Anodic Titania Nanotube Arrays Research Articles

Photocurrent response loss of dye sensitized solar cells owing to top surface nanograss growth and bundling of anodic TiO2 nanotubes

In this research, the effect of anodization time on the length of the titanium oxide nanotube arrays (TNAs) and photovoltaic parameters of back-side illuminated dye-sensitized solar cells (DSSCs) were investigated. The TNAs were characterized using X-ray diffraction (X-ray) or (XRD), and scanning electron microscopy (SEM). Anodic TNAs having tube lengths from 7.9 to 20.17 μm were produced in ethylene glycol containing ammonium fluoride-NH4F by increasing the anodizing time from 20 min to 6 h. Based on I–V curves, the power conversion efficiency (PCE) of back-side illuminated dye sensitized solar cells (DSSCs) increased for TNAs grown for up to 120 min, but decreased afterward. Using electrochemical impedance spectroscopy (EIS), we understand that the resistance of the TNAs decreased from 94.82 Ω cm−2 for TNAs anodized for 20 min down to 50.43 Ω cm−2 for those TNAs anodized for 120 min, however, it increases for TNAs anodized for longer periods of time. Furthermore, the short circuit current density (Jsc) increased from 3.14 to 5.67 mA cm−2 during 2 h anodic oxidation for TNAs, and leading to enhanced efficiency of about 200 % (from 1.19 % to 2.45 %). We interpret this behaviour with the top surface morphology evolution of TNAs as a function of anodization time which is associated with the formation of top surface nanograss and bundling the tubes for specific durations.

CuO/Cu/rGO nanocomposite anodic titania nanotubes for boosted non-enzymatic glucose biosensors

Highly arranged porous anodic titania (TiO2) nanotube arrays (ATNT) were fruitfully fabricated by the anodization of Ti foil in an ammonium fluoride electrolyte.

Phase transformation kinetics of anodic titania nanotube arrays in oxygen-rich atmosphere

Titania substrate and ambient atmosphere are pivotal in influencing the thermal stability of anodic TiO2 nanotube arrays (TNTs) due to anatase-to-rutile phase transition (ATRPT). This paper aimed to investigate detailed relationships between morphology and the crystallite structure and phase kinetics of O2-annealed TNTs with tube length > 10 μm and the inner diameter 60–80 nm. The study shows that below 700 °C, ARPT was very slow, but accelerated above 700 °C as nanotube structures showed signs of dramatic collapse, indicating that the thermal stability became poor. The resulting phase transformation kinetics of the O2-annealed TNTs are described by the general equation Ea= -∂ln(xr)·R/∂(1/T)·1000 , yielding approximate activation energy values of E1 = 150.71 ± 14.67 kJ/mol and E2 = 31.17 ± 1.53 kJ/mol for ARPT at temperatures below and above 600 °C, respectively. The transformation kinetics were found to be dominated by a “feeding effect” and a “size effect”, respectively. These findings serve to provide a useful method for preparing anodic TNTs with anticipant phase composition and thermal stability.

Fast fabrication of small pore anodic titania nanotube arrays under high voltage

Due to their unique structures and physicochemical properties, porous anodic metal oxides including Al2O3, Fe2O3, TiO2, Ta2O5 and so on, prepared by anodization of corresponding metal substrates in appropriate electrolytes have found applications in various fields. Pore diameter plays a significant role in applications of these anodic metal oxides. It is a common knowledge that the pore diameter of porous metal oxides increases with formation voltage despite of a vast variation of anodization parameters and electrolytes used. Here, we demonstrate that the pore diameter and cell size of anodic TiO2 nanotube arrays can decrease dramatically under high voltage accompanied by high current density. Impact factors determining the formation of small pore TiO2 nanotubes under high voltage were discussed. Typically, with the same electrolyte used, the average pore diameter of TiO2 nanotube arrays changes from ca 26 nm at a formation voltage of 10 V to ca 13 nm at 200 V. It is also demonstrated that at high voltage, small pore TiO2 nanotubes could be grown with a rate orders of magnitude faster than those grown in a classic way with low voltage and current density.

