Steam-Assisted Solid Wet-Gel Synthesis of High-Quality Nanorods of Boehmite and Alumina

Abstract

A simple solid-phase method was developed for synthesis of high-quality boehmite nanorods by steam-assisted wet-gel conversion process. γ-Al2O3 nanorods with clear-cut edge have been successfully obtained by thermal treatment of boehmite nanorods at 600 °C for 5 h. The nanorods of boehmite and γ-Al2O3 were characterized by X-ray diffraction (XRD), Raman spectroscopy, and field emission scanning electron microscope (FESEM) with energy-dispersive spectroscopy (EDS), transmission electron microscopy (TEM), and high-resolution tranmission electron microscopy (HRTEM) with selected area electron diffraction (SAED) spectroscopy, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR), magic-angle spinning (MAS) 27Al nuclear magnetic resonance (NMR), and thermogravimetric and differential thermal analysis (TGA-DTA). The growth of boehmite was found to be greatly affected by the conditions used for precipitation of Al(NO3)3 with NH4OH aqueous solution. When precipitation was conducted under pH 5.0 or pH 7.0, nanorods of boehmite with lengths in the range of 100−400 nm and uniform diameters (20−30 nm) were obtained by steaming the solid wet gel at 200 °C for 48 h, whereas irregular boehmite particles were obtained from the wet gel precipitated under alkaline condition (pH 10.0). The directed crystallization of boehmite nanorods was attributed to the preferential growth along the longitudinal axis under supersaturated hydrothermal condition with the assistance of steam. The 1D nanostructure of boehmite was well preserved after being converted to γ-Al2O3 without sintering among the highly dispersed nanorods. This approach allows us to fabricate high-quality nanorods of boehmite and γ-Al2O3 with controlled size and morphology using cost-effective solid-phase chemical methods at a large scale.

Precipitation of spherical boehmite from concentrated sodium aluminate solution by adding gibbsite as seed

“…Two main routes are usually used to prepare boehmite with a specific morphology: (1) Al 2 (SO 4 ) 3 , AlCl 3 , Al(NO 3 ) 3 , or NaAlO 2 is often used to prepare nanofiber [7], nanowire [8][9], nanorod [10], nanoribbon [11][12], or nanosheet [13] boehmite via neutralization or hydrolysis, and (2) aluminum alkoxide is extensively used to synthesize boehmite or pseudoboehmite with the specific morphology via hydrolysis. Moreover, boehmite with 3D superstructures (e.g., stalk-like [14], cantaloupe-like [15], leaf-like [16], and flower-like [17]) has been frequently prepared through the assembly of nanofiber, nanorods, or nanosheets using the aforementioned aluminum-bearing salts or aluminum alkoxide.…”

Synthesis and Characterization of Boehmite Nanofibers

“…In this study, the nanofibers were synthesized in the absence of surfactant and in a supersaturated hydrothermal condition, which was reported by Shen et al [9]. This steam-assisted self-assembly fabrication of boehmite yielded high-quality 1D nanostructures with clear-cut edges and high purity.…”

“…A solution-based chemical synthesis of boehmite nanofibers and alumina nanorods by a modified sol-gel process in the presence of organic solvents has been reported [8]. Shen et al reported a steam-assisted solid-phase conversion of amorphous aluminium hydroxide wet gel to well-crystallized 1D nanostructured boehmite nanorods without using surfactants and organic solvents [9]. The process is unique in the simplicity of preparation and the high efficiency of crystal growth, which can be operated on a large scale.…”

“…In this work, long, large boehmite nano/microfibers with high crystallinity and purity were synthesized based on Shen's methodology [9], and the characterization of these nano/microfibers is reported.…”

Synthesis and characterization of hierarchical nanoporous HY zeolites from acid-activated kaolin

“…This is because they have a uniform pore size, high specific surface area (SSA), and thermal stability [1]. They also have tunable pores and acidities, and are therefore useful in various petrochemical processes [2]. However, their average pore size is low, which limits their use in processes that involve bulky molecules.…”