Surface spectroscopic studies of pristine and fouled membranes part 1. Method development and pristine membrane characterization

Abstract

Studying the adsorption mechanism of foulants on polysulfone (PSf) membrane surfaces requires chemically and physically well-characterized membranes. This report deals with the chemical characterization of DDS GR61 PP and Dorr-Oliver S10 membranes by surface-sensitive spectroscopy, to subsequently investigate the interactions with solutes during fouling (Part II). Attenuated total reflection Fourier transform infrared spectroscopy (ATR FTIR) reveals the type of PSf used, Udel (polyethersulfone (PESf)+bisphenol A) and Victrex (PESf), respectively. Fast atom bombardment mass spectrometry (FAB MS), however, indicates also the presence of minor amounts of bisphenol A in the S10 surface. This might be caused by admixing of bisphenol A or block-copolymerization of Victrex with Udel. Deviations from the calculated bulk composition in both membrane surfaces [as detected by X-ray photoelectron spectroscopy (XPS)] are due to the preferential location of SO 2 functional groups in the bulk and aryl-O-aryl and aryl-C-aryl groups at the surface. This conclusion is supported by angular-dependent XPS. In contrast to the presumed chemical structure nitrogen is detected. Combination of all spectroscopic data illustrates this to be due to the presence of dimethylformamide (DMF) in the surfaces, DMF being the solvent employed during manufacturing of the PSf membranes. The GR61 and S10 could be characterized to such an extent that better insight into the surface structure and chemistry is obtained. Part II will show that these results as well as the method can be used to analyze fouled membranes.