Dynamics of photo-induced charge carriers in anodized titania nanotube array

Theoretical development of anodized TiO2 nanotube array was made by using high field conduction theory. The theory reveals that the high electric field (>106 V cm−1) due to low resistance offered by titanium electrode in the beginning of anodization results the rapid formation of compact TiO2 layer defined by pilling-bedworth ratio (PBR). The increasing thickness in the oxidized layer proportionally develops the stress in the oxide layer which results micro-cracks in the TiO2 layer to minimize the energy strain by increasing the surface area. These cracks steer the formation of TiO2 nanotube array throughout the anodization process. The presence of fluoride ions in the as prepared electrolyte etches at these preferred sites (micro-cracks) and leads the formation of bowl like ordered foot prints. The etching in the oxide layer undergoes continuously until an equilibrium is reached between electrochemically assisted oxidation and chemically assisted dissolution process. Furthermore, on account of frequent use of TiO2 nanotube array in light harnessing applications, the theoretical dynamics of photo-induced charge carriers were also studied using carrier continuity equation under quasi state condition.

Controlled synthesis of vertically aligned honeycomb TiO2 nanotube arrays: effect of high-temperature annealing on physical properties

Vertically aligned honeycomb titania (TiO2) nanotube arrays grown on Ti foil were synthesized by electrochemical anodization method. The changing of morphology, crystalline structural, and optical properties of anodic titania nanotube (ATNT) arrays systematically studied. A novel annealing approach is proposed to retain the ATNT arrays at high temperatures ranging from 700 to 900 °C. At 700 and 800 °C, FESEM images showed that the nanotubular structures were preserved from annihilation and the morphology of the structure was a mixture between anatase and rutile. However, the highlight of this research was the successful synthesis of the high-quality rutile ATNT arrays at 900 °C. The X-ray diffractometer measurements proved that the variations in the mean crystallite sizes of anatase and rutile phase occurred during annealing of ATNT samples. The corresponding optical bandgaps were determined by extracting the reflectance values and combining Kubelka–Munk function with the indirect Tauc plot for transition phases of ATNT arrays for high-temperature annealed films.

Detection of Pneumonia Volatile Organic Biomarkers Via Nanotube Sensing Platform

Infectious microorganisms are known to release volatile organic biomarkers (VOBs) that can be found in human breath, urine, blood, etc. Pneumonia, which is caused by a consortium of microorganisms residing in the lungs, is one of the deadliest infectious diseases in the world. It is responsible for 80% of deaths in children under 2 years1. Having a point of care, inexpensive device that can detect pneumonia in less than 20 minutes would make considerable improvement in disease detection. One proposed method of detecting pneumonia is measuring the presence and concentration of VOBs in the breath. At specific biased voltages, metal functionalized titanium dioxide sensors have shown promising results in the detection of tuberculosis from breath in our previous work2-3. Pneumonia microorganisms release several VOBs or will increase the concentration of some VOBs that are present in breath in low amounts. Heptane, 2-methyl butane, furan, ethylbenzene and ethanol are some examples of non-polar and polar VOBs present the breath of pneumonia patients at significant concentrations4. Depending on the polarity of the VOB metal functionalized or non-functionalized titanium dioxide nanotubes base sensors at specific based voltage will respond to the presence of these biomarkers. Figure 1 presents the preliminary sensor response to pneumonia biomarker, heptane. The result was conducted using a non-functionalized titanium dioxide sensor at a low biased voltage. The sensor was exposed to nitrogen gas as a negative check and nitrogen that was bubble through heptane using amperometric testing method. Initially the sensor was exposed to nitrogen followed by two heptane exposure then one more nitrogen exposure to confirm the negative check. Various range of biased voltages from -2 to 2 V was tested with 1.5V showing response to heptane. As shown in figure 1, when the sensor was exposed to heptane there is an increase in current whereas nitrogen exposure reduced the current. The current calculations are normalized to the background currents. Metal functionalized sensors would react to the presence of VOBs at lower biased voltages. Overall, the proposed method of disease detection device would help diagnosing pneumonia painlessly that does not require highly qualified technicians to perform. Additional results of the structured solid stat sensor interactions with polar and non-polar pneumonia VOBs using various electrochemical methods will be shown in the presentation. United for Lung Health. Fact Sheet: World Pneumonia Day 12 November 2018.Bhattacharyya D, Smith YR, Misra M, Mohanty SK. Electrochemical detection of methyl nicotinate biomarker using functionalized anodized titania nanotube arrays. Materials Research Express 2015;2(2):025002Bhattacharyya D, Smith YR, Mohanty SK, Misra M. Titania Nanotube Array Sensor for Electrochemical Detection of Four Predominate Tuberculosis Volatile Biomarkers. Journal of The Electrochemical Society 2016;163(6):B206-B214Schnabel R, Fijten R, Smolinska A, Dallinga J, Boumans M-L, Stobberingh E, Boots A, Roekaerts P, Bergmans D, van Schooten FJ. Analysis of volatile organic compounds in exhaledbreath to diagnose ventilator-associated pneumonia. Scientific reports. 2015;5. Figure 1

