Colorants, Volume 2, Issue 3 (September 2023) – 8 articles

Blue dyes are relatively uncommon in nature, and a novel dithiophene dye (RanB) is reported in this paper. This dye is derived from an old anti-osteoporotic drug and is a metal ion complexing agent, displaying a planar molecular structure, with two sets of carboxylate, isonitrile, thiophene, and iminodiacetate groups. The blue color originates from a strong absorption peak at 648 nm, accompanied by an unusual fluorescence at 555 nm, with higher energy compared to the main absorption band. RanB forms complexes with lanthanoid ions through the iminodiacetate groups and serves as an effective sensitizer for Tb³⁺ ions, heightening their emission and improving their use as luminescent agents. Its photo-physical properties and the interaction with Tb³⁺ have been investigated using absorption spectroscopy, steady-state and time-resolved fluorescence spectroscopy, along with computational methods (ZINDO/S and DFT). The RanB toxicity in human umbilical vein endothelial cells has also been tested, showing a lack of toxicity, holding promising prospects for application as a luminescent and coloring agent in pharmaceuticals and food. Full article

Zinc hydroxide nitrate (ZHN) was used as an anionic adsorbent for the removal of methyl orange (MO) dye from aqueous solutions. ZHN was characterized via X-ray diffraction (XRD) and infrared spectroscopy (FTIR) techniques. Investigations were carried out to see how the adsorption of MO was affected by factors such as initial MO concentration, contact time and temperature. Adsorption isotherms were analyzed using the Langmuir and Freundlich equations, with the first one being the better result for the equilibrium data. Adsorption kinetics was studied through applying pseudo-first and pseudo-second-order kinetic models, and the experimental data were better fitted to the pseudo-second-order model. The activation energy was determined using the Arrhenius equation to be 105.45 kJ mol⁻¹, revealing the chemical nature of the adsorption process. The thermodynamic parameters were also determined, showing the adsorption of MO onto ZHN to be a non-spontaneous and exothermic process. The experimental results showed ZHN as a potential adsorbent with adsorption capacity for removing anionic dyes from water medium. Full article

Surface fluorination with pure F₂ gas can easily make the surface on PP (polypropylene) hydrophobic, and it causes limited dyeability, as reported in a previous paper. In this study, to produce a more hydrophilic surface, surface fluorination of PP was performed at 25 °C, total gas pressure of 13.3 kPa, and reaction time of 1 h using F₂ and O₂ mixtures with different proportions of F₂ gas. The surface roughness of the fluorinated PP samples was about 1.5 times higher than that of the untreated sample (5 nm). Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy (XPS) results showed that the PP-derived bonds (-C-C- and -CH_x) decreased because they were converted into polar groups (-C–O, -CHF-, and -CF_x), which increased the surface electronegativity of the PP. The variation in the F₂ gas proportion in the gas mixture significantly affected the hydrophilicity and surface composition of the PP. At F₂ gas proportions of <70%, the hydrophilicity of the fluorinated PP samples was increased. Notably, the hydrophilic and negatively charged PP surface enhanced the dyeing of the polymer with basic methylene blue (MB). In contrast, at F₂ gas proportions of >90%, the PP surface became hydrophobic owing to increased numbers of hydrophobic -CF₃ bonds. Thus, enhanced PP dyeing can be controlled based on the composition of the F₂ and O₂ gas mixture. Full article

The 18th century roof tiles from the “Casa delle vigne”, located in the Aosta region (north-east Italy), were investigated as an example of a peculiar historical roof covering: ceramic tiles with a lead-based glaze finishing to waterproof them are used to create colourful patterns. A conservation project proposed the integration of the original tiles with new ones, produced according to traditional methods. Ancient and new tiles were analysed with Fiber Optics Reflectance Spectroscopy, micro-Raman, Fourier Transform Infrared Spectroscopy and X-ray Fluorescence Spectrometry, Thermogravimetry and Differential Scanning Calorimetry for understanding the composition and the production technology of this manufacture. Their resistance to freezing and thawing cycles was then tested, considering their exposure in the severe alpine climate of Aosta. The use of pure clays with low calcium contents, high firing temperature and lead-rich glazes was found in ancient tiles, able to outstand several freezing-thawing cycles without damages. Iron and copper pigments were used in old yellow and green glazes. Zinc-based pigment, low lead and calcium-rich glazes are used in the new ones, which remained mainly coherent to the ceramic body during the freeze-thaw test. Full article

