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Microbial contamination and biofilm formation present major challenges in numerous applications. Many types of nanoparticles possess high antibacterial activity and thus are being investigated to combat environmental microbial contamination, limit bacterial deposition, and inhibit or destroy biofilms. In addition to finding nanoparticles with high and broad antibacterial activity, the synthesis of nanoparticles must also be sustainable and the nanoparticles should have low toxicity and low environmental impact. In this study, we developed a simple one-step probe sonication method to synthesize a ZnO nanoparticle functionalized reduced graphene oxide (rGO–ZnO) nanocomposite by exfoliating oxidized graphite in the presence of Zn2+. The antibacterial activity of the nanocomposite was higher than that of graphene oxide (GO) and rGO against Gram-negative (Escherichia coliand Serratia marcescens) and Gram-positive (Bacillus subtilis) bacteria. Direct intracellular reactive oxygen species (ROS) and Zn2+leaching measurements indicated that the high antibacterial activity against different bacteria of the nanocomposite arises from the formation of ROS, whereas the effect of Zn2+is negligible. Furthermore, incorporating rGO–ZnO nanocomposite into a polyethersulfone (PES) membrane inhibited biofilm growth compared with a pristine PES membrane. Leaching experiments of Zn2+from the incorporated rGO–ZnO membrane during synthetic wastewater filtration revealed that Zn2+concentration in the effluent was below the environmental standards for potable and non-potable uses. Our research presents an effective, fast, and low-cost preparation method for developing nanocomposites with high antimicrobial activities. Also, it shows that a nanocomposite incorporated polymeric membrane can be safely applied for water and wastewater treatment with minimum environmental impact.

Virus removal from water using microfiltration (MF) membranes is of great interest but remains challenging owing to the membranes’ mean pore sizes typically being significantly larger than most viruses. We present microporous membranes grafted with polyzwitterionic brushes (N-dimethylammonium betaine) that combine bacteriophage removal in the range of ultrafiltration (UF) membranes with the permeance of MF membranes. Brush structures were grafted in two steps: free-radical polymerization followed by atom transfer radical polymerization (ATRP). Attenuated total reflection Fourier transform infrared (ATR–FTIR) and X-ray photoelectron (XPS) verified that grafting occurred at both sides of the membranes and that the grafting increased with increasing the zwitterion monomer concentration. The log reduction values (LRVs) of the pristine membrane increased from less than 0.5 LRV for T4 (∼100 nm) and NT1 (∼50 nm) bacteriophages to up to 4.5 LRV for the T4 and 3.1 LRV for the NT1 for the brush-grafted membranes with a permeance of about 1000 LMH/bar. The high permeance was attributed to a high-water fraction in the ultra-hydrophilic brush structure. The high measured LRVs of the brush-grafted membranes were attributed to enhanced bacteriophages exclusion from the membrane surface and entrapment of the ones that penetrated the pores due to the membranes’ smaller mean pore-size and cross-section porosity than those of the pristine membrane, as seen by scanning electron microscopy (SEM) and measured using liquid–liquid porometry. Micro X-ray fluorescence (μ-XRF) spectrometry and nanoscale secondary ion mass spectrometry showed that 100 nm Si-coated gold nanospheres accumulated on the surface of the pristine membrane but not on the brush-coated membrane and that the nanospheres that penetrated the membranes were entrapped in the brush-grafted membrane but passed the pristine one. These results corroborate the LRVs obtained during filtration experiments and support the inference that the increased removal was due to a combined exclusion mechanism and entrapment. Overall, these microporous brush-grafted membranes show potential for use in advanced water treatment.