Urea controlled hydrothermal synthesis of ammonium aluminum carbonate hydroxide rods

Fang Wang,Jianfeng Zhu,Hui Liu

doi:10.1063/1.5018826

Abstract

In this study, ammonium aluminum carbonate hydroxide (AACH) rods were controllably prepared using the hydrothermal method by manipulating the amount of urea in the reaction system. The experimental results showed that AACH in rod shape was able to be gradually transformed from γ-AlOOH in cluster shape during the molar ratios of urea to Al in the reactants were ranged from 8 to 10, and the yield of AACH has increased accordingly. When the molar ratio of urea to Al reaches 11, pure AACH rods with a diameter of 500 nm and a length of 10 μm approximately was able to be produced. Due to the slow decomposition of urea during the hydrothermal reaction, the nucleation and growth of AACH crystal proceed step by step. Therefore, the crystal can fully grow on each crystal plane and eventually produce a highly crystalline rod-shaped product. The role of urea in controlling the morphology and yield of AACH was also discussed in this paper systematically.

Highlights

INTRODUCTIONAlumina has been widely used as absorbents, catalysts, catalyst supports and ceramics et al because of the extraordinary merits of physical and chemical characters.[1,2,3,4,5,6,7] ammonium aluminum carbonate hydroxide (AACH), as a newly emerging precursor of alumina, is able to be converted into alumina with a mesoporous structure by calcining while maintains its original morphology.[8,9,10,11,12]
In order to investigate the effect of urea in the reaction, a series of samples are prepared with various molar ratios of urea to Al, while all the other experimental variables are remained as constant
It can be deduced that the adding molar ratio of urea to Al has an important influence on the formation of ammonium aluminum carbonate hydroxide (AACH) in the system

Summary

INTRODUCTION

Alumina has been widely used as absorbents, catalysts, catalyst supports and ceramics et al because of the extraordinary merits of physical and chemical characters.[1,2,3,4,5,6,7] AACH, as a newly emerging precursor of alumina, is able to be converted into alumina with a mesoporous structure by calcining while maintains its original morphology.[8,9,10,11,12]. The precipitation reaction is the most popular method to synthesize AACH using aluminum salt and NH4HCO3 as reactants.[13,14,15,16,17] by this method, the properties of the product, which are agglomeration degree, crystallite size and purity, are often affected by the mixing speed, stirring speed and other factors. This means that the process of synthesis is so complicated that the regular morphology of the product is hard to be obtained. The possible mechanism for the formation of the AACH and the role of urea in controlling the yield and morphology were proposed in the article

Synthesis of AACH

Characterization

RESULTS AND DISCUSSION

CONCLUSIONS