When you first started out, you were working as a materials chemist. How did you get involved in “nanochemistry”?

I literally stumbled into the research area and helped provide the foundation of the field we now call nanochemistry.

In the early seventies, the century-old field of colloid chemistry, pioneered by Thomas Graham (1805-1869), was undergoing its metamorphosis to today’s nanochemistry, and colloid science, propagated by Wolfgang Ostwald (1883-1943), was nucleating as today’s nanoscience. Graham had described the distinctive behavior of matter in the nanometer to micron size range, and Ostwald had enriched the subject in his book “The World of Neglected Dimensions” (1914). This work inspired me, a new assistant professor in the Chemistry Department at the University of Toronto, to address the challenge of self-assembling materials with nanoscale dimensions using a bottom-up chemistry approach.

As a synthetic chemist, however, I confronted an important unanswered question: How could chemistry be used to prepare nanoscale forms of well-known metals, semiconductors and insulators with physical dimensions in the quantum size regime of around 1-100 nm? I studied the size-tunable behavior of these materials with an eye to elucidating structure, property, function relations and determining utility. The “eureka” moment of performing chemistry with “naked” metal atoms under cryogenic conditions opened my mind to the tantalizing possibility that one could control nucleation and growth to atom-precise metal nanoclusters M_n, by allowing them to diffuse around and self-assemble in solid matrices. This scientifically significant feat had never been accomplished before. In this way, I observed metal atom-by-atom nucleation and growth reactions, and monitored and quantified their aggregation kinetics for the first time. Furthermore, I established that it was possible to observe previously unknown M_nL_m compounds when naked metal atoms and few atom metal nanoclusters were found in the presence of various small molecule ligands.

What is one of your favorite early-career projects?

One of my favorite early initiatives, undertaken while I worked as a Fairchild Fellow at Caltech in 1977 with William Goddard, was an experimental and theoretical study of Ni_n(C₂H₄)_m. This described for the first time the chemistry of “naked” nickel atoms and nickel clusters with ethylene, envisioning them as a localized bonding model for ethylene chemisorbed on bulk nickel. The ingenuity behind these 1970’s experiments, and expanded upon in my later papers, unveiled an unprecedented view of controlled size metal nanoclusters, the synthesis of which enabled the first explorations of the transition from molecular to quantum confined to bulk forms of metals. They also provided a unique platform for investigating cluster-surface relations. It is worth mentioning that I later enriched this work with the discovery of a collection of unprecedented metal atom and metal cluster photo-processes. These processes included naked metal atom photo-aggregation, naked metal cluster photo-dissociation and naked metal cluster photo-isomerization reactions as well as naked metal atom photo-insertion reactions into the carbon-hydrogen bonds of saturated hydrocarbons, such as methane.

Together, these early experiments on the chemistry and photochemistry of naked metal atoms and naked metal clusters, laid the groundwork for the development of the field of nanochemistry. The instrumentation to perform this kind of metal-atom-metal-vapor chemistry was manufactured and commercialized by a spin-off from my group, www.torrovap.com that was founded in 1981 and is still in business.

Where did your research take you after laying down this foundational groundwork in naked metal atom metal cluster chemistry?

My desire to take the insights gained from the nanochemistry work on naked metal atom and naked metal cluster cryochemistry “out of the cold” provided the link between my early work and the field of zeolite science. I envisioned making and stabilizing these tiny pieces of matter so that detailed studies of their structure, property, function, utility and relations could be undertaken. In this context, it occurred that because these M_n and M_nL_m nanoclusters were inherently metastable with respect to further agglomeration to thermodynamically stable bulk materials, they had to be stabilized by some kind of surface protecting sheath. I performed the nucleation and growth reactions within the nanometer-sized voids of zeolites, thereby “capping and trapping” the nanoclusters in a zeolite ligand cage, confirming that zeolites could serve as nanoporous hosts for synthesizing and stabilizing metal and semiconductor nanomaterials. 

