Photoelectrochemical properties of iron (III)-doped TiO2 nanorods

Fe (iron)-doped TiO₂ nanorods were grown on fluorine doped tin oxide (FTO) substrates with various Fe doping concentrations using modified chemical bath deposition (M-CBD). We investigated the effects of Fe doping concentration on the morphological, structural, optical, and photoelectrochemical (PEC) properties of the TiO₂ nanorods. From this study, it was found that the PEC properties were mainly dependent on the morphological and optical properties of the Fe-doped TiO₂ nanorods. At low Fe doping concentration, the PEC properties were highly affected by the optical properties. On the other hand, the PEC properties were significantly affected by the morphological properties at high doping concentration. We observed a maximum photocurrent density of 0.48 mA/cm² at a Fe doping concentration of 2 at% from this study. In addition, the donor density and flat-band potential of the Fe doping concentration from the Mott–Schottky plot were analyzed.     

Enhanced photocatalytic performance through the ferroelectric synergistic effect of p-n heterojunction BiFeO3/TiO2 under visible-light irradiation

A BiFeO₃/TiO₂ p-n heterojunction photocatalyst with ferroelectric synergistic effect under visible-light irradiation was developed through facile hydrolysis and precipitation by forming nanospheres of TiO₂ on BiFeO₃ nanocube to improve the photocatalytic efficiency. Analyses of the microstructure, optical properties, and photoelectrochemical performance indicate the formation of a core–shell heterostructure of BiFeO₃/TiO₂ with excellent energy band matching. The BiFeO₃/TiO₂ p-n heterojunction has enlarged specific surface area, higher sensitivity to visible-light, and improved separation and transfer efficiency of photoelectron-hole pairs than single TiO₂ and BiFeO₃. Moreover, the composite exhibits superior photocatalytic degradation performance for methylene blue (MB) and common antibiotic tetracycline (TC) under UV and visible-light irradiation. The MB degradation rate within 180 min reaches 78.4% and 90.4% under UV and visible-light irradiation, respectively. Furthermore, the enhanced photocatalytic mechanism of BiFeO₃/TiO₂ is explored by photoluminescence (PL), electrochemical impedance spectroscopy (EIS), transient photocurrent analysis, radical quenching, and band structure characterization.     

Molten salt synthesis of BaTiO3 nanorods: Dielectric,optical properties,and structural characterizations

Single-crystalline perovskite BaTiO₃ (BTO) nanorods were synthesized by (BaTi₂O₅-template) molten salt synthesis (MSS) methods. The effects of process parameters (eg, calcination temperature, reaction time, molten salt content, as well as different phase structures of TiO₂ and barium oxides) on the formation of BTO nanorods and their structural characteristics were systematically investigated. The BTO nanorods synthesized at 800°C for 5 hours by MSS method with the molar salt ratios of BaCO₃:TiO₂ (anatase):NaCl:KCl equal to 1:1:60:60, exhibited smooth and clean surfaces through their lengths. Their diameters were in the range of 130-200 nm with average length of 5 μm. Large-scale amount of BTO nanorods was synthesized by BaTi₂O₅-template MSS method at 650°C with molar salt ratios of BaC₂O₄:BaTi₂O₅ (template):NaCl:KCl equal to 1:1:60:60. The BTO nanorods successfully retained the one-dimensional morphology of the BaTi₂O₅ templates and their lengths were in the range of 5-10 μm with an average diameter of ~300 nm. The single-crystalline nature of individual BTO nanorod was revealed by its selected area electron diffraction patterns and high-resolution TEM images. The BTO nanorods exhibited good optical properties with optical bandgaps in the range of 2.5-2.6 eV. Such optical bandgaps make the present BTO nanorods promising candidates for ferroelectric photovoltaic devices. Dielectric properties of the BTO nanorods synthesized by MSS method were comparatively investigated with the BTO nanorods synthesized by the BaTi₂O₅-template MSS method. It is found that the later BTO nanorods exhibit better dielectric properties and their synthesized temperature is also much lower than the former ones.     

