One-Step Low Temperature Hydrothermal Synthesis of Flexible TiO₂/PVDF@MoS₂ Core-Shell Heterostructured Fibers for Visible-Light-Driven Photocatalysis and Self-Cleaning

Smart and Multifunctional Materials Based on Electroactive Poly(vinylidene fluoride): Recent Advances and Opportunities in Sensors, Actuators, Energy, Environmental, and Biomedical Applications

From scientific and technological points of view, poly(vinylidene fluoride), PVDF, is one of the most exciting polymers due to its overall physicochemical characteristics. This polymer can crystalize into five crystalline phases and can be processed in the form of films, fibers, membranes, and specific microstructures, being the physical properties controllable over a wide range through appropriate chemical modifications. Moreover, PVDF-based materials are characterized by excellent chemical, mechanical, thermal, and radiation resistance, and for their outstanding electroactive properties, including high dielectric, piezoelectric, pyroelectric, and ferroelectric response, being the best among polymer systems and thus noteworthy for an increasing number of technologies. This review summarizes and critically discusses the latest advances in PVDF and its copolymers, composites, and blends, including their main characteristics and processability, together with their tailorability and implementation in areas including sensors, actuators, energy harvesting and storage devices, environmental membranes, microfluidic, tissue engineering, and antimicrobial applications. The main conclusions, challenges and future trends concerning materials and application areas are also presented.

Electrospun Membranes Anchored with g-C3N4/MoS2 for Highly Efficient Photocatalytic Degradation of Aflatoxin B1 under Visible Light

The degradation of aflatoxin (AF) is a topic that always exists along with the food and feed industry. Photocatalytic degradation as an advanced oxidation technology has many benefits, including complete inorganic degradation, no secondary contamination, ease of activity under moderate conditions, and low cost compared with traditional physical, chemical, and biological strategies. However, photocatalysts are usually dispersed during photocatalytic reactions, resulting in energy and time consumption in the separation process. There is even a potential secondary pollution problem from the perspective of food safety. In this regard, three electrospun membranes anchored with g-C₃N₄/MoS₂ composites were prepared for highly efficient photocatalytic degradation of aflatoxin B₁ (AFB₁) under visible light. These photocatalytic membranes were characterized by XRD, SEM, TEM, FTIR, and XPS. The factors influencing the degradation efficiency of AFB₁, including pH values and initial concentrations, were also probed. The three kinds of photocatalytic membranes all exhibited excellent ability to degrade AFB₁. Among them, the photocatalytic degradation efficiency of the photocatalytic membranes prepared by the coaxial methods reached 96.8%. The experiment is with an initial concentration of 0.5 μg/mL (500 PPb) after 60 min under visible light irradiation. The mechanism of degradation of AFB₁ was also proposed based on active species trapping experiments. Moreover, the prepared photocatalytic membranes exhibited excellent photocatalytic activity even after five-fold use in the degradation of AFB₁. These studies showed that electrospun membranes anchored with g-C₃N₄/MoS₂ composites have a high photocatalytic ability which is easily removed from the reacted medium for reuse. Thereby, our study offers a highly effective, economical, and green solution for AFB₁ degradation in the foodstuff for practical application.

Rational construction of ZnO/CuS heterostructures-modified PVDF nanofiber photocatalysts with enhanced photocatalytic activity

PVDF/ZnO/CuS photocatalysts with ZnO/CuS heterojunctions were synthesized via electrospinning, hydrothermal, and ion-exchange techniques. As matrix materials, electrospun PVDF nanofibers are easy to be recycled and reused. ZnO nanorods anchored on PVDF nanofiber with high specific surface area provide abundant active reaction sites for photocatalysis. While the loaded CuS nanoparticles as a photosensitizer compensate the low quantum efficiency of ZnO and improve the visible-light photocatalytic efficiency. As a result, the PVDF/ZnO/CuS composited photocatalyst exhibits outstanding photocatalytic performance in exposure to UV and visible light owing to the suppressed recombination of electron-hole pairs and widened visible light absorption range. The kinetic constants of PVDF/ZnO/CuS nanocomposites under UV irradiation (9.01 × 10^-3 min^-1) and visible light (6.53 × 10^-3 min^-1) irradiation were 3.66 and 2.53 times higher than that of PVDF/ZnO (2.46 × 10^-3 min^-1 & 2.58 × 10^-3 min^-1), respectively. Furthermore, PVDF/ZnO/CuS nanocomposites demonstrate excellent robustness in terms of recycling and reuse, which is advantageous in practical applications.

