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

Visible-light-driven TiO2 photocatalysts are attractive for energy and environment applications, yet the currently developed TiO2 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/TiO2 pillars, TiO2 nanorods, and Pd nanoparticles serve as tree trunks, branches, and leaves, respectively. The hierarchical photocatalyst composed of Pd/C and anatase/rutile-type TiO2 heterojunction not only exhibits a high specific surface area (592.23 m2·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 mol4-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 TiO2 for efficient solar energy utilization and sustainable environment engineering.