Advancing green textile processing with Mirabilis jalapa colorants and natural mordant sources

The widespread use of synthetic dyes in cotton dyeing generates hazardous effluents and persistent environmental burdens, motivating the development of metal-free and biodegradable dyeing systems. This study provides a sustainable coloration system on cotton based on pigments obtained using Mirabilis jalapa L. flowers together with five natural bio-mordants- aloe vera gel, pomegranate peel, betel-nut soaking water, banana stem extract, and cow-dung slurry. Dye extraction, mordanting, and dyeing were performed under controlled aqueous conditions, and the resulting fabrics were analysed by colorimetry, fastness testing, FTIR spectroscopy, SEM/EDX characterization, and COD/BOD analysis of dye effluents. The choice of bio-mordant markedly influenced shade depth and chromaticity; pomegranate peel produced the highest color strength (K/S = 8.44), followed by betel-nut extract (K/S = 3.50), whereas aloe vera and banana stem yielded moderate hues. Fastness to washing, perspiration, saliva, and rubbing ranged from good to excellent (grades 4–5), while light fastness remained moderate, consistent with the intrinsic photolability of betalain chromophores. FTIR spectra confirmed the formation of additional hydrogen-bonding and phenolic interactions between the bio-mordants, betanin, and cellulose. Scanning Electron Microscopy (SEM) imaging revealed uniform deposition of plant-derived residues, which enhanced dye anchoring, as supported by energy-dispersive X-ray spectroscopy (EDX) evidence of adsorbed organic elements. Effluent analysis showed that all dye baths met the Bangladesh ECR-2023 discharge limits (COD ≤ 200 mg/L; BOD 5 ≤ 30 mg/L), indicating high biodegradability and no metal contamination. Overall, this work presents a fully natural, metal-free dyeing platform capable of delivering strong coloration and favorable fastness while maintaining minimum environmental impact.