Unmodified TiO2 Research Articles

Cr2O3 nanoparticles modified TiO2 nanotubes for enhancing visible photoelectrochemical performance.

TiO2 nanotube arrays modified by nanoparticles Cr2O3 with high sensibility in the visible spectrum were prepared by annealing the anodic TiO2 nanotube arrays pre-loaded with Cr(NO3)3 solution which was uniformly clung to the TiO2 nanotube arrays. The influence of the dipping time on the microstructure of the Cr2O3/TiO2-nanotubes was investigated. The microstructure and the elemental analysis were characterized by scanning electron microscope (SEM) and Energy dispersive X-ray (EDX). The photoelectrochemical performances of the as-prepared composite nanotubes were determined by measuring the photogenerated current and voltage under illumination of ultraviolet-visible (UV-vis)/visible light. The TiO2 nanotube arrays modified by Cr2O3 showed higher photocurrent values than those of unmodified TiO2 nanotube arrays. The enhanced photoelectrochemical behaviors can be attributed to the modified Cr2O3 which increases the probability of charge-carrier separation and extends the range of the TiO2 photoresponse from UV to visible region due to the low band gap of 2.3 eV of Cr2O3.

Preparation of a thin carbon coated TiO2 using humic acid for the enhanced removal of reactive red 4 dye

Carbon (C) coated TiO2 with a thin layer of C was successfully prepared using a humic acid reagent as the C precursor followed by a thermal treatment in N2 gas flow at 650 °C. The test of the photocatalytic activity of the improved phocatalyst was carried out using an anionic reactive red 4 dye as the model pollutant with a 45 W fluorescent lamp and solar light as the light source. The C layer was found to be in the graphitic form and it was coated to the surface of TiO2 at the optimum thickness of 0.68 nm. The C content for the modified photocatalysts ranged from 0.02 to 0.16 wt% with the optimum C content at 0.05 wt%. The photocatalytic activities of the C coated TiO2 were 4.5 and 7.6 times faster than that of the unmodified TiO2 under the 45 W fluorescent lamp and solar irradiation, respectively. The higher photocatalytic activity of the C coated TiO2 was attributed to the electron scavenging ability of the incorporated C in TiO2, thus hindering the electron–hole recombination process within the irradiated semiconductor.

Silver/titania nanocomposite-modified photoelectrodes for photoelectrocatalytic methanol oxidation

Silver deposited titania (Ag/TiO2) nanocomposite thin films were fabricated by the simple sonochemical deposition of Ag on preformed aerosol-assisted chemical vapor deposited TiO2 thin films. The photelectrocatalytic performance of a newly fabricated Ag/TiO2-modified photoelectrode was studied for methanol oxidation under simulated solar AM 1.5G irradiation (100 mW/cm2). The Ag/TiO2-modified photoelectrode showed a photocurrent density of 1 mA/cm2, which is four times that of an unmodified TiO2 photoelectrode. The modification of Ag on the TiO2 surface significantly enhanced the photoelectrocatalytic performance by improving the interfacial charge transfer processes, which minimized the charge recombination. Density functional theory (DFT) calculation studies revealed that methanol could be easily adsorbed onto the Ag surfaces of Ag/TiO2 via a partial electron transfer from Ag to methanol. The newly fabricated Ag/TiO2-modified photoelectrode could be a promising candidate for photoelectrochemical applications.

Induced self-cleaning properties towards Reactive Red 198 of the cement materials loaded with co-modified TiO2/N,C photocatalysts

The possibility of promoting the self-cleaning properties of the cement materials was verified by implementing the obtained nitrogen and carbon co-modified titania-based (TiO2/N,C) photocatalysts into the cement plates. Additionally, unmodified TiO2 (Grupa Azoty Zakłady Chemiczne POLICE S.A., Poland) and a commercial photocatalyst P25 (Evonik Industries AG, Germany) were used as reference materials. The impact of treatment temperature on the physicochemical properties of the obtained TiO2/N,C additives was discussed. The photocatalytic activity of the prepared cement plates was evaluated trough the degradation of a model organic compound (Reactive Red 198) under UV–vis light. It was found that cement plates containing TiO2/N,C photocatalyst calcined at 600 °C temperature exhibited the highest photocatalytic activity. The role of several factors such as crystallinity, phase composition and non-metals presence in the TiO2/N,C additives on the self-clearing properties of the cement samples was also included in the discussion.

