Rama Chennamsetty, Chemical Engineering, University of Toledo, Toledo, OH 43606 and Isabel Escobar, Chemical & Environmental Engineering, University of Toledo, 2801 West Bancroft Street, Toledo, OH 43606-3390.
For membranes to be competitive with conventional water treatment technologies, membrane processes need to operate at high flux rates , have high degrees of selectivity and have high fouling resistance. To accomplish these, modification of the membrane surface and/or microstructure may be necessary. One modification technique is ion beam irradiation. Ion beam irradiation is the bombardment of ions into the surface of the membrane. As the ions penetrate the membrane, they lose energy to the polymer [1]. This energy transfer results in bond breaking, bond formation and microstructure alterations, which cause changes in flux and selectivity as well as improve fouling resistance [2]. A sulfonated polysulfone water treatment membrane was used to study the effects of ion beam irradiation on surface morphology, microstructure, chemical structure, and performance. A beam of 25 keV H+ ions with three irradiation fluences (1×1013 ions/cm2, 5×1013 ions/cm2, and 1×1014 ions/cm2) was used for membrane irradiation. Attenuated total reflectance fourier transform infrared spectroscopy (ATR-FTIR) analyses were performed on the virgin and irradiated membranes in order to determine the changes to chemical structure incurred by ion beam irradiation. The results show that some of the sulphonic and C-H bonds were broken and new C-S bonds were formed after irradiation. Atomic force microscope (AFM) analyses show that membrane roughness decreased after irradiation. These changes in properties of the membrane were proportional to the change in ion fluence; that is, as the ion fluence increased, the magnitude of the effect of ion beam irradiation on the formation/breakage of bonds and decrease in roughness increased. The hydrophobicity and the pore size distribution of the membrane were not affected by ion beam irradiation. Changes incurred by the membrane after ion beam irradiation resulted in a decrease in fouling, as observed both by a lower flux decline during operation and by a decrease in cake accumulation on the membrane surface. The separation capability of the membrane was not changed by ion beam irradiation. Thus, ion beam irradiation was observed to be an effective membrane modification technique. References: [1] E.H. Lee. Nuclear Instruments and Methods in Physics Research B 151 (1999) 29-41. [2] X. Xu and M.R. Coleman. Nuclear Instruments and methods in Physics Research b., 152 (1999b) 325-334.