Modified TiO₂ nanotubes-zeolite composite photocatalyst: Characteristics, microstructure and applicability for degrading triclocarban

The study explored the characteristics and effectiveness of modified TiO₂ nanotubes with zeolite as a composite photocatalyst (MTNZC) for the degradation of triclocarban (TCC) from the aqueous solution. MTNZC samples have been produced via electrochemical anodisation (ECA) followed by electrophoretic deposition (EPD). Three independent factors selected include MTNZC size (0.5-1 cm²), pH (3-10), and irradiation time (10-60 min). The observation revealed that the surface of Ti substrate by the 40 V of anodisation and 3 h of calcination was covered with the array ordered, smooth and optimum elongated nanotubes with average tube length was approximately 5.1 μm. EDS analysis proved the presence of Si, Mg, Al, and Na on MTNZC due to the chemical composition present in the zeolite. The average crystallite size of TiO₂ nanotubes increased from 2.07 to 3.95 nm by increasing anodisation voltage (10, 40, and 60 V) followed by 450 °C of calcination for 1, 3, and 6 h, respectively. The optimisation by RSM shows the F-value (36.12), the p-value of all responses were less than 0.0001, and the 95% confidence level of the model by all the responses indicated the model was significant. The R² in the range of 0.9433-0.9906 showed the suitability of the model to represent the actual relationship among the parameters. The photocatalytic degradation rate of TCC from the first and the fifth cycles were 94.2 and 77.4%, indicating the applicability of MTNZC to be used for several cycles.

Materials characterization of TiO2 nanotubes decorated by Au nanoparticles for photoelectrochemical applications

The structural and chemical modification of TiO2 nanotubes (NTs) by the deposition of a well-controlled Au deposit was investigated using a combination of X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), Scanning Transmission Electron Microscopy (STEM), Raman measurements, UV-Vis spectroscopy and photoelectrochemical investigations. The fabrication of the materials focused on two important factors: the deposition of Au nanoparticles (NPs) in UHV (ultra high vacuum) conditions (1-2 × 10-8 mbar) on TiO2 nanotubes (NTs) having a diameter of ∼110 nm, and modifying the electronic interaction between the TiO2 NTs and Au nanoparticles (NPs) with an average diameter of about 5 nm through the synergistic effects of SMSI (Strong Metal Support Interaction) and LSPR (Local Surface Plasmon Resonance). Due to the formation of unique places in the form of "hot spots", the proposed nanostructures proved to be photoactive in the UV-Vis range, where a characteristic gold plasmonic peak was observed at a wavelength of 580 nm. The photocurrent density of Au deposited TiO2 NTs annealed at 650 °C was found to be much greater (14.7 μA cm-2) than the corresponding value (∼0.2 μA cm-2) for nanotubes in the as-received state. The IPCE (incident photon current efficiency) spectral evidence also indicates an enhancement of the photoconversion of TiO2 NTs due to Au NP deposition without any significant change in the band gap energy of the titanium dioxide (E g ∼3.0 eV). This suggests that a plasmon-induced resonant energy transfer (PRET) was the dominant effect responsible for the photoactivity of the obtained materials.

