Hierarchically organized nanostructured TiO₂for photocatalysis applications

Abstract

A template-free process for the synthesis of nanocrystalline TiO2 hierarchical microstructures by reactive pulsed laser deposition (PLD) is here presented. By a proper choice of deposition parameters a fine control over the morphology of TiO2 microstructures is demonstrated, going from classical compact/columnar films to a dense forest of distinct hierarchical assemblies of ultrafine nanoparticles (<10 nm), up to a more disordered, aerogel-type structure. Correspondingly, the film density varies with respect to bulk TiO2 anatase, with a degree of porosity going from 48% to over 90%. These structures are stable with respect to heat treatment at 400 degrees C, which results in crystalline ordering but not in morphological changes down to the nanoscale. Both as deposited and annealed films exhibit very promising photocatalytic properties, even superior to standard Degussa-P25 powder, as demonstrated by the degradation of stearic acid as a model molecule. The observed kinetics are correlated to the peculiar morphology of the PLD grown material. We show that the 3D multiscale hierarchical morphology enhances reaction kinetics and creates an ideal environment for mass transport and photon absorption, maximizing the surface area-to-volume ratio while at the same time providing readily accessible porosity through the large inter-tree spaces that act as distributing channels. The reported strategy provides a versatile technique to fabricate high aspect ratio 3D titania microstructures through a hierarchical assembly of ultrafine nanoparticles. Beyond photocatalytic and catalytic applications, this kind of material could be of interest for those applications where high surface-to-volume and efficient mass transport are required at the same time.

Enhanced photocatalytic generation of hydrogen by Pt-deposited nitrogen-doped TiO2 hierarchical nanostructures

“…Zheng et al synthesized hierarchical Pt/N-doped TiO 2 inorganic leaf photocatalysts for the production of H 2 from water in the presence of a sacrificial agent via a bio-templated route [26]. Several photocatalytic environmental abatements by photo-degradation of toxic pollutants [27,28], and the selective organic transformation reaction by hierarchical porous TiO 2 photocatalysts have also been reported in the last few years [2].…”

Fabrication of Nano-engineered Transparent Conducting Oxides by Pulsed Laser Deposition

“…WO 3 , Ag 4 O 4 , Al 2 O 3 and TiO 2 ), the capability to tune morphology, density, porosity, degree of structural order, stoichiometry and phase by modifying the material structure at the nanoscale [6][7][8][9][10][11] . This allows the design of materials for specific applications [12][13][14][15][16] . With reference to photovoltaic applications, we synthesized nanostructured TiO 2 hierarchically organized by assembling nanoparticles (<10 nm) in a nano-and mesostructure that resembles a 'forest of trees' 13 showing interesting results when employed as photoanodes in dye sensitized solar cells (DSSC) 17 .…”

“…This allows the design of materials for specific applications [12][13][14][15][16] . With reference to photovoltaic applications, we synthesized nanostructured TiO 2 hierarchically organized by assembling nanoparticles (<10 nm) in a nano-and mesostructure that resembles a 'forest of trees' 13 showing interesting results when employed as photoanodes in dye sensitized solar cells (DSSC) 17 . Based on these previous results we describe the protocol for the deposition of Al-doped ZnO (AZO) films as a transparent conducting oxide.…”

The design of a hierarchical photocatalyst inspired by natural forest and its usage on hydrogen generation

“…And some artificial photosynthetic systems, such as anisotropic CdSeAueTiO 2 nanojunction system [21], artificial inorganic leaf of Pt/N-doped TiO 2 [24], and CdS/TiO 2 /Pt hybrid system [9] were developed for efficient H 2 generation. However, those reports focused more on the chemical combinations of individual semiconductors, less on the structure innovation which greatly affects the improvement of photocatalytic activity [25].…”