Preparation Of Al₂O₃ And Spherical MgO By Coprecipitation And Their Application In Chromatographic Separation

Recently, Al₂O₃ and MgO have attracted much attention due to their special properties and wide applications. Cubic alumina, needle-like magnesium carbonate hydrate and spherical magnesia microspheres, were prepared by co-precipation in this paper, using cheap inorganic salts as the raw materials. The prepared Al₂O₃ and MgO were used as the chromatographic stationary phase and their separation performance of naphthalene anthracene etc were also evaluated.Cubic alumina with particle size of 500 nm was prepared at 110 oC by homogeneous coprecipitation of aluminum sulfate using basic magnesium carbonate as the basic source. The as-synthesized aluminum hydroxide was calcinated at different temperatures. It was found that amorphous Al₂O₃ was obtained in the temperature range of 450⁶00°C, theκ-,θ- andη- Al₂O₃ were obtained at temperature of 850°C and pure-phaseα-Al₂O₃ was obtained at 1200 oC. TEM and SEM results indicated that the morphology of the product remains cubic despite the different calcination temperatures.Needle-like magnesium carbonate hydrates were synthesized by using Mg(NO₃)₂·6H₂O and K₂CO₃ as precursors in aqueous solution. By systematically investigating the influence of stirring time on the morphologies and components of magnesium carbonate hydrates, it was found that needle-like magnesium carbonate hydrates with tunable sizes, ranging from 0.5 to 23μm in diameter and 2 to 200μm in length, can be synthesized by carefully adjusting the stirring time of the initial reaction solution in the range of 1-8 min. The IR and TG analyses indicate that the stirring time has a significant effect on the content of water in magnesium carbonate hydrates apart to their morphologies, and the corresponding composition has a simple formula of MgCO₃·xH₂O, in which the value of x is controlled between 1³ with by varying the stirring time from 1 to 20 min.The seed-induced co-precipitation method was applied to prepare monodisperse MgO microspheres with controllable morphology. The MgO particles with a diamter of ca. 10μm and specific surface area of ca. 170 m²Â·g⁽-1 could be facilely obtained. The obtained MgO miscrospheres was used as the stationary phase for normal-phase liquid chromatogrphy, the separation performance of different polycyclic aromatic hydrocarbons, as well as the column efficiency, were systematically investigated. Simultaneously, the Van't Hoff plots of these polycyclic aromatic hydrocarbons and the stability of MgO column was also analyzed.