Incorporation of silver nanoparticles in a kaolin hollow fiber membrane for efficient removal of Enterobacter cloacae and Escherichia coli from aqueous solutions

Abstract

Kaolin hollow fiber membranes were produced by the phase inversion method and silver nanoparticles (AgNPs) were sequentially impregnated in the fiber lumen side. The composite membranes were applied to treat aqueous solutions contaminated with Enterobacter cloacae and Escherichia coli. The prepared pristine kaolin hollow fibers presented an asymmetric pore size distribution. According to mercury intrusion analyses, the sponge like layer presented pore sizes between 1.14 and 2.16 μm, while the micro-voids in the finger like layer presented pore sizes between 7.86 and 9.17 μm. The kaolin hollow fibers presented water permeability of 8.46 ± 0.17 L h−1 m−2·kPa−1 and mechanical resistance of 103.58 ± 14.41 MPa. The AgNPs were properly synthetized and, according to spectroscopic analyses, the AgNP solution presented a single broad peak centered at 400 nm, which indicates a uniform dispersion of the synthetized AgNPs. The synthetized AgNPs presented a spherical and pseudospherical geometry, with average hydrodynamic size of 81.71 ± 8.05 nm, polydispersity index of 0.262 ± 0.012 and zeta potential of −20.7 ± 2.6 mV, which indicate a suitable AgNP stability in the aqueous suspension. The AgNPs were successfully impregnated in the lumen side of kaolin hollow fibers at a concentration of 0.51 ± 0.04 mg cm−1. Energy dispersive spectroscopy images showed that the AgNPs were more concentrated in the hollow fiber inner layer and a homogenous distribution of AgNPs were observed through the fiber cross-section. After AgNP impregnation, the composite hollow fiber membranes presented water permeability of 5.22 ± 0.32 L h−1 m−2 kPa−1. The pristine kaolin membrane enabled a log10 reduction value (LRV) of 2.47 ± 0.05 and 3.72 ± 0.13 for filtrations of aqueous solutions with E. cloacae and E. coli, respectively. For the kaolin hollow fiber membrane impregnated with AgNPs, the LRV value increased to 4.38 ± 0.83 and 4.35 ± 0.25 for filtrations of aqueous solutions with E. cloacae and E. coli, respectively. Thus, the synergetic action of the kaolin membranes impregnated with AgNPs enabled a bacterial reduction greater than 99.9%. The AgNPs decreased the permeate flux through the membrane but, for the filtration of the E. cloacae suspension, mitigated the cake formation on the membrane surface.