Porous TiO2 Nanofibers Research Articles

Enhanced acetone gas sensor via TiO2 nanofiber-NiO nanoparticle heterojunction

We present a high surface area sensor comprising NiO nanoparticles (NPs) incorporated within porous TiO2 nanofibers (NFs), showing a remarkable response to acetone. Initially, we synthesized Polyvinylpyrrolidone (PVP) NFs containing titanium (Ti) and nickel (Ni) salts using a simple electrospinning method. Subsequent calcination of the PVP NFs led to the formation of NiO NPs embedded within the porous TiO2 NFs. The resulting heterostructure material exhibited a significant response to acetone detection, with a ratio of electrical resistance in air (Ra) to that in the presence of gas (Rg) reaching 83 at its optimal operating temperature of 300 °C. Furthermore, it demonstrated stable performance under high relative humidity conditions.

Heterogeneous MoS2 Nanosheets on Porous TiO2 Nanofibers toward Fast and Reversible Sodium-Ion Storage.

2D layered molybdenum disulfide (MoS2) has garnered considerable attention as an attractive electrode material in sodium-ion batteries (SIBs), but sluggish mass transfer kinetic and capacity fading make it suffer from inferior cycle capability. Herein, hierarchical MoS2 nanosheets decorated porous TiO2 nanofibers (MoS2 NSs@TiO2 NFs) with rich oxygen vacancies are engineered by microemulsion electrospinning method and subsequent hydrothermal/heat treatment. The MoS2 NSs@TiO2 NFs improves ion/electron transport kinetic and long-term cycling performance through distinctive porous structure and heterogeneous component. Consequently, the electrode exhibits excellent long-term Na storage capacity (298.4mAhg-1 at 5Ag-1 over 1100 cycles and 235.6mAhg-1 at 10Ag-1 over 7200 cycles). Employing Na3V2(PO4)3 as cathode, the full cell maintains a desirable capacity of 269.6mAhg-1 over 700 cycles at 1.0Ag-1. The stepwise intercalation-conversion and insertion/extraction endows outstanding Na+ storage performance, which yields valuable insight into the advancement of fast-charging and long-cycle life SIBs anode materials.

Highly selective acetone sensor based on Co3O4-decorated porous TiO2 nanofibers

We report synthesis and characterization of Co 3 O 4 -decorated porous TiO 2 nanofibers obtained through a facile electrospinning followed by a hydrothermal process. A morphological characterization confirmed that the diameter of the nanofiber was 250–300 nm. It was composed of subgrains, while its surface was decorated with Co 3 O 4 nanoparticles with a diameter of 30–50 nm. The nanofiber had a porous body structure, which was conducive to the adsorption of acetone gas. The synthesized Co 3 O 4 -decorated porous TiO 2 nanofibers were used as sensing materials to fabricate acetone gas sensors. Their response and recovery times were systematically analyzed with respect to the operation temperature and acetone gas concentration. The observed gas response, response time, and recovery time of the nanofiber-based gas sensor were 71.88, 122 s, and 351 s, respectively, for 100-ppm acetone gas at an optimized temperature of 250 °C. Therefore, the Co 3 O 4 -decorated porous TiO 2 nanofibers could be a promising candidate for the fabrication of high-selectivity acetone gas sensors. • Porous TiO 2 nanofibers are synthesized through a facile electrospinning process. • Co 3 O 4 nanoparticles are decorated on nanofibers through a solvothermal process. • Various physical and electrical sensing characteristics of the nanofibers are analyzed. • Acetone sensing performance are analyzed and discussed its sensing mechanisms.

