Cellulose-based bi-layer hydrogel evaporator with a low evaporation enthalpy for efficient solar desalination

Interfacial evaporation through hydrogel-based evaporators is emerging as a sustainable and cost-effective strategy for drinkable water production. Herein, a specially designed bi-layer hydrogel evaporator was fabricated and used for efficient solar water desalination. With cotton linter as cellulose precursor, it was dispersed in a highly concentrated ZnCl2 (65 %) solution, and cross-linked by epichlorohydrin to prepare cellulose composite hydrogel. After removing inorganic salts by salt-leaching, polyaniline (PANi) with broadband and wide-range light absorption was then integrated into the top surface of hydrogel through in situ polymerization to construct a bi-layer evaporator. As a solar evaporator, the water could be evaporated with a low-energy demand, and the heat from the sunlight could be confined at the interface to achieve efficient water evaporation. Therefore, the hydrogel evaporator demonstrates an optimal water evaporation rate of 3.02 kg m-2 h-1 and photothermal conversion efficiency of 89.09 % under 1 sun (1 kW m-2) irradiation. This work provides new possibilities for efficient solar water purification systems with assured water quality.

Hierarchical ZnO nano-spines grown on a carbon fiber seed layer for efficient VOC removal and airborne virus and bacteria inactivation

Air purification through fiber-based filters has become a fundamental requirement for air contamination control. However, conventional filters depend on polymeric fibrous filters with adequate particulate matter removal ability but fewer degassing and biocidal effects. This study presents the photocatalytic volatile organic compound (VOC) oxidation and antimicrobial properties of zinc oxide (ZnO) nano-spines sprouted activated-carbon nanofibers (I@ZnO/ACNFs) and their potential for air contamination control and infection prevention. By developing a novel technique that can induce phase separation of inorganic salts during electrospinning, nanofibers with zinc (Zn) components concentrated on the surface could be synthesized. I@ZnO/ACNFs exhibit a surface densely covered with high aspect-ratio ZnO nano-spines with significant lethality to airborne pathogens and enhanced photocatalytic activity toward VOCs. Moreover, excellent adhesion stability of ZnO to ACNFs under rapid airflow was observed in I@ZnO/ACNFs. In combination with intriguing antimicrobial activity and strong VOC removal capability derived from their unique morphology, novel I@ZnO/ACNFs hold potential for airborne microbial disinfection, effective and sustainable VOC purification, and the design of photomicrobicidal and photocatalytic materials.

Electrospinning of Chitosan for Antibacterial Applications—Current Trends

Chitosan is a natural biopolymer that can be suitable for a wide range of applications due to its biocompatibility, rigid structure, and biodegradability. Moreover, it has been proven to have an antibacterial effect against several bacteria strains by incorporating the advantages of the electrospinning technique, with which tailored nanofibrous scaffolds can be produced. A literature search is conducted in this review regarding the antibacterial effectiveness of chitosan-based nanofibers in the filtration, biomedicine, and food protection industries. The results are promising in terms of research into sustainable materials. This review focuses on the electrospinning of chitosan for antibacterial applications and shows current trends in this field. In addition, various aspects such as the parameters affecting the antibacterial properties of chitosan are presented, and the application areas of electrospun chitosan nanofibers in the fields of air and water filtration, food storage, wound treatment, and tissue engineering are discussed in more detail.