In-Situ Functionalization of Cotton Fabric by TiO2: The Influence of Application Routes

The desirable chemical, physical, electronic, and optical properties of TiO2, as well as its high availability, non-toxicity, and low price, make it very popular in the modern functional textile industry. Here, TiO2 from titanium tetraisopropoxide (TTIP) precursors at concentrations of 2, 4, and 6% and commercial TiO2 nanoparticles (NPs) in dispersion form were applied to cotton textiles using low-temperature application methods (i.e., sol–gel pad–dry–cure, pad–hydrothermal, and exhaustion–hydrothermal methods) to provide a systematic study of the influence of low-temperature application processes and TIIP concentration and on the overall properties of TiO2-functionalized textile materials. The treated cotton fabric samples were characterized using scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDS), Fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction spectroscopy (XRD) to determine their surface morphology, chemical composition, and crystal structure, while the optical properties of the synthesized TiO2 were determined using the absorption method and Tauc plotting. Afterwards, corresponding UV protection properties and photocatalytic self-cleaning activity were evaluated. In contrast to commercial TiO2, a relatively thin TiO2 deposition with an amorphous structure and a blue-shifted band gap between 3.18 and 3.28 eV was formed when applied at low temperatures. A sol with a TIIP concentrations of 2 and 4% applied using the exhaustion–hydrothermal and sol–gel dry-cure method, respectively, proved to be optimal. Both applied sol concentrations provided good UV protection and excellent photocatalytic performance, which exceeded that of commercial TiO2, even though the Ti contents in the samples were two- to three-times lower and the synthesized TiO2 exhibited an amorphous structure.

Synergistic Interaction of MoS2 Nanoflakes on La2Zr2O7 Nanofibers for Improving Photoelectrochemical Nitrogen Reduction

Ammonia is a suitable hydrogen carrier with each molecule accounting for up to 17.65% of hydrogen by mass. Among various potential ammonia production methods, we adopt the photoelectrochemical (PEC) technique, which uses solar energy as well as electricity to efficiently synthesize ammonia under ambient conditions. In this article, we report MoS₂@La₂Zr₂O₇ heterostructures designed by incorporating two-dimensional (2D)-MoS₂ nanoflakes on La₂Zr₂O₇ nanofibers (MoS₂@LZO) as photoelectrocatalysts. The MoS₂@LZO heterostructures are synthesized by a facile hydrothermal route with electrospun La₂Zr₂O₇ nanofibers and Mo precursors. The MoS₂@LZO heterostructures work synergistically to amend the drawbacks of the individual MoS₂ electrocatalysts. In addition, the harmonious activity of the mixed phase of pyrochlore/defect fluorite-structured La₂Zr₂O₇ nanofibers generates an interface that aids in increased electrocatalytic activity by enriching oxygen vacancies in the system. The MoS₂@LZO electrocatalyst exhibits an enhanced Faradaic efficiency and ammonia yield of approximately 2.25% and 10.4 μg h^-1 cm^-2, respectively, compared to their corresponding pristine samples. Therefore, the mechanism of improving the PEC ammonia production performance by coupling oxygen-vacant sites to the 2D-semiconductor-based electrocatalysts has been achieved. This work provides a facile strategy to improve the activity of PEC catalysts by designing an efficient heterostructure interface for PEC applications.

Honeycomb-like V2O5 Based Films: Synthesis, Structural, Thermal, and Optical Properties for Environmental Applications

In the present study, new composite films consisting of hierarchical nanobelt V2O5 and polymer mixture were prepared via a simple casting method. The incorporation of 30 wt.% of V2O5 into the polymer matrix yielded a honeycomb like structure with abundant micro-voids (5.5 μm), higher roughness average by 45.8%, and a higher root mean square roughness by 52%, which are beneficial for the enhancement of active surface area for dye adsorption. Furthermore, optical property studies have shown that the incorporation of V2O5 has made the nanocomposite film a suitable UV–visible light-sensitive material, and thus the application of films can be expanded towards photocatalytic degradation of various toxic pollutants such as nitrophenol, Cr(VI), antibiotects, and so on. Finally, the composite film exhibited enhanced thermostability in comparison to unmodified film, as confirmed by TGA and DSC analysis. The optimal film showed 96.3% removal efficiency and 27.02 mg/g adsorption capacity. The dye sorption performance of V2O5 based films is studied at various times, dosages, and initial dye concentrations. The experimental data more closely fit the Langmuir isotherm model (R2 = 0.997) than the Freundlich, Temkin, and Dubinin–Radushkevich isotherm models, demonstrating a monolayer adsorption mechanism. The MB adsorption process on V2O5 film was controlled by the chemical adsorption step, which was evidenced by the good-fitting of kinetic adsorption results to the pseudo second order model (R2 = 0.991). The obtained results indicated that the V2O5 based films in this work are hopeful candidates for environmental applications.

