Colorants

Textile dyes often prove resistant to conventional wastewater treatment processes because of their complex molecular structures. Advanced oxidation methods, such as the Fenton reaction, have thus been recognized as a promising approach for environmental remediation by decomposing these pollutants. This work aimed to study the efficacy of modified zeolites as catalysts in the Fenton reaction for dye degradation, with a particular emphasis on techniques for modifying zeolites and incorporating iron. The zeolite ZSM-5 was selected as the parent structure and underwent desilication and acid treatment procedures. Iron was introduced into the zeolite structure via two distinct methods: ion exchange and mechanochemistry. The modified zeolites with incorporated iron were evaluated in terms of their crystallinity, textural properties, and iron content before being used to degrade methylene blue solutions through the Fenton reaction. The reaction was monitored using UV-Vis spectroscopy, while the experimental outcomes were analyzed using pseudo-first-order and pseudo-second-order kinetic models. The research findings indicate that different treatment methods led to varying impacts on the zeolite properties, which in turn influenced the kinetic results. Moreover, it was observed that an enhancement in the degradation process can be achieved through the harmonious balance between a high iron content, increased mesoporosity (to facilitate diffusion), and adequate crystallinity (essential for maintaining structural integrity). Full article

A series of compounds with both urea and urethane moieties have been developed as color developers for high-performance thermo-sensitive paper. The compounds have lower environmental loads than conventional phenolic developers. They were also found to greatly improve the speed of the printed images. In this study, we studied the coloring mechanism of the compounds when used as developers for a fluoran dye, and we investigated the stability of the colored solid state. The urea–urethane compounds were found to form black amorphous solids with the fluoran dye. Infrared (IR) measurements of the black solids, based on six urea–urethane derivatives, revealed that the colored dye has a ring-opened structure in a carboxylic acid form and that the urea group works as a proton donor for the ring-opening reaction. The stability of the black amorphous solids was also evaluated using thermal analysis and molecular orbital calculations in addition to IR data. The results indicate that the number of urea–urethane units and the planarity of the urea moiety are important parameters for the stability of the colored solid state. Full article

The use of indigo carmine dye in the textile industry, particularly in denim production, presents a significant sustainability challenge due to the large amounts of wastewater generated by this process, since this fabric is one of the most produced around the world. In order to face challenges like this, effluent treatment using polymeric materials has become an area of intense research. In this study, we developed an eco-friendly hydrogel based on oligoglycerol-malic acid polyester crosslinked with citric acid, which was applied to adsorb indigo carmine. The properties of the hydrogel and its precursors were analyzed using spectroscopic, thermal, and morphologic techniques. The hydrogel demonstrated water uptake capacity up to 187% of its own mass and adsorbed approximately 73% of the dye after 24 h of contact. Tests were conducted in the presence of sodium chloride and indicated that the presence of salt impairs the adsorption process. Additionally, the adsorption kinetics and isotherms were evaluated and demonstrated that the adsorption followed a pseudo-second-order model, indicating a chemisorption process, and a Langmuir isotherm, consistent with a monolayer adsorption. These results emphasize the potential of this hydrogel for removing dye and its application in textile industry wastewater treatment, aiming to minimize environmental impacts. Full article

Water contamination caused by dyes from increased human activities, in particular usage in the textile sector, has led to high rates of disposal of both natural and synthetic dyes in the water stream, affecting the color and the ability of the light to penetrate through the water system. Several methods have been used for the removal of these organic pollutants. However, due to the complex nature of these dyes, researchers have geared toward advanced oxidation processes (AOPs). This method allows for the degradation of these pollutants into more environmentally friendly pollutants. Green synthesis of known catalysts has been on the rise, in particular nickel oxide (NiO) NPs. This material has been shown to have the ability to degrade several pollutants. However, due to the high recombination rate and large bandgap, their limitation has also been highlighted along with the importance of modification. Thus, it is important to understand the work and progress made on green NiO as a photocatalyst for the degradation of dyes and the latest advancements in the field. Full article