Cu 2 AgInS 2 Se 2 quantum dots sensitized porous TiO 2 nanofibers as a photoanode for high‐performance quantum dot sensitized solar cell

Cu2AgInS2Se2 alloyed quantum dots are synthesized through a simple hot injection method. Its tetragonal structure and crystallite size are determined by using X-ray diffraction analysis. Its optical properties are observed by using Ultraviolet-Vis absorption and PL emission spectroscopies. The oxidation state and elemental composition of Cu2AgInS2Se2 quantum dots are confirmed by X-ray photoelectron spectroscope analysis and energy dispersive X-ray analysis, respectively. The optical bandgap of the synthesized quantum dots is measured to be 1.29 eV. The synthesized Cu2AgInS2Se2 quantum dots are sensitized onto the porous TiO2 nanofibers (CAISSe/P-TiO2) and its morphological and optical properties are examined. The quantum dot sensitized solar cell is assembled using CAISSe/P-TiO2, polysulfide and Cu2S as the photoanode, electrolyte and the counter electrode exhibited photoconversion efficiency (PCE) of 5.87%, which is significantly higher than that assembled using Cu2AgInSe4 (4.21%) and Cu2AgInS4 (4.89%) quantum dots sensitized porous TiO2 NFs as the photoanodes.

Cu2AgInSe4 QDs sensitized electrospun porous TiO2 nanofibers as an efficient photoanode for quantum dot sensitized solar cells

To obtain an efficient quantum dot sensitized solar cell (QDSC), a less toxic quaternary Cu2AgInSe4 QDs with 4.8 nm in size are synthesized by a simple hot injection method. The crystallite size and tetragonal structure are confirmed by XRD and HR-TEM analysis. Energy-dispersive X-ray spectroscopy analysis reveals that the atomic ratio of Cu: Ag: In: Se in the Cu2AgInSe4 QDs is 1.98:1.0:1.03:3.86. The oxidation state of the elements composed in Cu2AgInSe4 QDs is confirmed by XPS studies. Optical properties are studied from the UV–Vis–NIR absorption spectrum and photoluminescence emission spectrum. The porous TiO2 nanofibers (P-TiO2 NFs) are prepared from the conventional electrospun TiO2 NFs followed by the solvosonication process. The FE-SEM analysis is confirmed the porous texture of the TiO2 NFs. The bandgap of the Cu2AgInSe4 QDs and TiO2 NFs are determined from the Tauc plot and it was found to be 1.93 eV and 3.19 eV, respectively. QDSC is assembled using Cu2S counter electrode, polysulfide redox couple electrolyte and Cu2AgInSe4 QDs sensitized P-TiO2 NFs photoanode. The photoconversion efficiency (PCE) of the assembled QDSC is found to be 4.24%.

A wide solar spectrum light harvesting Ag2Se quantum dot-sensitized porous TiO2 nanofibers as photoanode for high-performance QDSC

A wide spectrum of light harvesting silver selenide (Ag2Se) quantum dots (QDs) with an average size of ~ 5 nm has been synthesized by a low-temperature one-pot hot injection method. To finely control the size of Ag2Se QDs, oleylamine was used as the solvent, and dodecanethiol was used as the capping agent as well as a stabilizer. The prepared Ag2Se QDs were ex situ sensitized on the porous TiO2 nanofiber (NF) substrate via a direct adsorption method to use as efficient photoanode for quantum dot-sensitized solar cell (QDSC). The UV-Vis-NIR absorption and photoluminescence studies revealed that Ag2Se QD-sensitized porous TiO2 NF photoanode (Ag2Se/P-TiO2) exhibited near-infrared (NIR) absorption and fast electron kinetics. Further, the QDSC fabricated using Ag2Se/P-TiO2 NFs as the photoanode, Cu2S as the counter electrode, and liquid polysulfide (S2−/Sx2− redox couple) as the electrolyte exhibited a photoconversion efficiency of 2.50% with an improved photocurrent density of 11.12 mA/cm2.

Distorted 1T-ReS2 Nanosheets Anchored on Porous TiO2 Nanofibers for Highly Enhanced Photocatalytic Hydrogen Production.

