Our Research Purifying water from boron contamination with highly selective metal-organic framework (MOF) membranes

Man drinking from water from pipe in ground

photo credit: iStock Images

Principal Investigator

Zachary Smith

  • Joseph R. Mares Career Development Professor
  • Department of Chemical Engineering

Prof. Zachary P. Smith joined the Department of Chemical Engineering of the Massachusetts Institute of Technology as an Assistant Professor in January 2017. His research focuses on the molecular-level design, synthesis, and characterization of polymers and inorganic materials for applications in membrane and adsorption-based separations. Prof. Smith has been recognized with several awards, including the U.S. Department of Energy (DOE) Early Career Award, the American Chemical Society PRF Doctoral New Investigator Award, and the DOE Office of Science Graduate Fellowship. He was also selected as a U.S. delegate to the Lindau Nobel Laureate meeting on chemistry in 2013. Prof. Smith earned his bachelor’s degree in Chemical Engineering from the Pennsylvania State University Schreyer Honors College and his Ph.D. in Chemical Engineering from the University of Texas at Austin. While at the University of Texas, he developed structure–property relationships for gas diffusion and sorption in polymeric membranes. His postdoctoral training at the University of California, Berkeley examined the design of metal–organic frameworks for selective adsorption-based separations.

Challenge:

Can we design better reverse osmosis membranes capable of rejecting low concentrations of boron?  Can metal-organic frameworks (MOFs) be used as water-stable materials for these separations?  

Research Strategy

  • Molecular level design and synthesis of novel metal-organic framework (MOF) materials for water separations
  • Develop a new generation of highly selective MOF membranes with size exclusion selectivity that can effectively remove contaminants from water
  • Rationally engineer a general and convenient method for the fabrication of highly selective MOF membranes for boron removal
  • Evaluate the thermodynamics and transport behavior of water, boron and ions in MOF membranes

Project description

This project leverages techniques and expertise at the interface of inorganic chemistry, materials science, and chemical engineering to achieve technical breakthroughs in water purification. The strategy uses water-stable metal-organic frameworks (MOFs) that have well-defined pore structures that can be engineered for the efficient removal of small neutral contaminants such as boron from water.

Boron is an essential micronutrient for both plants and animals, but becomes toxic at higher concentrations. However, due to its small molecular size and un-charged chemical structure, it is particularly difficult to remove with standard water purification technologies. Current desalination membrane technologies that operate with amorphous polymers cannot effectively remove boron from water due to its small molecule size and absence of ionic charge under normal operating conditions. This project is meeting this challenge by developing highly selective membrane materials and membranes with high boron rejection for water purification.

MOFs carry particular qualities that make them well-suited for highly selective water purification and desalination. The formation of materials with molecularly tuned pore apertures in combination with precisely designed chemistry allow MOFs to effectively reject small neutral molecules via size exclusion and solute-framework interactions. However, the design and synthesis of effective MOFs for discrimination of small molecules in aqueous conditions has not been well investigated. In order to address this critical need, this project focuses on the design, synthesis, and characterization of water-stable MOF materials with an optimized structure suitable for boron removal. In addition, Smith and his team are exploring new methods to fabricate these selective MOF materials into membrane separators.

The development of this technology could provide a solution to the challenge of the low selectivity of current state-of-the-art polymer-based membranes. These MOF membranes, once developed, could provide stable separation performance in aqueous environments while still providing high water permeability and high rates of boron rejection. The success would prove significant for water purification and desalination industries and, more importantly, provide a solution to an environmental challenge that is currently unmet by known water filtration polymers today.

Outcomes

  • Successfully synthesized and characterized three types of metal-organic frameworks (MOFs) that are stable in water, of small particle size, and of various pore size and chemistry
  • Thin-film nanocomposite (TFN) membranes were developed from thin-film composite (TFC) desalination membrane by integrating synthesized MOF nanoparticles into the polyamide selective layer
  • Compared the performance for desalination of the newly developed TFN membranes and state-of-the-art TFC membranes
  • Displayed high water permeability and NaCl rejection of TFN membranes that surpass those currently commercially available 

Additional Details

Impact Areas

  • Water

Research Themes

  • Water Purification & Desalination
  • Technology & Commercialization
  • Equity & Access

Year Funded

  • 2018

Grant Type

  • Seed Grant

Status

  • Ongoing