Letter pubs.acs.org/journal/estlcu
Layer-by-Layer Assembly of Zeolite/Polyelectrolyte Nanocomposite Membranes with High Zeolite Loading Yan Kang,† Laleh Emdadi,‡ Michael J. Lee,† Dongxia Liu,‡ and Baoxia Mi*,† †
Department of Civil and Environmental Engineering, University of Maryland, College Park, Maryland 20742, United States Department of Chemical and Biomolecular Engineering, University of Maryland, College Park, Maryland 20742, United States
‡
S Supporting Information *
ABSTRACT: Incorporation of zeolite nanoparticles into nanocomposite membranes is advantageous with respect to enhancing membrane permeability by providing preferential water flow paths through the subnanometer porous structure of zeolite while maintaining excellent separation capability. We present a layer-by-layer assembly approach to effectively incorporate zeolite nanoparticles into nanocomposite membranes. Negatively charged Linde type A (LTA) zeolite nanoparticles were sandwiched between two different polyelectrolyte layers, negatively charged poly(acrylic acid) (PAA) and positively charged polyethylenimine (PEI), to form a PEI−LTA−PAA trilayer. The zeolite loading in the multitrilayer membranes was between 30 and 60 wt %, which is attributed to the drastically improved compatibility between zeolite and polymers, a direct result of electrostatic interactions. The performance of the trilayer membrane was compared with that of a control PEI−PAA bilayer membrane in a forward osmosis membrane system. The incorporation of zeolite nanoparticles was found to enhance membrane water permeability by >2-fold without compromising the membrane selectivity for tested species.
■
poly(ether)sulfone,18,19 and poly(vinylidene fluoride)20] to make composite membranes that inherit the flexibility from the polymer as well as enhanced separation capability from zeolite. The typical embedding approach used in these studies was to blend zeolite nanoparticles into an organic solution during the phase inversion or interfacial polymerization process.21 However, current efforts to create novel zeolite/ polymer composite membranes for water purification are severely hindered by the difficulty of achieving high zeolite loading due to the poor compatibility between the zeolite and polymer matrix. So far, zeolite/polyamide thin-film nanocomposite membranes are one of the most successful state-ofthe-art zeolite membranes reported for water applications.7−12 To make these membranes, three-dimensional (3D) zeolite nanoparticles with sizes in the range of 50−150 nm were randomly embedded in polyamide thin films using interfacial polymerization. Such synthesized nanocomposite membranes can achieve a zeolite loading of ∼1 wt % (in solvent), with a water permeability nearly twice that of a control polyamide thin-film membrane.7,9 Although the doubled water flux is already considered remarkable progress, there is still much room to further enhance the performance of a zeolite/polymer nanocomposite membrane, because the water permeability of a
INTRODUCTION Membrane technology has been recognized as one of the most promising candidates for solving the global water scarcity problem. The membrane industry, after growth and development for ∼40 years, is still actively searching for new materials to improve membrane separation capability and energy efficiency. With the rapid advances in nanotechnology, numerous nanomaterials with superb properties have been used to improve membrane properties.1−8 Among these nanomaterials, zeolite has exhibited many unprecedented properties that can be promisingly exploited to make novel membranes with greatly enhanced performance.7−12 Zeolite is a nanoporous crystalline material with a well-defined framework of aluminosilicates. Because such a framework forms interconnected pores with dimensions of typically