Enhancing membrane performance by blending ATRP grafted PMMA–TiO2 or PMMA–PSBMA–TiO2 in PVDF

To improve PVDF (polyvinylidine fluoride) membrane property, TiO2 nano-particles can be blended in casting solutions to form composite membranes. In this study, TiO2 nano-particles were modified by coupling with γ-aminopropyl triethoxy silane (KH550), then grafted with PMMA (Polymethyl methacrylate) or co-grafted with PMMA and more hydrophilic PSBMA (polysulfobetaine methacrylate) via ATRP (atom transfer radical polymerization). ATRP grafting time and weight ratio of KH550 to TiO2 were two main identified factors affecting TiO2 modification and membrane hydrophilicity, flux and antifouling properties. These were shown by Scanning electron microscopy (SEM) characterization, contact angles measurements and filtration tests with yeast suspensions. The grafted TiO2–PMMA nano particles formed after coupling at 3:1 weight ratio of KH550 to TiO2 and 5h grafting, once composited with PVDF, formed a membrane with higher flux (up to 50%), higher flux recovery rate (FRR, 93.5%) and lower irreversible fouling (5.37%) than PVDF membrane composited with unmodified TiO2. Blending TiO2 co-grafted with PMMA and zwitterionic polymer PSBMA resulted in even better antifouling membranes (even lower Rir<2% and even higher FRR 99%). When the molar ratio of MMA to SBMA was 2 to 1, the highest steady flux and the highest FRR were obtained.

Branched titanium oxide/vanadium oxide composite nanofibers formed by electrospinning and dipping in vanadium sol

Titanium oxide/vanadium oxide composite nano-fibers were fabricated via a novel method involving electrospinning and dipping in vanadium sol. The fibers were developed to photocatalyze the degradation of pollutants from wastewater. Phases, morphologies, and chemical compositions of the nanofibers were characterized by X-ray diffraction (XRD), scanning electron microscopy, energy dispersive spectrometry (EDS), and X-ray photoelectron spectroscopy (XPS). The XRD patterns indicated an anatase structure, while imaging revealed branched morphologies due to sintering at 550°C in a N2 atmosphere. EDS and XPS indicated the presence of TiO2, Ti2O3, V2O5 and VO2. The formation of V4+ and surface Ti3+ improved the photocatalytic activity because they narrow the band gap and reduce electron–hole recombination rates. Specifically, the 3h methyl orange decomposition rate photocatalyzed by the composite nanofibers increased by 95.8% relative to the catalysis by unmodified TiO2 nanofibers.

Preparation of TiO2 particles and surface silanization modification for electronic ink

In this study, a sol–gel method has been adopted to synthesize titanium dioxide (TiO2) particles. In order to improve the surface properties of the TiO2 particles, vinyl triethoxysilane (VTES) has been used for their modification by silanization. The particles have been characterized by FTIR, scanning electron microscope, transmission electron microscopy, and X-ray diffraction (XRD) techniques. The results confirmed that VTES had been successfully grafted onto the surface of the TiO2 particles. The TiO2 particle size was not changed by the silanization modification, remaining at 100–200 nm. XRD results have shown the crystalline phase of the TiO2 particles to be of the anatase type, and this was also unaffected by the VTES modification. Dispersion properties and suspension stability characterization of TiO2 particles showed that VTES-modified TiO2 particles have better dispersion stability and suspension stability in the dispersant of tetrachloroethylene than that of unmodified TiO2 particles.

Photopotential decay delay on TiO2 surface modified with p‐benzaldehydes: consequences and applications