On the Interfacial Adhesion between TiO2 Nanotube Array Layer and Ti Substrate.

Anodic titania nanotube arrays (TNTAs) with higher aspect ratio are observed to be liable to spontaneous curling or delamination from the underlying titanium (Ti) metal once dried because of the poor interfacial adhesion of the TNTA layer to the underlying Ti, especially when a thin Ti sheet is used. The interfacial adhesion strength was shown to decrease with increasing thickness of the TNTA layer. In this work, although the preparation of TNTAs in a frequently used fluoride-containing solution was completed, different anodization processes were further performed at lower current densities or at lower voltages for a short time in the same electrolyte to increase the adhesion. The mechanical test demonstrated that better adhesion properties have been achieved by applying these anodization posttreatment processes. It is believed that during the fabrication of TNTAs, a large residual stress at the interface of the nanotube layer and the underlying Ti is created. It is the residual stress that leads to the weak interfacial adhesion. The anodization posttreatment processes can reduce or eliminate the residual stress, thereby improving the interfacial adhesion. Further, these processes can also boost the performances of TNTAs for supercapacitors. When the anodization posttreatment processes are implemented at 1 mA cm-2 or at 10 V for 5 min, considerable improvements in the interfacial adhesion are observed. Particularly, both posttreatment processes are also applicable to the very thin Ti sheet (∼18 μm). The realization of robust and adherent TNTAs grown on very thin Ti sheets can not only significantly improve the volumetric capacitances of TNTAs but also make TNTAs an attractive material in flexible supercapacitor applications.

Template synthesis of methylammonium lead iodide in the matrix of anodic titanium dioxide via the direct conversion of electrodeposited elemental lead

A new processing technique is proposed for composites based on the hybrid organic–inorganic perovskite MeNH3PbI3 and anodic titania nanotube arrays, which includes a direct gasphase conversion of metal lead nanorods electrodeposited inside the pores of anodic titanium dioxide. This technique may be useful for a design of solar cells and optoelectronics applications

Dynamic Diffraction Studies on the Crystallization, Phase Transformation, and Activation Energies in Anodized Titania Nanotubes.

The influence of calcination time on the phase transformation and crystallization kinetics of anodized titania nanotube arrays was studied using in-situ isothermal and non-isothermal synchrotron radiation diffraction from room temperature to 900 °C. Anatase first crystallized at 400 °C, while rutile crystallized at 550 °C. Isothermal heating of the anodized titania nanotubes by an increase in the calcination time at 400, 450, 500, 550, 600, and 650 °C resulted in a slight reduction in anatase abundance, but an increase in the abundance of rutile because of an anatase-to-rutile transformation. The Avrami equation was used to model the titania crystallization mechanism and the Arrhenius equation was used to estimate the activation energies of the titania phase transformation. Activation energies of 22 (10) kJ/mol for the titanium-to-anatase transformation, and 207 (17) kJ/mol for the anatase-to-rutile transformation were estimated.

Photoelectrocatalytic Synthesis of Hydrogen Peroxide by Molecular Copper-Porphyrin Supported on Titanium Dioxide Nanotubes.

