MasterClass #9 : Nanoparticles for every purpose

16 septembre 2024

Nanoparticles for every purpose

By Laurent Charlet, ISTerre

Within the Earth’s thin film where life thrives, known as the "critical zone", (nano)particles are ubiquitous and distinguished by the key role played by their surface. It would be easy to despise these particles (as words like "sludge", "mud", "dirt" and "dirty" imply), if they hadn’t been used very early on by mankind for artistic expression (cave paintings), shelter (ancient concretes), healing (clay poultices) and control of drink water quality, the abundance of food nutrients or for the containment of undesirable (pollutants, such as prions, antibiotics or nuclear energy residues) or desirable (e.g., hydrogen, our future fuel) molecules were not controlled by their immense reactive surface area. What are the dynamics of this "dirty" system, and how can we study them ? In the space of a quarter of a century, our knowledge and understanding of the geochemistry taking place at the water/particle interface has greatly progressed, enabling us to unravel what is due to electron exchange, electrostatic attraction or structural fit - similar to the "docking" used in the development of new drugs. Today, we can map what happens at this interface on a molecular scale, and trace its effects in drinkwater and food quality variations. These advances require a combination of observational, theoretical, experimental and numerical approaches. ISTerre’s geochemistry team stands out for its skills in these four approaches.

As a firm believer in the powerful confrontation between major societal problems (e.g., certain environmentally-induced diseases) and the molecular vision of the geochemical processes involved, I will follow the red thread of the major projects we have carried out at ISTerre, to paint a picture of this nano-bio-geochemistry, the progress made and the challenges ahead. I’ll introduce this scientific section with a glimpse into the career of an artist’s son.

The revival of low-carbon concrete

By Jean-Pascal Feltz (VINCI Construction, Director Civil Engineering SE Region) and Alejandro Fernandez-Martinez (CNRS, ISTerre)

Since time immemorial, mankind has been building structures to provide shelter, simplify movement, retain water, provide entertainment and display power. Over the centuries, these structures have become increasingly complex and resistant, thanks to the construction of stone and mortar structures, such as those inherited from the Romans. The 20th century saw the advent of reinforced concrete thanks to the invention of cement, a revolutionary binder with a major drawback in view of climate issues : its manufacture requires very high energy consumption and emits enormous quantities of CO2. Today, the building and civil engineering sector is the 2nd biggest carbon emitter, accounting for 8% of the total CO2 emissions. As a result, decarbonizing construction materials has become a major challenge for manufacturers. The main areas of focus are recycling by carbonation and reuse of materials, as on the site of the tunnel under the Alps for the Lyon-Turin rail link, and replacing cement in concrete manufacture with binders such as clays, requiring little energy for their manufacture.

Jean-Pascal Feltz’s presentation will review, from the industry point of view, the evolution of these new "low-carbon" concretes, their characteristics, and the constraints and obstacles to their development. One objective is to reach 90% of "low-carbon" concrete used by 2030, and as numerous examples show, we’re on the right track.

Alejandro Fernandez Martinez’s presentation will explore at the nanoscale crystallization processes via the formation of amorphous precursors in a cement (Portland) with a view to cement recycling, one of the methods making it possible to reduce the carbon footprint of concrete by sequestering CO2, but also by increasing their durability, as demonstrated by the study of Roman concretes.

Geo-bio-chemical-mechanical coupling in Earth science and toxicology

By Benjamin Gilbert, Lawrence Berkeley National Laboratory, USA

The mechanical properties of inorganic particles and their aggregates can exert major influences on the stability of soil, the deformation of rock, and the toxicity of engineered and natural nanomaterials. At the scale of cells and fine-grained soil particles, mechanical properties are determined both by intrinsic materials properties and by interfacial chemical interactions with water, solute ions and macromolecules. Moreover, chemical exchange and reaction can affect particle composition and strength leading to strong coupling between geo- or biochemical processes and mechanical properties causing time-varying behavior. This presentation will review prior and ongoing research that identified critical roles for such coupled processes and challenges and directions for observation and description.