Visible-light-induced photoelectrochemical behaviors of Fe-modified TiO2 nanotube arrays

Fe-modified TiO(2) nanotube arrays (TiO(2) NTs) were prepared by annealing amorphous TiO(2) NTs whose surface was covered with Fe(3+) by a dip-coating procedure, and characterized by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and UV-visible reflectance spectroscopy. The photoelectrochemical properties were evaluated by the photocurrent response and photoelectrocatalytic (PEC) degradation of methylene orange (MO) and 4-chlorophenol in water under visible-light irradiation (λ > 420 nm). The results showed that a Fe-modified TiO(2) NTs electrode exhibited a larger photocurrent response and higher PEC activity for the degradation of organic pollutants than a pure TiO(2) NTs electrode. At a bias potential of 0.4 V, the photocurrent response of a 0.5 M Fe-modified TiO(2) NTs electrode exceeded that of a pure TiO(2) NTs electrode by a factor of about 10, and the PEC degradation rates of MO and 4-chlorophenol on a 0.5 M Fe-modified TiO(2) NTs electrode exceeded those on a pure TiO(2) NTs electrode by a factor of about 2.5. The larger photocurrent response and higher PEC activity of Fe-modified TiO(2) NTs could be attributed to the enhancement of separation of charge-carriers at the external electric field and the extension of the light response range of TiO(2) to the visible-light region with the narrowing of the band gap.     

Synthesis, characterization, and electrochemical capacitance of amino-functionalized carbon nanotube/carbon paper electrodes

Amino-functionalization of carbon nanotubes (CNTs) attached to carbon paper (CP) has been achieved using one synthesis protocol: (i) chemical oxidation, (ii) acyl chlorination, and (iii) amidation. The amidation reaction of the carboxylic groups in oxidized the CNT/CP hybrids enables the formation of terminal amino groups on the CNT sidewalls. The functionalized CNTs were characterized by Raman spectroscopy, X-ray photoelectron spectroscopy, Fourier transformed infrared spectroscopy, thermal programmed desorption, and N₂ adsorption. The cyclic voltammetry curves of an amino-modified CNT-based capacitor showed a continuum of double-layer and pseudocapacitive behavior. The presence of surface oxides and amides on CNTs imparts not only hydrophilic coverage for the formation of double-layer (double-layer capacitance) but also active sites for the redox reaction (pseudocapacitance). Based on the result of the charge/discharge cycling test, the N-modified CNT/CP capacitor exhibits an enhanced capacitance, high-rate capability, and capacitance stability with high coulombic efficiency.     

High-efficiency photoelectrochemical performance of PbS nanoparticles sensitized TiO2 nanotube arrays

TiO₂ nanotube arrays sensitized by PbS nanoparticles (TiO₂ NTs/PbS) with enhanced visible-light activity were synthesized by a two-step approach including an electrochemical anodization technique followed by an in situ photodeposition approach. The structural investigations indicated that PbS nanoparticles grew uniformly on the walls of the TiO₂ NTs. The TiO₂ NTs/PbS exhibited more excellent photoelectrochemical properties than that of the TiO₂ NTs under visible-light irradiation. The enhanced photoelectrochemical activity of the TiO₂ NTs/PbS could be attributed to the improvement of visible-light absorption and charge separation derived from the coupling effect of the PbS nanoparticles and TiO₂ NTs.     

Optimal engineering of CdS/PbS co-sensitized TiO2 nanotube arrays for enhanced photoelectrochemical performance

