Accelerated confined mass transfer in piezoelectric semiconducting metal-organic frameworks for H₂O₂...

The piezo-photocatalytic O₂ reduction reaction offers a promising pathway towards H₂O₂ synthesis. However, in addition to rapid recombination of photogenerated electrons and holes, this gas-consuming reaction is inherently limited by O₂ dissolution and mass transfer dynamics. Here, energy band structures and dipole moments of piezoelectric semiconducting UiO-66 metal-organic frameworks (MOFs) are engineered by modulating functional groups (-NH₂, -CH₃, -OH, -NO₂ and -F₄) and metal nodes (Hf and Zr). This fine-tuning of MOF building blocks leads to an enhanced piezoelectric coefficient, gas capacity and light absorption to facilitate subsequent piezo-photocatalysis. Furthermore, the tunable band structure enables the construction of a Z-scheme heterojunction with another piezoelectric semiconductor. The resulting heterostructure CdS/NH₂-UiO-66(Hf) with increased structural asymmetry exhibits further boosted piezoelectricity, leading to rapid charge separation and transfer due to the enhanced piezoelectric-induced built-in electric field. In addition, the piezoelectric semiconducting MOF serves as a tri-functional nanoreactor synergistically improving gas solubility, confined mass transfer, and O₂ molecule activation under periodic piezoelectric deformation. Consequently, a H₂O₂ yield rate of 2079.1 µmol g^-1 h^-1 is achieved without sacrificial agents or O₂ bubbling via coupling of piezocatalytic and photocatalytic effects. This study opens a new avenue for tailoring microenvironments to design highly efficient piezo-photocatalytic systems.