Recently, loading TiO2 with transition-metal disulfides (TMDs) to construct dual functional heterostructures has been widely researched as an effective strategy to improve the photocatalytic performance of a TiO2 photocatalyst. For the TMD cocatalysts, the 2H-MoS2 and 1T-MoS2 have been widely studied and researched. However, they suffer from poor catalytic activity sites/low charge transfer ability and an unstable structure. In this regard, distorted 1T-phase TMDs with a stable structure are greatly fit for the cocatalyst due to their high charge transfer ability and rich catalytic sites on both the edge and basal plane. Therefore, it is highly desirable to develop distorted 1T-phase TMD/TiO2 heterostructures with well-identified interfaces for highly enhanced photocatalytic performance. Herein, we first introduce distorted 1T-ReS2 anchored on porous TiO2 nanofibers as a promising photocatalyst for achieving an excellent photocatalytic hydrogen production. The excellent performance is attributed to the strong chemical interaction of the Ti-O-Re bond between TiO2 and ReS2, the excellent electron mobility of distorted 1T-ReS2, and the abundant catalytic activity sites on both the plane and edge of the ReS2 cocatalyst.

Highly porous TiO2 nanofibers by humid-electrospinning with enhanced photocatalytic properties

Development of porous TiO2 nanostructures with high surface area and porosity is an active area of research due to their versatile properties for diverse applications. Owing to the large aspect ratio of nanofibers (NFs) and their impressive properties, electrospinning has been a widely adopted technology for developing TiO2 nanofibers. Conventionally, porous electrospun ceramic nanostructures are produced by using sacrificial materials and post-sintering secondary chemical treatments. In this work, we demonstrate that porous TiO2 nanofibers (NFs) could be synthesized by optimizing the humidity in the electrospinning chamber without any post-sintering treatments and the porous TiO2 nanofibers thereby produced show high catalytic activities. Three other TiO2 structures are used as benchmark materials in this work: (i) solid TiO2 NFs, (ii) TiO2 NFs obtained by the removal of glycerin and (iii) TiO2 NFs obtained by etching TiO2/ZnO composite nanofibers. The BET surface area of the materials (ii) and (iii) did not differ much (∼60–63 m2/g); however, the porous TiO2 NFs produced in high humidity nearly thrice surface area (∼128 m2/g) than (i). To demonstrate the variation of properties of the four types of TiO2 NFs, photocatalytic degradation of methylene blue (MB) is demonstrated. Over 70% of the MB could be degraded by the materials produced by high humidity in 30 min whereas it was 30% for the benchmark materials. The strategy presented here could be adopted for synthesizing highly porous TiO2 NFs for a range of applications.

Porous metal oxide-carbon composite with hollow structure for energy storage applications

Nanocomposite structure of porous hollow TiO2 nanofibers (NFs) and graphitic carbon nitride (g-C3N4) sheets were directly fabricated by means of a novel electrospinning combined with calcination process. Owing to the high porosity, these nanostructured demonstrate enhanced energy storage properties when used in supercapacitors (SCs). Nanomaterials in particular offer unique properties or combinations of properties as electrodes and electrolytes in a range of energy devices. The energy storage behavior of electrochemical capacitors (ECs) made from TiO2/g-C3N4 nanocomposites was investigated by cyclic voltammetry and electrochemical impedance spectra. These tests showed that the supercapacitive performance of g-C3N4 was significantly enhanced after attaching porous TiO2 nanofibers.

Improving of the Photovoltaic Characteristics of Dye-Sensitized Solar Cells Using a Photoelectrode with Electrospun Porous TiO₂ Nanofibers.

Porous TiO2 nanofibers (PTFs) and dense TiO2 nanofibers (DTFs) were prepared using simple electrospinning for application in dye-sensitized solar cells (DSSCs). TiO2 nanoparticles (TNPs) were prepared using a hydrothermal reaction. The as-prepared PTFs and DTFs (with a fiber diameter of around 200 nm) were mixed with TNPs such as TNP-PTF and TNP-DTF nanocomposites used in photoelectrode materials or were coated as light scattering layers on the photoelectrodes to improve the charge transfer ability and light harvesting effect of the DSSCs. The as-prepared TNPs showed a pure anatase phase, while the PTFs and DTFs showed both the anatase and rutile phases. The TNP-PTF composite (TNP:PTF = 9:1 wt.%) exhibited an enhanced short circuit photocurrent density (Jsc) of 14.95 ± 1.03 mA cm−2 and a photoelectric conversion efficiency (PCE, η) of 5.4 ± 0.17% because of the improved charge transport and accessibility for the electrolyte ions. In addition, the TNP/PTF photoelectrode showed excellent light absorption in the visible region because of the mountainous nature of light induced by the PTF light scattering layer. The TNP/PTF photoelectrode showed the highest Jsc (16.96 ± 0.79 mA cm−2), η (5.9 ± 0.13%), and open circuit voltage (Voc, 0.66 ± 0.02 V).

