Issue Date: February 1, 2016
Nanochemistry On My Mind
Across the span of my 40-plus-year career, I was fortunate to be involved in the birth and growth of a futuristic field of science that my colleagues and I came to call nanochemistry. The central tenet of nanochemistry is the synthesis of nanoscale materials from the bottom up, literally atom-by-atom. That’s in contrast to sculpting nanostructured materials with a top-down engineering-physics fabrication approach.
Today, nanoscale solids and materials filled with nanoscale voids enable a cornucopia of electronic, optical, magnetic, mechanical, and thermal applications. These advances have benefited from what I call the “nano advantage”—the unique properties exhibited by nanoscale materials that are not displayed by molecules or bulk materials of the same chemical composition.
Chemistry and nanotechnology are now forever united through nanochemistry. And despite the successes in advanced materials and biomedical technologies society has witnessed, it feels like we are only just getting started. What we have achieved so far with nanochemistry is a foundation for developing a new round of futuristic technologies that will allow us to tackle and wisely manage our interrelated energy, food, health, climate, and environmental needs to live in a sustainable world.
My adventure in nanochemistry began in 1969 as a new assistant professor at the University of Toronto. Those early days were full of monumental scientific and technological breakthroughs that included Sputnik and Apollo 11, DNA, Teflon, the microchip, optical fibers, and lasers. I was inspired by the famous 1959 lecture “There’s Plenty of Room at the Bottom” by California Institute of Technology physicist Richard P. Feynman and the idea of being able to carry out atom-by-atom self-assembly.
The big question, unanswered at the time, was how to use chemistry to prepare and stabilize nanoscale forms of well-known materials, with dimensions in the quantum regime of around 1 nm to 100 nm, and study their size-tunable behavior with an eye toward real-world applications.
Working initially under cryogenic conditions to slow reactions down, and using various in situ analytical techniques, I witnessed naked metal atoms forming nanoclusters. It occurred to me that because these nanomaterials were metastable compared with bulk materials they would have to be protected in some way. One approach was to perform the chemistry within the nanometer-sized voids of a solid material such as zeolites—a strategy coined host-guest chemistry.
Aspects of the work remained frustrating, however. For instance, there was a narrow focus on using zeolites in catalysis, gas separation, and ion exchange. I saw their potential in other areas, such as data storage, batteries and fuel cells, photocatalysis, chemical sensing, and drug delivery. Subsequent discoveries of metal-organic frameworks, covalent-organic frameworks, porous aromatic frameworks, hydrogen-bonded organic frameworks, and porous polymers—today’s leading contenders for gas separation and storage technologies—have enriched the field of nanoporous materials and brought those applications to life.
Another frustration with zeolite hosts is that their 1-nm maximum pore size imposes limits on their imbibed guests, which restricted our ability to work in the 1-nm to 1,000-nm regime. The discovery of mesoporous silica in the early 1990s with pore sizes up to 100 nm gave us a little elbow room. Later on, larger pore sizes up to 1,000 nm became accessible in silica and polymer opals, leading to breakthroughs in developing photonic crystals of wide-ranging compositions that spawned applications in optical telecommunications and tunable photonic color devices.
The new ability to synthesize materials with structural features that traversed all nanometer length scales set the scene for a “panomaterials” revolution. It became possible to produce nanomaterials from organic and inorganic components over all scales, composed of assemblies of 3-D frameworks, 2-D layers, 1-D wires, and 0-D dots, perfect in size and shape down to the last atom. The potential was breathtaking.
There’s now a rich opportunity to take the nanochemistry knowledge we have cultivated and apply it to today’s pressing problems. One example is developing new materials that enable global energy technologies to capture CO2 and convert it to fuels that will help replace fossil resources and ameliorate climate change.
Here, a prescient quote from a 1971 Life magazine interview with architect and inventor Richard Buckminster Fuller is worth recalling: “Pollution is nothing but resources we’re not harvesting. We allow them to disperse because we’ve been ignorant of their value. But if we got onto a planning basis, the government could trap pollutants in the stacks and spillages and get back more money than this would cost out of the stockpiled chemistries they’d be collecting.”
The nanochemistry needed to achieve that vision will require new adventurous cross-disciplinary torchbearers to seek out and discover innovative materials solutions. Learning how to exploit the “nano advantage” to enable advances with a high likelihood of widespread use by society is a monumental idea just as alive today as it was for me in 1969.
Beyond carbon capture and utilization and safer and more secure renewable energy, a few other “holy grails” come to mind as being ripe for nanochemistry solutions: next-generation information technology; improved health care in the developing world; safety from terrorism; water purification and desalination; pollution prevention and reduction; better nutrition and crop protection; and autonomous nanomachines for medical diagnosis, intracellular drug delivery, and surgery. Let’s see what we can do.
Views expressed on this page are those of the author and not necessarily those of ACS.
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