Construction of TiO<Subscript>2</Subscript> NP@TiO<Subscript>2</Subscript> NT double-layered structural photoanode to enhance photovoltaic performance of CdSe/CdS quantum dots sensitized solar cells

TiO₂ nanoparticles (NP) at top of TiO₂ nanotube (TiO₂ NP@TiO₂NT) double-layered architecture is constructed to combine the advantages of TiO₂ NP and TiO₂ NT together. This composite TiO₂ NP@TiO₂NT architecture as photoanode possesses a larger surface area for more QDs loading, and highly tubular structure for electron swift transport. Based on this architecture, CdSe/CdS quantum dots (QDs) have been successfully synthesized by successive ionic layer adsorption reaction (SILAR) method for quantum dots-sensitized solar cell application. The photovoltaic performance of QDSSCs based on TiO₂ NP@TiO₂ NT have been investigated in contrast with bare TiO₂ NP and bare TiO₂ NT architectures with almost the same thickness. The results show that the power conversion efficiency (PCE) of QDSSCs could be enhanced using TiO₂ NP@TiO₂ NT and improved to 3.26%, which is 80% and 38% higher than QDSSCs based on bare TiO₂ NT and bare TiO₂ NP, respectively. The BET surface area, UV–vis absorption spectra, and incident photon to current conversion efficiency (IPCE) measurements results show the evidence that the TiO₂ NP@TiO₂ NT can combine advantages of TiO₂ NP and TiO₂ NT structures together and lead to a higher light harvesting efficiency, electron collecting efficiency, and efficient electron transport.     

LiFePO<Subscript>4</Subscript>/TiO<Subscript>2</Subscript>/Pt composite film used as effective and robust counter electrode for dye sensitized solar cells

A series of composite films based on LiFePO₄/TiO₂/Pt were synthesized and used as counter electrodes for dye sensitized solar cells (DSSCs). The composites are characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and Brunauer–Emmett–Teller (BET). These analysis results demonstrate that the crystal structure of LiFePO₄ in composite is not changed, and the prepared LiFePO₄/TiO₂/Pt composite films hold a rough surface and porous structure which provide more catalytic activity sites for I₃ ^? reduction and more space for I^?/I₃ ^? diffusion. The DSSC based on LiFePO₄/TiO₂/Pt composite CEs shows a high power conversion efficiency of 6.23% at a low Pt dosage of 2%, comparable to the conventional magnetron sputtering Pt CE (6.31%). The electrochemical analysis reveals that the presented composite CEs have good electrocatalytic activity and low charge transfer resistance. Furthermore, the DSSCs based on LiFePO₄/TiO₂/Pt composite CE exhibit high stability under the continuous tests condition and electrolyte soaking. The results suggest that this LiFePO₄-based composite film could be a perspective electrode for practical application of DSSCs and it maybe provide a potential for further research about photo-charging lithium-ion batteries.     

Preparation,characterization and photocatalytic activity of TiO<Subscript>2</Subscript> / Methylcellulose nanocomposite films derived from nanopowder TiO<Subscript>2</Subscript> and modified sol–gel titania

TiO₂—methylcellulose (MC) nanocomposite films processed by the sol-gel technique were studied for phocatalytic applications. Precalcined TiO₂ nanopowder was mixed with a sol and heat treated. The sol suspension was prepared by first adding titanium tetra isopropoxide (Ti(OPr)₄ or TTP) to a mixture of ethanol and HCl (molar ratio TTP:HCl:EtOH:H₂O = 1:1.1:10:10) and then adding a 2 wt.% solution of methylcellulose (MC). The TiO₂ nanopowder was dispersed in the sol and the mixture was deposited on a microscope glass slide by spin coating. Problems of film inhomogeneity and defects which caused peeling and cracking during calcinations, because of film shrinkage, were overcome by using MC as a dispersant. Effect of MC on the structure evaluation, crystallization behavior and mechanical integrity with thermal treatment up to 500 °C are followed by SEM, XRD and scratch test. XRD Scanning electron microscopy (SEM) showed that the composite films with MC have much rougher surface than films made without MC. Composite films heat treated at approximately 500 °C have the greatest hardness values. For the composite thick film, the minimum load which caused the complete coating removal was 200 g/mm², an indication of a strong bond to the substrate. Photocatalytic activities of the composite film were evaluated through the degradation of a model pollutant, the textile dye, Light Yellow X6G (C.I. Reactive Yellow 2) and were compared with the activity of (i) a similar composite film without MC, and (ii) a TiO₂ nanopowder. The good mechanical integrity make this composite film an interesting candidate for practical catalytic applications.     

