Surface and adsorptive properties of Moringa oleifera bark for removal of V(V) from aqueous solutions

The bark of Moringa oleifera, a cheap and readily available natural biopolymeric resource material, found to significantly reduce coliform load and turbidity in contaminated water is investigated in this paper. Its surface and adsorptive properties are investigated to explore its adsorptive potential in removing V(V) from aqueous solutions. Surface properties were investigated using FTIR, HRSEM/EDS, IC, and BET-N₂ adsorption techniques. Adsorptive properties were investigated by optimizing adsorption parameters such as pH, temperature, initial metal concentration, and adsorbent dosage, using V(V) as an adsorbate. The adsorption-desorption isotherms are typical of type II with a H3 hysteresis loop and is characteristic of a largely macroporous material. Bottle ink pores are observed, which can provide good accessibility of the active sites, even though the internal BET surface area is typically low (1.79 g/m²). Solution pH significantly influences the adsorptive potential of the material. The low surface area negatively impacts on the adsorption capacity, but is compensated for by the exchangeable anions (Cl^-, F^-, PO₄^3-, NO₃^-, and SO₄^2-) and cations (Ca²⁺, K⁺, Mg²⁺, and Al³⁺) at the surface and the accessibility of the active sites. Adsorption isotherm modeling show that the surface is largely heterogeneous with complex multiple sites and adsorption is not limited to monolayer.