Ultrasound-induced membrane lipid peroxidation and cell damage of Escherichia coli in the presence of non-woven TiO2 fabrics

A non-woven titanium dioxide (TiO₂) fabric was applied to disinfection by ultrasound (US) irradiation, and the disinfection efficiency and lipid peroxidation of Escherichia coli (E. coli) cell membrane were evaluated to investigate the killing process. The addition of non-woven TiO₂ fabric enhanced hydroxyl (OH) radical generation and disinfection efficiency. Judging from the disinfection experiments using glutathione or t-butanol as a radical scavenger, the OH radical played a major role in cell killing in sonodynamic disinfection with non-woven TiO₂ fabric. Moreover, to understand the detailed killing process, damage to cell membrane was also evaluated using a diphenyl-1-pyrenylphosphine (DPPP) fluorescent probe, which detects the membrane’s lipid peroxidation. The addition of non-woven TiO₂ fabric aggravated this peroxidation. This aggravation was caused by the OH radical according to an assay using a radical scavenger. From these results, it was concluded that non-woven TiO₂ fabric as a sonocatalyst promoted peroxidation of the polyunsaturated phospholipid component of the lipid membrane initially and induced a major disorder in the E. coli cell membrane under US irradiation.     

Laser-sintered mesoporous TiO2 electrodes for dye-sensitized solar cells

Low-temperature laser sintering has been successfully demonstrated to improve the overall conversion efficiency of dye-sensitized solar cells. Mesoporous TiO₂ electrodes were prepared from a colloidal solution of TiO₂ nanopowders by a laser direct-write technique and then sintered by a quasi-continuous-wave UV laser (λ=355 nm) for the fabrication of dye-sensitized solar cells. The overall conversion efficiency of the cells based on the laser-sintered TiO₂ electrodes was double that of the devices with non-laser-treated TiO₂ electrodes. This enhancement is attributed to both the removal of organic additives and the improved inter-nanoparticle electrical contacts induced by the laser-sintering process, which led to an increase in porosity and dye-absorption sites in the TiO₂ electrodes. PACS 61.80.Ba; 61.46.+w; 73.22.-f; 84.60.Jt     

Sinoporphyrin sodium triggered sono-photodynamic effects on breast cancer both in vitro and in vivo

Sono-photodynamic therapy (SPDT) is a promising anti-cancer strategy. Briefly, SPDT combines ultrasound and light to activate sensitizers that produce mechanical, sonochemical and photochemical activities. Sinoporphyrin sodium (DVDMS) is a newly identified sensitizer that shows great potential in both sonodynamic therapy (SDT) and photodynamic therapy (PDT). In this study, we primarily evaluated the combined effects of SDT and PDT by using DVDMS on breast cancer both in vitro and in vivo. In vitro, DVDMS-SPDT elicits much serious cytotoxicity compared with either SDT or PDT alone by MTT and colony formation assays. 2′,7′-Dichlorodihydrofluo-rescein-diacetate (DCFH-DA) and dihydroethidium (DHE) staining revealed that intracellular reactive oxygen species (ROS) were significantly increased in groups given combined therapy. Terephthalic acid (TA) method and FD500-uptake assay reflected that cavitational effects and cell membrane permeability changes after ultrasound irradiation were also involved in the enhancement of combination therapy. In vivo, DVDMS-SPDT markedly inhibits the tumor volume and tumor weight growth. Hematoxylin-eosin staining and immunohistochemistry analysis show DVDMS-SPDT greatly suppressed tumor proliferation. Further, DVDMS-SPDT significantly inhibits tumor lung metastasis in the highly metastatic 4T1 mouse xenograft model, which is consistent well with the in vitro findings evaluated by transwell assay. Moreover, DVDMS-SPDT did not produces obvious effect on body weight and major organs in 4T1 xenograft model. The results suggest that by combination SDT and PDT, the sensitizer DVDMS would produce much better therapeutic effects, and DVDMS-SPDT may be a potential strategy against highly metastatic breast cancer.     

