Electrochemical oxidation of rhodamine B by PbO_2/Sb-SnO_2/TiO_2 nanotube arrays electrode

A PbO2/Sb-SnO2/TiO2 nanotube array composite electrode was successfully synthesized and its electrochemical oxidation properties were investigated.Field-emission scanning electron microscopy(FE-SEM)and X-ray diffraction(XRD)results showed that the PbO2 coating was composed of anα-PbO2 inner layer and aβ-PbO2 outer layer.Accelerated life measurement indicated that the composite electrode had a lifetime of 815 h.Rhodamine B(RhB)was employed as a model pollutant to analyze the electrocatalytic activity of the electrode.The effects of initial RhB concentration,current density,initial pH,temperature,and chloride ion concentration on the electrochemical oxidation were investigated in detail.Inductively coupled plasma atomic emission spectroscopy(ICP-AES)results suggested that the concentration of leached Pb^2+in the electrolyte during the electrocatalytic oxidation process can be neglected.Finally,the degradation mechanism during the electrocatalytic oxidation process was proposed based on the results of solid-phase micro-extraction-gas chromatography-mass spectrometry(SPME-GC-MS).The high electrocatalytic performance of the composite electrode makes it a promising anode for the treatment of organic pollutants in aqueous solution.

Different antibacterial mechanisms of titania nanotube arrays at various growth phases of E.coli

To clarify the antibacterial behavior at early adhesion,two titania nanotube(TNT)arrays were fabricated on polished commercially pure titanium(Ti),and the interaction mechanisms between TNT arrays and the model bacteria(Escherichia coli,E.coli)were investigated.The results show that TNT arrays exhibit a significant early antibacterial effect,which is highly related to the surface free energy and nano-topography.The underlying antibacterial mechanisms include:(1)the anti-initial-attachment effect at the lag phase(0−4 h);(2)the anti-proliferation and physical bactericidal effects at the logarithmic phase(4−12 h);(3)the reduced antimicrobial properties probably due to the overgrowth of bacteria on TNT arrays at the stationary phase(12 h and then).

Enhanced Photoelectrochemical Properties of Cu_2O-loaded Short TiO_2 Nanotube Array Electrode Prepared by Sonoelectrochemical Deposition

Copper and titanium remain relatively plentiful in earth crust.Therefore,using them in solar energy conversion technologies are of significant interest.In this work,cuprous oxide（Cu2O）-modified short TiO2 nanotube array electrode was prepared based on the following two design ideas:first,the short titania nanotubes obtained from sonoelectrochemical anodization possess excellent charge separation and transportation properties as well as desirable mechanical stability;second,the sonoelectrochemical deposition technique favours the improvement in the combination between Cu2O and TiO2 nanotubes,and favours the dispersion of Cu2O particles.UV-Vis absorption and photo-electronchemical measurements proved that the Cu2O coating extended the visible spectrum absorption and the solar spectrum-induced photocurrent response.Under AM1.5 irradiation,the photocurrent density of the composite electrode（i.e.sonoelectrochemical deposition for 5 min） was more than 4.75 times as high as the pure nanotube electrode.Comparing the photoactivity of the Cu2O/TiO2 electrode obtained using sonoelectrochemical deposition with others that synthesized using plain electrochemical deposition,the photocurrent density of the former electrode was 2.2 times higher than that of the latter when biased at 1.0 V（vs.Ag/AgCl）.The reproducible photocurrent response under intermittent illumination demonstrated the excellent stability of the composite electrode.Such kind of composite electrode material will have many potential applications in solar cell and other fields.

Tuning of plasmonic behaviours in coupled metallic nanotube arrays

We theoretically investigate the influence of the shape of nanoholes on plasmonic behaviours in coupled elliptical metallic nanotube arrays by the finite-difference time-domain （FDTD） method. We study the structure in two cases： one for the array aligned along the minor axis and the other for the array aligned along the major axis. It is found that the optical properties and plasmonic effects can be tuned by the effective surface charges as a result of the variation in the minor axis length. Based on the localized nature of electric field distributions, we also clearly show that the presence of localized plasmon resonant modes originates from multipolar plasmon polaritons and a large magnitude of opposing surface charges build up in the gap between adjacent nanotubes.

