Beyond the Compositional Threshold of Nanoparticle-Based Materials

Abstract

The design of inorganic nanoparticles relies strongly on the knowledge from solid-state chemistry not only for characterization techniques, but also and primarily for choosing the systems that will yield the desired properties. The range of inorganic solids reported and studied as nanoparticles is however strikingly narrow when compared to the solid-state chemistry portfolio of bulk materials. Efforts to enlarge the collection of inorganic particles are becoming increasingly important for three reasons. First, they can yield materials more performing than current ones for a range of fields including biomedicine, optics, catalysis, and energy. Second, looking outside the box of common compositions is a way to target original properties or to discover genuinely new behaviors. The third reason lies in the path followed to reach these novel nano-objects: exploration and setup of new synthetic approaches. Indeed, willingness to access original nanoparticles faces a synthetic challenge: how to reach nanoparticles of solids that originally belong to the realm of solid-state chemistry and its typical protocols at high temperature? To answer this question, alternative reaction pathways must be sought, which may in turn provide tracks for new, untargeted materials. The corresponding strategies require limiting particle growth by confinement at high temperatures or by decreasing the synthesis temperature. Both approaches, especially the latter, provide a nice playground to discover metastable solids never reported before. The aim of this Account is to raise attention to the topic of the design of new inorganic nanoparticles. To do so, we take the perspective of our own work in the field, by first describing synthetic challenges and how they are addressed by current protocols. We then use our achievements to highlight the possibilities offered by new nanomaterials and to introduce synthetic approaches that are not in the focus of recent literature but hold, in our opinion, great promise. We will span methods of low temperature "chimie douce" aqueous synthesis coupled to microwave heating, sol-gel chemistry and processing coupled to solid state reactions, and then molten salt synthesis. These protocols pave the way to metastable low valence oxyhydroxides, vanadates, perovskite oxides, boron carbon nitrides, and metal borides, all obtained at the nanoscale with structural and morphological features differing from "usual" nanomaterials. These nano-objects show original properties, from sensing, thermoelectricity, charge and spin transports, photoluminescence, and catalysis, which require advanced characterization of surface states. We then identify future trends of synthetic methodologies that will merit further attention in this burgeoning field, by emphasizing the importance of unveiling reaction mechanisms and coupling experiments with modeling.

Structural, Magnetic, and Catalytic Evaluation of Spinel Co, Ni, and Co–Ni Ferrite Nanoparticles Fabricated by Low-Temperature Solution Combustion Process

“…A ligand- or surfactant-free aqueous synthesis process generates nanoparticles of organic species-free surfaces, ready for catalysis and sensing. 29 Solution combustion is a method that allows the synthesis of nanoscale materials through mixing metal salts, a fuel (urea, glycine, citric acid, etc.) and an oxidizing agent (HNO 3 , NO 3 – ions of the precursor salts, etc.…”

Structure–Activity Relationship in Manganese Perovskite Oxide Nanocrystals from Molten Salts for Efficient Oxygen Reduction Reaction Electrocatalysis

“…The manganite perovskite particles we report exhibit small sizes and organic ligand-free surfaces that are beneficial for charge transfer at the electrocatalyst interfaces, hence for electron percolation in the electrode, and for adsorption of dioxygen reagent. They also exhibit low amounts of crystal defects, again beneficial for charge transport , compared to sol–gel-derived materials. Hence, the approach delivers highly active and stable manganite perovskite ORR electrocatalysts.…”

“…Hence, the approach delivers highly active and stable manganite perovskite ORR electrocatalysts. In addition to the pseudocubic manganite La 0.7 Sr 0.3 MnO 3 , , we synthesize the first layered manganite La 0.5 Sr 1.5 MnO 4 RP nanoparticles by tuning the oxo basicity of the molten medium. We report for the first time the mechanisms of nanoparticles formation in high-temperature molten salts and highlight the key experimental parameters enabling structural control.…”

Ultrasound‐Assisted Liquid‐Phase Synthesis and Mechanical Properties of Aluminum Matrix Nanocomposites Incorporating Boride Nanocrystals

“…[7][8][9][10][11] The continuous development of nanoparticle synthesis approaches, especially the emergence of molten salts synthesis offers an alternative solution. 12 Several classes of nanoparticles including borides, nitrides, carbides and silicides have been synthesized in molten salt solvents. 13 The use of inorganic molten salts as high temperature solvents (300 to 900 °C) could lead to nanoparticles stable at the processing temperature of liquid metallurgy.…”