TiO2 (Anatase) surface has been modified with p‐substituted benzaldehydes (p = OCH3, CH3, H, CN, and NO2) and 4‐stilbene carboxaldehyde. Fourier transform infrared spectroscopy attenuated total reflectance spectroscopy, UV–Vis reflectance spectra, and theoretical calculations indicate that the TiO2 surface has been chemically modified and supported acetal formation by means of TiO2–OH reaction with the aldehyde. A steady state photocurrent was obtained during simulated UV light irradiation of the acetal‐TiO2 in aqueous solution. Once the light irradiation is turned off, open‐circuit potential decay measurements were used in order to determine the electron life‐time (tn). Excited electron decay is inhibited down to 1 s when the electron withdrawing delocalization capacity of the modified TiO2 increases. Electron life‐time also depends on the solution reduction capacity. However, the unmodified TiO2 life‐time does not. The TiO2 modification results in a new series of photocatalysts that improve the organic contaminants degradation in solution because slow electron decay also induces retardation of the electron‐hole recombination. Therefore, there is a linear relationship between the electron decay life‐time and degradation rate constant. However, when electron delocalization is further increased in a way that the electron life‐time becomes ca. 7 s, degradation rate is kept constant. Therefore, the extra electron stability compromise degradation in such a way that the modified nanoparticle switches from a useful oxidant agent to a material that favors the charge carriers separation through a stable radical anion formation. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Aging of the photocatalytic TiO2 thin films modified by Ag and Pt

This work focuses on the investigation of the photocatalytic activity of the TiO2 thin films (either modified or unmodified by noble metal) and on its stability during 16 months after deposition. RF discharge was used to deposit the TiO2 thin films by PECVD from the mixture of titanium isopropoxide (TTIP) vapors and oxygen. The surface of TiO2 films was subsequently modified by Ag or Pt by means of magnetron sputtering. Several analytical methods were used to characterize the thin films properties. XPS was used to investigate the chemical composition of the surface, SEM to study the surface morphology. The photocatalytic activity was expressed in terms of photocatalytic efficiency and it was determined by decomposition of the organic dye Acid orange 7 (AO7). The results show that the enhancement of the photocatalytic efficiency achieved by the modification by Ag or Pt decreases with time, but it is still several times higher after 16 months aging than in case of unmodified TiO2 layers.

Visible Light Photocatalytic Activity in AACVD‐Prepared N‐modified TiO2 Thin Films

Nitrogen‐modified TiO2 thin films are obtained, for the first time, from aerosol‐assisted (AA)CVD‐prepared samples via a post‐treatment method involving immersion in liquid ammonia to achieve nitrogen‐modified TiO2 and visible‐light photo‐activity. The resulting modified and unmodified TiO2 films are characterized by X‐ray diffraction (XRD), Raman spectroscopy (RS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution (HR)TEM, energy dispersive X‐ray (EDX) spectroscopy, selected area electron diffraction (SAED), UV‐vis spectroscopy, and X‐ray photoelectron spectroscopy (XPS). This shows that the films are ∼200 nm thick and contain anisotropic crystals of anatase TiO2. XPS shows that the nitrogen is successfully added to the surface of the film interstitially at 0.7 at.‐%, but is only present to a film depth of 50 nm. The nitrogen doping causes a red shift in the absorption band and a band gap narrowing of ∼0.1 eV. The surface‐bound nitrogen results from the post‐treatment method of doping where the films are soaked in liquid ammonia before annealing. The photocatalytic efficiencies of the films under visible light (&gt;385 nm) are evaluated by measuring formaldehyde formation from the probe molecule tris(hydroxymethyl)aminomethane (Tris). Hydrogen abstraction from Tris, obtained from, e.g., photocatalytically produced OH radicals, leads to formaldehyde formation which is then detected through a modified version of the Hantzsch reaction. The results show that the N‐modified film possess remarkable photocatalytic properties with an apparent photochemical quantum yield of ∼8%.

A first principles investigation of Bi2O3-modified TiO2 for visible light Activated photocatalysis: The role of TiO2 crystal form and the Bi3+ stereochemical lone pair

Modification of TiO2 with metal oxide nanoclusters is a novel strategy for the design of new photocatalysts with visible light activity. This paper presents a first principles density functional theory (DFT) analysis of the effect of modifying TiO2 rutile (110) and anatase (101) and (001) surfaces with Bi2O3 nanoclusters on the band gap and the nature of the photoexcited state. We show that band gap modifications over unmodified TiO2 depend on the crystal form: modifying rutile (110) results in new Bi2O3 derived states that shift the valence band upwards. On anatase surfaces, there is little effect due to modification with Bi2O3 nanoclusters, but an enhanced UV activity would be expected. Analysis of electron and hole localisation in a model photoexcited state shows enhanced charge separation in Bi2O3-modified rutile (110) but not in Bi2O3-modified anatase. The effect of the Bi3+ lone-pair on the properties of Bi2O3-modified TiO2 contrasts with SnO-modified TiO2, consistent with the weaker lone pair in Bi2O3 compared with SnO.

