Air-Exposure-Driven Color and Optical Variations in Hydroxyapatite Extracted from Fish Scales

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dc.contributor.authorOkur, H. Esma
dc.date.accessioned2026-02-08T15:11:02Z
dc.date.available2026-02-08T15:11:02Z
dc.date.issued2025
dc.departmentBursa Teknik Üniversitesi
dc.description.abstractThe disposal of fish scales as waste presents an environmental challenge and an untapped opportunity for resource recovery. In this study, hydroxyapatite (HAp) was extracted from European seabass (Dicentrarchus labrax) scales to explore how air exposure during calcination affects its optical and surface properties. HAp powders were prepared under two distinct calcination conditions: fully exposed to air (producing white powder) and partially shielded from air (resulting in gray powder). Rietveld refinement of X-ray powder diffraction (XRPD) data confirms that both powders crystallize in the hexagonal HAp structure, with a minor Mg-whitlockite impurity. Despite these differences in air exposure, the bulk structure of the HAp remains unchanged. The color variations are linked to surface oxidation, as subsurface layers in the partially shielded scales retain a grayish tone while the exposed surfaces turn completely white. Scanning electron microscopy reveals subtle differences in particle morphology: the white powder had a smoother surface compared to the slightly rougher gray powder. Fourier transform infrared spectra confirm the presence of characteristic phosphate and hydroxyl groups in both powders, indicating that the core chemical structure of HAp is intact in both cases. The Ca/P ratios—1.504(7) for the white powder and 1.505(7) for the gray powder obtained from the Rietveld analysis—further support the stoichiometric integrity of the material. UV-Vis spectroscopy reveals direct bandgap values of 3.99 eV for the white powder and 3.87 eV for the gray powder. These bandgap values, which are lower than those typically reported for defect-free HAp (5–6 eV), suggest that the optical differences between the powders are driven by surface effects, such as oxygen vacancies or trace impurities. This study highlights how calcination conditions, particularly air exposure, influence surface properties and optical behavior, paving the way for potential applications of fish-scale-derived HAp in electronic and optical materials. © 2025, Sakarya University. All rights reserved.
dc.identifier.doi10.16984/saufenbilder.1589238
dc.identifier.endpage139
dc.identifier.issn1301-4048
dc.identifier.issue1
dc.identifier.scopus2-s2.0-86000089596
dc.identifier.scopusqualityQ3
dc.identifier.startpage125
dc.identifier.trdizinid1302330
dc.identifier.urihttps://doi.org/10.16984/saufenbilder.1589238
dc.identifier.urihttps://search.trdizin.gov.tr/tr/yayin/detay/1302330
dc.identifier.urihttps://hdl.handle.net/20.500.12885/5179
dc.identifier.volume29
dc.indekslendigikaynakScopus
dc.indekslendigikaynakTR-Dizin
dc.language.isoen
dc.publisherSakarya University
dc.relation.ispartofSakarya University Journal of Science
dc.relation.publicationcategoryMakale - Uluslararası Hakemli Dergi - Kurum Öğretim Elemanı
dc.rightsinfo:eu-repo/semantics/openAccess
dc.snmzScopus_KA_20260207
dc.subjectAir exposure
dc.subjectBand gap
dc.subjectFish scales
dc.subjectHydroxyapatite
dc.subjectRietveld refinement
dc.titleAir-Exposure-Driven Color and Optical Variations in Hydroxyapatite Extracted from Fish Scales
dc.title.alternativeBalık Pullarından Elde Edilen Hidroksiapatitin Renk ve Optik Özelliklerinde Hava Maruziyetine Bağlı Değişimler
dc.typeArticle

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