TiO2 nanowires sensitized with CdS quantum dots and the surface photovoltage properties

TiO₂ nanowires prepared by thermal annealing of anodized Ti foil were sensitized with CdS quantum dots (QDs) via chemical bath deposition (CBD). Microstructural characterizations by SEM, TEM and XRD show that the CdS nanocrystals with the cubic structure have intimate contact to the TiO₂ nanowires. The amount of CdS QDs can be controlled by varying the CBD cycles. The experiment results demonstrate that the surface photovoltage (SPV) response intensity was significantly enhanced and the surface photovoltage response region was also expanded obviously for the TiO₂ NWs sensitized by CdS QDs.     

Fabrication of quantum dot-sensitized solar cells with multilayer TiO2/PbS(X)/CdS/CdSe/ZnS/SiO2 photoanode and optimization of the PbS nanocrystalline layer

In this work, two multilayer photoanode structures of TiO₂/PbS(X)/CdS/ZnS/SiO₂ and TiO₂/PbS(X)/CdS/CdSe/ZnS/SiO₂ were fabricated and applied in quantum dot-sensitized solar cells (QDSCs). Then, the effect of PbS QDs layer on the photovoltaic performance of corresponding cells was investigated. The sensitization was carried out by PbS and CdS QDs layers deposited on TiO₂ scaffold through successive ionic layer adsorption and reaction (SILAR) method. The CdSe QDs film was also formed by a fast, modified chemical bath deposition (CBD) approach. Two passivating ZnS and SiO₂ layers were finally deposited by SILAR and CBD methods, respectively. It was shown that the reference cell with TiO₂/CdS/ZnS/SiO₂ photoanode demonstrated a power conversion efficiency (PCE) of 3.0%. This efficiency was increased to 4.0% for the QDSC with TiO₂/PbS(2)/CdS/ZnS/SiO₂ photoelectrode. This was due to the co-absorption of incident light by low-bandgap PbS nanocrystalline film and also the CdS QDs layer and well transport of the charge carriers. For the CdSe included QDSCs, the PbS-free reference cell represented a PCE of 4.1%. This efficiency was improved to 5.1% for the optimized cell with TiO₂/PbS(2)/CdS/CdSe/ZnS/SiO₂ photoelectrode. The maximized efficiency was enhanced about 25% and 70% compared to the PbS-free reference cells with and without the CdSe QDs layer.

     

Chemically deposited TiO2/CdS bilayer system for photoelectrochemical properties

In the present investigation, TiO₂, CdS and TiO₂/CdS bilayer system have been deposited on the fluorine doped tin oxide (FTO) coated glass substrate by chemical methods. Nanograined TiO₂ was deposited on FTO coated glass substrates by successive ionic layers adsorption and reaction (SILAR) method. Chemical bath deposition (CBD) method was employed to deposit CdS thin film on pre-deposited TiO₂ film. A further study has been made for structural, surface morphological, optical and photoelectrochemical (PEC) properties of FTO/TiO₂, FTO/CdS and FTO/TiO₂/CdS bilayers system. PEC behaviour of FTO/TiO₂/CdS bilayers was studied and compared with FTO/CdS single system. FTO/TiO₂/CdS bilayers system showed improved performance of PEC properties over individual FTO/CdS thin films.     

Enhanced photovoltaic performance of solar cell based on front-side illuminated CdSe/CdS double-sensitized TiO2 nanotube arrays electrode

