"One of the continuing scandals in the physical sciences is that it remains in general impossible to predict the structure of even the simplest crystalline solids from a knowledge of their chemical composition."
In a 1988 editorial from the journal Nature, then editor John Maddox made clear his position on what he saw as chemistry's lack of commitment to the study of crystals.
At the time, Maddox was writing that x-ray crystallography was becoming a relatively routine technique to determine the structure of crystal matter. Some of this advance was driven by the contributions of two Irish-born 20th-century scientists – JD Bernal and Kathleen Lonsdale.
The control and design of crystals, however, remained beyond anyone's reach. And simply not knowing how to do something is all the push required in science for a new field to emerge: crystal engineering.
Crystal engineering refers to the design and synthesis of molecular solid-state structures with intended properties. One of the most promising innovations from the field are what's known as metal organic frameworks (MOFs). "MOFs are a new class of porous materials made by using an approach similar to Lego or Meccano, where building blocks or linkers are made between the organic and inorganic," explains Prof Mike Zaworotko, Bernal chair of crystal engineering at the University of Limerick.
MOFs are a new class of porous materials that have applications anywhere gases and chemicals need to be captured, stored or separated. Like little sponges, they have been designed with storage in mind. Some can be up to 80 per cent empty space.
“One gram of MOF surface area is equal to 40 tennis courts in storage space,” says Dr Paschal McCloskey, chief executive of MOF Technologies, a Queen’s University Belfast spinout which was the first company in the world to successfully commercialise MOF technology.
"MOFs have two defining characteristics that give rise to their broad industrial interest: they have extremely large surface area, the largest of any known material, and a high degree of structural flexibility, allowing them to be very particular about what gases to select, and how much to absorb," he says.
McCloskey and his Belfast-based team see five industrial sectors, in particular, where MOF technology is a no-brainer – hazardous gas storage, carbon capture, natural gas-powered vehicles, smart packaging and heat transformation.
Back in Limerick, Prof Zaworotko – considered one of the world’s leading MOF experts – and his team have developed a panel of materials known as TIFSIX and SIFSIX MOFs that have unparalleled selectivity and capacity for CO2 capture.
“TIFSIX and SIFSIX are hybrid materials based upon metals and a combination of inorganic and organic linkers,” he says. “What we now know is that the inorganic linker is key to them being selective for CO2. Also key is the very good fit that these materials have for CO2. Technically the term is “ultramicroporous.”
Potential applications
This technology has the greatest number of potential applications in chemical processing and manufacturing, industrial sectors which already use one-third of all energy produced worldwide. MOFs have more than just green credentials going for them though.
“A large portion of the energy used in the chemical industry is for purification processes,” says Zaworotko.
“As demand for commodities rises, these advanced materials could cut the cost of purification by 90 per cent because they are much less energy-intensive than existing technologies such as chemical capture or distillation. In the long run, entirely new technologies based upon CO2 could be developed because CO2 can be turned into useful things. These technologies would likely be carbon neutral or carbon negative.”
The researchers at UL have been working on this project for almost five years. When they began, Prof Zaworotko admits he had his doubts. “These types of materials had simply not been studied and were different from all existing classes of porous materials,” he says.
Five years later and his confidence appears to be back. “Not only are they our best hope for CO2, they’re also able to separate other gases of commercial relevance like ethylene, natural gas and biogas. In all cases, they are not just better, they are a lot better.”
MOF Technologies in Belfast has agreed to license the TIFSIX and SIFSIX group of MOF materials from UL and commercialise them worldwide. “We are looking to produce and supply these materials on scale to our customers for a range of CO2 sequestration applications all with the ultimate aim of reducing greenhouse gases from both industrial and domestic settings,” says McCloskey.
Time crystals – first examples of non-equilibrium matter
Crystals are all around us. From everyday items like salt and sugar, to diamonds and even snowflakes, most are forms of matter in states of equilibrium. A diamond could be described as “an atomic carbon lattice that repeats in space”. Given their atomic joie de vivre, one assistant professor of physics from University of Berkeley, California, questioned why crystals couldn’t also also have a structure that repeated in time, hence, time crystals.
In a paper published in the journal Physical Review Letters, assistant professor Norman Yao describes how to go about making – and measuring the properties of – a time crystal. He even suggests what the various transitional 'phases' (similar to the gas, liquid and solid 'phases' of water) surrounding the time crystal should be.
Essentially, time crystals are created by repeatedly tweaking groups of ions. They repeat “in time” by being kicked over and over, almost like jelly being tapped continuously so it wobbles.
This isn't only hypothesis. Prof Norman Yao's blueprint has already been tested successfully by two different research teams. Physicists from the University of Maryland and Harvard University have reportedly created time crystals of their own, using two totally different set-ups.
“This is a new phase of matter,” says Yao. “But it is also really cool because it is one of the first examples of non-equilibrium matter. For the last half-century, we have been exploring equilibrium matter, like metals and insulators. We are just now starting to explore a whole new landscape of non-equilibrium matter.”
