TiO2 Nanorod Arrays Research Articles

Core-shell TiO2/ZnO nanorod array films on FTO: Two-step synthesis and improved ethanol sensing performance

In this work, highly regular TiO2 nanorod array films were synthesized in situ on FTO by a facile hydrothermal method, and then ZnO shell layers were grown on the surface of the nanorods to form a core-shell structure via an ion-layer adsorption-reaction way. Compared to the TiO2 nanorods, the prepared TiO2/ZnO nanocomposites exhibited enhanced ethanol sensing performances, including a low working temperature, higher sensitivity, and faster response capability. The optimum sensor based on 2c-TiO2/ZnO exhibited the maximum response value of 30.85 toward 50 × 10−6 C2H5OH at 340 °C, which was almost 4.15 times higher than that of the TiO2 sensor. The improved ethanol sensing mechanism was discussed in relation to the unique nanorod array structure and the heterojunctions between TiO2 and ZnO.

Inhibition of condensation-induced droplet wetting by nano-hierarchical surfaces

Superhydrophobic nanostructured surfaces can enhance water condensation efficiency by facilitating droplet departure via coalescence-induced jumping. However, condensed droplets tend to transit from a mobile jumping mode to a highly pinned state at high condensation heat flux because excessive water nucleates within the nanostructures and anchors the condensed droplets. The large pinned droplets act as a thermal barrier and insulate the cooling surface, thus severely degrading its heat transfer efficiency. This work developed a nano-hierarchical structured surface by growing branched TiO2 nanorod arrays to prevent condensation-induced droplet pinning. After hydrophobization, the nano-hierarchical structure can spontaneously push the water out of nanostructures with an outward Laplace capillary pressure gradient when the droplet size is only at the nanoscale level. This effective de-wetting process maintains the high droplet mobility on the nano-hierarchical surface over a wide subcooling range, resulting in an up to ∼ 90 % increase in heat transfer coefficient at a high heat flux of 132 kW∙m−2 compared to the single-tier nanorod surface. Our investigation of how the nano-hierarchical structures fundamentally suppress the condensation-induced wetting on superhydrophobic surfaces represents a significant advance in understanding multiphase wetting phenomena and paves the way for the rational design of cooling surfaces.

The coupling effect of carbon spheres and cobalt-involved carbon nitrides stacked on TiO2 nanorod arrays for promoted solar water oxidation

Photoanode materials typically exhibit good stability and environmentally and economically properties in solar water splitting cells, while they always suffer from the narrow light absorption range, heavy surface charge combination and sluggish surface reaction kinetics. Herein, we design an efficient and reproducible photoanode by stacking amorphous carbon spheres (CSs) and cobalt-involved carbon nitrides (Co-CNs) on surface of TiO2 nanorod arrays. CSs work as light sensitizer for broadening the light absorption range of photoanode and promoting the utilization of solar energy, which further improved by Co-CNs partially. In addition, CSs increase the conductivity of photoanode, as a transport channel for improving the charge migration. Co-CNs introduce many active sites on surface of photoanode for facilitated solar water oxidation. The best constructed TiO2/CSs/Co-CNs photoanode exhibits an impressive photocurrent density of ∼1.73 mA/cm2 (at 1.23 V vs RHE). The staking method of various functional materials provides one promising strategy for the modification of catalysts.

Constructing the Vo-TiO2/Ag/TiO2 Heterojunction for Efficient Photoelectrochemical Nitrogen Reduction to Ammonia

Photoelectrochemical (PEC) nitrogen (N2) fixation technology provides the possibility to produce ammonia (NH3) under mild conditions, but the efficiency of N2 reduction in this process is greatly limited due to the high bond energy and ionic potential of N2. Herein, the Vo-TiO2/Ag/TiO2 photoelectrode consisting of rutile TiO2 nanorod arrays, Ag nanoparticles, and anatase TiO2 nanosheets with oxygen vacancies (Vo-TiO2) was constructed for accelerating the PEC reduction of N2 into ammonia. The separation of photogenerated carriers can be promoted by the heterojunction among TiO2 nanorods, Ag nanoparticles, and Vo-TiO2 nanosheets. Furthermore, the photogenerated electrons from the conduction band of TiO2 and the hot electrons from Ag nanoparticles’ local surface plasmon resonance (LSPR) effect were injected into the conduction band of Vo-TiO2, and they were further captured by Vo-TiO2 oxygen vacancy and can reduce N2 that adsorbed on the catalyst to NH3. Without any sacrificial agent, the average NH3 production rate can reach 51.2 μg h–1 cm–2. The catalyst exhibited excellent stability even after multiple uses. The LSPR effect of Ag nanoparticles and heterojunction structure promote the better PEC performance of TiO2 nanorod arrays.