The detection of reactive dyes in food matrices is crucial for food safety and compliance with regulations, especially since the use of such in food products is not approved. This study investigates the potential of using tin(II)chloride and laccase to cleave anthraquinone reactive dyes and to detect their characteristic degradation products as markers for the presence of dye in food. Nine reactive blue anthraquinone dyes and one green anthraquinone dye were cleaved using tin(II)chloride and laccase. Reactions with reactive dyes bound to maize starch were also carried out to evaluate the suitability of these methods for detecting matrix-bound dyes. Model food matrices, including gummy candy, hard candy, and maize chips, were spiked with the reactive dyes, and the presence of degradation products was analysed using LC-ESI-MS/MS. Two common cleavage products were formed from each sample, namely 1,4-diaminoanthrahydroquinone-2-sulphonic acid (DAHS) and 1-aminoanthraquinone-2-sulphonic acid (AAS). In all examined cases, at least one of the characteristic cleavage products could be detected. Laccase showed lower effectiveness with matrix-bound dyes, whereas treatment with acidic tin(II)chloride was effective even in complex food matrices. These findings suggest that the analysis of cleavage products could be a valuable tool for the detection of reactive dyes in food matrices. Full article

Photodynamic therapy (PDT) is a light-activated chemical reaction used for the selective destruction of tissue. For this, various colorants may be applied, such as erythrosine (ERI), a dye already approved by the Food and Drug Administration (FDA) for various purposes. Although promising for PDT, ERI has a high hydrophilic profile that impacts its activity. To solve this, the combination of ERI with thermoresponsive and bioadhesive polymers may prove effective. Bio/mucoadhesive and thermoresponsive systems have attracted increasing interest in the development of novel pharmaceutical formulations for topical applications due to their ability to improve adhesion to the mucosa and prolong the residence time at the application site. In this study, systems based on poloxamer 407 (P407) in combination with cellulose derivatives (HPMC and NaCMC) were optimized, aiming at the topical release of ERI for PDT. The results demonstrated that the formulations containing low concentrations of cellulose derivatives exhibited greater adhesiveness and consistency at physiological temperature (37 °C), favoring the maintenance of the system at the application site. Regarding the gelation temperature (T_sol/gel), the formulations displayed values close to body temperature. The formulations with NaCMC showed a slightly higher T_sol/gel compared to HPMC ones, but it was adjustable by the polymer concentration. The addition of ERI influenced the mechanical and adhesive properties of the systems. In formulations containing HPMC, high concentrations of ERI increased bio/mucoadhesiveness, while in systems with NaCMC, the presence of ERI reduced this property. In both cases, the formulations maintained high consistency at 37 °C, contributing to the control of the active release at the application site. Rheological analysis revealed non-Newtonian behavior in all formulations, with greater consistency and elasticity at high temperatures. P407 was mainly responsible for the thermoresponsive transition from sol to gel, conferring desirable characteristics for topical application. Photodynamic activity was relevant in both formulations containing NaCMC and HPMC, which demonstrated greater capacity for degrading uric acid under light exposure. These systems are promising for the controlled release of drugs in photodynamic therapy, providing prolonged retention in the target tissue and maximizing the therapeutic efficacy of ERI. Full article

The effects of photochemical reactions induced by UV radiation in solutions of metal phthalocyanines were carried out to determine the factors that might influence the photostability of photosensitized phthalocyanines. Three different indium phthalocyanines, including the diindium triple-decker phthalocyanine, In₂Pc₃ (1), sandwich indium phthalocyanine, InPc₂ (2) and iodoindium phthalocyanine, InPcI (3) in benzene, N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), dichloromethane (DCM) and 1-chloronaphtalene, were studied. The rate of decay of absorption is explained by a decomposition reaction that is of first-order kinetics with respect to the phthalocyanine concentration. In general, the presence of ligand I⁻ in phthalocyanine InPcI enhances the rate of decomposition. The kinetics of the degradation process proved to depend on the molecular structure of the complex and seems to be controlled by interactions of the macrocycle bridging nitrogen atoms with the solvent molecules. The indium phthalocyanines in benzene displayed the capacity for singlet oxygen generation. Full article

