Unbiased spontaneous solar hydrogen production using stable TiO2–CuO composite nanofiber photocatalysts

We report on the optimization of electrospun TiO₂–CuO composite nanofibers as low-cost and stable photocatalysts for visible-light photocatalytic water splitting. The effect of different annealing atmospheres on the crystal structure of the fabricated nanofibers was investigated and correlated to the photocatalytic activity of the material. The presence of CuO resulted in narrowing the bandgap of TiO₂ and shifting the absorption edge into the visible region of the light spectrum. The effect of incorporating CuO within TiO₂ nanofibers on the crystal structure and composition was also investigated using X-ray diffraction (XRD), electron paramagnetic resonance (EPR), and X-ray photoelectron spectroscopy (XPS) techniques. The fabricated TiO₂–CuO composite nanofibers showed 117% enhancement in the amount of hydrogen evolved during the photocatalytic water splitting process compared to pure TiO₂. This enhancement was related to the created shallow defect states that facilitate charge transfer from TiO₂ to CuO and distinct characteristics of the composite nanofibers, such as the high surface area and directional charge transfer. The study showed that Cu is a promising alternative to noble metals as a catalyst in photocatalytic water splitting, with the advantage of being an Earth abundant element and a relatively cheap material.

We report on the optimization of electrospun TiO₂–CuO composite nanofibers as low-cost and stable photocatalysts for visible-light photocatalytic water splitting.     

Versatility of CoPcS in CoPcS/TiO2 for MB degradation: photosensitization,charge separation and oxygen activation

In this report, a composite photocatalyst consisting of cobalt phthalocyanine sulfate (CoPcS) and TiO₂ was prepared by a facile synthesis. Careful characterizations and measurements indicate a covalent grafting of CoPcS onto TiO₂ through Ti–O–S linkages, acquiring an intimate heterojunction between TiO₂ and CoPcS. The obtained composite was evaluated for its photocatalytic activity toward the degradation of methyl blue (MB) under visible light irradiation. The evaluation showed a significantly enhanced degradation rate of MB by CoPcS/TiO₂. The improved photocatalytic performance of CoPcS/TiO₂ was attributed to the photosensitization of TiO₂ by CoPcS, charge separation by electron transfer at the interface of the heterojunction formed between CoPcS and TiO₂, and oxygen activation via CoPcS. A synergetic mechanism in improving the photocatalytic performance of TiO₂ by CoPcS was investigated.

In this report, a composite photocatalyst consisting of cobalt phthalocyanine sulfate (CoPcS) and TiO₂ was prepared by a facile synthesis.     

Preparation of ZnO@TiO2 nanotubes heterostructured film by thermal decomposition and their photocatalytic performances

TiO₂ nanotubes (NTs) arrays prepared by anodic oxidation were modified with ZnO particles and their morphology and photocatalytic properties were investigated. A simple thermal decomposition process was involved in the modification method. Zinc acetate solution was filled into the TiO₂ NTs arrays, and ZnO@TiO₂ heterojunction films were formed after the thermal treatment. The morphology and catalytic properties of the heterojunction films could be manipulated by the concentration of zinc acetate solution. Compared to TiO₂ NTs arrays, the ZnO@TiO₂ heterojunction films with an optimized concentration of zinc acetate showed enhanced catalytic performances. Their photocatalytic activities were discussed with respect to the formation of ZnO@TiO₂ heterojunctions and enforced charge separation. This study demonstrates a simple method to prepare ZnO nanoparticles@TiO₂ NT heterojunction films, which is promising for other environmental and energy related applications.

Efficient and low-cost preparation method of ZnO nanoparticles@TiO₂ NT heterojunction films, has a positive effect on water pollution control.     

