TiO2 Nanowire Arrays Research Articles

Hetero-radial MgO capped TiO2 nanowire arrays as a deep UV and self-powered photodetector

Nanowires acts as a potential component in photodetectors (PDs) owing to its superior capacity to generate morphology-dependent broad absorption spectrum. In this study, we have demonstrated an efficient self-powered PD based on the radial heterostructure of the MgO capping layer on top of TiO2 nanowires (RHNWs). RHNWs are highly sensitive under deep ultraviolet (UV) illumination when compared to TiO2-MgO axial heterostructure nanowires (AHNWs) PD. The finite-difference time-domain (FDTD) method is used to simulate electric field distribution, absorption spectra and generation rate profile of the structures. The RHNWs device possesses two times lower leakage current (∼ 1.78 × 10−9 A) than AHNWs (∼ 3.84 ×10−9 A) at – 1.5 V. Theoretical analysis shows a higher photoconductive gain for RHNWs (∼ 12) than the corresponding AHNWs device (∼ 9.9). Maximum photoresponsivity of ∼ 18 A/W has been observed for RHNWs with a sharp rise time (Tr) ∼ 0.12 s and fall time (Tf) ∼ 0.13 s at 200 nm (– 9 V) and the device also behaves like a self-powered PD under white light illumination.

Electron Microscopy Characterization of Gold Nanoparticles Supported on an Ordered TiO2 Nanowires Array.

Electron Microscopy Characterization of Gold Nanoparticles Supported on an Ordered TiO2 Nanowires Array.

Wide-pH-compatible MoSx co-catalyst layer on TiO2 nanowire arrays photoanode for simultaneous acceleration of charge carrier separation and catalytic reactions

The water oxidation reaction is a key reaction for solar water splitting, which requires excellent oxygen evolution co-catalyst to accelerate charges separation efficiency and high catalytic reaction sites for O2 releasing. So far, many earth-abundant co-catalysts can only play roles at a single pH (only in neutral or alkaline electrolyte), but the development of wide-pH compatible co-catalyst with low price are rarely obtained. Herein, amorphous MoSx layer was conformally coated on TiO2 nanowire arrays (NAs) as an active co-catalyst for multi-pH water photo-oxidation. The experimental results showed that the MoSx greatly enhanced the photoelectrochemical (PEC) performance of TiO2 NAs with high photocurrent densities of 1.95, 1.67, and 1.55 mA/cm2 at 1.23 VRHE in acidic, alkaline, and neutral electrolyte, respectively, significantly higher than bare TiO2 and most TiO2/co-catalyst literature values. Density functional theory (DFT) calculations revealed that the MoSx on TiO2 improves electronic interaction at their interface and forms a type-II band structure for more efficient separation of charge carriers. It is also found that high-density active sites provided by MoSx can reduce the Gibbs free energy and overpotential of potential-determining step for OER, which further enhance the adsorption activity of reaction intermediates. Our work contributes to the in-depth understanding of amorphous MoSx as efficient water oxidation co-catalyst for multi-pH PEC water splitting.

Enhanced Photoelectrocatalytic Activity of TiO2 Nanowire Arrays via Copolymerized G-C3N4 Hybridization

Photoelectrocatalytic (PEC) oxidation is an advanced technology that combines photocatalytic oxidation (PC) and electrolytic oxidation (EC). PEC activity can be greatly enhanced by the PC and EC synergy effect. In this work, novel copolymerized g-C3N4 (denoted as CNx)/TiO2 core-shell nanowire arrays were prepared by chemical vapor deposition. CNx were deposited on the surface of TiO2 nanowire arrays using organic monomer 4,5-dicyanidazole and dicyandiamide as copolymerization precursor. TiO2 nanowire arrays provide a direct and fast electron transfer path, while CNx is a visible light responsive material. After CNx deposition, the light response range of TiO2 is broadened to 600 nm. The deposition of CNx shell effectively improves the PC efficiency and PEC efficiency of TiO2. Under visible light irradiation and 1 V bias potential, the rate constant k of PEC degradation of CNx/TiO2 core-shell nanowire arrays is 0.0069 min−1, which is 72% higher than that of pure TiO2 nanowires. The built-in electric field formed in the interface between TiO2 core and CNx shell would effectively promote photogenerated charge separation and PEC activity.

