Atomic layer deposition of TiO2 thin films on glass fibers for enhanced photocatalytic activity

Photocatalytic wastewater treatment is expected to become a sustainable way of eliminating toxic chemicals. Due to the surface-driven mechanism of the photocatalysis, surface area of the catalyst material plays a crucial role in the efficiency of the process, which is usually achieved by nanoparticles. However, using powder materials introduces a new problem: removing the catalyst materials out of clean water. As an alternative, atomic layer deposition (ALD) can form conformal thin films on high surface area substrates providing an immobilization route with high photocatalytic activity. Textile materials are inexpensive and accessible therefore good candidates for the substrate materials. Here, we deposit thin films on TiO₂ on fiberglass fabrics and investigate the photocatalytic activity. Since the as-deposited ALD TiO₂ films are amorphous, they have very limited photocatalytic activity. Upon thermal treatment of the films after deposition, photocatalytic activity is achieved. After four hours of exposure to the solar simulator and UV lamp, TiO₂-coated fibers demonstrated much higher photocatalytic activity than films on planar substrates previously described in the literature. The photocatalytic activity and structure of the coated fibers were investigated using XRD, XPS, UV–Vis, and PL analyses.

     

Preparation and dielectric properties of surface modified TiO2/PEN composite films with high thermal stability and flexibility

A series of surface modified titanium dioxide (TiO₂)/polyarylene ether nitriles (PEN) composite films with different modified TiO₂ contents were prepared by solution casting method combined with ultrasonic dispersion technology. TiO₂ particles were successfully surface modified by PEN–COOH polymer previously, which was confirmed by transmission electron microscopy, Fourier transform infrared spectroscopy and thermogravimetric analysis. Besides, SEM images of composite films revealed that the interfacial adhesion between surface modified TiO₂ particles and the PEN matrix was effectively improved because of their common cyano groups and similar structure units. Furthermore, thermal, mechanical and dielectric characterizations showed that the composite films possess excellent thermal properties and flexibility as well as good dielectric properties, their glass transition temperatures were as high as 223?°C and the initial decomposition temperatures were all above 480?°C. In addition, it was found that the tensile strength of modified TiO₂/PEN composites was better than raw TiO₂/PEN composites. More importantly, the dielectric constant of composite films increases linearly with increment of the surface modified TiO₂ particles content. When the mass fraction of modified TiO₂ particles reached 40?%, the dielectric constant of the composite film increased to 7.9 (1?kHz), while the dielectric loss is just 0.028 (1?kHz).     

Visible-light photocatalytic activity of semiconductor composites supported by electrospun fiber

The preparation and photocatalysis of TiO₂–ZnS/fluoropolymer fiber composites were investigated. The fluoropolymer nanofiber mats with carboxyl groups were prepared by electrospinning, and then titanium and zinc ions were introduced onto the fiber surfaces by the coordinating of carboxyl of fluoropolymer in solution. The TiO₂–ZnS composites with diameters 15 nm to 1 μm were immobilized on the surface of fluoropolymer electrospun fiber using hydrothermal synthesis. The Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analysis reveal that some chemical interaction exists between TiO₂–ZnS composites and fluoropolymer fibers, so the semiconductor composites were immobilized tightly on the surface of fluoropolymer fibers. The ultraviolet–visible absorption spectra show the TiO₂–ZnS/fluoropolymer fiber composites have low band gap and good visible-light response ability. The degradation rate of methylene blue in TiO₂–ZnS/fluoropolymer fiber composites system was considerably higher than that of TiO₂ or TiO₂–ZnS nanoparticles system under visible-light irradiation, because the TiO₂–ZnS/fluoropolymer fiber composites possess good visible-light response ability, high specific surface areas, and adsorption–migration–photodegradation process. The photocatalytic activity of TiO₂–ZnS/fluoropolymer fiber composites changes indistinctively after 10 repeating photocatalysis tests.     