The adsorption, kinetics, and interaction mechanisms of various types of estrogen on electrospun polymeric nanofiber membranes

This study focuses on the adsorption kinetics of four highly potent sex hormones (estrone (E1), 17β-estradiol (E2), 17α-ethinylestradiol (EE2), and estriol (E3)), present in water reservoirs, which are considered a major cause of fish feminization, low sperm count in males, breast and ovarian cancer in females induced by hormonal imbalance. Herein, electrospun polymeric nanostructures were produced from cellulose acetate, polyamide, polyethersulfone, polyurethanes (918 and elastollan), and polyacrylonitrile (PAN) to simultaneously adsorbing these estrogenic hormones in a single step process and to compare their performance. These nanofibers possessed an average fiber diameter in the range 174-330 nm and their specific surface area ranged between 10.2 and 20.9 m²g^-1. The adsorption-desorption process was investigated in four cycles to determine the effective reusability of the adsorption systems. A one-step high-performance liquid chromatography technique was developed to detect and quantify concurrently each hormone present in the solution. Experimental data were obtained to determine the adsorption kinetics by applying pseudo-first-order, pseudo-second-order and intraparticle diffusion models. Findings showed that E1, E2 and EE2 best fitted pseudo-second-order kinetics, while E3 followed pseudo-first-order kinetics. It was found that polyurethane Elastollan nanofibers had maximum adsorption capacities of 0.801, 0.590, 0.736 and 0.382 mg g^-1for E1, E2, EE2 and E3, respectively. In addition, the results revealed that polyurethane Elastollan nanofibers had the highest percentage efficiency of estrogens removal at ∼58.9% due to its strong hydrogen bonding with estrogenic hormones, while the least removal efficiency for PAN at ∼35.1%. Consecutive adsorption-desorption cycles demonstrated that polyurethane maintained the best efficiency, even after being repeatedly used four times compared to the other polymers. Overall, the findings indicate that all the studied nanostructures have the potential to be effective adsorbents for concurrently eradicating such estrogens from the environment.

De Novo Ion-Exchange Membranes Based on Nanofibers

The unique functions of nanofibers (NFs) are based on their nanoscale cross-section, high specific surface area, and high molecular orientation, and/or their confined polymer chains inside the fibers. The introduction of ion-exchange (IEX) groups on the surface and/or inside the NFs provides de novo ion-exchangers. In particular, the combination of large surface areas and ionizable groups in the IEX-NFs improves their performance through indices such as extremely rapid ion-exchange kinetics and high ion-exchange capacities. In reality, the membranes based on ion-exchange NFs exhibit superior properties such as high catalytic efficiency, high ion-exchange and adsorption capacities, and high ionic conductivities. The present review highlights the fundamental aspects of IEX-NFs (i.e., their unique size-dependent properties), scalable production methods, and the recent advancements in their applications in catalysis, separation/adsorption processes, and fuel cells, as well as the future perspectives and endeavors of NF-based IEMs.

Reusable membrane with multifunctional skin layer for effective removal of insoluble emulsified oils and soluble dyes

The organic pollutants, typical of emulsified oils and soluble organic dyes, is commonly found in wastewater, however simultaneous removal of them remains challenging because of their difference in surface charge, molecule size, and solubility in water. Inspired by the water purification of the earth's multilayer strata, a fibrous membrane with multifunctional skin is fabricated by coupling sub-micrometer pores layer of polyaniline (PANI) and nano molecular brush of polyacrylic acid (PAA)/polyethyleneimine (PEI) on polyacrylonitrile membrane, for cross-scale organic pollution/water separation. This ultrathin skin of PANI/PAA/PEI is endowed with sub-micrometer pores and strong hydration, which can effectively prevent tiny oil droplets from entering or adhering the membrane pores. Furthermore, this skin with double electric layer can selectively adsorb and even filtrate anionic/cationic dyes by protonation and deprotonation effect in different pH solutions. The synergy of these features enables this membrane with ultra-high water flux (>3000 L m^-2 h^-1 bar^-1), oil rejection rates (>99.6%), and anionic/cationic dyes adsorbability (>49.1 mg/g). Besides, the membrane also exhibits desirable reusability, excellent mechanical durability and outstanding acid/alkali resistance, promising for removal of insoluble emulsified oils and soluble organic dyes in wastewater.

