Bio-Inspired Fluorescent Calcium Sulfate for the Conservation of Gypsum Plasterwork
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2024-06-28Sponsorship
This research was funded by Spanish Government grant RTI2018-099565- B-I00; Spanish Government grant PID2021.125305NB.I00 funded by MCIN/AEI/10.13039/501100011033 and by ERDF “A way of making Europe”; Junta de Andalucía research group RNM-179; and University of Granada, Unidad Científica de Excelencia UCE-PP2016-05. M.B.-R. was granted with a predoctoral position funded by the Spanish Government (PRE2019-090256). This research was performed within the frame of the inter-institutional collaboration agreement “Patrimonio Cultural Árabe e Islámico (PACAI), UGR, Unidad Asociada al CSIC por la EEA-ILC (2024- 2027)”. HR-XRD analyses were performed at the SOLEIL Synchrotron Facility, with the invaluable technical assistance of E. Elkaim (CRISTAL Beamline, SOLEIL Synchrotron) and L. Monasterio-Guillot (Instituto Andaluz de Ciencias de la Tierra, CSIC). We are grateful for the cooperation of the Leeds Electron Microscopy and Spectroscopy Centre (LEMAS), at the University of Leeds, with the TEM measurements in both cryogenic and noncryogenic conditions. TEM analyses were also carried out at the Centro de Instrumentación Científica (CIC), UGR. Open access was funded by the University of Granada/CBUA.Abstract
In this work, the potential of bio-inspired strategies for the synthesis of
calcium sulfate (CaSO4·nH2O) materials for heritage conservation is explored.
For this, a nonclassical multi-step crystallization mechanism to understand
the effect of calcein– a fluorescent chelating agent with a high affinity for
divalent cations— on the nucleation and growth of calcium sulfate phases is
proposed. Moving from the nano- to the macro-scale, this strategy sets the
basis for the design and production of fluorescent nano-bassanite (NB-C;
CaSO4·0.5H2O), with application as a fully compatible consolidant for the
conservation of historic plasterwork. Once applied to gypsum (CaSO4·2H2O)
plaster specimens, cementation upon hydration of nano-bassanite results in a
significant increase in mechanical strength, while intracrystalline occlusion of
calcein in newly-formed gypsum cement improves its weathering resistance.
Furthermore, under UV irradiation, the luminescence produced by calcein
molecules occluded in gypsum crystals formed upon nano-bassanite
hydration allows the easy identification of the newly deposited consolidant
within the treated gypsum plaster without altering the substrate’s appearance.