UV-curable polyurethane acrylate–Ag/TiO2 nanocomposites with superior UV light antibacterial activity

Polyurethane acrylate (PUA)–Ag/TiO₂ nanocomposites were synthesized through in situ polymerization. The well-dispersed Ag/TiO₂ nanorods serve as photoinitiator. Meanwhile, the PUA–Ag/TiO₂ nanocomposite films exhibit superior activity toward the photocatalytic degradation of Escherichia coli under UV light. The excellent UV curing and antibacterial activities can be ascribed to the synergistic effect of Ag and TiO₂, which promotes the effective electron/hole separation and thus generates various reactive species. Thin films with these nanoparticles are more hydrophilic after UV illumination. And the antibacterial mechanism of the UV-curable PUA–Ag/TiO₂ nanocomposites was proposed.     

Morphology studies of doped polyaniline micro/nanocomposites containing TiO2 nanoparticles and Fe3O4 microparticles

To produce polyaniline (PAni) nanodevices that display excellent microwave absorbing behaviors, novel hexanoic acid-doped PAni micro/nanocomposites containing TiO₂ nanoparticles and Fe₃O₄ microparticles (PAni/HA/TiO₂/Fe₃O₄) were prepared by template-free method, particularly to improve the dielectric and magnetic property of PAni. PAni/HA/TiO₂/Fe₃O₄ synthesized at different polymerization temperatures and polymerization time by various TiO₂ and Fe₃O₄ contents, and particles size of TiO₂ were prepared. The aim of this research is to investigate the effect of synthesis condition on the morphology behaviors of nanorods/tubes. The resulted nanorods/tubes indicated that PAni micro/nanocomposites exhibited polymerization through elongation. PAni micro/nanocomposites synthesized at 0°C resulted in large amounts of nanorods/tubes compared with those synthesized at subzero temperature and above 0°C. PAni/HA/TiO₂ and PAni/HA/TiO₂/Fe₃O₄ synthesized using TiO₂ with diameter (particles size) 180 nm resulted in large amounts of nanorods/tubes (diameter nanorods/tubes = 80–140 nm) compared with those synthesized using TiO₂ with diameter of 30 and 6 nm. Increasing TiO₂ and Fe₃O₄ content above 10% will significantly reduce the amount of nanorods/tubes. In conclusion, synthesis parameters mentioned above are the significant factors that might affect the morphology behaviors of PAni nanostructures. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Nanocomposites of PVC/TiO2 nanorods: Surface tension and mechanical properties before and after UV exposure

In this study, nanocomposites of poly(vinyl chloride) (PVC), using the synthesized titanium dioxide (TiO₂) nanorods and commercial nanopowder of titanium dioxide (Degussa P25) were produced by melt blending. The presence of TiO₂ nanorods in PVC matrix led to an improvement in mechanical properties of PVC nanocomposites in comparison with unfilled PVC. The photocatalytic degradation behavior of PVC nanocomposites were investigated by measuring their structural change evaluations, surface tension, and mechanical properties before and after UV exposure for 500 h. It was found that mechanical and physical properties of PVC nanocomposites are not reduced significantly after UV exposure in the presence of TiO₂ nanorods in comparison with the presence of TiO₂ nanoparticles, which can be due to the amorphous structure of the synthesized nanorods. Therefore, it can be concluded that TiO₂ nanorods led to an improvement in photostability and mechanical properties of PVC nanocomposites. The interfacial adhesion between TiO₂ nanorods and PVC matrix was also investigated. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Polar bear hair inspired ternary composite ceramic aerogel with excellent interfacial bonding and efficient infrared transmittance for thermal insulation

