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In this work, a new AC@Catechol/PEI adsorbent was prepared via the copolymerization of catechol and polyethyleneimine (PEI) onto pretreated commercial activated carbon (AC). It achieved a high adsorption capacity of 411.52 mg/g for the anionic dye Congo red (CR), which was approximately 7 times that of pretreated AC without modification. In bath adsorption experiment, 1 g of adsorbent was used to treat 4 L of 100 mg/L CR solution, resulting in 98.5% CR removal. In addition, the prepared AC@Catechol/PEI adsorbent exhibited highly efficient CR competitive adsorption against SO 4 2À ions and cationic malachite green dye. The adsorption mechanism was mainly attributed to electrostatic interactions, hydrogen bonding, and π-π stacking. Catecholamine modification greatly improved the adsorption capacity and adsorption selectivity of commercial AC for CR dyes. This low-cost adsorbent may have broad prospects for the removal of anionic dyes in wastewater.

With the current situation of high-energy consumption and high pollution in the textile industry, developing an eco-friendly and universal dyeing technology is urgently required. Towards this goal, in this study, the dyeing technology with room temperature, salt-free, zero release, and rapid cycle dyeing for 20 min was realized using a polymer of catechol and polyethyleneimine as a