Selective photoelectrochemical oxidation of glucose to glucaric acid by single atom Pt decorated defective TiO2

Photoelectrochemical reaction is emerging as a powerful approach for biomass conversion. However, it has been rarely explored for glucose conversion into value-added chemicals. Here we develop a photoelectrochemical approach for selective oxidation of glucose to high value-added glucaric acid by using single-atom Pt anchored on defective TiO2 nanorod arrays as photoanode. The defective structure induced by the oxygen vacancies can modulate the charge carrier dynamics and band structure, simultaneously. With optimized oxygen vacancies, the defective TiO2 photoanode shows greatly improved charge separation and significantly enhanced selectivity and yield of C6 products. By decorating single-atom Pt on the defective TiO2 photoanode, selective oxidation of glucose to glucaric acid can be achieved. In this work, defective TiO2 with single-atom Pt achieves a photocurrent density of 1.91 mA cm−2 for glucose oxidation at 0.6 V versus reversible hydrogen electrode, leading to an 84.3 % yield of glucaric acid under simulated sunlight irradiation.

Hierarchical NiO/TiO2 heterojuntion-based conductometric hydrogen sensor with anti-CO-interference

Constructing a heterojunction is an effective way to improve the gas sensing properties of metal oxide semiconductors. In this work, a hydrogen sensor containing hierarchical and porous NiO/TiO2 heterojunction bilayer structure was designed. The top layer is formed by the NiO nanowalls grown along the [220] direction with exposed (111) facets, and the bottom layer is formed by the [002] oriented TiO2 nanorod arrays. The exposed high energy crystal surfaces of NiO and TiO2, together with the adapted surface depletion region, induced by the formation of the heterojunction, enable the hydrogen sensor to have both a wide detection range and a much higher response to hydrogen than single layer materials. With the optimized size of the pores existing between the walls, the hydrogen sensor shows excellent prevention to interference from CO. Both the gas diffusion regulated by the porous structure and the surface interaction between H2/CO and O2- controlled by the heterojunction barrier contribute to the distinctive detection of H2 and CO at room temperature (25 ℃ ± 2 ℃).

Mg-doped TiO2 nanorods-SrTiO3 heterojunction composites for efficient visible-light photocatalytic degradation of basic yellow 28

In this study, a series of Mg-doped TiO2/SrTiO3 heterojunctions were constructed using SrTiO3 nanoparticles anchored onto the surface of TiO2 nanorod arrays. Titanium dioxide (TiO2) nanorods and SrTiO3 nanoparticles were synthesized using the liquid phase deposition (LPD) and sol-gel methods, respectively. The photocatalytic activity of obtained photocatalysts was investigated towards the degradation of basic yellow 28 (BY28) dye under visible-light irradiation compared to the pristine TiO2 nanorods and SrTiO3 nanoparticles. The obtained samples were carefully characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field-emission scanning electron microscopy (FESEM), energy dispersive X-ray analysis (EDX), X-ray photoelectron (XPS), UV–Vis, and photoluminescence spectroscopy. 1.5 Mg–TiO2/SrTiO3 nanocomposite demonstrated the highest photocatalytic activity and the corresponding apparent rate constants of 0.0255 min−1 which is that is 2.9, 9.4, and 2.3 times higher than TiO2 nanorods, SrTiO3 nanoparticles, and TiO2/SrTiO3 nanocomposite, respectively. This enhanced photocatalytic performance can be attributed to the improved charge transfer, more effective electron-hole separation, and a red-shift in light absorption derived from the Mg doping and coupling effect of TiO2 nanorods and SrTiO3 nanoparticles.

