Chemical filtration of Cr (VI) with electrospun chitosan nanofiber membranes

Aggregation States and Segmental Dynamics of Poly(methyl methacrylate) in Nanofiber Mats

Nanofiber mats composed of polymers, having a large surface-to-volume ratio and high porosity, have been widely applied in the environmental and biomedical fields but fundamental knowledge on the polymer chains in the mats seems to be limited. We here report the aggregation states and segmental dynamics of poly(methyl methacrylate)s (PMMAs) with different stereoregularities in electrospun nanofiber mats. Attenuated total reflectance Fourier transform infrared (ATR/FTIR) spectroscopy revealed that, in the case of atactic PMMA (at-PMMA), the population of the trans-trans conformation of the main chain part, which allows carbonyl groups of the side group to interact affirmatively with each other, increased in the electrospun nanofiber mat. On the other hand, in the case of isotactic PMMA (it-PMMA), the skeletal conformation was unchanged even in the nanofiber mat. As a result of the aggregation states of PMMA chains, the glass-transition temperature (T_g) of the electrospun nanofiber mats increased and remained unchanged from the corresponding bulk value for at- and it-PMMA, respectively. These findings should be useful for designing materials and devices composed of electrospun nanofibers.

Boosted Cr(VI) sorption coupled reduction from aqueous solution using quaternized algal/alginate@PEI beads

APEI beads (algal/alginate-PEI) were quaternized for enhancing the sorption of Cr(VI) (Q-APEI). The readily reduction of Cr(VI) into Cr(III) in acidic solution and in the presence of organic material constitute an additional phenomenon to be taken into account for the removal of Cr(VI) by Q-APEI. The optimal pH value for both the sorption and reduction of Cr(VI) was close to 2. The sorption isotherm was well described by the Sips model in batch system; the experimental maximum Cr(VI) sorption capacity of Q-APEI was 334 mg Cr(VI) g^-1, including a reduction yield close to 25%. The pseudo-second-order kinetic model (PSORE) and the Yan model fit the uptake kinetics and breakthrough curves, in a fixed-bed system with circulation or single-path modes, respectively. The mechanism of reduction-assisted sorption allows boosting the global removal of chromate. Furthermore, the testing of Cr(VI) for three successive sorption and desorption cycles shows the remarkable stability of the sorbent for Cr(VI) removal. The Cr(VI) sorption coupled reduction mechanism and interactions between the sorbent and Cr(VI) were further explained using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS).

Chitin and chitosan on the nanoscale

In a matter of decades, nanomaterials from biomass, exemplified by nanocellulose, have rapidly transitioned from once being a subject of curiosity to an area of fervent research and development, now reaching the stages of commercialization and industrial relevance. Nanoscale chitin and chitosan, on the other hand, have only recently begun to raise interest. Attractive features such as excellent biocompatibility, antibacterial activity, immunogenicity, as well as the tuneable handles of their acetylamide (chitin) or primary amino (chitosan) functionalities indeed display promise in areas such as biomedical devices, catalysis, therapeutics, and more. Herein, we review recent progress in the fabrication and development of these bio-nanomaterials, describe in detail their properties, and discuss the initial successes in their applications. Comparisons are made to the dominant nanocelluose to highlight some of the inherent advantages that nanochitin and nanochitosan may possess in similar application.

Green Electrospun Membranes Based on Chitosan/Amino-Functionalized Nanoclay Composite Fibers for Cationic Dye Removal: Synthesis and Kinetic Studies