Growth and characterization of epitaxial anatase TiO2(001) on SrTiO3-buffered Si(001) using atomic layer deposition

Epitaxial anatase titanium dioxide (TiO₂) films have been grown by atomic layer deposition (ALD) on Si(001) substrates using a strontium titanate (STO) buffer layer grown by molecular beam epitaxy (MBE) to serve as a surface template. The growth of TiO₂ was achieved using titanium isopropoxide and water as the co-reactants at a substrate temperature of 225-250 °C. To preserve the quality of the MBE-grown STO, the samples were transferred in-situ from the MBE chamber to the ALD chamber. After ALD growth, the samples were annealed in-situ at 600 °C in vacuum (10^− 7 Pa) for 1-2 h. Reflection high-energy electron diffraction was performed during the MBE growth of STO on Si(001), as well as after deposition of TiO₂ by ALD. The ALD films were shown to be highly ordered with the substrate. At least four unit cells of STO must be present to create a stable template on the Si(001) substrate for epitaxial anatase TiO₂ growth. X-ray diffraction revealed that the TiO₂ films were anatase with only the (004) reflection present at 2θ = 38.2°, indicating that the c-axis is slightly reduced from that of anatase powder (2θ = 37.9°). Anatase TiO₂ films up to 100 nm thick have been grown that remain highly ordered in the (001) direction on STO-buffered Si(001) substrates.     

Electroplating to visualize defects in Al2O3 thin films grown using atomic layer deposition

Thin films grown using atomic layer deposition (ALD) are known for being continuous and nearly pinhole-free. These characteristics enable ALD films to be important in many applications such as gas or copper diffusion barriers, gate dielectrics, surface modification and functionalization layers. Few methods have been demonstrated to characterize defects in ALD films. In this study, a method to render the defects visible in Al₂O₃ ALD thin films on conductive substrates has been developed by growing copper bumps locally at the defect sites using electroplating. The electroplated copper can be easily observed or inspected using conventional optical- or electron-microscopy. Using this approach, the defect density in Al₂O₃ ALD thin films grown on nickel substrates has been shown to be as low as 38 /cm².     

On the initial growth of atomic layer deposited TiO2 films on silicon and copper surfaces

Atomic layer deposition (ALD) of TiO₂ using tetrakis(diethylamino)titanium precursor and H₂O was studied on silicon and copper surfaces in order to examine differences in nucleation. Both surfaces were patterned on the same substrate to assure identical deposition conditions. Spectral ellipsometry, X-ray photoelectron spectroscopy and surface profilometry were used to probe nucleation phenomena, growth rates, and surface morphology on both surfaces. The TiO₂ deposition on copper was found to exhibit a significant induction period of about 20-25 ALD cycles with no observable TiO₂ during the first 10-15 cycles on the copper side; in contrast, no such inhibited growth was observed in the TiO₂ deposition on silicon. This result opens up potential for selective ALD of TiO₂ films on silicon-based substrates patterned with a metal without the use of a mask, a self-assembled monolayer or soft lithography which is impractical for some nanoscale semiconductor fabrication processes. After film nucleation, the TiO₂ growth rate on both surfaces was found to be 0.10 nm/cycle.     

Microstructure and electrical conductivity in shape and size controlled molybdenum particle thick film

We study the effects of particle morphology on the microstructure and electrical conductivity of Mo particle thick films. In our study, the shape and size of molybdenum (Mo) particles are modified by mechanical ball-milling and atomic layer deposition (ALD). As the total number of collisions between Mo particles and ball-milling media increases, Mo particles are deformed, and the shape of Mo particles changed from irregular polyhedrons to thin flakes. In the ball-milling process, stress frequency is an important processing parameter governing the deformation and breakage of Mo particles. In addition, ALD-grown TiO₂ layer is found to significantly suppress the growth of Mo particles at high temperature. After 1000 °C annealing, the particle size of the TiO₂ layer-coated film is only half of that of bare Mo particle films. The shape of the particles changes electrical conductivity of the Mo thick films. Large contact area between flake shape particles can increase the carrier mobility of the film and the 5-nm thick TiO₂ layer can provide the inter-particle carrier transport path via a tunneling mechanism. Our results show that the combined use of the ball-milling and the ALD coating leads to Mo thick films with high electric conductivity and large surface area.     

