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

Herein, novel nanocomposites (Nix-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 Nix-MnO2/BC nanocomposites exhibited efficient Li+ adsorption and desorption performances. Conventional batch adsorption tests were done to optimize pa-rameters: pH, dose, contact time, Li+ initial concentration, and temperature that maximized Li+ uptakes ad-sorbents efficiency. The Ni0.01-MnO2/BC nanocomposite showed the greatest Li+ uptakes (89 mg g(-1)) under optimized parameters at ambient temperature. The high capacity of Ni0.01-MnO2/BC nanocomposite for Li+ uptakes arises from the specific extent of Ni-doping, large specific surface area (400 m(2) g(-1)), and high number of accessible active functionalities. Sorption kinetics and isothermal analysis illustrate that, Li+ adsorption mech-anism 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.