Pd Nanoparticle-Decorated 3D-Printed Hierarchically Porous TiO₂ Scaffolds for the Efficient Reduction of a Highly Concentrated 4-Nitrophenol Solution

The large amount of 4-nitrophenol (4-NP) wastewater produced by the chemical industry has received increased concern over the growing risk of environmental pollution. The ability to catalyze the reduction of highly concentrated 4-NP wastewater is highly desirable for the practical treatment of industrial wastewater, yet it remains a significant challenge. Herein, we report Pd nanoparticle-decorated 3D-printed hierarchically porous TiO₂ scaffolds (Pd/TiO₂ scaffolds) for the efficient reduction of highly concentrated 4-NP wastewater (2 g·L^-1, ∼14.38 mM). The millimeter-sized interconnected channels in the scaffolds are conducive to rapid mass and ion transportation; meanwhile, the abundant micrometer- and nanometer-sized pores on the surface of the scaffolds offer adequate anchoring sites for Pd nanoparticles. The turnover frequency of the hierarchically porous Pd/TiO₂ scaffold (16 layers) is up to 2.69 min^-1, which is 1063 times higher than that of the Pd/TiO₂-bulk material with the same size (0.00253 min^-1). Importantly, no obvious deactivation of the catalytic activity is observed even after 20 cycles of catalytic reduction of 4-NP, showing excellent catalytic stability and reusability. Our strategy of loading the nanostructured catalyst on 3D-printable hierarchically porous structures put forward a flexible and versatile approach for boosting the catalytic performance of the catalysts, including catalytic activity, stability, and reusability, which can help promote their practical application in industry.