Multilayer TiO2 Research Articles

Ti3C2 MXene derived carbon-doped TiO2 multilayers anchored with Fe2O3 nanoparticles as anode for enhanced lithium-ion storage

Transition-metal carbides, carbonitrides, and nitrides (MXene) as an emerging two-dimensional semiconductor has open an ideal pathway for fabricating various TiO2-based functional materials. In this work, we demonstrate a simple and one-step heat treatment for the fabrication of Ti3C2 MXene-derived carbon-doped TiO2/Fe2O3 composite for superior lithium-ion batteries (LIBs). As an anode, the as-fabricated composite delivers an excellent lithium-ion storage of 538 mA h/g at a current density of 0.1 A/g and superior rate performance of 152.6 mA h/g at a higher current density of 5 A/g, which is 6 times higher than that of C-doped TiO2 electrode. In addition, a remarkable cyclic stability with 88.46 % capacity retention is also obtained for the composite anode at a current density of 1 A/g after 1000 cycles. Based on various characterizations, the greatly enhanced electrochemical performance can be attributed to the synergistic effects of carbon doping, layered structures of TiO2, and the anchoring of Fe2O3 nanoparticles, which effectively promote the charge transport kinetics. This study will broaden the Ti3C2 MXene application in LIBs and meanwhile provide an alternative method for synthesizing more efficient anode materials.

UV Ozone based rapid low temperature fabrication of flexible dye sensitized solar cells

Herein, we have developed a multilayer TiO2 film thickness of around 4 µm at lower temperature (120 °C) by spin coating and doctor blade technique on polyethylene terephthalate (ITO-PET) substrate. Further, the additional processing step Ultravoilet-Ozone (UVO3) treatment was performed on TiO2 electron transport layer (ETL) to enhance the performance of FDSSCs. UVO3 treatment significantly improved the crystallinity and charge transport characteristic of ETL by removing the organic impurities. The photovoltaic devices based on 4 h of UVO3 treated TiO2 film exhibited superior device performance with an overall power conversion efficiency (PCE) of 2.53% compared to 1.43% (without UVO3 treatment). Electrochemical impedance measurement indicated that TiO2 layer treated with UVO3 decreased series resistance, electron recombination and improved electron life substantially. The improved device properties, simple preparation procedure and low processing cost, enable this FDSSCs fabrication method to be a credible alternative of conventional techniques.

Optical and mechanical properties of Zr-oxide doped TiO2/SiO2 anti-reflective coatings for PV glass covers

Multi-layer systems are frequently used as anti-reflective coatings (ARCs) due to their excellent optical properties. However, these systems suffer from erosive degradation (wear), thus urgently seeking alternative ways to improve their mechanical properties while maintaining their optical response. To tackle this problem, we propose to dope multi-layer TiO 2 /SiO 2 coatings with Zr-oxides to enhance their crystalline structure and density/compactness, as well as to form Si–Zr–O bonds. We explore the effect of Zr-oxide doping on the microstructure as well as the optical and mechanical properties of multi-layer TiO 2 /SiO 2 coatings with the overall aim to synergistically induce enhanced optical and mechanical properties. Therefore, homogeneous 250 nm thick multi-layer TiO 2 /SiO 2 coatings doped with Zr-oxides (different atomic concentrations) were deposited on glass substrates by magnetron sputtering. Based on our analysis, Zr-doping improves the optical and mechanical properties simultaneously. Among all ARCs, the sample annealed at 400 °C and doped with 1 at.-% Zr presented an excellent anti-reflective behavior and the best mechanical performance. These characteristics point towards an improved mechanical resistance (outstanding durability) and optical efficiency thus rendering them excellent candidates for the protection of glass covers on solar panels. • Design of anti-reflective coatings with TiO 2 /SiO 2 multi-layers doped with Zr-oxides. • Assessment of mechanical properties via XPM ultra-fast nanoindentation. • Zr-oxide doping and annealing synergistically improved mechanical properties.