Flake-like InVO4 modified TiO2 nanofibers with longer carrier lifetimes for visible-light photocatalysts

Highly efficient solar light absorption capabilities and quantum yields in photocatalysts are key to their application in photocatalytic fields. Towards this end, TiO₂/InVO₄ nanofibers (NFs) have been designed and fabricated successfully by a one-pot electrospinning process. The resulting TiO₂/InVO₄ NFs display excellent visible-light photocatalytic activity, owing to their prominent visible-light absorption and electron–hole separation properties. Time-resolved transient PL spectroscopy demonstrated that the TiO₂/InVO₄ NFs display longer emission decay times (22.0 ns) compared with TiO₂ NFs (15.5 ns), implying that the heterojunction can remarkably suppress the electron–hole recombination and promote the carrier transfer efficiency. With tailored heterostructure features, TiO₂/InVO₄ NFs exhibit superior visible-light photodegradation activity, and after 80 min of visible-light irradiation, almost 95% of RhB molecules can be decomposed by TiO₂/InVO₄ NFs, while only 18% of RhB molecules can be decomposed by pure TiO₂ NFs.

TiO₂/InVO₄ nanofibers have been designed and fabricated successfully by one-pot electrospinning process, which display longer carrier lifetime (22 ns) and enhanced visible-light photocatalytic activity.     

Microwave-assisted synthesis of an RGO/CdS/TiO2 step-scheme with exposed TiO2 {001} facets and enhanced visible photocatalytic activity

Semiconductor-based heterojunction photocatalysts with a special active crystal surface act as an essential part in environmental remediation and renewable energy technologies. In this study, an RGO/CdS/TiO₂ step-scheme with high energy {001} TiO₂ facets was successfully fabricated via a microwave-assisted solvothermal method. The photocatalytic performance of as-prepared samples was assessed by degrading methylene blue under visible light irradiation. We found that the photocatalytic activity of the RGO/CdS/TiO₂ step-scheme heterojunction was related to the proportion of TiO₂. A ternary sample with a TiO₂ content of 10 wt% exhibited superior photocatalytic performance, and approximately 99.7% of methylene blue was degraded during 50 min of visible illumination which was much higher than the percentages found for TiO₂, CdS, RGO/TiO₂, and RGO/CdS. The greatly improved photocatalytic performance is due to the exposure of the reactive {001} surface of TiO₂ and the formation of a CdS/TiO₂ heterojunction step-scheme, which effectively inhibits the recombination of charge carriers at the heterogeneous interfaces. Moreover, the incorporation of graphene further enhances the visible light harvesting and serves as an electron transport channel for rapidly separating photogenerated carriers. Based on the PL, XPS, photoelectrochemical properties and the free radical capturing experiment results, a possible photodegradation mechanism was proposed.

The photocatalytic enhancement of RGO/CdS/TiO₂ is due to the high-energy {001} surface of TiO₂ and CdS forming a stepped heterojunction, which is dispersed on the surface of reduced graphene oxide.     

Facile synthesis of a novel WO3/Ag2MoO4 particles-on-plate staggered type II heterojunction with improved visible-light photocatalytic activity in removing environmental pollutants

A novel WO₃/Ag₂MoO₄ heterojunction has been synthesized through a facile precipitation method with Ag₂MoO₄ particles firmly deposited on the surface of WO₃ nanoplates, forming “particles-on-plate” type II heterojunction structures. This heterojunction exhibited improved photocatalytic activities for the degradation of rhodamine B (RhB), 4 chlorophenol (4-CP) and tetracycline hydrochloride (TC) under visible-light irradiation compared to pure Ag₂MoO₄ and WO₃. In addition, the heterojunction with 10 wt% Ag₂MoO₄ displays the best photocatalytic performance, which was about 2 times better than that of pure WO₃ or Ag₂MoO₄. The TC photodegradation rate reaches up to 91% within 90 min visible light irradiation. Furthermore, the photocatalytic efficiency of the Ag₂MoO₄/WO₃ heterojunction is 1.3 times higher than that of the mixture of the two individual photocatalysts. This remarkable enhanced photocatalytic performance results from the staggered bandgap between Ag₂MoO₄ and WO₃, which can suppress the recombination of electron–hole pairs efficiently. Moreover, based on the radical trapping experiment, the superoxide radical anions (·OH) and photogenerated holes (h⁺) are the crucial active oxidizing species.

