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.     

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.     

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.     

氧化钛纳米管阵列制备及应用

氧化钛纳米管阵列因其独特的高度有序的阵列结构而具有良好的力学、化学稳定性以及抗腐蚀性能,在光解水制氢、太阳能电池、光催化、环境净化、气敏传感器等领域具有潜在的应用价值,引起了人们的广泛关注。对近年来TiO2纳米管在制备技术、形成机理、离子掺杂及其应用研究方面取得的成果做了综合评述,在此基础上探讨了TiO2纳米管制备及改性方面存在的问题,并对今后的发展方向予以展望。     

TiO2纳米管阵列粗糙度调控及其与蛋白相互作用

采用电化学阳极氧化法,通过改变电解液氟离子浓度(0.4%、0.3%、0.2%(质量))和电压(15、25、35、45 V),制备一系列不同管径和粗糙度的TiO₂纳米管阵列(TiO₂ nanotube arrays, TNAs)。通过扫描电子显微镜以及原子力显微镜(atomic force microscopy, AFM)表征,结果表明随着电解液中氟离子浓度的降低,制备得到的TNAs表面平整度更好,壁厚增大,粗糙度降低。采用AFM力学表征研究了表面粗糙度以及管径对TNAs表面力学性质以及与细胞色素C(Cytochrome C, Cyt C)相互作用的影响,结果表明,黏附力与接触面积呈正比,随着TNAs管径增加,壁厚减小,TNAs与Cyt C的有效接触面积先增大后减小,两者之间作用力也先增加后减小;同时,同管径条件下粗糙度降低,TNAs有效面积增加,相互作用力也增加;由此可见,通过改变电解液氟离子浓度可以有效调控TNAs表面粗糙度及有效接触面积,进一步利于促进与蛋白分子之间相互作用。     

Synthesis and growth mechanism of multilayer TiO2 nanotube arrays

High-aspect-ratio TiO(2) nanotube arrays formed by anodic oxidation have drawn extensive attention due to their easy fabrication and various excellent optical, electrical and biomedical properties. In contrast to conventional single-layer TiO(2) nanotubes prepared via constant-voltage anodization, we synthesize multilayer TiO(2) nanotube arrays with high surface area by using alternating-voltage anodization steps. This work presents synthesis and growth mechanisms of single-layer smooth TiO(2) nanotubes, bamboo-type nanotubes and double-layer nanotubes, by tuning various parameters such as voltage, time, and water content in the electrolyte. It is found that ion diffusion inside the nanotubes dominates growth of these three structures. A stable pH and ion-diffusion profile allows the steady growth of smooth TiO(2) tubes in NH(4)F-containing ethylene glycol (EG). The addition of a low-voltage anodization step reduces the pH and ion-diffusion gradient in the nanotubes and induces formation of bamboo-type nanotubes and double-layer nanotubes when a second high-voltage anodization is conducted. Ion diffusion through a nanotube takes time; thus formation of lower-layer TO(2) nanotubes costs more time if longer nanotubes are grown in the upper layer, since ions diffuse through these longer nanotubes. This ion-diffusion controlled growth mechanism is further confirmed by tailoring the water content (0-20 vol%) in the electrolyte and the voltage gaps to control the time needed for initiation of lower-layer TiO(2) nanotube arrays. The fundamental understanding of the growth characteristics of double-layer TiO(2) nanotubes presented in this paper offers us more flexibility in engineering morphology, tuning dimensions and phase compositions of multilayer TiO(2) nanotubes. In addition, we synthesize double-layer TiO(2) nanotube arrays composed of one layer of anatase phase and another layer of amorphous phase.     

Photoelectrochemical properties of Fe-doped TiO2 nanotube arrays fabricated by anodization

Ti–Fe alloys with Fe contents of 0.05, 0.5 and 1.0 wt% were obtained using the arc-melting method. Fe-doped TiO₂ nanotube arrays were prepared by anodizing Ti–Fe alloys in ethylene glycol solution containing 0.25 wt% NH₄F and 10 wt% H₂O. The microstructure, crystal structure and photoelectrochemical properties of the nanotube arrays were characterized using scanning electron microscopy, X-ray diffraction, UV–Vis diffuse reflectance spectroscopy and electrochemical analyzer. Results show that doping of 0.05 wt% Fe improves the photoelectrochemical properties of titania nanotube arrays significantly, whilst further increasing the Fe contents to 0.5 and 1.0 wt% degrades these properties. The external potential has a considerable influence on the photocurrent density at doping content of 0.5 wt% Fe.     

