1D TiO2 Nanorods Research Articles

Self-powered photodetector based on 1D TiO2-3D CdS mixed dimensional heterostructure fabricated at low temperature

Solution processed photodetectors have garnered great attention in applications such as, machine vision perception, neuromorphic computing and opto-electronic memory storage. Though, such photodetectors offer several advantages such as ease of fabrication, high scalability, low thermal budget and low-cost processing, multi-modal functionality etc. however, they suffer from the major drawback of inferior device performance −as low responsivity and slow rise time, particularly due to the intrinsic poor crystallinity of the photoactive material. In this work, we demonstrate a solution processed photodetector with impressive performance at comparatively low processing temperatures (<150 °C) based on the mixed dimensional heterostructure configuration of 1D TiO2 nanorods and 3D CdS nanoflowers. TiO2 nanorods have been synthesized by hydrothermal technique, whereas their CdS sensitization is done by chemical bath deposition. Low cost carbon paste is used as electrode instead of conventional non-economic noble metal electrodes. X-ray diffraction studies validated excellent crystallinity of the photoactive material even under low temperature processing condition. The type-II Heterojunction (TiO2 and CdS) configuration photodetector shows efficient response at zero bias, thus yielding a self-powered device. The detector shows response in UV and visible region, with excellent responsivity of 110 mA/W (5 V), 563 µA/W (0 V) and a quicker rise time of 81 ms. Albeit the simple fabrication scheme and low processing temperatures, the detector exhibited promising figures-of-merit, which aids in fabrication of novel solution processed photodetectors.

Non-noble plasmonic MoO2 as photosensitizer of 1D TiO2 nanorods for enhancing visible-light photoelectrochemical performance

Recent years, plasmonic materials have attracted great attentions due to their potential applications in visible-light photoelectrochemical (PEC) water splitting. Developing low-cost and efficient non-noble plasmonic photosensitizer is quite important, but urgent. Here, we report the decorating of non-noble plasmonic MoO2 onto one dimensional (1D) rutile TiO2 nanorods, by a simple hydrothermal method. After MoO2 decoration, the light absorption was extended from < 426 nm to 900 nm, and the corresponding optical band gap was narrowed from 2.91 eV for TiO2 to 1.39 eV for TiO2/MoO2. Besides, accompanied with totally suppression of photogenerated electron-hole pairs recombination, the photogenerated carrier transfer and separation were efficiently improved. As a result, the > 420 nm visible-light induced photocurrent was enhanced by about 3.15 times. Furthermore, the hydrogen production rate was enhanced from an undetectable level for TiO2 to 0.48 μmol/cm2/h for TiO2/MoO2. Our results inform that MoO2 should be a promising non-noble plasmonic photosensitizer to enhance the visible-light PEC performance of TiO2, and may be applied to other electro-optical systems.

A non-enzymatic photoelectrochemical sensor based on Co-Pi modified one-dimensional titanium oxide embedded microscale reactor

Photoelectrochemical (PEC) sensing systems are promising candidates for detecting low concentrations of biological molecules; they are particularly encouraging when offered in a non-enzymatic format. A pitfall of non-enzymatic PEC sensors is their specificity. This, however, is often resolved by utilizing inorganic nanocatalyst. Here, we describe a novel non-enzymatic sunlight-driven PEC sensor based on cobalt phosphate (Co-Pi) deposition on a one-dimensional titanium dioxide (1D-TiO2) nanorod array for the ultra-low detection of glucose. The 1D-TiO2 nanorod array was prepared through a simple hydrothermal method and modified with Co-Pi using photo-assisted electrodeposition. The result was a microscale fluidic reactor. The modified electrodes with various Co-Pi thicknesses photocatalyst were characterized through a variety of techniques, including HRTEM, XRD, UV–vis spectroscopy, electrochemical impedance spectroscopy, and chronoamperometry. The characterization methods served to study and confirm the optimal electrode structure. The novel 1D-TiO2/Co-Pi electrode exhibited enhanced absorbance in the visual range of the nanorods with increased photoactivity and no drastic modification of the array’s surface. The PEC sensor microscale reactor exhibited a low limit of detection of 0.031 nM and a high sensitivity of 900 μA mM−1 cm−2 over a linear range of 0.1–10000 nM, demonstrating ultrasensitive detection of glucose. Overall, the surface modification of TiO2 by Co-Pi improved the sensor properties resulting in high selectivity, high stability, and high reproducibility.

