Removal of contaminants from water using Moringa oleifera Lam. as biosorbent: An overview of the last decade

This review aims to evaluate the efficiency and the application of Moringa oleifera in water treatment, to remove emerging contaminants: heavy metals, pesticides, pharmaceuticals, and dyes. A systematic search was performed in four databases, where 51 eligible articles, published between 2010 and 2021, were found for this review. To confirm the efficiency of Moringa oleifera as a biosorbent, the adsorbent modifications, kinetic and thermodynamic studies, mechanism involved in adsorptive process and maximum adsorption capacity were observed in each article. In batch adsorption studies, the best fit of experimental data using Langmuir isotherm was noted (74.5%, n = 38), and the best model applied in kinetic studied was pseudo-second order (90.2%, n = 46); also, only two articles were found that performed fixed-bed column studies, in addition to batch adsorption. The authors chose to carry out adsorbent modifications (e.g., activated carbon, chemical functionalization, esterification, composite synthesis) that enhanced the adsorption capacity of material, characterized by analytical techniques, as infrared spectroscopy, scanning electron microscopy and x-ray diffraction. However, the raw material can present high values of adsorption capacity, confirming the efficiency of Moringa as a biosorbent. The main mechanisms in adsorbent-adsorbate interactions observed was electrostatic interaction, hydrogen bonds, and van der Waals forces, which can vary according to the chemical or physical nature of adsorption. Although it has been widely used for adsorption of heavy metals and dyes, M. oleifera can be still explored in adsorption studies of pesticides and pharmaceutical, given the low number of articles found in this systematic search.