Poly(4,4′-oxydiphenylene-pyromellitimide)/TiO2 nanocomposites with surface-modified titanium dioxide using 4,4′-methylene diphenyl diisocyanate

This study describes a facile method for preparing poly(4,4′-oxydiphenylene-pyromellitimide) (POPI)/TiO2 nanocomposites. 4,4′-Methylene diphenyl diisocyanate (MDI) was used as the surface modifier of TiO2 nanoparticles. MDI-modified and/or unmodified TiO2 were added to a viscose solution of poly(amic acid) (PAA) prepared by reacting 4,4′-oxydiphenylamine and pyromellitic dianhydride (PMDA). Casting the homogenized mixture onto glass Petri dishes gave the corresponding thermally cured films of POPI/TiO2 and POPI/TiO2-MDI nanocomposites through cyclodehydration of the PAA precursor. Diffuse reflectance UV/vis spectroscopy (UV/vis DRS) indicated that two absorption maxima are developed in the spectrum of MDI-treated TiO2 at about 440 and 580 nm, as well as a slight red shift in the absorption maxima of POPI/TiO2 and POPI/TiO2-MDI nanocomposites compared to the neat POPI occurred. From XRD measurements the mean sizes of nano-TiO2 in TiO2-MDI, POPI/TiO2, and POPI/TiO2-MDI were found to be 27, 22, and 19 nm, respectively. According to the SEM images of POPI/TiO2 and POPI/TiO2-MDI nanocomposites, the nano-sized TiO2 particles with globular shapes were dispersed into the polymer matrix. According to the TGA/DTG thermograms it could be deduced that the incorporation of nano-TiO2 particles into the polymer matrix can lead to an appreciable thermostability. Taking into account, the DTA thermograms a discrete endothermic transition could be detected at about 290 °C. MDI-grafted TiO2 seems to be a good candidate for incorporating into poly(4,4′-oxydiphenylene-pyromellitimide) as a commercial type polyimide.

Enhanced visible light photocatalytic activity of TiO2 nanotube arrays modified with CdSe nanoparticles by electrodeposition method

Highly ordered TiO2 nanotube arrays (NTAs) were fabricated on titanium substrate via electrochemical anodization method. CdSe nanoparticles were deposited on the TiO2 NTAs through the electrodeposition process. The influence of electrolyte concentration and deposition time on the visible light photocatalytic performance of CdSe/TiO2 NTAs was studied systematically. The photocatalytic activity of as-prepared samples was evaluated by degradation of methyl orange under visible light irradiation. The results indicated that the CdSe nanoparticles distributed uniformly on the surface of TiO2 NTAs when deposited in the electrolyte containing 0.02M CdCl2, 2mM SeO2 and 0.02M Na2SO4 with time of 600s. After irradiation under visible light for 2h, the degradation rate of CdSe/TiO2 NTAs composite material reached 94.4%, while the degradation rate of unmodified TiO2 NTAs was only 6.2 % under the same condition, demonstrating that the CdSe/TiO2 NTAs exhibited higher photocatalytic activity in visible light region. In addition, a reasonable degradation rate of 80.96% was achieved even after being used for 5 times.

Intermittent microwave heating-promoted rapid fabrication of sheet-like Ag assemblies and small-sized Ag particles and their use as co-catalyst of ZnO for enhanced photocatalysis

An easy and rapid intermittent microwave heating (IMH) method was developed for the synthesis of Ag nanostructures with high yields within the short time of 2 minutes. A Ag–DT (dodecanethiol) complex with sheet-like structure was used as precursor. After an IMH treatment of the solid Ag–DT, Ag nanoparticles (NPs) with a small size below 5 nm were obtained. Time-dependent experiments and a series of tests indicated that the Ag NPs were formed and grown in the sheet-like Ag–DT precursor. Specifically, the fewer IMH cycles (less than 3 times) would result in the formation of the sheet-like assemblies of Ag NPs linked by the Ag–DT. The sheet-like assemblies of Ag NPs were rarely observed in previous reports. The Ag NPs with small size below 5 nm would emerge as major products with increasing the number of IMH cycles to 5 times. With further increase of IMH cycles, Ag NPs with a large size of 20 nm were observed. Notably, due to the presence of DT groups on the surface of Ag NCs, the small-sized Ag NPs could directly combine with an oxide (ZnO here) to form Ag–oxide composites with no need for additional modification. The Ag–ZnO composites exhibited enhanced performance for the photocatalytic degradation of dye pollutants over unmodified ZnO and P25 TiO2, demonstrating the large application potential of composites in advanced areas. The IMH strategy developed here will be important for the practical application of Ag-based materials due to the fast synthesis process, high yields benefiting from the solid-based reaction, high stability, as well as the ability of the as-prepared Ag NCs to easily combine with oxide materials to form functional nanocomposites (ZnO here).