Preparation and photoelectric effect of Zn^(2+)-TiO_2 nanotube arrays

Zn 2+-TiO2 nanotube arrays were prepared by anodic oxidation method.The current-time curves were used to investigate their growth mechanism.Scanning electron microscopy and X-ray diffractometry were applied to characterizing their structures and properties.The photoelectrochemical properties were studied by electrochemical impedance spectrum(EIS).The optimised working conditions for TiO2 nanotube arrays were found to be pH 1,0.5%HF(mass fraction),20 V oxidation voltage and for 2 h.The produced sample was in anatase form,with length of 70-100 nm,thickness of 10 nm,uniform diameter and structure that does not collapse under the preparation conditions.The EIS results show that TiO2 nanotube arrays prepared with 0.5%HF(mass fraction) present a low impedance and TiO2 nanotube arrays loaded by Zn 2+could have a decreased resistance.This decrease could likely accelerate the transfer of carriers and even increase photoelectric conversion.

Plasmon resonance coupling in strongly coupled gold nanotube arrays with structural defects

We theoretically investigate the transmission spectra and the field distributions with different defects in the gold nanotube arrays by using the finite-difference time-domain method. It is found that the optical properties of the nanotube arrays are strongly influenced by different defects. When there are no defects in the central nanotube, the values of peaks located at both sides of the photonic band gap have their maxima. Based on the distributions of electric field component Ex and the total energy distribution of the electric and the magnetic field, we show that mainly a dipole field distribution is exhibited for the plasmon mode at the long-wavelength edge of the band gap but higher order modes of the composite are excited at the short-wavelength edge of the band gap. The plasmon resonant modes can also be controlled by introducing defects.

Study on Photocatalytic Degradation of Organic Dye by Titanium Dioxide Nanotube Array

Titanium based titanium dioxide （TiO2） nanotube arrays were prepared by electrochemical oxidation method, their microstructures were characterized, and the effects of sintering temperature and initial dye concentration and pH value on degradation performance of TiO2 nanotubc arrays wcrc investigated with methyl orange as a degradation object. The results showed that TiO2 nanotube arrays prepared by sintering at 500 ℃ exhibited good morphology and the highest photocata- lyric degradation efficiency; the degradation efficiency of the TiO2 nano material （500 ℃ ） to high concentration dye was higher than that to low concentration dye; the TiO2 nanotube array （500 ℃ ） exhibited higher degradation efficiency on dye solution at the pH of 3 than on that at the pH of 5.77 ; and the degradation efficien- cy of the TiO2 nanotube array （500 ℃） to 10 mg/L methyl orange solution （pH =3） reached 85.2%.

Field emission of carbon nanotube array with normal-gate cold cathode

A hexagon pitch carbon nanotube （CNT） array vertical to the normal gate of cold cathode field emission displayer （FED） is simulated by solving the Laplace equation. The calculated results show that the normal gate causes the electric field around the CNT tops to be concentrated and the emission electron beam becomes a column. The field enhancement factor and the emission current intensity step up greatly compared with those of the diode structure. Emission current density increases rapidly with the decrease of normal-gate aperture. The gate voltage exerts a critical influence on the emission current.

Enhanced degradation of refractory organics in ORR-EO system with a blue TiO_(2)nanotube array modified Ti-based Ni-Sb co-doped SnO_(2)anode

Recently,a novel 2-electron oxygen reduction reaction(ORR)based electro-oxidation(EO)system was developed,which utilizes a H_(2)O_(2)generation cathode instead of H_(2)evolution cathode.A Ti-based Ni-Sb co-doped SnO_(2)(Ti/NATO)anode was selected for efficient degradation of refractory organics and O_(3)production.The synergistic reaction of O3/H_(2)O_(2)further accelerated the generation of hydroxyl radicals(·OH)in the ORR-EO system.However,the catalytic activity and long-term effectiveness of the Ti/NATO anode limited the large-scale application of the ORR-EO process.In this study,a blue TiO_(2)nanotube array(blue-TiO_(2)-NTA)inter-layer was introduced into the fabrication process between the Ti substrate and NATO catalyst layer.Compared to the Ti/NATO anode,the Ti/blue-TiO_(2)-NTA/NATO anode achieved higher efficiency of organic removal and O_(3)generation.Additionally,the accelerated lifetime of the Ti/blue-TiO_(2)-NTA/NATO anode was increased by 7 times compared to the Ti/NATO anode.When combined with CNTs-C/PTFE air cathode in ORR-EO system,all anodic oxidation and O_(3)/H_(2)O_(2)processes achieved higher•OH production.Over 92%of TOC in leachate bio-effluent was effectively eliminated with a relatively low energy cost of 45 kWh/t.

