Abstract
AbstractIn recent years, photocatalytic reactions on anodic TiO2 nanotubes have been intensively investigated. In order to show photocatalytic activity, anodically formed nanotubes need to be crystallized to anatase. This is conventionally done by thermal annealing in air at temperatures 400–600 °C. Recently, a so‐called “water annealing” treatment has been reported to be effective to also create a highly active form for photocatalysis. Here we report on the feasibility of using a water annealing treatment of TiO2 nanotubes to create a photocatalyst for H2 production that is as active as conventional thermal annealing. If the water‐annealed samples are additionally hydrogenated to a so‐called “grey” modification, a further significant improvement of the photocatalytic activity for H2 evolution can be achieved – this without the use of any noble metal co‐catalyst. A combination of water annealing, thermal annealing, followed by hydrogenation can deliver a H2 generation activity that is more than five times higher than that achieved by thermal annealing of anodic TiO2 nanotubes.
Highlights
In recent years, photocatalytic reactions on anodic TiO2 nanotubes have been intensively investigated
A combination of water annealing, thermal annealing, followed by hydrogenation can deliver a H2 generation activity that is more than five times higher than that achieved by thermal annealing of anodic TiO2 nanotubes
We investigate if water annealed tubes can be competitive with thermal annealing
Summary
Water annealing provides a higher surface area, the thermal air treatment crystallinity, and hydrogenation induced Ti3 + defects that enable an enhanced electron transport and co-catalytic sites improving the reaction rate for H2 generation. The present work shows that the combination of water annealing, air annealing, and hydrogenation allows to achieve intrinsic cocatalytic centers, combined with effective electron transport mediation for the H2 generation reaction – well in line with earlier observations for hydrogenated tubes and other hydrogenated TiO2 nanostructures.[31]. The first anodization was performed at a constant potential of 60 V for 20 minutes and the formed TiO2 nanotube layer was removed by a gun type sonicator, followed by immediate rinsing with DI water and drying in N2 This procedure lead to formation of highly ordered dimples on the titanium substrate surface. Upon finishing the anodization process, the TiO2 nanotube layers were soaked in pure ethanol solution for 5 minutes to detach remnants of the electrolyte and the samples were dried with an N2 stream
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