Investigation of Synergistic Effects of Hydrogenation and Copper Decoration on the Electrocatalytic Application (HER) of TiO2 Nanotube Array Electrodes

Palladized TiO2 nanotube array electrode was prepared for the electrocatalytic hydrodehalogenation (HDH) of 2,4,5-trichlorobiphenyl (2,4,5-PCB). The TiO2 nanotube array electrode was successfully fabricated by anodic oxidation method, and Pd was loaded onto the TiO2 nanotubes by electrochemical deposition. The morphology and structure of the nanotube array electrodes with and without Pd catalysts were evaluated by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The results showed that the diameters and lengths of the TiO2 nanotubes were 30–50 nm and 200–400 nm, respectively. The particle size of the Pd was about 12 nm. Electrocatalytic HDH of 2,4,5-PCB with the Pd/TiO2 nanotube array electrode was performed in H-cell reactor. Under a constant potential of -1.0 V, the HDH efficiency of 2,4,5-PCB was 90% and the biphenyl yield was 83% (15% current efficiency) within 180min at the Pd/TiO2 nanotube array electrode. Compared with the Pd/Ti electrode, the Pd/TiO2 nanotube array electrode exhibited higher HDH efficiency and stability. Additionally, the effect of the primary HDH factors was also investigated.

Enhanced photoeletrocatalytic reduction dechlorinations of PCP by Ru-Pd BQDs anchored Titania NAEs composites with double Schottky junctions: First-principles evidence and experimental verifications

Dye-sensitized solar cells (DSCs) are more spotlighted than conventional photovoltaic devices due to their relatively low cost, easy fabrication and high efficiency. However, there are limitations to increase the conversion efficiency of DSCs. The limiting factors are the quantity of dye adsorption and charge recombination between TiO2 electrode and electrolyte. Coating other materials such as high energy band gap insulators or semiconductors on the TiO2 electrode enhances dye adsorption and reduces charge recombination. We fabricated DSCs based on bare TiO2 nanotube arrays and 0.02 and 0.04 M MgO coated TiO2 nanotube arrays. MgO layer increased the photovoltage and photocurrent. The overall conversion efficiency of DSCs using 0.02 M MgO coated TiO2 nanotubes was 1.61%. MgO formed insulating layers between TiO2 nanotube array electrode and electrolyte. Charge recombination was inhibited at the interfaces of TiO2 nanotube array electrode and electrolyte by MgO insulating layers. MgO coating also improved dye adsorption because iso-electric point (IEP) of MgO was larger than TiO2. When the IEP of coating material is larger than TiO2, the chemical attraction between the electrode surface and Ru-based dye molecule is increased.

Herein, black TiO2 nanotube arrays (NTAs) were fabricated using electrochemical self-doping approaches, and characterized systemically by scanning electron microscopy (SEM), powder X-ray diffraction (XRD), UV-visible absorption spectroscopy and photoluminescence spectroscopy (PL). The as-obtained black TiO2 nanotube arrays (NTAs) exhibited stronger absorption in the visible-light region, a better separation rate of light-induced carriers, and higher electrical conductivity than TiO2 nanotube arrays (NTAs). These characteristics cause black TiO2 nanotube array (NTA) electrodes to have higher photoelectrocatalytic activity for degrading anthraquinone dye (reactive brilliant blue KN-R) than the TiO2 nanotube array (NTA) electrode. Furthermore, a synergetic action between photocatalysis and electrocatalysis was also observed. The black TiO2 nanotube array (NTA) electrode is considered to be a promising photoanode for the treatment of organic pollutants.

Enhanced efficiency of dye-sensitized solar cells through TiCl4-treated, nanoporous-layer-covered TiO2 nanotube arrays

In the present study, ITO nanowires electrode within the anodized TiO2 nanotubes without using the polycarbonate membrane templates were attempted. The process begins with an anodized TiO2 nanotube arrays (TNA) and subsequent growth of indium‐tin‐oxide (ITO) nanowires into the TiO2 nanotube arrays via the electrophoretic process (EPD). The open‐end of TiO2 nanotubes were synthesized for the photoelectrode of DSSC. ITO nanowires were then grown into these TNA by EPD process. The composite of ITO/anodized TNA was employed as the working electrode for the assembly into DSSCs. The advantage of the present method is that the membrane templates in EPD process were not required. In addition, the ITO nanowires will surely not contact each other which might cause short circuit. The morphologies and the structures of ITO nanowires and TNA electrode were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM).