We report on a self‐assembled system comprising a molecular copper‐porphyrin photoelectrocatalyst, 5‐(4‐carboxy‐phenyl)‐10,15,20‐triphenylporphyrinatocopper(II) (CuTPP‐COOH), covalently bound to self‐organized, anodic titania nanotube arrays (TiO2 NTs) for photoelectrochemical reduction of oxygen. Visible light irradiation of the porphyrin‐covered TiO2 NTs under cathodic polarization up to −0.3 V vs. Normal hydrogen electrode (NHE) photocatalytically produces H2O2 in pH neutral electrolyte, at room temperature and without need of sacrificial electron donors. The formation of H2O2 upon irradiation is proven and quantified by direct colorimetric detection using 4‐nitrophenyl boronic acid (p‐NPBA) as a reactant. This simple approach for the attachment of a small molecular catalyst to TiO2 NTs may ultimately allow for the preparation of a low‐cost H2O2 evolving cathode for efficient photoelectrochemical energy storage under ambient conditions.

Surface modification of titania nanotube arrays with crystalline manganese-oxide nanostructures and fabrication of hybrid electrochemical electrode for high-performance supercapacitors

A hybrid electrochemical microelectrode is fabricated with a simple and cost-effective sono-chemical method, which consists of anodized titania nanotube arrays covered with manganese oxide nanostructures (nanorods+nanoparticles mixed morphology). The modification of the surface of the highly porous titania nanotube arrays with high-surface-area manganese oxide nanomaterials leads to considerable increment in the surface roughness of the composite electrode, which manifests high active surface sites of the electrode, and hence, leads to excellent electrochemical properties of the hybrid samples. The cyclic voltammetry and galvanostatic charge–discharge characterizations depict considerably improved electrochemical performance with high areal capacitance values. The areal capacitance of the composite electrode is obtained around 65mFcm−1 @ 1.0mVs−1 scan rate, which is more than 160 times higher than the control electrode (TNT, 0.4mFcm−1 @ 1.0mVs−1 scan rate). The composite electrode also depicts high capacity retention with only 4% decrement in the capacitance value over 2500 cycles. Also the composite electrode reveals almost 65 times increment in the power density for a mere 2 times decrement in the energy density. This high cyclic stability along with excellent energy-power performance indicates very good applicability in practical charge storage devices. The electrochemical impedance spectroscopic studies showed near-ideal capacitive performance with very low charge transfer resistance. This superior supercapacitive performance of the hybrid electrode is due to the combinatorial effect of electric double-layer capacitance of TNT and pseudocapacitance of MO as well as high active surface sites of the electrode for higher utilization of the active material. Therefore, this simple and low-cost technique to fabricate hybrid microelectrode with superior electrochemical properties can be very useful for high-performance supercapacitors.

Hierarchical in Situ functionalized TiO2 Nanotubular Substrate for Sensing Volatile Organic Compounds Associated with Tuberculosis

Mycobacterium tuberculosis (MTB) is a devastating disease that effects over 10 million people worldwide with approximately 1.8 million deaths1. One major issue contributing to this wide spread disease is lack of low cost point-of-care methods for screening/diagnosis of the disease. One method that has gained a significant amount of attention is the use of volatile organic compounds (VOCs) found in the breath of patients as a biomarker for the disease. These VOCs include methyl nicotinate and methyl p-anisate which are unique metabolic byproducts of the microorganism. To take advantage of the presence of these VOCs, a hierarchical in situ functionalized TiO2 nanotubular substrate has been synthesized to specifically detect methyl nicotinate and methyl p-anisate in a complex sample. These VOCs can be detected at very low levels using a solid-state sensor based on metal-functionalized 3D titanium dioxide (TiO2) nanotube arrays that bind the biomarkers at a specifically applied voltage. When a VOC of interest approaches the sensing substrate, it binds preferentially with the metal on the surface of the TiO2 nanotubes causing a large change in current (from nanoamp to microamp range). Our previous research has shown that a TiO2 nanotube array substrate functionalized with cobalt using wet incipient methods is capable of specifically detecting the MTB VOCs2-4. However, the sensor performance in this prior work, while promising, can be improved in terms of reliability, response time, and signal to noise ratio. The structure and consistency of the TiO2 sensing substrate is extremely important and methods for its improvement are constantly explored. In this work, we improve the MTB VOC sensors response time and accuracy by using a two-step method in the anodization process to create a hierarchical in situ functionalized TiO2 nanotubular substrate. In the first step, titanium metal was anodized for 30 minutes at 60V. In the second step the substrate was anodized at 30 V for 60 minutes. This process results in a hierarchical nanostructure composed of nanotubular and honey comb shapes (Figure 1). The smaller nanotubes inside each honeycomb shape structure are the result of anodizing at lower voltage. The two-step method of anodizing makes highly organized interconnected nanotubes and allows for improved sensor reliability when measuring current. In addition, we can improve our sensor respond to methyl nicotinate and methyl p-anisate by functionalizing the sensor while anodizing it (in situ functionalization). In this work cobalt was added to the anodizing solution resulting in the cobalt metal being integrated into the hierarchical nanostructure. The advantage of this approach is the reduction in sensor synthesis steps when compared to our previous work, and improved sensor response. Detailed analysis of nanostructured synthesis and sensor performance will be presented. 1. Tuberculosis (TB) Data and Statistics. https://www.cdc.gov/tb/statistics/ Accessed 12/16/2016, 2016. 2. Bhattacharyya D, Smith YR, Misra M, Mohanty SK. Electrochemical detection of methyl nicotinate biomarker using functionalized anodized titania nanotube arrays. Materials Research Express 2015;2(2):025002. 3. Bhattacharyya D, Smith YR, Mohanty SK, Misra M. Titania Nanotube Array Sensor for Electrochemical Detection of Four Predominate Tuberculosis Volatile Biomarkers. Journal of The Electrochemical Society 2016;163(6):B206-B214. 4. Smith YR, Bhattacharyya D, Mohanty SK, Misra M. Anodic functionalization of Titania nanotube arrays for the electrochemical detection of tuberculosis biomarker vapors. Journal of The Electrochemical Society 2016;163(3):B83-B89. Figure 1

