CO2 conversion under visible-light driven photocatalysis by employing porphyrin MOF encapsulated Keggin polyoxometalates

Abstract

Effective conversion solutions are required to minimize climate change due to an increasing atmospheric CO₂ concentration. Photocatalytic conversion of CO₂ into valuable chemicals, such as formic acid, is a viable strategy for environmental remediation and sustainable energy. In this study, a novel porphyrin based MOFs (Metal organic framework) encapsulated with the Keggin type Polyoxometalate (POMs) namely (CPMOF@KPOM) have been synthesized and characterized by using different analytical techniques. Energy Dispersive X-ray spectroscopy (EDX) confirmed the homogeneous presence of C, N, O, Al, K, B, and W, verifying the incorporation of Keggin type POMs (K.POMs) within the framework. Scanning Electron Microscopy (SEM) revealed a porous, irregular cubic morphology, while fluorescence spectroscopy exhibited strong emission with a red shift upon varying excitation wavelengths. Electrochemical analysis via Cyclic Voltammetry (CV) and Mott-Schottky measurements demonstrated an n-type semiconductor behavior with a narrow band gap of 0.97 eV, positioning CPMOF@KPOM as a promising material for photo-electrocatalytic applications. Optical investigations, including UV–Visible absorption and diffuse Reflectance spectroscopy (DRS), confirmed significant visible-light harvesting attributed to porphyrin components. Thermal analyses including Thermogravimetric analysis and Differential scanning calorimetry (TGA and DSC) and Powder X-Ray Diffraction (PXRD) affirmed high thermal stability and phase purity. Photocatalytic reduction tests under xenon lamp irradiation yielded formic acid from CO₂, with adsorption studies indicating a maximum CO₂ uptake of 4.78 mmol/g and a desorption efficiency of 20 % at 30 °C. These results establish CPMOF@KPOM as an efficient, stable, and versatile photocatalyst for CO₂ conversion and energy storage applications.