Reversible filtration redox of methylene blue in dimethylsulfoxide by manganese oxide loaded carbonaceous nanofibrous membrane through Fenton-like oxidation

The reversible redox of methylene blue in organic solvents was highly attractive, yet was rarely reported. In this study, we realized the continuous filtration redox of methylene blue (MB) in dimethylsulfoxide (DMSO) through Fenton-like oxidization by using MnO₂ loaded carbonaceous nanofibrous membrane (cPAN-MnO₂). The carbonaceous nanofibrous membrane (cPAN) was fabricated through electrospun of polyacrylonitrile and subsequent carbonization. The obtained cPAN nanofibrous membrane showed excellent stability in polar DMSO. MnO₂ can be readily coated on cPAN nanofibers through an in situ redox reaction between cPAN and potassium permanganate. The fabricated cPAN-MnO₂ membrane exhibited instantaneous reduction property towards MB in DMSO during a gravity-driven continuous filtration process. Interestingly, MB reduction was initiated by a typical Fenton-like oxidization, where hydroxyl radicals were firstly generated from hydrogen peroxide catalyzed by MnO₂ in DMSO. Then hydroxyl radicals attacked DMSO to further produce methyl radicals, which resulted in the reduction of MB. In addition, MB reduction process in DMSO was reversible. Our study provides a novel strategy for continuous redox of MB in polar organic solvent and might give new ideas for MB applications.

A Review on Heavy Metal Ions and Containing Dyes Removal Through Graphene Oxide-Based Adsorption Strategies for Textile Wastewater Treatment

Textile wastewater heavy metal pollution has become a severe environmental problem worldwide. Metal ion inclusion in a dye molecule exhibits a bathochromic shift producing deeper but duller shades, which provides excellent colouration. The ejection of a massive volume of wastewater containing heavy metal ions such as Cr (VI), Pb (II), Cd (II) and Zn (II) and metal-containing dyes are an unavoidable consequence because the textile industry consumes large quantities of water and all these chemicals cannot be combined entirely with fibres during the dyeing process. These high concentrations of chemicals in effluents interfere with the natural water resources, cause severe toxicological implications on the environment with a dramatic impact on human health. This article reviewed the various metal-containing dye types and their heavy metal ions pollution from entryway to the wastewater, which then briefly explored the effects on human health and the environment. Graphene-based absorbers, specially graphene oxide (GO) benefits from an ordered structured, high specific surface area, and flexible surface functionalization options, which are indispensable to realize a high performance of heavy metal ion removal. These exceptional adsorption properties of graphene-based materials support a position of ubiquity in our everyday lives. The collective representation of the textile wastewater's effective remediation methods is discussed and focused on the GO-based adsorption methods. Understanding the critical impact regarding the GO-based materials established adsorption portfolio for heavy metal ions removal are also discussed. Various heavy-metal ions and their pollutant effect, ways to remove such heavy metal ions and role of graphene-based adsorbent including their demand, perspective, limitation, and relative scopes are discussed elaborately in the review.

Optimizing the electrical conductivity of polyacrylonitrile/polyaniline with nickel nanoparticles for the enhanced electrostimulation of Schwann cells proliferation

Tissue engineering scaffolds made of biocompatible polymers are promising alternatives for nerve reparation. For this application, cell proliferation will be speeded up by electrostimulation, which required electrically-conductive materials. Here, a biomimicking scaffold with optimized conductivity was developed from electrospun polyacrylonitrile/electrically-conductive polyaniline (PAN/PANI) nanofibers doped with Ni nanoparticles. PAN/PANI/Ni was biocompatible for Schwann cells and exhibited a suitable tensile strength and wettability for cell proliferation. When compared with unmodified PAN/PANI, the electrical conductivity of PAN/PANI/Ni was 6.4 fold higher. Without electrostimulation, PAN/PANI and PAN/PANI/Ni exhibited similar Schwann cells' proliferation rates. Upon electrostimulation at 100 mV cm^-1 for one hour per day over five days, PAN/PANI/Ni accelerated Schwann cells' proliferation 2.1 times compared to PAN/PANI. These results demonstrate the importance of expanding the electrical conductivity of the tissue engineering scaffold to ensure optimal electrostimulation of nerve cell growth. Additionally, this study describes a straightforward approach to modulate the electrical conductivity of polymeric materials via the addition of Ni nanoparticles that can be applied to different biomimicking scaffolds for nerve healing.