During this period, thinking within the zeolite community focused solely on the properties and applications of zeolites in catalysis and gas separation. I, however, preferred to look at zeolites as solids filled with nanoscale voids and wondered how they could perform and compete in the advanced materials research space. I saw their potential in areas such as information storage, photovoltaics, batteries, fuel cells, photocatalyts, chemical sensors and drug delivery systems. Exploring this potential, I worked with Edith Flanigen at Union Carbide, Tarrytown, New York for five years to bring some of these ideas to practical fruition, ultimately describing my vision for the future direction of the field in the paper “Advanced Zeolite Materials Science”.

Coincidentally, around this time the Union Carbide team made the extraordinary discovery that nanoporous materials could be made from elements across the periodic table, thus expanding the composition field of zeolites way beyond aluminosilicates and silicates, inspiring me to focus attention on advanced materials applications of nanoporous metal chalcogenides, which I envisioned as self-assembled semiconductors filled with nanometer holes with perceived utility in molecular size- and shape-discriminating sensing devices enabling the development of an early “electronic nose”. To improve their crystalline perfection, I took self-assembly of these nanoporous semiconductor materials into space to see the effect of gravity on the nucleation and growth process.

What happened in space?

This was a highlight of my early career, scientifically exhilarating and technologically demanding. The project was a collaboration between the Canadian Space Agency and the National Aeronautical Space Agency, structured around earth and space-based research. The former was conducted in my research group at the University of Toronto, the latter performed robotically in a get-away-special on May 19, 1996 NASA space shuttle Endeavor, STS 77. This mission is credited as the maiden flight geared towards microgravity research and the commercialization of space. Coincidentally, one of the shuttles crew was mission specialist Canadian Marc Garneau, who became a member of the Canadian parliament in 2008. The goal of the project was to study the effect of microgravity on the crystallization of layered microporous tin(IV) sulphides. This material was selected because its crystal structure is determined by weak inter-layer and strong intra-layer covalent bonds and its self-assembly was expected to be very sensitive to the nucleation and growth conditions. The outcome of five years of inspiring research was the discovery that in the absence of sedimentation and convection gravity driven disturbances of crystal growth under microgravity conditions, we observed improved overall crystal quality, exemplified by more well-defined morphologies with smoother facets, enhanced crystallinity, optical quality and void volume, compared to the crystals produced on Earth.

How did this lead to the birth of nanochemistry?

In hindsight, my ensuing research laid out the essence of a chemical approach to nanomaterials — a futuristic field that I called “nanochemistry”. This paper set the scene for a nanomaterials revolution that continues unabated today. I envisioned the novel world of nanochemistry with its 0D dots, 1D wires, 2D layers, and 3D open frames, with configurations that surprised, and shape- and size-dependent behaviors that startled. Here were the conceptual foundations, the description of a bottom-up paradigm for synthesizing nanoscale materials with nanometer-level command over their size, shape, surface, and self-assembly. The potential I saw was breathtaking. It would be possible to produce nanoscale materials — perfect down to the last atom — from organic and inorganic components with structure-property relations designed to yield new materials characterized by an array of novel behaviors and these materials would have real-world applications.

The field of nanochemistry crystallized in 1992 and gave birth to journals that publish nanochemistry with citation impact-factors matching or exceeding the flagship journal in their respective society and include: Small, Nano Letters, ACS Nano, Nature Nanotechnology, Nanoscale and the list continues to grow. Chemistry and nanotechnology were forever united, as evidenced by the astronomical growth of Nano Chemistry ISI citations since 1992, more than 360 million hits on Google, and the creation of numerous global initiatives in academic, industry, government, and defense institutions around research and education in nanochemistry. These initiatives would not likely have been possible without that foundational work carried out in the seventies, which subsequently inspired others to employ fundamental scientific principles and practices of nanochemistry to solve challenging real world problems in nanotechnology.

What would you say is one of the hallmarks of your research?

The creative exploitation of the unique properties of regular arrangements of nanopores with dimensions that traverse nanometers to microns. For example, my research on periodic macroporous materials, which I aptly calls “light-scale” materials, a focus has been electrically, thermally, mechanically, and chemically tuned “colour from structure”. This revolutionary concept forms the basis of a new “photonic color” nanotechnology being developed by Opalux who are introducing three unique manifestations of this nanotechnology to the market.