In this study, a new red ceramic pigment has been developed within a perovskite structure, and microwave heat treatments have been applied. Those red ceramic pigments within the YAlO₃ system doped with chromium with the nominal composition Y_0.98Al_0.98Cr_0.04O₃ were synthesized by traditional routes and alternative methods like coprecipitation. Also, heat treatment has been studied comparing a traditional electric and microwave kiln. Different flux agents have been incorporated to improve the synthesis reaction. Prepared pigments have been characterized by X-ray diffraction (XRD) as having a predominant phase of perovskite structure, which is responsible for the red shade, and a minority garnet phase that causes more brown colorations. Studies by Ultraviolet-Visible spectroscopy gave rise to a series of absorption bands that indicate the presence of Cr(III) in the octahedral position corresponding to perovskite and Cr(IV) corresponding to garnet in both the octahedral and tetrahedral positions. The perovskite phase is favored with the use of flux mix, corroborating the UV-visible results and being more pronounced in traditional high temperature thermal treatments. The coprecipitation route has been studied to increase the reactivity of the particles given their nanometric size; however, this reactivity favors a greater appearance of undesirable garnet phases with both types of flux. Scanning Electron Microscopy (SEM) micrographs offer information obtained from the secondary electrons of predominantly cubic crystalline phases with sizes between 1 µm and 2 µm in pigments synthesized via the traditional method and sizes less than 1µm together with the glassy phase in pigments synthesized via coprecipitation. Microwave thermal treatments have been studied, obtaining pigments with a majority structure of perovskite and garnet at lower temperatures and relatively short synthesis times. The feasibility of use in porous single-fired ceramic glazes has been studied, whose chromatic coordinates have been collected using an Ultraviolet-Visible Spectrophotometer based on the CIEL*a*b* system. Full article

Contrary to the 4′- and 5′-nitro- and aminofluoresceins, the corresponding 3′-derivatives are practically unexplored. In this paper, we describe the synthesis and spectral properties of 3′-nitrofluorescein and 3′-aminofluorescein, as well as their methyl esters. Among other methods, X-ray analysis, ¹³C NMR spectroscopy, and ESI mass spectrometry made it possible to establish the molecular structure of the target compounds as well as intermediates and by-products. Some unexpected products, though in small amounts, were revealed within the course of study. Whereas the fluorescence of the double-charged R²⁻ ion of 3′-nitrofluorescein in both aqueous and organic solvents is weak, the R²⁻ anion of 3′-aminofluorescein in a non-hydrogen bonding donor solvent, but not in water, exhibits intensive fluorescence, analogous to the case of 4′- and 5′-aminofluoresceins. Interestingly, the ${\lambda }_{\max }$ values in water of the R²⁻ ions bearing an NO₂ group in the 3′- and 6′-positions are 7 to 10 nm higher than those of the 4′- and 5′-nitro derivatives. The difference was also observed in dimethyl sulfoxide. This correlates with the angles between the xanthene and phthalic planes of the dyes. The dye 3′-aminofluorescein could be used as a fluorescent indicator sensitive to hydrogen bonding ability of the solvent. It could also serve as a platform for synthesizing fluorescent molecular probes for biochemical research, analogous to the very popular application of 4′- and 5′-amino derivatives. Full article

In the present work, rock dust was evaluated as an adsorbent and heterogeneous photocatalyst in the discoloration of Basazol Yellow 46 L dye, which is widely used in the dyeing of molded pulp packages. Although rock dust is produced in large quantities in quarries as a byproduct of rock exploration, little is known about its application as a photocatalyst. Rock dust was characterized by XRD, SEM/EDS, photoacoustic spectroscopy, and N₂ physisorption and had its photocatalytic activity assessed through phenol and salicylic acid degradation tests. The characterization results showed that the rock dust is mainly composed of silica and alumina in a triclinic structure, has a bandgap energy of 2.36 eV, and has a specific area of 1.5 m²/g. Rock dust was proven to be photocatalytically active in phenol and salicylic acid degradation tests and also presented the adsorptive and photocatalytic capacity for the discoloration of effluent containing Basazol Yellow 46 L dye. Full article

Several medieval mural cycles in Austria were studied from the material and technical point of view, aiming to confirm (or reject) the art-historical hypothesis of their stylistic and workshop connection. These paintings can be found in the churches of Rust (“Fischerkirche”), Marz (Virgin’s Coronation parish church), Kobenz (St. Ruprecht parish church), Ofenbach (St. Veid parish church), and St. Johann am Steinfelde (St. John parish church). They were carried out around 1400 in the International Gothic style. Their workshop connections based on the style are doubtful, therefore, a material and technical study was carried out. Results showed different plaster composition, similar pigment palette, and diverse painting procedures. The murals in Marz, St. Johann, and the older register in Rust reveal important similarities such as plaster composition, predominant a fresco painting technique, the use of natural inorganic pigments, as well as many aspects of the painting procedure and modeling. On the contrary, those in Kobenz, Ofenbach, and the younger register in Rust differ considerably. The second group reveals lower quality in plaster composition, larger a secco parts, addition of synthetic pigments (Kobenz), and a rougher color modeling, indicating less skilled artists. The lower quality also results in a worse conservation state of these murals. The obtained results confirm the same workshop, but different artists in the first group, while in the second group no clear workshop/artist connection could be established. Full article