Pd Nanoparticles Decorated 3D Printed Hierarchically Porous TiO2 Scaffolds for Efficient Reduction of Highly Concentrated 4-Nitrophenol Solution.

The large amount of 4-nitrophenol (4-NP) wastewater produced from chemical industry has gained increasing concerns over the growing risk of environmental pollution. The ability to catalytic reduction of highly-concentrated 4-NP wastewater is highly desirable for the practical treatment of industrial wastewater yet remains a significant challenge. Herein, we report a Pd nanoparticles decorated 3D printed hierarchically porous TiO2 scaffolds (Pd/TiO2-scaffolds) for efficient reduction of highly concentrated 4-NP wastewater (2 g·L-1, ~ 14.38 mM). The mm-sized interconnected channels in the scaffolds are conducive to rapid mass and ions transport, meanwhile, the abundant micron- and nano-sized pores on the surface of 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 Pd/TiO2-bulk material with the same size (0.00253 min-1). Importantly, no obvious deactivation of catalytic activity is observed even after 20 cycles of catalytic reduction of 4-NP, showing excellent catalytic stability and reusability. Our strategy of loading nanostructured catalyst on 3D printable hierarchically porous structures put forwards a flexible and versatile approach for boosting the catalytic performance of catalysts, including catalytic activity, stability and reusability, which can help promote their practical application in industry.