Critical parameters and factors in the formation of spaced TiO2 nanotubes by self-organizing anodization

Abstract

Self-organized TiO2 nanotube arrays can be grown under a wide range of electrochemical conditions. In the present work, we evaluate the occurrence of spacing between tubes and the connection of this effect to organization of tubes on two-size scales. The results show that tubespacing is initiated in the very early stages of anodization between individual pore morphologies. Furthermore, the spacing, as well as the organization on two-size scales can be controlled by changing the anodization conditions, e.g., electrolyte composition, applied voltage and temperature. Namely, adjustment of H2O content, electrode temperature and voltage can lead to spaced nanotubes, and allow to control spacing. Finally, we draw conclusions on possible mechanism relevant to the growth of spaced tubes.

Optimized Spacing between TiO2 Nanotubes for Enhanced Light Harvesting and Charge Transfer

“…The XPS depth profiling in Figure e indicates somewhat higher fluoride content for DMSO and DEG NTs, which may arise from the high F‐ion concentration in the electrolytes used for anodization. Note that for the spaced tube formation, F‐ions play a key role to initiate tube‐to‐tube spacing, see previous report . Overall, the main compositional difference between spaced and close‐packed nanotubes can be summarized as follows: while EG NTs have a higher carbon content, DEG and DMSO NTs exhibit a slightly higher fluoride content (Figure S3).…”

“…Note that for the spaced tube formation, F-ions play a key role to initiate tube-to-tube spacing, see previous report. [40] Overall, the main compositional difference between spaced and close-packed nanotubes can be summarized as follows: while EG NTs have a higher carbon content, DEG and DMSO NTs exhibit a slightly higher fluoride content ( Figure S3).…”

“…The EG CP NTs are composed of tightly arranged NTs, different from the loosely-packed SP tubular arrays where the spacing is filled with secondary smaller size NTs, see previous reports. [40,41] To illustrate, Figure 1b2 and c2 exhibit SEM images of the nanotubes from bottom and cracked-off close to the bottom (small and large diameter nanotubes are highlighted), clearly showing that large diameter NTs are surrounded by smaller size nanotubes.…”

High-Field Growth of Semiconducting Anodic Oxide Films on Metal Surfaces for Photocatalytic Application

“…Electrochemically assisted photocatalysis shows superior performance in terms of purification of water from organic matter [12], polarization between two electrodes during the photocatalytic process assisting in separating the charge carriers and catalyzing the redox reactions, thus enhancing the efficiency of mineralization of the pollutants [12,15,16,23]. Moreover, efforts have been directed to developing nanostructured photocatalysts of different nature [24][25][26][27]. Most applications involve colloidal semiconductors [8,24,28], but the use of large area nanostructured thin solid films has been rapidly growing in the past few years [12,16], and methods to obtain films made of stable materials and/or composites under controlled conditions, with the possibility of modulating the morphology of the nanostructured films, are needed.…”

Accurate evaluations of both porosity and tortuosity of anodic films grown on rolled AA 1050 and on rolled or machined AA 2024 T3

“…Various authors have studied the morphological characteristics of porous anodic films formed on pure metals [1][2][3][4][5] or alloys. [6][7][8] The porosity of the anodic films grown on aluminium substrates depends on various operating conditions, related to the anodization electrolyte and to the applied electrical parameters, as well as the substrate itself.…”