Promoting the spatial charge separation by building porous ZrO2@TiO2 heterostructure toward photocatalytic hydrogen evolution.

The robust photocatalytic hydrogen evolution (PHE) from water needs an effective photogenerated charge spatial separation and enough contact between reactant and catalyst, but the synthesis of catalysts with the characteristics remains a challenge. Herein, we report the design of core-shell heterostructure consisted of thin TiO2 layer uniformly coated on porous ZrO2 polyhedron for effective PHE. In this system, UiO-66-NH2, one of popular MOF with Zr as metal node, has been chosen as the precursor template due to its plentiful pores, uniform morphology, as well as the rich NH2 groups. Our results show that Ti precursor can uniformly coat on UiO-66-NH2, by means of interaction of tetrabutyl titanate (TBT) with -NH3 in UiO-66-NH2. Followed by the calcination, the Ti precursor and UiO-66-NH2 can be converted into ZrO2 and TiO2, respectively, thus leading to the formation of ZrO2@TiO2 core-shell heterostructure. The ZrO2@TiO2-500 has the high specific surface area of 52.4 m2 g-1. Besides, the intimate contact of TiO2 shell with ZrO2 core facilitates the separation and migration of photoinduced carriers, exposing more active sites for the surface photocatalytic hydrogen evolution reaction. The spectrum and electrochemical characterization further exhibit the extended life of photon-generated carrier and easy mass transfer. The optimized ZrO2@TiO2-500 shows enhanced photocatalytic rate of 39.7 mmol h-1 g-1, much higher than those of ZrO2 (0.8 mmol h-1 g-1) and TiO2 (7.6 mmol h-1 g-1).