A novel WO₃/Ag₂MoO4 heterojunction was synthesized and it showed excellent photodegradation performance and stability for several sorts of organic pollutants.     

Enhanced photocatalytic activity of TiO2/UiO-67 under visible-light for aflatoxin B1 degradation

TiO₂ has great potential in photocatalytic degradation of organic pollutants, but poor visible light response and low separation efficiency of photogenerated electron–hole pairs limit its wide applications. In this study, we have successfully prepared TiO₂/UiO-67 photocatalyst through an in situ solvothermal method. The degradation rate of aflatoxin B1 (AFB1) is 98.9% in only 80 min, which is superior to the commercial P25, commercial TiO₂ and most of reported photocatalysts under visible light irradiation. In addition, the TiO₂/UiO-67 photocatalyst showed excellent recyclability. We demonstrated that the enhanced photocatalytic mechanism was owing to the heterojunction between TiO₂ and UiO-67, which enhanced effectively the separation photogenerated charge carriers and visible light response. The free radical trapping tests demonstrated that superoxide radicals (˙O₂⁻), holes (h⁺) and hydroxyl radicals (˙OH) were the main active species and then oxidized AFB1 to some small molecules.

Enhanced photocatalytic activity of TiO₂/UiO-67 under visible-light for aflatoxin B1 degradation.     

TiO2/Fe2O3 heterostructures with enhanced photocatalytic reduction of Cr(vi) under visible light irradiation

We report a study on the synthesis of TiO₂/Fe₂O₃ (TF) nanocomposites and their photocatalytic performance under visible-light irradiation. The characterization of structure and morphology shows that hematite Fe₂O₃ was deposited on anatase TiO₂ nanoparticles with particle sizes in the range of 20–100 nm. In contrast to pure TiO₂ and pure Fe₂O₃, the nanocomposites exhibited remarkable photocatalytic activity. For example, the photoreduction efficiency of TF0.5 reaches 100% for a 100 ppm Cr(vi) solution within 160 minutes. The photochemical properties were studied by various methods. Finally, we conclude that the excellent performance of the photocatalysts is mainly attributed to two aspects: the enhanced absorption of visible light and the synergistic effect of an internal electric field at the heterojunction and citric acid for promoting the separation of electron–hole pairs.

A TiO₂/Fe₂O₃ heterojunction with an internal electric field was constructed for enhancing photocatalytic reduction efficiency of Cr(vi).     

Mesoporous Cu–Cu2O@TiO2 heterojunction photocatalysts derived from metal–organic frameworks

This study reveals a unique Cu–Cu₂O@TiO₂ heterojunction photocatalyst obtained with metal–organic framework as the precursor, which can be utilized in dye photodegradation under visible light irradiation. The composition, structure, morphology, porosity, optical properties and photocatalytic performance of the obtained catalysts were all investigated in detail. The Cu–Cu₂O@TiO₂ nanocomposite is composed of lamellar Cu–Cu₂O microspheres embedded by numerous TiO₂ nanoparticles. Methylene blue, methyl orange and 4-nitrophenol were used as model pollutants to evaluate the photocatalytic activity of the Cu–Cu₂O@TiO₂ nanocomposite for dye degradation under visible light irradiation. Nearly 95% decolourisation efficiency of Methylene blue was achieved by the Cu–Cu₂O@TiO₂ photocatalyst within 3 h, which is much higher than that of TiO₂ or Cu₂O catalysts. The excellent photocatalytic activity was primarily attributed to the unique MOF-based mesoporous structure, the enlarged photo-adsorption range and the efficient separation of the charge carriers in the Cu–Cu₂O@TiO₂ heterojunction.

Cu–Cu₂O@TiO₂ heterojunction photocatalyst derived from a metal–organic framework shows high photocatalytic activity for dye degradation under visible light irradiation.     