Chitosan/poly(vinyl alcohol)/amino-functionalized montmorillonite nanocomposite electrospun membranes with enhanced adsorption capacity and thermomechanical properties were fabricated and utilized for the removal of a model cationic dye (Basic Blue 41). Effects of nanofiller concentrations (up to 3.0 wt %) on the morphology and size of the nanofibers as well as the porosity and thermomechanical properties of the nanocomposite membranes are studied. It is shown that the incorporation of the nanoclay particles with ∼10 nm lateral sizes into the polymer increases the size of the pores by about 80%. To demonstrate the efficiency of the adsorbents, the dye removal rate is investigated as a function of pH, adsorbent dosage, dye concentration, and nanofiller loading. The highest and fastest dye removal occurs for the nanofibrous membranes containing 2 wt % nanofiller, where about 80% of the cationic dye is removed after 15 min. This performance is at least 20% better than the pristine chitosan/poly(vinyl alcohol) membrane. The thermal stability and compression resistance of the nanocomposite membranes are found to be higher than those of the pristine membrane. In addition, reusability studies show that the dye removal performance of this nanocomposite membrane reduces by only about 5% over four cycles. The adsorption kinetics is explained by the Langmuir isotherm model and is expressed by a pseudo-second-order kinetic mechanism that determines a spontaneous chemisorption process. The results of this study provide a valuable perspective on the fabrication of high-performance, reusable, and efficient electrospun fibrous nanocomposite adsorbents.

Preparation and Performance Assessment of Low-Pressure Affinity Membranes Based on Functionalized, Electrospun Polyacrylates for Gold Nanoparticle Filtration

Electrospun nanofibrous membranes (ENM) possess many advantages over commonly utilized water purification systems. They provide high porosity with interconnected pores and a high surface to volume ratio, facilitating particle adsorption. Affinity separation moves into a promising future for application, for example, nanoparticle adsorption with excellent filtration efficiency, because of its highly specific adsorption mechanism. However, not all effects on filtration performance are entirely understood. In this paper, we investigate significant filtration parameters, such as pore size, mechanical stability, and hydrophilicity, and determine a sequence of importance for an optimal pressure drop. Copolymers with various hydrophilic functional groups such as acid, amide, pyridine, and quaternary amine were utilized. Effects on the pressure drop or nanoparticle filtration efficiency can then easily be attributed to the corresponding functional group. UV-light was used to induce cross-linking in the membranes, which subsequently surpassed the mechanical stability of commonly used hydrophobic membranes. A maximum tensile-stress of up to 11.6 MPa was obtained, whereby an optimization of at least 22% was achieved. Moreover, these cross-links reduce fiber swelling by a maximum of 26%. The membrane potential depends on the different functional groups and their incorporation number from 10 to 50 mol %. Successful gold nanoparticle (AuNP) filtration in flow mode was demonstrated and highlighted the outstanding membrane properties and selectivity. The Nplus membrane achieved 100% filtration efficiency over a duration of 6 min, surpassing the Pyr membrane's performance. This was attributed to the ionic interaction of the Nplus membrane, in contrast with the physical adsorption of the Pyr membrane.

A review of recent progress in polymeric electrospun nanofiber membranes in addressing safe water global issues

With rapid advancement in water filtration materials, several efforts have been made to fabricate electrospun nanofiber membranes (ENMs). ENMs play a crucial role in different areas of water treatment due to their several advantageous properties such as high specific surface area, high interconnected porosity, controllable thickness, mechanical robustness, and wettability. In the broad field of water purification, ENMs have shown tremendous potential in terms of permeability, rejection, energy efficiency, resistance to fouling, reusability and mechanical robustness as compared to the traditional phase inversion membranes. Upon various chemical and physical modifications of ENMs, they have exhibited great potential for emerging applications in environment, energy and health sectors. This review firstly presents an overview of the limiting factors influencing the morphology of electrospun nanofibers. Secondly, it presents recent advancements in electrospinning processes, which helps to not only overcome drawbacks associated with the conventional electrospinning but also to produce nanofibers of different morphology and orientation with an increased rate of production. Thirdly, it presents a brief discussion about the recent progress of the ENMs for removal of various pollutants from aqueous system through major areas of membrane separation. Finally, this review concludes with the challenges and future directions in this vast and fast growing area.

