Development of nanostructured membranes for environmental applications
Cortalezzi, Marta Fidalgo
Wiesner, Mark R.
Doctor of Philosophy
Two new methods for the fabrication of porous membranes were studied. Ceramic membranes were obtained from alumoxane and ferroxane nanoparticles casted onto porous support materials. The synthesis of ferroxane nanoparticles was further investigated, in particular the kinetics of the reaction and the structure of the materials obtained by particle size measurements and EXAFS. The ceramics were characterized by nitrogen absorption isotherms, scanning electron microscope, and atomic force microscope. The permeability and molecular weight cut off (MWCO) of the ferroxane derived membranes were measured. These membranes have an average pore size of 24 run and a MWCO of 180,000 Daltons, which corresponds to the ultrafiltration range. The ferroxane nanoparticles were reacted with compounds containing other metallic atoms and mixed metal oxide nanoparticles were obtained. The nanoparticles can be applied to the fabrication of mixed metal oxide ceramics used in catalysis, fuel cells and other applications. The conductivity and surface acidity were determined in order to evaluate these materials as possible proton exchange membranes for fuel cells. The second fabrication method considered in this study is the template-derived process. Deposits of silica nanoparticles of variable morphology were prepared to be used as templates for porous membranes. The variables that control the morphology of the deposits were investigated, in particular those related to the solvent chemistry of the nanoparticle suspensions. The templates were obtained by self-assembly and Langmuir-Blodgett layer-by-layer deposition. By controlling the template deposition process, the self-assembly method was used to create dendritic templates with an asymmetric structure. The Langmuir-Blodgett technique was used to create bilayers of different pore size. Polystyrene membranes were fabricated as replicas of these template structures. The pore structure of the polymeric membranes was studied by scanning electron microscopy.
Chemical engineering; Environmental engineering; Engineering; Materials science