Dye-sensitized solar cells using TiO<Subscript>2</Subscript> nanoparticles transformed from nanotube arrays

Dye-sensitized solar cells (DSSCs) were fabricated using TiO₂ mesoporous layers obtained by very simple method—transformation of TiO₂ nanotube (NT) films grown by electrochemical oxidation to nanoparticle (NP) films. This transformation is based on thermal annealing of TiO₂ NT arrays formed by anodization of titanium foil in fluorine ambient. Performance of DSSCs fabricated with different size NPs was studied in the range from 35 to 350 nm. Highest nominal efficiency (9.05%) was achieved for DSSC with NP size 65 nm while the lowest nominal efficiency (1.48%) was observed for DSSCs with NP size 350 nm. The dependence of the solar cell parameters with NP size is discussed.     

Preparation and characterization of TiO2 anode film with spinodal phase separation structure in dye-sensitized solar cells

Low electronic transmission efficiency and high charge recombination are the existing problems of photoanode film in traditional dye sensitized solar cells (DSSCs). This paper put forward the photoanode TiO₂ films with spinodal phase separation structure (SPSS) and continuous TiO₂ skeleton which were triggered by the photopolymerization of organic monomers in a photomonomer-inorganic precursor system. The photoanode TiO₂ films fabricated by different precursor solution compositions and different coating layers were characterized mainly by scanning electron microscopy (SEM), photocatalysis and photoelectric performance test. The results indicated that, the as-prepared TiO₂ anode film with seven coating layers and heat treated at 500 °C showed higher photoelectric conversion efficiency at about 2% than that of other samples with less coating layers and lower heat treatment temperature. The film also showed excellent photocatalytic activity by using methylene blue (MB) dye as a model organic substrate under fluorescent lamp irradiation. It is suggested that the film with SPSS structure has the potential to improve the electronic transmission efficiency and reduce the carrier recombination due to its particular structure, higher surface area, and lack of bottleneck in electronic transmission. It is worth noting that the SPSS structure provides new ideas to develop new photoanode films and further improve the photoelectric conversion performance of the DSSC in future.     

Structure,morphology, photocatalytic and antibacterial activities of ZnO thin films prepared by sol–gel dip-coating method

ZnO thin films were deposited on soda lime glass substrates by the sol–gel dip-coating method with variations of the initial Zn²⁺ concentrations. Various techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and transmission electron microscopy (TEM) were used to investigate the effects of the initial Zn²⁺ concentrations on the structure, and surface morphology and topography of the prepared films. All prepared ZnO thin films showed a high transparency of over 88% in the visible region. The particle size increased with an increased initial Zn²⁺ concentration. This also reduced the surface denseness and the energy band gap of the ZnO thin films. All the prepared films showed photocatalytic properties through photodegradation of the methylene blue (MB) dye. The ZnO thin film prepared from the 0.1 M Zn²⁺ concentration showed the greatest efficiency as it had the highest surface area because of its greatest surface roughness. Furthermore, the prepared ZnO thin film showed antibacterial activities against the Escherichia coli bacterium.     