Metal oxide blended ZSM-5 nanocomposites as ethanol sensors

Nano-ZSM-5 is synthesized without organic template via microwave-assisted hydrothermal technique. The synthesized nano-ZSM-5 zeolite is blended with metal oxides (ZnO and TiO₂) to have novel composites as ethanol sensors. The composites are characterized by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) techniques. A study on ethanol sensing behaviour of metal oxide blended composite screen-printed thick films is carried out and the effect of metal oxide concentration on various ethanol sensing features, specifically operating temperature, response/recovery time and active region of the sensor, are investigated. XRD and FTIR confirm the blending of metal oxides in ZSM-5 matrix. Both, ZnO and TiO₂ blended, composite films are sensitive to ethanol. It can be concluded that metal oxide blending improves the preformance of sensor for ethanol detection. The response/recovery time and active sensing regions depend upon the concentration of metal oxide in host zeolite. The ZnO/ZSM-5 and TiO₂/ZSM-5 composite films are the excellent ethanol sensors.     

The effect of the H2 flow rate on the structure and optical properties of TiO2 films deposited by inductively coupled plasma assisted chemical vapor deposition

The optical and photocatalytic properties of TiO₂ are closely related to crystalline structures, such as rutile and anatase. In this paper, TiO₂ films were produced by inductively coupled plasma (ICP) assisted chemical vapor deposition (CVD) without extra heating of the substrate, and the effect of H₂ addition on the structure and optical properties of the films was investigated. After increasing the partial pressure of H₂, the structure of the TiO₂ films changed from anatase to rutile, which usually appears at high temperatures (> 600 °C). The light transmittance decreased with increasing the H₂ flow rate due to the increased surface roughness. The photocatalytic activity of the anatase TiO₂ film was better than that of the rutile TiO₂ film.     

Nanoscale Manipulation of Spinel Lithium Nickel Manganese Oxide Surface by Multisite Ti Occupation as High‐Performance Cathode

A novel two‐step surface modification method that includes atomic layer deposition (ALD) of TiO₂ followed by post‐annealing treatment on spinel LiNi_0.5Mn_1.5O₄ (LNMO) cathode material is developed to optimize the performance. The performance improvement can be attributed to the formation of a TiMn₂O₄ (TMO)‐like spinel phase resulting from the reaction of TiO₂ with the surface LNMO. The Ti incorporation into the tetrahedral sites helps to combat the impedance growth that stems from continuous irreversible structural transition. The TMO‐like spinel phase also alleviates the electrolyte decomposition during electrochemical cycling. 25 ALD cycles of TiO₂ growth are found to be the optimized parameter toward capacity, Coulombic efficiency, stability, and rate capability enhancement. A detailed understanding of this surface modification mechanism has been demonstrated. This work provides a new insight into the atomic‐scale surface structural modification using ALD and post‐treatment, which is of great importance for the future design of cathode materials.     

Growth mode transition of atomic layer deposited Al2O3 on porous TiO2 electrodes of dye-sensitized solar cells

This study investigates the growth behavior of atomic-layer-deposited (ALD) Al₂O₃ overlayers on porous TiO₂ electrodes, which comprise an anatase nanoparticle layer and a rutile particle layer, for optimizing dye-sensitized solar cells. The growth mode of the ALD Al₂O₃ overlayers changes from island growth to layer-by-layer growth during the first few ALD reaction cycles, and the growth mode transition is much more pronounced for the anatase electrode layer. The transition is likely a result of the reduction in the contractive lattice strain of the TiO₂ nanoparticles. The lattice strain in the hydroxylated TiO₂ nanoparticles is progressively reduced during the ALD Al₂O₃ deposition, resulting in the growth mode transition.     

