Bead-Shaped Mesoporous Alumina Adsorbents for Adsorption of Ammonia

Abstract

It is of great importance to remove toxic gases by efficient methods for recovering the atmosphere to safe levels. The adsorption of the toxic gas molecules on solid adsorbents is one of the most useful techniques because of its simple operation and economic feasibility. Here, we report the uniform Bead-Shaped Mesoporous Alumina (BSMA) with tunable particle size for use as an adsorbent for removal of toxic ammonia. The BSMA particles with tunable diameters were synthesized by means of a sol-gel reaction of Al(NO 3 ) 3 ·9H 2 O as an alumina precursor in the presence of chitosan as a template. When the ammonia solution is added dropwise to the prepared viscose mixture containing chitosan, acetic acid, and the alumina precursor solution, the sol-gel condensation reaction of the alumina precursor occurs in the chitosan polymer metrics, resulting in bead-shaped chitosan-aluminum hydroxide particles. Then, final Bead-Shaped Mesoporous Alumina (BSMA) particles are obtained by calcination at a high temperature. During the synthesis, changing the mole ratio of the chitosan template to the alumina precursor allowed the particle diameter of the final bead sample to be finely controlled. In addition, the prepared BSMA particles have well-developed mesoporous characteristics with relatively large surface areas, which are beneficial for adsorption of gas molecules. In an ammonia adsorption experiment, the BSMA-1.5 sample, which has the smallest particle diameter among the bead samples, was the best in terms of adsorption capacity. In this manuscript, we systemically discuss the relationship between the characteristics of BSMA samples and their adsorption of ammonia. people can smell ammonia without significant symptoms at a level as low as 10 ppm, breathing 50-100 ppm of NH 3 can give rise to eye, throat, and nose irritation [12]. More severely, prolonged exposure at concentrations higher than 300 ppm can lead to either permanent damage to the body or even death. Therefore, the release of ammonia gas into the atmosphere must be controlled at a suitable level defined by Pollution Prevention and Control (PPC) regulations [13,14].To remove toxic ammonia molecules, there have been many techniques, including catalytic decomposition, combustion, absorption by solution, and adsorption by solids, employed in not only fundamental studies but also practical processes. Among the above techniques, the adsorption of ammonia on solid adsorbents has been widely studied because of the simple operation of the whole process and the easy regeneration of this valuable gas. To date, various porous materials, including activated carbon, zeolite, alumina, and a metal-organic framework (MOF), have been demonstrated as adsorbents for efficient ammonia removal, and there has been remarkable progress on adsorption of ammonia in terms of either adsorption capacity or adsorption kinetics [5,6,[15][16][17][18][19]. Helminen et al. studied the ammonia adsorption capacities of traditional inorganic adsorbents including activated carbon, alumina, silica gel, ...

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