Trapping and detecting nanoplastics by MXene-derived oxide microrobots

Nanoplastic pollution, the final product of plastic waste fragmentation in the environment, represents an increasing concern for the scientific community due to the easier diffusion and higher hazard associated with their small sizes. Therefore, there is a pressing demand for effective strategies to quantify and remove nanoplastics in wastewater. This work presents the “on-the-fly” capture of nanoplastics in the three-dimensional (3D) space by multifunctional MXene-derived oxide microrobots and their further detection. A thermal annealing process is used to convert Ti3C2Tx MXene into photocatalytic multi-layered TiO2, followed by the deposition of a Pt layer and the decoration with magnetic γ-Fe2O3 nanoparticles. The MXene-derived γ-Fe2O3/Pt/TiO2 microrobots show negative photogravitaxis, resulting in a powerful fuel-free motion with six degrees of freedom under light irradiation. Owing to the unique combination of self-propulsion and programmable Zeta potential, the microrobots can quickly attract and trap nanoplastics on their surface, including the slits between multi-layer stacks, allowing their magnetic collection. Utilized as self-motile preconcentration platforms, they enable nanoplastics’ electrochemical detection using low-cost and portable electrodes. This proof-of-concept study paves the way toward the “on-site” screening of nanoplastics in water and its successive remediation.

Unveiling the structural, electronic, and optical effects of carbon-doping on multi-layer anatase TiO2 (1 0 1) and the impact on photocatalysis

Carbon-doped (C-doped) TiO2 has demonstrated effective photocatalytic activity in the visible-light region. Here, we make use of density functional theory (DFT) methods to understand the photocatalytic activity of C-doped anatase-TiO2 (101) surfaces as a function of layer thickness. The formation energy results show that C-doped O sites (CO) are more stable in the bulk than in the subsurface or on the surface, while C-doped Ti sites (CTi) are more stable on the surface than in the bulk or subsurface. CO defects introduce impurity states in the band gap, do not affect the band gap energy, and induce an electron trap close to the conduction band edge and enhances light absorption in the visible and IR spectrum. CTi defects induce structural distortions caused by a CO covalent bond with no impurity states formed in the band gap although there is a reduction in the band gap energy, which leads to a red-shifted absorption. These results shed insight on how carbon doping influences the electronic and optical properties of anatase that can be implemented in the design of semiconductor materials with high photocatalytic activity.

Atomic-level thick TiO2–CoTiO3 multilayer p-n junction with extended built-in electric field as efficient photoanode

Formation of p-n junction was an effective method to improve the photocatalytic performance due to its built-in electric field. However, the electric field was distributed only on the interface between two semiconductors, which was insufficient in comparison to the entire material. In this work, a multilayer TiO 2 –CoTiO 3 p-n junction was designed and fabricated by atomic layer deposition. The charge transport and photoelectrochemical properties of multilayer TiO 2 –CoTiO 3 films of various thicknesses are thoroughly investigated. The PL and electrochemical tests demonstrate that TiO 2 –CoTiO 3 exhibits enhanced charge separation and transport. Additionally, the extra visible light response was achieved by introduction of CoTiO 3 . Also, theoretical calculations indicate that the electrons prefer to immigrate from TiO 2 to CoTiO 3 in a multilayer TiO 2 –CoTiO 3 structure. Benefited from the boosted light absorption and charge transfer, the multilayer TiO 2 –CoTiO 3 composite film exhibits a significantly increased photocurrent, much higher than pure TiO 2 and a single TiO 2 –CoO p-n junction. This multilayer p-n junction structure opens a rational and novel way for nanostructure construction in the energy conversion region.

Role of atomic layer deposited TiOxNy interlayer in tribological and corrosion properties of CrN coating

The growth defects in the sputtered CrN coatings can worsen their tribological and corrosion properties. To improve the above deficiency, the atomic layer deposited TiN was deposited on the sputtered CrN layer, oxidized and then again coated by CrN to form the sandwich-structured CrN/TiO x N y /CrN composite coating . The insertion of the TiO x N y interlayer resulted in (111) preferred orientation and the grain refinement of CrN crystals, leading to the improvement in its mechanical performance and corrosion resistance . As the thickness of the TiO x N y layer increased, the mechanical and corrosion properties of the composite coatings were further improved. The composite coating inserted with a 30 nm-thick TiO x N y interlayer delivered the greatest corrosion resistance, the lowest friction coefficient and wear rate as well as high hardness and adhesion strength , which could be attributed to the synergistic effect of the multilayered TiO x N y interlayer. • Atomic layer deposited TiN interlayer is inserted into CrN hard coating. • The oxidization of TiN results in a multilayer-structured TiO x N y interlayer. • Synergistic effect of the interlayers improves the tribological properties of CrN. • Corrosion resistance of CrN is also enhanced by inserting the TiN x O y interlayer.

