Immobilization of Ag3PO4 nanoparticles on electrospun PAN nanofibers via surface oximation: Bifunctional composite membrane with enhanced photocatalytic and antimicrobial activities

Advanced nanofibers for water treatment: Unveiling the potential of electrospun polyacrylonitrile membranes

The challenges pertaining to the potable water scarcity and pollution motivates us to envision innovative strategies. Industrial wastewater containing hazardous heavy metals, synthetic dyes, and oil exacerbates the pursuit of clean drinking water. Among the array of available technologies, electrospun nanofiber membranes have garnered attention due to their efficiency, high surface-to-volume ratio, cost-effectiveness, scalability, and multifunctionality. These membranes possess distinct physical and chemical attributes that position them as ideal solutions to water purification challenges. Their versatility enables effective contaminant removal through filtration, adsorption, and chemical interactions. Polyacrylonitrile (PAN) emerges as a frontrunner among electrospun polymers due to its affordability, remarkable physical and chemical characteristics, and the ease of production. Research efforts have been dedicated to the study of electrospun PAN membranes, exploring modifications in terms of the functionalization of PAN molecular chain, incorporation of appropriate nanoparticles, and composition with other functional polymers. Parameters such as functional groups, hydrophilicity, mechanical properties, porosity, pore structure, reusability, sustainability, zeta potential, and operational conditions significantly influence the performance of electrospun PAN membranes in treating the contaminated water. Despite progress, challenges surrounding fouling, toxicity, scalability, selectivity, and production costs ought to be addressed strategically to enhance their practicality and real-world viability. This review comprehensively scrutinizes the current landscape of available electrospun PAN membranes in water treatment encompassing diverse range of synthesized entities and experimental outcomes. Additionally, the review delves into various approaches undertaken to optimize the performance of electrospun PAN membranes while proposing potential strategies to overcome the existing hindrances. By carefully analyzing the parameters that impact the performance of these membranes, this overview offers invaluable guidelines for researchers and engineers, thus empowering them to design tailored electrospun nanofiber membranes for specific water purification applications. As the innovative research continues and strategic efforts address the current challenges, these membranes can play a pivotal role in enhancing water quality, mitigating water scarcity, and contributing to environmental sustainability. The widespread application of electrospun nanofiber membranes in water treatment has the potential to create a lasting positive impact on global water resources and the environment. A dedicated effort towards their implementation will undoubtedly mark a crucial step towards a more sustainable and water-secure future.

Polypropylene Modified with Ag-Based Semiconductors as a Potential Material against SARS-CoV-2 and Other Pathogens

The worldwide outbreak of the coronavirus pandemic (COVID-19) and other emerging infections are difficult and sometimes impossible to treat, making them one of the major public health problems of our time. It is noteworthy that Ag-based semiconductors can help orchestrate several strategies to fight this serious societal issue. In this work, we present the synthesis of α-Ag₂WO₄, β-Ag₂MoO₄, and Ag₂CrO₄ and their immobilization in polypropylene in the amounts of 0.5, 1.0, and 3.0 wt %, respectively. The antimicrobial activity of the composites was investigated against the Gram-negative bacterium Escherichia coli, the Gram-positive bacterium Staphylococcus aureus, and the fungus Candida albicans. The best antimicrobial efficiency was achieved by the composite with α-Ag₂WO₄, which completely eliminated the microorganisms in up to 4 h of exposure. The composites were also tested for the inhibition of SARS-CoV-2 virus, showing antiviral efficiency higher than 98% in just 10 min. Additionally, we evaluated the stability of the antimicrobial activity, resulting in constant inhibition, even after material aging. The antimicrobial activity of the compounds was attributed to the production of reactive oxygen species by the semiconductors, which can induce high local oxidative stress, causing the death of these microorganisms.

Tuning structural-response of PLA/PCL based electrospun nanofibrous mats: Role of dielectric-constant and electrical-conductivity of the solvent system