P-Ink is a flexible, electronic paper-like material offering a full spectrum of electrically-tunable, reflective colours. Being bi-stable and power-efficient, it is one of three competitive technologies vying to add colour to black-and-white electronic book readers such as Kindle and Kobo. P-Nose is an artificial nose comprised of a simple, cost-effective pixilated array of surface-functionalized nanoporous materials that enable discrimination of different analytes, such as molecules comprising the unique identifiers of different bacteria. Think of the possibilities for medical diagnostics, and food and water quality-control! Elast-Ink is a touch-sensitive material that responds to mechanical pressure while offering exceptional resolution and customizability. It is poised to answer global demand for effective authentication-technology, serving, for example, the pharmaceutical and banknote-printing industries.

It is worth pointing out that the P-Ink photonic colour technology developed by Oplaux was recognized by the Technical Development Materials Award in the USA in 2011, which identifies the most innovative and significant technical achievement in the field of materials development. Opalux follows in the footsteps of many previous illustrious industry winners of this award in the US, Europe and Asia. In 2013, Opalux P-Ink Photonic Technology received the Global Innovation Award for its potential impact on the specialty colour displays industrial sector. Opalux Opal-Print Technology was runner-up in the 2013 Excellence in Tax Stamps Awards for best new innovation in anti-counterfeiting, anti-diversion, document security, brand protection and holography technologies. They have won many awards since then in recognition of their achievement of taking photonic color from the laboratory to the market place.

What do you feel is the most sci-fi or intriguing discoveries made during your career?

I was among the first few scientists to demonstrate chemically-powered “nanolocomotion”. My work was based on chemical control of the motion of barcode nanorod motors, whose power is obtained from the decomposition of hydrogen peroxide into water and oxygen localized at the catalytic segment of the nanorod. The first experiments were aimed at nanorod rotors and motors and understanding the origin and control of their motion and speed. Subsequently I was the first to show how to make them flexible by integrating polymer hinges between the segments of the nanorod. These seminal papers inspired a veritable nanomotor industry. Activity in this field is now burgeoning around the world with envisioned nanomachine applications that include the removal of pollutants from water and as drug-carrying and delivery vehicles for targeted cancer therapy. In another burst of innovation, I discovered ultrathin inorganic nanowires which are characterized by unprecedented small < 2 nm diameters. These amazingly thin nanowires look, grow and behave like organic polymers. This work inspired a flurry of activity around the globe to explore the composition space and structure, properties, and functionality of these uniquely-thin one-dimensional constructs. This work raises an important question about how to expand and enrich the myriad applications enjoyed by organic polymers into the completely uncharted territory of ultrathin inorganic nanowires. The opportunities appear to be boundless!

What do your current research interests look like?

Lately, I developed a passion for a greener kind of nanochemistry and figured out how to separate poly-dispersions of quantum-confined silicon nanocrystals into mono-dispersed colloidally-stable fractions with tailored organic surfaces. Incredibly, for the archetype semiconductor silicon, this feat was the first of its kind since the discovery of silicon nanocrystals more than thirty years ago. The brightly coloured visible to near infrared photoluminescence of these size-separated silicon nanocrystals enabled determination of their size-dependent absolute quantum yields. These photoluminescence quantum yields were found to be surprisingly high and as a result are targeted for a range of “green” nanotechnologies that include multicolour light-emitting diodes and biomedical diagnostics, therapeutics and imaging for detecting and targeting tumors. I believe green nanochemistry founded on benign nanocrystalline silicon will help alleviate the fear of cytotoxicity that currently pervades the use of heavy metal chalcogenide and pnictide nanomaterials currently favored for advanced materials and biomedical nanotechnologies. Recently I discovered the hydride capped versions of silicon nanocrystals are efficacious photocatalysts for the gas-phase, light-assisted hydrogenation of carbon dioxide to value-added chemicals and fuels, one of the highlights of the research of the solar fuels group that I established and spearheaded since its inception around a decade ago. I am excited that as a result of our pioneering work on carbon dioxide chemical and engineering solutions to climate change, the spin-off company Solistra has been founded recently to take our kind of solar fuels science and technology into the market place. 

As a professor, has being a mentor and teacher been important to you during your career?