Control of Airborne Organic Pollutants Using Plug-Flow Reactor Coated With Carbon Material-Titania Mixtures Under Visible-Light Irradiation

Graphene oxide (GO)-titania composites have emerged as an attractive heterogeneous photocatalyst that can enhance the photocatalytic activity of TiO2 nanoparticles owing to their potential interaction of electronic and adsorption natures. Accordingly, TiO2-GO mixtures were synthesized in this study using a simple chemical mixing process, and their heterogeneous photocatalytic activities were investigated to determine the degradation of airborne organic pollutants (benzene, ethyl benzene, and o-xylene (BEX)) under different operational conditions. The Fourier transform infrared spectroscopy results demonstrated the presence of GO for the TiO2-GO composites. The average efficiencies of the TiO2-GO mixtures for the decomposition of each component of BEX determined during the 3-h photocatalytic processes were 26%, 92%, and 96%, respectively, whereas the average efficiencies of the unmodified TiO2 powder were 3%, 8%, and 10%, respectively. Furthermore, the degradation efficiency of the unmodified TiO2 powder for all target compounds decreased during the 3-h photocatalytic processes, suggesting a potential deactivation even during such a short time period. Two operational conditions (air flow entering into the air-cleaning devices and the indoor pollution levels) were found to be important factors for the photocatalytic decomposition of BEX molecules. Taken together, these results show that a TiO2-GO mixture can be applied effectively for the purification of airborne organic pollutants when the operating conditions are optimized.

Titanium dioxide–graphene oxide composites with different ratios supported by Pyrex tube for photocatalysis of toxic aromatic vapors

Titanium dioxide–graphene oxide (TiO2–GO) composites with different ratios of GO to TiO2 were synthesized using a colloidal blending process and evaluated for their heterogeneous photocatalytic purification of toxic aromatic vapors using a Pyrex tube reactor. Both SEM and FTIR demonstrated the presence of a carbon component in the as-prepared TiO2–GO composites. Unlike unmodified TiO2, the TiO2–GO composites showed a light-absorbance shift into the longer wavelength regions, indicating band-gap narrowing. The time-series ratios of outlet to inlet concentrations of selected aromatic vapors determined using the TiO2–GO composites under visible-light and UV exposure were lower than or similar to those obtained using unmodified P25 TiO2, suggesting that the TiO2–GO composites had superior photocatalytic activity to P25 TiO2 for degradation of vaporous aromatic pollutants. In addition, the time-series ratios of outlet to inlet concentrations determined using the TiO2–GO composites under both visible-light and UV irradiation decreased, as the ratio of GO to TiO2 increased from 0.01 to 0.10, while they increased as the ratio increased from 0.10 to 0.15, suggesting the presence of an optimal GO to TiO2 ratio. Overall, TiO2–GO composites supported by Pyrex tubes could be utilized effectively for degradation of toxic vaporous aromatic pollutants.

Dye-sensitized solar cells enhanced by optical absorption, mediated by TiO2 nanofibers and plasmonics Ag nanoparticles

Light harvesting in dye-sensitized solar cells (DSSCs) mediated by plasmonic metallic nanoparticles and sub-micron light-scattering metal oxides is a facile and cost-effective approach to achieving high device performance. Ag nanoparticles, protected by thin shells of TiO2, were incorporated in TiO2 photoanode. The large plasmonic near-field intensity generated by these nanoparticles caused an 18.3% rise in photocurrent, which resulted in an enhanced efficiency of 6.23% as compared to 5.29% efficiency of DSSC based on unmodified TiO2 photoanode. In addition, DSSC with TiO2 nanofibers (NFs) embedded in TiO2 photoanode was also constructed, which because of the efficient light scattering ability of the nanofibers, attained an efficiency of 7.14% as a result of a current rise of 36.9%. Another DSSC was assembled with Ag NPs added to the photoanode of the NFs-based DSSC to further boost cell performance. The addition of Ag NPs, however, did not produce an appreciable change in the cell performance. The reason for this unexpected outcome was probably due to the low internal resistance associated with charge recombination and large resistance to electron transport in the cell as determined by electrochemical impedance analysis computed in this work.