The role of optimum solvent systems on the fabrication of uniform, bead-free electrospun-nanofibrous-mats (ENMs) of polylactic acid (PLA), poly(ε-caprolactone) (PCL), and their blends, is investigated. The solvent systems influenced the fiber-diameters, morphology, crystallinity, thermal stability, hydrophobicity, quasi-static mechanical, and solid-state visco-elastic responses of the ENMs. Defect-free ENMs were obtained by using CF/DMF (80:20 v/v) binary solvent system while showing a relatively higher extent of crystallinity (PLA/PCL blend ∼ 34%), lower hydrophobicity (PLA ∼ 117⁰), higher strength (PLA ∼ 6 MPa), and moduli (PLA ∼ 305 MPa) for PLA and PLA/PCL blend systems whereas a higher strain-at-break (∼ 82%) was shown by PCL based ENMs. PLA/PCL blend based ENMs fabricated using DCM/DMF (80:20 v/v) solvent-mixture exhibited comparatively lower crystallinity (∼ 25%) but higher fiber diameter (1.03 ± 0.21 µm), strain-at-break (∼ 155%), and hydrophobicity (∼ 130⁰) compared to CF/DMF (80:20 v/v) system. Dynamic mechanical analysis (DMA) revealed the structural relaxation behaviors indicating the intrinsic structural deformability and flexibility of the mats. The study demonstrated the systematic role of solvent characteristics in terms of their volatility, dielectric constant, and solvent-mixture composition on the electro-spinnability and fabrication of high-strength, deformable, hydrophobic, bead-free ENMs with near monodisperse fibrous assemblies for biomedical applications.

Integration of biochar into Ag3PO4/α-Fe2O3 heterojunction for enhanced reactive oxygen species generation towards organic pollutants removal

A biochar (BC) harbored Ag₃PO₄/α-Fe₂O₃ type-Ⅰ heterojunction (Ag-Fe-BC) was prepared by a hydrothermal-impregnation method to transfer active center of heterojunctions. The electrochemical and spectroscopic tests demonstrated that BC enhanced the catalytic performance of the heterojunction by enhancing photocurrent, reducing fluorescence intensity, and facilitating separation of electron-hole pairs. The photocatalytic activity showed the Ag-Fe-BC (5:1:3) could degrade Rhodamine B (20 mg/L) by up to 92.7%, which was 3.35 times higher than Ag₃PO₄/α-Fe₂O₃. Tetracycline and ciprofloxacin (20 mg/L) were degraded efficiently by 58.3% and 79.4% within 2 h, respectively. Electron paramagnetic resonance and scavenging experiments confirmed the major reactive oxygen species (ROS) consisted of singlet oxygen (¹O₂) and superoxide (·O₂^-). Excellent RhB adsorption and electrons capturing capacity of BC facilitated electron-hole pairs separation and ROS transferring to target organics followed by elevated degradation. Thus, a facile method was proposed to synthesize a highly efficient visible-light responsive photocatalyst for degradation of various organics in water.

TiO2–Based Nanofibrous Membranes for Environmental Protection

Electrospinning is a unique technique that can be used to synthesize polymer and metal oxide nanofibers. In materials science, a very active field is represented by research on electrospun nanofibers. Fibrous membranes present fascinating features, such as a large surface area to volume ratio, excellent mechanical behavior, and a large surface area, which have many applications. Numerous techniques are available for the nanofiber’s synthesis, but electrospinning is presented as a simple process that allows one to obtain porous membranes containing smooth non-woven nanofibers. Titanium dioxide (TiO2) is the most widely used catalyst in photocatalytic degradation processes, it has advantages such as good photocatalytic activity, excellent chemical stability, low cost and non-toxicity. Thus, titanium dioxide (TiO2) is used in the synthesis of nanofibrous membranes that benefit experimental research by easy recyclability, excellent photocatalytic activity, high specific surface areas, and exhibiting stable hierarchical nanostructures. This article presents the synthesis of fiber membranes through the processes of electrospinning, coaxial electrospinning, electrospinning and electrospraying or electrospinning and precipitation. In addition to the synthesis of membranes, the recent progress of researchers emphasizing the efficiency of nanofiber photocatalytic membranes in removing pollutants from wastewater is also presented.

Synthesis of metal nanoclusters and their application in Hg2+ ions detection: A review

Mercuric (Hg²⁺) ions released from human activities, natural phenomena, and industrial sources are regarded as the global pollutant of world's water. Hg²⁺ ions contaminated water has several adverse effects on human health and the environment even at low concentrations. Therefore, rapid and cost-effective method is urgently required for the detection of Hg²⁺ ions in water. Although, the current analytical methods applied for the detection of Hg²⁺ ions provide low detection limit, they are time consuming, require expensive equipment, and are not suitable for in-situ analysis. Metal nanoclusters (MNCs) consisting of several to ten metal atoms are important transition missing between single atoms and plasmonic metal nanoparticles. In addition, sub-nanometer sized MNCs possess unique electronic structures and the subsequent unusual optical, physical, and chemical properties. Because of these novel properties, MNCs as a promising material have attracted considerable attention for the construction of selective and sensitive sensors to monitor water quality. Hence this review is focused on recent advances on synthesis strategies, and optical and chemical properties of various MNCs including their applications to develop optical assay for Hg²⁺ ions in aqueous solutions.

