Nanotube Array Photoelectrodes Research Articles

Fabrication of layered (CdS-Mn/MoS2/CdTe)-promoted TiO2 nanotube arrays with superior photocatalytic properties

A novel (CdS-Mn/MoS2/CdTe)-sensitized TiO2 nanotube arrays (NTAs) photoelectrode has been prepared by electrodeposite, successive ionic layer adsorption and reaction (SILAR) coupled with hydrothermal method. When a ZnS layer was added on the top of CdS-Mn/MoS2/CdTe/TiO2, a notable red-shift and high absorption was observed in the visible light region. The photocurrent density (mA/cm2) systematically increases from TiO2 NTAs (0.43), CdTe/TiO2 (1.09), MoS2/CdTe/TiO2 (1.80), CdS-Mn/MoS2/CdTe/TiO2 (2.40), to ZnS/CdS-Mn/MoS2/CdTe/TiO2 (3.41) under visible light irradiation, due to the type-II semiconductor heterostructures comprising multiple components with a staggered band offset. Such a heterostructure possesses an enhanced photocatalytic performance towards degradation of organic contaminant, e.g. P-Nitrophenol (PNP) and Rhodamine B (RhB).

Towards efficient visible-light active photocatalysts: CdS/Au sensitized TiO2 nanotube arrays

A visible-light active photocatalyst, CdS/Au/TiO2 nanotube array (NTA) photoelectrode, was prepared by electrodeposition of Au nanoparticles onto TiO2 NTA with subsequent deposition of visible-light absorbable 2.4eV band-gap CdS quantum dots using successive ion layer adsorption and reaction (SILAR). The Au nanoparticles here act as electron sinks facilitating charge carrier separation. Under AM1.5G illumination a photoconversion efficiency of 4.06% was achieved for the CdS/Au/TiO2 NTA photoelectrode, suggesting the promise of the material architecture for achieving high-performance cost-effective materials.

Fabrication of platinum nano-crystallites decorated TiO2 nano-tube array photoelectrode and its enhanced photoelectrocatlytic performance for degradation of aspirin and mechanism

In this study, Pt NCs/TiO2 NTAs photoelectrode was fabricated through anodization process, followed by recycle pulse electrodeposition strategy. Subsequently, physicochemical properties of the resulting samples were studied systematically. Results indicated that Pt NCs/TiO2 NTAs photoelectrode exhibited intense light absorbance both in the UV and visible region, high transient photocurrent density of 0.089mAcm−2 and open circuit potential of −0.275Vcm−2. In addition, 98.3% of aspirin could be eliminated within 4h Xenon illumination with the help of +0.4V potential. Furthermore, it can be concluded that two tentative pathways for PEC degradation of aspirin were proposed and confirmed.

Multi-functional CuO nanowire/TiO2 nanotube arrays photoelectrode synthesis, characterization, photocatalysis and SERS applications

Vertically aligned single crystalline CuO nanowire arrays (NWs) grown directly on TiO2 nanotube arrays (NTAs) supporting by Ti foil have been successfully fabricated using facile thermal oxidation of Cu nanocrystals in static air. CuO NWs growth behavior dependent on parent Cu nanocrystals sizes has been well investigated. Mass transport channel of Cu ions in horizontal and vertical for supporting CuO NWs diameter and length changes has been confirmed through a novel step-by-step surface diffusion process. CuO NWs, nano-mushrooms and nanosheets can be easily obtained by varying growth conditions. After photocatalytic synthesis of snow-like Ag nanocrystals upon CuO NWs/TiO2 NTAs, the hybrid photoelectrode exhibits superior catalytic property and detection sensitivity, which can clean themselves by photocatalytic degradation of RhB molecules adsorbed to the substrate under irradiation using surface enhanced Raman scattering (SERS) detection, a recycling can been achieved.

Ultrasmall graphitic carbon nitride quantum dots decorated self-organized TiO2 nanotube arrays with highly efficient photoelectrochemical activity

In the present study, a novel graphitic carbon nitride quantum dots (CNQDs) modified TiO2 nanotube arrays (NTAs) photoelectrode was successfully synthesized by a simple two-step method which includes an electrochemical anodization technique followed by a facile organic molecular linkage. The successful modification of TiO2 by CNQDs was found to improve the photoelectrochemical activity significantly because of enhanced light absorption and improved separation of photo-generated electron–hole pairs. The optimized CNQDs/TiO2 NTAs showed nearly 3.5-fold photocurrent of that from TiO2 NTAs alone at 0.3V vs Ag/AgCl and the maximum photoconversion efficiency reaches up to 0.63% in neutral solution under simulated solar light irradiation. Furthermore, the prepared CNQD/TiO2 NTAs demonstrated superior photoelectrocatalytic activity and stability in the degradation of RhB, with kinetic constants 3.0 times of that from TiO2 NTAs. The hydroxyl and superoxide radicals were proved to be the dominant active radicals during pollutants degradation. Additionally, the prepared CNQD/TiO2 sample was used as photoanodes for direct photoelectrochemical water splitting to produce H2 and O2 under simulated solar light illumination, achieving a H2 production rate with 22.0μmolh−1cm−2 at 0.3V vs Ag/AgCl.

