N-TiO2/FeMIL-88B- A Promising Photocatalyst for Photoconversion of CO2 into Methanol

The present objective of this work is to find photoactive materials capable of facilitating visible light-driven redox reactions between CO2 and H2O. Our research is primarily focused on the incorporation of nitrogen (N) into the crystal lattice of titanium dioxide (TiO2) and its deposition onto Fe-MIL-88B to improve light absorption properties, minimize recombination of photo-generated electron-hole pairs, and increase CO2 adsorption capacity. The N-TiO2/Fe-MIL-88B composite was successfully prepared and characterized using SEM, XRD, and EDX techniques. The introduction of N-TiO2 into Fe-MIL-88B does not damage the crystal structure of Fe-MIL-88B.  Anatase is the only crystalline phase observed from the XRD diffraction pattern. SEM images show that N-TiO2 is well dispersed on the Fe-MIL-88B surface. The results of quantum simulations indicate that TiO2 strongly interacts with Fe-MIL-88B. The binding energy is determined to be -78.2 kcal/mol. The calculated UV-Vis results revealed that the light absorption edge of the TiO2/Fe-MIL-88B was red-shifted in comparison with that of the pure TiO2 (from ca. 500 nm to 550 nm). The red-shifted light absorption of TiO2/FeMIL-88B suggests that the band gap of TiO2/Fe-MIL-88B is narrower compared to that of the pristine TiO2, indicating the better light utilization ability of the TiO2/Fe-MIL-88B. Results from high-performance liquid chromatography show that N-TiO2 has the capability to convert CO2, but at a significantly low rate. The methanol formation is distinctly observed only over the N-TiO2/Fe-MIL-88B catalyst. The CO2 conversion efficiency, estimated using gas chromatography, is calculated to be 11.94%.