Photo-reduction of heavy metal ions and photo-disinfection of pathogenic bacteria under simulated solar light using photosensitized TiO2 nanofibers

We report the photosensitization of electrospun titania nanofibers, with a mean diameter of 195 nm, by low bandgap silver sulfide nanoparticles of 11–23 nm mean size with the aim of treating heavy metal ions and pathogenic bacteria simultaneously under simulated solar light irradiation. The 17 nm Ag₂S/TiO₂ nanofibers showed 90% photocatalytic reduction of Cr(vi) at pH of 3 with a pseudo-first order rate constant of 0.016 min⁻¹ which is significantly better than the previously reported for Ag–Ag₂S/TiO₂ composite particles. The antibacterial capability of the Ag₂S/TiO₂ nanofibers was evaluated via photo-disinfection of the Gram-positive and Gram-negative bacterial strains. The smallest sized 11 nm Ag₂S/TiO₂ nanofiber showed the best bactericidal efficiency of 100% and 90.6% against Gram-negative E. coli and Gram-positive S. aureus after 1 h of irradiation, respectively, whereas, only 50% E. coli and 41% S. aureus were found to be inactivated in dark. Furthermore, a UV–O₃ treatment of the 11 nm Ag₂S/TiO₂ nanofibers remarkably enhanced the antibacterial activity where 89% E. coli and 81% S. aureus were inactivated in just 10 min of the irradiation. Enhanced photocatalytic activity is attributed to the efficient charge separation and transfer and reduced electron–hole recombination induced by the effective heterojunction formation between TiO₂ and the optimally sized Ag₂S nanoparticles. The disinfection nature of the Ag₂S nanoparticles, role of the generated hydroxyl species under irradiation, and the cell wall damage mechanism is also discussed. This study demonstrates the potential use of these multifunctional composite TiO₂ nanofibers for water remediation.

Photosensitization of titania nanofibers by low bandgap silver sulfide nanoparticles for treating heavy metal ions and pathogenic bacteria simultaneously under simulated solar light irradiation.     

Construction of Ag-modified TiO2/ZnO heterojunction nanotree arrays with superior photocatalytic and photoelectrochemical properties

The work involves the preparation of TiO₂/ZnO heterojunction nanotree arrays by a three-step: hydrothermal, sol–gel, and secondary hydrothermal method, and then modification of Ag quantum dots (QDs). In the above process, the ZnO nanoparticles attached to the TiO₂ surface were subjected to secondary growth by a hydrothermal method to form a unique nanotree structure with TiO₂, followed by Ag quantum dot modification by quantum dot deposition. In summary, TiO₂/ZnO nanotree arrays are cited for the first time. The prepared Ag-modified TiO₂/ZnO heterojunction nanotree arrays were found to exhibit enhanced photoelectrochemical and photocatalytic properties. The photocurrent of the Ag-modified TiO₂/ZnO heterojunction nanotree arrays is increased by 8-fold compared to the pure TiO₂ nanorod arrays, the photocatalytic degradation rate within 180 minutes increased from 37% to 77% and the kinetic rate constants for the degradation of methyl orange were three times higher than the pure TiO₂ nanorod arrays. The improved performance is partly due to the introduction of the TiO₂/ZnO heterojunction nanotree arrays which provide Ag QDs with greater adhesion area. Localized surface plasmon resonance (LSPR) leads to an increase in the intensity of absorbed light due to the modification of Ag QDs. On the other hand the generation of the TiO₂/ZnO heterojunction decreases the forbidden band width, resulting in the redshift of the light absorption edge. Therefore, TiO₂/ZnO heterojunction nanotree arrays are expected to play an important role in solar cells and photocatalytic materials.

The work involves the preparation of TiO₂/ZnO heterojunction nanotree arrays by a three-step: hydrothermal, sol–gel, and secondary hydrothermal method, and then modification of Ag quantum dots (QDs).     