Improved performance of anodic titanium oxide nanotube arrays synthesized by sonoelectrochemical anodization method for dye-sensitized solar cells

With rising demand for using solar cell systems for energy and environmental applications, considerable interest in anode materials of these cells has dramatically emerged. In this work, TiO2 nanotubular electrodes of varying thicknesses as anode were fabricated using effective process in a short time by sonoelectrochemical anodizing of Ti using an organic electrolyte, containing Na2[H2EDTA]. Long TiO2 nanotubes about 30–40 μm thick containing ordered hexagonal TiO2 were achieved through manipulating anodization parameters. Dye-sensitized solar cells (DSSCs) with different TiO2 electrode morphologies of varying thicknesses were compared to DSSCs based on TiO2 Nanoparticle electrodes. The effect of controlling parameters of the sonoelectrochemical process including surface preparation and anodizing time was investigated. This report brings to attention the desirable properties of the structurally oriented TiO2 for dye-sensitized solar cell applications. It found that the best cell performance was achieved about 3.14% in the case of using TiO2 NT layers that were treated by TiCl4 treatment.

Nano-structural variation of highly aligned anodic Titania nanotube arrays for gas phase photocatalytic application

Abstract Highly aligned titania (TiO 2 ) nanotube (NT) arrays have been grown on titanium sheet by using a self organized anodic oxidation method at different potentials (34–74 V) in a NH 4 F and ethylene glycol based electrolyte. Two sets of TiO 2 NT arrays have been fabricated with and without using cooling systems. Without cooling system, the solution temperature is increased from 25 °C (room temperature) to 63 °C with increase of anodization potential from 34 to 74 V. The temperature has been maintained to 25 °C by using water based cooling system. In both sets of samples, the pore diameter of TiO 2 NT arrays increases with increase of anodization potential. The maximum pore diameter has been (outer: 224 nm, inner: 172 nm) achieved with TiO 2 NT arrays (at 74 V) without using cooling system. The photocatalytic activity of the TiO 2 NT arrays is evaluated by the decomposition of methanol by the use of Fourier transform infrared spectrophotometer. The TiO 2 NT (at 44 V) sample has been fabricated without using cooling system, which shows the higher photocatalytic activity than the sample at other potentials. Using cooling system, the TiO 2 NT (at 54 V) sample shows the higher photo-decomposing property than the sample at other potentials. The TiO 2 NT (at 54 V) sample with cooling system shows the higher rate (photocatalytic activity) constant ( k = 0.0216) than the TiO 2 NT (at 44 V) sample without using cooling system ( k = 0.0186). The photocatalytic activity has been correlated with the nanostructural variation of TiO 2 NT arrays at different potentials without (self-grown solution temperature) and with water based cooling systems.