TiO₂ nanotube arrays (NTAs) are decorated with CdS/PbS nano-sensitizers by successive ionic layer adsorption and reaction (SILAR) method. The uniform growth of the CdS and PbS nanoparticles on the surface and inner side of TiO₂ Nanotube Arrays (NTAs) has been confirmed by Transmission Electron microscopy measurements. The impact of the CdS and PbS semiconductor quantum dots (SQDs) on the photoelectrochemical performance (PEC) of TiO₂ NTAs was systematically investigated, and the optimal decoration of the CdS and PbS SQDs on the TiO₂ NTAs was obtained. CdS/PbS co-sensitized TiO₂ NTA photoanode films show excellent response to visible light (with absorption extended to 825 nm) and enhanced PEC performance. The best performing device showed an enhanced photocurrent density under the 0.62V vs SCE up to 8.2 mA/cm², and high photoconversion efficiency up to 5.35%, which is 16.7 times higher than the pure TiO₂ NTAs. The enhanced PEC performance of TiO₂ NTAs is attributed to the co-sensitization, heterojunction formation and electron “pool” effect imparted on the NTAs by the coupling of CdS and PbS SQDs.     

Fabrication and characterization of copper doped TiO2 nanotube arrays by in situ electrochemical method as efficient visible-light photocatalyst

Highly ordered copper doped TiO₂ nanotube arrays (CuTiO₂NTs) thin-film were prepared in an aqueous solution containing NH₄F and different concentrations of copper nitrate via the electrochemical oxidation of titanium substrates. The resulting nanotubes were characterized by FE-SEM, XRD, XPS and EDX. The CuTiO₂NTs showed a tube diameter of 40–90 nm and wall thickness of 20–30 nm. Diffuse reflectance spectra showed a shift toward longer wavelengths relative to pure TiO₂ nanotubes (TiO₂NTs). The visible light photo-catalytic activity of the CuTiO₂NTs electrodes was evaluated by the removal of methylene blue (MB) dye and the production of hydrogen. The results showed that CuTiO₂NTs samples exhibited better photo-catalytic activity than the TiO₂NTs. This work demonstrated a feasible and simple anodization method to fabricate an effective, reproducible, and inexpensive visible-light-driven photo-catalyst for hydrogen evolution and environmental applications.     

Structural evolution of multi-walled carbon nanotube/MnO2 composites as supercapacitor electrodes

Multi-walled carbon nanotube (MWCNT)/MnO₂ supercapacitor electrodes containing MnO₂ nanoflakes in the MWCNT network are fabricated through the oxidation of manganese acetate with poly(4-styrenesulfonic acid) (PSS) dispersed MWCNTs. The structural evolution of the electrodes under charge/discharge (reduction/oxidation) cycles and its impact on the electrodes’ electrochemical properties are evaluated. Structural evolution involves the dissolution of MnO₂ upon reduction, the diffusion of the reduced Mn species from the MWCNT network toward the electrolyte solution, and the deposition of MnO₂ on the electrode surface upon oxidation. Electrode structural changes, including the electrode dissolution and the growth of the MnO₂ crystals, are scan rate dependent and have deteriorating effect on the electrode's electrochemical properties including the specific capacitance and cyclic stability.     

碳纳米管/纳米TiO2-聚苯胺复合膜电极的制备及电化学性能

在含有0.2 mol·L^-1苯胺的0.5 mol·L^-1 H2SO4溶液中;采用循环伏安法（CV）;以扫描速度50 mV·s^-1;扫描电位为-0.1～0.9 V;在碳纳米管/纳米TiO₂（CNT/nanoTiO₂）膜电极上实现了苯胺的电化学聚合;通过CV法和电化学阻抗谱（EIS）并结合电子扫描显微镜和红外谱图对制备的碳纳米管/纳米TiO₂-聚苯胺（CNT/nanoTiO₂-PAn）复合膜电极的电化学性质和结构进行了表征;同时研究了复合膜电极对抗坏血酸（AH₂）的电催化性能;发现该复合膜电极对抗坏血酸的氧化具有较高的电催化活性。     

Preparation of polyaniline nanowire arrayed electrodes for electrochemical supercapacitors

