Synthesis and characterization of alumina-CNT membrane for cadmium removal from aqueous solution

We report a simple approach for synthesizing an alumina-carbon nanotube (Al₂O₃-CNT) composite membrane through a powder metallurgical method. The membrane was fabricated via uniaxial pressing of the composite powder mixture and subsequent solid-state, pressure-less sintering. Homogeneous dispersion of the CNTs within the alumina matrix was achieved by using gum arabic and sodium dodecyl sulfate as dispersants. The phase composition and microstructure of the synthesized membrane were characterized using X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM), respectively. The effect of process parameters (i.e., initial compaction load and sintering temperature) on the porosity, strength, and water flux of the membrane was investigated, and the results highlighted a strong influence of the process parameters on these properties. In particular, when the compaction load and sintering temperature were increased from 50 to 200 kN and 1200 to 1500 °C, the porosity of the membrane decreased from 65% to 31% and its strength increased from 0.76 to 15.64 MPa respectively. Finally, batch adsorption experiments were used to determine the cadmium removal efficiency of the alumina and CNTs adsorbents, as well as that an Al₂O₃-CNT powder mixture, whereas the efficiency of the membrane based on the above mixture was assessed using a flow loop system. The membrane removed 93% of the Cd present in a water solution containing 1 ppm Cd at pH 6.