Electrospun cationic nanofiber membranes for adsorption and determination of Cr(vi) in aqueous solution: adsorption characteristics and discoloration mechanisms

In this study, a novel cationic nanofiber membrane with various functional groups, good structural stability, and high adsorption capacity of Cr(vi) is presented. This nanofiber membrane is prepared by electrospinning a mixed aqueous solution of a cationic polycondensate (CP) and polyvinyl alcohol (PVA). With the aid of PVA, CP can be smoothly electrospun without using any organic solvents, and the cross-linking between CP and PVA improves the stability of membrane in acidic solution. Chemical and morphology characterization reveals that the CP/PVA membrane is composed of interwoven nanofibers that contain numerous cationic groups. Due to its high cationicity and hydrophilicity, the CP/PVA membrane shows great affinity for HCr₂O₇⁻ and Cr₂O₇²⁻. Adsorption experiments indicate that the CP/PVA membrane can remove Cr(vi) from simulated wastewater rapidly and efficiently in both batch and continuous mode. Besides, the presence of most coexisting ions will not interfere with the adsorption. Due to the redox reaction between the CP/PVA membrane and adsorbed Cr(vi), the CP/PVA membrane exhibits distinct color change after Cr(vi) adsorption and the discoloration is highly dependent on the adsorption amount. Therefore, in addition to serving as a highly efficient adsorbent, the CP/PVA membrane is also expected to be a convenient and low-cost method for semi-quantitative determination of Cr(vi) in wastewater.

Cationic nanofiber membranes are prepared by electrospinning mixed aqueous solution of a cationic polycondensate (CP) and PVA. Apart from being a highly efficient Cr(vi) adsorbent, it can also serve as a convenient method for Cr(vi) determination.

Biological characteristics of dynamic expression of nerve regeneration related growth factors in dorsal root ganglia after peripheral nerve injury

The regenerative capacity of peripheral nerves is limited after nerve injury. A number of growth factors modulate many cellular behaviors, such as proliferation and migration, and may contribute to nerve repair and regeneration. Our previous study observed the dynamic changes of genes in L4-6 dorsal root ganglion after rat sciatic nerve crush using transcriptome sequencing. Our current study focused on upstream growth factors and found that a total of 19 upstream growth factors were dysregulated in dorsal root ganglions at 3, 9 hours, 1, 4, or 7 days after nerve crush, compared with the 0 hour control. Thirty-six rat models of sciatic nerve crush injury were prepared as described previously. Then, they were divided into six groups to measure the expression changes of representative genes at 0, 3, 9 hours, 1, 4 or 7 days post crush. Our current study measured the expression levels of representative upstream growth factors, including nerve growth factor, brain-derived neurotrophic factor, fibroblast growth factor 2 and amphiregulin genes, and explored critical signaling pathways and biological process through bioinformatic analysis. Our data revealed that many of these dysregulated upstream growth factors, including nerve growth factor, brain-derived neurotrophic factor, fibroblast growth factor 2 and amphiregulin, participated in tissue remodeling and axon growth-related biological processes Therefore, the experiment described the expression pattern of upstream growth factors in the dorsal root ganglia after peripheral nerve injury. Bioinformatic analysis revealed growth factors that may promote repair and regeneration of damaged peripheral nerves. All animal surgery procedures were performed in accordance with Institutional Animal Care Guidelines of Nantong University and ethically approved by the Administration Committee of Experimental Animals, China (approval No. 20170302-017) on March 2, 2017.

Preparation of keratin/PET nanofiber membrane and its high adsorption performance of Cr(VI)

In this study, we prepared wool keratin/PET composite nanofiber membrane to adsorb the Cr(VI) in acidic solution due to its strong adsorption ability. The adsorption ability of the composite membrane with different ratios of keratin to PET was investigated. The optimum adsorption ability can be obtained when the keratin concentration was 50% in the solution with a pH value of 3. With the higher content of keratin, the membrane possessed higher hydrophilicity, larger pore ratio, and larger extent amino protonation. The maximum adsorption ability of the composite membranes was 75.86 mg/g, while that of the pure PET nanofiber membrane was 27.27 mg/g. The FTIR and XPS analysis results demonstrated that both the disulfide bond of the keratin and the amino were involved in the adsorption process. The process was achieved by the electrostatic adsorption of the amino and the redox reaction of disulfide bond in cystine oxide. The removal property of the electrospun keratin/PET composite membrane was 75.86 mg/g.