Free-standing TiO₂ nanotube (NT) arrays have been prepared by a two-step anodization method. These translucent TiO₂ NT arrays can be transferred to the fluorine-doped tin oxide glass substrates to form front-side illuminated TiO₂ NT electrodes. The TiO₂ NT electrodes were double-sensitized by CdSe/CdS quantum dots (QDs) through successive ionic layer adsorption and reaction (SILAR) process. The absorption range of the TiO₂ NT electrode was extended from ~380 to 700 nm after sensitization with CdSe/CdS QDs. The SILAR cycles were investigated to find out the best combination of CdS and CdSe QDs for photovoltaic performance. The power conversion efficiency of 2.42 % was achieved by the CdSe(10)/CdS(8)/TiO₂ NT solar cell. A further improved efficiency of 2.57 % was obtained with two cycles of ZnS overlayer on the CdSe(10)/CdS(8)/TiO₂ NT electrode, which is 45.19 % higher than that of back-side illuminated solar cell. Furthermore, the ZnS(2)/CdSe(10)/CdS(8)/TiO₂ NT solar cell possesses a higher stability than CdSe(10)/CdS(8)/TiO₂ NT solar cell during the same period. The better photovoltaic performance of the ZnS(2)/CdSe(10)/CdS(8)/TiO₂ NT solar cell has demonstrated the promising value to design quantum dots-sensitized solar cells with double-sensitized front-side illuminated TiO₂ NT arrays strategy.     

A three-dimensional electrode for photoelectrochemical cell: TiO2 coated ITO mesoporous film

In this letter, TiO₂ coated ITO mesoporous film was prepared by dipping doctor-blade ITO mesoporous film in TiO₂ sol, followed by sintering at 500 °C for 30 min. The CdS quantum dots (QDs) were deposited on TiO₂ coated ITO mesoporous film using sequential chemical bath deposition (S-CBD) method to form a three-dimensional (3D) electrode. The photo-activity of ITO mesoporous film/TiO₂/CdS electrode was investigated by forming a photoelectrochemical cell, which indicated that the ITO mesoporous film/TiO₂/CdS electrode was efficient in photoelectrochemical cell as a working electrode. The 3D electrode showed lower performance than the conventional electrode of TiO₂ mesoporous film/CdS, and more works are needed to improve the performance of 3D electrode.     

Enhanced photoelectrochemical properties of TiO2 nanorod arrays decorated with CdS nanoparticles

TiO₂ nanorod arrays (TiO₂ NRAs) sensitized with CdS nanoparticles were fabricated via successive ion layer adsorption and reaction (SILAR), and TiO₂ NRAs were obtained by oxidizing Ti NRAs obtained through oblique angle deposition. The TiO₂ NRAs decorated with CdS nanoparticles exhibited excellent photoelectrochemical and photocatalytic properties under visible light, and the one decorated with 20 SILAR cycles CdS nanoparticles shows the best performance. This can be attributed to the enhanced separation of electrons and holes by forming heterojunctions of CdS nanoparticles and TiO₂ NRAs. This provides a promising way to fabricate the material for solar energy conversion and wastewater degradation.     

Synthesis of TiO2 nanotubes coupled with CdS nanoparticles and production of hydrogen by photocatalytic water decomposition

The CdS/TiO₂NTs composite was prepared by a simple two-step chemical solution routes to directly transfer trititanate nanotubes to TiO₂NTs and simultaneously coupled with CdS nanoparticles. The results of XRD, TEM, Diffuse reflectance UV-Visible absorption spectra revealed that the CdS nanoparticles were homogeneously embedded on the surface of TiO₂NTs and the absorption spectrum of TiO₂NTs was extended to visible region. The activity of hydrogen production by photocatalytic water decomposition for the CdS/TiO₂NTs composite was examined under visible light irradiation (λ > 400 nm) and the quantity of H₂ evolution was ca. 1708 μL/g for 6 h.     

Photoelectrochemical properties of TiO<Subscript>2</Subscript>/CdS heterostructures

The photoelectrochemical properties of TiO₂, CdS, and TiO₂/CdS anodes have been studied. The results demonstrate that, under illumination, CdS anodes are subject to photocorrosion, and Cd²⁺ ions pass into solution. Corrosion-resistant films of TiO₂ prevent CdS photocorrosion, and the CdS/TiO₂ system exhibits good photosensitivity in the visible range.     

