Nanofiber Adsorbent Research Articles

Adsorption of thorium(IV) from simulated radioactive solutions using a novel electrospun PVA/TiO2/ZnO nanofiber adsorbent functionalized with mercapto groups: Study in single and multi-component systems

The novel polyvinyl alcohol/titanium oxide/zinc oxide (PVA/TiO2/ZnO) nanofiber adsorbent functionalized with 3-mercaptopropyltrimethoxysilane (TMPTMS) was prepared by electrospinning method and its potential was investigated for the adsorption of thorium from single and multi-metal aqueous solutions. The prepared adsorbent was characterized by FTIR, SEM and BET analysis. The influences of different operational parameters such as pH, ionic strength, equilibrium time, initial concentration and temperature were studied in batch mode. Investigation of ionic strength effect showed that the addition of NaNO3 to metal solution has a slight effect on the thorium adsorption, whereas pH value has a serious effect on the thorium adsorption at pH values lower than 4. The double-exponential model described the adsorption of Th(IV) ions much better than other kinetic models within both the single and multi-component systems. Among various isotherm models used, the equilibrium data of Th(IV) conformed the Langmuir isotherm in the single system, while those were best fitted by Dubinin–Radushkevich (D-R) isotherm in multi-component system. Thermodynamic parameters such as ΔH°, ΔS°, and ΔG° indicated that the nature of adsorption process was spontaneous, endothermic and thermodynamically favored. The inhibitory effect of other metal ions on the adsorption capacity of Th(IV) was in order of Al(III)>Cu(II)>Cd(II)>Ni(II)>U(VI)>Fe(II).

Water-insoluble sericin/β-cyclodextrin/PVA composite electrospun nanofibers as effective adsorbents towards methylene blue

A novel water-insoluble sericin/β-cyclodextrin/poly (vinyl alcohol) composite nanofiber adsorbent was prepared by electrospinning and followed by thermal crosslinking for removal of cationic dye methylene blue from aqueous solution. Fourier transform infrared spectroscopy and solubility experiments confirmed that sericin and β-cyclodextrin were incorporated into the nanofibers and the crosslinking reaction occurred successfully. Kinetics, isotherms and thermodynamics analysis were studied for adsorption of methylene blue. The adsorption process is better fitted with the pseudo-second-order model and Langmuir isotherm model. The maximum adsorption capacities are 187.97, 229.89, and 261.10mg/g at the temperatures 293, 313 and 333K, respectively. Thermodynamic parameters showed that methylene blue adsorption was endothermic and spontaneous. In addition, the fiber membrane adsorbent could be easily separated from dye solution and showed high recyclable removal efficiency. All these results suggest that crosslinked sericin/β-cyclodextrin/poly(vinyl alcohol) composite nanofibers could be potential recyclable adsorbents in dye wastewater treatment.

Phosphine-functionalized electrospun poly(vinyl alcohol)/silica nanofibers as highly effective adsorbent for removal of aqueous manganese and nickel ions

Abstract Phosphine-functionalized PVA/SiO2 (pgf-PVA/SiO2) composite nanofiber adsorbent (porous) was prepared using a facile electrospinning technique. The successful fabrication of the pgf-PVA/SiO2 nanofibers was confirmed by field emission-scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) analyses. The nanofiber adsorbent was evaluated for water sensitivity, N2 adsorption–desorption isotherms, pore size distribution, and manganese (Mn+2) and nickel (Ni+2) ions removal from aqueous solution at various pH, contact times, and adsorbent dosages as well as at different regeneration/reuse cycles. The composite pgf-PVA/SiO2 nanofibers (with 0.5 g/L fiber loading) can remove almost completely (96–98%) the aforementioned ions from aqueous solutions (initial concentration of 120 mg/L, pH 6) within 15 min of contact time. A reasonably simple acid treatment (with a 1 M HCl solution) was found to be extremely effective in regenerating the nanofiber adsorbent, and 92.5% of the metal ions were removed from the adsorbent even in the fifth regeneration/reuse cycle. Additionally, the adsorption equilibrium studies revealed the excellent adsorption capacities of the pgf-PVA/SiO2 nanofiber for both Mn+2 and Ni+2 ions (234.7 and 229.9 mg/g, respectively).

Nanofiber adsorbents for high productivity continuous downstream processing

An ever increasing focus is being placed on the manufacturing costs of biotherapeutics. The drive towards continuous processing offers one opportunity to address these costs through the advantages it offers. Continuous operation presents opportunities for real-time process monitoring and automated control with potential benefits including predictable product specification, reduced labour costs, and integration with other continuous processes. Specifically to chromatographic operations continuous processing presents an opportunity to use expensive media more efficiently while reducing their size and therefore cost. Here for the first time we show how a new adsorbent material (cellulosic nanofibers) having advantageous convective mass transfer properties can be combined with a high frequency simulated moving bed (SMB) design to provide superior productivity in a simple bioseparation. Electrospun polymeric nanofiber adsorbents offer an alternative ligand support surface for bioseparations. Their non-woven fiber structure with diameters in the sub-micron range creates a remarkably high surface area material that allows for rapid convective flow operations. A proof of concept study demonstrated the performance of an anion exchange nanofiber adsorbent based on criteria including flow and mass transfer properties, binding capacity, reproducibility and life-cycle performance. Binding capacities of the DEAE adsorbents were demonstrated to be 10mg/mL, this is indeed only a fraction of what is achievable from porous bead resins but in combination with a very high flowrate, the productivity of the nanofiber system is shown to be significant. Suitable packing into a flow distribution device has allowed for reproducible bind-elute operations at flowrates of 2,400cm/h, many times greater than those used in typical beaded systems. These characteristics make them ideal candidates for operation in continuous chromatography systems. A SMB system was developed and optimised to demonstrate the productivity of nanofiber adsorbents through rapid bind-elute cycle times of 7s which resulted in a 15-fold increase in productivity compared with packed bed resins. Reproducible performance of BSA purification was demonstrated using a 2-component protein solution of BSA and cytochrome c. The SMB system exploits the advantageous convective mass transfer properties of nanofiber adsorbents to provide productivities much greater than those achievable with conventional chromatography media.

