Photocatalytic performance of freestanding tetragonal zirconia nanotubes formed in H₂O₂/NH₄F/ethylene glycol electrolyte by anodisation of zirconium

Abstract

ZrO nanotubes (ZrNTs) were produced by anodisation of zirconium foil in HO/NHF/ethylene glycol electrolyte. The as-anodised foils were then soaked in the anodising electrolyte for 12 h. Soaking weakens the adherence of the anodic layer from the substrate resulting in freestanding ZrNTs (FS-ZrNTs). Moreover, the presence of HO in the electrolyte also aids in weakening the adhesion of the film from the foil, as foil anodised in electrolyte without HO has good film adherence. The as-anodised FS-ZrNTs film was amorphous and crystallised to predominantly tetragonal phase upon annealing at >300 °C. Annealing must, however, be done at <500 °C to avoid monoclinic ZrO formation and nanotubes disintegration. FS-ZrNTs annealed at 450 °C exhibited the highest photocatalytic ability to degrade methyl orange (MO), whereby 82% MO degradation was observed after 5 h, whereas FS-ZrNTs with a mixture of monoclinic and tetragonal degraded 70% of MO after 5 h.

Sunlight activated anodic freestanding ZrO2 nanotube arrays for Cr(VI) photoreduction

“…As shown in figure 8, the optical band gap of the FSZNTs is within the range of 6.0-6.5 eV; typical values for ZrO 2 . ZrO 2 is a wide gap semiconductor and hence absorption under UV region is corresponding to the excitation of VB electrons to the CB which occurs normally at ∼230 nm [11]. Even though the band gap is large, high concentration of defects and oxygen vacancies in the sample could be responsible for the visible light absorption [47,48].…”

“…Zirconia (ZrO 2 ) is a n-type semiconductor with a band gap, E g ∼5-6 eV [8]. High negative value of the conduction band (CB) edge makes ZrO 2 as a suitable photocatalyst for water splitting [9,10], oxidation organic dyes [11,12], and reduction of inorganic contaminants [13][14][15][16]. Nevertheless, the wide band gap of ZrO 2 restricts its use under ultraviolet (UV) irradiation which accounts for less than 5% of the solar energy [17].…”

“…In this work, ZrO 2 nanotubes (ZNTs) were produced by anodization of zirconium (Zr) foil in fluoride ethylene glycol (EG) electrolyte. The as-anodized nanotubes were wellaligned and rather amorphous [11,15,16,26]. Moreover, as the electrochemical anodization process is controlled by ionic migration across the growing oxide, the ZNTs are expected to have significant amount of structural defects [27] and ionic contamination [28].…”

“…We then intentionally removed the anodic ZrO 2 from the substrate as to yield the freestanding ZrO 2 nanotube (FSZNT) arrays in a form of loose flakes. There are two main approaches implemented for the fabrication of FSZNTs in the literature: anodization parameters regulation [11,29,30] and chemically induced delamination [31]. Here, the first approach was adopted.…”

Green synthesis of ZrO2 nanoparticles and nanocomposites for biomedical and environmental applications: a review

“…It was also witnessed an enhancement of the photocatalytic activities of ZrO 2 to methylene blue (91%) and methyl orange (69%) for 240 min. These results of green ZrO 2 were remarkably higher than those obtained by the chemical methods such as anodization in H 2 O 2 /NH 4 F/ethylene glycol electrolyte (Rozana et al 2017 ), decomposition of Zr(OH) 4 -urea complex (Sudrajat et al 2016 ), polymer-assisted sol–gel synthesis (Dhandapani et al 2016 ).…”