Boosting the rate capability of multichannel porous TiO2 nanofibers with well-dispersed Cu nanodots and Cu2+-doping derived oxygen vacancies for sodium-ion batteries

The use of TiO2 as an anode in rechargeable sodium-ion batteries (NIBs) is hampered by intrinsic low electronic conductivity of TiO2 and inferior electrode kinetics. Here, a high-performance TiO2 electrode for NIBs is presented by designing a multichannel porous TiO2 nanofibers with well-dispersed Cu nanodots and Cu2+-doping derived oxygen vacancies (Cu-MPTO). The in-situ grown well-dispersed copper nanodots of about 3 nm on TiO2 surface could significantly enhance electronic conductivity of the TiO2 fibers. The one-dimensional multichannel porous structure could facilitate the electrolyte to soak in, leading to short transport path of Na+ through carbon toward the TiO2 nanoparticle. The Cu2+-doping induced oxygen vacancies could decrease the bandgap of TiO2, resulting in easy electron trapping. With this strategy, the Cu-MPTO electrodes render an outstanding rate performance for NIBs (120 mAh·g−1 at 20 C) and a superior cycling stability for ultralong cycle life (120 mAh·g−1 at 20 C and 96.5% retention over 2,000 cycles). Density functional theory (DFT) calculations also suggest that Cu2+ doping can enhance the conductivity and electron transfer of TiO2 and lower the sodiation energy barrier. This strategy is confirmed to be a general process and could be extended to improve the performance of other materials with low electronic conductivity applied in energy storage systems.

Polymer-Promoted Synthesis of Porous TiO2 Nanofibers Decorated with N-Doped Carbon by Mechanical Stirring for High-Performance Li-Ion Storage.

Extensive efforts have been devoted to developing simple, low-cost, and high-production-yield methods to prepare hybrid materials with desired structural features for high-performance lithium storage. Here, a novel strategy is reported for fabricating the porous TiO2 nanofibers decorated with N-doped carbon (TiO2/C nanofibers) by a combination of mechanical stirring and the addition of a polymer in a beaker at ambient temperature, followed by calcination. The mechanical stirring process can provide homogeneous mixing of reactants in a solution, whereas the polymer acts not only as a structure-directing agent for fabricating one-dimensional nanofibers but also as the carbon and nitrogen source to generate N-doped carbon framework and porous structures. The TiO2/C nanofibers have average diameters of 500 nm and lengths up to 65 μm and are further composed of intercrossed TiO2 nanocrystals with sizes of 8 nm, with micropores centered at 1.5 nm and mesopores at 3-6 nm. The TiO2/C electrodes demonstrated a high reversible capacity (368 mAh g-1 at 0.25C after 200 cycles), good cycling performance (176 mAh g-1 at 10C over 2000 cycles), and excellent rate capability (97 mAh g-1 at 20C).

Direct fabrication of highly porous graphene/TiO2 composite nanofibers by electrospinning for photocatalytic application

We reported the fabrication of highly porous graphene/TiO2 composite nanofibers in the form of a nonwoven mat by electrospinning followed by calcination in air at 450 °C. The graphene can uniformly disperse in highly porous TiO2 nanofibers. The highly porous graphene/TiO2 composite nanofibers exhibited excellent catalytic activities. The new method for producing graphene/TiO2 composite nanofibers is versatile and can be extended to fabricate various types of metal oxide and graphene nanocomposites.