Magnetic γ-Fe2O3/ZIF-7 Composite Particles and Their Application for Oily Water Treatment

Crude oil spills are about global challenges because of their destructive effects on aquatic life and the environment. The conventional technologies for cleaning crude oil spills need to study the selective separation of pollutants. The combination of magnetic materials and porous structures has been of considerable interest in separation studies. Here, γ-Fe₂O₃/ZIF-7 structures were prepared by growing a ZIF-7 layer onto supermagnetic γ-Fe₂O₃ nanoparticles with an average size of 18 ± 0.9 nm in situ without surface modification at low temperatures. The product composite particles were characterized using X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, vibrating sample magnetometry, and N₂ adsorption/desorption isotherms. The analyses revealed a time growth-dependent ZIF-7 rod thickness with abundant nanocavities. The γ-Fe₂O₃/ZIF-7 surface area available for sorption (647 m²/g) is ∼12-fold higher than that of the γ-Fe₂O₃ nanoparticles. Moreover, the crystal structure of γ-Fe₂O₃ remained essentially unchanged following ZIF-7 coating, whereas the superparamagnetism declined depending on the coating time. The γ-Fe₂O₃/ZIF-7 particles were highly hydrophobic and selectively and rapidly (<5 min) sorbed crude oil and other hydrocarbon pollutants from water. As high as 6 g/g of the hydrocarbon was sorbed by the γ-Fe₂O₃/ZIF-7 particles immersed into the hydrocarbon. A coefficient of determination, R ₂ ², consistently >0.96 at all pollutant concentrations suggested a pseudo-second-order sorption kinetics. The thermal stability and 15 cycles of use and reuse confirmed a robust γ-Fe₂O₃/ZIF-7 sorbent.

Amorphous MoSxOy/h-BNxOy Nanohybrids: Synthesis and Dye Photodegradation

Molybdenum sulfide is a very promising catalyst for the photodegradation of organic pollutants in water. Its photocatalytic activity arises from unsaturated sulfur bonds, and it increases with the introduction of structural defects and/or oxygen substitutions. Amorphous molybdenum sulfide (a-MoSxOy) with oxygen substitutions has many active sites, which create favorable conditions for enhanced catalytic activity. Here we present a new approach to the synthesis of a-MoSxOy and demonstrate its high activity in the photodegradation of the dye methylene blue (MB). The MoSxOy was deposited on hexagonal boron oxynitride (h-BNO) nanoflakes by reacting h-BNO, MoCl5, and H2S in dimethylformamide (DMF) at 250 °C. Both X-ray diffraction analysis and high-resolution TEM show the absence of crystalline order in a-MoSxOy. Based on the results of Raman and X-ray photoelectron spectroscopy, as well as analysis by the density functional theory (DFT) method, a chain structure of a-MoSxOy was proposed, consisting of MoS3 clusters with partial substitution of sulfur by oxygen. When a third of the sulfur atoms are replaced with oxygen, the band gap of a-MoSxOy is approximately 1.36 eV, and the valence and conduction bands are 0.74 eV and -0.62 eV, respectively (relative to a standard hydrogen electrode), which satisfies the conditions of photoinduced splitting of water. When illuminated with a mercury lamp, a-MoSxOy/h-BNxOy nanohybrids have a specific mass activity in MB photodegradation of approximately 5.51 mmol g-1 h-1, which is at least four times higher than so far reported values for nonmetal catalysts. The photocatalyst has been shown to be very stable and can be reused.

Electrospun-based TiO2 nanofibers for organic pollutant photodegradation: a comprehensive review

Titanium dioxide (TiO2) is commonly used as a photocatalyst in the removal of organic pollutants. However, weaknesses of TiO2 such as fast charge recombination and low visible light usage limit its industrial application. Furthermore, photocatalysts that are lost during the treatment of pollutants create the problem of secondary pollutants. Electrospun-based TiO2 fiber is a promising alternative to immobilize TiO2 and to improve its performance in photodegradation. Some strategies have been employed in fabricating the photocatalytic fibers by producing hollow fibers, porous fibers, composite TiO2 with magnetic materials, graphene oxide, as well as doping TiO2 with metal. The modification of TiO2 can improve the absorption of TiO2 to the visible light area, act as an electron acceptor, provide large surface area, and promote the phase transformation of TiO2. The improvement of TiO2 properties can enhance carrier transfer rate which reduces the recombination and promotes the generation of radicals that potentially degrade organic pollutants. The recyclability of fibers, calcination effect, photocatalytic reactors used, operation parameters involved in photodegradation as well as the commercialization potential of TiO2 fibers are also discussed in this review.

