Sustainable dyeing of cotton fabrics with carbene dyes: Covalent cross-linking for auxiliary-free coloration.

Large volumes of water are consumed in traditional cotton fabric dyeing, and auxiliaries such as salt and alkali are required to enhance dyeing efficiency, resulting in significant resource waste and environmental pollution. Therefore, the development of a green, efficient and sustainable dye and dyeing process is crucial for the sustainable development of the textile industry. In this study, four multicolor carbene dyes with diazirine moieties as carbene precursors were successfully synthesized and applied for the first time in salt-free and auxiliary-free eco-friendly dyeing process of cotton fabrics. The four dyes were applied to cotton fabrics in a methanol/water (4:6, v/v) mixed solution, where the effects of solvent ratio, dyeing temperature and time, as well as fixation temperature and duration on dyeing performance and fixation efficiency were systematically evaluated. The influence of solvent on the aggregation behavior of dyes was comprehensively investigated using ultraviolet-visible (UV-Vis) spectroscopy, transmission electron microscopy (TEM), and nanoparticle size analysis. The dyed cotton fabrics exhibited high color strength, excellent fixation rates, and outstanding color fastness properties, including washing, rubbing, and sublimation fastness. It was confirmed by energy-dispersive X-ray spectroscopy (EDS) analysis of the dyed fabric cross-sections that carbene dyes could penetrate deep into the cotton fibers to form covalent bonds for coloring. Importantly, no damage to the crystalline structure or thermal stability of the cotton fibers was observed during the dyeing and fixation processes. Therefore, the carbene dyes and their salt- and alkali-free dyeing process offer a promising eco-friendly strategy for cotton dyeing, providing a novel pathway toward sustainable textile coloration technologies.