Eco-Friendly Ammonia Adsorption from Aqueous Solutions Using Activated Madhuca indica Leaves Charcoal and Optimization of Parameters by RSM-BBD: A Sustainable Zero-Waste Approach

Ammonia separation from industrial effluents is a big concern for aquatic, plant, and human lives. Adsorption is best suited for separating ammonia from effluents due to its high effectiveness. In this paper, the activated Madhuca indica leaves charcoal (AMLC) adsorbent was synthesized and characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy with energy-dispersive X-ray analysis (SEM-EDX) to know the characteristics of the adsorbent before and after adsorption. Further, thermal gravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), and Brunauer–Emmett–Teller (BET) analysis were performed on the AMLC adsorbent, and a very high surface area of 964.252 m 2 /g was observed. The AMLC was utilized for adsorption experiments, and the adsorption parameters were optimized using response surface methodology-Box–Behnken design (RSM-BBD). The optimized parameters reported using RSM-BBD are a contact time of 123.19 min, an adsorbent dosage of 29.1 g/L, a pH of 10.33, an initial ammonia concentration of 312.28 mg/L, and a shaker speed of 82.70 rpm that gives the maximum ammonia removal efficiency of 100%. The adsorption equilibrium studies were analyzed using Langmuir, Freundlich, and Dubinin isotherms, with the Langmuir isotherm being the best fit for the data. The adsorption kinetics were modeled with pseudo-first-order (PFO), pseudo-second-order (PSO), and intraparticle diffusion (IPD) models, indicating that PSO best describes the rate of kinetics. In addition, adsorption thermodynamics is also studied. The change in enthalpy (Δ H ) was positive, suggesting that the adsorption is an endothermic process. The negative energy of entropy (Δ S ) indicated complex formation with the AMLC adsorbent. In contrast, the positive change in Gibb’s free energy showed that adsorption was not spontaneous. The present study supports UN SDG Goal 6 by providing sustainable and cost-effective solutions to water treatment. It also promotes biomass use and reduces chemical usage toward an eco-friendly water purification process.