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In this work, a salt-free and low alkali dyeing process was developed through cationic modification of cotton fabric with a series of quaternary ammonium salts (QAS). The dyeing performance indicated that the cationic cotton fabric treated with 3-chloro-2-hydroxypropyldimethyloctane ammonium chloride (CT-8) achieved better K/S value (8.87) and dye fixation (90.47 %) compared to the conventional dyeing process. Notably, the CT-8 treated fabric performed exceptionally under salt-free conditions and with a Na 2 CO 3 concentration of 5 g/L. The rationale behind the adoption of a salt-free and low-alkali dyeing process was attributed to the positive charge of quaternary ammonium groups, which had an augmenting impact on the hydroxyl reaction activity of cotton fabrics. The condensed Fukui function, atomic charge, and HOMO orbital calculations showed that the QAS structure could regulate the hydroxyl reactivity of cationic cotton fabric. Our salt-free and low alkali dyeing process not only achieved the aim of reducing chemical consumption and emissions, but also contributed to better understand the effect of hydroxyl reactivity of cationic cotton on the fixation reaction with reactive dye, and provided a new direction to achieve the require of sustainable development and clean production for a variety of industrial crops and products. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • The quaternary ammonium salt-modified hollow titanium dioxide was synthesized. • QAS-H-TiO 2 enhanced the dye adsorption capacity and photogenerated carrier separation for efficient dye removal. • The adsorption mechanism between QAS-H-TiO 2 and reactive dye was clarified. • The regulation mechanism of photogenerated carriers on QAS-H-TiO 2 was elucidated. Currently, titanium dioxide (TiO 2) has been demonstrated as a significant photocatalyst for the efficient removal of reactive dyes in dyeing effluents. However, due to the easy recombination of photogenerated carriers and electrostatic repulsion with reactive dye, single TiO 2 cannot achieve satisfactory removal efficiency to reactive dye which is commonly used in cellulose fibers dyeing. Therefore, we prepared hollow titanium dioxide (H-TiO 2) by alkaline treatment etching method and introduced quaternary ammonium groups on the surface of H-TiO 2 photocatalyst (QAS-H-TiO 2) by nucleophilic addition reaction. Improving the adsorption capabilities of C. I. reactive red 2 (RR2) and simultaneously separating the photogenerated carriers via the nitrogen cation of the quaternary ammonium groups facilitated the enhancement of its RR2 removal. The experimental results indicated that the utilization of QAS-H-TiO 2 substantially bolstered the removal efficiency of RR2. The impact of molecular structure of quaternary ammonium salts on the adsorption ability of RR2, and the mechanism of regulation for photogenerated carriers, were investigated. It was found that the grafting of the quaternary ammonium group enabled mass and electron transfer channels, resulting in faster adsorption of dyes and separation of photogenerated carriers. This study presents a novel approach for preparing efficient QAS-H-TiO 2 for high-performance organic dye removal. [ABSTRACT FROM AUTHOR]