Efficient removal of methylene blue by a biochar from neem tree shell wastes using adsorption technology

Keeping sustainability concept in view with combating the crises risen from pollution of environment with dyes, this study aims to efficiently remove methylene blue (MB) dye from wastewaters using an agricultural waste derived sorbent produced by pyrolyzing of neem tree shells at 700 °C. An extensive scrutinization was performed both on the effects physiochemical variables and adsorption properties of the recruited biochar. Results showed that the prepared bio-charcoal possesses a promising textural property, leading to a high capability to retrieve MB from aqueous solutions at pH range of 8.5 to 9.0. The equilibrium of adsorption was achieved within time durations lesser than 200 min of stirring. Several mathematical models were applied to elucidate the kinetic behavior, and the outcomes vouchsafed the rate-controlling role of adsorbate-adsorbent interaction and the effect of intraparticle diffusion in the adsorption process. The equilibrium adsorption behavior was extensively evaluated through various two-parameter and three-parameter isotherms, revealing the monolayer Langmuir mechanism of adsorption and an adsorption capacity as high as 134.13 mg/g at ambient temperature (25 °C). The maximal adsorption capacity (q_max of Langmuir) increased from 126.39 mg/g (at 15 °C) to 139.59 mg/g (at 35 °C), revealing the endothermic nature of MB adsorption, confirmed by the positive enthalpy (∆H°, 14.07 kJ mol⁻¹). The spontaneous adsorption of MB (∆G° at 25 °C =  − 27.02 kJ mol⁻¹) along with high adsorption capability and other properties of the produced biochar makes it a promising sorbent with high potential for usage in real MB-laden wastewaters.