Highly porous, heat resisting ceramic aerogels are considered as promising materials for high-temperature insulation. However, the general structural characteristics of ceramic aerogel, such as poor mechanical strength and transparency to infrared radiation, pose a major obstacle to their practical application. In this paper, we report a general strategy to prepare hollow mullite fiber (HMF) structures by coaxial electrostatic spinning and grow TiO₂ nanorods (TiO₂/NAs) in situ on HMF. The ternary composite ceramic aerogel material was prepared by filling the pores of HMF-TiO₂/NAs with SiCN aerogel. The TiO₂/NAs increased the fiber/aerogel interfacial bonding of the composite (0.392 MPa, 30% strain) and improved the IR transmittance (∼0%, 1200 ℃) without sacrificing their low density and thermal conductivity. In addition, low thermal conductivity (0.041 W/(m·K), 1200 °C) and excellent high-temperature insulation properties allow the composite aerogel to meet the urgent need for lightweight, high-strength, high-temperature insulation systems for spacecraft.     

Morphological exploration of chemical vapor–deposited P-doped ZnO nanorods for efficient photoelectrochemical water splitting

Photoelectrochemical (PEC) water splitting is beneficial and has received attractive attention due to a greater potential to generate hydrogen and oxygen from water by using plentiful solar light to solve the problem of energy crisis. Various active semiconductor materials are used in PEC water splitting applications. Nevertheless, in past decades, most of the researchers suggested that titanium oxide (TiO₂) is the best photoanode for this type of applications. Now, Zinc oxide (ZnO) is considered a perfect substitution to TiO₂ due to its comparable energy band structure and superior photogenerated electron transfer rate. In this study, bare and phosphorous-doped ZnO nanorods were successfully developed on fluorine-doped tin oxide-coated glass (FTO) substrate by chemical vapor deposition. X-ray diffraction (XRD) pattern authenticated hexagonal structure formation with strong diffraction peak of (101), which showed that ZnO nanorods were perfectly developed along c axis. The optical and morphological properties were analyzed by UV–Vis and scanning electron microscopy images. The energy-dispersive X-ray spectra demonstrated that doping agent phosphorous was present in ZnO nanorods. The PEC properties of the developed ZnO nanorods were further investigated and obtained results suggested that a small amount of phosphorous-doped ZnO nanorods enhances their PEC performance.     

Photostabilization of polypropylene by surface modified rutile‐type TiO2 nanorods

Rutile‐type titanium dioxide (TiO₂) nanorods were prepared, superficially modified and tested for the protection of polypropylene (PP) from the UVB and UVC irradiations. The silica coating blocked the active sites on the nanorods and the following calcination further reduced the amount of surface hydroxyl groups and thus, made the TiO₂ nanorods more efficient against the photodegradation. Compared with spherical TiO₂ nanoparticles, the calcined silica‐coated TiO₂ nanorods demonstrated good photostabilization efficiency due to the excellent shielding effect and the improved dispersion of the nanoparticles in PP matrix. When used in combination with the conventional hindered amine light stabilizer (HALS), CHIMASSORB^® 944, the surface modified TiO₂ nanorods revealed strong synergistic effect during the photo‐oxidation of the PP composites. The capacity of photostabilization was much higher than the combination with the commercial spherical TiO₂ nanoparticles and even higher than the typical HALS photostabilization system containing hindered phenol TINUVIN^® 328. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40601.     

Effect of annealing on UV-visible absorption and photoluminescence behavior of liquid phase deposited TiO2 nanorods

In this work, anatase and rutile TiO₂ nanorods were fabricated using one-step liquid phase deposition process, followed by heat treatment in the range 300-800°C. The direct and indirect band gap of the TiO₂ nanorods was estimated form optical absorption data which illustrated a red shift at higher temperatures owing to the different nature of excitons in anatase and rutile phases. The photoluminescence (PL) spectra revealed the presence of two main emission bands consisting of four peaks. It was found that two high-energy peaks located at 2.95-3.30 eV could be generated from exciton transitions from the conduction band to the valence band of TiO₂ nanorods, while two low-energy peaks located at 2.43-2.64 eV may arise from surface state transitions. The PL intensity firstly increased with temperature and at 500°C reached a maximum value, then decreased through increasing temperature up to 800°C. These variations in the intensity of PL emission could be explained in terms of changes in phase structure, crystallinity, and amount of the oxygen vacancies, which are all dependent to the annealing temperature based on X-ray diffractometer and X-ray photoelectron spectrometer studies. These results indicated that annealing temperature allows to manipulate the properties of TiO₂ nanorods for opto-electronic applications.     