Polyaniline (PANI) nanowire arrayed electrodes were successfully synthesized by means of anodic deposition technique using the membrane-template synthesis route. The desired three-dimensional architecture of PANI nanowire arrayed electrodes was characterized with field emission scanning electron microscope (FESEM) and X-ray diffraction (XRD) techniques. It was found that the co-deposition nanowires were regular size and continuous with an average diameter of about 30 nm, and the nanowires have an amorphous nature. The electrochemical characterization was performed in 2 M H₂SO₄ aqueous solution. The capacitance of the PANI nanowire arrayed electrode at a charge–discharge current density of 5 Ag⁻¹ is 1142 Fg⁻¹. The nanowire arrayed electrodes showed an excellent capacitive ability for the facility of electrolyte penetration, the ease of proton exchange/diffusion and the metallic conductivity of PANI nanowire arrayed electrodes.     

Graphene oxide modified TiO2 nanotube arrays: enhanced visible light photoelectrochemical properties

Novel nanocomposite films, based on graphene oxide (GO) and TiO(2) nanotube arrays, were synthesized by assembling GO on the surface of self-organized TiO(2) nanotube arrays through a simple impregnation method. The composite films were characterized with field emission scanning electron microscopy, X-ray diffraction, Raman spectroscopy and UV-vis diffuse reflectance spectroscopy. The photoelectrochemical properties of the composite nanotube arrays were investigated under visible light illumination. Remarkably enhanced visible light photoelectrochemical response was observed for the GO decorated TiO(2) nanotube composite electrode compared with pristine TiO(2) nanotube arrays. The sensitizing effect of GO on the photoelectrochemical response of the TiO(2) nanotube arrays was demonstrated and about 15 times enhanced maximum photoconversion efficiency was obtained with the presence of GO. An enhanced photocatalytic activity of the TiO(2) nanotube arrays towards the degradation of methyl blue was also demonstrated after modification with GO. The results presented here demonstrate GO to be efficient for the improved utilization of visible light for TiO(2) nanotube arrays.     

Fabrication and electrochemical properties of carbon nanotube film electrodes

Carbon nanotube (CNT) film electrodes were fabricated by a novel process involving the electrostatic spray deposition (ESD) of a CNT solution. Acid treated CNTs were dispersed in an aqueous solvent through sonication and then the CNT solution was electrostatically sprayed onto a metallic substrate by the ESD method. The CNT film electrodes showed well-entangled and interconnected porous structures with good adherence to the substrate. A specific capacitance of 108 F/g was achieved for the electrodes in 1 M H₂SO₄. In addition, the CNT film electrode showed good high rate capability.     

TiO2 nanostructures synthesized by electrochemical anodization in green protic ionic liquids for photoelectrochemical applications

This work studies the influence of the 2-hydroxyethylammonium acetate (2-HEAA) ionic liquid (IL) as an electrolyte in the electrochemical anodization of titanium for the synthesis of nanostructures for photoelectrochemical water splitting. Different 2-HEAA IL concentrations were used ranging from 0 to 4% v/v (IL-0 to IL-4) in electrolytes containing NH₄F, water and ethylene glycol. Morphological, structural and electrochemical characterization of the nanostructures was carried out by means of field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS), and Mott-Schottky (MS) analysis. Additionally, photoelectrochemical tests were carried out in order to evaluate the efficiency of these materials as catalysts for water splitting applications. According to the obtained results, the electrolyte used for electrochemical anodization should contain little amount of NH₄F (0.05 M) in order to obtain efficient nanostructures for photoelectrochemical purposes. However, small concentrations of IL (IL-0.25) resulted in nanostructures with higher photocurrents than doubling the NH₄F concentration to 0.1 M. Therefore, the IL addition contributes to a more sustainable electrolyte formulation. The best photoelectrochemical response for water splitting processes was obtained for the nanostructures anodized with 1% v/v of 2-HEAA IL (IL-1) due to their high surface/area (higher pore diameters, smaller nanotubes wall thickness and higher nanotubes lengths), better crystallinity and electrochemical response, showing photocurrents more than 100% higher than the ones obtained for the nanotubes anodized without IL.     

