BACKGROUND Dyeing wastewater has caused serious pollution of aquatic environments, and adsorption is one of the most commonly used water-purification methods with selection of suitable adsorbents being the key factor. These factors motivated us to develop new, more efficient adsorbents to purify dyeing wastewater. RESULTS A surface cross-linking co-polymerization of triallylmethylammonium chloride (TAMAC) and grafting cotton with unsaturated bonds (G-cotton) was designed to obtain multidimensional cationic cotton adsorbent (PT-cotton) with a high cationic degree of substitution of 0.129. A surface gel-adsorption effect of the multidimensional cationic construction on cotton surface occurring during PT-cotton adsorption was discovered resulting in the PT-cotton having an ultrahigh adsorption capacity for purifying dyeing wastewater. Compared to the untreated cotton, the adsorption capacity of the PT-cotton was 1344.10 times higher. Compared to the widely used activated carbon, the adsorption capacity of the PT-cotton was 145.31 times higher, and it was 11.05 and 7.25 times higher, respectively, than that of the similar G-cotton and polycationic cotton (PF-cotton) reported in our previous contribution. When PT-cotton materials were used to fill filter columns, the dye solution flowing through the filter columns immediately became clear, and the dye removal percentage for the PT-cotton filters reached 96.9%, which was clearly better than that of the activated carbon filter (26.2%). Moreover, the per-unit amount of water purification from filtering purification of a dye solution using PT-cotton was 7.02 times higher than that using PF-cotton. CONCLUSIONS Obtained PT-cotton has a greater potential for application in the purification of dyeing wastewater than the existing adsorbent materials. (c) 2018 Society of Chemical Industry