Preparation of graphene/TiO2 nanotube array photoelectrodes and their photocatalytic activity for the degradation of alachlor

Photocatalytic mechanism scheme of the degradation of alachlor by the GR/TNA photoelectrodes.

Effects of Hydroxylation on PbS Quantum Dot Sensitized TiO2 Nanotube Array Photoelectrodes

ABSTRACT The contact state at the heterojunction interfaces greatly influences the interfacial kinetics of the photoinduced charge carriers. In this study, we used a facile NaOH pretreatment to replenish the hydroxyl groups lost during the heat treatment for crystallization of TiO 2 nanotube arrays (TNAs) prepared via anodic oxidization. By reacting the carboxylic acid groups of thioglycolic acid (TGA) with the TiO 2 surface hydroxyl groups, TGA molecules were covalently linked to the TiO 2 surface and then PbS quantum dots (QDs) were anchored onto the TNAs via the successive ionic layer adsorption and reaction (SILAR) method. The sample microstructure and photoelectrochemical properties were analyzed with X-ray diffraction (XRD), transmission electron microscopy (TEM), field-emission scanning electron microscopy (FE-SEM),current–voltage characteristics ( J – V ), electrochemical impedance spectroscopy (EIS), transient photovoltage plots and Mott-Schottky curves. The contact state and electrostatic potential distribution between TiO 2 {1 0 1} and PbS {1 1 1} planes were estimated by using first principle simulation. It was found that the NaOH pretreatment could enhance the crystallization degree of PbS QDs, decrease the crystal face mismatch, dangling bond density and the interfacial resistance between PbS QDs and TiO 2 , and accelerate the interfacial separation and transfer of photoinduced charge carriers. The first principle calculations demonstrated that the PbS QDs and TiO 2 interfacial contact was strengthened, and the built-in electric field was induced from TiO 2 {1 0 1} towards PbS {1 1 1}. These combined effects apparently improved the device photoelectrochemical performance. Compared to the sample without pretreatment, the specimen pretreated with NaOH demonstrated 19.96% and 29.93% increases in peak photoconversion efficiency after five and ten cycles of SILAR deposition, respectively.

A CdS/ZnSe/TiO2 nanotube array and its visible light photocatalytic activities

A novel CdS/ZnSe/TiO2 nanotube array (NTA) photoelectrode was prepared by deposition of ZnSe nanoparticles (NPs) using pulse electrodeposition technique onto a TiO2 NTA. By successive ion layer adsorption and reaction (SILAR), CdS quantum dots (QDs) deposit onto a ZnSe/TiO2 NTA photoelectrode. The as-prepared CdS/ZnSe/TiO2 NTA photoelectrode performance is significantly improved, which not only greatly extends spatial separation of charges, but also enhance the utilization efficiency of visible-light. This system exhibits excellent charges transport property. The maximum photocurrent density of an 8.25mAcm−2 was observed in the CdS/ZnSe/TiO2 NTA photoelectrode, which is 37.5, 15.86 and 1.56 times higher than bare TiO2 NTA, ZnSe/TiO2 NTA, and CdS/TiO2NTA photoelectrodes, respectively. The photocatalytic activity of CdS/ZnSe/TiO2 NTA is tested by the degradation of methyl orange (MO) in distilled water under solar light irradiation of 100mW/cm2. Within about 120min of irradiation, 90.05% MO are removed.

Photoelectric performance of TiO2 nanotube array photoelectrodes sensitized with CdS0.54Se0.46 quantum dots

The photoelectrochemical performance of CdSSe quantum dots tethered to a framework of vertically oriented titania (TiO2) nanotubes was studied. The TiO2/CdSSe framework demonstrated improved charge transfer due to its unique band edge structure, thus validating the higher photocurrent generation. The composite film led to an 11-fold enhancement in comparison to the control TiO2 film, implying that the ternary quantum dots and the nanotubular structure of TiO2 work in tandem to promote charge separation and favorably impact photoelectrochemical performance. Further, the results also suggest that structural and optoelectronic properties of TiO2 films are significantly affected by the thicknesses of the CdSSe layer.