Unveiling the controversial mechanism of reversible Na storage in TiO2 nanotube arrays： Amorphous versus anatase TiO2

Due to their inherent safety, low cost, and structural stability, TiO2 nanostructures represent a suitable choice as anode materials in sodiumion batteries. In the recent years, various hypotheses have been proposed regarding the actual mechanism of the reversible insertion of sodium ions in the TiO2 structure, and previous reports are often controversial in this respect. Interestingly, when tested as binder- and conducting additive-free electrodes in laboratory-scale sodium cells, amorphous and crystalline （anatase） TiO2 nanotubular arrays obtained by simple anodic oxidation exhibit peculiar and intrinsically different electrochemical responses. In particular, after the initial electrochemical activation, anatase TiO2 shows excellent rate capability and very stable long-term cycling performance with larger specific capacities, and thus a clearly superior response compared with the amorphous counterpart. To obtain deeper insight, the present materials are thoroughly characterized by scanning electron microscopy and ex situ X-ray diffraction, and the insertion of sodium ions in the TiO2 bulk phases is systematically modeled by density functional theory calculations. The present results may contribute to the development of more systematic screening approaches to identify suitable active materials for highly efficient sodium-based energy storage systems.

Effects of the local environment on plasmonic coupling of metallic nanotube arrays

We have theoretically investigated the effect of the dielectric core and the dielectric embedding medium separately on the transmission spectra and plasmonic properties of coupled metallic nanotube arrays.It is found that the plasmonic properties of the nanotube arrays are strongly influenced by the presence of the dielectric which induces additional screening charges.We show that instead of one single photonic bandgap for the hollow nanotube arrays placed in air,an additional photonic bandgap arises from the presence of dielectric media in the transmission spectra.Based on the localized nature of the electric field distributions,we also clearly show the presence of the local plasmonic resonant modes that originate from multipolar plasmon polaritons in the cross section of these nanotube arrays,and that a large amount of opposing surface charges are built up in the gap between adjacent nanotubes.

Well-aligned carbon nanotube array membrane and its field emission properties

Ensembles of aligned and monodispersed carbon nanotubes (CNTs)can be prepared by templating method which involves fabrication of porous anodic aluminum oxide (AAO) template, control of catalytic iron particle size and chemical vapor deposition of carbon in the cylindrical pores of AAO. Here we show that template-synthesized CNTs can be fabricated as well-aligned nanoporous CNTs membrane, which can be directly used as an electron field emitter. A low threshold electric field of 2-4 V/μm and maximum emission current density of ～12 mA/cm2 are observed. The results also show that the electron emission current is a function of the applied electrical field and the Fowler-Nordheim (F-N) plot almost follows a linear relationship which indicates a Fowler-Nordheim tunneling mechanism, and the field enhancement factor estimated is about 1100-7500. The simple and convenient approach should be significant for the development of nanotube devices integrated into field emission displays (FEDs) technology.

Depositing natural stibnite on 3D TiO_(2) nanotube array networks as high-performance thin-film anode for lithium-ion batteries

Three-dimensional(3D) thin-film electrodes are promising solution to the volume change of active materials in lithium-ion batteries.As a conductive current collector,the 3D TiO_(2) nanotube array networks(TNAs) have a one-dimensional stable electronic conductive path and increase the adhesion between the current collector and raw material,thereby improving the cycle stability of active materials.In this study,a novel 3D-TNAs@Sb_(2)S_(3) anode was fabricated by directly depositing natural stibnite onto3D TNAs.The adhesion of Sb_(2)S_(3) particles to the substrate was enhanced due to the large surface area provided by 3D-TNAs.Moreover,the porous layered structure composed of Sb_(2)S_(3) nanoparticles relieved the stress generated during lithiation and adapted to the volume change of Sb_(2)S_(3) during cycling.Therefore,the resulting composite anode exhibits high cycle and rate performance,reaching0.36 mAh·cm^(-2) after 80 cycles at the galvanostatic rate of1 mA·cm^(-2),with high coulombic efficiency of 98%.

