David Chem, a Ph.D. candidate in chemical engineering at the University of Arkansas, has created an eco-friendly method for eliminating azo dyes by utilizing a typical byproduct from the pulp and paper sector. The study was published in the Journal of Polymers and the Environment.
David Chem, chemical engineering graduate student, holds on the right a vial of water with methyl orange dye. On the left, the water is clear after modified lignin bonds with the dye and falls to the bottom of the vial. Image Credit: Russell Cothren
Dyes such as Congo red and methyl orange produce vividly colored shirts, sweaters, and dresses. However, these frequently utilized azo dyes may be toxic, carcinogenic, and difficult to eliminate from wastewater.
Azo dyes account for 60-70 % of the textile production in the commercial sector. These dyes are highly soluble in water and resistant to biodegradation, posing a significant environmental threat. The highest concentrations of azo dyes are found in the runoff from garment manufacturing facilities, but they also contaminate municipal wastewater when clothes are washed.
Chem started using lignin, a biopolymer sourced from plant cell walls, to eliminate azo dyes from water. Lignin is low-cost and abundantly available. Annually, the pulping industry generates between 50 and 70 million tons of lignin, most of which is disposed of in landfills.
Lignin extraction is hard to process. It has a complex structure. It is underutilized as a biopolymer.
David Chem, Ph.D. Candidate, Chemical Engineering, University of Arkansas
Initially, the researchers incorporated phenol into powdered lignin, enhancing its surface reactivity. Subsequently, amino groups were introduced to impart a positive charge to the lignin, facilitating its bonding with negatively charged azo dyes.
This two-step, dual-functionalization modification of lignin has been previously evaluated as a method for the removal of heavy metal ions. However, the University of Alberta researchers were the pioneers in applying this technique to eliminate harmful dyes.
In laboratory experiments, the modified lignin successfully removed 96% of the Congo red dye and 81% of the methyl orange dye. This method allows for the reuse of both the dyes and the lignin.
The process is really scalable. It's a relatively green process. And it is highly effective.
David Chem, Ph.D. Candidate, Chemical Engineering, University of Arkansas
Journal Reference:
Chem, D., et al. (2025) Aminated Phenolated Lignin for Effective Anionic Dye Removal for Water Remediation. Journal of Polymers and the Environment. doi.org/10.1007/s10924-025-03650-0