Preparation and Characterization of Al-Rich Zn-Al Hydrotalcite-Like Compounds

Abstract

Abstract--Hydrotalcite-like compounds, described by the formula [Zn, xAlx(OH)2] [(CO3)x/2 9 nHzO], were prepared by coprecipitation methods at 80~ and characterized by bulk chemical analysis, X-ray powder diffraction (XRD), nuclear magnetic resonance (NMR), and scanning-transmission electron microscopy (STEM). An x value of 0.33 was previously assumed to be an upper limit, but recently, Al-rich hydrotalcitelike compounds have been prepared with x as large as 0.44 by hydrothermal synthesis. In the Zn-Al system, #p-rich hydrotalcite was synthesized at normal pressure by coprecipitation. Zn-#P hydrotalcitelike compounds were obtained in the range of x = 0.3 to 0.4. An #P-rich hydrotalcite-like compound with x = 0.44 was formed in mixtures containing large amounts of a poorly crystalline Zn-A1 phase. A continuous contraction of the hydrotalcite-like structure occurred as x increased, both the a and c lattice parameters decreasing for x values as large as 0.44. This study illustrates the advantages of using quantitative analytical electron microscopy with high spatial resolution to complement conventional (and bulk) characterization techniques for correlating structural and compositional characteristics of finely divided materials.

One-dimensional ZnO nanostructures: Solution growth and functional properties

“…20(a) [203,204]. In an alkaline environment, a thin layer of hydrotalcite-like zincowoodwardite plates was first formed as a result of the reaction between zinc and aluminum ions [203,205,206]. Zincowoodwardite belongs to a family of layered compounds with positively charged layers of Zn 2+ and Al 3+ with hydroxide anions, and interlayer charge-balancing anions SO 4 2− .…”

“…Moreover, the thin ZnO seed layer provided a continuous pathway for carrier transport for electronic applications [245,247]. In another report [203], a thin layer of Al was coated onto carbon nanotube so that a hydrotalcite-like zinc aluminum hydroxide interfacial compound formed [205,206], which was very effective in promoting the growth of ZnO nanorods.…”

The importance of proper crystal-chemical and geometrical reasoning demonstrated using layered single and double hydroxides

“…It is these two equations [(18)/(19) and (20)] that are widely reported in the literature when discussing the relationship between the composition of LDH phases, x, and the a parameter of the unit cell; for example, in papers concerned with Mg-Al LDH phases (Brindley & Kikkawa, 1979), Ni-Al (Brindley & Kikkawa, 1979), Zn-Al (Thevenot et al, 1989), Mg-Ga (Ló pez-Salinas et al, 1997), Co-Al (Leroux et al, 2001), Mg-Al,Fe (Rozov et al, 2010), and in the review articles by Cavani et al (1991), Drits & Bookin (2001), and Evans & Slade (2006); there is a typographical error in Evans and Slade's version of equation (19). Whilst the metal-oxygen octahedra in LDH phases are widely understood to be squashed -as in the layered single hydroxides -the discussions in the literature regarding the relationship between x and a have nevertheless not progressed since Brindley & Kikkawa's (1979) seminal paper, i.e.…”

Hydrodeoxygenation of furfuryl alcohol over Cu/MgAl and Cu/ZnAl catalysts derived from hydrotalcite-like precursors: A reaction for bio-oil upgrading

“…Small amount of boehmite in the HT-Mg-Al-0.5 was detected which cause a decrease in the material crystallinity. Also, weak peaks of ZnO and bayerite were identified in the HTZn-Al samples (Thevenot, Szymanski, & Chaumette, 1989).…”

“…The crystallite sizes of the hydrotalcites changed with the Mg/Al and Zn/Al molar ratios because it led to a modification in the interatomic distances, bond lengths and angles of the structures (Miyata, 1980;Pu & Zhang, 2005;Shannon, 1976;Thevenot et al, 1989).…”