Enhanced Cr(VI) removal by waste biomass derived nitrogen/oxygen co-doped microporous biocarbon

Herein, kitchen waste hydrolysis residue (KWHR) was utilized as the precursor to fabricate nitrogen/oxygen co-doped microporous biocarbons (NOMBs) with ultrahigh specific surface area via KOH activation. Activation temperature was found to be crucial for heteroatom doping and pore structure construction. Attractively, the obtained NOMB with high surface area (2417 m²/g) and microporosity (~ 90%) displayed an outstanding capacity of Cr(VI) removal (526.1 mg/g at pH 2). The kinetics and isotherm studies showed that the adsorption of Cr(VI) onto NOMB was well described by the pseudo-second-order kinetics and Langmuir isotherm. Moreover, it was found that Cr(VI) was partly reduced to Cr(III) during the removal process as the nitrogen/oxygen functionalities and unsaturated carbon bond played crucial roles of electron-donors, which revealed the fact that the removal of Cr(VI) by NOMB was attributed to the coupling of adsorption and reduction reaction. Overall, this study has demonstrated the possibility of preparing microporous biocarbons using KWHR as a renewable material and the resultant NOMB is of great potential to detoxify Cr(VI).

Fabrication of a PAN–PA6/PANI membrane using dual spinneret electrospinning followed by in situ polymerization for separation of oil-in-water emulsions

A polyacrylonitrile–polyamide 6/polyaniline (PAN–PA6/PANI) doped membrane was prepared using dual spinneret simultaneous electrospinning of PAN and PA6 and in situ polymerization of aniline at low temperature.

Treatment of Wastewater Using Seaweed: A Review

Inadequately treated or untreated wastewater greatly contribute to the release of unwanted toxic contaminants into water bodies. Some of these contaminants are persistent and bioaccumulative, becoming a great concern as they are released into the environment. Despite the abundance of wastewater treatment technologies, the adsorption method overall has proven to be an excellent way to treat wastewater from multiple industry sources. Because of its significant benefits, i.e., easy availability, handling, and higher efficiency with a low cost relative to other treatments, adsorption is opted as the best method to be used. However, biosorption using naturally found seaweeds has been proven to have promising results in removing pollutants, such as dyes from textile, paper, and the printing industry, nitrogen, and phosphorous and phenolic compounds, as well as heavy metals from various sources. Due to its ecofriendly nature together with the availability and inexpensiveness of raw materials, biosorption via seaweed has become an alternative to the existing technologies in removing these pollutants from wastewater effectively. In this article, the use of low-cost adsorbent (seaweed) for the removal of pollutants from wastewater has been reviewed. An extensive table summarises the applicability of seaweed in treating wastewater. Literature reported that the majority of research used simulated wastewater and minor attention has been given to biosorption using seaweed in the treatment of real wastewater.

Facile preparation of hybrid porous polyanilines for highly efficient Cr(vi) removal