Novel construction of CdS-encapsulated TiO2 nano test tubes corked with ZnO nanorods

A novel TiO₂ nanotube array/CdS nanoparticle/ZnO nanorod (TiO₂ NT/CdS/ZnO NR) photocatalyst was constructed by chemical assembling CdS into the TiO₂ NTs, and then laying ZnO NRs on the surface. The SEM results showed that the TiO₂ NTs looked like many “nano test tubes” and the ZnO NRs served as the corks to seal the nozzle. This photocatalyst exhibited a wide absorption range (200-535 nm) in both ultraviolet and visible regions (UV-vis region), and maintained very high photoelectrocatalytic (PEC) activities. The maximum photoelectric conversion efficiencies (η) of TiO₂ NT/CdS/ZnO NRs are 31.8 and 5.98% under UV light (365 nm) and visible light (420-800 nm), respectively.     

Effects of LP-MOCVD prepared TiO2 thin films on the in vitro behavior of gingival fibroblasts

We report on the in vitro response of human gingival fibroblasts (HGF-1 cell line) to various thin films of titanium dioxide (TiO₂) deposited on titanium (Ti) substrates by low pressure metal-organic chemical vapor deposition (LP-MOCVD). The aim was to study the influence of film structural parameters on the cell behavior comparatively with a native-oxide covered titanium specimen, this objective being topical and interesting for materials applications in implantology. HGF-1 cells were cultured on three LP-MOCVD prepared thin films of TiO₂ differentiated by their thickness, roughness, transversal morphology, allotropic composition and wettability, and on a native-oxide covered Ti substrate. Besides traditional tests of cell viability and morphology, the biocompatibility of these materials was evaluated by fibronectin immunostaining, assessment of cell proliferation status and the zymographic evaluation of gelatinolytic activities specific to matrix metalloproteinases secreted by cells grown in contact with studied specimens. The analyzed surfaces proved to influence fibronectin fibril assembly, cell proliferation and capacity to degrade extracellular matrix without considerably affecting cell viability and morphology. The MOCVD of TiO₂ proved effective in positively modifying titanium surface for medical applications. Surface properties playing a crucial role for cell behavior were the wettability and, secondarily, the roughness, HGF-1 cells preferring a moderately rough and wettable TiO₂ coating.     

Cu2ZnSnS4 solar cell prepared entirely by non-vacuum processes

Cu₂ZnSnS₄ (CZTS) solar cell with superstrate structure of fluorine-doped tin oxide glass/TiO₂/In₂S₃/CZTS/Carbon was prepared entirely by non-vacuum processes. The compact TiO₂ window and In₂S₃ buffer layers, CZTS absorber layer and Carbon electrode layer were prepared by spray pyrolysis method, ball milling and screen printing combination processes and screen printing process, respectively. The short-circuit current density, open-circuit voltage, fill factor and conversion efficiency of the best fabricated solar cell are 8.76 mA/cm², 250 mV, 0.27 and 0.6%, respectively. The fabrication process for the CZTS solar cell did not employ any vacuum conditions or high-toxic materials (such as CdS, H₂Se, H₂S or Se).     

TiO2 inverse opal based CdS/CdSe quantum dot co-sensitized solar cells

CdS and CdSe quantum dots were introduced as co-sensitizers into TiO₂ inverse opal quantum dot sensitized solar cells. Herein, the three-dimensionally ordered porous TiO₂ inverse opal film leads to a better infiltration of both sensitizers and hole transporting material, and the smaller surface area of TiO₂ inverse opal film is effectively offset by the incorporating of co-sensitization. It was found that the presence of CdS/CdSe co-sensitizers provides enhanced light absorption, and leads to a lower recombination rate of the electrons due to the stepwise structure of band edge in TiO₂/CdS/CdSe, which resulted in the observed enhanced photocurrent and energy conversion efficiency of the solar cells. A cell efficiency of 1.01 % has been attained.     