Simplified sonochemical preparation of titania embedded with selected metals for purification of benzene and toluene

Titania (TiO₂) photocatalysts, each embedded with one of six metals (Ag, Ce, Co, Fe, Mg, and Mn), were prepared using a simplified ultrasonic process. The characteristics of the prepared metal-embedded TiO₂ (metal–TiO₂) were determined using transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction spectroscopy, photoluminescence emission spectroscopy, UV–visible spectroscopy, and nitrogen adsorption–desorption. Except for Co–TiO₂, the metal–TiO₂ photocatalysts showed improved performance for the decomposition of gaseous benzene and toluene, which are two of the most problematic indoor air pollutants that can cause a variety of adverse health symptoms, under daylight lamp irradiation. Photocatalytic activity was greatest for the Mg–TiO₂ sample, followed by, in order, the Ag–TiO₂, Ce–TiO₂, Fe–TiO₂, Mn–TiO₂, unmodified TiO₂, and Co–TiO₂ samples. Although Mg–TiO₂ showed the least redshift in its light absorption and the highest electron–hole recombination rate among the metal–TiO₂ photocatalysts, it yielded the highest photocatalytic activity, likely because of its increased adsorption capacity and anatase composition. The degradation of benzene and toluene over Mg–TiO₂ improved as ultrasound treatment amplitude increased from 20 to 37 μm, then decreased gradually as amplitude was further increased to 49 μm. Degradation efficiency also improved as ultrasound operation time increased from 30 to 60 min, then decreased gradually as amplitude was further increased to 90 min. Overall, this process could be utilized to prepare metal–TiO₂ photocatalysts with improved performance for the decomposition of gas phase pollutants under daylight lamp irradiation.     

Synthesis of cauliflower-like ZnO-TiO2 composite porous film and photoelectrical properties

A series of cauliflower-like TiO₂-ZnO composite porous films with various molar ratios of Zn/Ti were prepared by the screen printing technique on the fluorine-doped SnO₂ (FTO) conducting glasses. The composite films were characterized by field-emission scanning electron microscopy (FE-SEM), X-ray energy-dispersive spectrometry (EDS) and UV-vis transmittance spectrum. The results showed composite film electrode had a novel cauliflower-like morphology, which could effectively increase the dye absorption. The corresponding dye-sensitized solar cells (DSCs) were made by the composite film, and effects of ZnO incorporation on the photovoltaic performances of the DSCs were studied. With the Zn/Ti molar ratio not more than 3% in ZnO-TiO₂ composite film of about 5 μm-thickness, the photocurrent density (J_sc) and the solar-to-electricity conversion efficiency (η) were greatly improved compared with those of the DSC based on bare TiO₂ film of same thickness. This increases in efficiency and J_sc were attributed to high electron conductivity of ZnO, the improved dye adsorption and large light transmittance of composite film.     

Magnetic carbon nanotubes: synthesis by a simple solvothermal process and application in magnetic targeted drug delivery system

A poly(vinyl chloride) (PVC) main chain was grafted with poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) containing a quaternary amine group using atom transfer radical polymerization. The successful synthesis of a PVC-g-PDMAEMA graft copolymer was confirmed by Fourier transform infrared, nuclear magnetic resonance, thermogravimetric analysis, and transmission electron microscopy. The PVC-g-PDMAEMA graft copolymer was used as a structure-directing agent (SDA) for the fabrication of a mesoporous thin film containing a titanium dioxide (TiO₂) layer. To control the porosity of the resultant inorganic layer, the ratio of SDA to TTIP as well as the concentration of the sol?Cgel was varied. The structure and porosity of the mesoporous film were characterized by XRD and SEM analysis. The mesoporous TiO₂ film fabricated on the FTO surface was used as a photoanode for the dye-sensitized solar cell (DSSC). DSSC performance was the greatest when using TiO₂ film with a higher porosity and lower interfacial resistance. The highest energy conversion efficiency reached 3.2?% at 100?mW/cm², which was one of the highest reported values for a quasi-solid-state DSSC with 600-nm-thick TiO₂ film.     