Free-standing TiO2 nanotube (NT) arrays have been prepared by a two-step anodization method. These translucent TiO2 NT arrays can be transferred to the fluorine-doped tin oxide glass substrates to form front-side illuminated TiO2 NT electrodes. The TiO2 NT electrodes were double-sensitized by CdSe/CdS quantum dots (QDs) through successive ionic layer adsorption and reaction (SILAR) process. The absorption range of the TiO2 NT electrode was extended from ~380 to 700 nm after sensitization with CdSe/CdS QDs. The SILAR cycles were investigated to find out the best combination of CdS and CdSe QDs for photovoltaic performance. The power conversion efficiency of 2.42 % was achieved by the CdSe(10)/CdS(8)/TiO2 NT solar cell. A further improved efficiency of 2.57 % was obtained with two cycles of ZnS overlayer on the CdSe(10)/CdS(8)/TiO2 NT electrode, which is 45.19 % higher than that of back-side illuminated solar cell. Furthermore, the ZnS(2)/CdSe(10)/CdS(8)/TiO2 NT solar cell possesses a higher stability than CdSe(10)/CdS(8)/TiO2 NT solar cell during the same period. The better photovoltaic performance of the ZnS(2)/CdSe(10)/CdS(8)/TiO2 NT solar cell has demonstrated the promising value to design quantum dots-sensitized solar cells with double-sensitized front-side illuminated TiO2 NT arrays strategy.

Preparation of short, robust and highly ordered TiO2 nanotube arrays and their applications as electrode

TiO2 nanotube arrays photoelectrodes were prepared by anode oxidation on pure Ti sheet. The donor material glycol (C2H6O2) added in the anode electrolyte significantly reduced the charge transfer im- pedance of TiO2 nanotubes to promote the photocatalytic water splitting for hydrogen production. TiO2 nanotube arrays electrodes were modified by cerium and oxidative cerium with electrochemical deposition and anodic oxidation. The flat band potential moves to the negative potential direction after modification. Electrochemical impedance spectrum (EIS) measurement was used to investigate the electron transfer char- acteristic in photoelectrodes and the interface characteristic in the photoelectrochemical cell (PEC) for hydrogen production. Arcs of EIS and corresponding electrode processes were discussed. Dynamic parameters of the electrodes were calculated by reasonable electrical equivalent circuit fitting. The results indicate that TiO2 nanotube arrays electrode modified by cerium and oxidative cerium could largely decrease the electron transfer resistance which contributes to hydrogen production. The mechanism of the cerium and oxidative cerium acting on TiO2 nanotube arrays to promote charge transfer is discussed.

TiO2 nanotube arrays sensitized with ZnFe2O4 nano-crystals were successfully fabricated by a two-step process of anodization and a vacuum-assistant impregnation method followed by annealing. The sample was studied by an environmental scanning electron microscope, a transmission electron microscope, energy-dispersive X-ray analysis, and X-ray diffraction to characterize its morphology and chemical composition. Ultraviolet-visible (UV-vis) absorption spectra and a photoelectrochemical measurement approved that the ZnFe2O4 sensitization enhanced the probability of photoinduced charge separation and extended the range of the photoresponse of TiO2 nanotube arrays from the UV to visible region. In addition, the behaviors of photoinduced charge transfer in a TiO2 nanotube array electrode before and after sensitization by ZnFe2O4 nanocrystals were comparatively studied. The photoluminescence of the TiO2 nanotube array electrode became suppressed, and the surface photovoltage responses on the spectrum were significantly enhanced after the introduction of ZnFe2O4 nanocrystals. The transfer dynamics of the photoinduced charges were observed directly by a transient photovoltage measurement, which revealed a fast charge separation at the interface between ZnFe2O4 nanocrystals and TiO2 nanotubes upon light excitation.

Self‐doped TiO2 nanotube array (DTNA) electrodes were fabricated through anodic oxidation combined with cathodic reduction. The morphology and structural features of pristine TiO2 nanotube arrays and DTNA electrodes were studied through scanning electron microscopy, X‐ray diffractometry, and X‐ray photoelectron spectroscopy. An accelerated life test was used to test the electrode service lifetime and thus the electrode's stability. The service lifetime of the DTNA electrode prepared at constant 40 V for 6 hr was approximately 338.7 hr at constant 1 mA/cm2 in a 1 M NaClO4 solution. Methyl orange (MO) was employed as the degradation probe for measuring electrochemical oxidation performance. The color removal rate of 200 mg/L MO of the DTNA electrode (85.2% at 1 mA/cm2) was greater than that of the Ti/IrO2 electrode (31.1% at 1 mA/cm2). The larger the surface area of the DTNA electrode is, the more conductive the electrode is for the degradation of organic substances. Organic degradation on the DTNA electrode occurred primarily through an indirect pathway (producing [∙OH]).

