Synthesis of alumina, titania, and alumina-titania hydrophobic membranes via sol?gel polymeric route

Abstract

Nanometer TiO2-Al2O3 composite membranes were synthesized through the sol?gel polymeric reaction of TiCl4 and AlCl3 in the presence of acrylic-acrylamide copolymer as a template. The dried samples were characterized by DTA, TGA, FTIR, XRD, and TEM to determine the thermal behavior, chemical composition, crystal structure, shape, and size of the particles. Octyltrichlorosilane was chosen as a silane coupling agent to increase the hydrophobic nature of the prepared membranes. The morphological structure, hydrophobic nature, water permeability, and desalination efficiency of the prepared membranes were studied by SEM, contact angle, permeability, and NaCl rejection coefficient (R%) measurements. The crystal structure of titania and alumina particles in the composite was affected by the AlCl3 and TiCl4 feed ratio. As the titania concentration increased, the average particle size of the composite particles became larger and the uniformity of the membrane layer decreased. The alumina (75%)-titania (25%) composite (AT25) showed a uniform crack-free membrane layer with a pore diameter of 12.9?nm and a porosity of 21.46%, with great hydrophobic nature, and with contact angle reaching 116?. This membrane can withstand calcination temperature up to 700?C, as the alumina and titania were present in their active forms: gamma-alumina and anatase, respectively. The membrane produced from this composite showed a high surface area of 333?m2/g with a respective particle size of 4.6?nm. Moreover, it showed a high ability to reject NaCl from water with a rejection coefficient of 73% and a high permeation flux of 4.8?l/h?m2 at 75?C.