Imagine a molecular world with rooms as structurally stable and freely accessible as those in the human world. These are the molecular architectures meticulously designed by scientists: Metal-Organic Frameworks (MOFs). On Wednesday, Oct. 8, the Royal Swedish Academy of Sciences announced that this year's Nobel Prize in Chemistry is awarded to Australian scientist Richard Robson, Japanese scientist Susumu Kitagawa, and Jordanian-American scientist Omar M. Yaghi, in recognition of their pioneering contributions to the research and development of MOF materials. Today, from extracting water from deserts to capturing carbon dioxide, MOFs have brought a series of miracles to the field of chemistry.
Scientific discoveries often begin with "outside-the-box" thinking. In 1974, while creating molecular models for a chemistry class at the University of Melbourne, Robson had a sudden idea: if atoms or molecules could be made to connect spontaneously according to their chemical properties, like building blocks, it might be possible to construct a completely new type of molecular architecture. Within these architectures, atoms and molecules might freely exchange and move in and out, potentially granting the materials catalytic properties.
Turning concept into reality: A new material is born
In 1989, Robson personally verified his hypothesis. He combined positively charged copper ions with a type of four-armed molecule, each arm ending with a chemical group capable of binding to the copper ions. Unexpectedly, their combination resulted in an orderly, structured crystal with spacious cavities, like a diamond full of hollow spaces. Inspired by this, Robson went on to synthesize several types of molecular networks containing cavities. He was the first to propose that these molecular networks held great potential, possibly endowing materials with unprecedented properties.
Early molecular network structures were unstable and prone to collapse. However, by 1992, Japanese scientist Kitagawa from Kinki University, building on Robson's research, constructed a two-dimensional molecular material using metal ions as pivotal points. In 1997, Kitagawa's research team went a step further, constructing a stable three-dimensional MOF structure. His research discovered that MOFs could be built using various metals and organic molecules, and their functions could be customized according to need. Whether adsorbing or releasing gases like methane, oxygen, or nitrogen, they would not easily deform.
In 1999, Yaghi and his research team first demonstrated the classic MOF material "MOF-5". This is a framework structure with immense space, akin to "skyscrapers" in the molecular world. The internal surface area of just a few grams of MOF-5, when unfolded, is equivalent to a standard football field. MOF-5 also exhibited remarkable stability, remaining undeformed even when heated to 300 degrees Celsius, meaning it could adsorb more gases than traditional materials in more extreme environments.
Breaking down trace drug residues in soil
In the years that followed, Yaghi and his team introduced various MOF variant materials with diverse uses, from storing methane and capturing carbon dioxide to extracting water from the air in deserts: specialized materials can adsorb moisture from the air at night, and then release liquid water during the day when heated by the sun, making fetching water in arid lands no longer an impossibility.
Thanks to the research of these three scholars, chemists have now synthesized tens of thousands of different MOF structures. These remarkable materials have broad application prospects in the environmental and energy sectors. Whether it's breaking down trace drug residues in soil, capturing carbon dioxide from the air to mitigate the greenhouse effect, or separating harmful perpetual chemicals (PFAS) from water, all rely on the application of MOFs.
"With science as the supreme driving force"
One of this year's Nobel Chemistry laureates, Yaghi, was born into a Palestinian refugee family in Jordan, where 80% of the land is desert, facing severe water scarcity. For years, Yaghi has been attempting to use MOF technology to effectively collect water resources from desert air, addressing drought issues. Reflecting on his scientific and life journey, Yaghi noted that, in his view, science is "a great equalizing force in the world."
In an interview, Yaghi recalled growing up in a family with over ten people. His home had no electricity, no running water, and his father had only completed elementary school, while his mother was totally illiterate.
Around age ten, Yaghi first discovered molecular structures in a book in the school library. He moved to the United States at 15, pursuing his studies and eventually embarking on a path of scientific research.
Yaghi stated that his love for science has sustained him to this day. "It's been quite a journey, and science allows you to do it."
Background: Practical applications areas of MOFs
Metal-Organic Frameworks (MOFs) have recently expanded into more and more application areas. Chemical experts point out that besides extracting water from deserts and absorbing carbon dioxide, MOFs have also been applied in nanomedicine in recent years, where they can be placed inside the human body to release drugs. In the new energy sector, MOFs can also be used to store clean fuels like hydrogen, bringing more possibilities for industries such as hydrogen fuel cell vehicles.
MOFs have advantages such as clear structures and ease of chemical functionalization, making them potential nanodrug carriers. When MOF particles are reduced to the nanoscale, these nano-MOFs can be used for medical imaging or as carriers for chemotherapy or photothermal therapy drugs. Over the past few years, nano-MOFs have continuously developed in early cancer diagnosis technologies, being used as potential contrast agents for various imaging modes, including Magnetic Resonance Imaging (MRI) and optical imaging.
In the environmental industry, traditional carbon dioxide adsorption methods use "chemical absorption" with water-based solvents to capture CO2. After the absorbent becomes saturated, CO2 is released via heating. Chemical absorption requires heating, which consumes significant energy, and the process can emit additional CO2. In comparison, MOFs have tiny pores, and their internal surfaces have an affinity for CO2. Due to the very large internal surface area of MOFs, only a limited amount of material is needed to adsorb a large quantity of CO2, and the energy-consuming step of heating for regeneration can be saved.
MOF materials can also be used to bind hydrogen molecules, solving the problem of safely storing and transporting this gaseous clean fuel. Scientists have already designed a MOF named NU-1501, which can safely and efficiently store and release large amounts of hydrogen under ambient pressure, clearing obstacles for the widespread adoption of hydrogen fuel cell vehicles.
Another MOF material named UiO-67 can precisely adsorb chemical pollutants like PFAS from water, making it a powerful tool for water purification and environmental remediation.
Some scientists point out that compared to traditional porous materials (such as zeolites primarily made of silica and alumina), MOFs require organic components, leading the industry to initially believe their cost might be relatively high. But, with various new materials in recent years, the cost of MOFs has become acceptable, and large-scale production is entirely feasible. Considering that MOFs have the potential to create application value exceeding their manufacturing cost, scientists generally believe they have good commercial prospects.
(Source: Wen Wei Po; English Editor: Darius)
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