Nanotube Arrays Research Articles

Exploring well-defined TiO2 nanotube arrays for enhancing SnO2-Sb-Nd-Pt electrode performance

The short service life and low catalytic activity of electrodes are the major bottlenecks limiting the practical applications of current electrocatalytic oxidation technology in wastewater treatment. In this study, a novel Ti/SnO2-Sb-Nd-Pt electrode loading TiO2 nanotube (TiO2-NTs) array was proposed and prepared. The optimized TiO2 nanotube (TiO2-NTs) arrays provided abundant anchoring sites for SnO2-Sb-Nd-Pt active coating and improved the bonding strength between the Ti matrix and the SnO2-Sb-Nd-Pt active coating as a mediator, as a result, higher electrocatalytic performance and stability. The nitrobenzene (NB) removal and service life were significantly higher in Ti/TiO2-NTs/SnO2-Sb-Nd-Pt (91.08 % and 4381.9 days) when compared to Ti/SnO2-Sb-Nd-Pt (80.61 % and 1151.2 days). In addition, the outstanding electrocatalytic performance of Ti/TiO2-NTs/SnO2-Sb-Nd-Pt with an oxygen evolution potential of 2.03 V and total voltametric charge of 5.88 mC cm−2 makes it a promising candidate for future industrial applications. These findings will lay a solid foundation for broadening the applications of well-defined TiO2-NTs arrays prepared via the two-step anodization.

Sensitization of TiO2 Nanotube Arrays by Mixed Oxovanadium(IV) Complex for Enhanced Photoelectrochemical Cells Performance

Sensitization of TiO2 Nanotube Arrays by Mixed Oxovanadium(IV) Complex for Enhanced Photoelectrochemical Cells Performance

Molybdenum-Modified Titanium Dioxide Nanotube Arrays as an Efficient Electrode for the Electroreduction of Nitrate to Ammonia

Electrochemical nitrate reduction (NO3−RR) has been recognized as a promising strategy for sustainable ammonia (NH3) production due to its environmental friendliness and economical nature. However, the NO3−RR reaction involves an eight-electron coupled proton transfer process with many by-products and low Faraday efficiency. In this work, a molybdenum oxide (MoOx)-decorated titanium dioxide nanotube on Ti foil (Mo/TiO2) was prepared by means of an electrodeposition and calcination process. The structure of MoOx can be controlled by regulating the concentration of molybdate during the electrodeposition process, which can further influence the electron transfer from Ti to Mo atoms, and enhance the binding energy of intermediate species in NO3−RR. The optimized Mo/TiO2-M with more Mo(IV) sites exhibited a better activity for NO3−RR. The Mo/TiO2-M electrode delivered a NH3 yield of 5.18 mg h−1 cm−2 at −1.7 V vs. Ag/AgCl, and exhibited a Faraday efficiency of 88.05% at −1.4 V vs. Ag/AgCl. In addition, the cycling test demonstrated that the Mo/TiO2-M electrode possessed a good stability. This work not only provides an attractive electrode material, but also offers new insights into the rational design of catalysts for NO3−RR.

Floating Bimetallic Catalysts for Growing 30cm-Long Carbon Nanotube Arrays with High Yields and Uniformity.

Ultralong carbon nanotubes (CNTs) are considered as promising candidates for many cutting-edge applications. However, restricted by the extremely low yields of ultralong CNTs, their practical applications can hardly be realized. Therefore, new methodologies shall be developed to boost the growth efficiency of ultralong CNTs and alleviate their areal density decay at the macroscale level. Herein, a facile, universal, and controllable method for the in situ synthesis of floating bimetallic catalysts (FBCs) is proposed to grow ultralong CNT arrays with high yields and uniformity. Ferrocene and metal acetylacetonates serve as catalyst precursors, affording the successful synthesis of a series of FBCs with controllable compositions. Among these FBCs, the optimized FeCu catalyst increases the areal density of ultralong CNT arrays to a record-breaking value of ≈8100CNTsmm-1 and exhibits a lifetime 3.40 times longer than that of Fe, thus achieving both high yields and uniformity. A 30-centimeters-long and high-density ultralong CNT array is also successfully grown with the assistance of FeCu catalysts. As evidenced by this kinetic model and molecular dynamics simulations, the introduction of Cu into Fe can simultaneously improve the catalyst fluidity and decrease carbon solubility, and an optimal catalytic performance will be achieved by balancing this tradeoff.

