Person:

Vecitis, Chad

Nanotechnology has potential to offer solutions to problems facing the developing world. Here, we demonstrate the efficacy of an anodic multiwalled carbon nanotube (MWNT) microfilter toward the removal and inactivation of viruses (MS2) and bacteria (E. coli). In the absence of electrolysis, the MWNT filter is effective for complete removal of bacteria by sieving and multilog removal of viruses by depth-filtration. Concomitant electrolysis during filtration results in significantly increased inactivation of influent bacteria and viruses. At applied potentials of 2 and 3 V, the electrochemical MWNT filter reduced the number of bacteria and viruses in the effluent to below the limit of detection. Application of 2 and 3 V for 30 s postfiltration inactivated >75% of the sieved bacteria and >99.6% of the adsorbed viruses. Electrolyte concentration and composition had no correlation to electrochemical inactivation consistent with a direct oxidation mechanism at the MWNT filter surface. Potential dependent dye oxidation and E. coli morphological changes also support a direct oxidation mechanism. Advantages of the electrochemical MWNT filter for pathogen removal and inactivation and potential for point-of-use drinking water treatment are discussed.

We propose an innovative approach to impart nanomaterial-specific properties to the surface of thin-film composite membranes. Specifically, biocidal properties were obtained by covalently binding single-walled carbon nanotubes (SWNTs) to the membrane surface. The SWNTs were first modified by purification and ozonolysis to increase their sidewall functionalities, maximize cytotoxic properties, and achieve dispersion in aqueous solution. A tailored reaction protocol was developed to exploit the inherent moieties of hand-cast polyamide membrane surfaces and create covalent amide bonds with the functionalized SWNTs. The reaction is entirely aqueous-based and entails activation of the carboxylate groups of both the membrane and the nanomaterials to maximize reaction with ethylenediamine. The presence of SWNTs was verified after sonication of the membranes, confirming the strength of the bond between the SWNTs and the membrane surface. Characterization of the SWNT-functionalized surfaces demonstrated the attainment of membranes with novel properties that continued to exhibit high performance in water separation processes. The presence of surface-bound antimicrobial SWNTs was confirmed by experiments using E. coli cells that demonstrated an enhanced bacterial cytotoxicity for the SWNT-coated membranes. The SWNT membranes were observed to achieve up to 60% inactivation of bacteria attached to the membrane within 1 h of contact time. Our results suggest the potential of covalently bonded SWNTs to delay the onset of membrane biofouling during operation.

The performance of an electrochemical multiwalled carbon nanotube (EC-MWNT) filter toward virus removal and inactivation in the presence of natural organic matter was systematically evaluated over a wide range of solution chemistries. Viral removal and inactivation were markedly enhanced by applying DC voltage in the presence of alginate and Suwannee River natural organic matter (SRNOM). Application of 2 or 3 V resulted in complete (5.8 to 7.4 log) removal and significant inactivation of MS2 viral particles in the presence of 5 mg L−1 of SRNOM or 1 mg L−1 of alginate. The EC-MWNT filter consistently maintained high performance over a wide range of solution pH and ionic strengths. The underlying mechanisms of enhanced viral removal and inactivation were further elucidated through EC-MWNT filtration experiments using carboxyl latex nanoparticles. We conclude that enhanced virus removal is attributed to the increased viral particle transport due to the applied external electric field and the attractive electrostatic interactions between the viral particles and the anodic MWNTs. The adsorbed viral particles on the MWNT surface are then inactivated through direct surface oxidation. Minimal fouling of the EC-MWNT filter was observed, even after 4-h filter runs with solutions containing 10 mg L−1 of natural organic matter and 1 mM CaCl2. Our results suggest that the EC-MWNT filter has a potential for use as a high performance point-of-use device for the removal of viruses from natural and contaminated waters with minimal power requirements