Bimetallic aluminum lanthanum modified coffee husk derived nanobiochar for nitrate adsorptive removal: kinetics and isothermal studies

Adsorption technology is a promising alternative to conventional methods in wastewater treatment owing to its simplicity and efficiency to remove even low-concentration of nitrate (NO₃⁻) and recover it. In this paper, advanced materials based on aluminum-lanthanum (Al-La) modified nanobiochar derived from coffee husk biomass (Al-LaCHNBC) was reported as NO₃⁻ adsorbent. The adsorbent was synthesized by first digesting the coffee husk with acid, followed by a co-precipitation method and characterized by FTIR, XRD, and BET methods. Through a series of batch adsorption experiments, the efficiency of the developed adsorbent for removing NO₃⁻ was evaluated through optimization of experimental parameters such as pH (2), initial concentration of NO₃⁻(20 mg/L), contact time (55 min), and adsorbent dose (40 mg/mL). The study found that an acidic environment (pH of 2) significantly enhanced the uptake processes of NO₃⁻ to obtain a maximum of 98% removal efficiency with the adsorption capacity of 41.75 mg/g. The data strongly adhered to the Freundlich isotherm (R2 = 0.9915), suggesting that the adsorbent surface is heterogeneous. Furthermore, the adsorption kinetics were best described by the pseudo-second-order model (R2 = 0.979), which implies that physisorption is the primary mechanism of adsorption. The thermodynamic study also suggests that the NO₃⁻ adsorption is spontaneous and endothermic in its nature because it has negative ∆G°, positive ∆H°, and ∆S° values. Notably, when tested on real wastewater from the Akaki River in Addis Ababa, the adsorbent maintained a maximum NO₃⁻ removal efficiency of 96.60% in the presence of other competing ions.