Plasma Nitriding of TiO2 Nanotubes: N-Doping in Situ Investigations Using XPS

The nitrogen doping of titanium dioxide nanotubes (TiO₂ NTs) was investigated as a result of well-controlled plasma nitriding of TiO₂ NTs at a low temperature. This way of nitrogen doping is proposed as an alternative to chemical/electrochemical methods. The plasma nitriding process was performed in a preparation chamber connected to an X-ray photoelectron spectroscopy (XPS) spectrometer, and the nitrogen-doped TiO₂ NTs were next investigated in situ by XPS in the same ultrahigh vacuum (UHV) system. The collected high-resolution (HR) XPS spectra of N 1s, Ti 2p, O 1s, C 1s, and valence band (VB) revealed the formation of chemical bonds between titanium, nitrogen, and oxygen atoms as substitutional or interstitial species. Moreover, the results provided a characterization of the electronic states of N-TiO₂ NTs generated by various plasma nitriding and annealing treatments. The VB XPS spectrum showed a reduction in the TiO₂ band gap of about 0.6 eV for optimal nitriding and heat-treated conditions. The TiO₂ NTs annealed at 450 or 650 °C in air (ex situ) and nitrided under UHV conditions were used as reference materials to check the formation of Ti-N bonds in the TiO₂ lattice with a well-defined structure (anatase or a mixture of anatase and rutile). Scanning electron microscopy microscopic observations of the received materials were used to evaluate the morphology of the TiO₂ NTs after each step of the nitriding and annealing treatments.

TiO2 Nanotubes with Pt and Pd Nanoparticles as Catalysts for Electro-Oxidation of Formic Acid

In the present work, the magnetron sputtering technique was used to prepare new catalysts of formic acid electrooxidation based on TiO₂ nanotubes decorated with Pt (platinum), Pd (palladium) or Pd + Pt nanoparticles. TiO₂ nanotubes (TiO₂ NTs) with strictly defined geometry were produced by anodization of Ti foil and Ti mesh in a mixture of glycerol and water with ammonium fluoride electrolyte. The above mentioned catalytically active metal nanoparticles (NPs) were located mainly on the top of the TiO₂ NTs, forming 'rings' and agglomerates. A part of metal nanoparticles decorated also TiO₂ NTs walls, thus providing sufficient electronic conductivity for electron transportation between the metal nanoparticle rings and Ti current collector. The electrocatalytic activity of the TiO₂ NTs/Ti foil, decorated by Pt, Pd and/or Pd + Pt NPs was investigated by cyclic voltammetry (CV) and new Pd/TiO₂ NTs/Ti mesh catalyst was additionally tested in a direct formic acid fuel cell (DFAFC). The results so obtained were compared with commercial catalyst-Pd/Vulcan. CV tests have shown for carbon supported catalysts, that the activity of TiO₂ NTs decorated with Pd was considerably higher than that one decorated with Pt. Moreover, for TiO₂ NTs supported Pd catalyst specific activity (per mg of metal) was higher than that for well dispersed carbon supported commercial catalyst. The tests at DFAFC have revealed also that the maximum of specific power for 0.2 Pd/TiO₂ catalyst was 70% higher than that of the commercial one, Pd/Vulcan. Morphological features, and/or peculiarities, as well as surface composition of the resulting catalysts have been studied by scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), and chemical surface analytical methods (X-ray photoelectron spectroscopy-XPS; Auger electron spectroscopy-AES).

TiO2 and Au-TiO2 Nanomaterials for Rapid Photocatalytic Degradation of Antibiotic Residues in Aquaculture Wastewater

Antibiotic residues in aquaculture wastewater are considered as an emerging environmental problem, as they are not efficiently removed in wastewater treatment plants. To address this issue, we fabricated TiO₂ nanotube arrays (TNAs), TiO₂ nanowires on nanotube arrays (TNWs/TNAs), Au nanoparticle (NP)-decorated-TNAs, and TNWs/TNAs, which were applied for assessing the photocatalytic degradation of eight antibiotics, simultaneously. The TNAs and TNWs/TNAs were synthesized by anodization using an aqueous NH₄F/ethylene glycol solution. Au NPs were synthesized by chemical reduction method, and used to decorate on TNAs and TNWs/TNAs. All the TiO₂ nanostructures exhibited anatase phase and well-defined morphology. The photocatalytic performance of TNAs, TNWs/TNAs, Au-TNAs and Au-TNWs/TNAs was studied by monitoring the degradation of amoxicillin, ampicillin, doxycycline, oxytetracycline, lincomycin, vancomycin, sulfamethazine, and sulfamethoxazole under ultraviolet (UV)-visible (VIS), or VIS illumination by LC-MS/MS method. All the four kinds of nanomaterials degraded the antibiotics effectively and rapidly, in which most antibiotics were removed completely after 20 min treatment. The Au-TNWs/TNAs exhibited the highest photocatalytic activity in degradation of the eight antibiotics. For example, reaction rate constants of Au-TNWs/TNAs for degradation of lincomycin reached 0.26 min⁻¹ and 0.096 min⁻¹ under UV-VIS and VIS irradiation, respectively; and they were even higher for the other antibiotics. The excellent photocatalytic activity of Au-TNWs/TNAs was attributed to the synergistic effects of: (1) The larger surface area of TNWs/TNAs as compared to TNAs, and (2) surface plasmonic effect in Au NPs to enhance the visible light harvesting.

