Harnessing encapsulated polyoxometalate in MOFs for sonophotocatalytic Cr(VI) reduction: Unveiling the pathway to eco-friendly chromium remediation

In this study aluminium-based porphyrin metal–organic framework encapsulated with Keggin polyoxometalate namely (POM @ T4CP–MOF) has been synthesized by hydrothermal process. The POM @ T4CP–MOF is thoroughly characterized to evaluate structural interaction, textural properties and morphology by fourier transform infrared, ultraviolet–visible, powder X-ray diffraction, scanning electron and energy dispersive spectroscopy, thermogravimetric and differential scanning calorimetric analysis, fluorescence, X-rays photoelectron emission spectroscopy and zeta potential. The presence of porphyrin with strong coordination of Al–O units and insertion of Keggin POM in the pores of MOF allowed the POM @ T4CP–MOF to demonstrate a wide range of visible light harvesting capacity, immediate photogenerated charge response and good chemical stability. In an aqueous solution composed of Cr(VI), POM @ T4CP–MOF demonstrated unique sonophotocatalytic and photocatalytic activities. The rate of reaction in sonophotocatalysis and photocatalysis for the POM @ T4CP–MOFs is found to be 0.48 mg/L min and 0.15 mg/L min respectively, which is 3.2 times higher than photocatalysis. Sonophotocatalytic technology in conjunction with porphyrin-based MOFs could prove to be a successful tactic in enhancing MOFs-based photocatalytic systems to be utilized in the reduction process of harmful chemicals like Cr(VI).