Enhanced dielectric and ferroelectric properties induced by TiO2@MWCNTs nanoparticles in flexible poly(vinylidene fluoride) composites

Flexible polymer based composites containing multi-walled carbon nanotubes (MWCNTs) have been reported to present high dielectric constant. However, the composites generally exhibit high dielectric loss and low dielectric breakdown strength, which prohibits their practical use in electronic and electric industry. MWCNTs were coated with a continuous layer of TiO₂ nanoparticles (TiO₂@MWCNTs) by a simple hydrothermal process and TiO₂@MWCNTs/poly(vinylidene fluoride) (PVDF) composites were prepared by a solution casting method. Compared to the pristine MWCNTs/PVDF composites, the TiO₂@MWCNTs/PVDF composites presented enhanced dielectric constant and lower dielectric loss. Additionally, the breakdown strength of the TiO₂@MWCNTs/PVDF composites was also improved, which is favorable for enhanced ferroelectric properties in the composites.     

Solar light induced rhodamine B degradation assisted by TiO2–Zn–Al LDH based photocatalysts

A series of TiO₂/Zn–Al layered double hydroxides (LDHs) based composites were synthesized and their photocatalytic efficiency in rhodamine B photodegradation reaction under solar light irradiation was tested. The aim of this study was to develop photocatalysts based on TiO₂/Zn–Al layered double hydroxides that can be activated by solar light irradiation. The influence of TiO₂ doping (1, 2 and 3 mass%) on the photocatalytic properties of developed TiO₂/Zn–Al LDHs nanocomposites was studied. Different photocatalytic behaviour of composites was interpreted in correlation to their structural, textural, morphological properties and kinetic parameters. All nanocomposites were active in the selected reaction. It was observed that the presence of Zn₂TiO₄ coupled with the ZnO phase contributes to the activity provoked by solar light irradiation. The photodegradation follows the pseudo first-order kinetics in accordance with the Langmuir–Hinshelwood model. The kinetic study suggested that the applied synthesis methodology resulted in homogeneous distribution of TiO₂ and other active components on the photocatalyst surface leading to better accessibility of active sites. The developed synthesis method enables favourable interactions among active phases. Novel TiO₂/LDH based photocatalysts are advantageous considering the low-cost and simple preparation, ensuring high photodegradation efficiency, making them appealing for the application in the field of water treatment.     

Hydrothermal preparation and characterization of TiO2:AC composites

A new photocatalyst titania:activated carbon (TiO₂:AC) composite was prepared by impregnating anatase type TiO₂ nanoparticulates onto the activated carbon surface through a mild hydrothermal route. A varied ratio of TiO₂ to AC was considered for impregnation. As-prepared TiO₂:AC composite was characterized by various techniques such as powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), BET surface area and positron annihilation lifetime spectroscopy (PALS). Powder XRD results showed the persisting nature of anatase phase of TiO₂ deposited on the activated carbon surface. The BET, FTIR and PALS results revealed the impregnation threshold. The TiO₂ particulates were well adhered and uniformly dispersed on the carbon surface as confirmed by SEM.     

Poly(vinylidene fluoride)/poly(methyl methacrylate)/TiO2 blown films: preparation and surface study

Blown films of poly(vinylidene fluoride) (PVDF) and poly(methyl methacrylate) (PMMA) blends and PVDF/PMMA/TiO₂ composites were prepared by melting-extrusion for the first time. The crystalline structure and surface morphology PVDF/PMMA (DFMA) blown films were investigated using differential scanning calorimeter (DSC), atomic force microscope (AFM), and X-ray diffractometry (XRD). PVDF/PMMA/TiO₂ blown films were further prepared and underwent surface treatment. The results show that PVDF/PMMA/TiO₂ blown films present good mechanical properties, and acrylic acid surface-grafted films exhibit good adhesion capability and long-lasting hydrophilicity, making them attractive as encapsulation materials.     