Copper complex/polyoxometalate‐based tunable multi‐color film for energy storage

AbstractPolyoxometalates (POMs) are considered as an attractive option for electrochromic energy storage (EES) system due to their unique electrochemical feature. Herein, a composite film NW/P2W17/Cu (phen)2 based on Dawson‐type monolacunary POMs K10P2W17O61 (abbreviated as P2W17) and copper complex [CuII (phen)2](NO3)2 (abbreviated as Cu (phen)2) formed on TiO2 nanowire (abbreviated as NW) array substrate was fabricated by hydrothermal process and layer‐by‐layer self‐assembly combination method. This rational designed film NW/P2W17/Cu (phen)2 exhibits excellent tunable multicolor electrochromic behavior and improved pseudocapacitive performance with large optical modulation (43.7% at 600 nm), fast switching time (tc = 2.9 s, tb = 9.5 s), and high volumetric capacitance (228.0 F cm−3 at 0.3 mA cm−2). In the process of charge and discharge, the composite film can realize the transformation from light green to orange, green, and finally to blue‐green color, successfully achieve the bridge between electrochromic behavior and energy storage, and monitor the level of stored energy by color change. This work showed great potential of POMs‐based electrode materials for integrated electrochromism and energy storage applications.

Long and Well-Separated TiO2 Nanowire Arrays Decorated with Au Nanoparticles for Visible-Light-Driven Photoelectrochemical Water Splitting

Long and Well-Separated TiO₂ Nanowire Arrays Decorated with Au Nanoparticles for Visible-Light-Driven Photoelectrochemical Water Splitting

Enhancement of super-hydrophilic/underwater super-oleophobic performance of ceramic membrane with TiO2 nanowire array prepared via low temperature oxidation

A gradient porous ceramic membrane with surface super-hydrophilic and underwater super-oleophobic performance was prepared by combining hydrogel directional freezing method and low temperature oxidation process. The effects of solid contents and sintering temperature on the ceramic membrane matrix were examined. The reaction time and synthesis temperature on the TiO2 nanowire array were also evaluated. In addition, the related effects on pore size distribution, permeation flux, contact angle, and oil-in-water emulsion separation were systematically investigated. The ceramic membrane matrix pore size changed from 0.5 μm to 25 μm gradually, indicating the gradient structure controlled by the growth of ice. The super-hydrophilic and underwater super-oleophobic performance of ceramic membrane surface was obtained with surface modification by TiO2 nanowire array, and the surface water contact angle and underwater oil contact angle were less than 5° and over 158°, respectively. The bonding strength between TiO2 nanowire and ceramic membrane matrix was high enough to withstand ultrasonic waves. The ceramic membrane modified with TiO2 nanowire array was used for 1000 ppm diesel oil-in-water emulsion separation, and the stable separation efficiency and flux were about 97% and 100–200 L/(m2 h bar) even after 10 filtration cycles.

Performance Enhancement of Actual Wastewater Treatment and Electricity Generation Through Surface Modified TiO₂ Nanotube Arrays Based Photoanode Photocatalytic Fuel Cell.

Herein, we report a surface modified TiO₂ nanowire arrays (NAs) photoanode based photocatalytic fuel cell (PFC) towards simultaneous enhancement of actual wastewater treatment and electricity generation under visible light irradiation. TiO₂ NAs were facile fabricated via two-step anodization process in ethylene glycol and glycerin solution, respectively. Actual wastewater samples were directly applied to evaluate the PFC performance in terms of wastewater degradation and electricity generation through the as-prepared TiO₂ NAs photoanode without loading noble-metals or semiconductors. TiO₂ NAs photoanode prepared from ethylene glycol solution demonstrated a highly ordered surface network, exhibiting short-circuit current density and fill factor nearly 4.3 times and 1.4 times higher than pristine TiO₂ NAs photoanode prepared according to previous reports. The experimental results revealed that the fabrication of TiO₂ NAs by a facile surface modification in ethylene glycol solution can be considered a low-cost and scalable routine for enhancing performance of PFC photoanode towards efficient actual wastewater treatment and electricity generation.