In this study, hybrid materials were synthesized incorporating curcumin, Cu²⁺ or Fe³⁺, and Kappa-carrageenan as a reducing agent to improve stability, considering that curcumin has low thermal and solution stability, which limits its applications. Colorimetric analysis showed color changes in the hybrids, ultraviolet–visible spectroscopy revealed band shifts in the hybrids, and infrared analysis indicated shifts in wavenumbers, suggesting changes in the vibrational state of curcumin after bonding with metal ions. These techniques confirmed the formation of hybrid materials. Thermogravimetric and chromatographic analyses demonstrated greater thermal and solution stability for the hybrids compared to curcumin. Additionally, the hybrid composites effectively developed natural and sebaceous latent fingerprints with good clarity and contrast on glass surfaces. Both composites performed similarly to commercial Gold^® powder. When applied to surfaces representative of forensic scenarios, the composites were versatile, revealing sufficient fingerprint details for human identification on both porous and non-porous surfaces. Scanning electron microscopy images showed greater clarity in sebaceous and natural fingerprints developed with the Fe composite compared to the Cu composite. Full article

Indigo leaves from various plant species are sources of dyes/pigments, not fully exploited for making sustainable textiles. Blue indigo vat dye extracted from indigo leaves yields high wash color fastness but fades slowly with light, and is not easily used for direct printing. Indigo leaves can be used to produce textiles of various color shades, while light-resistant Mayan-inspired hybrid pigments have not yet been used for textile coloring. Using blue indigo dyes from three plant species, with exhaustion dyeing, intense wash-resistant blue-colored textiles are produced, and in the case of Indigofera Persicaria tinctoria, textiles have antibacterial activity against S. epidermis and E. coli. A 100% natural Mayan-inspired blue indigo pigment, made from sepiolite clay and natural indigo dye, was used both in powdered and paste forms to perform pigment textile dyeing by pad cure process, and direct screen printing on textiles. A water-based bio-binder was used efficiently for both padding and printing. Bio-based Na Alginate thickener allowed to produce prints with good color-fastness on both polyester and cotton fabrics, while bio-based glycerin produced excellent print color fastness on polyester only: wash fastness (5/5), dry and wet rub fastness (5/5) and light fastness (7/8). Full article

Aryl polyene (APE) are bacterial pigments which show great biotechnological potential because of their biological activities. In this study, the presence of gene clusters associated with APE synthesis was investigated in the genome of Chryseobacterium sp. kr6 and Lysobacter sp. A03. The pigments extracted from strains kr6 and A03 were further characterized by liquid chromatography coupled to a high-resolution mass spectrometer (LC-DAD-MS). These bacteria harbor the relevant genes for APE biosynthesis; while kr6 may produce flexirubin pigments and have a 75% similarity with the flexirubin cluster from Flavobacterium johnsoniae UW101, Lysobacter sp. A03 showed a 50% similarity with the xanthomonadin I gene cluster from Xanthomonas oryzae pv. oryzae. A comparison with the gene clusters of APE-producing bacteria revealed that kr6 and A03 harbor genes for key proteins that participate in APE biosynthesis, such as acyl carrier proteins, acyl dehydratases and acyl reductases. The LC-DAD-MS analysis revealed that kr6 produces a possible mixture of flexirubins, whereas the yellow pigment from A03 is proposed to be a xanthomonadin-like pigment. Although the fine molecular structure of these pigments are not yet fully elucidated, strains kr6 and A03 present great potential for the production of natural bioactive pigments. Full article

Advancements in cellular imaging have significantly enhanced our understanding of membrane potential and Ca²⁺ dynamics, which are crucial for various cellular processes. Voltage-sensitive dyes (VSDs) are pivotal in this field, enabling non-invasive, high-resolution visualization of electrical activity in cells. This review discusses the various types of VSDs, including electrochromic, Förster Resonance Energy Transfer (FRET)-based, and Photoinduced Electron Transfer (PeT)-based dyes. VSDs are essential tools for studying mitochondrial activity and neuronal function and are frequently used in conjunction with Ca²⁺ indicators to elucidate the complex relationship between membrane potential and Ca²⁺ fluxes. The development of novel dyes with improved photostability and reduced toxicity continues to expand the potential of VSDs in biomedical research. This review underscores the importance of VSDs in advancing our understanding of cellular bioenergetics, signaling, and disease mechanisms. Full article

N-Phenylphenothiazine derivatives extended with various aryl groups were designed and synthesized. These derivatives have bent conformation in crystal and exhibit high solubility. Radical cations obtained by one-electron oxidation of these derivatives gave stable radical cations in solution and showed absorption in the near-infrared region. A radical cation was isolated as a stable salt, which exhibited heat resistance up to around 200 °C. A design strategy for radical cation-based near-infrared absorbing dyes, which are easily oxidized and stable not only as a solution but in solid form, is described. Full article