CdS and CdSe nanoparticles activated 1D TiO2 heterostructure nanoarray photoelectrodes for enhanced photoelectrocatalytic water splitting

Herein, we report the fabrication of nanocrystals activated 1D TiO2 nanorods heterostructure photoanode with top-open vertical photoanode structure by hydrothermal and SILAR method. The vertical nanorod heterostructure could effectively manifest the interface with electrolyte and photoanode for dynamic water oxidation. Furthermore, thermodynamically stable TiO2 nanorod and its conduction band alignment with CdS and CdSe nanocrystals uphold the charge separation and culminate the photocurrent density to 2.01 mA cm−2 at 1.23 V RHE. The decoration of CdS and CdSe co-crystals on TiO2 exhibited a significantly enhanced photoresponse and clear evidence of the negative shift of onset-potential with a five-fold increment of solar to hydrogen generation.

Toward the Intrinsic Superiority of Aligned One‐Dimensional TiO2 Nanostructures: the Role of Defect States in Electron Transport Process

AbstractElectrodes made up of aligned 1D semiconductor nanostructures have drawn much attention in photoelectrochemical applications, as they are expected to be ideal configuration for channeling electrons towards the substrate without lateral electron scattering. However, efforts were hardly made to optimize the defect states in such systems. Herein, we observed significant enhancement (∼20 fold) in photoelectrochemical performance of TiO2 nanorod arrays (NRAs) after a simple calcination procedure. Through a series of structural and electrochemical characterizations, we revealed an underlying role of defects states in electron transport: even in electrodes composed of 1D TiO2 nanorods, lateral electron scattering would be avoided, which was confirmed by measuring the trap‐free electron diffusion coefficient (D0), the electron transport process can be severely affected by defect states distributed in the band gap. The calcination procedure can bring structural optimization for TiO2 NRAs, therefore facilitates electron transport process. Intrinsically, this work provides a structural view for realizing the superior performance of aligned 1D semiconductor nanostructures.

Photoelectrochemical Bioanalyte Sensor Based on Engineered One-Dimensional Nanostructured Oxide

Photoelectrochemical (PEC) non-enzymatic sensing systems are beneficial for the detection of low concentrations of biological molecules. Among different potential nanostructured materials, one dimensional TiO2 and ZnO nanorods are promising semi-conductor which can be successfully applied in many photoelectrochemical applications, mainly due to their photoactive properties, and long-term stability. In spite of their advantages, the wide band gap of 1D TiO2 and ZnO along with their high recombination rate confine their applications dramatically. These properties, prevent 1D TiO2 and ZnO from absorbing visible light; therefore, the semiconductor is only photoactive in the UV range. Here, we describe novel non-enzymatic sunlight-driven PEC sensors based on a modified 1D TiO2 nanorod array with cocatalyst and 1D ZnO core-shell structure for the aim of improved PEC non-enzymatic detection of glucose and H2O2, respectively. The 1D TiO2 and ZnO nanorods array were prepared through facile hydrothermal at and electrodeposition methods, respectively. The modified electrodes were characterized through FESEM, HRTEM, XRD, and UV-vis spectroscopy. The novel 1D TiO2 and 1D ZnO@TiO2 core shell electrodes exhibited enhanced PEC sensing properties with a low limit of detection and a high sensitivity, over a linear range of 0.1 – 1000 nM of glucose and 1 pM-100 mM of H2O2 in PBS. Additionally, the sensor displayed high selectivity, high stability, and high reproducibility. Overall, our engineered PEC sensor demonstrated ultrasensitive detection of glucose and H2O2 and a capable platform for continued development into the field of PEC non-enzymatic sensors.

Fabrication and characterisation of the dye‐sensitised solar cells with the mixture of one‐dimension TiO 2 nanorods and graphite nanosheets as the mesoporous scafford

One-dimension (1D) TiO2 nanorods (TiO2-N) has been fabricated via electro-spinning method. The composites of 1D TiO2-N and graphite nanosheets, termed as (TiO2-N/G-N), have been obtained by the physical doping method. The structure and properties of TiO2-N and TiO2-N/G-N have been characterised by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Raman spectrum. Dye-sensitised solar cells devices with TiO2 nanoparticles, TiO2-N and TiO2-N/G-N as the mesoporous scaffolds have been developed and investigated, respectively. Device 2 based on TiO2-N scaffolds showed short-circuit current (J sc) of 5.57 mA·cm−1, open-circuit voltage (V OC) of 0.68 V, filling factor of 0.75, and the power conversion efficiency of 2.85%, respectively. Compared with device 2, device 3 based on TiO2-N/G-N exhibited reduced photovoltaic properties.