Photocatalytic properties and energy band offset of a tungsten disulfide/graphitic carbon nitride van der Waals heterojunction

Semiconductor heterojunctions have higher photocatalytic performance than a single photocatalytic material. However, the energy band offset and the photocatalytic reaction mechanism of these heterojunctions remain controversial. Here, tungsten disulfide (WS₂)/graphitic carbon nitride (GCN) heterojunction photocatalytic water splitting is investigated with the hybrid density functional method. The band structures and the density of states (DOS) indicate that the WS₂/GCN heterojunction is a type-II heterojunction, and its valence band offset and conduction band offset are 0.27 and 0.04 eV, respectively. The differential charge density distribution and the work function calculation indicate that a built-in electric field is formed in the WS₂/GCN heterojunction. The potential of the built-in electric field is 0.16 V, and its direction is from the GCN surface to the WS₂ surface. The built-in electric field separates the photogenerated electrons and the holes in space, effectively improving the photocatalytic efficiency of the WS₂/GCN heterojunction. Our work provides insights into the electronic properties and the photocatalytic hydrogen evolution mechanism of the WS₂/GCN heterojunction.

WS₂/GCN heterojunction is a type-II heterostructure and its electric field separates the electrons and the holes in space.     

Plasmonic enhanced photocatalytic activity of Ag/TiO2 tube-in-tube fibers

Ag nanoparticle was found to significantly enhance the photocatalytic activity of self-organized TiO₂ nanotube structures. Herein, novel Ag/TiO₂ tube-in-tube fibers have been prepared by a facile electrospinning technology and calcination process. Employed as the photocatalyst, the composite could efficiently catalyze the photodegradation of the model organic pollutant, rhodamine B under visible light irradiation, exhibiting a superior photocatalytic activity than the undoped TiO₂ tube-in-tube fibers. This enhanced activity has been ascribed to plasmonic characteristics of Ag nanoparticles, which promote the light absorption and charge transfer feasibility. The simple, low-cost and green fabrication route of the composite provides a novel means for preparing similar materials, holding great promise for wider application in the future.

Ag nanoparticle was found to significantly enhance the photocatalytic activity of self-organized TiO₂ nanotube structures.     

Synthesis of vertical WO3 nanoarrays with different morphologies using the same protocol for enhanced photocatalytic and photoelectrocatalytic performances

Tungsten trioxide (WO₃) nanoarrays with different morphologies were successfully synthesized by a hydrothermal method on an FTO substrate. Various nanostructures of WO₃ including nanoflakes, nanoplates, nanoflowers and nanorods were obtained by adjusting only the acidity of the precursor solution. XRD patterns confirmed that the as-prepared orthorhombic WO₃·0.33H₂O transformed to the monoclinic WO₃ phase under annealing at 500 °C. UV-Vis absorbance spectroscopy indicated that the absorption edge of WO₃ nanoflowers exhibited a slight red-shift compared to other morphologies of WO₃. The obtained WO₃ nanoflower arrays exhibit the highest photocurrent density and photocatalytic degradation activity towards methylene blue. Finally, the mechanism of the photocatalytic degradation of methylene blue by WO₃ is discussed.

Hexagonal nanoflower WO₃ arrays were synthesized via a facile hydrothermal method without the assistance of any seed layer or structure directing agent. The nanoflower WO₃ has the highest photocatalytic activity for the degradation of methylene blue.     