In the present work, leucoemeraldine-based hybrid porous polyanilines (LHPPs) have been synthesized by the Friedel-Crafts reaction of leucoemeraldine and octavinylsilsesquioxane (OVS) for Cr(vi) removal. The resulting LHPPs were characterized by Fourier transform infrared spectroscopy, powder X-ray diffraction, thermogravimetric analysis, scanning electron microscopy and N2 adsorption-desorption. The findings indiated that the LHPPs were amorphous, with apparent surface areas (S BET) in the range of 147 to 388 m2 g-1 and total volumes in the range of 0.13 to 0.44 cm3 g-1. Cr(vi) removal experiments displayed that the LHPPs exhibited highly efficient Cr(vi) removal performance. The maximum Cr(vi) removal capacity of LHPP-1 was 990.1 mg g-1 at 308 K and pH 1, which is higher than those of other reported polyaniline-based adsorbents. The adsorption process was a spontaneous, endothermic and chemical adsorption process. The adsorption behavior agreed well with Langmuir models and pseudo second-order equations. X-ray photoelectron spectroscopy and Fourier transformed infrared (FTIR) spectroscopy analysis revealed that the highly efficient Cr(vi) removal performance can be mainly attributed to the existence of numerous amine and imine groups on the surface of the LHPPs; these can function as adsorption active sites for Cr(vi) removal through electrostatic adsorption and reduction to Cr(iii) under acidic conditions. Moreover, the LHPPs exhibited excellent adsorption selectivity for Cr(vi) despite the presence of other metal ions (K+, Cu2+, Mn2+) and anions (NO3 -, SO4 2-). Therefore, the LHPPs have potential applications for Cr(vi) removal in industrial wastewater.

Nitrogen-Containing Fabric Adsorbents Prepared by Radiation Grafting for Removal of Chromium from Wastewater

To remove chromium from wastewater effectively, two types of nitrogen-containing fabric adsorbents, having amidoxime ligand groups and quaternary ammonium anion exchange groups, respectively, were prepared by radiation grafting. In brief, the amidoxime adsorbent is obtained by grafting of acrylonitrile (AN)/methacrylic acid (MAA) onto a nonwoven fabric and subsequent amidoximation with hydroxylamine, while the ammonium adsorbent is obtained by grafting of chloromethylstyrene (CMS) followed by quaternization with trimethylamine. The AN/MAA-grafting reaches a high degree of grafting more than 100%, and the resulting amidoxime adsorbent reaches a high amidoxime density of 4.53 mmol/g. On the other hand, the CMS-grafting reaches a much higher degree of grafting above 200%, and the resulting ammonium adsorbent reaches a high ammonium density of 3.51 mmol/g. FTIR/ATR and TGA/DTA are used for the characterization of the grafted fabrics as well as the relevant fabric adsorbents. Furthermore, the chromium removal of the prepared fabric adsorbent is tested in both batch and column modes. It has been confirmed that the chromium removal was largely dependent on the pH of the solution. At pH 5.0, the amidoxime adsorbent shows a high Cr(III) adsorption capacity of 31.68 mg/g, while the ammonium adsorbent shows a much higher Cr(VI) adsorption capacity of 130.65 mg/g.

Polyaniline-based adsorbents for removal of hexavalent chromium from aqueous solution: a mini review

Hexavalent chromium (Cr(VI)) is a common hazardous contaminant in the environment and carcinogenic or mutagenic to aquatic animals and human beings. Therefore, the removal and detoxification of Cr(VI) have been attracting increasing attention of researchers. Among various conducting polymers, polyaniline (PANI)-based adsorbents have shown an excellent performance on the removal of Cr(VI) because of their redox properties, eased synthesis, and favorable biocompatibility. In this review, the characteristics of various PANI-based adsorbents were described, including PANI-modified nanofiber mats and membranes, PANI/bio-adsorbents, PANI/magnetic adsorbents, PANI/carbon adsorbents, PANI-modified clay composites, and PANI-inorganic hybrid composites. The mechanisms for the detoxification and adsorption of Cr(VI) were also discussed. The results indicated the potential applications of PANI-based adsorbents for the removal of Cr(VI). Graphical abstract ᅟ.