Phase transformation of nanostructured titanium dioxide from anatase-to-rutile via combined ultrasound assisted sol–gel technique

An effort was made to synthesize nanostructured TiO₂ via sol–gel technique to obtain a 100% rutile polymorph of nanostructured TiO₂. The sol–gel synthesis technique was suitably modified by incorporating ultrasound to study the effect of cavitation on the phase transformation, crystallite size, crystallinity and morphological (scanning electron microscopy) properties of the obtained nano-TiO₂. It was observed that using ultrasound, yield of the nano-TiO₂ was improved from 86.35% to 95.078%. The phase transformation of anatase-to-rutile of TiO₂ was studied for both (ultrasound assisted and conventional) the processes. Complete phase transformation of the TiO₂ was observed as expected with and without the use of ultrasound but the marked reduction in the required calcination temperature for obtaining 100% phase transformation with ultrasound was the major achievement in the present study, leading to 70% energy savings during calcination.     

Dye-sensitized solar cells based on ZnO nanowire array/TiO2 nanoparticle composite photoelectrodes with controllable nanowire aspect ratio

The ZnO nanowire (NW) array/TiO₂ nanoparticle (NP) composite photoelectrode with controllable NW aspect ratio has been grown from aqueous solutions for the fabrication of dye-sensitized solar cells (DSSCs), which combines the advantages of the rapid electron transport in ZnO NW array and the high surface area of TiO₂ NPs. The results indicate that the composite photoelectrode achieves higher overall photoelectrical conversion efficiency (η) than the ZnO NW alone. As a result, DSSCs based on the ZnO NW array/TiO₂ NP composite photoelectrodes get the enhanced photoelectrical conversion efficiency, and the highest η is also achieved by rational tuning the aspect ratio of ZnO NWs. With the proper aspect ratio (ca. 6) of ZnO NW, the ZnO NW array/TiO₂ NP composite DSSC exhibits the highest conversion efficiency (5.5 %). It is elucidated by the dye adsorption amount and interfacial electron transport of DSSCs with the ZnO NW array/TiO₂ NP composite photoelectrode, which is quantitatively characterized using the UV-Vis absorption spectra and electrochemical impedance spectra. It is evident that the DSSC with the proper aspect ratio of ZnO NW displays the high dye adsorption amount and fastest interfacial electron transfer.     

Nanocoral architecture of TiO2 by hydrothermal process: Synthesis and characterization

TiO₂ thin films with novel nanocoral-like morphology were successfully grown directly onto the glass and conducting fluorine doped tin oxide coated glass substrates via multi-step hydrothermal (MSH) process. Titanium chloroalkoxide [TiCl₂ (OEt)₂ (HOEt)₂)] precursor was used in an aqueous saturated NaCl in presence of 1 mM HCl catalyst and HNO₃ peptizer at 120 °C. Reaction time varied from 3 to 12 h. The morphological features and physical properties of TiO₂ films were investigated by field emission scanning electron microscopy, high resolution transmission electron microscopy, X-ray diffraction, Fourier transform IR spectroscopy, Fourier transform Raman spectroscopy, room temperature photoluminescence spectroscopy and X-ray photoelectron spectroscopy. The surface morphology revealed the formation of TiO₂ corals having nanosized (30-40 nm) polyps. The photoelectrochemical properties of the TiO₂ nanocoral electrodes were investigated in 0.1 M NaOH electrolyte under UV illumination. The results presented in this study highlight two major findings: (i) ability to tune the photoelectrochemical response and photoconversion efficiency via controlled thickness of TiO₂ nanocorals and (ii) the substantial increase in short circuit photocurrent (J_sc) due to the improved charge transport through TiO₂ nanocorals prepared via MSH process. This approach would be quite useful for the fabrication of nanocoral architecture that finds key applications in photocatalysis, dye-sensitized solar cells and hybrid solar cells.     

Dye-sensitized solar cells based on trench structured TiO2 nanotubes in Ti substrate