A comparative study of electrochemical and photoelectrochemical reactions at semiconducting oxidized Ti and TiO2 single crystal electrodes in view of energy conversion applications

An experimental investigation was made on the electrode properties of oxidized Ti and of rutile single crystals. Polycrystalline samples were prepared by oxidation in air and partial reduction in H₂ at various temperatures. The current-voltage characteristics in aqueous-indifferent electrolyte solutions in darkness and under illumination demonstrate that it is possible to obtain samples with photoelectrolytic performances at least equivalent to those of monocrystalline TiO₂ samples. Moreover, a pronounced similarity is found between both types of electrodes with regard to the reactivity of the reducing agents added. The influence of different gases (H₂, N₂ or O₂) on the current-voltage behaviour of these electrodes reveals some important aspects concerning their possible use for the conversion of optical energy into chemical or electrical energy.     

A composite CdS thin film/TiO2 nanotube structure by ultrafast successive electrochemical deposition toward photovoltaic application

Fabricating functional compounds on substrates with complicated morphology has been an important topic in material science and technology, which remains a challenging issue to simultaneously achieve a high growth rate for a complex nanostructure with simple controlling factors. Here, we present a novel simple and successive method based on chemical reactions in an open reaction system manipulated by an electric field. A uniform CdS/TiO₂ composite tubular structure has been fabricated in highly ordered TiO₂ nanotube arrays in a very short time period (~90 s) under room temperature (RT). The content of CdS in the resultant and its crystalline structure was tuned by the form and magnitude of external voltage. The as-formed structure has shown a quite broad and bulk-like light absorption spectrum with the absorption of photon energy even below that of the bulk CdS. The as-fabricated-sensitized solar cell based on this composite structure has achieved an efficiency of 1.43% without any chemical doping or co-sensitizing, 210% higher than quantum dot-sensitized solar cell (QDSSC) under a similar condition. Hopefully, this method can also easily grow nanostructures based on a wide range of compound materials for energy science and electronic technologies, especially for fast-deploying devices.     

MoS2 nanosheet/ZnO nanowire hybrid nanostructures for photoelectrochemical water splitting

As an efficient cocatalyst, the 2D MoS₂ is thought to be a promising substitute to noble metals in the hydrogen evolution reaction (HER). In the past few years, single and few‐layer MoS₂ nanosheets have attracted a wide range of concerns for HERs. In this paper, single crystalline ZnO nanowires and MoS₂ nanosheets are fabricated to form MoS₂ nanosheet/ZnO nanowire hybrid nanostructure to enhance the hydrogen photogeneration. The results show that the hybridization of ZnO with moderate MoS₂ loading could enhance the PEC activity by producing more electrons and holes and reducing their recombination. The synthesis of MoS₂/ZnO composites proposed an effective way to build low cost and highly active HER catalysts. Moreover, the study on MoS₂/ZnO composites sheds light to the deep insight into the mechanism of photoelectrocatalytic HERs.     

Preparation and characterization of TiO2/Ti film electrodes by anodization at low voltage for photoelectrocatalytic application

Multiporous TiO₂/Ti film electrodes were prepared by different anodic oxidation processes at low voltage, in which the micro-structured TiO₂ thick films were prepared in H₂SO₄–H₂O₂–H₃PO₄–HF solution for 2 h and the nano-structured TiO₂ thin films were prepared in H₃PO₄–HF solution for 30 min with post-calcination. Both types of TiO₂/Ti films were characterized by scanning electron microscopy and X-ray diffraction analysis. The photocatalytic (PC) and photoelectrocatalytic (PEC) reactivity of the TiO₂/Ti electrodes were evaluated in terms of bisphenol A (BPA) degradation in aqueous solution. The experimental results demonstrated that the nano-structured TiO₂/Ti thin-film electrodes had higher reactivity in the BPA degradation reaction. The PEC degradation of BPA was further studied using different cathodes, either a reticulated vitreous carbon (RVC) electrode or a platinum (Pt) electrode. The experimental results confirmed that the efficiency of BPA degradation could be significantly enhanced in the TiO₂/Ti–RVC reaction system due to the generation of H₂O₂ on the RVC cathode. It is believed that such a H₂O₂-assisted TiO₂ PEC oxidation process may have good potential for water and wastewater treatment.     