Visible light photocatalytic degradation of paraoxon and parathion pesticides on carbon-doped TiO<Subscript>2</Subscript> nanorod thin films

In the present work the nanostructured carbon-doped TiO₂ thin films with nanorod morphology were deposited on glass substrate by a combination of ultrasonic and chemical vapor deposition methods, and for the first time were applied for the photocatalytic degradation of paraoxon and parathion organophosphorus pesticides under visible light irradiation. X-ray Diffraction, X-ray photoelectron spectroscopy, diffuse reflectance spectroscopy, and scanning electron microscopy techniques were used for characterization of the prepared thin films. Obtained results show that presence of carbon element and also special nanorod morphology of the thin films remarkably improve the optical properties of TiO₂ in visible light region and results in the good visible light photocatalytic activity of the thin films for degradation of the pesticides. The photonic efficiencies of the prepared thin films were also examined based on the international ISO-10678:2010 standard protocol for photocatalytic degradation of methylene blue under UV light irradiation. The results show a maximum photonic efficiency of 0.0312% for the carbon-doped TiO₂ thin film with 570 nm thickness, which compared to a reference standard TiO₂ films indicates a 30% improvement in photonic efficiency.     

TiO2 nanotube membranes on transparent conducting glass for high efficiency dye-sensitized solar cells

Crack-free TiO(2) nanotube (NT) membranes were obtained by short time re-anodization of a sintered TiO(2) NT array on Ti foil, followed by dilute HF etching at room temperature. The resulting freestanding TiO(2) membranes were opaque with a slight yellow color having one end open and another end closed. The membranes were then fixed on transparent fluorine-tin-oxide glass using a thin layer of screen-printed TiO(2) nanoparticles (NPs) as a binding medium. It was found that low temperature treatment of the resulting NT/NP film under appropriate pressure before sintering at 450?°C was critical for successful fixation of the NT membrane on the NP layer. The resulting films with open-ends of NT membranes facing the NP layer (open-ends down, OED, configuration) exhibited better interfacial contact between NTs and NPs than those with closed-ends facing the NP layer (closed-ends down, CED, configuration). The cells with an OED configuration exhibit higher external quantum efficiency, greater charge transfer resistance from FTO/TiO(2) to electrolyte, and better dye loading compared to CED configurations. The solar cells with the OED configuration gave 6.1% energy conversion efficiency under AM1.5G condition when the commercial N719 was used as a dye and I(-)/I(3)(-) as a redox couple, showing the promise of this method for high efficiency solar cells.     

Performance and electron transport properties of TiO(2) nanocomposite dye-sensitized solar cells

TiO(2) nanowire (NW)/nanoparticle (NP) composite films have been fabricated by hybridizing various ratios of hydrothermal anatase NWs and TiO(2) NPs for use in dye-sensitized solar cells (DSSCs). Scanning electron microscopy (SEM) images reveal that uniform NW/NP composite films were formed on fluorine-doped tin oxide?(FTO) substrates by the dip-coating method. The NWs are randomly but neither vertically nor horizontally oriented within the composite film. The TiO(2) NP DSSC possesses superior performance to those of the NW/NP composite and the pure NW cells, and the efficiency of the NW/NP composite DSSC increases on increasing the NP/NW ratio in the composite anode. All types of DSSC possess the same dependence of performance on the anode thickness that the efficiency increases with the anode thickness to a maximum value, then it decreases when the anode is thickened further. Electrochemical impedance spectroscopy analyses reveal that the NP DSSCs possess larger effective electron diffusion coefficients (D(eff)) in the photoanodes and smaller diffusion resistances of I(3)(-) in electrolytes compared to those in the NW/NP and the NW DSSCs. D(eff) decreases when NWs are added into the photoanode. These results suggest that the vertical feature of the NWs within the anodes is crucial for achieving a high electron transport rate in the anode.     