We have proposed dye-sensitized solar cells (DSSCs) with trench-type TiO₂ nanotube structure to improve the low device efficiency of conventional TiO₂ nanotube DSSCs using Ti substrate. Compared to the conventional standing-type TiO₂ nanotube structure based DSSCs, the trench-type TiO₂ nanotube structure based DSSCs have shown an improvement of device efficiency of approximately 40% due to the large increase of Jsc. In the trench-type TiO₂ nanotube structure, the contact area between the TiO₂ nanotube sidewall and the Ti substrate is significantly increased. This increase of contact area provides more charge transport paths than exist in the conventional standing-type TiO₂ nanotube structure and reduces the electrical resistance between the Ti substrate and the TiO₂ nanotubes. Therefore, the remarkable increase of Jsc is the result of the charge collection efficiency, which is improved due to the increase of contact area between the TiO₂ nanotube sidewall and the Ti substrate in the trench-type TiO₂ nanotube structure. The fabrication of the trench-type TiO₂ nanotube structure is an effective manufacturing process for improving the device efficiency of TiO₂ nanotube based DSSCs using Ti substrate. DSSCs having an 11.9 μm thick trench-type TiO₂ nanotube structure have shown an efficiency of 5.74%.     

Enhanced photocatalytic activity of In2O3-decorated TiO2

Titania (TiO₂)-based photocatalysts decorated with different amounts of indium oxide (In₂O₃) were prepared by a pore impregnating method and characterized by the Brunauer–Emmett–Teller (BET) method, X-ray diffraction (XRD), UV–Vis diffuse reflectance spectroscopy (DRS), and X-ray photoelectron spectroscopy (XPS). The separation efficiency of photogenerated charges was investigated using benzoquinone (BQ) as scavenger. The activities of the photocatalysts were evaluated by decolorization of methyl orange (MO) aqueous solution under ultraviolet-light irradiation. Compared to TiO₂, In₂O₃/TiO₂ composites show improved photocatalytic performance due to the coupling effect of TiO₂ and In₂O₃, which greatly improves the separation of photogenerated electrons and holes.     

Fabrication and characterization of Fe-doped titania semiconductor electrodes with p-n homojunction devices

The nano-TiO₂ electrode with a p-n homojunction device was designed and fabricated by coating of the Fe³⁺-doped TiO₂ (p-type) film on top of the nano-TiO₂ (n-type) film. These films were prepared from synthesized sol-gel TiO₂ samples which were verified as anatase with nano-size particles. The semiconductor characteristics of the p-type and n-type films were demonstrated by current-voltage (I-V) measurements. Results show that the rectifying curves of undoped TiO₂ and Fe³⁺-doped TiO₂ sample films were observed from the I-V data illustration for both the n-type and p-type films. In addition, the shapes of the rectifying curves were influenced by the fabrication conditions of the sample films, such as the doping concentration of the metal ions, and thermal treatments. Moreover, the p-n homojunction films heating at different temperatures were produced and analyzed by the I-V measurements. From the I-V data analysis, the rectifying current of this p-n junction diode has a 10 mA order higher than the current of the n-type film. The p-n homojunction TiO₂ electrode demonstrated greater performance of electronic properties than the n-type TiO₂ electrode.     

ZnS overlayer on in situ chemical bath deposited CdS quantum dot-assembled TiO2 films for quantum dot-sensitized solar cells

ZnS overlayers were deposited on the CdS quantum dot (QD)-assembled TiO₂ films, where the CdS QDs were grown on the TiO₂ by repeated cycles of the in situ chemical bath deposition (CBD). With increasing the CdS CBD cycles, the CdS QD-assembled TiO₂ films were transformed from the TiO₂ film partially covered by small CdS QDs (Type I) to that fully covered by large CdS QDs (Type II). The ZnS overlayers significantly improved the overall energy conversion efficiency of both Types I and II. The ZnS overlayers can act as the intermediate layer and energy barrier at the interfaces. However, the dominant effects of the ZnS overlayers were different for the Types I and II. For Type I, ZnS overlayer dominantly acted as the intermediate layer between the exposed TiO₂ surface and the electrolyte, leading to the suppressed recombination rate for the TiO₂/electrolyte and the significantly enhanced charge-collection efficiency. On the contrary, for Type II, it dominantly acted as the efficient energy barrier at the interface between the CdS QDs and the electrolyte, leading to the hindered recombination rate from the large CdS QDs to the electrolyte and thus enhanced electron injection efficiency.     