An irregular-octagonal-prism-shaped host–guest supramolecular network based on silicotungstate and manganese-complex for light-driven hydrogen evolution

A novel irregular-octagonal-prism-shaped host–guest supramolecular network was synthesized and showed excellent photocatalytic splitting of water performance.

Facile synthesis and defect optimization of 2D-layered MoS2 on TiO2 heterostructure for industrial effluent, wastewater treatments

Current research is paying much attention to heterojunction nanostructures. Owing to its versatile characteristics such as stimulating morphology, affluent surface-oxygen-vacancies and chemical compositions for enhanced generation of reactive oxygen species. Herein, we report the hydrothermally synthesized TiO₂@MoS₂ heterojunction nanostructure for the effective production of photoinduced charge carriers to enhance the photocatalytic capability. XRD analysis illustrated the crystalline size of CTAB capped TiO₂, MoS₂@TiO₂ and L-Cysteine capped MoS₂@TiO₂ as 12.6, 11.7 and 10.2 nm, respectively. The bandgap of the samples analyzed by UV–Visible spectroscopy are 3.57, 3.66 and 3.94 eV. PL spectra of anatase phase titania shows the peaks present at and above 400 nm are ascribed to the defects in the crystalline structure in the form of oxygen vacancies. HRTEM reveals the existence of hexagonal layered MoS₂ formation on the spherical shaped TiO₂ nanoparticles at the interface. X-ray photoelectron spectroscopy recommends the chemical interactions between MoS₂ and TiO_2, specifically, oxygen vacancies. In addition, the electrochemical impedance spectroscopy studies observed that L-MT sample performed low charge transfer resistance (336.7 Ω cm²) that promotes the migration of electrons and interfacial charge separation. The photocatalytic performance is evaluated by quantifying the rate of Congo red dye degradation under visible light irradiation, and the decomposition efficiency was found to be 97%. The electron trapping recombination and plausible photocatalytic mechanism are also explored, and the reported work could be an excellent complement for industrial wastewater treatment.

In situ preparation of 2D MoS2 nanosheets vertically supported on TiO2/PVDF flexible fibers and their photocatalytic performance

Two-dimensional (2D) MoS₂ nanosheets vertically supported on TiO₂/PVDF flexible fibers have been successfully synthesized by combining electrospinning with a low temperature hydrothermal method without acid. The morphology of the 2D MoS₂ nanosheets could be controlled by adjusting the experimental parameters. The loaded 2D MoS₂ nanosheets can not only broaden the light capture range of TiO₂, but also greatly inhibit the recombination rate of photogenerated electron-hole pairs. Due to the synergistic effect between MoS₂ and TiO₂, the photocatalytic rate for levofloxacin hydrochloride is about 40 times higher than that for MoS₂ only. Recycle experiments have proved the stability and reusability of TiO₂/PVDF@2D MoS₂ nanosheets. The mechanism is investigated by quenching experiments. The results show that the superoxide anion radical (•O₂ ^-), the hydroxyl radical (•OH) and the hole (h⁺) all have contributions to photocatalysis. This work widens the range of materials to synthesize the composites of 2D MoS₂ nanosheets and provides a new and gentle method for preparing flexible large-scale heterostructures for environmental protection.

Bi-Polymer Electrospun Nanofibers Embedding Ag3PO4/P25 Composite for Efficient Photocatalytic Degradation and Anti-Microbial Activity

Using a bi-polymer system comprising of transparent poly(methyl methacrylate) (PMMA) and poly(vinyl pyrrolidone) (PVP), a visible light active Ag3PO4/P25 composite was immobilized into the mats of polymeric electrospun nanofibers. After nanofibers synthesis, sacrificial PVP was removed, leaving behind rough surface nanofibers with easy access to Ag3PO4/P25 composite. The remarkable photocatalytic efficiency was attained using a PMMA and Ag3PO4/P25 weight ratio of 1:0.6. Methyl orange (MO) was used to visualize pollutant removal and exhibited stable removal kinetics up to five consecutive cycles under simulated daylight. Also, these polymeric nanofibers (NFs) revealed an important role in the destruction of microorganisms (E. coli), signifying their potential in water purification. A thin film fibrous mat was also used in a small bench scale plug flow reactor (PFR) for polishing of synthetic secondary effluent and the effects of inorganic salts were studied upon photocatalytic degradation in terms of total organic carbon (TOC) and turbidity removal. Lower flow rate (5 mL/h) resulted in maximum TOC and turbidity removal rates of 86% and 50%, respectively. Accordingly, effective Ag3PO4/P25 immobilization into an ideal support material and selectivity towards target pollutants could both enhance the efficiency of photocatalytic process under solar radiations without massive energy input.

