Production of green biosorbent from chemically modified moringa leaves for enhanced removal of heavy metal in aqueous environment

The production of valuable materials from plants has attracted the attention of scientists worldwide. In this study, a novel biosorbent from Moringa oleifera leaves (MOL), an agricultural waste, material that is inexpensive and environmentally friendly, was successfully modified with citric acid (CA) to remove heavy metal from the aqueous environment. The CA-MOL sample showed significantly better adsorption of heavy metal than MOL. The optimum adsorption conditions are the modifier content of 0.1 M, solution pH of 5, biosorbent dosage of 0.25 g/L, and Pb²⁺ concentration of 60 ppm, with a Pb²⁺ removal efficiency of 86.72% and an adsorption capacity of 208.13 mg.g⁻¹ and a rate constant of 0.004 g.mg⁻¹.min⁻¹. The adsorption increases rapidly in the initial 5 min and reaches equilibrium in 10 min. The experimental profiles are in best agreement with Langmuir’s isothermal model, showing a correlation coefficient of 0.994 and an adsorption capacity of 253.81 mg.g⁻¹ at 303 K. In a multi-metal system, the Pb²⁺ removal efficiency was 86.72% compared to only 29.81% in the case of Ni²⁺. In addition, the CA-MOL is relatively stable. After 5 cycles, the adsorption efficiency still reaches 75.34% and the mass loss after 48 h soaking in HCl solution is 73.17%. Moreover, the activation energy is 671.15 kJ.mol⁻¹ and the adsorption efficiency of the CA-MOL was compared with other materials in the literature.