This study investigates the effects of varying CuO doping concentrations on the performance of titanium dioxide (TiO₂)-based or zinc oxide (ZnO)-based dye-sensitized solar cells (DSSCs). TiO₂ or ZnO mixed with CuO at different weight percentages (0–50 wt %) was employed as photoanodes in DSSCs, prepared via mechanical mixing. X-ray diffraction analysis revealed the structural changes, showing that as the CuO content increased in the hybrid, the CuO peaks (notably at 35.5° and 38.7°) became more prominent. Morphological and elemental characterizations were conducted using SEM and XRF, respectively. The solar cells were photosensitized by Vitis lasbrusca (V.L.) extract and N3 dye. The presence of anthocyanin molecules in the extracted V.L. was confirmed using UV-VIS and FTIR spectroscopy. The electrochemical characterization demonstrated optimal solar conversion efficiencies at a 20% doping level for both photosensitizers. Specifically, in the V.L. dye, TiO₂-CuO achieved a conversion efficiency of 7.18%, and ZnO-CuO reached 5.77%. In the N3 dye, TiO₂-CuO showed an efficiency of 11.34%, and ZnO-CuO, 9.55%. Notably, undoped photoanodes displayed a significantly lower photovoltaic performance: for V.L. dye, TiO₂ showed 1.12% and ZnO 0.87%; for N3 dye, TiO₂ showed 6.02% and ZnO 4.39%. Doping was therefore effective, yielding up to a seven-fold increase in performance in the case of V.L. with TiO₂, compared to undoped DSSCs. The results demonstrate that using the hybrid photoanode led to a considerable increase in performance compared to using only TiO₂ or ZnO photoanodes, highlighting the potential of DSSCs as sustainable energy sources. Full article

This work addresses the implementation of the co-sensitization technique to increase the energy efficiency of organic dye-sensitized solar cells (DSSCs). Fluorescent dyes derived from boron complexes— (BORANIL) and (BODIPY)— were successfully synthesized and used as co-sensitizers in different volume percentage ratios to verify the most effective concentration for photon capture through these sensitizers. The dyes were optically characterized using ultraviolet–visible spectroscopy (UV-VIS) and Fourier transform infrared (FTIR), analyzing them through the optical performance of each hybrid combination of dyes, an optimization of the photon collection capacity in the tests performed in a volume percentage ratio of 25:75 or 1:3. The morphology and surface roughness of the electrodes were analyzed using scanning electron microscopy (SEM) and atomic force microscopy (AFM), respectively. Through electrochemical characterizations, it was found that the highest photovoltaic conversion efficiency was obtained with the ATH1005 (D) dye mixed with ATH032 (G) in the proportion of 25%:75% or DG 1:3, with efficiency (η) of 3.45%, against 2.43% and 1.90% for DG 1:1 and DG 3:1 cells, respectively. Cells with BODIPY dyes also present higher conversion efficiencies compared to BORANIL cells. The results corroborate the presentation of organic solar cells as a viable option for electricity generation. Full article

Hybrid pigments were obtained by combining zinc oxide with the anionic dye Congo red (CR), a breakthrough with significant environmental implications. By adjusting the ratio of solid mass to dye concentration, it is possible to obtain pigments with pink hues from a white solid (ZnO) through its adsorption of CR. The process involved using ZnO, prepared at 800 °C using cassava starch suspension as a suitable fuel. The oxide was characterized using XRD, SEM, and BET, and the results showed that the textural properties are typical of nanoparticles, with a size of 50.5 nm, a pore size of 3.48 nm, and a surface area of 3.03 nm, making it suitable for molecular dye removal. Controlling the adsorbent mass (in grams) and dye concentration (in mg L⁻¹) makes it possible to consistently produce hybrid pigments in various shades of pink that exhibit good thermal resistance. When dispersed in white waterborne paint, they are chemically stable in different solvents, have excellent painted surface coverage, and resist photochemical degradation. The results demonstrate technical feasibility and compatibility with the Sustainable Development Goals, particularly Goals 6, 11, 12, 14, 15, and 17, offering a promising solution for a more sustainable future. Full article

