Analysis of Anionic Azo-Dye-Functionalized Porous Polycarbonate Membranes for Water Decolorization*

Recent research has shown that anionic azo dyes themselves can be used to functionalize track-etched porous polycarbonate filtration membranes with decolorized water obtained as a byproduct. This research investigates if the observed dye rejection is dependent on the magnitude of the intrinsic charge of the dye molecule or on the structure of the dye molecule by using two selectively chosen anionic azo dye series during functionalization. The first group is a negative two intrinsic charge series with six dyes, each differing in structure, and the second group is a five-dye series that increases from -1 to -6 in intrinsic charge. Rejection measurements as a function of both time and concentration during functionalization are made using ultraviolet visible-light spectroscopy. For the 100 µM aqueous dye solutions, comparing pre- and post- functionalization, a systematically increasing trend in the ability to functionalize porous polycarbonate based on the number of double 6-carbon ring structures in the dyes is illustrated and found to be independent of intrinsic charge. Dyes with zero, one, and two double 6-carbon ring structures demonstrate a systematic increase in rejection post functionalization of 14.5 % ± 3.7 %, 36.5 % ± 15.7 %, and 47.1 % ± 2.5 %, respectively.