Xia Shu

Enhanced visible-light photoelectrochemical behaviour of heterojunction composite with Cu2O nanoparticles-decorated TiO2 nanotube arrays

Heterojunction composites based on n-type TiO2 nanotubes arrays (TNAs) coupled with p-type Cu2O nanoparticles were synthesized using a square wave voltammetry deposition method for in situ deposition of Cu2O nanoparticles onto the inner surfaces and interfaces of TNAs. The prepared samples were characterized by field-emission scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and UV-vis spectroscopy. When compared with pure TNAs, the Cu2O–TNAs heterojunction composites exhibit considerably higher photocurrent density under visible-light irradiation and enhanced photocatalytic activity for the visible-light-driven photodegradation of methyl orange. Moreover, the photocurrent densities and photocatalytic activity of the Cu2O–TNAs heterostructures largely depend on the deposition potential which determines the content of the Cu2O nanoparticles. The Cu2O–TNAs prepared by the deposition potential of −1.0 V showed the highest photocurrent density (0.91 mA cm−2) and the largest photodegradation rate of methyl orange (88.8%) at the applied potential of 0.5 V under visible light irradiation. The enhanced photoelectrocatalytic activity can be attributed to reducing the recombination rate of the photoexcited electron–hole pairs in TNAs when coupled with Cu2O nanoparticles.

A flake-tube structured BiOBr–TiO2 nanotube array heterojunction with enhanced visible light photocatalytic activity

In this study, a new flake-tube structured BiOBr–TiO2 nanotube array (TNTA) heterojunction has been successfully prepared by anodization followed by a sequential chemical bath deposition (S-CBD) method. The as-prepared samples were characterized by X-ray diffraction (XRD), electron microscopy, X-ray photoelectron spectroscopy (XPS) and nitrogen sorption. The photocatalytic activities toward degradation of methyl orange (MO) were evaluated under simulated sunlight. The transient photocurrent response under visible-light irradiation was measured to further confirm the photocatalytic activity enhancement. The results revealed that BiOBr nanoflakes were uniformly dispersed on both inner and outer walls of TiO2 nanotubes, and the BiOBr–TNTAs-2 displayed the best photocatalytic activities, favorable stability and highest photocurrent density among all the BiOBr–TNTAs heterostructured samples. The combined effects of several factors may contribute to the remarkably enhanced photocatalytic activity for the BiOBr–TNTAs-2 sample including an open tube-mouth structure, strong visible-light absorption by BiOBr, the formation of a BiOBr–TNTAs heterojunction and a larger specific surface area.

Flow-through TiO2 nanotube arrays: a modified support with homogeneous distribution of Ag nanoparticles and their photocatalytic activities

Silver decorated TiO2 nanotube arrays (TNTAs) show great potential applications for photocatalysis and gas sensors. In this work, we report an improved strategy to modify the morphology of flow-through TiO2 nanotube arrays (f-TNTAs) for homogeneous Ag nanoparticle loading, and their photocatalytic activities are also investigated. Firstly, TNTAs were fabricated by potentiostatic anodization in fluoride-containing electrolytes. Subsequently, a high voltage was immediately exerted, and then a low potential was applied at the end of anodization process. The as-prepared f-TNTAs with improved bottom morphologies were finally obtained. This new kind of support was immersed in AgNO3 solution, and then the absorbed silver ions were reduced to metallic Ag0 by UV light. Compared with conventional TiO2 nanotube arrays (c-TNTAs), the modified f-TNTAs show a better ability for the dispersion of Ag nanoparticles (Ag NPs) in different regions (upper, central and bottom region) of the nanotubes. A series of testing measures (XPS, EDX, SEM and XRD) were adopted to confirm this facile process. Ag decorated f-TNTAs were used as photocatalysts for the degradation of Methyl Orange (MO) under UV light. The degradation rate could reach 54% in 10 min, and the complete degradation of MO was observed after 30 min. These results were much better than that of Ag decorated c-TNTAs. The modified f-TNTAs via our method can also be used to couple with other noble metals or compound semiconductors. These composite structures are expected to find potential applications in photoelectric devices, gas sensors, and photocatalysis.