Glancing angle deposited titania films for dye-sensitized solar cells

A series of sculptured porous nano-columnar titanium oxide films were prepared by glancing angle deposition (GLAD) method using an electron-beam evaporation system. The films were deposited on ITO glasses at various incident angles from 53° to 86°and used as photoanode in a dye-sensitized solar cell (DSSC). The as-deposited TiO₂ films are comprised of helical nano-columns and assembled in an orderly manner with gaps or pores in between. The porous nanostructured films provide a synergetic effect of high surface area, effective route for electron transfer, tight interfaces, and enhanced light trapping, which are all beneficial for higher cell efficiency. The DSSCs incorporated with the GLAD films of 4 μm thick exhibited a high fill factor (FF) up to 0.77. The TiO₂ film deposited at an incident angle of 73° provides the largest internal surface area and the largest amount of dye absorption and results in the highest light conversion efficiency of 2.78%.     

活性炭载体对TiO2/活性炭中二氧化钛晶粒生长及相变的影响

以活性炭为载体,采用溶胶-凝胶法制备了TiO2/活性炭(TiO2/AC)复合体,并利用SEM和XRD手段对复合体进行表征,通过Dt2=ktnexp(-E/RT)方程的计算,分析,研究活性炭对复合体中TiO2晶粒生长及其相变的影响.结果表明TiO2/AC复合体晶粒粒径增长的时间比TiO2本体短;TiO2/AC复合体纳米粒子平均尺寸为50nm比TiO2本体小;锐钛矿向金红石转变的相变温度和晶粒生长最快温度TiO2/AC复合体比TiO2本体高.锐钛矿和金红石晶粒生长的表观活化能TiO2/AC复合体分别为6.21±1.27和46.54±1.56kJ/mol,TiO2本体分别为5.764±1.02和36.4±1.14kJ/mol.在锐钛矿阶段和金红石阶段TiO2/AC复合体反应指数分别为0.19和0.35,而TiO2本体分别为0.13和0.26.原因是活性炭的强吸附力和非晶相层对TiO2晶粒生长的阻遏作用.     

The preparation and characterization of photocatalytically active TiO2 thin films and nanoparticles using Successive-Ionic-Layer-Adsorption-and-Reaction

Photocatalytically active TiO₂ thin-films were deposited on silicon wafers using the Successive-Ionic-Layer-Adsorption-and-Reaction technique and subsequent hydrothermal and/or furnace annealing. Atomic-force-microscopy images and X-ray diffraction measurements of the TiO₂ films obtained under various annealing conditions show how changes of the micro-scale surface structure depend on the post-SILAR treatment. The hydrogen evolution over various TiO₂ films was measured. Hydrothermally treated TiO₂ films show a higher photocatalytic activity and a much better mechanical stability compared to furnace-annealed films. The optical transmittance of TiO₂ thin films on glass substrates was also studied. A red shift was observed with increasing film thickness. TiO₂ nanoparticles (∼10 nm) that were peeled off from the TiO₂ films were investigated using high-resolution-transmission-electron-microscopy.     

Apatite formation from simulated body fluid on various phases of TiO2 thin films prepared by filtered cathodic vacuum arc deposition

Hydroxyl (OH⁻)-free TiO₂ thin films with amorphous and crystalline phases were deposited onto (100) silicon substrates using filtered cathodic vacuum arc deposition in order to investigate the in vitro apatite formation in simulated body fluid (SBF). The surface morphology, composition and structure of the TiO₂ thin films were characterized. The X-ray photoelectron spectroscopy results confirmed the presence of calcium and phosphorus on all TiO₂ thin film surfaces after immersion in SBF at 37 °C. Fourier transform infra red results showed the presence of carbonated apatite on the surface of these films. Amorphous structured TiO₂ thin film showed poor ability to form apatite on its surface in SBF. Apatite formation was more pronounced on the surfaces of the anatase films in comparison to those of rutile. The carbonated apatite deposition rate increased significantly when the TiO₂ film was illuminated with UV light prior to immersing in the SBF. In particular, the UV-treated anatase and rutile films showed increased rates of carbonated apatite formation on their surfaces in comparison to samples not treated with radiation. The increase in hydrophilicity due to UV treatment appears beneficial for the apatite growth on these surfaces.