Yolk-shell CdS@void@TiO2 composite particles with photocorrosion resistance for enhanced dye removal and hydrogen evolution

Yolk-shell CdS@void@TiO₂ (cadmium sulfide@void@titanium dioxide) composite particles (CPs), consisting of three parts: core (CdS) synthesized by solvent thermal reaction, void generated by polypyrrole (PPy) sacrificed layers and porous shell (TiO₂) by sol-gel method, were innovatively fabricated. The actual yolk-shell structure and chemical composition of the resultant CdS@void@TiO₂ were verified by field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray powder diffraction analyses (XRD), and X-ray photoelectron spectroscopy (XPS). CdS@void@TiO₂ CPs possessed enhanced visible light response due to its narrower energy gap (2.9 eV) than TiO₂ (3.2 eV). With the support of photocatalytic performance test results, CdS@void@TiO₂ exhibits much higher hydrogen evolution rate up to 1893.5 μmol h⁻¹ g⁻¹ as well as dye removal efficiency both under visible and UV light irradiation than pristine TiO₂. The covering of TiO₂ shell remarkably promotes the photocorrosion resistance of CdS. The unique yolk-shell structure promotes striking photocatalytic performance in dye removal and hydrogen evolution. A possible photocatalytic mechanism about enhanced photocatalytic activity and robust photostability is also proposed.     

Visible light irradiated photocatalytic and magnetic properties of Fe-doped SnS<Subscript>2</Subscript> nanopowders

Fe-doped SnS₂ (SnS₂:Fe) nanopowders were synthesized by cost effective chemical method and characterized by thermo gravimetric-differential thermal analysis, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and vibrating sample magnetometer techniques. The photocatalytic activity was evaluated for the degradation of congo red dye under visible light irradiation. XRD studies indicate that both the undoped and doped SnS₂ nanopowders exhibit hexagonal crystal structure with a strong (1 0 1) preferential growth. Nanosized grains are evinced from the TEM images. XPS spectra confirmed the presence of Fe in the doped samples. Photodegradation efficiency increased with increase in Fe doping concentration and the SnS₂:Fe nanopowder with 10 wt% Fe doping concentration exhibits a maximum efficiency of 93.94% after 180 min light irradiation. Ferromagnetic ordering of pure SnS₂ improved with Fe doping. The outcome of the results indicated that Fe-doped SnS₂ nanopowders are well suited as diluted magnetic semiconductor and also can be used as an efficient photocatalyst.     

玻璃固载TiO2/纳米纤维素复合薄膜的制备及其光催化性能

将微晶纤维素溶解于NaOH-尿素的低温溶液中形成纤维素溶液, 在水浴中再生形成纳米纤维素溶液。然后将纳米纤维素溶液与TiO₂(P25)混合, 并添加少量的钛酸正丁酯作为交联剂形成复合溶液。将制备得到的复合溶液通过流延法固载到玻璃片表面形成玻璃固载的TiO₂/纳米纤维素复合膜。通过SEM、XRD表征了复合膜的形貌与结构。将玻璃固载的TiO₂/纳米纤维素复合膜在紫外光下进行光催化降解甲基橙(MO)以评估复合膜的光催化性能, 研究了纳米TiO₂含量对复合膜光催化性能的影响, 复合膜的重复使用性能以及光降解的动力学过程。结果表明: 复合膜对MO的光催化降解能力可达90%以上, 与纯TiO₂粉末相当, 并重复使用3次光催化性能基本保持不变。复合膜对甲基橙的降解动力学符合一级动力学特征。当纳米TiO₂相对于纤维素的质量分数为33.3%时, 光催化活性最高, 动力学速率常数为0.035 min^-1。     

TiO2 nanotubes infiltrated with nanoparticles for dye sensitized solar cells

We present a detailed study of the infiltration of titanium dioxide (TiO(2)) nanotubes (NTs) with TiO(2) nanoparticles (NPs) for dye sensitized solar cells (DSSCs). The aim is to combine the merits of the NP's high dye loading and high light harvesting capability with the NT's straight carrier transport path and high electron collection efficiency to improve the DSSC performance. On infiltrating NTs with TiCl(4) solution followed by hydrothermal synthesis, 10 nm size NPs were observed to form a conformal and dense layer on the NT walls. Compared with the bare NT structure, dye loading of this mixed NT and NP structure is more than doubled. The overall photon conversion efficiencies of the fabricated DSSCs are improved by 152%, 107%, and 49% for 8, 13, and 20 μm long NTs, respectively. Electron transport and recombination parameters were extracted based on electrochemical impedance spectroscopy measurements. Although a slight reduction of electron lifetime was observed in the mixed structures due to enhanced recombination with a larger surface area, the diffusion length is still significantly longer than the NT length used, suggesting that most electrons are collected. In addition to dye loading and hence photocurrent increment, the photovoltage and filling factor were also improved in the mixed structure due to a low serial resistance, leading to the enhancement of the overall efficiency.     