Silver-modified TiO2 nanorods with enhanced photocatalytic activity in visible light region

Silver-modified TiO₂ nanorods (SMTN) have been synthesized via controlled hydrolysis of tetrabutyltitanate (TBOT) in ethanol and immersion method by using AgNO₃ as an Ag source. The physical and chemical properties of SMTN were studied by XRD, SEM, TEM, and UV–vis diffuse reflectance spectra (DRS). The photocatalytic activity of the as-prepared products was evaluated by photocatalytic decolorization of Rhodamine B (Rh B) aqueous solution at ambient temperature under visible light irradiation. The experimental results reveal that the TiO₂ nanorods, which are well dispersed and uniform, attached large numbers of silver nanoparticles on the surface, and the major crystalline phase of TiO₂ is anatase. The photocatalytic activity research shows that the SMTN exhibit an enhanced photocatalytic activity in visible light region compared with that of pure TiO₂ nanorods and commercial TiO₂ (P25).     

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.     

Structural Modification of TiO2 Nanorod Films with an Influence on the Photovoltaic Efficiency of a Dye-Sensitized Solar Cell (DSSC)

TiO₂ nanorod films have been deposited on ITO substrates by dc reactive magnetron sputtering technique. The structures of these nanorod films were modified by the variation of the oxygen pressure during the sputtering process. Although all these TiO₂ nanorod films deposited at different oxygen pressures show an anatase structure, the orientation of the nanorod films varies with the oxygen pressure. Only a very weak (101) diffraction peak can be observed for the TiO₂ nanorod film prepared at low oxygen pressure. However, as the oxygen pressure is increased, the (220) diffraction peak appears and the intensity of this diffraction peak is increased with the oxygen pressure. The results of the SEM show that these TiO₂ nanorods are perpendicular to the ITO substrate. At low oxygen pressure, these sputtered TiO₂ nanorods stick together and have a dense structure. As the oxygen pressure is increased, these sputtered TiO₂ nanorods get separated gradually and have a porous structure. The optical transmittance of these TiO₂ nanorod films has been measured and then fitted by OJL model. The porosities of the TiO₂ nanorod films have been calculated. The TiO₂ nanorod film prepared at high oxygen pressure shows a high porosity. The dye-sensitized solar cells (DSSCs) have been assembled using these TiO₂ nanorod films prepared at different oxygen pressures as photoelectrode. The optimum performance was achieved for the DSSC using the TiO₂ nanorod film with the highest (220) diffraction peak and the highest porosity.     

Crystalline phase of TiO2 nanotube arrays on Ti–35Nb–4Zr alloy: Surface roughness,electrochemical behavior and cellular response

An investigation was made into the electrochemical, structural and biological properties of self-organized amorphous and anatase/rutile titanium dioxide (TiO₂) nanotubes deposited on Ti–35Nb–4Zr alloy through anodization-induced surface modification. The surface of as-anodized and heat-treated TiO₂ nanotubes was analyzed by field emission scanning electron microscopy (FE-SEM), revealing morphological parameters such as tube diameter, wall thickness and cross-sectional length. Glancing angle X-ray diffraction (GAXRD) was employed to identify the structural phases of titanium dioxide, while atomic force microscopy (AFM) was used to measure surface roughness associated with cell interaction properties. The electrochemical stability of TiO₂ was examined by electrochemical impedance spectroscopy (EIS) and the results obtained were correlated with the microstructural characterization. The in vitro bioactivity of as-anodized and crystallized TiO₂ nanotubes was also analyzed as a function of the presence of different TiO₂ polymorphic phases. The results indicated that anatase TiO₂ showed higher surface corrosion resistance and greater cell viability than amorphous TiO₂, confirming that TiO₂ nanotube crystallization plays an important role in the material's electrochemical behavior and biocompatibility.     

