Fabrication of Pd-TiO2 nanotube photoactive junctions via Atomic Layer Deposition for persistent pesticide pollutants degradation

The design of nano-structured heterogeneous catalytic junctions with high interface to volume ratio and discrete surface distribution is critical to promote the photoelectron activity in the catalytic degradation of organic pollutants. In this work, photocatalytic palladium-titanium dioxide nano-junctions were fabricated via Atomic Layer Deposition (ALD) of palladium nanoparticles over the surface of titanium dioxide nanotubes. The Pd catalytic interface and resulting active site density was tailored by varying the nanoparticle growth and coalescence via ALD, leading to Pd-TiO2 junctions with distinctive morphological aspects and interface properties. The visible light response of the Pd-TiO2 junctions was attributed to the Surface Plasmon Resonance effect and correlated to the variation of the catalyst morphology tuned by ALD. Uniform, discrete distribution of Pd nanoparticles with diameter lower than 5 nm led to high catalytic interface to deposited volume ratio. The nano-engineered Pd-TiO2 junctions showed enhanced photocatalytic activity towards the degradation of methylene blue selected as a model contaminant and 2,4 D, with a kinetic constant 4.5 higher than as-annealed anatase TiO2 nanotubes. The design of well-defined catalytic junctions obtainable by a scalable, accurate deposition technique such as ALD represents a promising route to develop cutting-edge photoactive devices with high performance and minimum noble-metal loading.