Construction of Cu-N coordination into natural biopolymer lignin backbone for highly efficient and selective removal of cationic dyes

[Display omitted] •Robust & eco-friendly adsorbent Cu2+-doped aminated-lignin (Cu-AL) was fabricated.•The Cu-AL had high adsorption capacities of azure B (AB) and saffron T (ST).•The Cu-AL maintained high removal efficiency (>80%) of dyes after 4 reuses.•The Cu-AL could remove and separate AB and ST from dye mixtures in real-time. Here, a Cu2+-doped lignin-based adsorbent (Cu-AL) was fabricated via the amination and Cu2+-doping of industrial alkali lignin for massive and selective adsorption of cationic dyes azure B (AB) and saffron T (ST). The Cu-N coordination structures endowed Cu-AL with stronger electronegativity and higher dispersity. Through the electrostatic attraction, π-π interaction, H-bonding, and Cu2+ coordination, the adsorption capacities of AB and ST reached up to 1168 and 1420 mg g−1, respectively. The pseudo-second-order model and Langmuir isotherm model were more relevant to the AB and ST adsorption on Cu-AL. Based on the thermodynamic study, the adsorption progresses were endothermic, spontaneous, and feasible. The Cu-AL maintained high removal efficiency to dyes after 4 reuses (>80%). Importantly, the Cu-AL could efficiently remove and separate AB and ST from dye mixtures even in real time. All the above characteristics demonstrated that Cu-AL was an excellent adsorbent for fast wastewater treatment.