Nickel Ferrite Nanoparticles Anchored onto Silica Nanofibers for Designing Magnetic and Flexible Nanofibrous Membranes

Improvement strategies for oil/water separation based on electrospun SiO2 nanofibers

Oil spills and oily effluents from industry and daily life pose a great threat to all organisms in the ecosystem, while aggravating the problem of water scarcity, which has developed into a global challenge. Therefore, the development of advanced materials and technologies for oil/water separation has become a focus of attention. One-dimensional (1D) SiO2 nanofibers (SNFs) have become one of the most widely used inorganic nanomaterials in the past due to their stable chemical properties, excellent biocompatibility, and high temperature resistance etc. Meanwhile, electrospinning technique, as an emerging technology for treating oil/water emulsions, electrospun SNFs on this basis also has a number of advantages such as adjustable wettability, diverse structure and good connectivity. This review provides a systematic overview of the research progress of electrospun SNFs in different aspects. In this review, we first introduce the basic principles of electrospun SNFs, then focus on the design structures of various SNFs, propose corresponding strategies for the property improvement of SNFs, also analyze and consider the applications of SNFs. Finally, the challenges faced by electrospun SNFs in the field of oil/water separation are analyzed, and the future directions of electrospun SNFs are summarized and prospected.

Efficacy of Electrospun Nanofiber Membranes on Fouling Mitigation: A Review

Despite the advantages of high contaminant removal, operational flexibility, and technical advancements offered, the undesirable fouling property of membranes limits their durability, thus posing restrictions on their usage. An enormous struggle is underway to conquer this major challenge. Most of the earlier reviews include the basic concepts of fouling and antifouling, with respect to particular separation processes such as ultrafiltration, nanofiltration, reverse osmosis and membrane bioreactors, graphene-based membranes, zwitterionic membranes, and so on. As per our knowledge, the importance of nanofiber membranes in challenging the fouling process has not been included in any record to date. Nanofibers with the ability to be embedded in any medium with a high surface to volume ratio play a key role in mitigating the fouling of membranes, and it is important for these studies to be critically analyzed and reported. Our Review hence intends to focus on nanofiber membranes developed with enhanced antifouling and biofouling properties with a brief introduction on fabrication processes and surface and chemical modifications. A summary on surface modifications of preformed nanofibers is given along with different nanofiller combinations used and blend fabrication with efficacy in wastewater treatment and antifouling abilities. In addition, future prospects and advancements are discussed.

From 1D Nanofibers to 3D Nanofibrous Aerogels: A Marvellous Evolution of Electrospun SiO2 Nanofibers for Emerging Applications

One-dimensional (1D) SiO2 nanofibers (SNFs), one of the most popular inorganic nanomaterials, have aroused widespread attention because of their excellent chemical stability, as well as unique optical and thermal characteristics. Electrospinning is a straightforward and versatile method to prepare 1D SNFs with programmable structures, manageable dimensions, and modifiable properties, which hold great potential in many cutting-edge applications including aerospace, nanodevice, and energy. In this review, substantial advances in the structural design, controllable synthesis, and multifunctional applications of electrospun SNFs are highlighted. We begin with a brief introduction to the fundamental principles, available raw materials, and typical apparatus of electrospun SNFs. We then discuss the strategies for preparing SNFs with diverse structures in detail, especially stressing the newly emerging three-dimensional SiO2 nanofibrous aerogels. We continue with focus on major breakthroughs about brittleness-to-flexibility transition of SNFs and the means to achieve their mechanical reinforcement. In addition, we showcase recent applications enabled by electrospun SNFs, with particular emphasis on physical protection, health care and water treatment. In the end, we summarize this review and provide some perspectives on the future development direction of electrospun SNFs.

Electrospun Nanofibers for Chemical Separation

The separation and purification of specific chemicals from a mixture have become necessities for many environments, including agriculture, food science, and pharmaceutical and biomedical industries. Electrospun nanofiber membranes are promising materials for the separation of various species such as particles, biomolecules, dyes, and metals from liquids because of the combined properties of a large specific surface, light weight, high porosity, good connectivity, and tunable wettability. This paper reviews the recent progress in the design and fabrication of electrospun nanofibers for chemical separation. Different capture mechanisms including electrostatic, affinity, covalent bonding, chelation, and magnetic adsorption are explained and their distinct characteristics are highlighted. Finally, the challenges and future aspects of nanofibers for membrane applications are discussed.

