Colorants

Water hyacinth (Eichhornia crassipes) is one of the most invasive plants around the world. In the state of Hidalgo, Mexico it has invaded several water bodies. Nevertheless, its management is an ongoing challenge because of its rapid growth and the expensiveness of its removal. Therefore, alternatives to valorize its biomass are needed. One of them is the production of optical materials from it. Past reports have demonstrated the viability to obtain fluorophores from lignin and that it is present in E. crassipes biomass. Nevertheless, most works focus on its extraction using harsh process conditions and strong acids or alkalis. No reports about the use of E. crassipes in such processes exist. As the demand for more environmentally friendly processes increases, avoidance of such chemicals is needed. Therefore, in this work the extraction of fluorophores directly from biomass of E. crassipes via a hydrothermal process using water as the sole solvent and catalyzer was studied. The liquid to solid ratio (LSR) varied from 25 to 50 and time from 8 to 16 h. Biomass was almost completely dissolved. Fluorophores with different photoluminescent emissions were obtained. Their extraction was confirmed by photoluminescence spectroscopy. The emission of the obtained materials could be tuned by changing processing time and LSR.

In this work, molecular and elemental spectroscopic analyses were carried out on the preparation base, the paintings, the repaintings, and the gilding of an 18th century sacred sculpture of Our Lady found on Anhatomirim Island, where the Santa Cruz fortress was built in 1739 in the state of Santa Catarina, southern Brazil. The preparation base of the sculpture was characterized as gypsum (calcium sulfate dihydrate, (CaSO₄.2H₂O) [µ-Raman, SEM-EDS], applied directly to the wooden support. The blue paint comprised a mixture of Prussian blue (Fe₄[Fe(CN)₆]₃) and ultramarine (Na_xAl₆Si₆O₂₄S_x) [µ-Raman, FTIR, SEM-EDS]; hematite (Fe₂O₃) was identified in the brown paint [µ-Raman, SEM-EDS]; and the white paint consisted of lead white (2 PbCO₃·Pb(OH)₂) [µ-Raman, FTIR, SEM-EDS]. Repainted areas were identified by the presence of lithopone (ZnS + BaSO₄) [µ-Raman, SEM-EDS, FTIR], likely resulting from later interventions. In the gilded areas, gold was identified along with traces of iron [SEM-EDS], indicating a lower-quality gilding compared to, for example, silver alloys. Lead white was also identified in the polychrome areas, where it served to produce different tones in the painting. FTIR analyses revealed traces of aged oil used as a binder in the older layers. Mineral oil was detected in some samples, which may indicate that wax was used as a protective layer on the sculpture. The results will assist professionals in the iconographic characterization of the sacred image of Our Lady and in the conservation and restoration processes based on the identified constituent materials.

This study investigates effective antioxidants to stabilize chlorophyll, a valuable and most abundant but unstable natural green pigment, adsorbed on a silica surface. Although fixing chlorophyll on silica offers some protection, significant photo-induced oxidative degradation still occurs. To enhance photostability, the prepared chlorophyll–silica composites were combined with various well-known antioxidants. The stability of these samples was evaluated by the deterioration ratio of the chlorophyll under visible light irradiation. The results showed that gallic acid provided the most significant stabilization effect. This was attributed to its moderate hydrophilicity, allowing it to be positioned near the chromophore part of the chlorophyll molecule adsorbed on the silica surface. Further tests with the derivatives of gallic acid revealed that smaller molecular size and less steric hindrance were also crucial for effectiveness as an antioxidative stabilizer. Pyrogallol and gallic acid, being the smallest molecules, performed best. It was concluded that the ability of an antioxidant to approach a chlorophyll molecule is essential for stabilization. This requires an appropriate balance of hydrophilicity and a small molecular size. Considering the nontoxicity together, gallic acid is recommended as a superior stabilizer for chlorophyll on silica surfaces.