Unveiling the Susceptibility of Functional Groups of Poly(ether sulfone)/Polyvinylpyrrolidone Membranes to NaOCl: A Two-Dimensional Correlation Spectroscopic Study.

A clear understanding of membrane aging process is essential for the optimization of chemical cleaning in membrane-based facilities. In this study, two-dimensional (2D) Fourier transformation infrared (FTIR) correlation spectroscopy (CoS) analysis was first used to decipher the sequential order of functional group changes of NaOCl-aged poly(ether sulfone)/polyvinylpyrrolidone (PES/PVP) membranes. The synchronous maps showed 12 major autopeaks in total. Based on the asynchronous maps, a similar aging sequence of membrane groups was clearly identified at three pHs (i.e., 6, 8, and 10): 1463, 1440, and 1410 (cyclic C-H structures) > 1662 (amide groups) > 1700 (succinimide groups) > 1320, 1292 (S═O asymmetric) > 1486, 1580 (aromatic structures) > 1241 (aromatic ether bands) > 1105, 1150 cm-1 (O═S═O symmetric). Among them, membrane chlorination occurred at 1241, 1410, and 1440 cm-1. Moreover, the initial degradation of PVP and the subsequent transformation of PES could be highly responsible for the increased water permeability and the enlargement of membrane pores, respectively, both leading to serious fouling with humic acid filtration. In summary, the 2D-FTIR-CoS analysis is a powerful approach to reveal the interaction mechanisms of NaOCl-membrane and could be also useful to probe the process of membrane fouling and chemical cleaning.