Photoreduction of Cr(VI) in water using BiVO4-Fe3O4 nano-photocatalyst under visible light irradiation

The residuals of hexavalent chromium in the aquatic environment have raised much concern for water decontamination. In this study, BiVO₄-Fe₃O₄ was synthesized using a solvothermal method and adopted as a photoreduction catalyst to removal of Cr(VI) in water under visible light irradiation. The physical and chemical properties of BiVO₄-Fe₃O₄ were characterized by UV-vis-DRS, SEM, XRD, FTIR, and BET. The results demonstrated that the band gap for the obtained material is 1.74 eV with an average size of 15 nm and a specific surface area of 55.16 m²/g. A high photocatalytic performance was observed on the photoreduction of Cr(VI) and the removal efficiency was increased in the lower pH condition. The ascending catalyst dosages made the promotion effect, while the increase of Cr(VI) concentration contributed the inhibition for the reduction performance. The structural characteristics of the selected hole scavengers (ethanol, isopropanol, formic acid, citric acid, and oxalic acid) showed the various effects on the reactions due to the amounts of α-OH. For the optimal condition, 79.37% Cr(VI) was removed. Based on the excellent reusability of BiVO₄-Fe₃O₄, this study demonstrated a potential method for the economic-friendly removal of high-valence metals with easier separation in the water.

Synthesis of monodisperse core shell PVA@P(AMPS-co-NIPAm) nanogels structured for pre-concentration of Fe(III) ions

Core shell-structured poly(vinyl alcohol) @ poly(2-acrylamido-2-methyl-1-propane-sulfonic acid-co-N-isopropylacrylamide) PVA@P(AMPS-co-NIPAm) spheres are synthesized. The well-defined PVA@P(AMPS-co-NIPAm) core shell nanogels with diameter nearly 30 nm enriches Fe(III), and the nanogels are characterized by FT-IR, TEM, SEM and X-ray diffraction (XRD). The many factors affecting adsorption were successfully investigated. The maximum capacity of Fe(III) ions was 320 (mg/g) for PVA@P(90AMPS-co-10NIPAm) (wt.: wt%). The equilibrium data matching well with the Langmuir model and the pseudo-second-order form described the adsorption process better than the pseudo-first-order model. Findings of the present study highlight using a simple synthesis of PVA@P(AMPS-co-NIPAm) nanogels as superior and recyclable nanoadsorbents.

Effective Adsorption/Reduction of Cr(VI) Oxyanion by Halloysite@Polyaniline Hybrid Nanotubes

Halloysite@polyaniline (HA@PANI) hybrid nanotubes are synthesized by the in situ chemical polymerization of aniline on halloysite clay nanotubes. By facilely tuning the dopant acid, pH, and apparent weight proportion for aniline (ANI) and halloysite (HA) nanotubes in the synthesis process, PANI with tuned oxidation state, doping extent, and content are in situ growing on halloysite nanotubes. The reaction system's acidity is tuned by dopant acid, such as HCl, H₂SO₄, HNO₃, and H₃PO₄. The adsorption result shows the fabricated HA@PANI hybrid nanotubes can effectively adsorb Cr(VI) oxyanion and the adsorption ability changes according to the dopant acid, pH, and apparent weight proportion for ANI and HA in the synthesis process. Among them, the HA@PANI fabricated with HCl as dopant acid tuning the pH at 0.5 and 204% apparent weight proportion for ANI and HA (HP/0.5/204%-HCl) shows the highest adsorption capacity. The adsorption capacity is in accordance well with the doping extent of PANI in HA@PANI. Furthermore, when HP/0.5/204%-HCl is redoped with HNO₃, H₂SO₄, and H₃PO₄, the adsorption capacity declines, implying the dopant acid in the process of redoping exhibits a marked effect on Cr(VI) oxyanion adsorption for the HA@PANI hybrid nanotubes. HP/0.5/204%-HCl and HP/0.5/204%-H₃PO₄ have demonstrated good regenerability with an above 80% removal ratio after four cycles. Moreover, the HA@PANI adsorbent has better sedimentation ability than that of pure PANI. The adsorption behavior is in good agreement with Langmuir and pseudo second-order equations, indicating the adsorption of HA@PANI for Cr(VI) oxyanion is chemical adsorption. FT-IR and XPS of HA@PANI after Cr(VI) oxyanion adsorption indicate that the doped amine/imine groups (-NH⁺/═N⁺- groups) are the main adsorption sites for the removal of Cr(VI) oxyanion by electrostatic adsorption and reduction of the adsorbed Cr (VI) oxyanion to Cr(III) simultaneously.

