Synthesis of a Lignin-Fe/Mn Binary Oxide Blend Nanocomposite and Its Adsorption Capacity for Methylene Blue

A high-performance modified lignin adsorbent was prepared through coprecipitation of ferrous, ferric, and permanganate with lignin in sodium hydroxide solution. The structural characteristics of the synthesized lignin-Fe/Mn binary oxide blend nanocomposite (L-F/M) and its performance on the methylene blue (MB) removal from aqueous solution were evaluated. Influence factors of adsorption effects were analyzed including pH, contact time, dye concentration, temperature, and thermodynamics. The pseudo-second-order kinetic model well described the adsorption kinetics, and the adsorption isotherms best fitted the Langmuir model with a maximum adsorption capacity of 252.05 mg g^-1 at 298 K. The adsorption mechanism showed that the L-F/M introduced the metallic element and negative charges to the lignin surface, which improved the adherence of MB via hydrogen bonding, electrostatic interaction, and coordination. Moreover, the removal ratio of MB maintained 81.2% after being used in five adsorption-desorption cycles. Results indicated that the L-F/M obtained was an efficient candidate for dye wastewater treatment.