(396b) Removal of Congo Red Dyes from Aqueous Solutions By Porous ?-Al2O3 Nanoshells

Alumina coating on carbon black (alumina/CB) was prepared by a condensed layer deposition (CLD) coating process to enable nanoscale structure with high surface areas. Al₂O₃ nanoshells were derived after burning the alumina/CB under oxygen gas at 500 ⁰C, with a high specific surface area. Both Al₂O₃ nanoshells and alumina/CB were used as adsorbents to remove Congo Red dye from aqueous solutions in batch adsorption processes. The adsorbents were characterized using various techniques, such as N₂ adsorption-desorption isotherms (BET), X-ray diffraction (XRD), thermo-gravimetric analysis and differential thermal analysis (TGA - DTA), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR), and zeta potential. Characterization results indicated that the alumina/CB and Al₂O₃ nanoshells yield high surface area of 290 and 217 m²/g, respectively. While wide angle XRD and FTIR studies confirmed the phase transformation of γ- Al₂O₃ after the removal of CB at 500 ⁰C. A series of parameters were investigated in adsorption experiments, including contact time, initial dye concentrations, ionic strength and pH of the solutions. It was found that equilibrium for Congo red adsorption can be reached within 30 min, much faster than reported by other studies in the literature on similar adsorbents. The adsorption mechanism for both samples followed the Langmuir isotherm with a pseudo second order reaction. The adsorption isotherm studies showed that Al₂O₃ nanoshells achieved a 44.8 % higher adsorption capacity than that of alumina/CB. The Al₂O₃ nanoshells have a maximum adsorption capacity of 370.4 mg/g(25 ⁰C; pH 7; no salt added), better than or comparable to those previously reported adsorbents. The adsorption capacity of Al₂O₃ nanoshells was more favorable at lower pH, and the optimal adsorption ability was achieved at pH 4.0 with a removal efficiency at 98.6%. The adsorption process was associated with the H-bonding and electrostatic attraction between the Congo red dye and Al₂O₃ nanoshells surface. Overall, these results suggest that the low cost Al₂O₃ nanoshells is a very efficient adsorbent for anionic Congo red dye removal from contaminated water due to their fast kinetics along with high adsorption capacity.