Uniformly Dispersed and Controllable Ligand-Free Silver-Nanoparticle-Decorated TiO2 Nanotube Arrays with Enhanced Photoelectrochemical Behaviors

Homogeneously dispersed silver nanoparticles (AgNPs) were successfully decorated onto the surface of TiO2 nanotube arrays (TNTA) by means of an in situ photoreduction method. TNTA films as supports exhibit excellent properties to prevent agglomeration of AgNPs, and they also avoid using polymer ligands, which is deleterious to enhancing the properties of the fabricated NPs. The silver particle size and its content could be controlled just by changing the immersion time. Detailed SEM and TEM analyses combined with energy-dispersive X-ray spectroscopy analyses with different immersion times (5, 10, 30, 60 min) have revealed the variation tendency. The prepared Ag/TNTA composite films were also characterized by XRD, X-ray photoelectron spectroscopy, and high-resolution TEM. The UV/Vis diffuse reflectance spectra displayed a redshift of the absorption peak with the growth of AgNPs. The photocurrent response and the photoelectrocatalytic degradation of methyl orange (MO) were used to evaluate the photoelectrochemical properties of the fabricated samples. The results showed that the photocurrent response and photoelectrocatalytic activity largely depended on the loaded Ag particle size and content. TNTA films with a diameter of 17.92 nm and silver content of 1.15 at% showed the highest photocurrent response and degradation rate of MO. The enhanced properties could be attributed to the synergistic effect between AgNPs and TiO2. To make good use of this effect, particle size and silver content should be well controlled to develop the electron charge and discharge process during the photoelectrical process. Neither smaller nor larger AgNPs caused decreased photoelectrical properties.

Supercapacitive performance of electrochemically doped TiO2 nanotube arrays decorated with Cu2O nanoparticles

Highly ordered TiO2 nanotube arrays (TNAs) with enhanced electronic conductivity treated by introducing oxygen vacancies have been considered to be a promising electrode material for supercapacitors. In this work, we fabricated electrochemically doped TiO2 nanotube arrays (ED-TNAs) through a facile cyclic voltammetry method, and then deposited the uniformly dispersed Cu2O nanoparticles onto ED-TNAs to synthesise a high performance electrode for a supercapacitor. The ED-TNAs electrode exhibited a high specific capacitance of 5.42 mF cm−2 at a scan rate of 10 mV s−1, which was about 59 times higher than for the pristine TNAs electrode. Moreover, the ED-TNAs were demonstrated to be an appropriate support for Cu2O nanoparticles. The highest specific capacitance of the Cu2O/ED-TNAs electrode could reach 198.7 F g−1 at the current density of 0.2 A g−1, and approximately 88.7% of the initial capacitance was retained after 5000 cycles of galvanostatic charge–discharge.

Supercapacitive performance of hydrogenated TiO2 nanotube arrays decorated with nickel oxide nanoparticles

Highly ordered self-organized TiO2 nanotube arrays (TNTAs) could not only be used as current collectors, but also adopted as highly ion-accessible and charge transfer-channels for the construction of supercapacitors. In this paper, hydrogenated TNTAs were obtained and then nickel oxide (NiOx) nanoparticles were successfully deposited onto the inner surface and interface of HTNTAs through a cyclic voltammetry electrochemical deposition process (NiOx/HTNTAs). The FESEM images of the samples showed that the diameter of the NiOx nanoparticles ranged from 7 to 60 nm. The as-fabricated NiOx/HTNTAs exhibited an obviously pseudocapacitive performance with a specific capacitance of 689.28 F g−1 at a current density of 1.5 A g−1 and 91.9% of the initial capacitance remaining after 5000 charge/discharge cycles at a current density of 3 A g−1 in 1 M KOH. This work reveals a feasible and green method for the fabrication of TNTAs modified with electroactive metal oxide nanoparticles as functional electrode materials for supercapacitors.