The improvement of pyroelectric properties of PZT thick films on Si substrate by TiOx barrier layer

The effects of TiO_x diffusion barrier layer thickness on the microstructure and pyroelectric characteristics of PZT thick films were studied in this paper. The TiO_x layer was prepared by thermal oxidation of Ti thin film in air and the PZT thick films were fabricated by electrophoresis deposition method (EPD). To demonstrate the barrier effect of TiO_x layer, the electrode/substrate interface and Si content in PZT thick films were characterized by scanning electron microscope (SEM) and X-ray energy dispersive spectroscopy (EDS), respectively. The TiO_x barrier thickness shows significant influence on the bottom electrode and the pyroelectric performance of the PZT thick films. The average pyroelectric coefficient of PZT films deposited on 400 nm TiO_x layer was about 8.94 × 10⁻⁹ C/(cm² K), which was improved by 70% than those without diffusion barrier layer. The results showed in this study indicate that TiO_x barrier layer has great potential in fabrication of PZT pyroelectric device.     

Inactivation of Escherichia coli by sonoelectrocatalytic disinfection using TiO2 as electrode

This is the first study to demonstrate sonoelectrocatalytic disinfection using titanium dioxide (TiO₂) as an anode for effective inactivation of Escherichia coli. In brief, a non-woven TiO₂ fabric used as an anode and a platinum cathode were immersed in an E. coli suspension in which a positive potential was applied to TiO₂ concomitant with ultrasound (US) irradiation. Two control experiments were performed using E. coli suspensions to exhibit the effects of the sonoelectrocatalytic disinfection. One was disinfection by applying a positive potential to a TiO₂ electrode, but without US irradiation (electrochemical disinfection). The other was disinfection without applying a potential, but with US irradiation in the presence of TiO₂ (sonocatalytic disinfection). The cell inactivation rate in sonoelectrocatalytic disinfection was synergistically much more enhanced than the combined inactivation rates in electrochemical disinfection and sonocatalytic disinfection. This synergistically enhanced inactivation rate of E. coli cells was attributable to effective reaction of the sonocatalytically generated OH radicals with E. coli cells at the surface of the TiO₂ anode, which resulted from the electroadsorption of E. coli cells toward the TiO₂ anode.     

Applications of vertically oriented TiO2 micro-pillars array on the electrode of dye-sensitized solar cell

In this research, dye-sensitized solar cells based on TiO₂ micro-pillars fabricated by inductive couple plasma etcher were investigated by analyses of X-ray diffraction (XRD), scanning electron microscopy (SEM), contact angle, ultraviolet-visible absorption spectra (UV-vis), and current-voltage characteristics. X-ray diffraction patterns show that the TiO₂ anatase phase forms while sintering at 450 °C for 30 min. The SEM images reveal that the diameter and height of TiO₂ micro-pillars are about 3 and 0.8 μm, respectively. The measurements of contact angle between TiO₂ micro-pillars and deionized water (DI water) reveal that the TiO₂ micro-pillars is super-hydrophilic while annealed at 450 °C for 30 min.The absorption spectrum of TiO₂ micro-pillars is better than TiO₂ thin film and can be widely improved in visible region with N3 dye adsorbed. The results of current-voltage (I-V) characteristics analysis reveal that dye-sensitized solar cell with TiO₂ micro-pillars electrode has better I-V characteristics and efficiency than TiO₂ film electrodes. This result may be due to the annealed TiO₂ micro-pillars applied on the electrode of dye-sensitized solar cell can increase the contact area between TiO₂ and dye, resulting in the enhancement of I-V characteristics and efficiency for dye-sensitized solar cell.     

Optimal levels of oxygen deficiency in the visible light photocatalyst TiO2−x and long-term stability of catalytic performance

The dependence of the visible light-responsive photocatalytic activity of oxygen deficient TiO₂ (TiO_2−x) prepared by Ar/H₂ plasma surface treatment on the degree of oxygen deficiency (x) was assessed to determine the deficiency region associated with highest performance. The highest activity was obtained at x=0.06 (TiO_1.94). The maximum visible light activity for this material, estimated from the formaldehyde (HCHO) removal rate, was three times higher than that exhibited by nitrogen-doped TiO₂ (TiO_2−xN_x). The catalytic ability was found to decrease over the first week after fabrication of the material, after which it became stable, and the performance of TiO_2−x at this point was found to be nearly equal to that of TiO_2−xN_x. The results of ab initio calculations of density of states for TiO_2−x suggest that new oxygen deficiency states emerge at almost the exact center between the valence and conduction bands when x>0.06, which increases the recombination rate between electrons and holes. Therefore the declining performance of TiO_2−x at larger x values is attributed to the emergence of new oxygen deficient states.     