Design of Graphene- and Polyaniline-Containing Functional Polymer Hydrogel as a New Adsorbent for Removal of Chromium (VI) Ions

Hydrogels find applications in various fields, and the ever-growing spectrum of available monomers, crosslinking, and nanotechnologies widen the application of polymer hydrogels. Herein, we describe the preparation of a new graphene (G)- and polyaniline (PANI)-containing functional polymer gel (G/PANI/FG) through a facile crosslinking copolymerization approach. Several characterization techniques such as field-emission scanning electron microscopy, Fourier-transform infrared, and X-ray photoelectron spectroscopy were employed to understand the physicochemical characteristics of the G/PANI/FG. The new G/PANI/FG was used as an adsorbent for chromium (VI) and exhibited the highest Cr (VI) removal efficiency (~97%). The inclusion of G and PANI in the gel results in high surface area, 3D porous structure, and Cr (VI)-chelating amine sites, which enhanced the Cr (VI) removal efficiency and thermal stability of the gel adsorbent. The results of our study revealed that G/PANI/FG is suited for the removal of Cr (VI) from aqueous solution.

Simultaneous regulation of morphology, crystallization, thermal stability and adsorbability of electrospun polyamide 6 nanofibers via graphene oxide and chemically reduced graphene oxide

The spinnable concentration range, crystalline structure and performance of polyamide 6 nanofibers were modulated simultaneously via GO and RGO.

Needleless electrospinning for scaled-up production of ultrafine chitosan hybrid nanofibers used for air filtration

This filter media showed better performance than commercial HEPA for nanoparticles filtration.

Adsorption–reduction of chromium(vi) from aqueous solution by phenol–formaldehyde resin microspheres

A novel adsorbent of phenol–formaldehyde resin (PF) microspheres was prepared at a low temperature, and had an excellent performance for the adsorption–reduction of Cr(vi).

Cost effective nanofiber composite membranes for Cr(vi) adsorption with high durability

PANI/EVOH composite nanofiber membranes were prepared though melt-blending extrusion, high-speed flow deposition and in situ chemical oxidative polymerization for the removal of hexavalent chromium [Cr(vi)].

Iron oxide nanoparticle-immobilized PAN nanofibers: synthesis and adsorption studies

Iron oxide nanoparticles grown on the surface of an electrospun PAN nanofiber membrane can be used as a next generation nanoadsorbent for effective removal of CR dye.

Fabrication and Formation Mechanism of Ag Nanoplate-Decorated Nanofiber Mats and Their Application in SERS

We report a new simple method to fabricate a highly active SERS substrate consisting of poly-m-phenylenediamine/polyacrylonitrile (PmPD/PAN) decorated with Ag nanoplates. The formation mechanism of Ag nanoplates is investigated. The synthetic process of the Ag nanoplate-decorated PmPD/PAN (Ag nanoplates@PmPD/PAN) nanofiber mats consists of the assembly of Ag nanoparticles on the surface of PmPD/PAN nanofibers as crystal nuclei followed by in situ growth of Ag nanoparticles exclusively into nanoplates. Both the reducibility of the polymer and the concentration of AgNO3 are found to play important roles in the formation and the density of Ag nanoplates. The optimized Ag nanoplates@PmPD/PAN nanofiber mats exhibit excellent activity and reproducibility in surface-enhanced Raman scattering (SERS) detection of 4-mercaptobenzoic acid (4-MBA) with a detection limit of 10(-10)  m, making the Ag nanoplates@PmPD/PAN nanofiber mats a promising substrate for SERS detection of chemical molecules. In addition, this work also provides a design and fabrication process for a 3D SERS substrate made of a reducible polymer with noble metals.

