The chemical industry faces the urgent challenge of reducing its carbon footprint and developing sustainable synthesis pathways to advanced functional materials. As solvents account for a large fraction of the mass and energy inputs in chemical manufacturing, innovation in solvent systems offers a powerful route toward more sustainable processes. In this context, we explore water as a highly versatile and sustainable reaction medium for the synthesis and processing of chemically diverse materials, reducing reliance on conventional organic solvents.

Under hydrothermal conditions (i.e., water above its boiling point, T >100 °C), key physicochemical properties of H₂O, including dielectric constant, density, ionic product, viscosity, and solvation characteristics, change dramatically with temperature. These changes enable control over solubility, reactivity, transport phenomena, and phase behavior, effectively expanding the accessible reaction space without reliance on hazardous organic solvents. Geological processes within the Earth’s crust provide a natural precedent, demonstrating that aqueous environments can generate inorganic, organic, and hybrid compounds across a wide range of bonding motifs and structural hierarchies.

In this presentation, we highlight selected case studies illustrating how hydrothermal synthesis provides access to a broad spectrum of chemical systems. These examples span diverse molecular architectures (small molecules, polymers, networks), structural orders (amorphous, crystalline, semicrystalline), bonding types (covalent, metallic, ionic), and chemical compositions (organic, inorganic, hybrid). Finally, we demonstrate how integrating hydrothermal synthesis platforms with automation and high-throughput experimentation enables systematic exploration of a largely unexplored aqueous chemical space. By combining green solvent principles with digitally accelerated discovery, water-based materials chemistry emerges as a scalable strategy for sustainable innovation in synthesis and processing.