Waterproof and Breathable Electrospun Nanofibrous Membranes

Waterproof and breathable (W&B) membranes combine fascinating properties of resistance to liquid water penetration and transmitting of water vapor, playing a key role in addressing problems related to health, resources, and energy. Electrospinning is an efficient and advanced way to construct nanofibrous materials with easily tailored wettability and adjustable pore structure, therefore providing an ideal strategy for constructing W&B membranes. In this review, recent progress on electrospun W&B membranes is summarized, involving materials design and fabrication, basic properties of electrospun W&B membranes associated with waterproofness and breathability, as well as their applications. In addition, challenges and future trends of electrospun W&B membranes are discussed.

Upconversion nanocrystal 'armoured' silica fibres with superior photoluminescence for miRNA detection

We have fabricated a flexible membrane, consisting of SiO2 nanofibres armoured with upconversion nanoparticles, exhibiting intense photoluminescence. These assemblies were subsequently grafted with molecular beacons to produce a biosensor suitable for the detection of specific microRNA and with applications in early cancer detection and point-of-care diagnosis.

Luminescent, Fire-Resistant, and Water-Proof Ultralong Hydroxyapatite Nanowire-Based Paper for Multimode Anticounterfeiting Applications

Counterfeiting of valuable certificates, documents, and banknotes is a serious issue worldwide. As a result, the need for developing novel anticounterfeiting materials is greatly increasing. Herein, we report a new kind of ultralong hydroxyapatite nanowire (HAPNW)-based paper with luminescence, fire resistance, and waterproofness properties that may be exploited for anticounterfeiting applications. In this work, lanthanide-ion-doped HAPNWs (HAPNW:Ln³⁺) with lengths over 100 μm have been synthesized and used as a raw material to fabricating a free-standing luminescent, fire-resistant, water-proof paper through a simple vacuum filtration process. It is interesting to find that the luminescence intensity, structure, and morphology of HAPNW:Ln³⁺ highly depend on the experimental conditions. The as-prepared HAPNW:Ln³⁺ paper has a unique combination of properties, such as high flexibility, good processability, writing and printing abilities, luminescence, tunable emission color, waterproofness, and fire resistance. In addition, a well-designed pattern can be embedded in the paper that is invisible under ambient light but viewable as a luminescent color under ultraviolet light. Moreover, the HAPNW:Ln³⁺ paper can be well-preserved without any damage after being burned by fire or soaked in water. The unique combination of luminescence, fire resistance, and waterproofness properties and the nanowire structure of the as-prepared HAPNW:Ln³⁺ paper may be exploited toward developing a new kind of multimode anticounterfeiting technology for various high-level security antiforgery applications, such as in making forgery-proof documents, certificates, labels, and tags and in packaging.

Hierarchical Porous Structured SiO2/SnO2 Nanofibrous Membrane with Superb Flexibility for Molecular Filtration

The separation and purification of chemical molecules from organic media under harsh chemical environments are of vital importance in the fields of water treatment, biomedical engineering, and organic recycling. Herein, we report the preparation of a flexible SiO₂/SnO₂ nanofibrous membrane (SiO₂/SnO₂ NFM) with high surface area and hierarchical porous structure by selecting poly(vinyl butyral) as pore-forming agent and embedding crystalline phase into amorphous matrix without using surfactant as sacrificial template. Benefiting from the uniform micropore size on the fibers and negatively charged properties, the membranes exhibit a precise selectivity toward molecules based on electrostatic interaction and size exclusion, which could separate organic molecule mixtures with the same electrostatic charges and different molecular sizes with a high efficiency of more than 97%. Furthermore, the highly tortuous open-porous structures and high porosity give rise to a high permeate flux of 288 000 L m^-2 h^-1. In addition, the membrane also displays excellent stability and can be reused for ten consecutive filtration-regeneration cycles. The integration of high filtration efficiency, large permeate flux, good reutilization, and easy to industrialization provides the SiO₂/SnO₂ NFM for potential applications in practical molecular purification and separation science.

Hierarchical structured MnO2@SiO2 nanofibrous membranes with superb flexibility and enhanced catalytic performance

Constructing nanostructured catalyst-embedded ceramic fibrous membranes would facilitate the remediation or preliminary treatment of dyeing wastewater, however, most of such membranes are brittle with low deformation resistance, thus, restricting their widely applications. Herein, the flexible and hierarchical nanostructured MnO₂-immobilized SiO₂ nanofibrous membranes (MnO₂@SiO₂ NFM) were fabricated by combining the electrospinning technique with hydrothermal method. The morphologies of membranes could be regulated from nanowires and nanoflower to mace-like structure via varying concentration of reactants. The resultant MnO₂@SiO₂ NFM could cooperate with hydrogen peroxide to form a Fenton-like reagent for the degradation of methylene blue (MB). The resultant membrane exhibited prominent catalytic performance towards MB, including high degradation degree of 95% within 40min, fast degradation rate of 0.0865min^-1, and excellent reusability in 5 cycles. Moreover, the membranes could be used in a wide pH range of 0 to 14 and the degradation degree reached 76% during dynamic filtration process with a flux of 490,000Lm^-2h^-1. The successful fabricating of such membrane with extraordinary catalytic performance would provide a platform for preparing high-performance catalysts for remediation of dyeing wastewater.