Perovskite-SrTiO3/TiO2/PDA as photoelectrochemical glucose biosensor

The complexity of the biological sample to be tested requires the sensor to have a wide monitoring range, accurate selectivity, and excellent environmental tolerance. Here, we report a new strategy of in situ transformation of perovskite to form a heterojunction and combined with bioactive enzyme protective substances, thereby achieving a collection of multiple sensing properties. Through in situ conversion of TiO₂ to SrTiO₃ to form a heterojunction to provide high oxidation activity and protection for GOx through PDA, the TiO₂/SrTiO₃/PDA/GOx biosensor achieves an ultra-wide linear detection range of 0–32 mM. Such a range can effectively monitor the physical condition of people with high blood sugar levels (above 20 mM). Good stability, anti-interference, environmental tolerance, and accurate human blood detection all prove the excellent sensing performance and practical application potential of the TiO₂/SrTiO₃/PDA/GOx biosensor.     

Improvement in the photoelectrochemical responses of PCBM/TiO2 electrode by electron irradiation

ABSTRACT: The photoelectrochemical (PEC) responses of electron-irradiated 66-phenyl-C61-butyric acid methyl ester (PCBM)/TiO2 electrodes were evaluated in a PEC cell. By coating PCBM on TiO2 nanoparticle film, the light absorption of PCBM/TiO2 electrode has expanded to the visible light region and improved the PEC responses compared to bare TiO2 electrode. The PEC responses were further improved by irradiating an electron beam on PCBM/TiO2 electrodes. Compared to non-irradiated PCBM/TiO2 electrodes, electron irradiation increased the photocurrent density and the open-circuit potential of PEC cells by approximately 90% and approximately 36%, respectively at an optimum electron irradiation condition. The PEC responses are carefully evaluated correlating with the optical and electronic properties of electron-irradiated PCBM/TiO2 electrodes.     

碳纳米管表面结构的分析方法概述

阐述了一系列碳纳米管(CNT)表面结构的分析方法以及他们的优缺点.介绍了各种技术获得的CNT表面化学结构的信息.着重强调了XPS以及XPS谱线模糊时,XPS与化学衍生化方法联合确定CNT表面有机官能团含量的方法.     

Template-free fabrication of silicon micropillar/nanowire composite structure by one-step etching

A template-free fabrication method for silicon nanostructures, such as silicon micropillar (MP)/nanowire (NW) composite structure is presented. Utilizing an improved metal-assisted electroless etching (MAEE) of silicon in KMnO₄/AgNO₃/HF solution and silicon composite nanostructure of the long MPs erected in the short NWs arrays were generated on the silicon substrate. The morphology evolution of the MP/NW composite nanostructure and the role of self-growing K₂SiF₆ particles as the templates during the MAEE process were investigated in detail. Meanwhile, a fabrication mechanism based on the etching of silver nanoparticles (catalyzed) and the masking of K₂SiF₆ particles is proposed, which gives guidance for fabricating different silicon nanostructures, such as NW and MP arrays. This one-step method provides a simple and cost-effective way to fabricate silicon nanostructures.     

Morphological and photoelectrochemical propertiesof porous, superimposed Au/TiO2 layers

Porous semiconducting ceramics deposited on a porous metallic film acting both as catalyst and electronic collector gave large photocurrents and considerably enhanced electrooxidation currents when irradiated in the presence of small amounts of alcohol vapours. The morphological properties of these layered materials, was studied by electron (SEM, ESEM) and atomic force (AFM) microscopy in order to observe the modification in shape and size of the precursor particles because such knowledge is helpful to the preparation of suitable anodes for photo-assisted processes in the gas-phase.