Surface spectroscopic studies of pristine and fouled membranes part II. Method development and adsorption mechanism

Abstract

The complicated problem of membrane fouling has been tackled by applying several surface spectroscopical methods. The results elucidate various chemical aspects of the interaction between polysulfone (PSf) membranes and polypropylene glycol (PPG), which combination was chosen as a model system. All analyses of the DDS GR61 PP and Dorr-Oliver S10 membranes fouled by adsorption of PPG, show that the latter is present as an additional layer on the surfaces. The atomic composition, as revealed by X-ray photoelectron spectroscopy (XPS), of the pristine membranes changes towards that of PPG in the fouled surfaces. In fast atom bombardment mass spectrometry (FAB MS) some m/z fragments occur that are not observed in the spectra of the membranes and of the foulant separately. Unfortunately, assignment of these ions, which could contribute in clarifying the chemical mechanism of adsorption, is not possible due to their complexity. On the other hand, attenuated total reflection Fourier transform infrared spectroscopy (ATR FTIR) demonstrates that the major interaction between PSf and PPG proceeds through the aryl—C (CH 3) 2—aryl structure in PSf and the CH 3 groups in PPG. Also in S10, consisting mainly of Victrex polyethersulfone with Udel as a minor surface constituent (see Part I), this interaction is clearly observed. This study shows integrated application of various surface spectroscopic techniques to be a powerful means in unravelling the mechanisms of fouling. It is especially helpful in directing research on membrane materials for special purposes or in designing cleaning agents and procedures for membranes.