Modified crystal structure and improved photocatalytic activity of MIL-53 via inorganic acid modulator

Metal-organic frameworks (MOFs) as photocatalysts have attracted considerable attention due to their potential for environment remediation, of which MIL-53 is a representative member of MOFs. However, the photocatalytic performance was affected by the recombination of photo-generated electron-hole pairs. On the one hand, acid-modulated MOFs have received much attention, however, more attention have been paid to the adsorption capacity and there is still a big gap in the application of photocatalysis. This work focused on the effect of HCl modulator on crystal structure and photocatalytic activity. In the morphology aspect, the presence of smaller crystals and layer structure and mesoporous distribution was due to the regulatory effect of HCl, and it had a double function: slowing down the hydrolysis of FeCl3·6H2O as well as conteracting the deprotonation of the dissovled carboxylic acids. Notablely, as demonstrated by XRD, the change of crystal form from MIL-53 to MIL-88 was attributed to the presence of 40 μL. Increased specific surface area could provide more adsorptive and catalytic sites. Compared with the MIL-53, the photocatalytic activity of acid-regulated MIL-53 increased by 1.5 times. Meanwhile, the quantitative relationship between the photocatalytic activity and the content of HCl was revealed. Finally, O2− and OH as the main active free radicals in photocatalytic degradation process were confirmed by the EPR analysis. This work provides a basis for the application of modulated MOFs by acid modulator in photocatalysis.