Optical and structural investigations of TiO2 multilayers on glass prepared via sol–gel spin-coating technique

Titanium di-oxide (TiO2) multilayer thin films were deposited on glass substrates by using sol–gel spin-coating technique. The TiO2 thin film coatings were varied from two- to six layers and each layers calcinated at 600°C for 1 hour. The prepared samples were characterized by UV–visible spectrophotometer (UV–Vis), Fourier transform infra-red (FTIR) spectroscopy and X-ray diffractometer (XRD) techniques. The UV–Vis spectra showed the highest reflectance with the effect of six (6L) layers of TiO2 thin films as compared to the two- (2L) and four (4L) layers of thin films. The XRD patterns revealed the anatase-TiO2 phase with six layers of TiO2 and amorphous-TiO2 nature confirmed by two and four layered films. The obtained results proved that the use of enhanced multilayers (6L) of TiO2 thin films were effectively improved the quality of film crystallinity (8.3 nm) and corresponding optical performance as compared to reduced layers.

Construction of multi-layered Zn-modified TiO2 coating by ultrasound-auxiliary micro-arc oxidation: Microstructure and biological property

Surfaces with desirable cytocompatibility and bactericidal ability are favoured for orthopaedic implants to stimulate osteogenic activity and to prevent implant-associated infection. In this work, we creatively introduce ultrasonic vibration (UV) to micro-arc oxidation (MAO) process and explore its influence on the microstructure, corrosion property and biological responses of Zn-modified TiO2 coating. With the introduction of UV, a uniform surface layer with homogeneously-distributed clusters could be produced as the outer layer, which possesses a fusion band with the underlying TiO2. The microstructural modification associated with UV results in the enhanced corrosion resistance, increased adhesive strength and improved biological performances of the resultant coating relative to that with the absence of UV. Hence, the ultrasonic auxiliary micro-arc oxidation (UMAO) is regarded as a promising surface modification method to produce Ti-based orthopaedic implants of high quality.

(INVITED) Tungsten oxide films by radio-frequency magnetron sputtering for near-infrared photonics

Tungsten oxide WO3-x is a transition metal oxide and a wide bandgap semiconductor, with a wide range of possible optical and photonic applications. In dependence on the fabrication techniques different stoichiometric ratios (x) and crystalline phases are obtained, which end up with an overall polymorph and extremely versatile material, characterized by tailorable dielectric properties. In particular, WO3-x thin film deposition by Radio-Frequency (RF) sputtering techniques provides a precise control of thickness, composition and nanostructure. In this work we introduce and discuss a specific process of deposition, that is magnetron RF-sputtering as a suitable way to grow WO3-x thin films with selected properties. Possibility of integrating WO3-x thin film on to one-dimensional (1D) photonic crystal structures is also explored. Films are transparent in the near and short-wavelength infrared optical spectral range. Their quality is assessed by morphological, structural and compositional characterizations. Dielectric properties are characterized by optical spectroscopy and ellipsometry, the latter also evaluates the degree of optical anisotropy of thin films in their crystalline phase. An 1D photonics bandgap structure is designed, formed by a SiO2–TiO2 multilayer and capped with a 450 nm-thick transparent WO3-x film, so that surface confinement and local enhancement of the optical field at 1416 nm in the topmost WO3-x layer is obtained.

Titanium-Based Alloy Surface Modification with TiO2 and Poly(sodium 4-styrenesulfonate) Multilayers for Dental Implants.

Implant placement is an important repair method in dentistry and orthopedics. Increasing efforts have focused on optimizing the biocompatibility and osseointegration properties of titanium (Ti) and Ti-based alloys. In this work, Ti-based alloys were modified by the layer-by-layer (LbL) technique, which is a simple and versatile method for surface modification. The morphology and chemical structure of LbL films of poly(sodium 4-styrenesulfonate) (PSS) and Ti dioxide (TiO2) nanoparticles were first characterized employing ultraviolet-visible and Fourier-transform infrared spectroscopies as well as atomic force microscopy for further application in Ti-based alloy implants. The changes provoked by the LbL PSS/TiO2 film on the Ti-based alloy surfaces were then investigated by scanning electron microscopy and micro-Raman techniques. Finally, in vivo tests (immunolabeling and biomechanical analysis) performed with screw implants in rats suggested that PSS/TiO2 multilayers promote changes in both topography and chemical surface properties of the screw, providing beneficial effects for osteoblast activity. This simple and relatively low-cost growth process can open up possibilities to improve dental implants and, probably, bone implants in general.