Cu2ZnSnSe4 QDs sensitized electrospun porous TiO2 nanofibers as photoanode for high performance QDSC

An earth-abundant and relatively less toxic, quaternary Cu2ZnSnSe4 (CZTSe) quantum dots (QDs) were prepared by hot injection method at low temperature to use as a sensitizer for QDSC. The formation of tetragonal phase and stoichiometry were confirmed by X-ray diffraction (XRD), Raman spectroscopy and energy dispersive X-ray (EDX) analysis, respectively. The UV–Vis-NIR and photoluminescence spectroscopy was used to determine the bandgap (1.66 eV) and narrow emission (1050–1130 nm) range. Moreover, transmission electron microscopy (TEM) was used to find out the average size of CZTSe QDs and it was found to be ∼5 nm. It can highly adsorb on the porous TiO2 nanofibers (NFs) and enhance the absorbance due to its smaller size. The photoconversion efficiency was investigated using the prepared CZTSe QDs sensitized porous TiO2 NFs based QDSC and its photoconversion efficiency (PCE) was found to be 3.61% which is higher than that of the conventional TiO2 NFs based QDSC (η ≈ 2.84%).

Development of porous TiO2 nanofibers by solvosonication process for high performance quantum dot sensitized solar cell

In the present study, we synthesized TiO2 nanofibers (NFs) by electrospinning technique and they were subject to solvosonication process using glycerol as a pore forming agent to produce porous TiO2 NFs. The prepared porous TiO2 NFs are seen to improve the light harvesting capability as a result of enhanced light scattering inside the TiO2 NFs and offer a high surface area for maximum adsorption of pre-synthesized CdSe (~4 nm) QDs. The FE-SEM and BET analysis were performed to confirm the surface texture and surface area of porous TiO2 NFs, respectively. Finally, QDSSCs were fabricated using these porous TiO2 NFs sensitized with CdSe QDs as the photoanode, Cu2S nanoparticles as the counter electrode and polysulfide redox couple (S2−/Sx2−) as the electrolyte. The porous TiO2 NFs obtained by solvosonication at the time duration of 90 min has enhanced photocurrent density (Jsc) of 9.21 mA/cm2 with high power conversion efficiency (η) of 2.15% than the conventional TiO2 NFs (η ≈ 1.50%).

Design and synthesis of interconnected hierarchically porous anatase titanium dioxide nanofibers as high-rate and long-cycle-life anodes for lithium-ion batteries.

We suggest an efficient and simple synthetic strategy to prepare interconnected hierarchically porous anatase TiO2 (IHP-A-TiO2) nanofibers by two synergetic effects: phase separation between polymers and relative humidity control during electrospinning. The macro channels formed by polystyrene decomposition were interconnected by numerous mesopores that were formed by evaporation of infiltrated water vapor in the structure. The resulting IHP-A-TiO2 nanofibers showed better Li+ ion storage performances than the TiO2 materials reported in the literature. The discharge capacity of IHP-A-TiO2 nanofibers for the 3000th cycle at 1.0 A g-1 and corresponding coulombic efficiency from the 20th cycle onward were 142 mA h g-1 and >99.0%, respectively. Well-interconnected, ultrafine TiO2 nanocrystals within the nanofiber showed structural stability during cycling and facilitated facile charge transfer at the electrode-electrolyte interface.

Fabrication of hierarchically porous TiO2 nanofibers by microemulsion electrospinning and their application as anode material for lithium-ion batteries.