Preparation, characterization and kinetics study of chitosan/PVA electrospun nanofiber membranes for the adsorption of dye from water

In this study, chitosan (CS) nanofibers with two different degrees of deacetylation (DDA) were first successfully fabricated from its solution in 1% aqueous acetic acid solution by mixing with poly(vinyl alcohol) (PVA) solution at a weight ratio of 50/50 via the electrospinning method. Then, the CS/PVA membranes were further modified by glutaraldehyde vapor. The prepared nanofibers were characterized by field electron scanning electron microscopy (FESEM), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA), the tensile test, the contact angle test, the weight loss test and the adsorption test for Congo red (CR). SEM analysis showed defect-free nanofibers and a uniform diameter distribution, with an average diameter of 100–125 nm. Subsequently, FTIR spectroscopy, XRD and TGA indicated that the modified CS/PVA membranes had a relatively higher thermal stability, because the thermal decomposition temperature of the unmodified CS/PVA membranes (~250°C) increased to a higher temperature (~ 300°C) for the modified CS/PVA. The nanofiber membranes after modification possessed better mechanical tensile properties. The membranes with lower DDA had a relatively higher tensile strength, which can withstand the maximum tensile strength of up to 6.36 MPa. Furthermore, the resulting membranes showed excellent hydrophilicity and kept their stability in distilled water, acidic, and basic media for 20 days. In the adsorption study, the maximum adsorption capacity of the membrane for CR was 358 mg/l in the optimum operating conditions of 25°C, pH = 6, 0.3 g membrane and 50 ml of 100 mg/l CR solutions. The resulting nanofibers membranes showed a better fitting to the Langmuir isotherm model and pseudo-second-order kinetic model.

Electrospun AOPAN/RC blend nanofiber membrane for efficient removal of heavy metal ions from water

In this study, an innovative nano-material was prepared, which was ultilized to removal of heavy metal ions from wastewater. Polyacrylonitrile/cellulose acetate (PAN/CA) composite nanofibrous membranes were generated by the electronspinning technique first, and then amidoxime ployarcylonitrile/regenerate cellulose (AOPAN/RC) composite nanofibrous membranes were prepared by combining hydrolysis and amidoximation modification. The modification of composite nanofibers (AOPAN/RC) were consequently used in heavy metal ions adsorption. The characterizations of various different nanofibers were analyzed using scanning electron microscopy, Fourier transform infrared spectroscopy, surface area and pore size distribution analyzer and energy dispersive X-ray spectroscopy. Meantime, the adsorption equilibrium studies were studied. In addition, the saturation adsorption amount of nanofibrous membranes (at 25°C) for Fe(III), Cu(II) and Cd(II) of 7.47, 4.26 and 1.13mmolg^-1, respectively. The effects of pH value of solution, adsorption time and ions concentration on adsorption capacity were also investigated. Furthermore, the composite nanofibrous membranes after five times consecutive adsorption and desorption tests, the desorption rate of the Fe(III), Cu(II) and Cd(II) mental ions maintained more than 80% of their first desorption rate, AOPAN/RC composite nanofibrous reflected excellent resuability.

BioArtificial polymers

Nowadays, the polymer science has impact in practically all life areas. Countless benefits coming from the usage of materials with high mechanical and chemical resistance, variety of functionalities and potentiality of modification drive to the development of new application fields. Novel approaches of combining these synthetic substances with biomolecules lead to obtain multifunctional hybrid conjugates which merge the bioactivity of natural component with outstanding properties of artificial polymer. Over the decades, an immense progress in bioartificial composites domain allowed to reach a high level of knowledge in terms of natural-like systems engineering, leading to diverse strategies of biomolecule immobilization. Together with different available options, including covalent and noncovalent attachment, come various challenges, related mainly with maintaining the biological activity of fixed molecules. Even though the amount of applications that achieve commercial status is still not substantial, and is expanding continuously in the disciplines like “smart materials,” biosensors, delivery systems, nanoreactors and many others. A huge number of remarkable developments reported in the literature present a potential of bioartificial conjugates as a fabrics with highly controllable structure and multiple functionalities, serving as a powerful nanotechnological tool. This novel approach brings closer biologists, chemists and engineers, who sharing their effort and complementing the knowledge can revolutionize the field of bioartificial polymer science.

Preparation of diethylenetriamine-modified magnetic chitosan nanoparticles for adsorption of rare-earth metal ions

The development of a sustainable method to conveniently separate rare-earth metal ions remains a challenge waiting for breakthrough in numerous of advanced technologies.