Extremely sensitive and reusable surface-enhanced Raman scattering substrate based on 3D Ag-titanium dioxide nanowires

A three dimensional surface enhanced Raman scattering (SERS) substrate has been obtained by assembling Ag nanoparticles onto multilayered TiO2 nanowires (NWs) synthesized via modified hydrothermal method. The as-prepared Ag-TiO2 NW substrate exhibits high SERS sensitivity, achieving a detection limit of 10−19 M for R6G solution. The rough surfaces and 3D porous network structure of Ag-TiO2 NWs cause strong adsorption of probe molecules. The small curvature radii, rough surfaces of the TiO2 NWs, and their intercrossed 3D network contribute to formation of abundant nanogaps. The substrate exhibits recyclability due to photocatalytic activity of TiO2. The Outstanding performance of the substrate facilitates the industrial application in the ultrasensitive chemical and biological molecule detection.

Structural and optical properties of multilayered un-doped and cobalt doped TiO2 thin films

The present investigation reports the effect of multilayers (1, 3 and 7 layers) and cobalt (Co) doping on structural and optical properties like transmittance, refractive index, extinction coefficient, etc. of TiO2 thin films prepared by a sol–gel spin coating technique. X-ray diffraction (XRD) and Raman spectroscopy were used to investigate the phase and structure of the prepared films which confirm the formation of single phase anatase TiO2 structure of the films. Morphology study by SEM indicate development of cracks with increase in number of layers at large scale but in the small (nano) scale the films are compact and smooth. Thickness study by cross sectional SEM shows increase in thickness with increase in number of layers. Energy Dispersive X-ray spectra were used to study the presence of cobalt in doped films. UV–Visible spectroscopy was used to study the transmittance of the films and spectroscopic ellipsometry was used to study the optical constants like refractive index and extinction coefficient which indicate the highest refractive index and the lowest extinction coefficient for single layered cobalt doped TiO2 thin films while 7 layered films show the lowest refractive index and the highest transmittance. Spectroscopic ellipsometry studies indicate increase in packing density of coated layers in Co-doped TiO2 films due to which refractive index as well as transmittance of these films are significantly more in comparison to undoped films. Photoluminescence spectra show increase in oxygen vacancies in Co-doped multilayered TiO2 films indicating increase in blue emission. Thus, the enhanced values of refractive index as well as transmittance and blue emission in Co-doped TiO2 multilayers films are promising for optical device applications.

Effect of annealing treatment on multilayer TiO2 films on the performance of dye-sensitized solar cells

In this work, four layers of TiO2 films have been prepared and applied as photoanode of dye-sensitized solar cell (DSSC). The multilayer TiO2 underwent annealing treatment at various temperatures, in the range 300−550 °C at 50 °C interval. The influence of annealing temperature on the properties of multilayer TiO2 and the performance of the device has been investigated. The samples possess higher optical absorption in UV region than in visible region. The morphology of the sample is active nanoparticle and scatter nanoparticle with its size is bigger than active nanoparticle. The highest η of 2.51 % was obtained from the device utilizing the sample annealed at 500 °C due to the lowest charge transfer resistance at the interface of Pt/electrolyte and electrolyte/N719 dye/TiO2.

Multilayer TiO2 Inverse Opal with Gold Nanoparticles for Enhanced Photocatalytic Activity.

Three-dimensional highly ordered multilayer titanium dioxide (TiO2) inverse opal (TIO) structures with two pore sizes were fabricated over a large surface using a self-convective method. The fabricated TIO multilayers were functionalized with gold nanoparticles (AuNPs) by immersing the samples in solution with gold nanoparticles. The photocatalytic activity of TiO2 was enhanced by 85% via plasmonic activation of AuNPs that increased the lifetime of photogenerated holes and electrons. The improved photocatalytic activity was characterized with both UVA and visible light irradiation using an in-house built gas-phase photoreactor.

Photocatalytic and Gas Sensitive Multiwalled Carbon Nanotube/TiO2-ZnO and ZnO-TiO2 Composites Prepared by Atomic Layer Deposition.

TiO2 and ZnO single and multilayers were deposited on hydroxyl functionalized multi-walled carbon nanotubes using atomic layer deposition. The bare carbon nanotubes and the resulting heterostructures were characterized by TG/DTA, Raman, XRD, SEM-EDX, XPS, TEM-EELS-SAED and low temperature nitrogen adsorption techniques, and their photocatalytic and gas sensing activities were also studied. The carbon nanotubes (CNTs) were uniformly covered with anatase TiO2 and wurtzite ZnO layers and with their combinations. In the photocatalytic degradation of methyl orange, the most beneficial structures are those where ZnO is the external layer, both in the case of single and double oxide layer covered CNTs (CNT-ZnO and CNT-TiO2-ZnO). The samples with multilayer oxides (CNT-ZnO-TiO2 and CNT-TiO2-ZnO) have lower catalytic activity due to their larger average densities, and consequently lower surface areas, compared to single oxide layer coated CNTs (CNT-ZnO and CNT-TiO2). In contrast, in gas sensing it is advantageous to have TiO2 as the outer layer. Since ZnO has higher conductivity, its gas sensing signals are lower when reacting with NH3 gas. The double oxide layer samples have higher resistivity, and hence a larger gas sensing response than their single oxide layer counterparts.

