Highly Efficient Sorption of Methyl Orange by a Metal-Organic Resin-Alginic Acid Composite

The composite anion-exchange material MOR-1-HA (metal-organic resin-1-alginic acid) was investigated as sorbent for the capture of the methyl orange anion (MO^- ) from aqueous solutions. MOR-1-HA shows a remarkably high sorption capacity (up to 859 mg g^-1 ) and rapid sorption kinetics, the fastest among the reported metal-organic sorbents. It is capable of absorbing MO^- over a wide pH range (1-8) and, in addition, it exhibits significant MO^- sorption affinity even in the presence of large excesses of competing anions (e.g., Cl^- , NO₃ ^- , SO₄ ^2- ). The exceptional MO^- -sorption properties of MOR-1-HA arise not only from its highly porous structure and easily exchangeable Cl^- anions, but also from a multitude of interaction effects, such as electrostatic interactions between MO^- and the NH₃ ⁺ groups of the material, hydration/dehydration, hydrophobicity/hydrophilicity, size and capacity of generating lateral interactions, and intercalation as revealed by theoretical studies. An ion-exchange column with a stationary phase containing MOR-1-HA and silica sand showed high efficiency for the removal of MO^- from various types of aqueous samples. The column can be readily regenerated and reused for many runs with minimal loss (2.3-9.3 %) of its exchange capacity. The simplicity of the MOR-1-HA/sand column and its high regeneration capability and reusability make it particularly attractive for application in the remediation of MO^- -contaminated industrial wastewater.