The simultaneous removal of heavy metals and organic contaminants over a Bi2WO6/mesoporous TiO2 nanotube composite photocatalyst

In this study, Bi₂WO₆/mesoporous TiO₂ nanotube composites (BWO/TNTs) were successfully synthesized to remove the heavy metal Cr(vi) and refractory organic compound dibutyl phthalate (DBP) from contaminated water under visible light. Coupling TNTs with BWO can greatly improve the photocatalytic activity of the catalyst for treating Cr(vi)–DBP mixed pollutants because of synergetic effects from Cr(vi) and DBP. Specifically, the visible-light photocatalytic activities of 3% BWO/TNTs for removing DBP and Cr(vi) from mixed pollutant solutions were 10.8 and 3.8 times higher than those of BWO. Firstly, this system can take full advantage of charge carriers and can spatially separate reduction sites and oxidation sites in the photocatalyst. Secondly, TNTs has a unique multiscale channel structure that can enhance mass transfer and light utilization. These characteristics lead to very obvious photocatalytic activity improvements. In addition, the BWO/TNTs composite photocatalysts exhibited excellent stability and durability under visible and UV light irradiation. This work demonstrated a feasible method for fabricating composite photocatalysts and applied them to the simultaneous removal of heavy metal and refractory organic pollutants from contaminated water.

In this study, Bi₂WO₆/mesoporous TiO₂ nanotube composites (BWO/TNTs) were successfully synthesized to remove the heavy metal Cr(vi) and refractory organic compound dibutyl phthalate (DBP) from contaminated water under visible light.     

Highly efficient In2S3/WO3 photocatalysts: Z-scheme photocatalytic mechanism for enhanced photocatalytic water pollutant degradation under visible light irradiation

A Z-scheme system In₂S₃/WO₃ heterojunction was fabricated via a mild hydrothermal method and further applied for photocatalytic degradation of tetracycline (TCH) and Rhodamine B (Rh B) under visible light irradiation. The morphological structure, chemical composition and optical properties were studied by XRD, SEM, HRTEM and UV-visible absorption spectra. The results revealed that In₂S₃/WO₃ hierarchical structures were successfully constructed, and the prepared In₂S₃/WO₃ photocatalysts exhibited enhanced visible-light absorption compared to pure WO₃ nanorods, which are essential to improve the photocatalytic performance. The degradation rate of TCH using the In₂S₃(40 wt%)/WO₃ heterostructure (WI40) photocatalyst was about 212 times and 22 times as high as that for pure WO₃ and pure In₂S₃, respectively. The degradation rate of Rh B with the WI40 photocatalyst was about 56 times the efficiency of pure WO₃ and 7.6 times that of pure In₂S₃. The results of the surface photovoltage (SPV), transient photovoltage (TPV) and reactive oxidation species (ROS) scavenger experiments indicated that the Z-scheme system of In₂S₃/WO₃ is favorable for photoexcited charge transfer at the contact interface of In₂S₃ and WO₃, which benefits the charge separation efficiency and depresses the recombination of photoexcited charge, resulting in favorable photocatalytic pollutant degradation efficiency under visible light irradiation.

A Z-scheme system In₂S₃/WO₃ heterojunction was fabricated via a mild hydrothermal method and further applied for photocatalytic degradation of tetracycline (TCH) and Rhodamine B (Rh B) under visible light irradiation.     

Mesoporous TiO2 anatase films for enhanced photocatalytic activity under UV and visible light

Mesoporous TiO₂ films with enhanced photocatalytic activity in both UV and visible wavelength ranges were developed through a non-conventional atomic layer deposition (ALD) process at room temperature. Deposition at such a low temperature promotes the accumulation of by-products in the amorphous TiO₂ films, caused by the incomplete hydrolysis of the TiCl₄ precursor. The additional thermal annealing induces the fast recrystallisation of amorphous films, as well as an in situ acidic treatment of TiO₂. The interplay between the deposition parameters, such as purge time, the amount of structural defects introduced and the enhancement of the photocatalytic properties from different mesoporous films clearly shows that our easily upscalable non-conventional ALD process is of great industrial interest for environmental remediation and other photocatalytic applications, such as hydrogen production.

Mesoporous TiO₂ films with enhanced photocatalytic activity in both UV and visible wavelength ranges were developed through a non-conventional atomic layer deposition (ALD) process at room temperature.     

