Research News

A New Method Developed to Fabricate and Fine Tune 3D-Covalent Organic Framework Membranes

March 22, 2022
A representation of the 3D organic polymer membrane was published on the cover of the Angewandte Chemistry International Edition.


Khalifa University researchers discover new way to fabricate 3D organic polymer membranes and fine tune their water-repelling property using simple solvents — a breakthrough that could lead to cheaper, more efficient membranes for water and air filtration technologies. 


Membrane technology plays an increasingly important role in addressing social issues such as water scarcity, environmental pollution, and carbon neutrality. For example, membranes act as the filters that turn seawater into drinking water, and separate carbon dioxide and other pollutants from air. Developing new materials to make these filtration membranes more efficient and affordable is critical.  


In recent years, scientists have identified covalent organic frameworks (COFs) as a material with great potential for membrane applications. COFs are a class of material that form two- or three-dimensional structures through reactions between their organic components, resulting in strong dynamic covalent bonds that create porous, crystalline materials. They are uniquely tunable, with well-defined structures, good chemical stability, and plenty of pores for adsorption applications.


3D-COF membranes are particularly attractive candidates for molecular separation applications owing to their interconnected open pores, which promote molecular diffusion, or the movement of molecules, across the membrane.


But fabricating 3D-COFs remains a challenge. Because their unique structure originates from their spatially-oriented covalent bonds, it is difficult to crystallize and assemble them into large macroscopic structures such as membranes.



The KU research team included Dr. Abdul Khayum Mohammed, Prof. Maguy Abi Jaoude and Prof. Mohammad Abu Haija all from the Department of Chemistry, and Dr. Ayesha A. Al Khoori and Prof. Kyriaki Polychronopoulou, both from the Department of Mechanical Engineering. Their work has been published as a cover story in Angewandte Chemistry International Edition, one of the world’s top research journals.


“Attempts to fabricate 3D-COFs into larger structures have been limited to mixed matrix membranes or support-based thin films, limiting the full exploration of its pristine structure and open porosity,” Dr. Shetty said.


Directly fabricating free-standing 3D-COF membranes is a challenging task. Plus, the functional tenability of a COF is generally limited to the strategic selection of its molecular building blocks. Hydrophobicity is one such property that is difficult to control without altering said building blocks.


“Hydrophobicity is one of the important physiochemical properties of membranes for many applications, including oil-water separation, membrane distillation, and molecular sieving,” Dr. Shetty said. “A simple method to tune the hydrophobicity of a membrane would be incredibly useful.”


The research team successfully synthesized free-standing 3D-COF membranes and introduced a novel pre-synthetically controlled framework growth strategy to tune the hydrophobicity of the resulting membranes.


At room temperature, the team can use different solvents to regulate the hydrophobicity by adding defects to the structure. The resulting membranes exhibit unique physicochemical properties because of the extent of these defect sites within the network. The defects added to the structure can be precisely controlled depending on the concentration and makeup of the solvent systems used in their fabrication, with the research team using either ethyl acetate and water or chloroform and water.


The team tested their 3D-COF structures on a water-oil mixture using simple gravity filtration and found the oil molecules were successfully removed from the mixture.


“This work is the first to develop a freestanding 3D-crystalline organic polymer membrane,” Dr. Shetty said.


“We’ve proved it is possible to tune the physiochemical properties of the membranes without changing their building blocks or using chemical modifications. Such developments can benefit membrane fabrication for critical applications, including molecular separation, water purification, and membrane distillation. Other than the novelty and merit of the science behind the research, it’s exciting that the entire experimental portion of the work was conducted at Khalifa University, highlighting our ability to produce world-class research at KU.” Dr. Shetty.


Jade Sterling
Science Writer
22 March 2022