Electrospun Poly(acrylic acid)/Silica Hydrogel Nanofibers Scaffold for Highly Efficient Adsorption of Lanthanide Ions and Its Photoluminescence Performance

Combined with the features of electrospun nanofibers and the nature of hydrogel, a novel choreographed poly(acrylic acid)-silica hydrogel nanofibers (PAA-S HNFs) scaffold with excellent rare earth elements (REEs) recovery performance was fabricated by a facile route consisting of colloid-electrospinning of PAA/SiO2 precursor solution, moderate thermal cross-linking of PAA-S nanofiber matrix, and full swelling in water. The resultant PAA-S HNFs with a loose and spongy porous network structure exhibited a remarkable adsorption capacity of lanthanide ions (Ln(3+)) triggered by the penetration of Ln(3+) from the nanofiber surface to interior through the abundant water channels, which took full advantage of the internal adsorption sites of nanofibers. The effects of initial solution pH, concentration, and contact time on adsorption of Ln(3+) have been investigated comprehensively. The maximum equilibrium adsorption capacities for La(3+), Eu(3+), and Tb(3+) were 232.6, 268.8, and 250.0 mg/g, respectively, at pH 6, and the adsorption data were well-fitted to the Langmuir isotherm and pseudo-second-order models. The resultant PAA-S HNFs scaffolds could be regenerated successfully. Furthermore, the proposed adsorption mechanism of Ln(3+) on PAA-S HNFs scaffolds was the formation of bidentate carboxylates between carboxyl groups and Ln(3+) confirmed by FT-IR and XPS analysis. The well-designed PAA-S HNFs scaffold can be used as a promising alternative for effective REEs recovery. Moreover, benefiting from the unique features of Ln(3+), the Ln-PAA-S HNFs simultaneously exhibited versatile advantages including good photoluminescent performance, tunable emission color, and excellent flexibility and processability, which also hold great potential for applications in luminescent patterning, underwater fluorescent devices, sensors, and biomaterials, among others.

An aggregation-induced emission enhancement fluorescent benzoxazine-derived macromolecule: catalyst-free synthesis and its preliminary application for the determination of aqueous picric acid

An aggregation-induced emission enhancement macromolecular benzoxazine derivative was synthesized by a catalyst-free Mannich reaction and showed a fluorescence quenching response towards nitro compounds.

Magnetic memory effect in self-assembled nickel ferrite nanoparticles having mesoscopic void spaces

We report a novel approach for fabricating nanocrystalline and mesoporous nickel ferrite nanoparticles of ca. 5–9 nm size and it showed interesting memory effect as a consequence of interparticle interaction of self-assembled nanoparticles.

Synthesis of β-Cyclodextrin-Based Electrospun Nanofiber Membranes for Highly Efficient Adsorption and Separation of Methylene Blue

Water-insoluble β-cyclodextrin-based fibers were synthesized by electrospinining followed by thermal cross-linking. The fibers were characterized by field-emission scanning electron microscopic (FE-SEM) and Fourier transformed infrared spectrometer (FT-IR). The highly insoluble fraction obtained from different pH values (3-11) indicates successful cross-linking reactions and their usability in aqueous solution. After the cross-linking reaction, the fibers' tensile strength increases significantly and the BET surface area is 19.49 m(2)/g. The cross-linked fibers exhibited high adsorption capacity for cationic dye methylene blue (MB) with good recyclability. The adsorption performance can be fitted well with pseudo-second-order model and Langmuir isotherm model. The maximum adsorption capacity is 826.45 mg/g according to Langmuir fitting. Due to electrostatic repulsion, the fibers show weak adsorption toward negatively charged anionic dye methyl orange (MO). On the basis of the selective adsorption, the fiber membrane can separate the MB/MO mixture solution by dynamic filtration at a high flow rate of 150 mL/min. The fibers can maintain good fibrous morphology and high separation efficiency even after five filtration-regeneration cycles. The obtained results suggested potential applications of β-cyclodextrin-based electrospun fibers in the dye wastewater treatment field.