Lignosulfonate-Based Hybrid Hydrogels Functionalized with Hyperbranched Polyamide Amine as Ultra-High-Capacity Adsorbent for Congo Red Removal from Aqueous Solutions

Fast and efficient removal of organic dyes from industrial wastewater by practical and cost-effective adsorption method has been in the spotlight. Herein, lignosulfonate-based hybrid hydrogel adsorbents (HPAS) were one-pot synthesized via cross-linking reaction with lignosulfonate amine, hyperbranched polyamide amine, and polyethylene glycol diglycidyl ether, then were characterized by FTIR, XPS, and SEM measurements. The adsorption capacity of HPAS for separate organic dyes and metallic ion were further studied. HPAS with hierarchical porous structures showed ultra-high capacity for dye removal, especially for Congo red (CR). The actual maximum adsorption capacity of CR can reach 5120 mg/g, when the initial concentration of CR is 6000 mg/L, natural pH, temperature is 298 K, and the amount of adsorbent HPAS-4 is 0.8 g/L. Simultaneously, HPAS-4 also showed a relatively strong adsorption performance for Cu(II); the maximum uptake capacity was obtained at 249 mg/g (initial Cu(II) concentration = 100 mg/L). After 5 adsorption–desorption cycles, HPAS-4 still maintains a high adsorption capacity for CR and Cu(II). The CR and Cu(II) adsorption mechanisms by HPAS were further validated using X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The adsorption of CR and Cu(II) by HPAS was a spontaneous endothermic process, which conforms to the pseudo-second-order kinetic model and Langmuir adsorption model. The key mechanism of CR adsorption process is H-bond interactions due to abundant N and O atoms in HPAS accompanied with electrostatic attraction and π-π stacking interaction. The adsorption of Cu(II) on HPAS is mainly determined by the complexation/chelation accompanied with precipitation of copper derivatives on HPAS. The results of this study provide a new method for the preparation of high-performance biomass-based adsorbents in the field of wastewater treatment.