Facile synthesis of a lightweight three-dimensional polymer scaffold dip-coated with multiple layers of TiO2 aerogel for X-band microwave absorption applications

The multi-layer TiO2 aerogel-coated polymer scaffold (PS) composite containing 5 wt% of Fe3O4 nanoparticles was synthesized via the chemical liquid deposition of multiple layers of TiO2 aerogel onto the macroporous PS. The combination of the toughness, magnetic, and lightweight nature of the PS and the excellent microwave absorption properties of TiO2 specify that the composite could be used as a novel microwave absorbing material. The surface morphological results indicate that the pores of PS were mostly filled and covered by the TiO2 aerogel. The PS was used to reduce the weight of the microwave absorber, while the porous TiO2 aerogel and Fe3O4 particles were introduced to provide enhancement in the microwave absorption properties of the composite. Although the pristine PS showed 40% microwave absorption in the X-band region, the 10-times dip-coated TiO2 aerogel-PS composite enhanced the microwave absorption up to 70%, and this value reached 80% for the 15-times dip-coated sample.

Positron annihilation analysis of nanopores and growth mechanism of oblique angle evaporated TiO2 and SiO2 thin films and multilayers

The nano-porosity embedded into the tilted and separated nanocolumns characteristic of the microstructure of evaporated thin films at oblique angles has been critically assessed by various variants of the positron annihilation spectroscopy. This technique represents a powerful tool for the analysis of porosity, defects and internal interfaces of materials, and has been applied to different as-deposited SiO2 and TiO2 thin films as well as SiO2/TiO2 multilayers prepared by electron beam evaporation at 70° and 85° zenithal angles. It is shown that, under same deposition conditions, the concentration of internal nano-pores in SiO2 is higher than in TiO2 nanocolumns, while the situation is closer to this latter in TiO2/SiO2 multilayers. These features have been compared with the predictions of a Monte Carlo simulation of the film growth and explained by considering the influence of the chemical composition on the growth mechanism and, ultimately, on the structure of the films.

Hybrid Hydrophilic-Hydrophobic CuO@TiO2-Coated Copper Mesh for Efficient Water Harvesting.

Fresh water scarcity has been a worldwide problem to be solved urgently. Inspired by the outstanding hydrophobic-hydrophilic patterns on the back of Namib desert beetles, hierarchical CuO@TiO2-coated surface with alternating hydrophilic-hydrophobic chemistry patterns were fabricated utilizing the photocatalysis of titanium dioxide through ultraviolet irradiation. The results indicated that the as-prepared hybrid dual-coated copper mesh enhanced the fog-collection efficiency compared with the uniformly superhydrophobic or superhydrophilic surface. This enhancement can be regulated by controlling the deposition cycle times of TiO2 multilayers on CuO and UV irradiation time. The best water harvesting behavior was determined at the deposition cycle times of 10 times and UV irradiation time of 4 h. This work findings offer new insights into the fabrication of hybrid hydrophilic-hydrophobic surfaces for highly efficient water harvesting.

An investigation on titania multilayer coatings for enhanced corrosion resistance of carbon steel in simulated seawater by sol–gel dip coating

A TiO2 multilayer was investigated to be a low cost and high protection efficiency for carbon steel in simulated seawater. This study applied group theory for crystalline materials in a combination with DFT+U simulation to predict Raman spectra of TiO2 – anatase and rutile phases. The simulated spectra were used as a peak-search-match reference for experimental Raman spectra. It also indicated that the coatings produced out of polycrystalline structures including anatase and rutile phases with large grain sizes and boundaries. Furthermore, the electrochemical measurements including potentiodynamic polarization and electrochemical impedance spectroscopy for the 1–8 TiO2 layers were performed to reveal the anticorrosion properties of the coatings and the optimal values were pointed out. Based on those results, the protection mechanism of the TiO2 multilayer coating was also suggested in the manuscript.