Bingru Zhang

Thioether-functionalized mesoporous fiber membranes: sol-gel combined electrospun fabrication and their applications for Hg2+ removal.

Mesoporous polyvinylpyrrolidone (PVP)/SiO(2) composite nanofiber membranes functionalized with thioether groups have been fabricated by a combination method of sol-gel process and electrospinning. The precursor sol was synthesized by one-step co-condensation of tetraethyl orthosilicate (TEOS) and 1,4-bis(triethoxysilyl)propane tetrasulfide (BTESPTS, (CH(3)CH(2)O)(3)Si(CH(2))(3)S-S-S-S(CH(2))(3)Si-(OCH(2)CH(3))(3)), with the triblock copolymer poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (P123, EO(20)PO(70)EO(20)) as template. After the addition of PVP, nanofiber membranes were prepared by electrospinning. The membranes were characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) images, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), N(2) adsorption-desorption isotherms, and an Elementar Vario EL analyzer. The composites were used as highly selective adsorbents for Hg(2+) due to the modification with thioether groups (-S-), and were conveniently separated from the waste water. The composite could be regenerated through acidification.

Laccase–Polyacrylonitrile Nanofibrous Membrane: Highly Immobilized, Stable, Reusable, and Efficacious for 2,4,6-Trichlorophenol Removal

Increasing attention has been given to nanobiocatalysis for commercial applications. In this study, laccase was immobilized on polyacrylonitrile (PAN) nanofibrous membranes through ethanol/HCl method of amidination reaction and successfully applied for removal of 2,4,6-trichlorophenol (TCP) from water. PAN membranes with fiber diameters from 200 nm to 300 nm were fabricated via electrospinning and provided a large surface area for enzyme immobilization and catalytic reactions. Images of scanning electron microscope demonstrated the enzyme molecules were aggregated on the nanofiber surface. The immobilized laccase exhibited 72% of the free enzyme activity and kept 60% of its initial activity after 10 operation cycles. Moreover, the storage stability of the immobilized laccase was considered excellent because they maintained more than 92% of the initial activity after 18 days of storage, whereas the free laccase retained only 20%. The laccase-PAN nanofibrous membranes exhibited high removal efficiency of TCP under the combined actions of biodegradation and adsorption. More than 85% of the TCP was removed under optimum conditions. Effects of various factors on TCP removal efficiency of the immobilized laccase were analyzed. Results suggest that laccase-PAN nanofibrous membranes can be used in removing TCP from aqueous sources and have potential for use in other commercial applications.

Preparation and application of amino functionalized mesoporous nanofiber membrane via electrospinning for adsorption of Cr3+ from aqueous solution

Novel amino (-NH2) functionalized mesoporous polyvinyl pyrrolidone (PVP)/SiO2 composite nanofiber membranes were fabricated by a one-step electrospinning method using poly (vinyl alcohol) and tetraethyl orthosilicate (TEOS) mixed with cationic surfactant, cetyltrimethyl ammonium bromide (CTAB) as the structure directing agent. Ureidopropyltriethoxysilane was used for functionalization of the internal pore surfaces. The membranes were characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) images, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), element analyzer and N2 adsorption-desorption isotherms. The nanofiber diameters, average pore diameters and surface areas were 100-700 nm, 2.86 nm and 873.62 m2/g, respectively. These mesoporous membranes functionalized with -NH2 groups exhibited very high adsorptions properties based on the adsorption of Cr3+ from an aqueous solution. Equilibrium adsorption was achieved after approximately 20 min and more than 97% of chromium ions in the solution were removed. The membrane could be regenerated through acidification.