Fabrication of nitrogen-doped TiO2 layer on titanium substrate

In this paper, macropores TiO₂ layer was fabricated on titanium substrates based on plasma based ion implantation (PBII). In order to increase the photodegradation efficiency of fabricated TiO₂ layer, two approaches are used: (1) preparation of macropores on TiO₂ layer to increase the total photodegradation area and (2) nitrogen doping (N-doping) to increase light absorption efficiency. The fabrication process of the N-doped macropores TiO₂ layer comprises four steps: firstly, helium plasma based ion implantation (He-PBII) is employed to generate He bubbles in substrate; secondly, oxygen plasma based ion implantation (O-PBII) and a followed annealing in air are executed to obtain rutile and anatase mixture TiO₂ phases; thirdly, He bubbles are exposed to the surface via an Ar ion sputter process; lastly, the samples are doped by nitrogen PBII (N-PBII). The photodegradation of Rhodamine B solution under Xe lamp indicates that the TiO₂ layer with surface macropores and N-doping has higher light photocatalysis efficiency.     

Inclusion of SWCNTs in Nb/Pt co-doped TiO2 thin-film sensor for ethanol vapor detection

Nb-Pt co-doped TiO₂ and the hybrid SWCNTs/Nb-Pt co-doped TiO₂ thin films have been prepared by the sol–gel spin-coating process for gas-sensor fabrication. Field emission scanning electron microscope (FE-SEM, TEM and X-ray diffraction (XRD) characterizations indicated that the SWCNTs inclusion did not affect the morphology of the TiO₂ thin film and the particle size. Additionally, the SWCNTs were well embedded in the TiO₂ matrix. The gas-sensing properties of Nb–Pt co-doped TiO₂ thin films with and without SWCNTs inclusion were investigated. The hybrid sensors with the inclusion of different SWCNTs contents are examined to elucidate the effect of SWCNTs content on the gas-sensing properties. Experimental results revealed that the responses to ethanol of Nb–Pt co-doped TiO₂ sensors with SWNCTs inclusion increase by factors of 2–5 depending on the operating temperature and the ethanol concentration, compared to that of the sensor without SWCNTs inclusion. Moreover, all hybrid sensors can operate with high sensitivity and stability at a relatively low operating temperature (<335 °C). The responses of the hybrid sensors are greatly affected by SWCNTs content inclusion. The optimized SWCNTs content of 0.01% by weight was obtained for our experiment. The improved gas-sensing performance should be attributed to the additional formation of the p/n junction between SWCNTs (p-type) and TiO₂ (n-type).     

Contact potential barriers and characterization of Ag-doped composite TiO2 nanotubes

Ag-doping TiO₂ composite nanotubes (Ag-TNTs) were synthesized by alkaline fusion followed by hydrothermal treatment. The microstructure and morphology of the materials were characterized by XRD, TEM, XPS, SPS (surface photovoltage spectroscopy), FISPS (electric field-induced surface photovoltage spectroscopy) and Raman spectroscopy. First-principles calculations based on density-functional theory (DFT) showed the formation of several impurity levels near the top of the valence band in the band gap (E_g) of rutile TiO₂ due to Ag doping. A “double junction” is proposed, involving a Schottky junction and p–n junction (denoted as “Ag-p–n junction”) occurring between the Ag particles and the nanotube surface, as well as forming inside TiO₂ nanotubes, respectively. The strongly built-in electric field of the junctions promotes the separation of photo-holes and photoelectrons, enhancing the photocatalytic efficiency. XRD results indicated that the composite Ag-TNTs exist as a mixture of anatase and rutile phases. XPS results showed that Ti⁴⁺ is the primary state of Ti. Raman spectral analysis of Ag-TNTs revealed the presence of a new peak at 271 cm⁻¹. The red-shift of the absorption light wavelength of Ag-TNTs was 0.16 eV (20 nm) due to a considerable narrowing of E_g by the existing impurity levels.