Photocatalytic Nanofiber Membranes for the Degradation of Micropollutants and Their Antimicrobial Activity: Recent Advances and Future Prospects

This review paper systematically evaluates current progress on the development and performance of photocatalytic nanofiber membranes often used in the removal of micropollutants from water systems. It is demonstrated that nanofiber membranes serve as excellent support materials for photocatalytic nanoparticles, leading to nanofiber membranes with enhanced optical properties, as well as improved recovery, recyclability, and reusability. The tremendous performance of photocatalytic membranes is attributed to the photogenerated reactive oxygen species such as hydroxyl radicals, singlet oxygen, and superoxide anion radicals introduced by catalytic nanoparticles such as TiO₂ and ZnO upon light irradiation. Hydroxyl radicals are the most reactive species responsible for most of the photodegradation processes of these unwanted pollutants. The review also demonstrates that self-cleaning and antimicrobial nanofiber membranes are useful in the removal of microbial species in water. These unique materials are also applicable in other fields such as wound dressing since the membrane allows for oxygen flow in wounds to heal while antimicrobial agents protect wounds against infections. It is demonstrated that antimicrobial activities against bacteria and photocatalytic degradation of micropollutants significantly reduce membrane fouling. Therefore, the review demonstrates that electrospun photocatalytic nanofiber membranes with antimicrobial activity form efficient cost-effective multifunctional composite materials for the removal of unwanted species in water and for use in various other applications such as filtration, adsorption and electrocatalysis.

Preparation and characterization of silver orthophosphate photocatalytic coating on glass substrate

The photocatalytic activity of silver orthophosphate Ag3PO4 has been studied and shown to have a high photo-oxidation capability. However, there is few reported example of a simple method to prepare Ag3PO4 coatings on various substrates. In this study a novel and simple method to immobilize Ag3PO4 on the surface of glass substrates has been developed. A silver phosphate paste based on a polyelectrolyte solution was applied to a smooth glass surface. The resulting dried material was calcined to obtain a coating that remained on the glass substrate. The coating layer was characterized by X-ray diffraction and energy dispersive X-ray spectrometry, and the optical band gap of the material was determined. The results indicated that an Ag3PO4 coating responsive to visible light was successfully prepared. The coating, under visible light irradiation, has the ability to decompose methylene blue. Although the coating contained some elemental silver, this did not adversely affect the optical band gap or the photocatalytic ability.

High efficient reduction of 4-nitrophenol and dye by filtration through Ag NPs coated PAN-Si catalytic membrane

Catalytic membrane plays an important role in environmental remedy. In this study, we reported an Ag coated membrane (PAN-Si-Cu-Ag) with a high catalytic activity to reduce 4-nitrophenol (4-NP) and methyl orange (MO) from water. The best performance is 99% reduction degree and 280 L m^-2.h^-1.bar^-1 flux for (4-NP) reduction at 4-NP: NaBH₄ = 1:50 (mM) during a 12-h filtration. The reduction degree for MO is above 90% and the flux is about 230 L m^-2·h^-1·bar^-1, which is almost the best report till now. The Ag coated membrane was prepared by metal displacement-epitaxial growth on silica covalent grafted PAN membrane (PAN-Si). Silica atoms were used as linker to ensure the good adhesion between polymer and metal NPs, the loss amount of Ag NPs from the coated catalytic membrane is loss about 2 μg/cm² after one month storage. Cheap metal NPs were firstly reduced on the surface of PAN-Si membrane and then used to displace Ag ions. Thus the obtained catalytic membrane showed a very high loading (28%). Finally, the catalytic filtration mechanism of 4-NP was distinguished by Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and adsorption measurement.

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.

