Colorants, Volume 3, Issue 1 (March 2024) – 5 articles

Effluents from the textile industry are an active problem in the sector and one of the world’s main environmental problems. The conventional treatments applied are not always efficient in terms of compliance with legislation, and, in many cases, the efficiency of treatment is guaranteed by the enormous energy expenditure involved, camouflaging the momentary problem and not effectively treating it. In this work, batch reactors with immobilized biomass of Aspergillus niger AN400 were arranged in series for the treatment of real textile wastewater containing approximately 20 mg/L of indigo carmine. Sucrose was added as a co-substrate in concentrations of 1 g/L and 0.5 g/L, in the first and second reactors, respectively, over 19 cycles of 48 h. The highest decolorization rate in the system was (93 ± 4) %, with the largest amount removed in the first reactor (90 ± 6) %, occurring mainly by biological means. The production of aromatic by-products from the initial degradation of the dye molecule was reflected in the lower removal efficiency of dissolved organic matter: 52% in the first reactor, and 25% in the second reactor. The number of colonies of fungi was higher than that of bacteria, 2.24:1 and 2.44:1 in the first and second reactors, respectively. The treated effluent in the system showed less toxicity than the raw effluent, and this demonstrates the potential of this technology in the treatment of textile effluents containing indigo carmine. Full article

Azo-Schiff bases contain an azo photochrome showing isomerization accompanying with color change, and an imine moiety (which can contribute to the metal complexation capability). The syntheses of these molecules will be described, and their dyes applications will be discussed, such as for fuel cells, as photometric or colorimetric sensors. In addition, liquid crystals and their antibacterial efficiencies will also be discussed. Full article

Dunaliella salina has been recognized as an excellent biomass source of carotenoid, which can be used as a natural orange coloring agent for food products. The most eco-friendly approach for extracting carotenoid is through supercritical carbon dioxide extraction, as it yields highly concentrated extracts while preventing pigment thermal degradation. However, there are limitations when a lipophilic extract is considered a food ingredient, in particular very difficult handling and low solubility in water-based products. The aim of this study was to develop a hydrosoluble form of a natural carotenoid-rich extract recovered from algae biomass within a biorefinery concept to be incorporated in aqueous-based food products. A two-step process was developed, starting with the emulsification of the supercritical extract into a mixture of maltodextrin and gum arabic, using soy lecithin as an emulsifier. The emulsification was followed by a spray-drying step. The impact of process variables on the encapsulation yield, efficiency, emulsion properties, and particle characteristics was studied. The resulting particles exhibited an intense orange color and good water dispersibility, facilitating uniform yellow coloring when incorporated into an aqueous-based product. Overall, spray-drying emulsions containing carotenoids derived from Dunaliella salina prove to be a promising strategy for the global market demand for natural colorants. Full article

A library of seven novel 1,3-benzothiazole-substituted BODIPY derivatives with tunable optical properties was synthesized. The new fluorescent dyes exhibited bathochromically shifted absorptions (up to 670 nm) and emissions centered in the red and near-infrared spectral region (up to 677 nm) in comparison to the parent compound 8-phenyl BODIPY (λ_abs: 499 nm, λ_emi: 508 nm). (TD)DFT calculations were performed to rationalize the spectroscopic properties of the new dyes. The cellular biodistribution of the new BODIPY dyes, their fluorescence stability and toxicity were investigated in both living and fixed fibroblasts using time-lapse fluorescent imaging and confocal microscopy. Six of the seven new dyes were photostable and non-toxic in vitro at 10 μM concentration. In addition, they efficiently stained the cell membrane, showing diffuse and dotty localization within the cell at low concentrations (1.0 and 0.1 μM). Specifically, dye TC498 was localized in vesicular structures in both live and fixed cells and could be used as a suitable marker in co-staining studies with other commonly used fluorescent probes. Full article

Remediation of organic dyes in natural waters is a significant environmental need under active study. This review analyzes bimetallic catalytic degradation systems that are based on the Fenton chemistry concept and that generate reactive oxygen species (ROS) as the agent of dye breakdown. Recently developed advanced oxidation processes (AOPs) take advantage of bimetallic heterogeneous catalysts to facilitate rapid rates and full degradation. Catalysts based on two metals including iron, copper, molybdenum, cobalt and magnesium are discussed mechanistically as examples of effective radical ROS producers. The reactive oxygen species hydroxyl radical, superoxide radical, sulfate radical and singlet oxygen are discussed. System conditions for the best degradation are compared, with implementation techniques mentioned. The outlook for further studies of dye degradation is presented. Full article