Dynamic and reversible electrowetting with low voltage on the dimethicone infused carbon nanotube array in air

Unremitting efforts have been intensively making for pursuing the goal of the reversible transition of electrowetting owing to its vital importance to many practical applications,but which remains a major challenge for carbon nanotubes due to the irreversible electrochemical damage.Herein,we proposed a subtly method to prevent the CNT array from electrochemical damage by using liquid medium instead of air medium to form a liquid/liquid/solid triphase system.The dimethicone dynamically refills in CNT arrays after removing of voltage that makes the surface back to hydrophobic,which is an elegant way to not only decrease energy dissipation in electrowetting process but also obtain extra energy in reversible dewetting process.Repeated cycles of in situ experiments showed that more than four reversible electrowetting cycles could be achieved in air.It wo rth mention that the in situ reve rsible electro wetting voltage of the dimethicone infused CNT array has been lowered to 2 V from 7 V which is the electrowetting voltage for the pure CNT array.The surface of the dimethicone infused CNT array can maintain hydrophobicity with a contact angle of 145.6°after four cycles,compared with 148.1°of the initial state.Moreover,a novel perspective of theoretical simulations through the binding energy has been provided which proved that the charged CNTs preferred binding with water molecules thereby replacing the dimethicone molecules adsorbed on the CNTs,whereas reconnected with dimethicone after removing the charges.Our study provides distinct insight into dynamic reversible electrowetting on the nanostructured surface in air and supplies a way for precise control of wettability in surface chemistry,smart phase-change heat transfer enhancement,liquid lenses,microfluidics,and other chemical engineering applications.

An Energy-Efficient Electrochemical Method for CuO-TiO_2 Nanotube Array Preparation with Visible-Light Responses

A rapid and energy-efficient method was presented for preparing CuO-TiO2 nanotube arrays. TiO2 nanotube arrays were first prepared by anodic oxidation using titanium anode and platinum cathode. Then, the formed TiO2 nanotube arrays and Pt were used as cathode and anode, respectively, for subsequent formation of CuO-TiO2 nanotube arrays, through an electro- chemical process in a solution of 0.1 mol/L CuSO4. The morphology and composition of the CuO-TiO2 nanotube arrays were characterized using field-emission scanning electron microscopy, X-ray photoelectron spectroscopy （XPS）, X-ray diffraction （XRD）, and UV-Vis diffusion reflection spectroscopy （UV-Vis DRS）. XPS and XRD analyses suggested that the Cu element in the nanotubes existed in CuO form, and its content changed along with the voltage during the second electrochemical process. The photocatalytic activities of the CuO-TiO2 nanotube arrays were evaluated by the degradation of a model dye, rhodamine B. The results showed that Cu incorporation aroused wide visible-light adsorption and improved the photocatalytic efficiency of TiO2 nanotube arrays significantly under visible-light irradiation. The stability of the CuO-TiO2 nanotube arrays was also detected.

Fabrication, Characterization and Optical Properties of TiO2 Nanotube Arrays on Boron-doped Diamond Film Through Liquid Phase Deposition

TiO2 nanotube（TiNT） arrays were deposited on boron-doped diamond films by a liquid-phase deposition method with ZnO nanorod arrays as the template.The different morphologies of TiNTs have been obtained by controlling the morphology of ZnO template.The X-ray diffraction and energy-dispersive X-ray analysis show that the ZnO nanorod array template has been removed in the TiNTs formation process.The crystalline quality of the TiNTs is improved by increasing the annealing temperature.The band gap of the TiNTs is about 3.25 eV estimated by the UV-Vis absorption spectroscopy,which is close to the value of bulk TiO2.In the photoluminescence spectrum,a broad visible emission in a range of ca.550-750 nm appears due to the surface oxygen vacancies and defects.

