Silver nanoparticles catalyzed reductive decolorization of spent dye bath containing acid dye and its reuse in dyeing

Decolorization of spent dye baths after dyeing of nylon, silk and wool fabrics with C.I. Acid Red 249 was attempted followed by their reuse in repeated dyeing. The system comprised of a non-sulfur reducing agent, sodium borohydride, along with silver nanoparticles synthesized by plant mediation technique using fresh curry leaves (Murraya koenigii). Response surface methodology was used to optimize the conditions of decolorization for reproducibility of results. Box-Behnken design matrix with three variables namely, dosage of nanoparticles, concentration of reducing agent and time of treatment, was employed to design the experimental runs. Analysis of variance was employed to estimate the statistical parameters and evaluate the statistical significance of the model. Fisher's F- test was used to evaluate the quality and model terms. Three-dimensional response surface plots were used to study the interactive effect of operating variables on the response. Decolorized spent dye bath solutions were reused up to five times to dye fresh samples of nylon, silk and wool with the same dye. Negligible difference was observed in color depth and the fastness properties were identical for all the dyed samples even with respect to that dyed using dye liquor made from fresh water. Phytotoxicity studies revealed considerable reduction in toxicity of Acid Red 249 dye due to degradation. Thus, the treatment system for dye decolorization and repeated use of decolorized dye bath in dyeing was successful.