Adsorption of molybdenum (VI) from wastewater using a metal-organic framework material

With the aim of removing ⁹⁹Mo from radioactive wastewater, a metal-organic framework Zr-MOF and its functionalized derivatives (Zr-MOF-SO₄ and Zr-MOF-C₂O₄) were prepared as adsorbents, and characterized by SEM, XPS and FI-IR. The results showed the –SO₄ and –C₂O₄ groups were successfully loaded onto the surface of the original Zr-MOF; the obtained Zr-MOF-SO₄ and Zr-MOF-C₂O₄ presented different morphologies as small pellets. Both exhibit high adsorption efficiency and fast adsorption rates due to their abundant –SO₄ and –C₂O₄ surface groups, that provide many adsorption sites for Mo(VI). The maximum adsorption capacities for Mo(VI) of Zr-MOF-SO₄ and Zr-MOF-C₂O₄ are 192.5 mg g⁻¹ and 432.3 mg g⁻¹, respectively, which is an improvement over other similar adsorbents. In addition, thermodynamic studies indicate a spontaneous exothermic mechanism for the adsorption process. These results demonstrate that anchoring of the functionalized groups is a good way to improve Mo(VI) adsorption capacity of MOF materials.