Immobilization of horseradish peroxidase on electrospun microfibrous membranes for biodegradation and adsorption of bisphenol A

Horseradish peroxidase (HRP) from roots of horseradish (Amoracia rusticana) was successfully immobilized on novel enzyme carriers, poly(methyl methacrylate-co-ethyl acrylate) (PMMA CEA) microfibrous membranes, and used for removal of bisphenol A from water. PMMA CEA fibrous membranes (PFM) with fiber diameters of 300-500 nm, were fabricated by electrospinning. HRP was covalently immobilized on the surface of microfibers previously activated by polyethylenimine and glutaraldehyde. HRP loading reached 285 mg/g, and enzyme activity was 70% of free HRP after immobilization. Both stabilities and reusability of HRP were greatly improved after immobilization. After six repeated runs, immobilized HRP retained about 50% of its initial activity. Immobilized HRP exhibited significantly higher removal efficiency for bisphenol A (BPA) in 3h (93%) compared with free HRP (61%) and PFM alone (42%). The high BPA removal can be resulted by improvement of catalytic activity of immobilized HPR with adsorption on modified PMMA CEA support.

Electrospun fibrous mats as a skeleton for fabricating hierarchically structured materials as sorbents for Cu2

Based on the combination of the electrospinning and evaporation-induced self-assembly mesopore-forming technique, a facile strategy is developed to fabricate self-standing thiol-functionalized membranes with hierarchical structures (Macro-Mesopores and binding sites). This membrane is prepared using electrospun polystyrene (PS) fibers as the skeleton and non-ionic surfactant F127 as the structure-directing agent with co-condensation of tetraethyl orthosilicate (TEOS) and 3-mercaptopropyltrimethoxysilane (MPTMS). The prepared membranes were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscope (SEM), nitrogen sorption, mercury intrusion porosimetry, and Fourier transform infrared (FT-IR) spectra. The macropore constructed by the electrospun PS membrane ranged from 1 to 10 μm, while the highly ordered mesopore formed by F127 was around 5 nm and heavy metals binding cites of thiol groups were also presented, respectively. Using Cu2+ ions as the model bivalent cation, an excellent removal capacity of the prepared membrane was confirmed by the static sorption and dynamic filtration experiments with a high flux up to 1.30 × 104 L h−1 m−2bar−1. We find that regeneration of the membranes and the metal ion recovery can be facially realized by the treatment using acid solution. These results demonstrate that the developed strategy has significant potential for the design and fabrication of high-performance membranes with hierarchical structures and could find impactful application in the field of industrial catalysis, separation, and environmental pollution control and resources reuse.

Adsorption of Rhodamine B dye by biomimetic mesoporous SiO2 nanosheets

Efficient treatment of solutions and solid wastes containing Rhodamine B (RB), a common dye with potential carcinogenicity and sometimes used illegally in food industry, is of great importance because inappropriate treatment may lead to serious human and environmental risks. A novel nanomaterial, the mesoporous silica nanosheets prepared via electrospinning and calcination are applied to the adsorption of RB from aqueous solutions in this work. This sheet-like material is superior to classic powder adsorbents in recoverability, while good availability and stability favor its practical application. The effects of key parameters such as system pH, stirring rate, initial concentration, and contact time are studied. The adsorption isotherm type and the kinetic characteristic are analyzed. The results show that the mesoporous SiO2 nanosheets are efficient in removing RB from aqueous phase, presenting great potential to become a practical dye adsorbent. Regeneration experiments show that this novel adsorbent can be activated by ethanol extraction process. This study provides the academic field with a successful application case of nanostructured materials, which can be applied to a wider range of dyes similar to RB in physicochemical properties, showing prosperous value in advanced environmental purification.