ZnO-embedded S-doped g-C3N4 heterojunction: mediator-free Z-scheme mechanism for enhanced charge separation and photocatalytic degradation

The design of UV-visible light active photocatalysts for organic pollutant removal is a challenging task. Herein, we have developed an LED light active ZnO-embedded S-doped g-C₃N₄ (SCN) heterojunction by a facile sol–gel assisted calcination method. The heterojunction between ZnO and SCN nanoparticles generates a Z-scheme photocatalyst, which helps to separate the photo-induced charge carriers in the opposite direction, and is beneficial for more visible light absorption for photocatalytic dye degradation. The composite heterojunction shows better photocatalytic redox in comparison with pristine nanomaterials. The enhanced degradation efficiency is attributed to the high production rate of ˙OH (hydroxyl) radicals during the photocatalysis process, which is analyzed by the TA test and elemental trapping experiment. Hence, we hope that this Z-scheme heterojunction provides a new way to develop UV-visible light active photocatalysts for environmental remediation applications.

We have developed the LED light active ZnO-embedded S-doped g-C₃N₄ (SCN) mediator free Z-scheme heterojunction photocatalyst for effective organic pollutant degradation.     

Fabrication of TiO2 on porous g-C3N4 by ALD for improved solar-driven hydrogen evolution

Porous graphitic carbon nitride (P-g-C₃N₄) thin sheets were fabricated by a one-step calcination of a mixture of urea, melamine, and ammonia chloride at 550 °C. P-g-C₃N₄ showed 48% higher photocatalytic H₂ production from methanol aqueous solution than conventional urea-derived graphitic carbon nitride (g-C₃N₄) because the existence of numerous pores reduces the recombination rate of charge carriers. In order to further enhance the photocatalytic activity, TiO₂ was uniformly deposited on P-g-C₃N₄ by 60–300 cycles of atomic layer deposition (ALD) to form the TiO₂@P-g-C₃N₄ composite. They exhibited much higher photocatalytic hydrogen production rates than both TiO₂ and P-g-C₃N₄. Among all composites, the sample deposited with 180 ALD cycles of TiO₂ showed the highest H₂ production because of optimal diffusion length for electrons and holes. It also performed better than the sample of g-C₃N₄ deposited with 180 cycles of TiO₂.

Schematic of Pt-loaded TiO₂@P-g-C₃N₄ 2D/2D heterojunction structure and the proposed mechanism of charge transfer for photocatalytic H₂ evolution.     

Nanofibrous TiO2 produced using alternating field electrospinning of titanium alkoxide precursors: crystallization and phase development

High-yield, free-surface alternating field electrospinning (AFES) was effectively used in the fabrication of titanium oxide nanofibrous materials from the precursors based on titanium alkoxide and a blend of polyvinylpyrrolidone and hydroxypropyl cellulose. The alkoxide/polymer mass ratio in the precursor solution has significant effects on the precursor fiber production rate as well as the structure of resulting TiO₂ nanofibers after thermal processing of precursor fibers at temperatures from 500 to 1000 °C. Within the range of tested process parameters, the best fiber production rate of ∼5.2 g h⁻¹ was achieved, in terms of the mass of crystallized TiO₂ nanofibers, with the precursor that corresponded to 1.5 : 1 TiO₂/polymer mass ratio. TiO₂ nanofibers produced by calcination at 500 °C for 3 h had 100–500 nm diameters and were composed of anatase (20–25 nm crystallite size) with rutile content 0.1–6.0 mol%, depending on the precursor composition. A considerable amount of anatase phase (up to 80 mol%) can be retained after thermal processing of TiO₂ nanofibers at 750 °C for 3 h. A nanofibrous material composed of smooth and long, predominantly monocrystalline rutile, fibrous segments was produced at 1000 °C from the precursor with 2.5 : 1 TiO₂/polymer mass ratio.

An uncommon alternating field electrospinning of titanium alkoxide/polyvinylpyrrolidone/hydroxypropyl cellulose precursors leads to high-yield synthesis of TiO₂ nanofibers with controllable microstructure and phase composition.