P(VDF-HFP)-based micro-porous composite polymer electrolyte prepared by in situ hydrolysis of titanium tetrabutoxide

A micro-porous composite polymer electrolyte (MCPE) was prepared in situ by adding TiO₂ nanoparticles from the hydrolysis of titanium tetrabutoxide to a solution of poly(vinylidenefluoride-co-hexafluoropropylene) [P(VDF-HFP)] copolymer. The prepared microporous polymer films (MCPFs) were characterized by scanning electronic microscopy, X-ray diffraction, thermogravimetric analysis, FT-IR and electrochemical interface resistance. After the addition of TiO₂ nanoparticles the polarity of CF₂ groups in the polymer chains and the crystallinity of the MCPFs decreased. When the composite polymer film contained 8.5 wt% of TiO₂ nanoparticles the MCPE exhibited excellent electrochemical properties such as high ionic conductivity, up to 2.40 × 10⁻³ S cm⁻¹ at room temperature.     

The enhanced performance of Cr(VI) photoreduction and antibiotic removal on 2D/3D TiO2/ZnIn2S4 nanostructures

In this study, 2D/3D TiO₂/ZnIn₂S₄ nanostructures with TiO₂ sheet cluster embedded into ZnIn₂S₄ micro flowers were fabricated via hydrothermal method. The matched band structure, the enlarged surface area and the efficient photo-induced charge transfer offered by effective heterostructures formed between the two components endowed the TiO₂/ZnIn₂S₄ nanoarchitecture with excellent photocatalytic Cr(VI) reduction and tetracycline hydrochloride (TC) degradation performance. Especially, the Cr(VI) photoreduction efficiency of 50% TiO₂/ZnIn₂S₄ was 8.8 times higher compared to pure ZnIn₂S₄. The enhanced separation efficiency of photo-excited charge carriers was induced by the matched band structure, the enlarged surface area and the strong interaction between TiO₂ and ZnIn₂S₄. The key roles of ·O₂^? was confirmed via trapping experiments. Otherwise, the pathway of TC degradation was investigated. The proposed mechanism during photocatalysis process was also discussed according to the photocatalytic and characterization results.     

Controlled fabrication of Sn/TiO2 nanorods for photoelectrochemical water splitting

In this work, we investigate the controlled fabrication of Sn-doped TiO₂ nanorods (Sn/TiO₂ NRs) for photoelectrochemical water splitting. Sn is incorporated into the rutile TiO₂ nanorods with Sn/Ti molar ratios ranging from 0% to 3% by a simple solvothermal synthesis method. The obtained Sn/TiO₂ NRs are single crystalline with a rutile structure. The concentration of Sn in the final nanorods can be well controlled by adjusting the molar ratio of the precursors. Photoelectrochemical experiments are conducted to explore the photocatalytic activity of Sn/TiO₂ NRs with different doping levels. Under the illumination of solar simulator with the light intensity of 100 mW/cm², our measurements reveal that the photocurrent increases with increasing doping level and reaches the maximum value of 1.01 mA/cm² at −0.4 V versus Ag/AgCl, which corresponds to up to about 50% enhancement compared with the pristine TiO₂ NRs. The Mott-Schottky plots indicate that incorporation of Sn into TiO₂ nanorod can significantly increase the charge carrier density, leading to enhanced conductivity of the nanorod. Furthermore, we demonstrate that Sn/TiO₂ NRs can be a promising candidate for photoanode in photoelectrochemical water splitting because of their excellent chemical stability.     