Integration of mesoporous nickel cobalt oxide nanosheets with ultrathin layer carbon wrapped TiO2 nanotube arrays for high-performance supercapacitors

Decorated TiO2 nanotube array-based electrodes for supercapacitors are successfully fabricated by a facile and green process in this paper. Firstly, TiO2 nanotube arrays are modified with ultrathin carbon layers by in situ pyrolysis with residual ethylene glycol from anodization as a carbon resource, then electroactive materials, nickel cobalt oxides with different stoichiometric nickel and cobalt contents, are synthesized by chemical bath deposition and a controlled post-calcination process. The sample demonstrates a superb specific capacitance of 934.9 F g−1 at a current density of 2 A g−1 and a better rate capability of 865.8 F g−1 at 20 A g−1 while maintaining 92.6% capacity after 5000 cycles at a high current density of 10 A g−1. The outstanding supercapacitive performance is attributed to the unique hierarchical mesoporous architectures and the desirable design of the nanocomposites, and it also suggests that carbon modified TiO2 nanotube arrays decorated with nickel cobalt oxides are promising candidates for supercapacitor applications.

Hierarchical three-dimensional MnO2/carbon@TiO2 nanotube arrays for high-performance supercapacitors

Highly ordered TiO2 nanotube arrays (TNAs) modified by other materials with enhanced conductivity and capacitance have been considered to be promising anode materials for supercapacitors. In this work, carbon@TiO2 nanotube arrays (CTNAs) were firstly synthesized through a calcination process under an Ar atmosphere. Then the hierarchical three-dimensional MnO2/carbon@TiO2 nanotube arrays (CMTNAs) were further developed via hydrothermal deposition of uniformly dispersed MnO2 nanoparticles with the help of the in situ reduction effect of the as-obtained carbon layers. The CTNA electrode exhibited a high area capacitance of 5.58 mF cm−2 at a scan rate of 100 mV s−1, which is about 11 times higher than that of the TiO2 nanotube arrays annealed under an air atmosphere (ATNAs). The highest gravimetric capacitance 521.4 A g−1 was achieved with the CMTNAs at a current density of 2 A g−1, and 88.6% of the initial capacitance could be maintained at a current density of 5 A g−1 up to 2000 cycles via a galvanostatic charge–discharge test.

In situ growth of PEDOT/graphene oxide nanostructures with enhanced electrochromic performance

Poly(3,4-ethylenedioxythiophene) (PEDOT)/graphene oxide (GO) hybrid nanostructures have been obtained by an in situ electro-polymerization process. Field emission scanning electron microscope observation indicates that the hybrid nanostructures consist of uniform and well-dispersed PEDOT nanoparticles integrated on the networked GO nanosheets. Surface chemistry and structure of the hybrid nanostructures have been characterized by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Electrochemical and optical property measurements demonstrate that the hybrid nanostructures exhibit significantly improved electrochromic performance compared with the pristine PEDOT nanostructure. The contrast between coloring and bleaching state of the PEDOT nanostructure at 480 nm increases from 23.4% to 31.4% after hybridizing with GO nanosheets. The coloring time and bleaching time are shortened from 1800 ms to 300 ms and 1500 ms to 400 ms, respectively, while the coloring efficiency increases from 53.5 cm2 C−1 to 64.9 cm2 C−1 after the hybridization. The obtained PEDOT/GO hybrid nanostructures promise great potential in developing novel electrochromic materials for smart windows and other energy saving applications.

Preparation of Cu2O/TiO2 nanotube heterojunction arrays with enhanced photoelectrocatalysis performance

Highly ordered TiO2 nanotube arrays (TNAs) were firstly fabricated by two-step anodization process. Then the Cu2O nanoparticles were deposited onto the as-fabricated TNAs via potentiostatic electrochemical deposition method in a three-electrode cell (the TNAs, Ag/AgCl and graphite performed as working electrode, reference electrode and counter electrode, respectively). The field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were adopted for the morphology characterization, the crystalline phases and composition analyzation of the as-prepared Cu2O/TNAs heterojunctions, repectively. The photoelectrochemical performance of the Cu2O/TNAs samples was evaluated by measuring the enhanced photocurrent response under intermittent Xe lamp irradiation. Then the photocatalytic properties were further investigated based on the photocatalytic degradation of methyl orange (MO) solution under simulated visible light. The results indicated that the inner surface and interface of the TNAs had been successfully modified with uniformly distributed Cu2O nanoparticles, which further ameliorated the photoelectrochemical and photocatalytic activities.