Vertically Aligned Multiscale Heterojunction Arrays via 3D Printing for Efficient Photocatalytic Nitro-Hydrogenation

Visible-light-driven TiO 2 photocatalysts are attractive for energy and environment applications, yet the currently developed TiO 2 photocatalysts generally feature a wide band gap, activation solely to UV wavelength, and rapid charge carrier recombination. Herein, inspired by the light absorption strategy of the plant structure, a vertically aligned multiscale photocatalyst based on 3D printing is developed, where the carbonized lignin/TiO 2 pillars, TiO 2 nanorods, and Pd nanoparticles serve as tree trunks, branches, and leaves, respectively. The hierarchical photocatalyst composed of Pd/C and anatase/rutile-type TiO 2 heterojunction not only exhibits a high specific surface area (592.23 m 2 ·g –1 ) for multiple light scattering but also expands the UV activation region into the visible light spectrum, with the visible light absorption over 80% and the work function as low as 2.81 eV, which can highly promote the mass transfer for surface/interface reaction under visible light. As a proof of concept, the photocatalyst demonstrates an outstanding photocatalytic nitro-hydrogenation performance to industrial concentrated 4-nitrophenol (2.0 g·L –1 ), with the turnover frequency up to ∼16.0 mol 4-NP ·mol –1 ·min –1, and no obvious deterioration is observed even after 10 cycles. This study provides a facile and scalable 3D printing strategy to promote the light-harvesting capacity of TiO 2 for efficient solar energy utilization and sustainable environment engineering.