University of Helsinki
In a world awash with synthetic dyes, a hidden reality hides beneath the enchanting spectrum of colours. Recently, synthetic dyes have claimed the spotlight across various industries, owing to their cost-effectiveness and superior efficiency compared to their natural alternatives. These artificial compounds stealthily make their way into unexpected places such as cosmetics, food, pharmaceuticals, and inevitably find their way into our waters.
The careless disposal of liquid waste into our waterways wreaks havoc on aquatic life, degrading water quality, and hinders plant growth. Our water bodies face an increasing cocktail of chemicals, but fortunately, there’s a glimmer of hope in the form of ionising radiation.
High-energy x-rays present a groundbreaking solution, wielding the power to dismantle the resilient molecular structures of synthetic dyes. This advanced oxidation process (AOP) distinguishes itself as one of the select methods capable of effectively neutralising the conjugated bonds within dye molecules.
Conjugation takes place when molecules contain adjacent double bonds, leading to the delocalisation of electrons throughout the chain. These liberated electrons gain the freedom to move among elements and bonds, spreading and stabilising the energy distribution of the molecule.
These conjugated systems lay the groundwork for chromophores, the light-absorbing constituents responsible for the distinctive colours of dyes. But why are these robust systems problematic? The longer the conjugation chain, the higher the stability of the molecule, complicating the chemical and biological treatment of wastewater.
How, then, can radiation make a difference? Radiolysis, or the molecular damage of chemical bonds by ionising radiation, becomes a crucial player in water treatment. It generates hydroxyl radicals that oxidise and reduce the molecular weight of contaminants, gradually decreasing the concentration of pollutants in wastewater.
A research team from the Russian Academy of Sciences delved into the impact of hydroxyl radicals on dye discoloration. With a LINS-03-350-EURF linear accelerator, they irradiated four distinct groups of universal dyes. The visible colour of the solutions, or optical absorption, was measured using a spectrophotometer. The results revealed that even with the slight addition of both hydroxyl and hydrogen radicals, significant discoloration occurred across a range of dye solutions.
Hydroxyl radicals prove to be effective tools in dismantling the complex conjugation of vulnerable dye molecules. The addition of a hydroxyl radical induces stress on the conformation of the dye molecule, ultimately damaging intramolecular conjugate bonds.
Despite radiolysis presenting itself as a viable option for large-scale wastewater treatment, its implementation faces hurdles due to high costs and inherent complications. t was found that at this stage in the development of radiolysis, wastewater simply could not be irradiated quickly enough, leading to low yields of actual dye decomposition. Yet, even with these flaws, the potential role of radiation and radiochemistry in shaping our future remains a compelling prospect.
Sofia Vilkman
Kholodkova, E.M., & Ponomarev, A.V. (2022). Degradation of the Chromophore Functions of Dyes in Irradiated Solutions. High Energy Chemistry, Vol. 57(2), 146–150. Springer Link.