Stabilization/solidification of lead in MSWI fly ash with mercapto functionalized dendrimer Chelator

This work compares the performance of stabilizing Pb by Sodium sulfide (Na2S), Sodium phosphate (Na3PO4), thiourea (H2NCSNH2), and mercapto functionalized dendrimer (TEPA-SNa) in MSWI fly ash, including leaching toxicity analysis and leaching behavior analysis, as a function of pH. The leaching toxicity in fly ash indicated that leaching value of Pb stabilized by Na2S, Na3PO4, and H2NCSNH2 has remained higher than the limit value (0.25mg/L) with a dosage of 10%. However, the leaching value associated with TEPA-SNa approaches zero at a dosage of 3%. The effective leaching test results showed the leaching amount of Pb stabilized by TEPA-SNa with a dosage of 3% to be 3.58 mg/kg less than the maximum allowable amount of leaching (5mg/kg), but the amount of Pb leached by Na2S, Na3PO4, and H2NCSNH2 was much higher than 5mg/kg. The leaching behavior of Pb as a function of pH showed that the leaching concentration of Pb stabilized by TEPA-SNa can approach zero at a dosage of 5% no matter how the pH changes. In summary, TEPA-SNa can interact with Pb(2+) in the acid-base environment and effectively immobilize Pb(2+) in fly ash in the long term.

An environmentally-friendly enzyme-based nanofibrous membrane for 3,3′,5,5′-tetrabromobisphenol removal

Chitosan (CS)/poly(vinyl alcohol) (PVA) nanofibrous membranes have inherently poor mechanical strength. To improve the mechanical strength of these membranes, nanocrystalline cellulose (NCC) prepared by a simplified method was added to the former system. The results showed that the tensile strength of the membrane with 5% NCC addition was 370% higher than that of the membrane without NCC. Horseradish peroxidase (HRP) was immobilized on the membrane through covalent binding with HRP previously activated with 1,1′-carbonyldiimidazole, and the maximum enzyme loading was approximately 384 mg g−1. The physical, chemical properties of immobilized HRP and its application in 3,3′,5,5′-tetrabromobisphenol (TBBPA) removal were examined. The results showed that HRP immobilized on CS/PVA–NCC membranes showed greater stability and reusability than free HRP and the membrane without NCC. The former also exhibited an effective performance (95.9% removal, 3 h) for TBBPA removal under the optimum conditions (pH 7, 35 °C). The results showed that HRP immobilized on NCC-incorporated CS/PVA membranes could be used to remove brominated flame-retardants, especially TBBPA from wastewater. Thus, these membranes have potential industrial applications.

Estrone removal by horseradish peroxidase immobilized on a nanofibrous support with Fe3O4 nanoparticles

The occurrence, fate, and removal of estrone (E1) from environmental systems have attracted considerable research interests in recent years because of the potential risks of human and wildlife exposure to E1. This study aims to develop an efficient enzymatic method to remove E1 from water. Electrospinning composite fibers (200–300 nm in diameter), comprising poly(vinyl alcohol) (PVA), poly(acrylic acid) (PAA), SiO2, and Fe3O4 nanoparticles (NPs), were used as supports for horseradish peroxidase (HRP) immobilization. The immobilized HRP was used for E1 removal. The effects of Fe3O4 NPs on the degradation and adsorption of E1 by the prepared materials were investigated. The results showed that the immobilized HRP was less sensitive to the changes in pH and temperature compared with free HRP. The immobilized HRP also exhibited relatively high stability and reusability. HRP-PAA/PVA/SiO2 nanofibrous membranes with Fe3O4 NPs (HRP-Fe3O4 NPs/NFM) showed a significantly higher relative activity for E1 removal (84.5%) than the nanofibrous membranes without Fe3O4 NPs (79.4% P < 0.05). This improvement can be attributed to the addition of Fe3O4 NPs which increased the adsorption ability of the membranes and improved the catalytic activity of the immobilized HRP. The HRP-Fe3O4 NPs/NFM is suitable for use in wastewater treatment owing to its high reusability.

Preparation of mesoporous silica nanosheets through electrospinning: a novel scroll mechanism

Mesoporous silica nanosheets with high surface area and large pore volume have been produced by a combined process of sol–gel/electrospinning/calcination. The polymer–silica nanofibers were obtained through electrospinning, yet they converted into nanosheets after calcination with the template effect of the dendrimer polyamidoamine. A novel scroll mechanism is proposed to explain this conversion.