With the increasing awareness of socio-environmental issues, a global trend has emerged emphasizing the valorization of natural ingredients that promote health and well-being within sustainable production systems, such as microalgae-based carotenoids. Currently, little is understood about the correlation between biomass productivity and carotenoid content, which is a fundamental parameter for facilitating the immediate expansion of microalgae bioprocesses and ensuring the availability and industrial viability of these compounds. In this context, this study aims to investigate the carotenoid profile of Chlorella vulgaris through growth curve experiments conducted under photoautotrophic and heterotrophic regimes. Additionally, a trade-off analysis was performed for the production of carotenoids from microalgae. Carotenoids were quantified using high-performance liquid chromatography coupled with diode array and mass spectrometry detectors (HPLC-PDA-MS/MS). The performance of kinetic phases and energy demands across growth regimes was assessed to provide insights into production trade-offs. The results indicated that a total of 22 different carotenoids were identified in all the extracts. The all-trans-lutein and all-trans-β-carotene were the majority compounds. The total carotenoid content of Chlorella vulgaris revealed significant differences in the kinetic phases of carotenoid production, indicating that carotenoid volumetric production is only viable if the cultures are conducted until the log and stationary phases, based on the function of the biomass volumetric production (weight.volume⁻¹). Therefore, the best trade-off for the process was to provide photoautotrophic growth until the exponential phase (log). Under this condition, the maximum carotenoid and lutein content was 2921.70 µg.L⁻¹, reaching a maximum cell biomass of 1.46 g.L⁻¹. From an environmental/economic point of view, the energy demand was 7.74 kWh.L⁻¹. Finally, the scientific advances achieved in this study provide a holistic view of the influence of the main cultivation methods on the production of microalgae carotenoids, suggesting a viable initial direction for different industrial applications. Full article

(1) Background: This work evaluated the optical characterization of aqueous fluorescent chitosan-based carbon dots (or carbon nanoparticles CNPs) embedded in natural dye for potential functional packaging applications. Chitosan-based materials are nontoxic, biodegradable, biocompatible, bactericidal, and produced from renewable polymer sources. Anthocyanins are pigments of different colors with a large range of potential applications, such as in bioindicators and biomonitoring; (2) Methods: The CNPs were synthetized in aqueous solutions using chitosan as a carbon source. The natural dye was extracted from the leaves of Tradescantia pallida Purpurea in aqueous solutions. The fluorescence quantum efficiency (η) and fluorescence lifetime (τ) were determined using the mode-mismatched pump–probe thermal lens (TL) technique and time-resolved fluorescence lifetimes (TRFL) measurements, respectively; (3) Results: The η and τ were measured for CNPs embedded in natural dye solution at different concentrations (5.2, 12.09, and 21.57 mass percentage composition). The η and τ photophysical parameters obtained for CNPs embedded in natural dye were compared with those of other CNPs synthesized using different carbon sources, such as leaves, seeds, and protein; (4) Conclusions: Fluorescence spectra and time-resolved fluorescence measurements corroborate the TL results, and relatively high values of η were obtained for the CNP synthesized and embedded in natural dye. Full article

This perspective presents an account of the underlying features associated with the photofading of organic colorants. Photofading is commonly known to the scientific community as photodegradation or photooxidation, while in earlier times the more grandiose term “light fastness” was commonplace. This is a subject of immense diversity and significance, but there are many challenges to be faced when attempting mechanistic reasoning. The text is illustrated by descriptions of several systems taken from the scientific literature, together with anecdotes related to the principal researchers. The chemical challenges to be overcome in order to design photostable materials are outlined and reference is made to the natural world. It is stressed that the journal Colorants would welcome submissions in this field. Full article

Inorganic cool pigments are widely used as cooling agents in residential coatings due to their ability to achieve near-infrared reflectance. These coatings can be designed to exhibit a variety of colors independent of their reflectivity and absorption properties. Recent studies have highlighted the development of novel near-infrared (NIR) blue pigments, with an increasing emphasis on environmentally sustainable options that demonstrate high NIR reflectivity. This trend highlights the importance of creating novel and eco-friendly NIR reflective blue pigments. This study presents the synthesis of cobalt aluminates with varying concentrations of coloring ions (Co²⁺), achieved through the recycling of aluminum can seals via chemical precipitation. The formation of the spinel phase was confirmed through X-ray diffraction (XRD), and a colorimetric analysis was performed in the CIEL*a*b* color space. The synthesized pigments exhibited high near-infrared solar reflectance, with R% values ranging from 34 to 54%, indicating their potential as energy-efficient color pigments for use in coatings. Full article