Morphology and Electronic Properties of TiO2 Nanotubes Arrays Synthesized by Electrochemical Method

Background:

A nano-tubular structure of Titanium dioxide (TiO2) was obtained using an electrochemical process based on the anodization of titanium foil in an organic electrolyte prepared with ethylene glycol (HOCH2CH2OH) containing Ammonium fluorides (NH4F) and ultrapure water under different anodization voltage. The morphological characteristics showed the formation of TiO2 nanotubes with different geometrical parameters. The electronic properties of the TiO2 NTs films were measured by the Mott-Schottky (MS) plots, indicating a positive slope for all graphs implying the n-type semiconductor nature of the TiO2 nanotubes (TiO2 NTs). The donor density (Nd) and the flat band potential (Efb) increases slightly with increase the anodization voltage.

Methods:

Prior the anodization, the titanium (Ti) foils were cut into square shape (2.25 cm2) with a selected work area of 0.6 cm2. The samples were subjected to a final polishing using a rotating felt pad (01 &µm) impregnated with alumina until a metallic mirror surface was obtained. The Ti foils were degreased by sonication in acetone, methanol and 2-Propanol for 10 minutes respectively, rinsed with ultrapure water and dried in a stream of compressed air. To form a TiO2 NTs, electrochemical anodization process was carried out at room temperature in Ethylene Glycol (EG) solution containing 0.3 wt% Ammonium fluorides (NH4F) and 2wt % ultrapure water for three (03) hours at different anodization voltage (20, 40 and 60V). A two-electrode cell was used for all the anodization measurements, with a platinum plate as the counter electrode, separated from the working electrode (titanium foil) by 1.5 cm. Immediately after anodization, the samples were soaked in ultrapure water to remove residual electrolyte for 10 minutes and then dried in an oven at 50 °C for 10 minutes.

Results:

TiO2 NTs grown from anodization of Ti foil in fluoride EG solution for 3h by varying the anodization voltage. The micrographic analysis shows a strong influence of the anodizing voltage on the morphology and geometrical parameters of the TiO2 NTs. Non homogenous NTs morphology was observed at 20 V with the presence of corrugations along the walls of the tubes. A perfect and regular nanotublar structure with smooth’s walls tubes was obtained at an anodization voltage of 60V. Moreover, the increase of anodization voltage leads to an increase in both the diameter and the length of tubes. In fact, the inner diameter and the length of the tubes (Di and L) values increase with increasing potential, being around (39 nm and 2 &µm) respectively at 20 V and (106 nm and 16,1 &µm) at 60 V. The measured electronic properties of TiO2 NTs indicating the n type semiconducting nature. It is remarkable that the donor density Nd increases toward higher values by increasing the anodizing voltage until 40V. However, for an anodization at 60V, the Nd has a small decrease value (7, 03 * 1019 cm-3) indicating a diminution of defects present in the material. Also, by increasing the anodizing voltage, Efb takes increasingly more positive values. In fact, the Efb values are – 0.12, 0.05 and 0.15 V for films prepared at 20, 40 and 60 V respectively. Therefore, this behavior can be attributed to a displacement of the Fermi level toward the conduction band edge which leads to a larger band bending at the interface.