Reactive P and S co-doped porous hollow nanotube arrays for high performance chloride ion storage

Developing stable, high-performance chloride-ion storage electrodes is essential for energy storage and water purification application. Herein, a P, S co-doped porous hollow nanotube array, with a free ion diffusion pathway and highly active adsorption sites, on carbon felt electrodes (CoNiPS@CF) is reported. Due to the porous hollow nanotube structure and synergistic effect of P, S co-doped, the CoNiPS@CF based capacitive deionization (CDI) system exhibits high desalination capacity (76.1 mgCl– g–1), fast desalination rate (6.33 mgCl– g–1 min–1) and good cycling stability (capacity retention rate of > 90%), which compares favorably to the state-of-the-art electrodes. The porous hollow nanotube structure enables fast ion diffusion kinetics due to the swift ion transport inside the electrode and the presence of a large number of reactive sites. The introduction of S element also reduces the passivation layer on the surface of CoNiP and lowers the adsorption energy for Cl– capture, thereby improving the electrode conductivity and surface electrochemical activity, and further accelerating the adsorption kinetics. Our results offer a powerful strategy to improve the reactivity and stability of transition metal phosphides for chloride capture, and to improve the efficiency of electrochemical dechlorination technologies.

Analytical modeling of nucleation and growth of graphene layers on CNT array and its application in field emission of electrons

Carbon Nanotube (CNT) arrays and graphene have undergone several investigations to achieve efficient field emission (FE) owing to CNT’s remarkable large aspect ratio and graphene’s exceptional FE stability. However, when dense CNT arrays and planar graphene layers were used as field emitters, their field enhancement factor reduced dramatically. Therefore, in this paper, we numerically analyze the growth of a dense CNT array with planar graphene layers (PGLs) on top, resulting in a CNT-PGL hybrid and the associated field enhancement factor. The growth of the CNT array is investigated using Plasma Enhanced Chemical Vapor Deposition (PECVD) chamber in C2H2/NH3 environment with variable C2H2 flow, Ni catalyst film thickness, and substrate temperature followed by PGL precipitation on its top at an optimized cooling rate and Ni film thickness. The analytical model developed accounts for the number density of ions and neutrals, various surface elementary processes on catalyst film, CNT array growth, and PGLs precipitation. According to our investigation, the average growth rate of CNTs increases and then decreases with increasing C2H2 flow rate and catalyst film thickness. CNTs grow at a faster rate when the substrate temperature increases. Furthermore, as the chamber temperature is lowered from 750 °C to 250 °C in N2 environment and Ni film thickness grows, the number of the graphene layers increases. The field enhancement factors for the CNT array and hybrid are then calculated based on the optimal parameter values. The average height of the nanotubes, their spacing from one another, and the penetration of the electric field due to graphene coverage are considered while computing the field enhancement factor. It has been found that adding planar graphene layers to densely packed CNTs can raise its field enhancement factor. The results obtained match the current experimental observations quite well.

Mn/Fe co-doped TiO2 nanotube arrays for photoelectrochemical water splitting in neutral medium

