TiO2 Nanowires on TiO2 Nanotubes Arrays (TNWs/TNAs) Decorated with Au Nanoparticles and Au Nanorods for Efficient Photoelectrochemical Water Splitting and Photocatalytic Degradation of Methylene Blue

Abstract

In this study, TiO2 nanowires on TiO2 nanotubes arrays (TNWs/TNAs) and Au-decorated TNWs/TNAs nanostructures are designed and fabricated as a new type of photoanode for photoelectrochemical (PEC) water splitting. The TNWs/TNAs were fabricated on Ti folds by anodization using an aqueous NH4F/ethylene glycol solution, while Au nanoparticles (NPs) and Au nanorods (NRs) were synthesized by Turkevich methods. We studied the crystal structure, morphology, and PEC activity of four types of nanomaterial photoanodes, including TNWs/TNAs, Au NPs- TNWs/TNAs, Au NRs-TNWs/TNAs, and Au NPs-NRs-TNWs/TNAs. The TiO2 and Au-TiO2 samples exhibited pure anatase phase of TiO2 with (0 0 4), (1 0 1), and (1 0 5) preferred orientations, while Au-TiO2 presented a tiny XRD peak of Au (111) due to a small Au decorated content of 0.7 ± 0.2 at.%. In addition, the samples obtained a well-defined and uniformed structure of TNAs/TNWs; Au NPs (size of 19.0 ± 1.9 nm) and Au NRs (width of 14.8 ± 1.3 nm and length of 99.8 ± 15.1 nm) were primarily deposited on TNWs top layer; sharp Au/TiO2 interfaces were observed from HRTEM images. The photocurrent density (J) of the photoanode nanomaterials was in the range of 0.24–0.4 mA/cm2. Specifically, Au NPs-NRs- decorated TNWs/TNAs attained the highest J value of 0.4 mA/cm2 because the decoration of Au NPs and Au NRs mixture onto TNWs/TNAs improved the light harvesting capability and the light absorption in the visible-infrared region, enhanced photogenerated carriers’ density, and increased electrons’ injection efficiency via the localized surface plasmon resonance (LSPR) effect occurring at the Au nanostructures. Furthermore, amongst the investigated nanophotocatalysts, the Au NPs-NRs TNWs/TNAs exhibited the highest photocatalytic activity in the degradation of methylene blue with a high reaction rate constant of 0.7 ± 0.07 h−1, which was 2.5 times higher than that of the pristine TNWs/TNAs.

Facile and economical preparation method of TiO₂/activated carbon for photocatalytic degradation of methylene blue

“…The crystallite size (D) in TiO2 P25 and AC were estimated using the Scherrer equation and TiO2 (101) and G(200) peaks, respectively. The Scherrer equation is given as, D = 0.9λ/βcosθ, where λ, β, and θ are the X-ray wavelength, full width at half maximum of the diffraction peak, and Bragg diffraction angle, respectively [19,21,31]. The D value for TiO2 P25 in S1-S5 samples was a range of 20.6 -21.0 nm, while the D of AC was 48.9 nm.…”

“…Therefore, many nanostructured TiO2 films developed on rigid substrates (e.g. TiO2 nanotubes [16], TiO2 nanowires on TiO2 nanotube arrays [17][18][19]) have been studied for photocatalyst, solar energy conversion, and other applications [16]. The film forms of TiO2 nanomaterials face a big challenge in scaling up to the practical scale of water treatment.…”

Facile Preparation Method of TiO2/Activated Carbon for Photocatalytic Degradation of Methylene Blue

“…The crystallite size ( D ) in TiO 2 P25 and AC was estimated using the Scherrer equation and TiO 2 (101) and G(200) peaks, respectively. The Scherrer equation is given as D = 0.9 λ / β cos θ , where λ , β , and θ are the X-ray wavelength, full width at half maximum of the diffraction peak, and Bragg diffraction angle, respectively [ 18 , 23 , 34 ]. The D value for TiO 2 P25 in S1–S5 samples was a range of 20.6–21.0 nm, while the D of AC was 48.9 nm ( Figure 2 b).…”

“…However, TiO 2 P25 use in the form of suspension (slurry) may pose an ecological risk to aquatic organisms [ 14 ], which should require an expensive filtration process to separate the suspension catalyst from the treated water. Therefore, many nanostructured TiO 2 films developed on rigid substrates by the anodizing method (e.g., TiO 2 nanotubes [ 15 ], TiO 2 nanowires on TiO 2 nanotube arrays [ 16 , 17 , 18 ]) have been studied for photocatalyst, solar energy conversion, and other applications [ 15 ]. In addition, nanoparticular TiO 2 films can be synthesized successfully on various substrates (Si, quartz, or sapphire) using a gas-phase method of supersonic cluster beam deposition (SCBD) for studying the photodegradation of salicylic acid [ 19 ] and propane oxidation under 375 nm UV-LED illumination (8 mW/cm 2 ) [ 20 ].…”

Precursor-concentration-controlled Morphology of TiO2 Nanorod/Nanoflower Films for Enhanced Photoelectrochemical Water Splitting and Investigating Their Growth Mechanism

“…However, TiO2 has its own set of drawbacks as a photocatalytic material due to its wide band gap (3.0-3.2 eV) and rapid recombination of photogenerated charge carriers [6][7][8][9]. Therefore, various strategies have been used to overcome its drawbacks and enhance its performance in PEC water splitting, including metal and non-metal doping [10][11][12][13], heterostructures [14,15], and depositing noble metals [16,17]. Moreover, the morphology of nanostructured TiO2 materials with different dimensions has been used as one of the most important strategies to enhance their performance in PEC water splitting.…”