Preparation and photoelectrochemical properties of CdS quantum dot-sensitized ZnO nanotube arrays

CdS/ZnO nanotubes (NTs) arrays were synthesized on a transparent conductive glass (FTO) substrate by hydrothermal method, chemical bath etching and successive ionic layer adsorption and reaction (SILAR) method, which were used in semiconductor-sensitized photoelectrochemical cells (PECs). The crystal structure, morphology and photoelectrochemical conversion properties of different photoanodes were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscope (TEM), high resolution transmission electron microscope (HRTEM), and electrochemical workstation. The results show a heterojunction has been formed between ZnO and CdS QDs. The ZnO NTs and CdS QDs played a remarkable controllability for PEC performances. The photoelectrochemical conversion efficiency of ZnO NTs photoanodes was 3 times that of ZnO nanorods (NRs) arrays photoanodes. After sensitization of CdS quantum dots, the photoelectrochemical conversion efficiency of CdS/ZnO NRs was improved by 7 times and the CdS/ZnO NTs was increased by 4 times. These results demonstrate that the CdS/ZnO core-shell structure can provide a facile and compatible frame for the potential applications in nanotube-based solar cells.     

Structural and photoelectrochemical characterization of TiO2 nanowire/nanotube electrodes by electrochemical etching

TiO₂ nanowire/nanotube electrodes were synthesized by anodization of titanium foils in ethylene glycol solution containing 0.5 wt% NH₄F and 1 wt% water at 60 V for 6 h. The microstructure and morphology of the asprepared electrodes were investigated by XRD and SEM. A possible formation mechanism and oxidation parameters of nanocomposite structure were discussed. The relationship between structural characteristics of TiO₂ nanowire/nanotube electrodes and its photoelectrochemical characterization were evaluated by electrochemical analyzer and photocatalytic degradation of methylene blue (MB) solution. Furthermore, these TiO₂ nanowire/nanotube electrodes promoted the photoelectrochemical characterization due to the larger surface areas, enhanced light harvesting and electron transport rate. The results show that photocurrent density of 1.44mA/cm² and photocatalytic degradation of 95.51% was achieved for TiO₂ nanowire/nanotube electrodes, which were 0.55mA/cm² and 20.52% higher than the TiO₂ nanotube electrodes under a similar condition, respectively.     

Preparation and photocatalytic properties of RuO2/TiO2 composite nanotube arrays

RuO₂/TiO₂ composite nanotube arrays were prepared using an anodic oxidation method combined with dipping. The photocatalytic properties of RuO₂/TiO₂ nanotube arrays in methylene blue solution were investigated under visible light irradiation. The results showed that Ru existing in the form of RuO₂ was dispersed uniformly on the surface of TiO₂ nanotubes, and the RuO₂ did not change the crystal structure of TiO₂ nanotubes. The load of RuO₂ on TiO₂ had a little influence on the band-gap energy and the absorption band edge, but could increase the amount of Ti-OH functional groups on the surface of TiO₂ nanotubes. The RuO₂/TiO₂ nanotube arrays with the optimal photocatalytic activity were formed in the ruthenium chloride solution with a concentration of 0.0030 mol/L. The 2 h photocatalytic degradation rate of methylene blue increased from 38% for pure TiO₂ nanotubes to 69% for RuO₂/TiO₂ nanotube arrays. This work demonstrated that RuO₂/TiO₂ nanotube arrays showed an improved photocatalytic property over pure TiO₂ nanotubes due to the fact that RuO₂ could capture the photo-generated holes, which greatly decreased the recombination of the photo-generated electrons and holes, and hence lengthen the lifetime of photo-induced electrons and increased the amount of hydroxyl groups absorbed on the TiO₂ nanotubes surface.     

The growth and morphology of copper phthalocyanine on TiO2 nanotube arrays

Nanostructured copper phthalocyanine was deposited by thermal vacuum evaporation, spin-coating, immersion, and electrochemical reactions onto titania nanotubes prepared by the anodization of titanium foil so as to attain interdigited heterojunctions between them for improved interfacial contact. The effects of the titania's crystal structure on the deposition were analyzed. A sodium salt derivative of copper phthalocyanine was used to enhance its affinity to the titania. The deposited copper phthalocyanine could be grown and transformed into diverse morphologies such as polyhedrons, nanorods, and nanowires. The factors affecting the morphology of the deposited copper phthalocyanine were analyzed by SEM and crystal structure analysis.     

