual de perda de massa ocorrido em cada região referente a cada amostra analisada.…”

Section: Resultsunclassified

SÍNTESE E IMOBILIZAÇÃO DA LIPASE DE Rhizomucor miehei EM NANOPARTÍCULAS MAGNÉTICAS MODIFICADAS COM MOLÉCULAS DE LAURIL SULFATO

Bork¹,

Henriques²,

Weinsberger³

et al. 2015

Anais Do XX Congresso Brasileiro De Engenharia Química

View full text Add to dashboard Cite

RESUMO -Nanopartículas magnéticas são térmica, química e biologicamente estáveis para em aplicações in vivo, motivando pesquisas para aplicação como suporte enzimático, uma vez que o núcleo magnético facilita a remoção destas do meio reacional e seu reuso. O suporte foi sintetizado por precipitação em meio alcalino contendo oxalato, sendo a seguir reagido com lauril sulfato de sódio (LS). A lipase de Rhizomucor miehei dissolvida em NaCl aquoso foi agitada por 24 h e o acompanhamento da imobilização mostrou que 57 % foi imobilizada na primeira hora. A caracterização do suporte foi feita por espectrometria no infravermelho com transformada de Fourier (FTIR), mostrando redução dos picos do oxalato em 1390 e 1660 cm -1 e o aparecimento de picos de LS na região de 2900 cm -1 . A imobilização da lipase foi evidenciada pelos picos em 1650 cm -1 atribuídos a ligações com proteínas. A atividade de esterificação foi medida com reação de ácido oleico e etanol usando 2 % de enzima resultando em 27,57 U.mg -1 de atividade.

show abstract

The thermal stability of maghemite-silica nanocomposites: An investigation using X-ray diffraction and Raman spectroscopy

Cited by 50 publications

References 23 publications

The influence of silicate on transformation pathways of synthetic 2-line ferrihydrite

The influence of silicate on transformation pathways of synthetic 2-line ferrihydrite

Formation of nitrogen-doped graphene nanoscrolls by adsorption of magnetic γ-Fe2O3 nanoparticles

SÍNTESE E IMOBILIZAÇÃO DA LIPASE DE Rhizomucor miehei EM NANOPARTÍCULAS MAGNÉTICAS MODIFICADAS COM MOLÉCULAS DE LAURIL SULFATO

Contact Info

Product

Resources

About