Luke Liu: Metal-Organic Frameworks
Story by Emma Timewell Luke Liu builds molecular sponges—known as metal-organic frameworks, or MOFs, these molecular sponges have the potential to store and separate industrial compounds such as hydrogen, methane and carbon dioxide with high efficiency. The energy required to separate these compounds using current methods is high—for example, about a third of the power generated from coal burning is used to capture the carbon dioxide from the post-combustion gas mixtures produced during the coal burning process. The use of MOFs has the potential to greatly improve the efficiency of the system, reducing the energy used to less than 15 percent. For industries where separating these gases is important, this level of cost-efficiency is in high demand. Luke’s interest in MOFs started during his undergraduate project at Shanghai Jiao Tong University in China, where he focused on making catalysts. After spending two years in industry, he realised that he much preferred the discovery of science—finding out how and why something works—and searched the globe for a PhD project that interested him. An advert for a project researching metal-organic frameworks with Shane Telfer, Principal Investigator at the MacDiarmid Institute, fitted the bill. MOFs have a highly ordered structure, with repeating units of metal ions or clusters joined by organic components, or linkers, in a net-like structure that can be assembled as a two or three dimensional structure. The large surface area within the pores of the framework provides multiple sites for compounds to ‘stick’; the structures of these binding sites are highly specific and rely on the environment within the framework to bind their targets. As much of the structure is free space, the compounds are also very light and easy to manoeuvre. Luke’s research focuses on building a MOF with three distinct organic components that maintain their structure and order once in the framework. Components that react to each other, or the environment around them, can dramatically modify the whole framework, closing the pores and changing the structure of the binding sites. This research has been recognised by the Chinese Scholarship Council, and Luke was one of 500 students awarded an Outstanding PhD Student this year, presented to students across all academic disciplines. He has also been the lead author on two papers published in the Journal of the American Chemical Society, the leading journal for chemical research, during the time of his PhD. The first of these papers describes a family of MOFs that bind carbon dioxide that Luke serendipitously discovered a few months into his PhD. The paper demonstrated the unprecedented use of three organic ligands in a precisely ordered structure, designed to atomic precision, the first step in building more advanced materials such as artificial enzymes. The most recent paper, published in March this year, describes research into a class of MOFs with a zinc carboxylate component that holds stability at high (70 percent) humidity levels, very rare for zinc carboxylate MOFs which usually collapse at 15–40 percent humidity, which can be tuned to bind carbon dioxide or methane. Holding stability at these high humidity levels means these MOFs could potentially be used in ambient environments that require no careful handling, a potentially game-changing discovery. Luke recently submitted his PhD and has been accepted to a Postdoctoral postition at Northwestern University. Luke is a speaker in this year’s MacDiarmid lecture series, presenting his work on MOFs in Tauranga on 20 July and Nelson on 30 July.