TiO2 nanorod films grown on Si wafers by a nanodot-assisted hydrothermal growth

We report the controlled hydrothermal growth of rutile TiO₂ nanorods on Si wafers by using an anatase TiO₂ nanodot film as an assisted growth layer. The anatase nanodot film was prepared on the wafer by phase-separation-induced self-assembly and subsequent heat-treatment at 500 °C. The nanodots on the wafer were then subjected to hydrothermal treatment to induce the growth of rutile TiO₂ nanorod films. The size and dispersion density of the resulting TiO₂ nanorods could be varied by adjusting the Ti ion concentration in the growth solution. The TiO₂ nanorods were of the rutile phase and grew in the [001] direction. The growth mechanism reveals that the growth of the rutile nanorods was wholly dependent on the existence of rutile TiO₂ seeds, which could be formed by the dissolution-reprecipitation of the anatase nanodots during hydrothermal treatment or under the high-temperature conditions of the subsequent heat-treatment of the as-prepared nanodots. In controlling the rutile nanorod growth, the anatase nanodots show more efficiency than a dense anatase film. Preliminary evaluations of the rutile nanorod films have demonstrated that the wettability changed from highly hydrophobic to superhydrophilic and that the photocatalytic activity was enhanced with increasing nanorod dispersion density.     

CdS-sensitized ZnO nanorod arrays coated with TiO2 layer for visible light photoelectrocatalysis

A novel ZnO/CdS/TiO₂ nanorod array composite structure was fabricated by depositing CdS-sensitized layer onto ZnO nanorod arrays via chemical bathing deposition and subsequently coated by TiO₂ protection layer via a vacuum dip-coating process. The films were characterized by x-ray diffraction, field emission scanning electron microscopy, energy dispersive spectrum, and UV–Vis diffuse reflectance spectroscopy. For the films severed as the photoanodes, linear sweep voltammetry and transient photocurrent (i _ph) were investigated in a three-electrode system. The photoelectrocatalytic activity was evaluated by the degradation of methylene blue (MB) under visible light irradiation. The results show that the oriented ZnO nanorods are adhered by relatively uniform CdS-sensitized layer and coated with TiO₂ layer. Both the coated and uncoated CdS-sensitized ZnO nanorod arrays exhibit the visible light response and the photoelectrocatalytic activity on the degradation of MB under visible light irradiation. The ZnO/CdS/TiO₂ nanorod array film possesses stable and superior photoelectrocatalytic performance owing to the TiO₂ thin layer protecting the CdS from photocorrosion.     

Photoconductivity of n-type semiconductor nanoparticle-doped poly(N-vinylcarbazole) films

TiO₂, CdS and ZnS nanoparticles that disperse stably in organic solvents are synthesized. Poly(N-vinylcarbazole) films doped with the n-type semiconductor nanoparticles are prepared with a cast method. The films exhibit a transient photocurrent when irradiated by a light pulse and act such as a diode when AC voltage is applied under continuous illumination. The transient photocurrent response and diode-like properties are significantly different depending on the kind of the nanoparticles and their amounts. The films doped with TiO₂ and CdS nanoparticles increase the transient photocurrent at lower doped amounts, which is remarkable for TiO₂-doped films. Time of flight analysis of the transient photocurrent shows that mobility of hole in PVK increases with increase in the amount of CdS and TiO₂. From the studies on the diode-like properties, the current increase at lower dopant concentration is concluded to be due to increase in the amount of holes by an electron transfer from PVK to the photo-excited nanoparticles. At higher doping with CdS nanoparticles, main charge carrier of the films is found to change from holes to electrons.     

Synthesis of TiO2/CdS nanocomposite via TiO2 coating on CdS nanoparticles by compartmentalized hydrolysis of Ti alkoxide

Hydrolysis of Ti alkoxide in the presence of inverse micelles containing CdS nanoparticles in their hydrophilic interior results in formation of TiO₂/CdS nanocomposites in which the CdS nanoparticles are embedded in a TiO₂ matrix with a thickness of 10 nm at the surface of the particles. The primary hydroxyl groups introduced by 2-mercaptoethanol as a capping agent used for preparation of the CdS nanoparticles are considered to play an important role for successful adhesion and growth of the TiO₂ layer on the CdS surfaces. TEM observation strongly supports formation of semiconductor-in-semiconductor heteronanostructure by compartmentalized hydrolysis of Ti alkoxide within the inverse micelles in which the surface-capped CdS nanoparticles coexist.     