Structural Refinement and Photoluminescence Properties of MnWO4 Nanorods Obtained by Microwave-Hydrothermal Synthesis

Manganese tungstate (MnWO₄) nanorods were prepared at room temperature by the co-precipitation method and synthesized after processing in a microwave-hydrothermal (MH) system at 140 °C for 6–96 min. These nanorods were structurally characterized by X-ray diffraction (XRD), Rietveld refinements and Fourier transform (FT)-Raman spectroscopy. The growth direction, shape and average size distribution of nanorods were observed by means of transmission electron microscopy (TEM) and high resolution TEM (HR-TEM). The optical properties of the nanorods were investigated by ultraviolet visible (UV-vis) absorption and photoluminescence (PL) measurements. XRD patterns, Rietveld refinement data and FT-Raman spectroscopy indicate that the MnWO₄ precipitate is not a single phase structure while the nanorods synthesized by MH processing have a wolframite-type monoclinic structure without deleterious phases. FT-Raman spectra exhibited the presence of 17 Raman-active modes from 50 to 1,000 cm⁻¹. TEM and HR-TEM micrographs indicated that the nanorods are aggregated due to surface energy by Van der Waals forces and grow along the [100] direction. UV–vis absorption measurements confirmed non-linear values for the optical band gap (from 3.2 to 2.72 eV), which increased as the MH processing time increased. The structural characterizations indicated that the presence of defects in the MnWO₄ precipitate promotes a significant contribution to maximum PL emission, while MnWO₄ nanorods obtained by MH processing decrease the PL emission due to the reduction of defects in the lattice.     

Novel direct Z-scheme AgI/N–TiO2 photocatalyst for removal of polluted tetracycline under visible irradiation

In the study, we doped N into TiO₂ lattice to narrow its band gap energy. Then, the synthesized N doped TiO₂ material was combined with AgI to form AgI/N–TiO₂ (ANT) direct Z scheme materials. The synthesized materials were utilized for photocatalytic removal of tetracycline (TC) using visible irradiation as an excitation source. We also conducted radical scavenging experiments to determine photocatalytic degradation mechanism. We investigated that these photo-excited electrons (e⁻) in N–TiO₂ conduction band tended to combine with the left holes (h⁺) in AgI valence band maintaining h⁺ in the valence band of the N–TiO₂ and e⁻ in the conduction band of the AgI. The remained e⁻ and h⁺ have high redox potential to initiate for photocatalytic decomposition of TC. Thus, the TC degradation by the ANT materials were significant greater than those by single components (AgI or N–TiO₂). We also investigated that the TC degradation by the ANT-30 material, which the AgI: N–TiO₂ molar ratio was 30%, exhibited that highest degradation efficiency. Finally, the ANT photocatalyst exhibited excellent stability during TC degradation processes supporting for its promising potential application in practical systems.     

Physical and electrochemical characterization of nanostructured composites formed by TiO2 templates and PEDOT-PPS films

We report the physical and electrochemical characterization of nanostructured composites formed by TiO₂ templates and PEDOT-PPS films. TiO₂ templates were prepared by sol-gel techniques using TiCl₄ and TiF₄ as the titania precursors, and also by adding a soluble polymer at the initial stages of the TiCl₄ sol-gel synthesis to induce porous oxide networks. The effect of different precursors and annealing environments in the crystallite and particle size of the templates was followed by XRD and SEM studies, and correlated to the electrochemical properties of TiO₂ templates dip-coated in a conducting polymer solution (PEDOT-PSS 1.3%). We found that the microstructure had a strong influence in the adsorption of the conductive polymer, which shows superior electrochemical activity in matrices with abundant surface hydroxylation, broad particle size distribution and residual carbon. Cyclic voltammetry and electrochemical impedance data revealed the differences between the several TiO₂/PEDOT-PSS systems, with the best performance observed in systems based on TiO₂ templates obtained from the TiCl₄ sol-gel route and containing residual mesoporous carbon.