Water-splitting properties of bi-phased TiO2 nanotube arrays subjected to high-temperature annealing

An extended study was conducted to correlate between morphological, crystalline phase conversion and the photoelectrochemical water-splitting properties of anodic TiO₂ nanotube arrays (TNTs) films annealed at elevated temperatures, starting from 450 °C to 850 °C. A distinct visualization was provided to support the effect of the high temperature annealing up to 850 °C on the photocurrent productivity of the TNTs films, which acted as photoanodes based on the crystalline anatase-rutile composition ratio. To assess the photoelectrochemical productivity for different annealed materials, several electrochemical techniques were utilized namely; electrochemical impedance spectroscopy (EIS), chronoamperometry and potentiodynamic polarization (PP). Results indicated that the crystalline bi-phased (anatase/rutile) TiO₂ nanotube arrays synergistically influenced the photoelectrochemical water splitting. It was found that the annealed TNTs film with bi-phase content composition (66% anatase and 34% rutile) at 650 °C exhibited maximum photoelectrochemical water-splitting properties with a significant applied bias photon-to-current conversion efficiency (ABPE%) of 0.41%. These results describe a promising target for the fabrication of high performance bi-phase crystalline (anatase and rutile) nanoporous TNTs for improving the photoelectrochemical water-splitting efficiency. Incident photon-to-electron conversion efficiency measurements (IPCE%) also showed the superiority of annealed sample at 650 °C (43.4%), which agrees with EIS, PP and ABPE% calculations.     

TiO_2纳米管在不同条件光催化降解的活性研究

本文利用阳极氧化法在纯钛片表面制备了TiO2纳米管阵列膜,解决TiO2光催化剂的涂敷固定问题。采用场发射扫描电镜(FESEM)和XRD对制备TiO2纳米管阵列膜的形貌和晶体结构进行表征。结果发现,所制得的纳米管管径70～80nm,壁厚5～10nm,XRD显示经420℃热处理的TiO2纳米管为锐钛矿晶型,经500℃热处理的TiO2纳米管出现金红石晶型。以10mg·L-1的甲基橙溶液为降解物进行光催化试验,分别研究了溶液的初始pH值、TiO2纳米管阵列膜的晶型、TiO2膜的使用次数对降解率的影响。试验结果表明,当溶液初始pH值为1时,TiO2纳米管阵列的光催化性能最好,同时随着TiO2膜使用次数的增加,其光催化效果有所下降。     

Preparation of CdS/TiO2 nanotube arrays and the enhanced photocatalytic property

In this paper, a series of CdS/TiO₂ NTs have been synthesized by SILAR method. The as-prepared CdS/TiO₂ NTs have been analyzed by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive spectrometer (EDS), and ultraviolet–visible (UV–vis). And their photocatalytic activities have been investigated on the degradation of methylene blue under simulated solar light irradiation. XRD results indicate that TiO₂ NTs were anatase phase, CdS nanoparticles were hexagonal phase. FESEM results indicate that low deposition concentration can keep the nanotubular structures. UV–vis results indicate that CdS can be used to improve the absorbing capability of TiO₂ NTs for visible light, and the content of CdS affects the band gap. Photocatalytic results indicate that CdS nanoparticles are conducive to improve the photocatalytic efficiency of TiO₂ NTs, and the highest degradation rate can reach 93.8%. And the photocatalytic mechanism of CdS/TiO₂ NTs to methylene blue is also described.     

Hydrogen evolution promotion of Au-nanoparticles-decorated TiO2 nanotube arrays prepared by dip-loading approach

Au nanoparticle (NPs)@TiO₂ nanotube arrays (NTAs) heterostructured films with enhanced H₂ generation rate under full spectrum were synthesized, by using a controllable and facile dip-loading approach. Size of the Au NPs was well-distributed around 7 nm, and the TiO₂ NTAs were found vertically aligned. Due to LSPR effect and Schottky contact, the as-prepared Au NPs@TiO₂ NTAs heterostructured films exhibited improved H₂ generation abilities as well as photocatalytic degradation abilities. H₂ evolution rate of the obtained samples (effective area: 5.25 cm²) reached 74.56 μmol/h, which was 38 times higher than that of the raw TiO₂ NTAs. And the Au NPs@TiO₂ NTAs samples also showed an obvious advantage over the raw TiO₂ NTAs, in methyl orange degradation under UV illumination. Repetition experiments were further carried out to ensure the dip-loading method was a reliable fabrication process, and the amount of Au particles attached on TiO₂ tube walls could be manipulated by changing the dip-loading cycle times.     