Conclusion:

By varying the anodization voltage, titanium dioxide nanotubes (TiO2 NTs) were grown using electrochemical anodization of titanium foil in fluoride ethylene glycol solution for 3 hours. The morphology of the TiO2 NTs obtained was considerably affected; the anodizing potential determines the migration of ions in electrolyte during anodization process and simultaneously the tube diameter. An average small a nanotube diameter around 39 nm was obtained for 20V corresponding to 106 nm average diameter for TiO2 NTs structure synthesized at 60V. Furthermore, the semiconductor properties of the TiO2 NTs films have also been modified with increased values while increasing the anodization voltage. This behavior was attributed that the TiO2 NTs structure is more disordered, having much more defects provide abundant local donor energy levels which increases conductivity and decrease the probability of recombination of electrons and holes in these films, that can be integrated as active layer in the solar cells, in particular the Gratzel cells.

Enhanced Photocatalytic Performance of Nitrogen-Doped TiO₂ Nanotube Arrays Using a Simple Annealing Process

Nitrogen-doped TiO₂ nanotube arrays (N-TNAs) were successfully fabricated by a simple thermal annealing process in ambient N₂ gas at 450 °C for 3 h. TNAs with modified morphologies were prepared by a two-step anodization using an aqueous NH₄F/ethylene glycol solution. The N-doping concentration (0–9.47 at %) can be varied by controlling N₂ gas flow rates between 0 and 500 cc/min during the annealing process. Photocatalytic performance of as-prepared TNAs and N-TNAs was studied by monitoring the methylene blue degradation under visible light (λ ≥ 400 nm) illumination at 120 mW·cm⁻². N-TNAs exhibited appreciably enhanced photocatalytic activity as compared to TNAs. The reaction rate constant for N-TNAs (9.47 at % N) reached 0.26 h⁻¹, which was a 125% improvement over that of TNAs (0.115 h⁻¹). The significant enhanced photocatalytic activity of N-TNAs over TNAs is attributed to the synergistic effects of (1) a reduced band gap associated with the introduction of N-doping states to serve as carrier reservoir, and (2) a reduced electron‒hole recombination rate.

Polydopamine Surface Chemistry: A Decade of Discovery

Polydopamine is one of the simplest and most versatile approaches to functionalizing material surfaces, having been inspired by the adhesive nature of catechols and amines in mussel adhesive proteins. Since its first report in 2007, a decade of studies on polydopamine molecular structure, deposition conditions, and physicochemical properties have ensued. During this time, potential uses of polydopamine coatings have expanded in many unforeseen directions, seemingly only limited by the creativity of researchers seeking simple solutions to manipulating surface chemistry. In this review, we describe the current state of the art in polydopamine coating methods, describe efforts underway to uncover and tailor the complex structure and chemical properties of polydopamine, and identify emerging trends and needs in polydopamine research, including the use of dopamine analogs, nitrogen-free polyphenolic precursors, and improvement of coating mechanical properties.

TiO2 nanotubes/Ti plates modified by silver–benzene with enhanced photocatalytic antibacterial properties

A novel Ag/Benzene-Mod/TiO₂ nanotubes/Ti plate was fabricated via photo-modification by benzene, followed by electrodeposition of Ag on the TiO₂ nanotubes/Ti plate.

Synthesis of Reduced Grapheme Oxide as A Platform for loading β-NaYF4:Ho3+@TiO2Based on An Advanced Visible Light-Driven Photocatalyst

