Piezo-photocatalytic Flexible PAN/Zr-MOFs Nanofiber Membranes for Photocatalytic Hydrogen Evolution Reaction

Metal–organic frameworks (MOFs) have recently been under intense study for photocatalytic hydrogen evolution reaction (HER) as a class of crystalline porous materials. However, the efficiency of HER is still low due to the low separation efficiency of photo-generated carries of MOFs. Here, we report surface enriched Zr-MOFs (UiO-66, UiO-66-NH₂, UiO-66-SO₃H, UiO-66-NH₂-SO₃H) nanoparticles to be incorporated in polyacrylonitrile nanofibers, which were synthesized by suing electrospinning technology. By incorporating photocatalytic Zr-MOFs in flexible piezoelectric PAN nanofiber, the composite membranes exhibited both piezoelectric and photocatalytic effects. The piezoelectric fields of PAN generated due to the mechanical deformation promoted the separation of the photogenerated electrons and holes. The PAN/Zr-MOFs composite membranes showed higher hydrogen evolution activity under the synergistic effect of mechanical vibration and light irradiation than that under light irradiation alone. Among the PAN/Zr-MOFs composite membranes, the PAN/UiO-66-NH₂-SO₃ H nanofiber membranes showed the highest hydrogen evolution rate, reaching 2306 μmol^-1·g^-1·h^-1, which was 4.2 times higher than that of photocatalysis alone. The working mechanism for the promoted HER by the mechanical vibrations was attributed to the piezoelectric effect of the PAN nanofibers, which accelerated the separation of photogenerated electrons and holes in the Zr-MOFs. It is believed that the synergistic effect of mechanical vibration and light irradiation significantly enhanced the photocatalytic performance of these composite membranes, making them promising candidates for sustainable hydrogen production and other photocatalytic applications.