Preparation and characterization of CeO2 decorated TiO2 nanotube arrays photoelectrode and its enhanced photoelectrocatalytic efficiency for degradation of methyl orange

The highly oriented CeO2/TiO2 nanotube arrays (CeO2/TiO2 NTAs) were fabricated by the electrodeposition of CeO2 in 1.0 mol/L Na2SO4 aqueous solution on TiO2 NTAs. CeO2/TiO2 NTAs were characterized by SEM, TEM, XRD, XPS. Its ultraviolet–visible absorption and photoelectrochemical properties were investigated. The degradation of methyl orange was used to evaluate the photoelectrocatalytic activity of CeO2/TiO2 NTAs. The results showed that the CeO2 nanoparticles with a homogenous spherical size of about 15 nm were uniformly deposited onto the surface of TiO2 NTAs. The CeO2 composed with Ce4+ and Ce3+ ions could be observed. CeO2/TiO2 NTAs exhibited a stronger UV and visible light absorptions with 40 nm red-shift of the absorption edge compared with TiO2 NTAs. The separation efficiency of the photogenerated charge carriers of CeO2/TiO2 NTAs can significantly enhanced by the CeO2 deposited. The removal efficiencies (98.1 %) of methyl orange at the CeO2/TiO2 NTAs photoelectrodes was larger than that of the bare TiO2 nanotube arrays photoelectrode (78.1 %).

Molybdenum-doped and anatase/rutile mixed-phase TiO2 nanotube photoelectrode for high photoelectrochemical performance

Molybdenum-doped TiO2 nanotube arrays (Mo-doped TiO2 NTs) photoelectrodes with anatase/rutile mixed phase are successfully fabricated via two-step anodization of titanium followed by a hydrothermal doping treatment process. The Mo-doped TiO2 NT material shows higher photocurrent density and enhanced incident photon to current conversion efficiency (IPCE) compared with the pristine TiO2 NTs for photoelectrochemical (PEC) water-splitting. The improvement of PEC response results from not only the increasing of oxygen vacancies and reducing of the recombination of photoexcited charges by Mo-doping, but also the new formed heterojunctions of anatase/rutile mixed-phase by hydrothermal treatment. Moreover, the Mo-doped TiO2 NTs show high stability and obvious visible absorption with considerable photocurrent density under visible light (λ > 420 nm).

Achieving Enhanced Dye‐Sensitized Solar Cell Performance by TiCl4/Al2O3 Doped TiO2 Nanotube Array Photoelectrodes

For various reasons, low cost, easy fabrication, and so forth, dye‐sensitized solar cells (DSSCs) have been consistently studied in many laboratories. To improve the DSSCs performance, using an aqueous solution of titanium tetrachloride (TiCl4) treatment is one of many processes. Before the treatment of TiCl4, nanoporous TiO2 nanotubes (TNTs) are fabricated through a secondary anodization process. TiCl4 treatment on TNTs film enhanced short‐circuit current density (JSC) and aluminum oxide (Al2O3) posttreatment enhanced open‐circuit voltage (VOC). As a result, Al2O3 posttreatment on TNTs film conversion efficiency of 8.65% is realized, which is 7% higher than TiCl4 treatment on TNTs film. In this work, we investigated that double dip‐coating of TiCl4/Al2O3 treatment on TiO2 nanotubes film had an effect on enhancement of JSC and VOC due to improvement of electron transfer, increment of dye adsorption, and reduction of recombination rate of charge. Photoelectrode DSSCs with light‐to‐electric energy conversion efficiency were achieved under a simulated solar light irradiation of 100 mW·cm2 (AM 1.5).

Heterojunction Engineering of CdS and Ag2S Quantum Dots Co-Sensitized TiO2 Nanotube Array Photoelectrode

CdS and Ag2S heteojunctions sensitized TiO2 nanotube arrays (TiO2 NTs/CdS-Ag2S) were prepared by cation exchange between Cd2+ and Ag+ on the basis of the TiO2 NTs/CdS. The deposition of CdS and Ag2S heteojunctions on the upper and inner surface of the TiO2 NTs was confirmed by field emission scanning electron (FE-SEM) and transmission electron microscopes (TEM). The UV-vis spectrum of the TiO2 NTs/CdS-Ag2S revealed the photoresponse range covering the full visible and near-infrared regions, and showed considerable enhanced photoelectrochemical properties. The corresponding charge transfer path of the TiO2 NTs/CdS-Ag2S photoelectrode was also illuminated.

Photoelectrochemical label-free immunoassay of octachlorostyrene based on heterogeneous CdSe/CdS/Pt/TiO2 nanotube array

A novel heterogeneous CdSe/CdS/Pt/TiO2 nanotube array photoelectrode (denoted as CdSe/CdS/Pt/TiO2 NTA) was developed by dipping and deposition technique as well as successive ionic layer adsorption and reaction (SILAR). An octachlorostyrene (OCS) photoelectrochemical immunosensor was constructed by cross-linking anti-OCS antibody onto the CdSe/CdS/Pt/TiO2 NTA using anti-OCS antibody prepared in this laboratory. The as-prepared photoelectrochemical immunosensor is highly stable, sensitive and selective to octachlorostyrene with a limit of detection (LOD) of 2.08pM and a linear range from 0.1 to 10μM. The practical application of the photoelectrochemical immunosensor is also realized in the selective determination of octachlorostyrene in sewage sample.