Fabrication of plasmonic Au/TiO2 nanotube arrays with enhanced photoelectrocatalytic activities

Uniformly dispersed Au nanoparticles (NPs) deposited on the surface of highly ordered TiO₂ nanotube arrays (Au/TiO₂ NTs) were synthesized through a two-step process including anodization method and microwave-assisted chemical reduction route. The investigation indicated that Au NPs grew uniformly on the walls of TiO₂ NTs. Au/TiO₂ NTs exhibited excellent visible light absorption due to the LSPR effect of Au NPs. Au/TiO₂ NTs exhibited much higher photocurrent density and the photoconversion efficiency of Au decorated TiO₂ NTs was about 2.05 times greater than that of bare TiO₂ NTs. Besides, the PL intensity of Au/TiO₂ NTs was much lower than that of TiO₂ NTs, revealing a decrease in charge carrier recombination. The prepared Au/TiO₂ NTs exhibited superior photoelectrocatalytic activity and stability in the degradation of MB under simulated solar light irradiation. The synergy effect between nanotubular structures of TiO₂ and uniformly dispersed Au nanoparticles, as well as the small bias potential and strong interaction between Au and TiO₂, facilitated the Au plasmon-induced charge separation and transfer, which lead to highly efficient and stable photoelectrocatalytic activity.     

Effect of concentration of Fe-dopant on the photoelectrochemical properties of Titania nanotube arrays

TiO₂ nanotubes have attracted great attention because of their photoelectrochemical activity. Metallic doping using a simple and rapid synthesizing approach can be a way to enhance this application. This paper describes a novel one-step anodization synthesis of Fe-doped TiO₂ nanotubes with various concentrations of iron doping. FESEM, XRD, and EDX were used to analyze the effect of doping concentration on the morphology, structure, and composition of the prepared samples respectively, and the results showed the formation of the anatase phase of TiO₂ nanotube arrays with Fe incorporation in the TiO₂ lattice. Although the Fe insertion in the TiO₂ lattice leads to better crystallinity, the non-uniformity in the morphology of doped samples suggests that adequate doping is required to maintain uniformity in the morphology. The absorption spectra of all the Fe-doped TiO₂ samples showed a red shift in their absorption edges compared to pristine TiO₂. This shift was observed more in the samples with higher doping concentrations. The photocurrent density of Fe-doped samples was observed to be significantly higher than that of the pristine TiO2 sample. This improvement was found to be concentration-dependent, with the best results being obtained from a sample doped at a level of 0.5%. The samples also showed high photostability, which, together with the increased photocurrent density, points to Fe-doped TiO₂ as a promising photoanode material.     

TiO2纳米管阵列孔径调控葡萄糖氧化酶生物传感器性能

采用电化学阳极氧化法制备出不同孔径（21、62、83、102 nm）的TiO₂纳米管阵列（TNA）,研究了孔径对固定化葡萄糖氧化酶（GOx）的传感器性能的影响。循环伏安测试结果表明固定在不同孔径大小的TNA上的GOx在葡萄糖溶液中均具有良好的酶活性。计时电流法和交流阻抗法测试发现,当孔径是83 nm时,灵敏度达到最大值27.2 μA·（mmol·L^-1）^-1·cm^-2。调控TNA的孔径可改变固定化GOx的活性及溶液扩散阻抗,从而显著提高生物传感器性能。     

TiO2纳米管阵列的制备改性及应用研究进展

TiO₂纳米管阵列作为一种新型的三维立体纳米材料,因其大的比表面积及特殊的几何结构而受到了广泛的关注与研究。本文回顾了近年来阳极氧化法在Ti基底上原位生成TiO₂纳米管阵列所用电解液的发展趋势,介绍了TiO₂纳米管阵列的特性,如晶型结构、光学和电学特性以及催化活性,阐述了TiO₂纳米管阵列的金属离子掺杂、非金属离子掺杂、金属沉积、导电聚合物复合、半导体复合以及其他等多种改性手段,探讨了TiO₂纳米管阵列在光电催化降解污染物、光解水制氢、染料敏化太阳能电池和传感器以及其他多个领域的应用研究进展。最后,展望了TiO₂纳米管阵列的主要研究方向是对其形貌调控与表面改性等方面作进一步研究,以期为后续研究提供参考依据。