Manganese and iron co-doped TiO2 nanotube arrays (TNTs) are grown on Ti foil by in situ electro-anodization method and employed for overall photoelectrochemical water splitting. The band gap of TiO2 is reduced from 3.3 eV to 3.1 eV with co-doping of Mn and Fe in Mn/Fe-TNT@Ti sample. Annealing Mn/Fe-TNT@Ti at 500 °C leads to the formation of trap states associated with the Fe3+ and Mn2+ ions present in the TiO2 lattice. The anatase structure of TNTs in Mn/Fe-TNT@Ti-500 sample is confirmed by XRD and Raman spectroscopy. An anodic shift in the onset potential from 0.2 VRHE to 0.08 VRHE is observed in Mn/Fe-TNT@Ti-500 sample compared to Mn/FeTNT@Ti sample. The overall photocurrent density at −0.4 VRHE is higher for Mn/Fe-TNT@Ti-500 sample (331μA/cm2) than Mn/Fe-TNT@Ti sample (251μA/cm2). The oxygen evolution activity shows similar trend with Mn/Fe-TNT@Ti-500 displaying a photocurrent density of 13.6 μA/cm2 at 1.23 VRHE. The anodic photocurrent density of Mn/Fe-TNT@Ti-500 sample is six times higher than that of the Mn/Fe-TNT@Ti at 0.8 VRHE. The incident photon to current efficiency (IPCE) measurements show that the photon absorption and conversion efficiency of the Mn/Fe-TNT@Ti-500 sample are significantly higher than that of the Mn/Fe-TNT@Ti sample. The results of this study complement the DFT calculations carried out with the generalized gradient approximation (GGA) technique. This work demonstrates possibility of designing composite materials for efficient photoreduction studies using n-type titanium nanotubes as precursors.

Single‐cluster Functionalized TiO2 Nanotube Array for Boosting Water Oxidation and CO2 Photoreduction to CH3OH

AbstractSolar‐driven CO2 reduction and water oxidation to liquid fuels represents a promising solution to alleviate energy crisis and climate issue, but it remains a great challenge for generating CH3OH and CH3CH2OH dominated by multi‐electron transfer. Single‐cluster catalysts with super electron acceptance, accurate molecular structure, customizable electronic structure and multiple adsorption sites, have led to greater potential in catalyzing various challenging reactions. However, accurately controlling the number and arrangement of clusters on functional supports still faces great challenge. Herein, we develop a facile electrosynthesis method to uniformly disperse Wells‐Dawson‐ and Keggin‐type polyoxometalates on TiO2 nanotube arrays, resulting in a series of single‐cluster functionalized catalysts P2M18O62@TiO2 and PM12O40@TiO2 (M=Mo or W). The single polyoxometalate cluster can be distinctly identified and serves as electronic sponge to accept electrons from excited TiO2 for enhancing surface‐hole concentration and promote water oxidation. Among these samples, P2Mo18O62@TiO2‐1 exhibits the highest electron consumption rate of 1260 μmol g−1 for CO2‐to‐CH3OH conversion with H2O as the electron source, which is 11 times higher than that of isolated TiO2 nanotube arrays. This work supplied a simple synthesis method to realize the single‐dispersion of molecular cluster to enrich surface‐reaching holes on TiO2, thereby facilitating water oxidation and CO2 reduction.

Single-cluster Functionalized TiO2 Nanotube Array for Boosting Water Oxidation and CO2 Photoreduction to CH3OH.

Solar-driven CO2 reduction and water oxidation to liquid fuels represents a promising solution to alleviate energy crisis and climate issue, but it remains a great challenge for generating CH3OH and CH3CH2OH dominated by multi-electron transfer. Single-cluster catalysts with super electron acceptance, accurate molecular structure, customizable electronic structure and multiple adsorption sites, have led to greater potential in catalyzing various challenging reactions. However, accurately controlling the number and arrangement of clusters on functional supports still faces great challenge. Herein, we develop a facile electrosynthesis method to uniformly disperse Wells-Dawson- and Keggin-type polyoxometalates on TiO2 nanotube arrays, resulting in a series of single-cluster functionalized catalysts P2M18O62@TiO2 and PM12O40@TiO2 (M=Mo or W). The single polyoxometalate cluster can be distinctly identified and serves as electronic sponge to accept electrons from excited TiO2 for enhancing surface-hole concentration and promote water oxidation. Among these samples, P2Mo18O62@TiO2-1 exhibits the highest electron consumption rate of 1260 μmol g-1 for CO2-to-CH3OH conversion with H2O as the electron source, which is 11 times higher than that of isolated TiO2 nanotube arrays. This work supplied a simple synthesis method to realize the single-dispersion of molecular cluster to enrich surface-reaching holes on TiO2, thereby facilitating water oxidation and CO2 reduction.

