Fouling behavior of silica nanoparticle-surfactant mixtures during constant flux dead-end ultrafiltration

The increasing use of engineered nanoparticles in customer products results in their accumulation in water sources. In this experimental study, we investigated the role of surfactant type (cationic, anionic and non-ionic) and concentration on fouling development, nanoparticle rejection and fouling irreversibility during dead-end ultrafiltration of model silica nanoparticles. Our work demonstrates that the type of surfactant influences the nanoparticle stability, which in turn is responsible for differences in fouling behavior of the nanoparticles. Moreover, the surfactant itself interacts with the PES-PVP membrane and contributes to the fouling as well. We have shown that anionic SDS (sodium dodecylsulfate) does not interact extensively with the negatively charged silica nanoparticles and does not change significantly the surface charge and size of these nanoparticles. Adsorption of the cationic CTAB (cetyltrimethylammonium bromide) onto the silica nanoparticles causes charge transition and nanoparticle aggregation, whereas non-ionic TX-100 (Triton X-100) neutralizes the surface charge of the nanoparticles but does not change significantly the nanoparticle size. The most severe fouling development was observed for the silica nanoparticle – TX-100 system, where nanoparticles in the filtration cake formed exhibited the lowest repulsive interactions. Rejection of the nanoparticles was also highest for the mixture containing silica nanoparticles and TX-100.