# Biebrich scarlet

Biebrich scarlet (C.I. 26905) is a molecule used in Lillie's trichrome. It is an anionic mono-azo dye, which is an important pigmenting agent in the textile and paper industries, used to color wool, silk, cotton, and papers. The dye was created in 1878 by the German chemist Rudolf Nietzki. He was employed by Kalle & Co. and completed his contributions on August of 1880, where he claimed to be the inventor of Biebrich scarlet. The name, Biebrich scarlet, originated from the location where a company, Kalle & Co., marketed the dye in Biebrich (Wiesbaden).

## Properties

Biebrich scarlet has two alternative structures: the keto form, with the IUPAC name of 2-[(2Z)-2-(2-oxonaphthalen-1-ylidene)hydrazinyl]-5-[(4-sulfonatophenyl)diazenyl]benzene-1-sulfonate, and the enol form, with the IUPAC name of 2-[(2-hydroxynaphthalen-1-yl)diazenyl]-5-[(4-sulfophenyl)diazenyl]benzene-1-sulfonic acid. The dye has the molecular weight formula of C$_{22}$H$_{16}$N$_4$Na$_2$O$_7$S$_2$, molecular weight of 512.52 grams per mol, and has the maximum absorption of 510 nm.

## Environmental impacts and applications

Biebrich scarlet dyes are used to color hydrophobic materials like fats and oils. It's also one of the most often used dyes for plasma staining. The dye is an illegal dye for food additives because of its carcinogenic properties. Biebrich scarlet can have harmful effects on living and non-living organisms in natural water. This dye is strongly pigmented, and its presence in water bodies, even at low quantities (10-50 mg/L), can be detected, reducing the transparency of the water ecosystem. It also hinders the entry of sunlight into the water, affecting both zooplankton and phytoplankton in the water ecosystem, therefore the pollutant must be removed. Removal of the pollutant involves absorption, membrane filtration, precipitation, ozonation, fungal detachment, and electrochemical separation. Hydrogel absorbents have active sites to which the dye is held using electrostatic interactions. Photocatalysis allows for almost total degradation of Biebrich scarlet azo dye bonds in less than 10 hours. Degradation of Biebrich scarlet is also observed using lignin peroxidase enzyme from wood rotting fungus in the presence of mediators like 2-chloro-1,4-dimethoxybenzene.
With such a significant impact on the environment and surrounding resources, researchers are working to reduce the dye's presence in water bodies. Studies have shown techniques to remove the red dye Biebrich Scarlet (BS) from water using UV light and nanophotocatalysts like TiO₂, ZnO, CdS, and ZnS. Among these, ZnO performed the best in dye removal. To enhance the process, researchers adjusted factors such as catalyst concentration (0.25-1.25 g/L), solution pH (3-11), and dye concentration (5-100 mg/L). Precipitation was used to form the ZnO nanoparticles, which were then studied utilizing advanced technologies (XRD, FT-IR, TGA, SEM, and TEM) to confirm their characteristics. Experiments revealed that, under optimal conditions, these produced ZnO particles beat commercial ZnO powders in dye breakdown. Furthermore, the study found that the produced ZnO could be reused well, making it a suitable material for water treatment applications.