In this study, high-performance modified biochar/alginate composite bead (MCB/ALG) adsorbents were prepared from recycled agricultural waste corncobs by a high-temperature pyrolysis and KOH/FeCl₃ activation process. The prepared MCB/ALG beads were tested for the adsorption of methylene blue (MB) dye from wastewater. A variety of analytical methods, such as SEM, BET, FTIR and XRD, were used to investigate the structure and properties of the as-prepared adsorbents. The effects of solution pH, time, initial MB concentration and adsorption temperature on the adsorption performance of MCB/ALG beads were discussed in detail. The results showed that the adsorption equilibrium of MB dye was consistent with the Langmuir isothermal model and the pseudo-second-order kinetic model. The maximum adsorption capacity of MCB/ALG−1 could reach 1373.49 mg/g at 303 K. The thermodynamic studies implied endothermic and spontaneous properties of the adsorption system. This high adsorption performance of MCB/ALG was mainly attributed to pore filling, hydrogen bonding and electrostatic interactions. The regeneration experiments showed that the removal rate of MB could still reach 85% even after five cycles of experiments, indicating that MCB/ALG had good reusability and stability. These results suggested that a win-win strategy of applying agricultural waste to water remediation was feasible.

Wastewater containing heavy metals and organic dye pollutants discharged into receiving waters poses a serious environmental concern. Herein, a novel EDTA-chitosan/alginate porous composite bead adsorbent (EC–AB) was reported for the simultaneous removal of lead (Pb(II)) and methyl blue (MB) complexes from wastewater. Characterization results showed that EC–AB contained plenty of oxygen/nitrogen functional groups. The effect of CaCO₃ addition, pH of the initial solution, contact time, initial pollutant concentration, and ionic strength on EC–AB pollutant removal performance and the adsorption mechanism were systematically analyzed. These findings indicated that EC–AB exhibited high removal efficiency over a wide pH range and at high ionic strength. The maximum adsorption capacities of EC–AB for Pb(II) and MB were 504.11 mg g⁻¹ and 660.76 mg g⁻¹, respectively, at 298 K. Adsorption kinetics and isotherm studies indicated that the adsorption well fitted the pseudo-second-order kinetic model and the Langmuir isotherm. A possible adsorption mechanism involving electrostatic attraction, chelation, ion exchange, H-bonding and synergistic effects was proposed. Moreover, EC–AB showed superior stability and reusability, with removal efficiencies of 76.64% for Pb(II) and 80.29% for MB after five continuous adsorption–desorption cycles for treating complex wastewater. In summary, this work provides a beneficial strategy for designing high-performance adsorbents for the treatment of wastewater.

A novel pyridine-modified chitosan (PYCS) adsorbent was prepared in a multistep procedure including the successive grafting of 2-(chloromethyl) pyridine hydrochloride and crosslinking with glutaraldehyde. Then, the as-prepared materials were used as adsorbents for the removal of metal ions from acidic wastewater. Batch adsorption experiments were carried out to study the impact of various factors such as solution pH value, contact time, temperature, and Fe (III) concentration. The results showed that the absorbent exhibited a high capacity of Fe (III) and the maximum adsorption capacity was up to 66.20 mg/g under optimal experimental conditions (the adsorption time = 12 h, pH = 2.5, and T = 303 K). Adsorption kinetics and isotherm data were accurately described by the pseudo-second-order kinetic model and Sips model, respectively. Thermodynamic studies confirmed that the adsorption was a spontaneous endothermic process. Moreover, the adsorption mechanism was investigated using Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The results revealed the pyridine group forms a stable chelate with iron (III) ions. Therefore, this acid-resistant adsorbent exhibited excellent adsorption performance for heavy metal ions from acidic wastewater compared to the conventional adsorbents, helping realize direct decontamination and secondary utilization.