In this paper a novel visible light-driven ternary compound photocatalyst (β-NaYF₄:Ho³⁺@TiO₂-rGO) was synthesized using a three-step approach. This photocatalyst was characterized using X-ray diffraction, Raman scattering spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, Transmission electron microscopy, X-ray photoelectron spectroscopy, fluorescence spectrometries, ultraviolet-visible diffuse reflectance spectroscopy, Brunauer–Emmett–Teller surface area measurement, electron spin resonance, three-dimensional fluorescence spectroscopy, and photoelectrochemical properties. Such proposed photocatalyst can absorb 450 nm visible light while emit 290 nm ultraviolet light, so as to realize the visible light-driven photocatalysis of TiO₂. In addition, as this tenary compound photocatalyst enjoys effecitve capacity of charge separation, superior durability, and sound adsorb ability of RhB, it can lead to the red shift of wavelength of absorbed light. This novel tenary photocatalyst can reach decomposition rate of RhB as high as 92% after 10 h of irradiation by visible-light Xe lamp. Compared with the blank experiment, the efficiency was significantly improved. Recycle experiments showed that theβ-NaYF₄:Ho³⁺@TiO₂-rGOcomposites still presented significant photocatalytic activity after four successive cycles. Finally, we investigated visible-light-responsive photocatalytic mechanism of the β-NaYF₄:Ho³⁺@TiO₂-rGO composites. It is of great significance to design an effective solar light-driven photocatalysis in promoting environmental protection.

Enhanced Performance of Nanoporous Titanium Dioxide Solar Cells Using Cadmium Sulfide and Poly(3-hexylthiophene) Co-Sensitizers

This work reports the effect of co-sensitization of nanoporous titanium dioxide using Cadmium Sulfide (CdS) and poly(3-hexylthiophene) (P3HT) on the performance of hybrid solar cells. CdS nanolayer with different thicknesses was grown on Titanium Dioxide (TiO₂) nanoparticles by chemical bath deposition technique with varying deposition times. Both atomic force microscopy (AFM) and UV–Vis–NIR spectroscopy measurements of TiO₂ electrode sensitized with and without CdS layer confirm that the existence of CdS layer on TiO₂ nanoparticles. AFM images of CdS-coated TiO₂ nanoparticles show that the surface roughness of the TiO₂ nanoparticle samples decreases with increasing CdS deposition times. Current density–voltage and external quantum efficiency (EQE) measurements were carried out for corresponding solar cells. Both short circuit current density (J_SC) and fill factor were optimized at the CdS deposition time of 12 min. On the other hand, a steady and continuous increment in the open circuit voltage (V_OC) was observed with increasing CdS deposition time and increased up to 0.81 V when the deposition time was 24 min. This may be attributed to the increased gradual separation of P3HT and TiO₂ phases and their isolation at the interfaces. The higher V_OC of 0.81 V was due to the higher built-in voltage at the CdS–P3HT interface when compared to that at the TiO₂–P3HT interface. Optimized nanoporous TiO₂ solar cells with CdS and P3HT co-sensitizers showed external quantum efficiency (EQE) of over 40% and 80% at the wavelengths corresponding to strong absorption of the polymer and CdS, respectively. The cells showed an overall average efficiency of over 2.4% under the illumination of 70 mW/cm² at AM 1.5 condition.

A novel hexanuclear titanium(iv)-oxo-iminodiacetate cluster with a Ti6O9 core: single-crystal structure and photocatalytic activities

A new family of hexanuclear titanium(iv)-oxo-carboxylate cluster K7H[Ti6O9(ida)6]Cl2·13H2O {Ti6O9} has been synthesized via the H2O2-assisted reaction between TiCl4 and iminodiacetate ligands. This cluster was fully characterized by single-crystal X-ray diffraction and a wide range of analytical methods, including FT-IR, UV/vis spectroscopy as well as electrochemistry and thermogravimetric analysis. As a new type of carboxylate substituted Ti-oxo-cluster, the structural motif of the {Ti6O9} cluster consists of one symmetric {Ti6O6} hexagonal prism with two staggered triangular {Ti3O3} subunits linked by three μ2-O bridges. The {Ti6O9} polyanions are linked by K(+) cations to form a novel 3D architecture. The structural information and stability of the {Ti6O9} polyanion in aqueous solution were thoroughly investigated by solid-state/solution NMR, ESI-MS spectroscopy. Moreover, this Ti-oxo cluster exhibits remarkable potential as a visible-light homogeneous photocatalyst for degradation of rhodamine B (RhB). Finally, a proposed peroxotitanium(iv)-mediated photocatalytic pathway involved is illustrated by spectroscopic data.

