Hybrid biochar supported transition metal doped MnO₂ composites: Efficient contenders for lithium adsorption and recovery from aqueous solutions

Herein, novel nanocomposites (Ni_x-MnO₂/BC) were synthesized by hybrid biochars (h-BC) that derived from coconut shell and rice husk, and subsequently decorating the surfaces of these h-BC with nickel-doped MnO₂ nanorods at various ratios of nickel doping. The as-fabricated Ni_x-MnO₂/BC nanocomposites exhibited efficient Li⁺ adsorption and desorption performances. Conventional batch adsorption tests were done to optimize parameters: pH, dose, contact time, Li⁺ initial concentration, and temperature that maximized Li⁺ uptakes adsorbents efficiency. The Ni_0.01-MnO₂/BC nanocomposite showed the greatest Li⁺ uptakes (89 mg g⁻¹) under optimized parameters at ambient temperature. The high capacity of Ni_0.01-MnO₂/BC nanocomposite for Li⁺ uptakes arises from the specific extent of Ni-doping, large specific surface area (400 m² g⁻¹), and high number of accessible active functionalities. Sorption kinetics and isothermal analysis illustrate that, Li⁺ adsorption mechanism follows pseudo 1st order kinetic and Langmuir model. Based on identified thermodynamic parameters, the adsorption of Li⁺ on adsorbents was exothermic and spontaneous in nature, signifying the physical adsorption process. Subsequent desorption experiments demonstrate that 98% of the Li⁺ can be recovered in the desorbing agent. Furthermore, the selective Li⁺ adsorption and intermediate stable nature of nanocomposites make them suitable contenders for Li⁺ adsorption and recovery applications at a broad scale.