Preparation and photocatalytic properties of graphene/TiO2 nanotube arrays photoelectrodes

Graphene/TiO2 Nanotube Arrays (GR/TNAs) photoelectrodes were fabricated by in-situ anodization and electro-deposition method. The surface morphology, structure, photoluminescence spectra (PL), and photocatalytic activity of the samples were investigated. The as-prepared graphene/TNAs (GR/TNAs) photoelectrodes showed significant improvement in the separation of photogenerated carriers and excellent photocatalytic stability. The effects of irradiation time, initial concentration, ionic strength and bias potential on the removal of rhodamine B (Rh.B) by TNAs and GR/TNAs were studied. Results showed that degradation rate of Rh.B for GR/TNAs photoelectrodes reached 75% after 60min illumination at pH of 6.0. The GR/TNAs exhibited significantly enhanced photocatalytic activity compared to unmodified TNAs. When the bias potential was applied, Rh.B degradation rate increased to 90% at 0.5V. NO3−, Ca2+ and Mg2+ in the solution promoted the degradation of Rh.B, while SO42−, Cl− and F− suppressed the removal rate.

Natural-dye-sensitised solar cells based on TiO2 nanotube arrays

Dye-sensitised solar cells (DSSCs) were fabricated using TiO2 nanotube array photoelectrodes with natural-dye sensitizers composed of extracts of mango, pumpkin and banana. Conversion of visible light into electricity was accomplished, with a performance comparable to any that has been reported for DSSCs based on TiO2 nanoparticles. The power conversion efficiencies of cells sensitised with dyes based on mango, pumpkin and banana extracts reached 0·15%, 0·06% and 0·21%, respectively, with short-circuit current densities of 0·44, 0·13 and 0·78 mA cm−2, respectively.

Controlled synthesis of Cu nanoparticles on TiO2 nanotube array photoelectrodes and their photoelectrochemical properties

TiO2 NTs/Cu photoelectrodes were prepared by coating Cu nanoparticles on the tube wall of the self-organized TiO2 nanotube arrays using a successive ionic layer adsorption and reaction method. The structural investigation by X-ray diffraction and scanning electron microscopy indicated that Cu nanoparticles grew uniformly on the walls of TiO2 nanotubes. The modification of Cu nanoparticles improved the photoresponse and photocurrent density of TiO2 NTs into the visible light region.

Stability of Photoactive Oxide Semiconductors

ZnxCd1-xSe quantum dot-sensitized TiO2 nanotube (TiO2 NT) array photoelectrodes were synthesized employing successive ionic layer adsorption and reaction (SILAR) technique. The influence of the number of deposition cycles and post-deposition annealing temperature on photoelectrochemical properties and stability behavior of photoanodes was investigated. The photoanodes were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques. Photoelectrochemical measurements indicated that TiO2 NTs coupled with ZnCdSe quantum dots synthesized with 7 SILAR cycles, annealed at 400oC for 1hr under N2 atmosphere exhibited excellent photoelectrochemical properties. The high and stable photocurrent produced demonstrates the potential of ZnxCd1-xSe/TiO2 heterostructure as an efficient photoanode.

The increased interface charge transfer in dye-sensitized solar cells based on well-ordered TiO2 nanotube arrays with different lengths

Abstract

Photoelectrocatalytic degradation of 4-nonylphenol in water with WO3/TiO2 nanotube array photoelectrodes

WO3 decorated TiO2/Ti Nanotube arrays (WO3/TNAs) photoelectrodes were fabricated using in situ anodization and electrochemical deposition method. The morphology and structure of WO3/TNAs photoelectrodes were studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The effects of different parameters, such as initial pH, bias potential and anions in solution, on photoelectrocatalytic (PEC) activity of WO3/TNAs photoelectrodes were investigated. The degradation mechanism and degradation products of 4-NP were analyzed using liquid-mass spectrometry (LC/MS). The results showed that the degradation percent of 4-nonylphenol (4-NP) on WO3/TNAs photoelectrodes could reach 90% under neutral conditions after 120min illumination. After a bias potential of 2.0V was applied, the degradation percent increased to 98% and the total organic carbon (TOC) removal efficiency was 60%. 4-NP transformed to carboxylic acid substances, CO2 and H2O by hydroxylation, dealkylation role, broken bonds and open-loop. Acid and base as well as SO42-, Cl−, HCO3- and NO3- ions in solution undermined the removal of 4-NP.