Enhancement of pollutant degradation and solar-driven water evaporation by architecting hierarchical 1D/2D TiO2 @ MoS2 core–shell networks

Solar absorbers with a wider absorption range are attracting extensive interest in the fields of photocatalysis and solar-driven water evaporation. Here we designed hierarchical TiO2 nanowire arrays (TiO2 NWAs) in situ grown on Ti mesh, and utilizing the microstructure engineering strategy, ultrathin MoS2 nanosheets were further decorated on the surface of TiO2 NWAs (TiO2 NWAs @ MoS2). The multistage 1D TiO2 NWAs @ 2D MoS2 core–shell networks enhanced the light trapping in the full solar spectrum in comparison to bare MoS2 nanosheet arrays (MoS2 NSAs), which benefitted photocatalysis and solar-driven water evaporation. The number of photogenerated charge carriers on the surface of TiO2 NWAs @ MoS2 increased, which dramatically enhanced the photocatalytic rate constant by over an order of magnitude relative to MoS2 NSAs. As for solar-driven water evaporation, TiO2 NWAs @ MoS2 achieved a light absorption of 96.5% and a water evaporation rate of 1.42 kg m–2h−1 under one sun. In addition, the self-supporting solar absorber with favorable stability overcame the intractable recovering of photocatalysts from treated water. This study provided a pathway for designing efficient semiconductor-based solar absorbers used in solar energy conversion.

Au Nanoparticle-Decorated TiO2 Nanowires for Surface Plasmon Resonance-Based Photoelectrochemical Bioassays with a Solid–Liquid–Air Triphase Interface

Surface plasmon resonance (SPR)-induced photoelectrochemical (PEC) reaction has great potential in developing high-performance bioassay systems. In this study, we report a high-performance visible-light-active SPR-based PEC bioassay system by immobilizing oxidase on Au nanoparticle-decorated superhydrophobic TiO2 nanowire arrays with a solid–liquid–air triphase interface. Based on the triphase bio-photoelectrode, sufficient reactant oxygen can be directly acquired from the air phase with constant and rapid supply, which stabilizes and enhances the kinetics of oxidase catalytic reaction, leading to increased detection accuracy and a wider linear detection range. Moreover, the Au–TiO2 nanowire array-based bio-photoelectrode can be operated under visible light irradiation due to the SPR effect, which improves the stability of PEC bioassay system by avoiding potential deterioration of oxidase molecules in a traditional UV light environment. The SPR-based PEC bioassay with the solid–liquid–air triphase bio-photoanode is an alternative for better disease diagnosis and health monitoring.

Effective stabilization of atomic hydrogen by Pd nanoparticles for rapid hexavalent chromium reduction and synchronous bisphenol A oxidation during the photoelectrocatalytic process

Atomic hydrogen (H*) plays a vital role in the synchronous redox of metallic ions and organic molecules. However, H* is extremely unstable as it is easily converted to hydrogen. Herein, we designed a novel strategy for the effective stabilization of H* to enhance its utility. The synthesized Pd nanoparticles grown on the defective MoS2 (DMS) of TiO2 nanowire arrays (TNA) (TNA/DMS/Pd) photocathode exhibited rapid Cr(VI) reduction (~95% in 10 min) and bisphenol A (BPA) oxidation (~97% in 30 min), with the kinetic constants almost 24- and 6-fold higher than those of the TNA photocathode, respectively. This superior performances could be attributed to: (i) the generated interface heterojunctions between TNA and DMS boosted the separation efficiencies of photogenerated electrons, thereby supplying abundant valance electrons to lower the overpotential to create a suitable microenvironment for H* generation; (ii) the stabilization of H* by Pd nanoparticles resulted in a significant increase in the yield of hydroxyl radical (•OH). This research provides a new strategy for the effective utilization of H* toward rapid reduction of heavy metals and synchronous oxidation of the refractory organics.

Ag nanoparticles capped TiO2 nanowires array based capacitive memory

Glancing angle deposition technique was used to fabricate Ag nanoparticles (NPs) capped TiO2 Nanowire (NW) array structure for capacitive memory application. Electron microscopes confirmed the sandwiched structure of Ag NPs between TiO2 thin-film (TF) and NW. The average length of the vertical TiO2 NW and diameter of Ag NPs (with density ~ 1012 cm2) were found to be ~ 350 ± 5 nm and ~ 3.2 ± 0.4 nm, respectively. An enhanced photoluminescence was observed in case of Ag NPs capped TiO2 NWs due to the presence of high carriers as compared to bare TiO2 NW. The capacitance (C)–voltage (V) hysteresis was measured for both Ag NPs capped TiO2 NW and bare TiO2 NW at different sweeping voltage (± 3– ± 10 V) at 1 MHz frequency. A high capacitive memory window of 7.12 V was obtained for Ag NP capped TiO2 NW at ± 10 V with an excellent endurance upto 1000 cycle. Significantly lesser charge loss of 23% was obtained after a span of 104 s with a hole and electron loss of 10.6% and 17.8% respectively. The program and erase process in the device was explained with the help of a band diagram.

