Magnetically Aligned Nanotubes in Nanocomposite Membranes for High- Performance Filtration Applications P.A. Ignacio-de Leon * , X. Chen ** , E.J. Rabe, M. Urgun-Demirtas *** , M. Puga, Z. Zhou and R.W. Brotzman * Argonne National Laboratory, Energy Systems 9700 S. Cass Ave. Argonne, IL USA 60439, patriciadl@anl.gov ** Argonne National Laboratory, Argonne, IL, USA, xchen@anl.gov *** Argonne National Laboratory, Argonne, IL, USA, demirtasmu@anl.gov ABSTRACT Nanocomposite membranes, with magnetic nanotubes embedded in polyethersulfone (PES) membrane to form a permselective layer on microporous supports, are reported for potential applications in wastewater treatment. Iron cobalt oxide (Fe2CoO4) nanotubes, with 20-25 nm diameter and aspect ratio ca. 10,000, function as nanochannels spanning the permselective layer. We obtained pure water flux values of 9.4 and 4.8 L/m 2 -h through membranes with vertically-aligned and randomly-oriented nanotubes, respectively, at 40 psi. We used these membranes to filter lignin, a contaminant in effluent wastewater from paper and mill industries and lignocellulosic biofuels production. The lignin % rejection from a 10,000 ppm feed at 40 psi through a PES support increases from 7.3% to 39.1% (5.3 higher) and 62.8% (8.6 higher) through membranes prepared with and without a magnetic field, respectively. Keywords: magnetic nanotube, vertically-aligned nanotube, iron cobalt oxide nanotube, nanocomposite membrane, lignin filtration 1 INTRODUCTION The need for new, energy-efficient water treatment and purification methods has been increasing with the rising demand for clean drinking water and process water. 1 Ultrafiltration (UF) is a promising technique for water treatment, producing high quality water without exceedingly high pressures. 2 The energy-efficiency of current commercial UF membranes can be improved by increasing water flux through the membrane and can be achieved through the development of novel materials with higher permeability. 3 Carbon nanotubes (CNT) composite membranes have received a great deal of attention in this area for their controllable pore size and high-flux potential. 4 However there is a trade-off between achieving maximum flux and ease of membrane fabrication. For maximum flux, the nanotubes must be aligned to obtain a high pore density. This requires the tubes to be grown vertically from nanoparticle catalysts, which then must be removed from the system by secondary treatment. 5 Alternatively, CNT alignment can be achieved by inducing a direct current electric field. 4 Without employing these methods, CNTs are dispersed randomly throughout the composite, lacking a consistent vertical orientation. 6 Recently, other groups have also reported the use of halloysite nanotubes (HNTs) composed of alumina-silicates with tubular structure similar to CNTs as alternative materials due to its lower production cost. 7 While much work has been done using CNTs, there are limited studies on iron cobalt oxide (Fe2CoO4) nanotubes, which offer two key advantages: (1) The metal oxide surface is already hydrophilic, eliminating a functionalization step needed to treat the hydrophobic surfaces of CNTs. 3, 6 The inherent hydrophilic surface also provides improved antifouling properties, as increased hydrophilicity has been correlated with a decrease in fouling. 8 (2) The magnetic properties of this material coupled with the high aspect ratio of the structure allow for tube alignment via a magnetic field. The ability to take nanotubes synthesized at gram scale and efficiently align them in minutes, and maintain orientation in a polymer matrix demonstrates the potential scalability of this process. 9 To maintain vertical alignment and ensure that nanotubes remain in the permselective layer, we used interfacial polymerization to provide a polyamide encapsulant. 10 Interfacial polymerization is a facile method for generating thin polymeric layers as monomers dissolved in immiscible solvents react in the boundary between the two phases. 6 In this study, we demonstrate that MNTs can be vertically aligned in the presence of an external magnetic field onto a polymer support to create a permselective layer in a nanocomposite membrane. 2 EXPERIMENTAL 2.1 Nanotube Production Fe2CoO4 nanotubes were prepared using an in-house instrument with integrated electrospinning, heating and pneumatic collection of engineered nanomaterials (U.S. patent pending, serial number 14/665,932), following the nanotube formation principles by electrospinning and heat treatment first introduced by Chen et al. 11 The precursor solution consisted of 5 weight % PVP, 5 weight % total Advanced Materials: TechConnect Briefs 2016 257