Simultaneous TG-FTIR analyses on molluscan shells: Characterization and thermal stability of organic-inorganic components

• Published in: Chemical geology 2022-11, Vol.611, p.121132, Article 121132
• Main Authors: Chaudhari, Rahul R., Bhongale, Chetan J.
• Format: Article
• Language: English
• Subjects: Aragonite; Biomineralization; Molluscan shells; Nanocomposite; TGA-FTIR
• ISSN: 0009-2541; 1872-6836
• DOI: 10.1016/j.chemgeo.2022.121132

Here we demonstrate simultaneous analysis of evolved gases by thermogravimetry (TG) coupled with Fourier Transform Infra-red (FTIR) spectroscopy and correlate the weight losses with water, CO2 and other possible gaseous products evolved during progressive thermal degradation of shells of various mollusc species (gastropods and bivalves) in an inert atmosphere. Subsequent interpretation of the functional groups present in the sea shells is carried out. Our study infers that the water molecules and to some extent CO2 are continuously getting emitted during progressive thermal degradation of sea shells during stage-I with just about 1–2% weight loss. No peaks related to amides, carboxylic acid functionality or thermal degradation products thereof are observed during this stage. These degraded products are either from associated water and non-mineral carbonate species or from low molecular weight biomacromolecules. This, contrary to usually accepted data, shows organic matrix (mixture of organic components/proteins) do not degrade completely in the first step (lower temperature), indicating their presence with strong bonding in inter-platelet regions and also probably in the crystal lattice of mineral phase and reveals greater thermal stability of the organic matrix in mollusc shells. Our findings enable previous studies, both quantitative and qualitative, to be re-evaluated resulting in a more consistent and inclusive view of organic matrices and water with potential implications in biomineralization processes. Simultaneous TG-FTIR analysis on molluscan shells show no significant peaks for functionality like amides, carboxylic acid, or thermal degradation products thereof in gas phase FTIR spectra in both the stages I and II of linear thermal degradation, apart from calcitic CO2 liberation; indicating very high thermal stability of organic proteinous matrix in the biomineral composite. [Display omitted] •The biominerals are formed within the framework of the organic matrix comprising of various macromolecules like the polysaccharide β-chitin.•Generally, these organic matrices are considered to be degraded between 200 and 450 °C (stage-I) during linear thermal analysis.•Simultaneous TG-FTIR hyphenated studies on molluscan shells reveal very high thermal stability of organic matrix.•These findings enable previous studies, both quantitative and qualitative, to be re-evaluated resulting in a more consistent and inclusive view of organic matrices.