Effect of silane-coupling modification on bioactivity and in vitro properties of anodized titania nanotube arrays

Titanium dioxide nanotube arrays (TNTs) were fabricated by anodization method on Titanium (Ti) substrate then hydrothermally functionalized with γ-glycidoxypropyltrimethoxysilane (GPTMS) to study the synergetic effect of both nanotopography and chemical cues of TiO2 based nanotubes on the cellular behavior and bioactivity property. As a result, the bare anatase TNT and functionalized with GPTMS demonstrated great potential in promoting the proliferation, adhesion of osteoblast cells with excellent biocompatibility and enhanced the bioactivity than conventional and polished Ti surface.

Interdigitated CuS/TiO2 Nanotube Bulk Heterojunctions Achieved via Ion Exchange

In photovoltaic and optoelectronic applications, a three-dimensional bulk heterojunction is highly desirable in view of the large interfacial area for rapid charge separation. An additional benefit of oriented charge transport is furnished when using anodized titania nanotube arrays as the substrates. However, filling the nanotubes with another p-type semiconductor integrate film, rather than discrete nanoparticles, is difficult with solution-based process. In this study, an interdigitated CuS/TiO2 bulk heterojunction was achieved by filling up TiO2 nanotube arrays with ZnS nanoparticles, and subsequently converting the ZnS nanoparticles into CuS film. Such a combination of pre-filling and post-exchanging process is essential in formation of the interdigitated structure. The rational design of the unique architecture demonstrated in this work provides a facile and general approach to fabricate bulk heterojunctions with other potential semiconductors.

Communication—Ultrafast Anodized Titania Nanotube Arrays Loaded with Quantum Dots via Ultrasonic Assistance

Self-aligned and firmly-structured titania nanotube arrays (TNAs) with excellent photoelectric response were fabricated by anodization in tens of seconds. Furthermore, TNAs were decorated with CdS quantum dots by ultrasonic-assisted successive ionic layer adsorption and reaction (U-SILAR) method. The resulted CdS/TNAs hybrid shows higher visible light absorption, stronger photo current and stable structure than those of the sample by traditional SILAR method.

Anodic Functionalization of Titania Nanotube Arrays for the Electrochemical Detection of Tuberculosis Biomarker Vapors

Anodic titania nanotube arrays have been extensively explored for gas sensing applications due to their high chemical and thermal stability and robust synthesis method. In this study, we explore the use of functionalized titania nanotube arrays for the electrochemical detection of gaseous volatile organic biomarkers associated with tuberculosis. The synthesis method developed allows for in situ functionalization of titania nanotubes with oxygen containing metal species (i.e., Co(OH)2) during anodization. Amperometric detection of volatile organic biomarkers with concentrations of 275 ∼ 360 ppm using next generation titania nanotubes functionalized with Co(OH)2 where compared with Co(OH)2 functionalized titania nanotubes via a wet incipient method. Improved sensor response and sensitivity was observed with next generation titania nanotubes, which can be attributed to homogeneous distribution of reactive sites directly in contact with the parent titania. A mechanism for sensor response and in situ functionalization is presented.

Tube-Super Dielectric Materials: Electrostatic Capacitors with Energy Density Greater than 200 J·cm-3.

The construction and performance of a second generation of super dielectric material based electrostatic capacitors (EC), with energy density greater than 200 J·cm−3, which rival the best reported energy density of electric double layer capacitors (EDLC), also known as supercapacitors, are reported. The first generation super dielectric materials (SDM) are multi-material mixtures with dielectric constants greater than 1.0 × 105, composed of a porous, electrically insulating powder filled with a polarizable, ion-containing liquid. Second-generation SDMs (TSDM), introduced here, are anodic titania nanotube arrays filled with concentrated aqueous salt solutions. Capacitors using TiO2 based TSDM were found to have dielectric constants at ~0 Hz greater than 107 in all cases, a maximum operating voltage of greater than 2 volts and remarkable energy density that surpasses the highest previously reported for EC capacitors by approximately one order of magnitude. A simple model based on the classic ponderable media model was shown to be largely consistent with data from nine EC type capacitors employing TSDM.