Development of polyoxometalate-loaded MOFs for heterogeneous catalysis and enhanced dye adsorption

Abstract

This study focuses on the enhancement of MIL-117 functionality by incorporating a well-known polyoxometalate (POM), tetrabutylammonium octamolybdate [(n-C₄H₉)₄N]₄[Mo₈O₂₆]. Using an encapsulation method with conventional heating, Mo₈O₂₆⁴⁻ anions were for the first time successfully integrated into MIL-117 tubular channels (Mo₈O₂₆@MIL-117). Comprehensive characterization of the material through FTIR, XRD, BET, FE-SEM, EDX, and XPS confirmed the uniform distribution of Mo₈O₂₆⁴⁻ within MIL-117 without compromising its structural integrity. The Mo₈O₂₆@MIL-117 composite demonstrates exceptional catalytic performance in oxidative C–N bond formation and Paal–Knorr pyrrole synthesis, achieving high yields under optimized conditions with diverse amine substrates. Characterization and stability assessments confirm Mo₈O₂₆@MIL-117 as a robust and recyclable catalyst, maintaining structural integrity and catalytic activity over multiple cycles, highlighting its potential for sustainable applications in synthetic chemistry. The composite material was also evaluated for its efficacy in dye removal, specifically targeting methylene blue (MB) and Rhodamine B (RHB) from aqueous solutions. Mo₈O₂₆@MIL-117 exhibited superior adsorption capacity for MB compared to MIL-117 alone, demonstrating high efficiency even at elevated concentrations. The composite showed improved selectivity towards MB over RHB, highlighting its potential for selective dye removal in wastewater treatment applications.