Bipolar resistive switching and memristive properties of hydrothermally synthesized TiO2 nanorod array: Effect of growth temperature

In the present work, the hydrothermal approach is employed to develop 1D-TiO2 nanorod array memristive devices and the effect of hydrothermal growth temperature on TiO2 memristive devices is studied. X-ray diffraction (XRD) analysis suggested that the rutile phase is dominant in the developed TiO2 nanorod array. Field emission scanning electron microscopy (FESEM) images show well adherent and pinhole free one dimensional (1D) TiO2 nanorods. The presence of titanium and oxygen in all the samples was confirmed by energy dispersive X-ray spectroscopy (EDS). Furthermore, growth of the 1D TiO2 nanorods depends on the growth temperature and uniform growth is observed at the higher growth temperatures. The well-known memristive hysteresis loop is observed in the TiO2 nanorod thin films. Furthermore, resistive switching voltages, the shape of I-V loops and (non)rectifying behavior changed as the growth temperature varied from 140 °C to 170 °C. The biological synapse properties such as paired-pulse facilitation and short-term depression are observed in some devices. The detailed electrical characterizations suggested that the developed devices show doubled valued charge-magnetic flux characteristic and charge transportation is due to the Ohmic and space charge limited current.

Photo-assisted electrocatalytic methanol oxidation based on an efficient 1D-TiO 2 nanorods arrays support electrode

In this paper, one-dimensional (1D) TiO2 nanorods arrays (NRs) are adopted as Pt nanoparticles support for electrocatalytic methanol oxidation. We show that high aspect ratio 1D-TiO2 NRs not only own the advantages of excellent photogenerated carrier transport with low recombination rate but also serve to anchor the Pt nanoparticles for well-dispersing onto the surface of nanorods. The Pt-1D TiO2 NRs electrodes show improved activities toward electrocatalytic methanol oxidation when they exposed into the simulated solar light irradiation. Synergistic effects between electro- & photo-catalytic methanol oxidation as well as the efficient interfacial charger separation in Pt-1D TiO2 NRs electrode contribute to the enhanced electrocatalytic methanol oxidation activities. Our results suggest that 1D-TiO2 NRs can be used as promising photo-assisted Pt noble metal support in direct methanol fuel cell.

Assembly of CdSe Quantum Dots onto TiO2 Flower-rod Films for Quantum Dot-sensitized Solar Cell Applications

A hierarchical double-layered TiO2 flower-rod structure composed of three-dimensional (3D) TiO2 flowers and one-dimensional (1D) nanorods on transparent fluorine-doped tin oxide (FTO) conducting glass has been synthesized by a facile hydrothermal method and was applied as photoanode in CdSe quantum dots sensitized solar cells (QDSSCs). The 3D TiO2 flowers with the increased surface areas can adsorb more QDs, which reinforce the absorption of light; meanwhile 1D TiO2 nanorods beneath the flowers offer a direct electrical pathway for photogenerated electrons, accelerating the electron transfer rate. The effect of coating cycles of QDs on the photovoltaic performance was investigated by successive ionic layer adsorption reaction (SILAR) cycles. The best power conversion efficiency of solar cell based on flower-rod structure with 12 SILAR cycles of CdSe QDs can reached to 1.98% under one sun illumination (AM 1.5G, 100 mW/cm2).

Controlled Assembly of Nanorod TiO2 Crystals via a Sintering Process: Photoanode Properties in Dye-Sensitized Solar Cells

We present for the first time a synthetic method of obtaining 1D TiO2 nanorods with sintering methods using bundle-shaped 3D rutile TiO2 particles (3D BR-TiO2) with the dimensions of around 100 nm. The purpose of this research is (i) to control crystallization of the mixture of two kinds of TiO2 semiconductor nanocrystals, that is, 3D BR-TiO2 and spherical anatase TiO2 (SA-TiO2) on FTO substrate via sintering process and (ii) to establish a new method to create photoanodes in dye-sensitized solar cells (DSSCs). In addition, we focus on the preparation of low-cost and environmentally friendly titania electrode by adopting the “water-based” nanofluids. Our results provide useful guidance on how to improve the photovoltaic performance by reshaping the numerous 3D TiO2 particles to 1D TiO2-based electrodes with sintering technique.

Partial Ion Exchange Derived 2D Cu-Zn-In-S Nanosheets as Sensitizers of 1D TiO2 Nanorods for Boosting Solar Water Splitting.