Grey Rutile TiO2 with Long-Term Photocatalytic Activity Synthesized Via Two-Step Calcination

Colored titanium oxides are usually unstable in the atmosphere. Herein, a gray rutile titanium dioxide is synthesized by two-step calcination successively in a high-temperature reduction atmosphere and in a lower-temperature air atmosphere. The as-synthesized gray rutile TiO₂ exhibits higher photocatalytic activity than that of white rutile TiO₂ and shows high chemical stability. This is attributed to interior oxygen vacancies, which can improve the separation and transmission efficiency of the photogenerated carriers. Most notably, a formed surface passivation layer will protect the interior oxygen vacancies and provide long-term photocatalytic activity.

One-Step Hydrothermal Synthesis of P25 @ Few Layered MoS2 Nanosheets toward Enhanced Bi-catalytic Activities: Photocatalysis and Electrocatalysis

P25 loaded few layered molybdenum disulfide (MoS₂) nanosheets (P25@MoS₂) are successfully synthesized through a facile one-step hydrothermal process. The bi-catalytic activities, i.e., photocatalytic and electrocatalytic activities, of the as-prepared nanomaterials have been investigated. For the as-prepared products, the photocatalytic performances were investigated by degrading simulated pollutant under sunlight irradiation, and the hydrogen evolution reaction evaluated the electrocatalytic performances. The results indicate that P25@MoS₂ possesses excellent activities in both photocatalysis and electrocatalysis. The presence of MoS₂ broadens the light absorption range of P25 and improves the separation and transformation efficiency of photogenerated carriers, thus improving its photocatalytic performance. The existence of P25 inhibits the aggregation of MoS₂ to form more dispersed MoS₂ nanosheets with only few layers increasing its active sites. Thereby, the electrocatalytic performance is heightened. The excellent multifunction makes the as-prepared P25@MoS₂ a promising material in the fields of environment and energy.

Recent Advances and Applications of Semiconductor Photocatalytic Technology

Along with the development of industry and the improvement of people’s living standards, peoples’ demand on resources has greatly increased, causing energy crises and environmental pollution. In recent years, photocatalytic technology has shown great potential as a low-cost, environmentally-friendly, and sustainable technology, and it has become a hot research topic. However, current photocatalytic technology cannot meet industrial requirements. The biggest challenge in the industrialization of photocatalyst technology is the development of an ideal photocatalyst, which should possess four features, including a high photocatalytic efficiency, a large specific surface area, a full utilization of sunlight, and recyclability. In this review, starting from the photocatalytic reaction mechanism and the preparation of the photocatalyst, we review the classification of current photocatalysts and the methods for improving photocatalytic performance; we also further discuss the potential industrial usage of photocatalytic technology. This review also aims to provide basic and comprehensive information on the industrialization of photocatalysis technology.

The Relationships between Process Parameters and Polymeric Nanofibers Fabricated Using a Modified Coaxial Electrospinning

The concrete relationship between the process parameters and nanoproduct properties is an important challenge for applying nanotechnology to produce functional nanomaterials. In this study, the relationships between series of process parameters and the medicated nanofibers’ diameter were investigated. With an electrospinnable solution of hydroxypropyl methylcellulose (HPMC) and ketoprofen as the core fluid, four kinds of nanofibers were prepared with ethanol as a sheath fluid and under the variable applied voltages. Based on these nanofibers, a series of relationships between the process parameters and the nanofibers’ diameters (D) were disclosed, such as with the height of the Taylor cone (H, D = 125 + 363H), with the angle of the Taylor cone (α, D = 1576 − 19α), with the length of the straight fluid jet (L, D = 285 + 209L), and with the spreading angle of the instable region (θ, D = 2342 − 43θ). In vitro dissolution tests verified that the smaller the diameters, the faster ketoprofen (KET) was released from the HPMC nanofibers. These concrete process-property relationships should provide a way to achieve new knowledge about the electrostatic energy-fluid interactions, and to meanwhile improve researchers’ capability to optimize the coaxial process conditions to achieve the desired nanoproducts.