TiO2 Nanowire Arrays in situ Grown on Ti Foil Exhibiting Superior Uranyl-Adsorption Properties

TiO2 nanowire arrays in situ grown on Ti foil (TiO2/Ti) were prepared to remove uranium (VI) from aqueous solution. As the Ti foil serves as a carrier for TiO2, the TiO2/Ti adsorbent can be effortlessly retrieved from aqueous solutions by tweezers after adsorption. The presence of TiO2 nanowire arrays on Ti foil was verified by X-ray diffraction and scanning electron microscopy. Parameters in the adsorption process were fully evaluated, including solution pH, contact time, temperature, and uranium (VI) concentration. The adsorption was most efficient in the pH range of 5.0 to 9.0. The maximum uranium (VI) adsorption capacity of TiO2/Ti, based on the Langmuir model, was 354.5 mg g–1 at pH 5.0 and T = 323 K. Thermodynamic parameters showed that the adsorption of uranium (VI) on TiO2/Ti is endothermic and spontaneous. The adsorption capacity of TiO2/Ti remained essentially unchanged after three adsorption–desorption cycles in uranium (VI) solutions. Our results support the application of this adsorbent to removal of uranium (VI) from diversified aqueous samples.

Branching TiO2 nanowire arrays for enhanced ethanol sensing

Nanostructure modulation is effective to achieve high performance TiO2-based gas sensors. We herein report a wet-chemistry route to precipitate directly branched TiO2 nanowire arrays on alumina tubes for gas sensing applications. The optimized branched TiO2 nanowire array exhibits a response of 9.2 towards 100 ppm ethanol; whilst those of the pristine TiO2 nanowire array and the branched TiO2 nanowire powders randomly distributed are 5.1 and 3.1, respectively. The enhanced response is mainly contributed to the unique porous architecture and quasi-aligned nanostructure, which provide more active sites and also favor gas migration. Phase junctions between the backbone and the branch of the branched TiO2 nanowire arrays help the resistance modulation as a result of potential barriers. The facile precipitation of quasi-aligned arrays of branched TiO2 nanowires, which are in situ grown on ceramic tubes, thus provides a new economical synthetic route to TiO2-based sensors with excellent properties.

New insight into the effect of interface supercapacitance on the performance of titanium dioxide/carbon nanowire array for photoelectrochemical water oxidation

The electrode/electrlyte interface is of great signifance to photoelectrochemical (PEC) water oxidation as the reaction mainly occur here. Herein, we focus on the effect of supercapactance of the electrode/electrlyte interface on the performance of PEC. It is discovered that the supercapacitor on the interface is crucial because it links the charge transport and solution ion adsorption on its two sides. In this study, we demonstrate an approach to promote the performance of TiO2 nanowire array (TiO2 NWs) photoanode in photoelectrochemical cells (PECs) by increasing its supercapacitance. A 2−5 nm carbon layer was coated and the interface supercapacitance increases by about 150 times. This enhances the separation rate of electron-hole pairs by collecting more holes. Meanwhile, it also promotes the water oxidation rate by adsorbing more OH− on its surface. As a result, the photocurrent density of C-TiO2 NWs was about 8 times higher than that of its carbon-free counterpart. This approach of increasing the supercapacitance of photoanodes would be attractive for enhancement of the efficiency of PECs and this work demonstrate the importance of supercapacitance of the interface for PECs.

Fabrication of rutile – TiO2 nanowire on shape memory alloy: A potential material for energy storage application

Herein, we reported a novel and a facile method to fabricated TiO2 nanowire arrays on Nitinol alloy substrate as electrode material for supercapacitors. The rutile TiO2 nanowire arrays on alloy substrates were developed using chemical vapor deposition technique with camphor as the source. A systematic study for the growth of nanostructure TiO2@NiTi has been carried out along with its exceptional physical and chemical properties for energy storage application. The growth of the nanostructure for different concentration at the elevated temperature has been studied through different characterization techniques like scanning electron microscopy, X-ray diffraction and Raman spectroscopy, which resulted in confirming the formation of rutile phase having length and diameter of 10 ± 3 µm and 80 ± 10 nm, respectively. In addition, the COMSOL simulation was carried out to determine the temperature gradient in the furnace tube at elevated temperature. The presence of nickel in the bi-metallic alloys played a vital role in the growth of TiO2 nanostructures array. The synthesized TiO2 nanowire arrays on Nitinol substrate exhibited the specific capacitance of ∼ 1F/g with long term stability, making it a potential candidate for supercapacitor applications.