A facile route for the fabrication of a novel ZnS shell/Cu-Zn-In-S nanosheets/TiO2 nanorods heterojunction was reported in this work. Especially, the quaternary Cu-Zn-In-S nanosheets were synthesized creatively from the ternary ZnIn2S4 nanosheets by partial exchange reaction, leading to substantial enhancement on the light absorbance. Such heterojunction could increase the surface area and accelerate the charge transfer resulting from its hierarchical 2D/1D structure and favorable energy bands. Moreover, the ZnS coating acted as a passivation layer as well as a potential barrier, significantly suppressing the interface recombination. The above synergistic effects resulted in the largely increased photocurrent density from 0.34 mA cm-2 for the pristine TiO2 to 0.81 mA cm-2 for the heterojunction at 0.8 V vs RHE.

3D Bi2S3/TiO2 cross-linked heterostructure: An efficient strategy to improve charge transport and separation for high photoelectrochemical performance

Abstract A novel 3D cross-linked heterostructure of TiO2 nanorods connecting with each other via ultrathin Bi2S3 nanosheets is constructed by a facile and effective strategy. The growth mechanism has been investigated and proposed based on the evolution of microstructure by changing the reaction parameters. Benefiting from the unique cross-linked heterostructure, the as-prepared Bi2S3 nanosheets modified TiO2 nanorods arrays could achieve a high energy conversion efficiency of 3.29% which is the highest value to date for Bi2S3-only sensitized solar cells as the reported highest value is 2.23% and other reported values are less than 1%. Furthermore, the photoelectrochemical studies clearly reveal that the novel cross-linked heterostructure exhibits much better activity than 0D nanoparticles decorated TiO2 nanorods under visible light irradiation, which may be primarily ascribed to the efficient electron transfer from 2D ultrathin Bi2S3 nanosheets to 1D TiO2 nanorod arrays. The promising results in this work confirm the advantages of cross-linked heterostructure and also undoubtedly offer an attractive synthesis strategy to fabricate other nanorod-based hierarchical architecture as well as nano-devices for solar energy conversion.

Influence of deposition temperature on the optical, structural, morphological, compositional and photoelectrochemical properties of TiO2 thin films

In this investigation, we are reporting a photoelectrochemical (PEC) performance of TiO2 thin films. Initially, TiO2 thin films were synthesized by using a single step hydrothermal method. The influence of temperature on the optical, structural, morphological, compositional and PEC properties of TiO2 thin films is investigated. The optical study reveals direct allowed type of transition. The XRD pattern confirms pure rutile phase with tetragonal crystal structure. The SEM analysis shows morphological transitions from 1D TiO2 nanorods to give a 3D TiO2 nanoflowers with increase in reaction temperature. The compositional data confirms the presence of titanium and oxygen in their respective oxidation state. HRTEM results confirm single crystalline nature of TiO2 thin films. As the reaction temperature increased from 120 to 180 °C photoconversion efficiency is enhanced from 0.33 to 0.47 %. Along with PEC performance electrochemical impedance spectra of all the samples is measured.

Heterostructures of MoS2 nanofilms on TiO2 nanorods used as field emitters

Heterostructures of 2-dimensional (2D) layered MoS2 nanofilms on ordered 1-dimensional (1D) TiO2 nanorods (MoS2@TiO2 heterostructures) are synthesized on Si substrates using a simple and low-cost hydrothermal method and then used as field emitters. Results of comparative experiments show that the MoS2@TiO2 heterostructures outperform the as-synthesized 1D TiO2 nanorods in field emission. This advantage is mainly attributed to three factors. First, in MoS2@TiO2 heterostructures, besides the high aspect ratio of the TiO2 nanorods, the sharpness of the MoS2 layer edges also contributes to the enhancement of the local electric field. Second, the large number of the MoS2 layer edges gives rise to more emission sites. Third, more electrons are available in the conduction band of MoS2.

High-efficiency dye-sensitized solar cells based on electrospun TiO2 multi-layered composite film photoanodes

High-efficiency DSSCs (dye-sensitized solar cells) based on multi-layered composite film photoanodes consisting of the TiO2 blocking layer, the commercial Degussa P25 nanoparticles layer and 1D (one-dimensional) TiO2 nanorods layer were fabricated. The 1D TiO2 nanorods were prepared by a simple electrospinning technology and grinding process. The photovoltaic properties of different DSSCs based on nanoparticles/nanoparticles (DNP), nanorods/nanorods (DNR) and nanoparticles/nanorods (NPR) photoanodes were investigated and their photoelectric conversion efficiencies were 6.37, 4.92 and 8.03%. The dye-sensitized solar cells based on NPR photoanodes exhibited the best photovoltaic performance with a short-circuit current of 15.7 mA cm−2. The enhanced photo-electricity performance of NPR solar cells could be attributed to the synergistic effect of following factors. (1) The P25 underlayer ensured intimate contact in DSSCs films structure and superior dye adsorption. (2) The nanorods overlayer with 1D structure showed strong light scattering ability, which significantly enhanced light harvesting efficiency. In addition, the 1D geometry of TiO2 nanorods provided a fast and long charge carrier transfer pathway, thus improving the transfer of photo-induced electrons in the DSSCs.

