Antimony (V) Oxide Adsorbed on a Silica-Zirconia Mixed Oxide Obtained by the Sol-Gel Processing Method: Preparation and Acid Properties

Abstract

A preparação, o grau de dispersão, estabilidade térmica e a acidez de Lewis e de Brφnsted do óxido de antimônio (V) adsorvido sobre SiO 2 /ZrO 2 , preparado previamente pelo processo sol-gel, são descritas neste trabalho. Amostras de SiO 2 /ZrO 2 /Sb 2 O 5 de composições (% em massa): (a) Zr= 8,1 e Sb= 6,3; (b) Zr= 11,4 e Sb= 11,4, foram preparadas. As imagens de microscopia eletrônica de varredura conectada a um espectrômetro de energia dispersiva de raios X mostraram que os metais, Zr e Sb, estão homogeneamente dispersos em ambas as matrizes. Os padrões de difração de raios X de SiO 2 /ZrO 2 /Sb 2 O 5 aquecido a diversas temperaturas mostraram que até 1023 K a amostra apresentou-se amorfa. Em 1273 K a formação da fase cristalina ZrO 2 (baddeleita) foi observada e elevando-se a temperatura a 1573 K, as fases cristalinas de SiO 2 (cristobalita) e possivelmente de ZrO 2 /Sb 2 O 5 foram observadas. Utilizando a piridina como sonda molecular, sítios ácidos de Brφnsted do sólido SiO 2 /ZrO 2 /Sb 2 O 5 , aquecido até 523 K, mostraram ser bastante estáveis.The preparation, degree of dispersion, thermal stability and Lewis and Brfnsted acidity of antimony (V) oxide adsorbed on SiO 2 /ZrO 2 mixed oxide, previously prepared by the sol-gel processing method, are described herein. The samples SiO 2 /ZrO 2 /Sb 2 O 5 , with compositions (in wt %): (a) Zr= 8.1 and Sb= 6.3; (b) Zr= 14.9 and Sb= 11.4, were prepared. Scanning electron microscopy images connected to a X-ray energy dispersive spectrometer showed that both metals, Zr and Sb, were highly dispersed in the matrices. The X-ray diffraction patterns of SiO 2 /ZrO 2 /Sb 2 O 5 heated at different temperatures showed that, up to 1023 K, the matrix was amorphous. At 1273 K a crystalline phase of ZrO 2 (baddeleyite) was observed and raising the temperature to 1573 K, crystalline phases of SiO 2 (cristobalite) and presumably of ZrO 2 /Sb 2 O 5 were observed. Using pyridine as a molecular probe, Brφnsted acid sites on the SiO 2 /ZrO 2 /Sb 2 O 5 matrix, heat treated up to 523 K, were shown to be very stable.

Removal of malachite green from aqueous solution by activated carbon prepared from the epicarp of Ricinus communis by adsorption

“…Activated carbon, as an adsorbent has been widely investigated for the adsorption of dyes [9], but its high cost limits its commercial application. In recent years, there has been growing interest in finding inexpensive and effective alternatives to carbon, such as rice husk [10], chitin [11], orange waste [12], lemon peel [13], granular kohlrabi peel [14], raw barley straw [15], eggshell [16], silica-zirconia mixed oxide [17], akash kinari coal [18] and TiO 2 /AC [19].…”

Surface Modification with Phosphoric Acid of SiO2/Nb2O5 Prepared by the Sol−Gel Method: Structural−Textural and Acid Sites Studies and an Ion Exchange Model

“…In mixed oxides of the type SiO 2 /M x O y , prepared by the sol−gel processing method, the metallic oxides are, in general, highly dispersed in the silica matrix, exposing large surface areas suitable to be modified through chemical reactions. Many reactions have been made by immersing SiO 2 /M x O y [M = Zr(IV) and Ti(IV)] in H 3 PO 4 or in Sb(V) solutions. − As a result, solid Brønsted acids such as SiO 2 /MO 2 /phosphate or SiO 2 /MO 2 /Sb 2 O 5 have been obtained. − …”

“…Many reactions have been made by immersing SiO 2 /M x O y [M ) Zr(IV) and Ti(IV)] in H 3 PO 4 or in Sb(V) solutions. [1][2][3][4] As a result, solid Brønsted acids such as SiO 2 /MO 2 /phosphate or SiO 2 /MO 2 /Sb 2 O 5 have been obtained. [1][2][3][4] There is particular interest in niobium oxide impregnated with phosphate, obtained by immersing bulk phase Nb 2 O 5 in a phosphoric acid solution, for use as heterogeneous catalysts [5][6][7][8] or as ion exchangers.…”

Sol–gel zirconia nanopowders with α-cyclodextrin as organic additive

“…Chen et al [58] give for zirconia an absorption peak at 230 nm, which is assigned to Zr O Zr linkage. For bulk phase ZrO 2 , a band maximum in the UV-vis spectrum is also signalled between 230 and 240 nm, by Zaitseva and Gushikem [59]. According to López et al [60] monoclinic phase of zirconia absorbs at lower energy (corresponding to 240 nm) than the tetragonal one (which absorbs around 200-210 nm).…”