Towards the Enhancement in Photocatalytic Performance of Ag3PO4 Nanoparticles through Sulfate Doping and Anchoring on Electrospun Nanofibers

Present work reports the enhancement in photocatalytic performance of Ag3PO4 nanoparticles through sulfate doping and anchoring on Polyacrylonitrile (PAN)-electrospun nanofibers (SO42--Ag3PO4/PAN-electrospun nanofibers) via electrospinning followed by ion-exchange reaction. Morphology, structure, chemical composition, and optical properties of the prepared sample were characterized using XRD, FESEM, FTIR, XPS, and DRS. The anchoring of SO42--Ag3PO4 nanoparticles on the surface of PAN-electrospun nanofibers was evidenced by the change in color of the PAN nanofibers mat from white to yellow after ion-exchange reaction. FESEM analysis revealed the existence of numerous SO42--Ag3PO4 nanoparticles on the surface of PAN nanofibers. Photocatalytic activity and stability of the prepared sample was tested for the degradation of Methylene blue (MB) and Rhodamine B (RhB) dyes under visible light irradiation for three continuous cycles. Experimental results showed enhanced photodegradation activity of SO42--Ag3PO4/PAN-electrospun nanofibers compared to that of sulfate undoped sample (Ag3PO4/PAN-electrospun nanofibers). Doping of SO42- into Ag3PO4 crystal lattice could increase the photogenerated electron-hole separation capability, and PAN nanofibers served as support for nanoparticles to prevent from agglomeration.

Cone-shaped titanate immobilized on polyacrylonitrile nanofibers: hierarchical architecture for effective photocatalytic activity

A new photocatalytic composite material, based on flexible functional polyacrylonitrile nanofibers (denoted as f-PAN NF), was developed by depositing composite layers of α-TiO₂ and cone-shaped titanate (H₂Ti₅O₁₁·3H₂O) successively. The α-TiO₂ coated on f-PAN NF as a seed accelerated the nucleation of titanate. Cone-shaped titanate deposited on α-TiO₂@f-PAN NF tightly at 35 °C with the assistance of cyanuric acid via Ostwald ripening. Due to the uniform distribution of cone-shaped titanate, the photocatalytic performance of hybrid f-PAN NF was remarkable under LED light irradiation and yielded additional photocatalytic applications as well. In addition, the composite photocatalyst exhibited better reusability and retrievability because of the special design involving a bonding between the nanofibers and layers.

Enhanced Antibacterial Property of Sulfate-Doped Ag3PO4 Nanoparticles Supported on PAN Electrospun Nanofibers

Heterojunction nanofibers of PAN decorated with sulfate doped Ag₃PO₄ nanoparticles (SO₄²⁻-Ag₃PO₄/PAN electrospun nanofibers) were successfully fabricated by combining simple and versatile electrospinning technique with ion exchange reaction. The novel material possessing good flexibility could exhibit superior antibacterial property over sulfate undoped species (Ag₃PO₄/PAN electrospun nanofibers). FESEM, XRD, FTIR, XPS and DRS were applied to characterize the morphology, phase structure, bonding configuration, elemental composition, and optical properties of the as fabricated samples. FESEM characterization confirmed the successful incorporation of SO₄²⁻-Ag₃PO₄ nanoparticles on PAN electrospun nanofibers. The doping of SO₄²⁻ ions into Ag₃PO₄ crystal lattice by replacing PO₄³⁻ ions can provide sufficient electron-hole separation capability to the SO₄²⁻-Ag₃PO₄/PAN heterojunction to generate reactive oxygen species (ROS) under visible light irradiation and enhances its antibacterial performance. Finally, we hope this work may offer a new paradigm to design and fabricate other types of flexible self-supporting negative-ions-doped heterojunction nanofibers using electrospinning technique for bactericidal applications.

Local extraction and detection of early stage breast cancers through a microneedle and nano-Ag/MBL film based painless and blood-free strategy

Early diagnosis is the key to the good prognosis of breast cancer. At present, clinical tumor diagnosis is mainly through serum analysis, which is painful and can only detect relatively advanced tumors that have already metastasized from the glands into the blood circulation. Here, we developed an earlier diagnostic method (before tumor cells entering the blood) of breast cancers through a convenient and painless process with blood-free samples. The microneedles were utilized to insert into the animals' testing areas, while the tissue fluid was collected through our synthesized breathable thin film. The obtained tissue fluid sample was then incubated to form blue products. In the area where tumors occurred, the blue changes were more obvious than the healthy area, a semi-localization and semi-quantitative detection of the tumorous area thus could be realized. The results of corresponding animal experiments showed that, after the injection of tumor cells, the proposed nano-Ag based colorimetric method can detect the occurrence of breast cancers in 7 days. What is more, these early tumors could be effectively suppressed through classical DOX treatment. For comparison, the classical blood test needed 14 days to validate the occurrence of breast cancers. The subsequent human tests further demonstrated the feasibility of the present method. The development of this work could provide a more convenient, accurate and comfortable technology to support for the early screening and diagnosis of cancer patients, so as to fundamentally reduce the mortality of the breast cancers.

