Metal-organic frameworks (MOFs) are remarkable next-generation materials that possess the most extensive internal surface area of any identified substance. The sponge-like crystals can be used to capture, store, and discharge chemical compounds, in this case, the ions and salt in seawater.
Dr Huacheng Zhang, Professor Huanting Wang, Associate Professor Zhe Liu and their team at the Faculty of Engineering, Monash University in Melbourne, Australia, in partnership with Dr Anita Hill of CSIRO and Professor Benny Freeman of the McKetta Department of Chemical Engineering at the University of Texas, have learnt that MOF membranes can imitate the filtering operation, or 'ion selectivity', of organic cell membranes.
With more development, these membranes have major potential to perform the twofold functions of removing salts from seawater and extrication metal ions in a very efficient and economical manner, offering a ground-breaking new technological method for the water and mining sectors.
At present, reverse osmosis membranes are responsible for over half of the world's desalination capacity, and the last stage of most water treatment processes, yet these membranes have room for development in energy consumption by a factor of 2 to 3. They do not function on the principles of ion dehydration or selective ion transport in biological channels (the topic of the 2003 Nobel Prize in Chemistry awarded to Peter Agre and Roderick MacKinnon), and thus have significant limitations.
In the mining sector, membrane processes are being developed to decrease water pollution, as well as for recovering valuable metals. For instance, lithium-ion batteries are currently the most popular power source for mobile electronic devices; however, at curent consumption rates, there is increasing demand. This is likely to require lithium production from non-traditional sources, such as recovery from waste process streams and salt water. If technologically and economically feasible, direct extraction and purification of lithium from such a composite liquid system would have profound economic impacts.
We can use our findings to address the challenges of water desalination. Instead of relying on the current costly and energy-intensive processes, this research opens up the potential for removing salt ions from water in a far more energy efficient and environmentally sustainable way.
Also, this is just the start of the potential for this phenomenon. We'll continue researching how the lithium-ion selectivity of these membranes can be further applied. Lithium ions are abundant in seawater, so this has implications for the mining industry who current use inefficient chemical treatments to extract lithium from rocks and brines. Global demand for lithium required for electronics and batteries is very high. These membranes offer the potential for a very effective way to extract lithium ions from seawater, a plentiful and easily accessible resource.
Professor Huanting Wang - Monash University
Building on the growing scientific insight of MOFs, CSIRO's Dr. Anita Hill said the research offers another probable real-world use for the next-generation material. "The prospect of using MOFs for sustainable water filtration is incredibly exciting from a public good perspective while delivering a better way of extracting lithium ions to meet global demand could create new industries for Australia,"
Produced water from shale gas fields in Texas is rich in lithium. Advanced separation materials concepts, such as this, could potentially turn this waste stream into a resource recovery opportunity. I am very grateful to have had the opportunity to work with these distinguished colleagues from Monash and CSIRO via the Australian-American Fulbright Commission for the U.S. Fulbright Distinguished Chair in Science, Technology, and Innovation sponsored by the Commonwealth Scientific and Industrial Research Organization (CSIRO).
Professor Benny Freeman - The University of Texas