Mesoporous BaTiO₃@SBA-15 derived via solid state reaction and its excellent adsorption efficiency for the removal of hexavalent chromium from water

We report the synthesis of a barium-titanate/mesoporous silica nanocomposite material BaTiO3@SBA-15 via aerosol assisted solid state reaction using SBA-15 as a hard template. Hexavalent chromium is one of the most harmful contaminants of industrial waste-water. We have used BaTiO3@SBA-15 nanocomposite as an adsorbent for the removal of chromium(vi)-contaminated water and it showed an adsorption capacity of 98.2 wt% within only 40 min contact time in a batch reactor. This mesoporous composite has retained this excellent adsorption efficiency of hexavalent chromium for several repetitive cycles, suggesting its future potential for the remediation of water contaminated with Cr(vi).

Controlled growth of polyhedral and plate-like Ag nanocrystals on a nanofiber mat as a SERS substrate

We report chemical deposition of silver nanocrystals (AgNCs) of different sizes and morphologies, such as polyhedra and plates, on a polyacrylonitrile (PAN) nanofiber mat. High performance surface-enhanced Raman scattering (SERS) substrates are achieved. The effect of the experimental parameters, such as the temperature, concentration and pH of [Ag(NH3)2]OH aqueous solution, on the morphology evolution and density of AgNCs is systematically investigated. The results suggest that the optimized nanofiber mat exhibits a significant SERS performance with superior stability and reproduction, and the SERS enhancement factor (EF) can reach as high as 10(8) for 4-mercaptobenzoic acid (4-MBA). The optimized nanofiber mat also shows high SERS activity for p-aminothiophenol (4-ATP) over the whole nanofiber mat demonstrating the feasibility for detection of both analytes. The detection limit of 4-MBA and 4-ATP is as low as 10(-9) M and 10(-10) M respectively, making the nanofiber mat a promising candidate for SERS detection of chemical pollutants.

Hierarchical composite polyaniline-(electrospun polystyrene) fibers applied to heavy metal remediation

We describe the in situ preparation of a multipurpose hierarchical polyaniline-polystyrene (PANI-PS) composite based in the chemical polymerization of PANI on nonwoven (NW) electrospun PS mats. We performed a detailed study of the properties of these materials to select the best strategies to incorporate PANI chains into pristine NW PS mats without compromising the original porosity and mechanical flexibility of the matrices. The resulting composites presented nanostructured PANI chains highly dispersed in the interior of the NW PS mat and showed good electrical properties and surface-wetting characteristics that could be easily controlled. In particular, we show that these NW PANI-PS mats exhibit interesting properties in their interaction with heavy metal ions. For instance, their high adsorption capacities toward dispersed Hg(II), Cd(II), Pb(II), Cr(VI), and Cu(II) ions make them promising materials for water remediation, by providing a simple manner of collecting and removing these metals from aqueous systems. In fact, the NW electrospun mats here presented do not suffer from the usual limitations found in materials commonly employed as adsorbents, such as a tendency to agglomerate or accumulate in the environment because of difficulties of properly recovering them after use. To better understand the nature of each pairwise metal-PANI interaction, we performed a thorough investigation of the optical and electrical changes induced by the metal adsorption in the NW PANI-PS mats. As a consequence of their interaction with the metal ions, the visual aspect of the mats change, a fact more evident in the case of Cr(VI) removal, when the matrices vary their color from green to purple. These changes are related to the variation of the oxidation state of the PANI chains: as the ion metals are progressively adsorbed into the mat, they promote the conversion in varying degrees of the PANI chains from salt emeraldine to the pernigraniline form, and the mats become more resistive. We implemented an electrical impedance investigation of the charge transport characteristics of NW PANI-PS mat, and the results indicate that they are sensitive to the type of metal ion adsorbed and that the amount of ions adsorbed in each case is mostly related to the standard electrode potential of the metal considered.