Thermal analysis methods have a wide range of nanotechnology applications, including the characterization of nanomaterials during synthesis and the control of final product properties. This article discusses the use of thermogravimetric analysis (TGA) in the rapidly expanding field of nanotechnology research.
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What is Thermogravimetric Analysis?
TGA, or thermogravimetric analysis, determines mass or changes in mass as a function of temperature. The mass of material is monitored continuously during thermogravimetric analysis as it is heated or cooled in a specified atmosphere. As a result, TGA is primarily used to comprehend specific thermal events such as desorption, adsorption, sublimation, vaporization, reduction, and oxidation.
In thermogravimetric analysis, the material sample is heated and subjected to thermal decomposition in a controlled atmosphere up to 1000 °C to record the mass change. Before the heating ramp begins, thermogravimetric analysis initially measures the mass of the sample.
As the temperature increases, the pyrolysis of organic substances and polymer starts. At about 600 °C, the atmosphere is switched from nitrogen to air to achieve oxidative condition. After the sample is heated to 1000°C, the inorganic substances remain behind as a residue at the end. The step due to mass loss provides valuable information about the material's composition, such as polymer and filler content.
The TGA curve depicts typical mass loss as a function of temperature, and the corresponding first derivative (DTG) graph depicts mass loss rate as a function of temperature. Distinct peaks are displayed on the TGA curve with the temperature of maximum mass decomposition rates (Tmax) in particular ranges, which can aid in understanding the sample's purity.
Thermogravimetric Analysis (TGA) in Nanotechnology
Thermogravimetric analysis is used to study the processes like vaporization and decomposition, as well as to perform compositional analysis. TGA combined with Fourier transform infrared spectroscopy (FTIR) can be used to analyze volatile products released by the sample. The technique provides information on the stability of nanomaterials or the matrix in which they are embedded.
When combined with mass spectroscopy, thermogravimetric analysis can detect very low concentrations of impurities in evolved gases in real-time.
Investigating Carbon-Based Nanomaterials with Thermogravimetric Analysis
Thermogravimetric analysis is one of the quickest techniques for determining the relative proportions of amorphous carbon, adsorbed hydrocarbon, structured carbon, and metal catalyst particles in a CNT powder sample.
The observed temperatures of oxidation for amorphous carbons are around 200 °C, 400 °C for single-wall carbon nanotubes, 600 °C for multi-wall carbon nanotubes, and anything above 650 °C is credited to a metal catalyst and its oxidation products.
Thermogravimetric analysis can provide a measure of purity for CNT materials by calculating the percentage of the sample that degrades at the desired temperature range. Thermogravimetric analysis is also useful for studying carbon nanotubes' thermal behavior in an oxidative environment.
Similarly, thermogravimetric analysis is a reliable analytical tool for characterizing and controlling the quality of powdered few-layer graphene (FLG) and non-graphene impurities. The derivative TGA curves of graphene oxide, FLG, and graphite powders have distinct peaks with a temperature of maximum mass decomposition rates (Tmax) in specific ranges, which can aid in distinguishing few-layer graphene from fake graphene.
Thermogravimetric Analysis for Nanoparticles
Nanocalorimetry is a microchip-based system that can measure the thermal properties of samples in nanolitres or nanograms at very fast rates. Due to the small sample volumes, it is possible to measure interactions between nanomaterials and cells, which is important in nanomedicine.
Using nanocalorimetry has aided in the understanding of binding reactions between biological systems and nanoparticles, melting behavior and particle crystallization, and size-dependent thermodynamics and kinetics.
Further Applications of Thermogravimetric Analysis
Thermogravimetric analysis and DSC can be used to assess crystallization behaviors and the interaction of drug nanoparticle-based delivery systems. For example, to assess the interactions of indomethacin, a lipophilic drug, and solid lipid nanoparticles designed for pharmaceutical drug delivery.
Proteins or lipid layers are now being coated onto nanoparticles such as carbon nanotubes (CNTs) for biomedical applications. Microscale thermogravimetric analysis is frequently used to assess the purity and amount of surface coating.
Catalytic properties of zeolites are determined by the distribution of acid sites. Thermogravimetric analysis is used to determine the relative strength of a catalyst.
Nanocomposites are materials in which nanoparticles are infused with a matrix material to enhance their electrical, optical, or magnetic properties. Thermal analysis methods are frequently used to investigate the differences between the matrix and the matrix with nanoparticles incorporated.
Future Prospectives and Limitations of Thermogravimetric Analysis (TGA)
Thermogravimetric analysis techniques and the determination of thermophysical properties through thermal analysis provide a wealth of information on nanoparticle-containing materials.
The primary limitation of thermogravimetric analysis methods is that mass loss of volatiles does not equal degradant formation. As a result, mass loss should only be regarded as an indicator of degradation. Nevertheless, thermogravimetric analysis is an extremely useful tool for interpreting the thermal events associated with nanomaterials.
References and Further Reading
Loganathan, S., Valapa, R., Mishra, R., Pugazhenthi, G. and Thomas, S., (2017) Thermogravimetric Analysis for Characterization of Nanomaterials. Thermal and Rheological Measurement Techniques for Nanomaterials Characterization, pp.67-108. https://doi.org/10.1016/B978-0-323-46139-9.00004-9
Farivar, F., Yap, P., Hassan, K., Tung, T., Tran, D., Pollard, A. and Losic, D., (2021) Unlocking thermogravimetric analysis (TGA) in the fight against “Fake graphene” materials. Carbon, 179, pp.505-513. https://doi.org/10.1016/j.carbon.2021.04.064
Buzarovska, A., Stefov, V., Najdoski, M. and Bogoeva-Gaceva, G., (2022) Thermal analysis of multi-walled carbon nanotubes material obtained by catalytic pyrolysis of polyethylene. Macedonian Journal of Chemistry and Chemical Engineering. http://dx.doi.org/10.20450/mjcce.2015.620