Environmental pollution and shortage of energy resources are considered the most serious threats faced by mankind. Heterogeneous photocatalysis has become one of the most investigated technologies, thanks to its dual ability to store solar energy and perform environmental remediation. However, the low quantum efficiencies achieved so far over TiO2 photocatalysts represent a big challenge that needs to be overcome before their potential is fully realized. Among other possibilities, the loading of noble metals (e.g. platinum) is a proven strategy to enhance the activity toward both the photooxidation of organic pollutants and molecular hydrogen evolution via water reduction. However, the method, in which Pt/TiO2 is prepared has a crucial role in tuning the photocatalytic activity.
In this work, platinum-loaded anatase TiO2 photocatalysts were prepared using two alternative methods: photodeposition by reduction of PtCl62- (PtPD-TiO2), and physical mixing of TiO2 with Pt nanoparticles synthesized by laser ablation (PtLA-TiO2). The influence of Pt and its deposition method was evaluated in the photoreforming reaction of two organic substrates: naphthalene, and methanol. To explain the different activities, a full physicochemical characterization was performed on these samples, applying inductively coupled plasma - optical emission spectrometry (ICP-OES), X-ray diffraction (XRD), high resolution-transmission electron microscopy (HR-TEM), diffuse reflectance (DR) UV-vis spectroscopy, and Brunauer, Emmett and Teller adsorption (BET) methods. Moreover, the charge-carrier dynamics in pristine and platinized TiO2 were investigated by transient absorption spectroscopy (TAS) in complement with the electron paramagnetic resonance (EPR) technique.
The deposition of Pt evinced a significant decrease in the charge carrier recombination rates, which in turn led to increased performances in the photocatalytic reactions. This effect was mainly attributed to the strong metal-support interaction resulting from the photodeposition process, aided by the preferential deposition on crystalline facets with strong reducing properties.