Synthesis and Characterization of α-Al(2)O(3)/Ba-β-Al(2)O(3) Spheres for Cadmium Ions Removal from Aqueous Solutions

The search for adsorbent materials with a certain chemical inertness, mechanical resistance, and high adsorption capacity, as is the case with alumina, is carried out with structural or surface modifications with the addition of additives or metallic salts. This research shows the synthesis, characterization, phase evolution and Cd(II) adsorbent capacity of α-Al(2)O(3)/Ba-β-Al(2)O(3) spheres obtained from α-Al(2)O(3) nanopowders by the ion encapsulation method. The formation of the Ba-β-Al(2)O(3) phase is manifested at 1500 °C according to the infrared spectrum by the appearance of bands corresponding to AlO(4) bonds and the appearance of peaks corresponding to Ba-O bonds in Raman spectroscopy. XRD determined the presence of BaO·Al(2)O(3) at 1000 °C and the formation of Ba-β-Al(2)O(3) at 1600 °C. Scanning electron microscopy revealed the presence of spherical grains corresponding to α-Al(2)O(3) and hexagonal plates corresponding to β-Al(2)O(3) in the spheres treated at 1600 °C. The spheres obtained have dimensions of 4.65 ± 0.30 mm in diameter, weight of 43 ± 2 mg and a surface area of 0.66 m(2)/g. According to the curve of pH vs. zeta potential, the spheres have an acid character and a negative surface charge of −30 mV at pH 5. Through adsorption studies, an adsorbent capacity of Cd(II) of 59.97 mg/g (87 ppm Cd(II)) was determined at pH 5, and the data were fitted to the pseudo first order, pseudo second order and Freundlich models, with correlation factors of 0.993, 0.987 and 0.998, respectively.