Design of highly ordered hierarchical catalytic nanostructures as high-flexibility counter electrodes for fiber-shaped dye-sensitized solar cells

Ordered array structures will greatly reduce the stress formation in wearable electric devices during dynamic bending operation. In this work, highly flexible TiN-based fiber counter electrodes (FCEs) were designed via a post-ammonization treatment on the hydrothermally grown TiO2 nanowire arrays. Results show that the obtained TiN nanorod arrays (NRAs) are well aligned with a diameter of 200–320 nm and a length of several hundred nanometers to ∼1 μm. Moreover, fiber-shaped dye-sensitized solar cells assembled using TiN FCEs showed the maximum photoelectric conversion efficiency (PCE) of 5.69%, which is 16.3% higher than that of the ones based on Pt FCEs. Analysis indicated that this enhancement in PCE could be mainly due to the better electrochemical catalytic activity of TiN NRAs. Furthermore, the optimizations of the nanoscale morphologies of TiN NRAs suggest that both small diameters and large lengths can benefit the PCE and the dynamic bending stability, while the diameters show a major influence on them. The optimal FCEs show an ultralow decay rate of 0.017‰ per bending cycle.

Amorphous ReS2 decorated TiO2 nanowire arrays for highly-efficient nitrogen reduction.

Herein, we constructed amorphous ReS2 nanosheets anchored on TiO2 nanowires by delicately forming Ti-O-Re bonds, which exhibited considerable average ammonia yield and faradaic efficiency as high as 5.3 μg h-1 cm-2cat. and 49.8% at an applied potential of -0.2 V (vs. RHE) in 0.1 M Na2SO4. The high NRR performance could be attributed to the amorphous feature of the ReS2 nanosheets, the rich oxygen vacancies in the TiO2 nanowires and their semiconducting feature, which not only facilitate the sufficient exposure of active sites but also efficiently boost the faradaic efficiency due to the good regulation of surface proton or electron accessibility.

Enhanced Dielectric and Hydrophobic Properties of Poly(vinylidene fluoride-trifluoroethylene)/TiO2 Nanowire Arrays Composite Film Surface Modified by Electrospinning.

In this research, we designed a feasible method to prepare composite films with high permittivity and significantly enhanced hydrophobic performance, which showed huge potential in the electrowetting field. TiO2 nanowire arrays were prepared by a one-step hydrothermal process, and poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) was spin-coated on the nanowire arrays to form composite, the surface of which was modified by electrospinning. Due to the great orientation of TiO2 nanowires, dipoles and space charges are in ordered arrangement along the electric field, and this strongly reinforced the Maxwell–Wagner–Sillars (MWS) polarization, thus the permittivity of the composite (TiO2 nanowire length/film thickness is 0.769) reaches 53 at 1 kHz, which is nearly 3 times higher than pure P(VDF-TrFE). Meanwhile the composite film possesses low dielectric loss (0.07) and low conductivity (2.69 × 10−9 S/cm), showing good insulation. The contact angle of the composite after electrospinning (about 137°) was greatly enhanced from pure P(VDF-TrFE) spin-coated film (about 89°), which can be attributed to the microrough structure built by P(VDF-TrFE) nanofibers.

Indium Nanoparticles Capped TiO₂ Nanowire Array for Boosted Photosensing Adoption

The boosted photosensing performances have been reported for Indium (In) nanoparticles (NPs) capped TiO2 nanowire (NW) array using Glancing angle deposition (GLAD) technique. The In NP based photosensor possessed high ideality factor of ~12.8 and the enhancement in photoresponsivity has been also observed. The ON/OFF switching irradiation for the In NPs based photosensor has increased from $4.6~\mu \text{A}$ to $6.2~\mu \text{A}$ and vice versa with a rise time of 0.45 sec and fall time of 0.56 sec.