An effective strategy for promoting charge separation by integrating heterojunctions and multiple homojunctions in TiO2 nanorods to enhance photoelectrochemical oxygen evolution.

It is important to achieve high photoelectrochemical (PEC) oxygen evolution performance in titanium oxide (TiO2) via the separation and transportation of photogenerated carriers. Herein, three-dimensional (3D) TiO2 nanorod arrays growing on flexible carbon cloth (CC) were decorated with graphitic carbon nitride (g-C3N4) to yield a 3D g-C3N4/TiO2/CC heterojunction composite (TCN). The photocurrent density of TCN is 10.6 times that of the bare TiO2 nanorod arrays, which can be attributed to the promoted separation and transportation of photogenerated carriers by the heterojunction. Then, a simple rapid cooling and heating (RCH) treatment was creatively introduced to form a gradient Ti3+ self-doping TiO2 multiple homojunction (GTSD-TiO2) in the bulk during the hydrothermal growth of the TiO2 nanorod array. This can further facilitate the separation and transportation of carriers in the bulk owing to the formation of a built-in electric field. The GTSD-TiO2 was decorated with g-C3N4 to form a core-shell heterojunction composite (GTSD-TCN). Notably, the photocurrent density of the GTSD-TCN core-shell heterojunction reached 1.23mAcm-2 at 1.23V (vs reversible hydrogen electrode (RHE)) under air mass (AM) 1.5 G illumination without the use of hole scavengers or cocatalysts; this was twice the photocurrent density of the TCN heterojunction (0.64mAcm-2) and is one of the best values obtained from the previously reported TiO2 and g-C3N4 heterojunction. This performance may be ascribed to the enhanced charge separation and transportation efficiency of the heterojunction after the RCH treatment; the efficiency rises from 51% (TCN) to 71% (GTSD-TCN). We believe that the RCH treatment is a highly promising method towards fabricating unique multiple homojunctions by gradient self-doping. This simple and novel design provides a new route for the preparation of high-performance PEC photoelectrodes.

Au nanoparticle sensitized blue TiO2 nanorod arrays for efficient Gatifloxacin photodegradation.

TiO2 nanorod arrays have been widely used in photocatalytic processes, but their poor visible light absorption and rapid carrier recombination limit their application. Both introducing oxygen vacancies and using precious metals as surface plasmon resonance (SPR) stimulators are effective strategies to enhance their photocatalytic performance. Herein, Au nanoparticle sensitized blue TiO2 nanorod arrays (Au/B-TiO2) were successfully fabricated for efficient Gatifloxacin photodegradation. The degradation efficiency of Gatifloxacin was up to 95.0%. Moreover, the corresponding reaction rate constant (Ka) was up to 0.02007 min-1. Additionally, it was suggested that Gatifloxacin could be subject to three different degradation pathways. The superior catalytic activity of Au/B-TiO2 is a result of the combined effect of the two components. Firstly, TiO2 nanorod arrays provide a larger surface area for Au deposition and act as efficient transfer channels. Secondly, the presence of oxygen vacancies in blue TiO2 nanorod arrays enhances the catalytic activity. Thirdly, Au acts as a SPR activator, providing a large number of high-energy electrons in the photocatalysis process. Lastly, the improved light capture capabilities are essential for efficient removal of Gatifloxacin. This work provides a new approach for the construction of a high-performance heterojunction photocatalyst in advanced oxidation processes.

Preparation of a TiO2/PEDOT nanorod film with enhanced electrochromic properties.

The designed growth of titanium dioxide (TiO2)/poly(3,4-ethylenedioxythiophene) (PEDOT) nanorod arrays has been achieved by the combination of hydrothermal and electrodeposition methods. Due to the use of one-dimensional (1D) TiO2 nanorod arrays as the template of the nanocomposites (TiO2/PEDOT), the surface area of the active materials is enlarged and the diffusion distance of the ions is shortened. The nanorod structure also contributes to increasing the length of PEDOT conjugated chains and facilitates the transfer of electrons in the conjugated chains. Consequently, the TiO2/PEDOT film delivers a shorter response time (∼0.5 s), higher transmittance contrast (∼55.5%) and long-cycle stability compared to the pure PEDOT film. In addition, the TiO2/PEDOT electrode is further developed to be a smart bi-functional electrochromic device exhibiting energy storage performance. We expect that this work may lead to new designs for powerful intelligent electrochromic energy storage devices.