1. Introduction Dye-sensitized solar cells (DSSCs) based on nanocrystalline semiconductor oxides are a low-cost alternative to conventional solid-state photovoltaic devices [1-6]. However, as one of the major way of enhancing light absorption, light scattering plays an important role in improving DSSC efficiency. Both theoretical and experimental studies have demonstrated that a light-scatting structure can increase the optical length within a film and enhance the light absorption of porous film, resulting in improved conversion efficiency of DSSC [3,4]. Metal nanoparticles can contribute to the effective light absorption of solar cells, both by local field enhancement through the localized surface plasmon resonance and by light scattering leading to prolonged optical-path lengths [5]. Many researchers demonstrated that the size of the metal nanoparticles is a key factor for determining the plasmonic phenomena, and especially, light scattering occurs more dominantly than light absorption as the size of the metal nanoparticles increases [6]. In this study, the synthesis of anatase TiO2 nanotube (TNT) arrays with Ag nanoparticles by anodic oxidation has been proposed. The influence of the length of the TNT arrays on the photovoltaic characteristics of the prepared devices was also examined. DSSCs based on TiO2 nanotube arrays with Ag nanoparticles showed significantly enhanced performance than DSSCs consisting of bare TiO2nanotube arrays. 2. Experimental Ti foils (0.25 mm thickness, 99.7 wt% purity) were degreased by sonication in acetone, deionized (DI) water, and ethanol for 20 min, to remove surface impurities, and finally to dried in a nitrogen stream. Electrochemical anodic oxidation of the Ti foils was carried out in a two-electrode cell, with platinum (Pt) as the counter electrode at room temperature. The electrolyte for anodic oxidation was prepared with anhydrous ethylene glycol (EG) with NH4F (0.25 wt%) and H2O (3 vol%) mixture solution was stirred for 1h. The voltage was supplied by a DC power supply with a condition of 30/40/50 V at RT for 1h. After anodic oxidation, the samples were rinsed in ethanol and dried in air, followed by heat treatment at 450°C in N2 for 2h to produce TiO2 nanotube arrays. Ag nanoparticles was carried out by immersing the as-prepared TiO2 nanotube in an aqueous electrolyte composed of 0.2 M Silver nitrate (AgNO3) solution and 0.15 M Sodium borohydride (NaBH4) for 5 min at room temperature. The TiO2 nanotube arrays with Ag nanoparticles were then rinsed with DI water and dried in vacuum at 50°C overnight. To fabricate DSSCs, TiO2 nanotube arrays with or without Ag modifications were soaked with N719 dye was added tert-butanol and acetonitrile solution, such mixing ratio 1:1 to prepare a concentration of 5 × 10-4 M dye solution. The DSSCs were finally packed by sealing the dye-coated electrode with a thermally platinized FTO counter electrode through a thin thermal plastic film (Surlyn, 25 ƒÝm, Solaronix). An electrolyte composed of 0.1 M N-methyl benzimidiazoium, 0.6 M 1-propyl-3-methylimidiazolium iodide, 0.05 M I2, 0.1 M guanidinium thiocyanate, and 0.2 M NaI in 3-methoxypropionitrile was introduced into the cell through a pre-drilled hole in the counter electrode. The hole was subsequently sealed with a microscope slip using Surlyn film. 3. Results and Discussion Fig. 1 XRD patterns of TNT arrays by anodic oxidation at 30 V (a) without Ag nanoparticles, (b) with Ag nanoparticles, (c) TNTs peak, and (d) Ag peak.Fig. 2 I-V characteristic curves of DSSCs with and without Ag nanoparticles by anodic oxidation at different voltage. 4. Conclusions In conclusion, anatase TiO2 nanotube arrays with Ag nanoparticles were synthesized by anodic oxidation. At the deposition voltage of 30 V and Ag-coated TiO2 nanotube arrays, the η, Jsc, and FF all reached the maximum. Compared with the conventional DSSCs Jsc, Voc, and η were increased from 7.28 to 8.45 mA/cm2, 0.7 to 0.72 V, and 4.03 to 4.81%. It is expected that the proposed approach for the synthesis of high-quality TiO2nanotube arrays with Ag nanoparticles might open up potential applications for solid or liquid DSSCs and nanostructure devices in the near future.

Plasmon-induced photoelectrocatalytic activity of Au nanoparticles enhanced TiO2 nanotube arrays electrodes for environmental remediation

In this study, a ternary z-scheme heterojunction of Bi2WO6 with carbon nanoparticles and TiO2 nanotube arrays was used to remove paracetamol from water by photoelectrocatalysis. The materials and z-scheme electrode were characterised using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), EDS mapping, ultraviolet diffuse reflection spectroscopy (UV-DRS), photocurrent measurement, electrochemical impedance spectroscopy (EIS), uv-vis spectroscopy and total organic carbon measurement (TOC). The effect of parameters such as current density and pH were studied. At optimal conditions, the electrode was applied for photoelectrocatalytic degradation of paracetamol, which gave a degradation efficiency of 84% within 180 min. The total organic carbon removal percentage obtained when using this electrode was 72%. Scavenger studies revealed that the holes played a crucial role during the photoelectrocatalytic degradation of paracetamol. The electrode showed high stability and reusability therefore suggesting that the z-scheme Bi2WO6-CNP-TiO2 nanotube arrays electrode is an efficient photoanode for the degradation of pharmaceuticals in wastewater.

Cyclic voltammetry studies of TiO2 nanotube arrays electrode: Conductivity and reactivity in the presence of H+ and aqueous redox systems