Titanium dioxide nanotube membranes for solar energy conversion: effect of deep and shallow dopants

Here we show the effect of shallow and deep dopants on titanium dioxide (TiO₂) nanotube membranes, for applications in photocatalytic, photoelectrochemical, photovoltaic, and other photosensitized devices for converting light into chemical feedstocks or electricity.

Carbon-doped freestanding TiO2 nanotube arrays in dye-sensitized solar cells

DSSCs with TiO₂ nanotube arrays that were doped with carbon to improve their electron transport for energy conversion efficiency.

Preparation of a novel nanocomposite NaLuF4:Gd,Yb,Tm@SiO2@Ag@TiO2 with high photocatalytic activity driven by simulated solar light

A novel nanocomposite photocatalyst NaLuF₄:Gd,Yb,Tm@SiO₂@Ag@TiO₂ was developed for the first time.

The formation and study of poly(ethylene oxide)-poly(norbornene) block-copolymers on the surface of titanium-dioxide particles: a novel approach towards application of si-ROMP to larger surface modification

This work highlights the potential of si-ROMP through use of easier to functionalize titania particles that form hybrid titania-copolymers applied to larger scale coatings.

Fabrication of carbon and sulphur-doped nanocomposites with seaweed polymer carrageenan as an efficient catalyst for rapid degradation of dye pollutants using a solar concentrator

Here we demonstrate direct use of sulphate rich seaweed polysaccharides, carrageenans, namely kappa (κ-), iota (ι-) and lambda (λ-) as a source of sulphur and carbon doping in TiO₂ photocatalysts.

A graphene oxide incorporated TiO2 photoanode for high efficiency quasi solid state dye sensitized solar cells based on a poly-vinyl alcohol gel electrolyte

An effective self assembly method was used to synthesize hybrid nanocomposites of TiO₂ nanoparticles on graphene oxide (GO) sheets for application in Dye Sensitized Solar Cells (DSSCs).

Influence of Exciton Localization on the Emission and Ultraviolet Photoresponse of ZnO/ZnS Core-Shell Nanowires

The structural and optical properties of ZnO and ZnO/ZnS core-shell nanowires grown by a wet chemical method are investigated. The near-bandgap ultraviolet (UV) emission of the ZnO nanowires was enhanced by four times after coating with ZnS. The enhanced emission was attributed to surface passivation of the ZnO nanowires and localized states introduced during ZnS growth. The emission of the ZnO and ZnO/ZnS core-shell nanowires was attributed to neutral donor-bound excitons and localized excitons, respectively. Localized states prevented excitons from diffusing to nonradiative recombination centers, so therefore contributed to the enhanced emission. Emission from the localized exciton was not sensitive to temperature, so emission from the ZnO/ZnS core-shell nanowires was more stable at higher temperature. UV photodetectors based on the ZnO and ZnO/ZnS core-shell nanowires were fabricated. Under UV excitation, the device based on the ZnO/ZnS core-shell nanowires exhibited a photocurrent approximately 40 times higher than that of the device based on the ZnO nanowires. The differing photoresponse of the detectors was consistent with the existence of surface passivation and localized states. This study provides a means for modifying the optical properties of ZnO materials, and demonstrates the potential of ZnO/ZnS core-shell nanowires in UV excitonic emission and detection.