Functionalization of electrospun magnetically separable TiO<Subscript>2</Subscript>-coated SrFe<Subscript>12</Subscript>O<Subscript>19</Subscript> nanofibers: strongly effective photocatalyst and magnetic separation

Magnetically separable TiO₂-coated SrFe₁₂O₁₉ electrospun nanofibers were obtained successfully by means of sol–gel, electrospinning, and coating technology, followed by heat treatment at 550–650 °C for 3 h. The average diameter of the electrospun fibers was 500–600 nm. The fibers were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), and vibrating sample magnetometer (VSM). The optimized calcining temperature was determined by XRD and the analysis of decolorizing efficiency of methylene blue (MB) under UV–vis irradiation. The photocatalytic activity of the TiO₂-coated SrFe₁₂O₁₉ fibers was investigated using ultraviolet–visible absorbance by following the photooxidative decomposition of a model pollutant dye solution, MB in a photochemical reactor. In contrast to pure TiO₂ fibers, the TiO₂-coated SrFe₁₂O₁₉ fibers have higher absorption in 250–750 nm wavelength regions. The presence of SrFe₁₂O₁₉ not only broadened the response region of visible-light, but also enhanced the absorbance for UV light. The decolorizing efficiency of MB under UV–vis irradiation was up to 98.19%, which was a little higher than that of Degussa P25 (97.68%). Furthermore, these fibers could be recollected easily with a magnet in a photocatalytic process and had effectively avoided secondary pollution of treated water.     

Solar photocatalytic generation of hydrogen under ultraviolet-visible light irradiation on (CdS/ZnS)/Ag<Subscript>2</Subscript>S + (RuO<Subscript>2</Subscript>/TiO<Subscript>2</Subscript>) photocatalysts

In order to efficiently use the UV-vis light in the photocatalytic reaction, a novel (CdS/ZnS)/Ag₂S + RuO₂/TiO₂ was synthesized by chemical coprecipitation and metal ion implantation. The composition and structure of this composite were characterized by BET, UV-vis spectroscopy, SEM, XRD and EDX. This composite exhibited much higher photocatalytic activity for the generation of hydrogen (H₂).     

SnO<Subscript>2</Subscript>-based thin films with excellent photocatalytic performance

SnO₂ semiconductor is a new-typed promising photocatalyst, but wide application of SnO₂-based photocatalytic technology has been restricted by low visible light utilization efficiency and rapid recombination of photogenerated electrons–holes. To overcome these drawbacks, we prepared B/Fe codoped SnO₂–ZnO thin films on glass substrates through a simple sol–gel method. The photocatalytic activities of the films were evaluated by degradation of organic pollutants including acid naphthol red (ANR) and formaldehyde. UV–Vis absorption spectroscopy and photoluminescence (PL) spectra results revealed that the B/Fe codoped SnO₂–ZnO film not only enhanced optical absorption properties but also improved lifetime of the charge carriers. X-ray diffraction (XRD) results indicated that the nanocrystalline SnO₂ was a single crystal type of rutile. Field emission scanning electron microscopy (FE-SEM) results showed that the B/Fe codoped SnO2–ZnO film without cracks was composed of smaller nanoparticles or aggregates compared to pure SnO2 film. Brunauer–Emmett–Teller (BET) surface area results showed that the specific surface area of the B/Fe codoped SnO₂–ZnO was 85.2 m² g^?1, while that of the pure SnO₂ was 20.7 m² g^?1. Experimental results exhibited that the B/Fe codoped SnO₂–ZnO film had the best photocatalytic activity compared to a pure SnO₂ or singly-modified SnO₂ film.     