A TiO2 nanorod and perylene diimide based inorganic/organic nanoheterostructure photoanode for photoelectrochemical urea oxidation.

Visible light-driven photoelectrochemical (PEC) urea oxidation using inorganic/organic nano-heterostructure (NH) photoanodes is an attractive method for hydrogen (H2) production. In this article, inorganic/organic NHs (TiO2/PDIEH) consisting of a N,N-bis(2-ethylhexyl)perylene-3,4,9,10-tetracarboxylic diimide (PDIEH) thin layer over TiO2 nanorods (NRs) were fabricated for the PEC urea oxidation reaction (UOR). In these NHs, a PDIEH layer was anchored on TiO2 NR arrays using the spin-coating technique, which is beneficial for the uniform deposition of PDIEH on TiO2 NRs. Uniform deposition facilitated adequate interface contact between PDIEH and TiO2 NRs. TiO2/PDIEH NHs achieved a high current density of 1.1 mA cm-2 at 1.96 VRHE compared to TiO2 NRs. TiO2/PDIEH offers long-term stability under light illumination with 90.21% faradaic efficiency. TiO2/PDIEH exhibits a solar-to-hydrogen efficiency of 0.52%. This outcome opens up new opportunities for inorganic/organic NHs for high-performance PEC urea oxidation.

TiO2 compact layer induced charge transfer enhancement in a three-dimensional TiO2-Ag array SERS substrate for quantitative and multiplex analysis.

A highly sensitive and uniform surface-enhanced Raman scattering (SERS) substrate is the guarantee for reliable quantitative analysis. Herein, a three-dimensional TiO2-Ag SERS substrate was prepared by growing a TiO2 nanorods (NRs) array on a TiO2 compact layer (c-TiO2), followed by modification with Ag nanoparticles (AgNPs). The synergy between the c-TiO2, semiconductor TiO2 NRs and the plasmonic AgNPs collaboratively endowed it with high sensitivity, in which c-TiO2 effectively blocked the recombination of electrons and holes, and the charge transfer enhancement contributed 10-fold improvement over that without the c-TiO2 substrate. Besides the high sensitivity, the TiO2-Ag hybrid array SERS substrate also showed quantitative and multi-component detecting capability. The limit of detection (LOD) for crystal violet (CV) was determined to be 10-9 M even with a portable Raman instrument. The TiO2-Ag composite structure was extended to detect organic pesticides (thiram, triazophos and fonofos), and the LODs for thiram, triazophos and fonofos were measured to be 10-7 M, 10-7 M and 10-6 M, respectively. In addition, the realistic simulation detecting pesticide residues for a real sample of dendrobium was demonstrated. The sensitive, quantitative and multiplex analysis of the TiO2-Ag hybrid array substrate indicated its great potential in the rapid detection of pesticide residues in real samples.

Flame doping of indium ions into TiO2 nanorod arrays for enhanced photochemical water oxidation.

Indium (In) ions were diffused into a TiO2 (In-TiO2) photoelectrode via a facile and efficient flame doping method resulting in improved photo-induced carrier separation. The dopant concentration was systematically investigated, and a volcano-type relationship between the dopant concentration and photoelectrochemical (PEC) performance was observed. The optimum incident photon-to-current efficiency and photocurrent density of In-TiO2 were 38.6% and 0.70 mA cm-2 at 1.23 V, respectively, 2.1 and 11.2 times the values of pristine TiO2, respectively. In doping resulted in improved charge separation and lower surface adsorption energies for reactant molecules, as evidenced by experimental and computational methods.

Enhanced photoelectrochemical performance of NiS-modified TiO2 nanorods with a surface charge accumulation facet.