Mn-doped CdS quantum dots sensitized hierarchical TiO2 flower-rod for solar cell application

Abstract A double-layered TiO2 film which three dimensional (3D) flowers grown on highly ordered self-assembled one dimensional (1D) TiO2 nanorods was synthesized directly on transparent fluorine-doped tin oxide (FTO) conducting glass substrate by a facile hydrothermal method and was applied as photoanode in Mn-doped CdS quantum dots sensitized solar cells (QDSSCs). The 3D TiO2 flowers with the increased surface areas can adsorb more QDs, which increased the absorption of light; meanwhile 1D TiO2 nanorods beneath the flowers offered a direct electrical pathway for photogenerated electrons, accelerating the electron transfer rate. A typical type II band alignment which can effectively separate photogenerated excitons and reduce recombination of electrons and holes was constructed by Mn-doped CdS QDs and TiO2 flower-rod. The incident photon-to-current conversion efficiency (IPCE) of the Mn-doped CdS/TiO2 flower-rod solar cell reached to 40% with the polysulfide electrolyte filled in the solar cell. The power conversion efficiency (PCE) of 1.09% was obtained with the Mn-doped CdS/TiO2 flower-rod solar cell under one sun illumination (AM 1.5G, 100 mW/cm2), which is 105.7% higher than that of the CdS/TiO2 nanorod solar cell (0.53%).

Multifunctional graphene oxide-TiO2-Ag nanocomposites for high performance water disinfection and decontamination under solar irradiation

Multifunctional nanocomposites (GO-TiO2-Ag) integrating 2D GO sheets, 1D TiO2 nanorods and 0D Ag nanoparticles were synthesized via a facile two-phase method and characterized by various analytical techniques including TEM, EDS and XRD. The GO-TiO2-Ag nanocomposites demonstrate remarkably enhanced photocatalytic activities in degrading AO 7 and phenol under solar irradiation compared with GO-TiO2 and GO-Ag. They also exhibit excellent intrinsic antibacterial activity toward Escherichia coli, as well as significantly enhanced photo-biocidal capability over GO-TiO2 and GO-Ag. Through systematically investigating the influence of Ag content in the nanocomposites for their photocatalytic activities, it indicates that the optimal Ag content in the GO-TiO2-Ag nanocomposites varies for dye degradation and for phenol/bacterial degradation with different mechanisms. The superior photocatalytic activities under solar irradiation and the easy recovery make the GO-TiO2-Ag nanocomposites a good promising candidate for water purification.

Single-step synthesis of 3D nanostructured TiO2 as a scattering layer for vertically aligned 1D nanorod photoanodes and their dye-sensitized solar cell properties

In the present investigation we have successfully synthesized 1D vertically aligned rutile TiO2 nanorods (TNR) and 3D TiO2 nanostars (TNS) as a scattering layer by a single step hydrothermal route. The synthesized nanostructures were characterized by X-ray diffraction, scanning-and transmission electron microscopy and X-ray photoelectron spectroscopy. The 1D TiO2 nanorod and 3D TiO2 nanostar samples were further used for N-719 dye sensitized solar cells (DSSC) application. Compared to a nanorod based cell, the photovoltaic performance of the nanostars/nanorods TiO2 cell exhibits excellent DSSC performance, including superior light scattering, rapid electron transport and lower electron recombination rate. The 3D/1D TNS/TNR based DSSC cell exhibits 5.39% power conversion efficiency, which is remarkably higher than that of the bare 1D nanorod based (3.74%) photoelectrode. The detailed interface and transient properties of these nanorod and nanostar based photoanodes in DSSCs were analyzed by electrochemical impedance spectroscopy measurements and open circuit voltage decay measurements in order to understand the critical factors contributing to such high power conversion efficiency. The enhancement of the efficiency for the 3D/1D TNS/TNR photoanode based cell compared to the 1D TNR is mainly attributed to better light scattering capability, faster electron transport and lower electron recombination.