Insights into conduction band flexibility induced by spin polarization in titanium-based metal–organic frameworks for photocatalytic water splitting and pollutants degradation

Solar energy is becoming the most promising option to mitigate the energy crisis in the future and can be applied in renewable and economical technologies such as water splitting and pollutants degradation. The promotion of the electronic energetic level is considered an efficient method to enhance the photocatalytic performance of semiconductor materials for solar energy conversion. The highly energetic electrons exhibit a remarkable reduction ability by virtue of the electronic spin polarization, which is associated with the conduction band (CB) position. Thus, the regulation of the CB position due to the redistribution of electrons by means of defect engineering presents potential. Here, a series of titanium-based metal-organic frameworks (Ti-based MOFs) named MIL-125-m% containing different extents of defects are reported to enable photocatalytic activity under simulated sunlight and visible light illumination for remarkably enhanced photocatalytic hydrogen evolution and pollutant degradation. The experimental results illustrated that MIL-125-5 % exhibited a superior photocatalytic hydrogen evolution rate (16507.27 μmol·g-1·h-1), much higher than that of MIL-125-0 % (1.444 μmol·g-1·h-1). The excellent photocatalytic performance was attributed to upshift of d-band center, which strengthened the adsorption of H*, facilitating the H2 evolution reaction. In addition, the degradation rate of MIL-125-5 % was up to twice the original rate, for the highly energetic electrons induced by the CB flexibility alleviated the photoinduced electron recombination in defective MIL-125. The strategy of defect engineering provides a new path to control the flexibility of the CB position by electronic spin polarization on adjustable metal-organic frameworks (MOFs), and the photocatalytic effect is changed accordingly.