Photoelectrochemical (PEC) water splitting for hydrogen production technology is considered as one of the most promising solutions to energy shortage and environmental remediation. TiO2/NiS nanorod arrays were successfully prepared using hydrothermal deposition followed by the successive ionic layer adsorption and reaction (SILAR) method. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and photoluminescence (PL) spectra characterization studies indicate the successful deposition of NiS on TiO2 NRs. The NiS deposition on TiO2 was optimized by controlling the impregnation cycle. The optimal sample exhibits a photocurrent density of 1.16 mA cm-2 at 0.6 V vs. Ag/AgCl, which is a 1.9-fold enhancement over that of pristine TiO2 nanorod arrays. The enhanced photoelectrochemical performance can be attributed to two aspects. On the one hand, the (101) crystal plane of rutile TiO2 is the facet where photogenerated holes accumulate and is an efficient active plane for the oxygen evolution reaction; on the other hand, NiS is a narrow band gap semiconductor, and its deposition on TiO2 nanorods can further promote the separation and transport of photogenerated charge carriers.

Ordered growth of metal oxides in patterned multi-angle microstructures.

Herein, we report a facile method combining top-down patterning transfer and bottom-up nanorod growth for preparing large-area and ordered TiO2 nanorod arrays. Pre-crystallization seeding was patterned with nanostructured morphologies via interfacial tension-driven precursor solution scattering on various types and period templates. This is a widely applicable strategy for capillary force-driven interfacial patterns, which also shows great operability in complex substrate morphologies with multiple-angle mixing. Moreover, the customized patterned lithographic templates containing English words, Arabic numerals, and Chinese characters are used to verify the applicability and controllability of this hybrid method. In general, our work provides a versatile strategy for the low-cost and facile preparation of hydrothermally growable metal oxide (e.g., ZnO and MnO2) nanostructures with potential applications in the fields of microelectronic devices, photoelectric devices, energy storage, and photocatalysis.

Tailoring the density of states of Ni(OH)2 with Ni0 towards solar urea wastewater splitting.

Solar urea wastewater splitting is capable of producing hydrogen and degrading the urea pollutant simultaneously. Nickel hydroxide (Ni(OH)2) has been recognized as an effective cocatalyst for the urea oxidation reaction (UOR). But the lack of an efficient preparation method and a suitable Ni(OH)2 based cocatalyst limits the performances of solar urea wastewater splitting. Herein, a potential-cycling method is developed with a high-purity nickel plate serving as the counter electrode and nickel source in a three-electrode configuration. Spherical Ni0-doped Ni(OH)2 nanoparticles are successfully synthesized on the surface of TiO2 nanorod arrays. The photocurrent density of TiO2/Ni0:Ni(OH)2 can reach 0.56 mA cm-2 at 1.23 VRHE in 1 M NaOH and 0.33 M CO(NH2)2 mixed electrolyte under AM1.5G illumination, which is 1.75 and 1.93 times those of TiO2/Ni(OH)2 deposited using a normal potentiostatic method with nickel salt solution and pristine TiO2, respectively. Ni0 doping can significantly decrease the charge transfer resistance and provide a more favorable distribution of density of states of Ni(OH)2 for the UOR. Furthermore, Ni0:Ni(OH)2 decorated TiO2 photoanodes exhibit good photocurrent retention during 12 h continuous testing. This work expands the preparation technique of urea catalysts and the strategy for developing highly efficient nickel-based catalysts.

Butea monosperma, crown of thorns, red lantana camara and royal poinciana flowers extract as natural dyes for dye sensitized solar cells with improved efficiency

The cost-effective and eco-friendly natural dyes are sustainable alternatives to synthetically prepared ruthenium-based dyes. This study aims to explore the effect of natural dyes extracted from four different flowers on improving solar cell efficiency. The natural dyes are extracted from butea monosperma (BM), crown of thorns (CT), red lantana camara (RL) and royal poinciana flowers (RP). The dye-sensitized solar cells (DSSCs) were constructed using TiO2 nanorods (NRs) and light-harvesting natural dyes. Highly ordered and vertically oriented TiO2 NRs arrays were synthesized on FTO substrate and used as photoanode to fabricate natural dye based DSSCs. TiO2 NRs facilitate the infiltration of the liquid-state electrolyte and good binding with dye molecules; their one-dimensional structural feature provides effective charge transport. A significant improvement in the photo conversion efficiency (PCE) of TiO2 NRs sensitized and light-harvesting natural dye-based DSSCs has been observed. The structural, morphological, and optical properties of the TiO2 photoanode as well as the optical properties of the extracted dyes were studied using characterization techniques. The PCE of DSSCs based on natural dye extracts from BM, CT, RL and RP flowers were observed to be 2.89%, 1.20%, 1.02% and 0.72%, respectively. This work reports the highest PCE (2.89%) to date for DSSC fabricated using BM flower-based natural dyes; therefore, it can be a sustainable alternative to synthetic dyes.

