Fabrication, Characterization, and Photoelectrocatalytic Application of ZnO Nanorods Grafted on Vertically Aligned TiO₂ Nanotubes

Abstract

In this article, ZnO nanorods (NRs) were grafted on Ti-based vertically aligned TiO 2 nanotubes (NTs) by a feasible seed-induced hydrothermal reaction. Through such a simple but interesting structure combination of the two semiconductors, a novel composite photocatalytic anode of ZnO NRs/TiO 2 NTs with high efficiency was accordingly obtained. In this coupling, ZnO NRs could grow to flowerlike clusters directly grafted on the tops of TiO 2 NTs, acting just like a large number of lead wires, outstretched from the trunk TiO 2 NTs. Thus, the grafted ZnO NRs could serve conveniently as favorable hole channels and receptors for the efficient separation of photoelectrons and holes, which resulted in a slight shift of the band gap absorption edges and consequently changed the band gap energy (Eg). Moreover, the graft amount would further make a certain impact on the Eg. With an appropriate graft amount, ZnO NRs/TiO 2 NTs exhibited broader optical absorption range and higher photocatalytic activity than pure TiO 2 NTs or ZnO NRs did. Under the illumination of 365 nm UV light, the photoelectric conversion efficiency was enhanced from 7.0% of pure TiO 2 NTs to 23.6% of ZnO NRs/TiO 2 NTs. In the photoelectrocatalytic oxidation application, ZnO NRs/TiO 2 NTs exhibited higher removal ability for bisphenol A (BPA). The kinetic constant was 21.4 × 10 -5 s -1 , almost 2.3 times faster than that on pure TiO 2 NTs. Also, the stability of ZnO NRs was promoted on TiO 2 NTs with a stable BPA cyclic removal percentage because the receipted holes on ZnO NRs could prevent ZnO from photocorrosion efficiently.

One-Dimensional Core/Shell Structured TiO2/ZnO Heterojunction for Improved Photoelectrochemical Performance

“…To date, a variety of inorganic heterojunction architectures have been developed to enhance the efficiency of photoelectrochemical water splitting cell. [22][23][24][25][26][27][28][29][30] In our study, we adapted this long-established strategy to enhance the photocatalytic activity of hydrothermally grown TiO 2 nanorod array. As a coupling material, we chose ZnO because its conduction band-edge is positioned at more negative potential in comparison with that of TiO 2 , thus being suitable for building the type-II band alignment (Scheme 1).…”

“…The improved photoelectrochemical activity due to the electron-hole separation in the TiO 2 /ZnO heterojunction has been well-documented in previous reports. [28][29][30] This improved charge separation is also capable of raising the Fermi level of the TiO 2 /ZnO heterojunction, rendering it more favorable for H 2 evolution. 28 The preparation of TiO 2 /ZnO heterojunction array, however, remains challenging in spite of well-developed wet chemistry of ZnO.…”

“…[28][29][30] This improved charge separation is also capable of raising the Fermi level of the TiO 2 /ZnO heterojunction, rendering it more favorable for H 2 evolution. 28 The preparation of TiO 2 /ZnO heterojunction array, however, remains challenging in spite of well-developed wet chemistry of ZnO. A difficulty in the synthesis is associated with the highly hydrophobic surface of the hydrothermally grown TiO 2 nanorod array, which prevents any aqueous ZnO precursor solutions from penetrating into grooves along the nanorods.…”

A Review on the Fabrication of Hierarchical ZnO Nanostructures for Photocatalysis Application

“…Combining this with the former could efficiently prolong the life span of photoexcited electron-hole pairs and enhance the anti-photocorrosion ability, owing to the synergistic contribution of each unit in the composites [100][101][102]. For example, Xiao et al [103] prepared branched hierarchical ZnO nanorod-TiO 2 nanotube array heterostructures (ZnO NRs/NP-TNTAs) via a two-step assembly method.…”

Preparation and characterisation of AgIn(WO4)2photocatalyst with high photoreduction activity

“…Since Fujishima and Honda [1] discovered the evolution of oxygen and hydrogen from water using TiO 2 electrode under the irradiation of light in 1972, the field of photodegradating pollutant and splitting water using TiO 2 as photocatalyst has been widely studied [2][3][4][5][6]. However, the photocatalytic activity of TiO 2 (the band gap of anatase TiO 2 is 3.2 eV and it can be excited by photons with wavelengths below 387 nm) is limited to irradiation wavelengths in the UV region; thereby the effective utilisation of solar energy is limited to about 3-5% of the total solar spectrum.…”