Mesoporous Au/TiO2 composites preparation,characterization, and photocatalytic properties

In this work, mesoporous Au/TiO₂ composites have been synthesized and tested on photodegradation of methylene blue dye solution. Mesoporous TiO₂ prepared at 450 °C using triblock polymer F127 as structure-directing agent was applied as substrate, while various HAuCl₄ concentrations were used for Au loading through deposition-precipitation method using urea as precipitator and hydrogen reducing process. The influences of Au loading on the microstructures of mesoporous TiO₂ including degree of dispersion, particle size, surface area, light absorption, and band gap were studied with transmission electron microscopy (TEM), X-ray diffraction (XRD), diffuse reflection infrared Fourier transformed spectroscopy (DRIFT), N₂ adsorption–desorption isotherm analysis (BET), and UV–Vis diffuse reflectance spectra. With Au loading, the size of TiO₂ nanoparticles in Au/TiO₂ composites is similar as that of TiO₂ substrate. However, the degree of dispersion was greatly improved. Furthermore, an obvious surface plasmon resonance centered at 570 nm was found in UV–Vis diffuse reflectance spectra for Au/TiO₂ composites. Au loading also induced an obvious red shift of light absorption from UV region to visible region and strengthened both UV and visible light absorption in contrast to substrate. Photodegradation results verified that photocatalytic activity of mesoporous TiO₂ was improved by Au loading. 0.25%Au/TiO₂ composite showed the highest activity, which may be ascribed to its high surface hydroxyl content and the formed Schottky junction after Au loading. These results suggested that noble metal modification is a promising way to synthesize photocatalysts with both high activity and visible light sensitivity.     

碳纤维/TiO2改性树脂复合材料的制备及力学性能

针对环氧树脂脆性大、与碳纤维形成的界面性能较差等问题,本文选用纳米TiO₂对5284环氧树脂进行改性,并以角联锁机织物为增强体制备了碳纤维/环氧树脂复合材料。使用FT-IR、旋转流变仪、表面张力仪等设备对TiO₂/环氧树脂进行表征,并研究了树脂改性对复合材料压缩与层间剪切性能的影响。研究表明：TiO₂的羟基与环氧树脂的环氧基和羟基发生了反应;经1wt.%TiO₂改性的树脂复数黏度为0.066 Pa·s,纤维与树脂间接触角为28.85°,浸润效果较好;相较于未改性复合材料,树脂改性的复合材料纵向压缩强度与模量分别提高了7.46%和11.03%,横向压缩强度与模量分别提高了6.99%和4.96%,纵向、横向的剪切强度分别提高了6.88%和4.65%。TiO₂改性环氧树脂提高了复合材料的承载能力,改善了界面结合强度。     

TiO2光催化剂的研究与应用进展

为了解决日益严重的环境污染问题和能源问题,越来越多的研究者将精力投入到ZnO、CdS、TiO_2和BiVO_4等半导体材料的研究中。其中,TiO_2以优异的氧化能力、较强的化学稳定性、较低的价格以及无毒性吸引了广泛的目光。针对近年来TiO_2的光催化性能研究及其改性方法的研究进展,以及应用热点进行了综述,并对如何进一步提升其性能进行了展望。     

Chemical synthesis of CdS onto TiO2 nanorods for quantum dot sensitized solar cells

A quantum dot sensitized solar cell (QDSSC) is fabricated using hydrothermally grown TiO₂ nanorods and successive ionic layer adsorption and reaction (SILAR) deposited CdS. Surface morphology of the TiO₂ films coated with different SILAR cycles of CdS is examined by Scanning Electron Microscopy which revealed aggregated CdS QDs coverage grow on increasing onto the TiO₂ nanorods with respect to cycle number. Under AM 1.5G illumination, we found the TiO₂/CdS QDSSC photoelectrode shows a power conversion efficiency of 1.75%, in an aqueous polysulfide electrolyte with short-circuit photocurrent density of 4.04 mA/cm² which is higher than that of a bare TiO₂ nanorods array.