Influence of growth acidic solution and etching time on rutile TiO2 nanorod arrays synthesized by hydrothermal method in dye-sensitized solar cells

Titanium butoxide (Ti(OBu)4) precursor was used to prepare titanium dioxide (TiO2) nanorods as a photoanode by hydrothermal method directly on FTO glass with different hydrochloric acid (HCl) – water (H2O) ratio (12.5-7.5, 10-10, 7.5-12.5 and 5-15) ml and etching times (24, 48, and 72)h. The (XRD) results show good crystallinity of TiO2 with rutile phase and preferred orientations (101) and (002) for all samples. The grain size of the TiO2 nanorods increases with decrease the HCl concentration. The (FESEM) images show that an increase in HCl concentration leads to an increase in the rod diameter of the TiO2 NRs and a decrease in their length. The optimum efficiency (η) of DSSC based on TiO2 NRs was 3.255% at sample ET, where the preparation condition (7.5 ml HCl + 12.5 H2O) with a 48 h etching time.

Nickel-doped TiO2 and thiophene-naphthalenediimide copolymer based inorganic/organic nano-heterostructure for the enhanced photoelectrochemical urea oxidation reaction

To overcome the global challenges of energy crises and environmental threats, urea oxidation is a hopeful route to utilize urea-rich wastewater as an energy source for hydrogen production. Herein, we report an inorganic/organic type of nano-heterostructure (NHs–Ni-TiO2/p-NDIHBT) as a photoanode with excellent urea oxidation efficiency driven by visible light. This heterostructured photoanode consists of nickel (Ni)-doped TiO2 nanorods (NRs) arrays as an inorganic part and a D-A-D type organic polymer i.e p-NDIHBT as an organic part. The as-prepared photoanode was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The morphological studies of TEM confirm the coating of p-NDIHBT on Ni–TiO2 NPs (∼1 μm). The consequence of heterostructure formation on optical and photoelectrochemical (PEC) properties of photoanode were explored through photoelectrochemical responses under visible light irradiation. The photoelectrochemical activity of Ni–TiO2 and Ni–TiO2/p-NDIHBT photoanode from linear sweep voltammetry (LSV) shows the ultrahigh photocurrent density of 0.36 mA/cm2 and 2.21 mA/cm2, respectively measured at 1.965 VRHE. Electrochemical impedance spectroscopy (EIS) of both photoanodes shows a highly sensitive nature toward the urea oxidation reaction. The hybrid photoanode also exhibits high photostability, good solar-to-hydrogen conversion efficiency, and high faradaic efficiency for urea oxidation.

Gradient band alignment of N-doped titania nanosheets on TiO2 nanorod arrays for improved solar water oxidation

TiO2 is a typical semiconducting material for photoelectrochemical (PEC) hydrogen generation, but still suffers from poor light capturing capability and slow surface water oxidation kinetics. Herein, a homologous heterojunction has been designed and fabricated based on TiO2 nanorod arrays (NAs) and N-doped titania (Ti0.91O2−xNx) nanosheets (TON NSs). Owing to the narrower band gap, TON broadens light absorption range and enhances absorption intensity. More importantly, the employment of TON for interfacial modulation could accelerate the surface water splitting kinetics due to the gradient band alignment of TON/TiO2. The upshifted valence band could better drive the holes to travel across the surface of photoanode for water oxidation reaction. Consequently, the optimal TON/TiO2 photoanode has achieved a significantly improved photocurrent of 1.62 mA/cm2 at 1.23 V vs RHE, which is 2.45 times of that of TiO2. This work provides an effective strategy for the design and construction of homologous heterojunctions for energy catalytic reactions.