Surface functionalization of electrospun PAN nanofibers with ZnO-Ag heterostructure nanoparticles: synthesis and antibacterial study

In this work, we have prepared polyacrylonitrile (PAN) polymer nanofibers by electrospinning method. The surface of the electrospun PAN nanofibers membrane has been functionalized with ZnO-Ag heterostructure nanoparticles by using three different chemical pathways such as reflux, blending, hydrothermal methods and accordingly the prepared composite nanofibers membranes were named as PAN/ZnO-Ag (R), PAN/ZnO-Ag (B) and PAN/ZnO-Ag (H) respectively. The obtained heterostructure nanoparticles functionalized PAN nanofibers membranes were characterized using ATR-FTIR, XRD, FESEM and TEM analytical techniques. From the FESEM and TEM images it was clearly observed that 20-30 nm size spherical nanoparticles have been decorated uniformly on the surface of PAN nanofibers. XRD study confirmed the formation of ZnO-Ag mixed/hybrid nanoparticles on PAN nanofibers surface. The ZnO-Ag heterostructure nanoparticles functionalized PAN nanofibers membranes were used for antibacterial application. It was observed from inhibition zone study that the ZnO-Ag heterostructure nanoparticles functionalized PAN nanofibers membrane shows excellent antibacterial properties towards both gram-negative Escherichia coli and gram-positive Micrococcus luteus bacteria than their single component counterparts. Thus this study demonstrated the simple and cost-effective approach to develop antibacterial functional membrane that has many potential applications in water and air filtration, protective mask, textile and packaging industries.

Membrane-based separation of potential emerging pollutants

The potential emerging pollutants (PEPs) such as hazardous chemicals, toxic metals, bio-wastes, etc., pose a severe threat to human health, hygiene and ecology by way of polluting the environment and water sources. The PEPs are originated from various industrial effluent discharges including pharmaceutical, food and metal processing industries. These PEPs in contact with water may pollute the water and disturb the aquatic life. Innumerable methods have been used for the treatment of effluents and separating the toxic chemicals/metals. Of these methods, membrane-based separation processes (MBSPs) are effective over the conventional techniques for providing clean water from wastewater streams at an affordable cost with minimum energy requirement. Microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), reverse osmosis (RO), and forward osmosis (FO) methods as well as hybrid technologies are discussed citing the published results of the past decade.

Photocatalytic degradation of naphthalene using calcined FeZnO/ PVA nanofibers

Recently, the incorporation of metal oxide nanoparticles into polymers has gained great attention owing to their ample of applications. The green mediated synthesis Fe-doped ZnO nanoparticles have been incorporated into PVA nanofibers through electro spinning for the application of photocatalytic degradation. The PVA polymer concentration was optimized to obtain uniform fibers without beads. The Fe-doped ZnO nanofibers were characterized by various analyzing techniques. The results show that good physicochemical with high surface area, uniformity in fiber with an average diameter ranges from 150 to 300 and 50-200 nm for un-calcined and calcined Fe-doped ZnO nanofiber respectively. The photocatalytic activity of nanofibers was examined by the degradation of naphthalene. The efficiency was observed 96 and 81% for calcined and un-calcined nanofibers, respectively. The reusable efficacy of Fe-doped ZnO calcined nanofiber as a catalyst was studied. These studies corroborated that the calcined Fe-doped ZnO nanofiber as promising material for catalytic applications.

Graphene-Carbon-Metal Composite Film for a Flexible Heat Sink

The heat generated from electronic devices such as light emitting diodes (LEDs), batteries, and highly integrated transistors is one of the major causes obstructing the improvement of their performance and reliability. Herein, we report a comprehensive method to dissipate the generated heat to a vast area by using the new type of graphene-carbon-metal composite film as a heat sink. The unique porous graphene-carbon-metal composite film that consists of an electrospun carbon nanofiber with arc-graphene (Arc-G) fillers and an electrochemically deposited copper (Cu) layer showed not only high electrical and thermal conductivity but also high mechanical stability. Accordingly, superior thermal management of LED devices to that of conventional Cu plates and excellent resistance stability during the repeated 10 000 bending cycles has been achieved. The heat dissipation of LEDs has been enhanced by the high heat conduction in the composite film, heat convection in the air flow, and thermal radiation at low temperature in the porous carbon structure. This result reveals that the graphene-carbon-metal composite film is one of the most promising materials for a heat sink of electronic devices in modern electronics.