Facile synthesis of composition-tuned ZnO/Zn x Cd1-x Se nanowires for photovoltaic applications

ZnO/Zn x Cd1-x Se coaxial nanowires (NWs) have been successfully synthesized by combining chemical vapor deposition with a facile alternant physical deposition method. The shell composition x can be precisely tuned in the whole region (0 ≤ x ≤ 1) by adjusting growth time ratio of ZnSe to CdSe. As a result, the effective bandgaps of coaxial nanowires were conveniently modified from 1.85 eV to 2.58 eV, almost covering the entire visible spectrum. It was also found that annealing treatment was in favor of forming the mixed crystal and improving crystal quality. An optimal temperature of 350°C was obtained according to our experimental results. Additionally, time resolved photo-luminescence spectra revealed the longest carrier lifetime in ZnO/CdSe coaxial nanowires. As a result, the ZnO/CdSe nanowire cell acquired the maximal conversion efficiency of 2.01%. This work shall pave a way towards facile synthesis of ternary alloys for photovoltaic applications.

CNT–G–TiO2 layer as a bridge linking TiO2 nanotube arrays and substrates for efficient dye-sensitized solar cells

This study incorporated a 3-D hybrid material comprising graphene and carbon nanotubes (CNTs) into a TiO₂ composite paste to adhere TiO₂ nanotube arrays (NTAs) as photoanodes.

Are TiO2 nanotubes worth using in photocatalytic purification of air and water?

Titanium dioxide nanotubes (TNT) have mainly been used in dye sensitized solar cells, essentially because of a higher transport rate of electrons from the adsorbed photo-excited dye to the Ti electrode onto which TNT instead of TiO₂ nanoparticles (TNP) are attached. The dimension ranges and the two main synthesis methods of TNT are briefly indicated here. Not surprisingly, the particular and regular texture of TNT was also expected to improve the photocatalytic efficacy for pollutant removal in air and water with respect to TNP. In this short review, the validity of this expectation is checked using the regrettably small number of literature comparisons between TNT and commercialized TNP referring to films of similar thickness and layers or slurries containing an equal TiO₂ mass. Although the irradiated geometrical area differed for each study, it was identical for each comparison considered here. For the removal of toluene (methylbenzene) or acetaldehyde (ethanal) in air, the average ratio of the efficacy of TNT over that of TiO₂ P25 was about 1.5, and for the removal of dyes in water, it was around 1. This lack of major improvement with TNT compared to TNP could partially be due to TNT texture disorders as seems to be suggested by the better average performance of anodic oxidation-prepared TNT. It could also come from the fact that the properties influencing the efficacy are more numerous, their interrelations more complex and their effects more important for pollutant removal than for dye sensitized solar cells and photoelectrocatalysis where the electron transport rate is the crucial parameter.

Photoactive rolled-up TiO2 microtubes: fabrication, characterization and applications†Electronic supplementary information (ESI) available. See DOI: 10.1039/c4tc00796dClick here for additional data file

Because of its unique properties, titania (TiO2) represents a promising candidate in a wide variety of research fields. In this paper, some of the properties and potential applications of titania within rolled-up nanotechnology are explored. It is shown how the structural and optical properties of rolled titania microtubes can be controlled by properly tuning the microfabrication parameters. The rolling up of titania films on different sacrificial layers and containing different shapes, achieving a control on the diameter of the fabricated titania microtubes, is presented. In order to obtain the more photoactive crystalline form of titania, one during-fabrication and two post-fabrication methods are demonstrated. Interesting applications in the fields of photocatalysis and photonics are suggested: the use of titania rolled-up microtubes as micromotors and optical microresonators is presented.

Mg-doped TiO2 nanorods improving open-circuit voltages of ammonium lead halide perovskite solar cells

Mg-doped TiO₂ nanorods were synthesized from colloidal titanate by a microwave hydrothermal reaction. Use of such TiO₂ having an elevated conduction band edge as an electron extracting material for ammonium lead halide perovskite solar cells resulted in a marked improvement of V_oc.

Hierarchically porous N–F codoped TiO2 hollow spheres prepared via an in situ bubbling method for dye-sensitized solar cells

Hierarchically porous N–F codoped TiO₂ hollow spheres were prepared via an in situ bubbling method for solar energy conversion application.

