Abstract
We report on a combined chemical vapor deposition (CVD)/radio frequency (RF) sputtering synthetic strategy for the controlled surface modification of ZnO nanostructures by Ti-containing species. Specifically, the proposed approach consists in the CVD of grown-on-tip ZnO nanopyramids, followed by titanium RF sputtering under mild conditions. The results obtained by a thorough characterization demonstrate the successful ZnO surface functionalization with dispersed Ti-containing species in low amounts. This phenomenon, in turn, yields a remarkable enhancement of photoactivated superhydrophilic behavior, self-cleaning ability, and photocatalytic performances in comparison to bare ZnO. The reasons accounting for such an improvement are unravelled by a multitechnique analysis, elucidating the interplay between material chemico-physical properties and the corresponding functional behavior. Overall, the proposed strategy stands as an amenable tool for the mastering of semiconductor-based functional nanoarchitectures through ad hoc engineering of the system surface.
Highlights
The resulting porous nanopyramid arrays were likely endowed with a high surface area and predominantly exposed high surface energy (001) and (101) reactive facets.[22,46−48] Based on these favorable features, in this study we focus our attention on the chemical vapor deposition (CVD) growth of ZnO nanopyramids on fluorine-doped tin oxide (FTO) substrates and their subsequent functionalization with Ti-containing species via radio frequency (RF) sputtering
The CVD growth of ZnO nanopyramids on FTO substrates was followed by their surface functionalization with Ti-containing species via RF sputtering for different process durations (2 or 4 h) to tailor the overall Ti content in the obtained systems
Higher resolution HAADF-STEM imaging and energy dispersive X-ray spectroscopy (EDXS) elemental mapping were performed on individual ZnO nanopyramids (Figure 3c), and the results demonstrated that Ti-containing species were very finely dispersed over ZnO nanostructures
Summary
ZnO, to TiO2, is an important n-type semiconductor that, due to its appealing optoelectronic and structural properties, has been widely studied for photocatalytic, selfcleaning, and other light-triggered applications.[1−8] In this regard, examples on the use of ZnO-based materials encompass various fields, ranging from water and air photocatalytic purification[2−4,9−11] and solar fuels generation by photocatalytic/photoelectrochemical routes[12−16] to the conversion of radiant energy into electricity in dye-sensitized solar cells[17−19] and up to the fabrication of smart surfaces with antifogging properties.[2,3,5]. Notwithstanding the impressive research efforts devoted to zinc(II) oxide, technological advancements based on the use of ZnO systems are still hindered by some material limitations, among which are the moderate catalytic activity, the rapid recombination of photogenerated charge carriers, and the tendency to photocorrosion.[12,20−22] To overcome such drawbacks, two main strategies have been proposed:[4,11,20,23,24] (i) the fabrication of composites based on the combination of ZnO with other semiconductors and (ii) the modification of ZnO by doping with foreign elements In this context, ZnO− TiO2 composites and Ti(IV)-doped ZnO are appealing systems to address issues i) and ii), respectively, resulting in nanomaterials with improved functional performances.
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