Titanium dioxide (TiO2) nanofibers have been widely applied in various fields including photocatalysis, energy storage and solar cells due to the advantages of low cost, high abundance and nontoxicity. However, the low conductivity of ions and bulk electrons hinder its rapid development in lithium-ion batteries (LIB). In order to improve the electrochemical performances of TiO2 nanomaterials as anode for LIB, hierarchically porous TiO2 nanofibers with different tetrabutyl titanate (TBT)/paraffin oil ratios were prepared as anode for LIB via a versatile single-nozzle microemulsion electrospinning (ME-ES) method followed by calcining. The experimental results indicated that TiO2 nanofibers with the higher TBT/paraffin oil ratio demonstrated more axially aligned channels and a larger specific surface area. Furthermore, they presented superior lithium-ion storage properties in terms of specific capacity, rate capability and cycling performance compared with solid TiO2 nanofibers for LIB. The initial discharge and charge capacity of porous TiO2 nanofibers with a TBT/paraffin oil ratio of 2.25 reached up to 634.72 and 390.42 mAh·g−1, thus resulting in a coulombic efficiency of 61.51%; and the discharge capacity maintained 264.56 mAh·g−1 after 100 cycles, which was much higher than that of solid TiO2 nanofibers. TiO2 nanofibers with TBT/paraffin oil ratio of 2.25 still obtained a high reversible capacity of 204.53 mAh·g−1 when current density returned back to 40 mA·g−1 after 60 cycles at increasing stepwise current density from 40 mA·g−1 to 800 mA·g−1. Herein, hierarchically porous TiO2 nanofibers have the potential to be applied as anode for lithium-ion batteries in practical applications.

Dual-Phase Li4Ti5O12/TiO2(B) Heteronanostructures As Anodes for High-Performance Lithium-Ion Batteries

The synthesis of dual phase Li4Ti5O12/TiO2(B) composite remains a tremendous challenge due to the easy formation of anatase TiO2 instead of Li4Ti5O12 in the process. In this work, Li4Ti5O12/TiO2(B) heteronanostructures comprising porous TiO2(B) nanofibers integrated with Li4Ti5O12 nanocrystals are synthesized and applied as anode for lithium-ion batteries. Benefiting from the complementary advantages of higher theoretical capacity of TiO2(B) with favourable pseudocapacitive behaviour and excellent cyclability of Li4Ti5O12, this heteronanostructure demonstrates a superior lithium-ion storage performance in terms of high discharge capacity and remarkable long-term stability. As a result, Li4Ti5O12/TiO2(B) heteronanostructures manifest discharge capacity of 130 mAhg−1 and capacity retention of 93 % at high rate of 1.75 Ag-1, compared to those of TiO2(B) pristine of 90 mAhg−1 and 75 %. The superior electrochemical performance demonstrated by Li4Ti5O12/TiO2(B) heteronanostructure reveals a new direction of integration of Li4Ti5O12 into TiO2(B) to improve both the capacity performance and cyclability. Acknowledgements This project is financially supported by Innovation and Technology Fund (ITS/378/13) and Internship Programme (InP/299/14) from Innovation and Technology Commission, Hong Kong, HKU Strategic Research Theme on Clean Energy, University Development Fund for Initiative for Clean Energy and Environment, and our industry partner – Gold Peak (GP) Batteries Limited. Figure 1

Surfactant-assisted synthesis of porous TiO2 nanofibers as an anode material for secondary lithium ion batteries

An optimized amount of cetyltrimethylammonium bromide (CTAB) as a surfactant was used for the first time to fabricate porous TiO2 nanofibers by an electrospinning technique combined with post-annealing at 500 °C for 5 h in air medium.

Pore volume and distribution regulation of highly nanoporous titanium dioxide nanofibers and their photovoltaic properties

By combining the initial solvent volatilization and ultimate calcination to form highly nanoporous polystyrene/titanium dioxide (PS/TiO2) composite nanofibrous mats were fabricated via electrospinning, then the PS was removed afterwards by calcination, and finally porous TiO2 nanofibers were formed successfully. The porous structure of the nanofibers was characterized by field emission scanning electron microscopy and Brunauer-Emmett-Teller measurements, which indicated that the size and the diameter of the pore and the ratio of the surface area to the volume of the mats were regulated by adjusting the weight ratios of tetrahydrofuran and N,N-dimethylformamide in the binary solvent mixtures. X-ray photoelectron spectroscopy and Raman analysis confirmed that the addition of TiO2 into the fibers was successful and that PS decomposed completely from fibers after calcination at 500°C. The photovoltaic measurements showed that the obtained TiO2 nanofibers were ideal candidates for the fabrication of the photoanodes on the dye-sensitized solar cells.