One-Pot Synthesis and Combined Use of Modified Cotton Adsorbent and Flocculant for Purifying Dyeing Wastewater

A one-pot polymerization system using tetradecyl allyldimethylammonium chloride (TADMAC) and grafting cotton with unsaturated bonds (G-cotton) was designed to synthesize novel long-chain alkylation polycationic cotton (LP-cotton) and the homopolymer of TADMAC (PTADMAC). The LP-cotton had a high cationic degree of substitution of 0.108. The high monomer conversion of 98.8% suggests that almost all the TADMAC monomers participated in the polymerization. It is possible that when only LP-cotton was used as the adsorbent, its long-chain alkylation cationic TADMAC unit played the role of a similar surfactant in enhancing the association between the dye and cotton surface, resulting in a great improvement in adsorption capacity. The adsorption capacities were 57.5, 531.7, 4.4, and 2.9 times higher than those of the widely used activated carbon, untreated cotton, G-cotton, and polycationic film-coated cotton (PF-cotton), respectively, reported in our previous study. Using only PTADMAC as the flocculant led to a wide range of application adaptability, removing more than 97.0% of various anionic dyes in the water by forming flocs. As a result, PTADMAC could also be used as an enhancer at a low dosage for improving the flocculation ability of some conventional flocculants. Moreover, due to the mutual associations of the long-chain tetradecyl groups, the combined use of the LP-cotton adsorbent and PTADMAC flocculant not only reduced the dosage of LP-cotton adsorbent to 30% of that required for adsorption-only treatments but also decreased the dye removal time to 10 s. The dye solution became clear almost instantly, enhancing the removal of water-soluble dyes from water more comprehensively than the use of adsorbent or flocculant alone.