Flexoelectricity-enhanced photovoltaic effect in trapezoid-shaped NaNbO_(3)nanotube array composites

In this work,we successfully prepared vertically aligned NaNbO_(3)nanotube(NN-NT)with trapezoidal shapes,in which the orthorhombic and monoclinic phases coexisted.According to the structure analysis,the NN-NT/epoxy composite film had excellent flexoelectric properties due to the lattice distortion caused by defects and irregular shape.The flexoelectric effect is the greatest in the vertical direction in the flexible NN-NT/epoxy composite film,and the flexoelectric coefficient()is 2.77×10^(−8)C·m^(−1),which is approximately 5-fold higher than that of the pure epoxy film.The photovoltaic current of the NN-NT/epoxy composite film increased from 39.9 to 71.8 nA·cm^(−2)in the direction of spontaneous polarization when the sample was bent upward due to the flexoelectricity-enhanced photovoltaic(FPV)effect.The flexoelectric effect of the NN-NT/epoxy composite film could modulate the photovoltaic response by increasing it by 80%or reducing it to 65%of the original value.This work provides a new idea for further exploration in efficient and lossless ferroelectric memory devices.

Transient competition between photocatalysis and carrier recombination in TiO_2 nanotube film loaded with Au nanoparticles

Highly ordered TiO2 nanotube array （TNA） films are fabricated by using an anodic oxidation method. Au nanoparticles （NPs） films are decorated onto the top of TNA films with the aid of ion-sputtering and thermal annealing. An enhanced photocatalytic activity under ultraviolet C （UVC, 266 nm） light irradiation is obtained compared with that of the pristine TNA, which is shown by the steady-state photoluminescence （PL） spectra. Furthermore, a distinct blue shift in the nanosecond time-resolved transient photoluminescence （NTRT-PL） spectra is observed. Such a phenomenon could be well explained by considering the competition between the surface photocatalytic process and the recombination of the photo-generated carriers. The enhanced UV photocatalytic activities of the Au-TNA composite are evaluated through photo-degradation of methyl orange （MO） in an aqueous solution with ultraviolet-visible absorption spectrometry. Our current work may provide a simple strategy to synthesize defect-related composite photocatalytic devices.

Lithiophilic seeds and rigid arrays synergistic induced dendrite-free and stable Li anode towards long-life lithium-oxygen batteries

High energy density lithium-oxygen battery(LOB) is currently regraded as a promising candidate for next-generation power system.However,the dendrite and instability issues of Li metal anode lead to its poor cyclic stability and low energy density.In this work,lithiophilic Al_(2) O_(3) seeds induced rigid carbon nanotube arrays(CNTA)/three-dimensional graphene(3 DG) is developed as a host material for Li anode,namely Al_(2) O_(3)-CNTA/3 DG.It is demonstrated that the lithiophilic feature of Al_(2) O_(3) seeds and the enhanced rigidity of arrays can synergistically induce the uniform Li flux,inhibit the collapse of arrays,and stabilize electrolyte/electrode interfaces.As a result,the Al_(2) O_(3)-CNTA/3 DG-Li anode delivers a high Coulombic efficiency above 97% after 140 cycles(8 mAh cm^(-2) at 4 mA cm^(-2)).With this anode and the breathable CNTA/3 DG cathode,the full LOB exhibits a significantly increased life-span up to 160 cycles(500 mAh g^(-1) at 100 mA g^(-1)),which is almost 3 times longer than that with pure Li foil as the anodes.This work demonstrates a new approach to highly reversibly long-cycling performance of LOBs towards practical application.

INFLUENCES OF DENSITY AND DIMENSION OF CARBON NANOTUBES ON THEIR FIELD EMISSION

The influences of density and dimension of carbon nanotubes on their electron emission from arrays are studied. The tip electric field of nanotubes, electric field enhancement factor, and optimum nanotube density are expressed by analytic equations. The theoretical analyses show that the field enhancement factor is sensitive to nanotube density, and can be sharply improved at a specific and optimum density. Some experiments have demonstrated these. Owning to electrostatic screening effect, the length of carbon nanotubes has little effect on their emission. A uniformly-distributed carbon nanotube array model is set up, and applied to analysis of carbon nanotube arrays. The results obtained here are in good agreement with the experimental data.