Glass’s newest chemical cousin, and the promise it shows for CO2 capture, energy technologies medical advances, and more

4 March, 2025

For most of us, glass is simply something we look through or drink from.

And while it’s true that nearly all glass is the type we see (or rather don’t see) in our houses, two other types of glass have been known about for some time (organic glass and metallic glass).

And more recently another type of glass has been discovered: metal-organic or ‘hybrid’ glass is now considered to constitute a fourth category of glass chemistry.

'Glass can be described as a frozen liquid,’ says AMN11 Plenary Speaker Prof Tom Bennett (newly arrived from the University of Cambridge in the UK to take up a position in chemistry at the University of Canterbury). ‘Glass can be amazing – a solid with the atomistic structure of a liquid.'

He explains that as well as windows and bottles (the 'inorganic' glass we're familiar with), there’s also organic glass (used in transparent rulers kids use at school, as well as in antimicrobial coatings and for shatter-proof screens), and metallic glass (used in tennis racquets, golf clubs, and skis, and which also promise surgical tools for life-saving interventions).

‘Despite humans having made glass for centuries, in 2015 a new type of glass was discovered,' he says.

And Tom was one of the first to know.

‘From the time I was a PhD student at Cambridge I had been pretty interested in these new materials: they’re not brittle (as inorganic glass is), and they don’t scratch (as organic glass does). So they can be both hard and scratch resistant. And they melt at a temperature that’s useful for engineering.’

Prof Tom Bennett speaking at AMN11

'Beyond its gas separation properties, hybrid glass could be used in thermoelectrics, drug delivery and ion conduction.'
Professor Tom Bennett

In 2015, while Tom was looking at how materials expand or contract when heated, a colleague in Denmark who he was collaborating with, emailed to say that that the material melts.

‘My first thought was “no it doesn’t”, but then I saw a picture and realised it had melted, and that it had actually formed a new glass.’

The timing couldn’t have been better.

‘This opened up a thousand questions for me – what’s its structure, how are the atoms bonded, what are its physical and mechanical properties? I later realised that these ‘hybrid glasses’ could separate gases, like a MOF’. (A ‘MOF’, or Metal Organic Framework is a material, usually in powder form, that is used to separate e.g. CO₂ from waste streams due to its kitchen sieve like structure.)

Despite this being a new finding, it took a while for the work to be noticed.

‘My colleagues and I submitted our findings to ‘Science’ and were rejected – they said it wasn’t novel. We didn’t get much traction in the physics journals either and it wasn’t until 2017 that we managed to get a paper in Nature Materials with my colleague François-Xavier Coudert based at Chimie ParisTech, showing the melting behaviour and liquid state of MOF glasses.’

And it turns out this new 4^th type of glass might be an even better sieve than traditional crystalline MOFs.

‘Compared to powdered MOFs, hybrid glass is one continuous material, so there are no gaps for things to slip through.’

Unlike the crystalline MOFs, hybrid glasses can be structured in ‘messy’ ways like spaghetti.

Not surprisingly, the traditional MOF chemists took some winning over: ‘It was hard to convince people that order wasn’t crucial to MOFs.'

Tom says that beyond its gas separation/MOF properties, hybrid glass has an array of multifunctional properties.

‘For example, they could be used in thermoelectrics, drug delivery and ion conduction, but at the same time, they possess desirable characteristics from the glass domain, such as mechanical stability, processability and transparency.’

Tom already has collaborations with MacDiarmid Institute researchers working in the MOF space (including Shane Telfer, Paul Kruger and Matt Cowan) researching together making MOF glass membranes to separate CO2 and N2.

‘I’m wanting to get scientists to think differently about MOFs, and keen to establish connections between the field of MOFs and those of ionic liquids and glasses’, he says.

So next time you pour yourself a glass of something, think about your glass’s newest chemical cousin, and the promise it shows for CO2 capture, energy technologies medical advances, and more.