Construction of g-C3N4/SnSe2/H-TiO2 Ternary Heterojunction for High-Performance Photodetectors

Two-dimensional layered materials have been widely used in the field of photodetectors because of their unique photoelectric properties. Among them, the multi-heterojunction based on two-dimensional materials with high carrier separation efficiency is expected to be designed as a high-performance photodetector (PD). This work focuses on the fabrication of g-C3N4/SnSe2/H-TiO2 ternary heterojunctions for photodetectors, obtained by depositing SnSe2 and g-C3N4 nanosheets onto TiO2 nanotube arrays using chemical vapor deposition and impregnation methods, respectively. The formation of the g-C3N4/SnSe2/H-TiO2 ternary heterojunction enhances and broadens absorption in the ultraviolet-visible range. Photoelectrochemical measurements have confirmed that the fabricated g-C3N4/SnSe2/H-TiO2 ternary heterojunction photodetector exhibits remarkable light detection capabilities at 370, 450, and 520 nm, meaning broadband photodetection behavior. Notably, under light illumination of 370 nm wavelength, it demonstrates a high responsivity of 2.742 A W−1, an impressive detectivity of 5.84 × 1010 Jones, an external quantum efficiency of 9.21 × 102 %, and excellent stability. This high performance can be attributed to the effective separation and transfer of photogenerated carriers within the ternary heterojunction, significantly enhancing the photoresponse. The construction of the novel broadband-responsive ternary g-C3N4/SnSe2/TiO2 heterojunction holds promise for driving the future development of wideband, high-performance, and highly integrated photodetectors.

Superior long service life of a porous Ti-foam/TiOxHy-NTs/SnO2-Sb anode for highly efficient degradation of the pretreatment polyacrylamide-containing fracturing flowback fluid

Doped-SnO2 electrodes have shown outstanding performances in electrochemical oxidation (EO), but limitations in long service life and high durability have necessitated further advances in electrode design. Herein, this study proposes a porous Ti-foam/TiOxHy-NTs/SnO2-Sb anode with superior long service life for efficient degradation of polyacrylamide (PAM) - containing fracturing flowback fluid. The Ti-foam/TiOxHy-NTs/SnO2-Sb anode was designed by preferably choosing reduced TiO2 nanotube arrays grown in situ on porous Ti foam (Ti-foam/TiOxHy-NTs) as substrate coated with SnO2-Sb coating through the sol-gel method. The superiority of the design concept is verified by achieving a superior long service life of 735.2 h (0.5 M H2SO4) and 53.2 h (0.5 M HCl) at a current density of 1.0 A cm−2 by the tests of accelerated service life. The superior long service life originates from multidimensional and hierarchical architecture for lowering electrical resistance by shorting the transport path of electrolyte ions and electrons, and loading more active material without aggregation. Furthermore, the Ti-foam/TiOxHy-NTs/SnO2-Sb electrode displays excellent ability in efficiently degrading the real and simulated PAM-containing fracturing flowback fluid, achieving a chemical oxygen demand decomposition of above 90.0 % after 120 min of EO process. Therefore, the synthesized Ti-foam/TiOxHy-NTs/SnO2-Sb electrode exhibits great potential industrial application for efficient decomposition of PAM-containing fracturing flowback fluid using in EO process.

NiCoMn-LDH with core-shell heterostructures based on CoS nanotube arrays containing multiple ion diffusion channels for boosted supercapacitor applications

Nanostructure engineering and composition rationalization are crucial for materials to become candidates for high-performance supercapacitor. Herein, a novel core-shell heterostructured electrode, combining CoS hollow nanorods with NiCoMn-layered double hydroxides (LDH) ternary metal nanosheets, were prepared on carbon cloth by reasonably controlled vulcanization and electrodeposition. By optimizing electrodeposition conditions, the material's structure and properties can be fine-tuned. The enhanced capacitance of the optimized carbon cloth (CC)@CoS/NiCoMn-LDH-300 electrode (4256.0 F g−1) lies in the open space provided by CoS and the establishment of a new charge transfer channel across the interfaces of CC@CoS/NiCoMn-LDH-300 nanosheets. This is further demonstrated by Density functional theory (DFT) simulations based on OH− adsorption energy, which produces faster redox charge kinetics and significantly enhances the electrode's energy storage capacity. The hybrid supercapacitor, integrating the optimized CC@CoS/NiCoMn-LDH-300 electrode with active carbon, demonstrates the highest energy density of 86 Wh kg−1 (under the power density of 850 W kg−1) and the long cycle stability of 89.7%. This study aims to go beyond simple binary LDH by constructing a ternary LDH with a hierarchical core-shell heterostructure to provide an effective and feasible new concept for high-performance supercapacitor electrode materials via rational structure design.

