Thermal stability is a critical property of nanoparticles that determines their suitability for high-temperature applications such as catalysis, coatings, and energy storage. Thermogravimetric analysis (TGA) is a widely used technique to evaluate this stability by measuring mass changes as a function of temperature under controlled atmospheres. The method provides insights into decomposition temperatures, oxidation resistance, and degradation mechanisms, all of which are influenced by factors such as surface functionalization, capping agents, and core composition.

The core material of nanoparticles plays a fundamental role in their thermal stability. Metal oxides like titanium dioxide (TiO2) and zinc oxide (ZnO) exhibit high thermal resistance, often remaining stable up to 800°C or higher, depending on crystallinity and phase composition. In contrast, organic or polymer-based nanoparticles degrade at much lower temperatures, typically between 200°C and 400°C, due to the breakdown of molecular bonds. Metallic nanoparticles, such as gold or silver, may show stability in inert atmospheres but can oxidize rapidly in air at elevated temperatures. For example, silver nanoparticles begin oxidizing around 200°C, forming silver oxide, which is detectable as a mass gain in TGA curves.

Surface functionalization significantly impacts thermal stability. Ligands or surfactants used to stabilize nanoparticles during synthesis often decompose at relatively low temperatures, leading to mass loss. For instance, citrate-capped gold nanoparticles show a distinct mass loss step between 150°C and 300°C due to the combustion of organic species. Similarly, oleylamine-coated iron oxide nanoparticles exhibit degradation around 250°C as the capping agent burns off. The choice of functional group thus directly influences the upper temperature limit for nanoparticle applications. Inert coatings like silica shells can enhance stability by acting as a barrier against oxidation, delaying degradation to higher temperatures.

Capping agents not only prevent aggregation but also introduce vulnerabilities in thermal performance. Thiol-based ligands, commonly used for gold and quantum dots, degrade between 200°C and 350°C, while polymeric stabilizers like polyvinylpyrrolidone (PVP) decompose in stages, with initial weight loss starting near 200°C and continuing up to 500°C. The removal of these agents can lead to particle agglomeration, further accelerating degradation. TGA profiles often reveal multi-step decomposition processes, where each step corresponds to the loss of different organic components or the onset of core material oxidation.

Degradation mechanisms observed in TGA include desorption, decomposition, and oxidation. Desorption of physisorbed water or solvents typically occurs below 150°C, followed by ligand decomposition at higher temperatures. In oxidative environments, metals and some semiconductors undergo mass gain due to oxide formation. For example, copper nanoparticles show a sharp mass increase above 300°C as they convert to copper oxide. Non-oxidative atmospheres like nitrogen or argon may reveal sublimation or reduction effects instead. The shape of TGA curves—whether sharp or gradual—provides clues about reaction kinetics and the homogeneity of the nanoparticle sample.

Oxidation resistance is a key consideration for nanoparticles in high-temperature applications. Materials like carbon nanotubes and graphene exhibit excellent stability in inert conditions but oxidize rapidly in air above 400°C, forming CO2 and resulting in mass loss. Doping or functionalization can alter this behavior; nitrogen-doped carbon nanostructures, for instance, show delayed oxidation onset due to the incorporation of more stable bonds. Similarly, alloying metallic nanoparticles with refractory metals like platinum or palladium can enhance their oxidation resistance, shifting degradation to higher temperatures.

Applications demanding thermal stability benefit from TGA-guided material selection. In catalysis, nanoparticles must withstand reaction temperatures without sintering or losing activity. For example, platinum nanoparticles supported on alumina retain structural integrity up to 600°C, making them suitable for automotive catalytic converters. Thermal barrier coatings incorporating yttria-stabilized zirconia nanoparticles rely on their stability above 1000°C to protect turbine blades. Energy storage materials, such as silicon nanoparticles in lithium-ion battery anodes, must resist degradation during cycling, where localized heating can exceed 300°C.

The interpretation of TGA data requires careful consideration of experimental conditions. Heating rate influences observed degradation temperatures; faster rates may shift peaks to higher values due to thermal lag. Gas flow rate and composition also play critical roles, as oxidative versus inert environments produce vastly different profiles. Sample preparation, including packing density and particle dispersion, can affect heat transfer and mass loss uniformity. Baseline corrections and derivative thermogravimetry (DTG) analysis help distinguish overlapping processes, such as simultaneous ligand decomposition and core oxidation.

Limitations of TGA include its inability to provide direct morphological or structural information. Complementary techniques like X-ray diffraction or electron microscopy are often needed to correlate mass changes with phase transformations or particle sintering. Nevertheless, TGA remains indispensable for screening nanoparticle stability, optimizing synthesis protocols, and predicting performance in extreme environments. Future developments may involve high-pressure TGA to simulate industrial process conditions or coupled gas analysis to identify evolved species during degradation.

In summary, TGA provides a robust framework for assessing the thermal stability of nanoparticles, with key insights derived from mass loss profiles, oxidation behavior, and degradation thresholds. Core composition, surface chemistry, and environmental conditions collectively determine performance limits, guiding the design of nanomaterials for demanding applications. By understanding these factors, researchers can engineer nanoparticles with tailored stability, ensuring reliability in high-temperature settings.