TiO2nanotubes/ZnO/CdS ternary nanocomposites: preparation, characterization and photocatalysis

TiO2 nanotube arrays were prepared by electroanodization of titanium metal foils, and then modified with two semiconductor thin films. First, a ZnO layer was deposited onto the TiO2 surface by sequential chemical bath deposition of a zinc salt complex followed by a thermal annealing process. A CdS thin film was then formed on the TiO2/ZnO surface by layer-by-layer deposition of Cd(NO3)2 and Na2S, leading to the production of ternary TiO2/ZnO/CdS nanocomposites. The structures of the resulting nanocomposites were characterized by using a variety of experimental tools including field-emission scanning electron microscopy, X-ray diffraction, X-ray photoelectron and ultraviolet-visible (UV-vis) diffuse reflectance spectroscopy. Importantly, the resulting nanocomposites exhibited markedly enhanced photocatalytic activity, as highlighted by the photodegradation of alizarin red S under UV light, in comparison to the unmodified TiO2 nanotubes or the nanotubes modified only with ZnO or CdS. This was accounted for ...

Photocatalytic conversion of greenhouse gases (CO2 and CH4) using copper phthalocyanine modified TiO2

In the present study, the direct photoconversion of carbon dioxide and methane in an appropriate gas-phase batch reactor under visible light was investigated. In the photocatalytic reaction system copper phthalocyanine (CuPc) modified titanium dioxide (CuPc/TiO2) photocatalyst that was coated on stainless steel mesh was used. The morphology of CuPc/TiO2 photocatalysts were characterized using XRD, SEM, FTIR and UV–vis analyses, and photoreduction products were identified using GC-TCD, GC–MS and FTIR in gas medium. The results of SEM have shown limited presence of CuPc on TiO2 surface, also the results of UV–vis have shown that the absorbance spectra of titania extended to visible spectral region. The results of photocatalytic activity have shown the conversion of 14% and 18% for CO2 and CH4 under modified TiO2 and visible light, respectively. However, the conversions of CO2 and CH4 under unmodified TiO2 and visible light were zero, approximately. Based on GC–MS and FTIR analyses, final products of conversion were characterized to be formate and acetate derivatives, and a mechanism involving the photoactivation of both TiO2 and CuPc sensitizer is proposed.

Electrophoretic deposition of reduced graphene oxide nanosheets on TiO2 nanotube arrays for dye-sensitized solar cells

In the present work, electrophoretic deposition (EPD) is used to deposit reduced graphene oxide (RGO) nanosheets onto a TiO2 nanotube array for application as photoelectrode in dye-sensitized solar cells (DSSCs). The as-deposited RGO nanosheets are very uniform and can be obtained with controllable thickness. Due to the enhanced electronic conductivity caused by RGO, the short-circuit current of DSSCs based on RGO-modified TiO2 nanotube arrays is much higher than that of DSSCs based on unmodified TiO2 nanotube arrays. In addition, the short-circuit current (Jsc) increases with longer EPD time for RGO deposition but decreases with increased EPD time later; a peak value of 8.87mAcm−2 is reached for Jsc at an EPD time of 30s. Therefore, DSSC based on TiO2 nanotubes (6.8μm long) modified using EPD time 30s delivers the highest energy conversion efficiency of 4.10%, while DSSC consisting of bare nanotubes exhibits efficiency of 2.97% and short-circuit current of 6.24mAcm−2, which represents a 38.0% enhancement of energy conversion efficiency in DSSC consisting of TiO2 nanotubes modified with RGO compared to that of DSSC based on bare nanotubes. Moreover, RGO-deposition on longer bamboo-type TiO2 nanotube arrays (16.8μm long) can further increase the energy conversion efficiencies to 6.01% by utilizing higher surface area of bamboo-type nanotubes for dye loading.