Applying density functional theory to predict the reduction potential in the indigo dyeing process

This study employs density functional theory (DFT) to quantify the electron donor-acceptor properties and polarizability of organic iron(II) salts as reducing agents in indigo dyeing processes. The potential of some iron(II) salts to serve as environmentally friendly alternatives to the ecologically harmful sodium dithionite in the indigo dyeing process was investigated. A comparative analysis assessed the redox potential of reduced indigo and the color strength of dyed fabrics. Experimental results identified iron(II) gluconate as the most efficient, yielding superior color intensity. Theoretical calculations using B3LYP/LANL2DZ confirmed the superior electron-donating ability of iron(II) gluconate compared to the other iron(II) salts. The indigo reduction ability with the iron(II) salts was evaluated on the basis of complexation energies. The theoretical thermodynamic study reveals that the indigo-iron(II) gluconate complex is the most thermodynamically stable, requiring less energy input for its formation compared to the other complexes. Iron(II) salts-to-indigo electron donations in the complexes studied have been revealed by Mulliken charge analysis. These findings highlight the efficiency of DFT-based approaches in accurately predicting the reducing capacity of iron(II) salts and their suitability as eco-friendly alternatives in indigo dyeing applications.