Facile Synthesis of 3D Cu(OH)2@NiCo-Binary Hydroxide Core–Shell Nanotube Arrays with High Mass Loading for High-Performance Asymmetric Supercapacitors

Facile Synthesis of 3D Cu(OH)₂@NiCo-Binary Hydroxide Core–Shell Nanotube Arrays with High Mass Loading for High-Performance Asymmetric Supercapacitors

Formation of Diamond Films with Different Grain Sizes on TiO2 Nanotubes and Its Field Emission Properties

Diamond films with different grain sizes are deposited on TiO2 nanotube (TNT) arrays prepared by anodic oxidation using a microwave plasma chemical vapor deposition reactor. The scanning electron microscope, X‐Ray diffractometer, and Raman results indicate that the diamond film is successfully deposited and that the substrate undergoes a phase transition due to the diamond deposition temperature, resulting in the rutile phase becoming dominant with lower energy bandgap and work function. Notably, after 5 h of deposition, a relatively continuous microcrystalline film is formed on the TNTs, and the diamond grains change from spherical to pyramidal and show excellent electron field emission behavior, with a low turn‐on field of 0.5 V μm−1 and a current density of 85.9 μA cm−2. In addition, the deposition environment of the nanocrystalline diamond has a large impact on the substrate morphology, resulting in a blocked electron transport path, which reduces the overall field emission performance. The enhanced performance is attributed to the synergistic effect between the highly efficient 1D electron path of the TNTs, the negative electron affinity of the diamond surface, and the lower work function of rutile TiO2.

Enhancing interfacial thermal conductivity of copper-carbon nanotube array composite via metallic bonding: Molecular dynamics simulations

In this work, a novel strategy for improving the interface thermal conductivity (ITC) between the vertically aligned carbon nanotube (VACNT) arrays and copper was proposed and verified using the non-equilibrium molecular dynamics (NEMD) simulations. The introduced metal elements (Ag, Al, Ti, and Ni) enhanced the ITC of the Cu-VACNT interface region via a strong adhesive force. Notably, different from the physisorption between Ag/Al elements and VACNT, a strong interfacial interaction was introduced between the chemically bonded Ni/Ti and VACNT. In addition, the matching degree of the phonon state density (PDOS) at the Ni-VACNT interface increases with increasing contact area between the Ni atoms and Cu substrate. Nevertheless, it was found that over-strong interfacial interaction between the VACNT and Ti element deteriorates the matching degree of high-frequency phonons at the Ti-VACNT interface. These findings offer valuable criteria for designing and selecting materials to enhance interfacial thermal conduction in composite electronic packaging.

Antimony Trisulfide with Graphene Oxide Coated Titania Nanotube Arrays as Anode Material for Lithium-ion Batteries

Antimony Trisulfide with Graphene Oxide Coated Titania Nanotube Arrays as Anode Material for Lithium-ion Batteries

Graphene oxide-coated metallic nanotube array as a surface-enhanced Raman scattering (SERS) substrate

This paper presents a highly-ordered metallic nanotube array (MeNTA) coated with graphene oxide (GO) to serve as a surface-enhanced Raman scattering (SERS) substrate. The MeNTA was fabricated using a top-down wafer-scale lithographic and sputter-deposition process, after which a thin layer of GO was deposited uniformly via dip coating. Scanning electron microscopy revealed that GO dip coating did not mar the highly ordered periodic structures on the MeNTA substrate. Raman scattering spectra of Rhodamine 6G (R6G) molecules revealed that coating MeNTA substrates with GO enhanced peak intensity by as much as 2.9 times. Among the substrates examined in this study, the Ag GO MeNTA presented the strongest SERS behavior, with a detection limit of 10−8 M and enhancement factors of 5.38 × 105 for R6G and 2.23 × 105 for Crystal Violet (CV). The uniform distribution of GO and array of periodic structures returned highly consistent (i.e., reproducible) analyte Raman signals, with a relative standard deviation of 12.7 % for R6G and 9.3 % for CV and excellent linear relationship between Raman signal intensity and analyte concentration (R2 = 0.9974 for R6G, 0.9844 for CV).