TiO<Subscript>2</Subscript>/graphene composite from thermal reaction of graphene oxide and its photocatalytic activity in visible light

In this study, the P25 TiO₂ nanoparticles and graphene sheets (GSs) composite were prepared from a facile thermal reaction of graphene oxide. Its microstructures and photocatalytic properties were characterized and measured using X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), Brunauer–Emmett–Teller (BET) specific area analysis, X-ray photoelectron spectroscopy (XPS), FT-IR spectra, and ultraviolet–visible (UV–vis) diffuse reflectance spectroscopy. Compared with pure P25 nanoparticles, the results reveal that (1) there is a red shift about 20 nm in the absorption edge of the P25/graphene composite; (2) the photocurrent of the composite is about 15 times higher than that of pure P25; (3) the visible light photocatalytic activity of the composite is enhanced greatly on decomposition of methylene blue (MB). The photocatalytic mechanism of the P25/graphene composite is also discussed.     

Fabrication of TiO<Subscript>2</Subscript>/ZnO composite nanofibers with enhanced photocatalytic activity

TiO₂/ZnO composite nanofibers have been successfully prepared by electrospinning technique. X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, Raman spectrum, X-ray photoelectron spectroscopy and UV–Vis diffuse reflectance spectroscopy, were used to characterize the as-synthesized nanofibers. The photocatalytic studies revealed that the TiO₂/ZnO nanofibers exhibited enhanced photocatalytic efficiency of photodegradation. Additionally, the recycling experiment of TiO₂/ZnO nanofibers had been done, demonstrating that TiO₂/ZnO nanofibers have high efficiency and stability.     

Highly Functional TNTs with Superb Photocatalytic,Optical, and Electronic Performance Achieving Record PV Efficiency of 10.1% for 1D‐Based DSSCs

Different nanostructures of TiO₂ play an important role in the photocatalytic and photoelectronic applications. TiO₂ nanotubes (TNTs) have received increasing attention for these applications due to their unique physicochemical properties. Focusing on highly functional TNTs (HF‐TNTs) for photocatalytic and photoelectronic applications, this study describes the facile hydrothermal synthesis of HF‐TNTs by using commercial and cheaper materials for cost‐effective manufacturing. To prove the functionality and applicability, these TNTs are used as scattering structure in dye‐sensitized solar cells (DSSCs). Photocatalytic, optical, Brunauer‐Emmett‐Teller (BET), electrochemical impedance spectrum, incident‐photon‐to‐current efficiency, and intensity‐modulated photocurrent spectroscopy/intensity‐modulated photovoltage spectroscopy characterizations are proving the functionality of HF‐TNTs for DSSCs. HF‐TNTs show 50% higher photocatalytic degradation rate and also 68% higher dye loading ability than conventional TNTs (C‐TNTs). The DSSCs having HF‐TNT and its composite‐based multifunctional overlayer show effective light absorption, outstanding light scattering, lower interfacial resistance, longer electron lifetime, rapid electron transfer, and improved diffusion length, and consequently, J _SC, quantum efficiency, and record photoconversion efficiency of 10.1% using commercial N‐719 dye is achieved, for 1D‐based DSSCs. These new and highly functional TNTs will be a concrete fundamental background toward the development of more functional applications in fuel cells, dye‐sensitized solar cells, Li‐ion batteries, photocatalysis process, ion‐exchange/adsorption process, and photoelectrochemical devices.     

Orientation and microstructure of chemoepitaxial ZrO<Subscript>2</Subscript> films

The orientation and microstructure of ZrO₂ films produced by oxidizing oriented thin Zr films have been studied by transmission electron microscopy and high-energy electron diffraction. The results demonstrate that biaxial textures of the oxide are governed by the textures of the parent zirconium film. We have established a set of orientation relationships between the Zr and ZrO₂ lattices. The nanocrystalline structure of the oxide is due to the fact that there are several equivalent orientations within one Zr grain (multiple-orientation chemoepitaxy). Using high-resolution transmission electron microscopy, we detected twin boundaries, stacking faults, and intragranular dislocations.