Double-layer electrode based on TiO2 nanotubes arrays for enhancing photovoltaic properties in dye-sensitized solar cells

The present work reports a rapid and facile method to fabricate a novel double-layer TiO2 photoanode, which is based on highly ordered TiO2 nanotube arrays and monodispersive scattering microspheres. This double-layer TiO2 sphere/TNTA photoanode have got many unique structural and optical properties from TiO2 scattering microspheres, such as high specific surface area, multiple interparticle scattering, and efficient light-harvesting. Results indicate that this as-fabricated double-layer TiO2 sphere/TNTA front-illumination dye-sensitized solar cell, which is fabricated from the TiO2 nanotube arrays with a 17.4 μm length after TiCl4 treatment, exhibits a pronounced power conversion efficiency of 7.24% under an AM1.5 G irradiation, which can be attributed to the increased incident photon-to-current conversion and light-harvesting efficiency.

A simple template-free 'sputtering deposition and selective etching' process for nanoporous thin films and its application to dye-sensitized solar cells

A facile and straightforward method is suggested to synthesize nanoporous-TiO₂ thin films for dye-sensitized solar cells (DSSCs). Silver/TiO₂ co-sputtering led to the formation of nanocomposite films which consisted of silver nanoclusters with surrounding TiO₂ matrices, and metal particles were subsequently etched by just immersing in nitric acid. Nanoporous-TiO₂ DSSCs fabricated by this simple and effective process showed power-conversion efficiencies of up to 3.4% at a thickness of only 1.8 μm, which is much superior to that of conventional nanoparticulate-TiO₂ DSSCs with similar thickness.

Synergistic modification of electronic and photocatalytic properties of TiO2 nanotubes by implantation of Au and N atoms

The structural and electronic properties of N-doped, Au-adsorbed, and Au/N co-implanted TiO2 nanotubes (NTs) were investigated by performing first-principle density functional theory (DFT) calculations. For all the possible implanted configurations, the radius and bond length do not change significantly relative to the clean NTs. Our results indicate that the introduction of N into NTs is in favor of implantation of Au, and Au pre-adsorption on the NTs can also enhance the N concentration in NTs. The synergistic stability can be mainly attributed to charge transfer between Au and N atoms. In co-implanted configurations, the empty N 2p states in the band gap are occupied by one electron; denoted by Au 5s states. Thus, the associated electron transition among the valence band, the conduction band and the gap states results in redshift of the light absorption. In addition, the disappearance of N 2p empty states can effectively decrease the photogenerated carrier combination. Therefore, the Au/N implanted NTs should be regarded as a promising photocatalytic material under the visible light region.

Novel preparation of anatase TiO2@reduced graphene oxide hybrids for high-performance dye-sensitized solar cells

An effective method was developed to prepare hybrid materials of TiO2 nanoparticles on reduced graphene oxide (RGO) sheets for application in solar cells. The morphology, size, and crystal phase of the TiO2 nanoparticles and TiO2@reduced graphene oxide (TiO2@RGO) hybrids were investigated in detail by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), X-ray photoelectron spectroscopy (XPS), Raman, and UV-vis diffuse reflectance spectroscopy. A possible growth mechanism of TiO2@RGO hybrids is proposed based on observations of the TiO2 nanoparticles obtained from the hydrolysis process under different conditions. The effects of different reduced graphene oxide contents on the energy conversion efficiency of the dye-sensitized solar cells (DSSCs) based on J-V and incident photon-to-current conversion efficiency (IPCE) spectra are also discussed. DSSCs based on TiO2@RGO hybrid photoanodes with a graphene content of 1.6 wt % showed an overall light-to-electricity conversion efficiency of 7.68%, which is much higher than that of pure anatase nanoparticles (4.78%) accompanied by a short-circuit current density of 18.39 mA cm(2), an open-circuit voltage of 0.682 V, and a fill factor of 61.2%.