Effect of graphene oxide loaded on TiO2-nanotube-modified Ti on inflammatory responses

Although a titanium matrix modified with titanium dioxide nanotube (TNT) arrays can have anti-inflammatory effects in vitro, these effects are limited. In this study, the TNT surface was modified by electrodepositing graphene oxide (GO) to enhance the anti-inflammatory effect of the material. Scanning electron microscopy (SEM), Raman spectroscopy, and x-ray diffraction were used to characterize each of these materials. Cell Counting Kit-8 (CCK-8) was used to determine the cell proliferation status. Enzyme-linked Immunosorbent Assay (ELISA), immunofluorescence staining, and RNA sequencing were used to assess the regulation of inflammation in each group. Raman spectroscopy confirmed that GO was successfully loaded onto the surface. The SEM, ELISA, fluorescence staining, and RNA sequencing results indicated that TNT-GO can effectively inhibit the inflammatory response and induce the M2 polarization of macrophages. TNT-GO can weaken the surface inflammatory responses of materials, suppress the secretion of pro-inflammatory factors, and promote the M2 polarization of macrophages. These advantageous properties render TNT-GO a promising material for dental implants.

(Invited) CdS/Ti-Si-O Composite Photoanode for Photoelectrochemical Hydrogen Generation

Advancements in clean energy drive socio-economic development and foster a sustainable future by restructuring energy systems and promoting low-carbon development. In this paper, we presented a comprehensive investigation on the design and performance characterization of CdS/Ti-Si-O composite photoanodes for photoelectrochemical (PEC) hydrogen generation. Silicon-doped TiO2 nanotube arrays were fabricated through anodization of Ti-5Si alloy, followed by the deposition of CdS using the SILAR (successive ionic layer adsorption and reaction) process, resulting in nanostructured Ti-Si-O photoanodes modified with CdS. The composite photoanodes were characterized in terms of their composition, microstructure, optical properties and photoelectrochemical hydrogen production performance. The composite photoanodes revealed a notable enhancement in PEC hydrogen generation properties with a photocurrent density of 7.86 mA/cm2，which was 19.15 times and 9.59 times to those of the undoped TiO2 photoanode and Ti-Si-O photoanode, respectively. The Si-doping mechanism of the photoanodes was elucidated through Density Functional Theory (DFT) calculations. The synergistic combination of Si-doping and CdS modification represents a novel and promising approach for the design of efficient nanostructured photoanodes.

Remarkable fluorescence enhancement of acridine orange and rhodamine B through immobilization on zirconia nanotube array film and its application on nitrite sensing

Zirconia nanotube array films (ZNAF) prepared by anodic oxidation method were used as immobilization materials for acridine orange (AO), rhodamine B (RB) and AO-RB systems. A comparative study on their fluorescence emission intensity, fluorescence resonance energy transfer (FRET) and fluorescence detection of nitrite in aqueous solutions and on immobilization films with ZNAF as carriers was carried out. Results demonstrate that the solution pH values and immobilization on ZNAF have a great influence on the performance of these fluorescent molecules. Compared with aqueous solutions, the fluorescence emission intensity of AO and RB is considerably increased by immobilization, which is 8.0 and 4.2 times higher than the original, respectively. The energy transfer efficiency (E) of the AO-RB system increases from 40.9 % to 84.8 % by loading it on ZNAF. Moreover, after immobilization onto ZNAF, the fluorescence detection performance of nitrite is also significantly improved. The limit of detection decreases from 0.95 ng/mL to 0.22 ng/mL and the sensitivity increases from 939.18 to 15,031.68 mL/μg through loading AO onto ZNAF.