A particularly important and satisfying aspect of my careers work involves education. First and foremost has been the honor, pleasure and delight of mentoring students through one of the most challenging phases of their career development. It is a truism that everything I know I learned together with my students. I am mighty proud of their accomplishments and the fact that around 50 have secured faculty positions in top notch universities around the world and the rest have established excellent and diverse careers that include industry, government, business and law.

I am also thrilled with my textbooks “Concepts in Nanochemistry” and “Nanochemistry: A Chemical Approach to Nanomaterials” co-authored with former students Andre Arseault and Ludovico Cademartiri that are globally acclaimed as the gold standard reference works for teaching nanochemistry to both undergraduate and graduate students.

Most recently, my passion for research and development in the field of energy materials discovery for a sustainable future has culminated in my most recent book entitled “The Story of CO₂ — Big Ideas for a Small Molecule”, co-authored with my graduate student, Mireille Ghoussoub, to be published by University of Toronto press, October 2020.

In addition, my tireless out-reach efforts through insightful and engaging lectures and more than one hundred opinion editorials for Advanced Science News over the past ten years, aim to inform scientists and engineers in academia, industry, government, media, business, investment sectors of society, on pressing issues affecting our collective future. These inspiring, thought-provoking perspectives offer viable ways of improving the state of the world.

Tell me about your project ArtNanoInnovations.

ArtNanoInnovations was co-founded in 2011 with artist Todd Siler — our mission was to explore the realization of nature-inspired innovations in nanoscience and nanotechnology, which aim to benefit humankind by meeting our global challenges. This work entails metaphorming (connecting & transforming) the myriad forms of nanometer scale science through multimedia artworks and aesthetic experiences that connect us with nature’s inventions, which we can build on in creating a sustainable future. Our collaboration began with a chance meeting at a ceremony hosted by the World Cultural Council where the art and science work of Todd and I were recognised by the award of the Leonardo da Vinci and Albert Einstein prizes, respectively, in 2011.

There is an art to catalyzing collaborations and there is a science to developing innovations that are naturally connected by the creative process. The ArtScience collaboration described as the ArtNano© project, shows how we use one-and-the-same process of creative learning and idea-generation. Our exploratory work considers the potential of numerous practical innovations in the field of nanoscience and nanotechnology, and is designed to help solve many of our most pressing world problems. Moreover, our work explores some new ways of communicating complex information to a worldwide public; in particular, the various strategies and technological means by which human beings currently manipulate matter ingenuously on an atomic and molecular scale to produce the smallest, multi-purpose functional structures and systems ever conceived. Our collaborations provide some essential lessons learned from combining our complementary practices of connecting and transforming information (data, knowledge, ideas, concepts, theories). The ArtNano© project offers some uncommon wisdom about moving beyond the roadblocks that form mental barriers, as well as our compartmentalized ways of knowing the world, and representing our knowledge.

Note: This © symbol in ArtNano© stands not only for “copyright,” but also for “creativity,” “communication,” and “collaboration.” Moreover, it symbolizes the phenomenal versatility and transformations of “carbon” into the myriad manifestations, forms, and applications of this element to the whole of life.

What are your future plans?

Being a vulnerable senior citizen in a pandemic without a vaccine my future plans have become rather uncertain. Of course health is number one in any work-life plan. The jury is still out on where my wife Linda and I decide to end up working and residing, either part or full time; it could be Canada or America, England or Belgium. We have always been dedicated to eating healthily and keeping physically fit and this will continue along with spending as much time as possible with our family in the mentioned countries.

Anything special planned for your birthday?

I would imagine this will be online, if I am lucky, a cyber-celebration with my past coworkers.

What do you hope your legacy will be?

It is probably fair to say that the fundamental research contributions that have emerged from my careers research have helped to define and secure credibility for a novel scientific discipline, nanochemistry, the fruits of which pervade products, processes and devices emerging from essentially every corner of the industrial world. To my mind, this achievement constitutes the very essence of working at the frontiers of knowledge. Further, the new discipline of nanochemistry continues to serve as an integral driver of further developments in many tangential scientific undertakings, which we now count upon to catalyze scientific, industrial and economic advancement.

Put another way, I believe my work first envisioned the nano materials future and then enabled a bridge into this new world of diminishing dimensions.