Preparation and characterization of a novel electrospun ammonium molybdophosphate/polyacrylonitrile nanofiber adsorbent for cesium removal

Adsorption of Cs+ ion from aqueous solution onto a novel electrospun ammonium molybdophosphate/polyacrylonitrile nanofiber adsorbent with variation in AMP content, adsorbent concentration, pH, contact time, initial concentration and temperature was studied. The physicochemical characterization was performed by FTIR, XRD, BET and SEM analyses. Langmuir, Freundlich and Dubinin–Radushkevich models were used for analysis of equilibrium data. Kinetic results showed that the experimental data best fitted the pseudo-second-order kinetic model. The adsorption affinity of metal ions onto adsorbent was in order of Cs+ > Co2+ > Mg2+ > Ca2+ > Sr2+. The adsorbent could be easily regenerated after five cycles of adsorption–desorption.

Adsorption of Pb(II) and Cu(II) ions from aqueous solution by an electrospun CeO2 nanofiber adsorbent functionalized with mercapto groups

A novel PVP/CeO2/TMPTMS nanofiber adsorbent was prepared by the electrospinning method. The prepared nanofibers were characterized by scanning electron microscope (SEM), Brunauer–Emmert–Teller (BET), Fourier transform infrared (FTIR) and Brrett–Joyner–Halenda (BJH) analysis. The results showed that surface area of PVP/CeO2/TMPTMS/P123 is almost five times greater than PVP/CeO2/TMPTMS nanofiber adsorbent. Batch experiments were carried out as a function of solution pH, contact time, initial concentration and temperature. The kinetic data of Pb(II) and Cu(II) ions were well described by the double-exponential model. The maximum adsorption capacities of PVP/CeO2/TMPTMS nanofiber by applying the Langmuir equation were found to be 0.439mmol/g (90.9mg/g) for Pb(II) and 1.390mmol/g (88.3mg/g) for Cu(II) ions. qm of PVP/CeO2/TMPTMS/P123 nanofiber was found to be 1.315mmol/g (272.3mg/g) for Pb(II) and 4.145mmol/g (263.4mg/g) for Cu(II) ions. Thermodynamic studies showed that adsorption process was favored at higher temperature. The adsorbent can be easily regenerated with desorbing agent of 0.1M HNO3. The inhibitory effect of competitive Cu(II) ion on the Pb(II) adsorption was greater than the inhibitory effect of competitive Pb(II) ion on the Cu(II) adsorption in the binary systems and the adsorption affinity of the tested metals is Cu(II)>Pb(II).

A novel electrospun PVA/ZnO nanofiber adsorbent for U(VI), Cu(II) and Ni(II) removal from aqueous solution

A novel electrospun polyvinyl alcohol (PVA)/zinc oxide (ZnO) nanofiber adsorbent was prepared and its application for sorption of U(VI), Cu(II) and Ni(II) ions from aqueous solutions was investigated. The adsorbent was characterized by Fourier Transform Infrared spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Brunauer–Emmett–Teller (BET) and Thermal gravimetric (TG) analyses. The influence of several variables such as ZnO contents, contact time, initial concentration of ions and temperature was studied in batch experiments. The equilibrium data showed that the capacity values of 370.86, 162.48 and 94.43mg/g for sorption of U(VI), Cu(II) and Ni(II) ions, respectively, were obtained at contact time 6h, temperature 45°C, adsorbent concentration 1g/L and pH 5.0. The kinetic data were described with pseudo-first-order, pseudo-second-order and double-exponential models and it was found that the kinetic data were perfectly fitted double-exponential kinetic model. Three isotherm models, namely Langmuir, Freundlich and Dubinin–Radushkevich were used for analysis of equilibrium data. Thermodynamic parameters (ΔG°, ΔH° and ΔS°) were evaluated to understand the nature of sorption process for U(VI), Cu(II) and Ni(II) ions.

Selective sorption of U(VI) from aqueous solutions using a novel aminated Fe3O4@SiO2/PVA nanofiber adsorbent prepared by electrospinning method

A novel electrospun Fe3O4@SiO2@APTES/PVA nanofiber adsorbent for U(VI) sorption was synthesized and characterized by FTIR, SEM, BET and TG analyses. The effects of pH, nanoparticles content, adsorbent dose, contact time, initial U(VI) concentration, temperature and co-existing ions were studied in batch experiments. The sorption affinity of metal ions onto adsorbent was U(VI) > Cu(II) > Cd(II) > Pb(II) > Ni(II) > Th(IV). The kinetic and isotherm data were accurately described by the double-exponential and Langmuir model, with a maximum sorption capacity of 68.96 mg/g with a pH of 5. Thermodynamic parameters were evaluated to understand the nature of sorption process. The reusability of adsorbent was determined after five sorption–desorption cycles.

Recyclable composite nanofiber adsorbent for Li+ recovery from seawater desalination retentate

Composite poly(acrylonitrile) (PAN) nanofibers with H1.6Mn1.6O4 (HMO) lithium ion-sieves were prepared, characterized and tested for lithium ion (Li+) recovery. Nanofibers were prepared by electrospinning 10 wt% HMO/PAN dope solutions in dimethylformamide with varied HMO loadings. Characterizations performed via XRD, SEM-EDS, capillary flow porometry and mechanical testing revealed highly porous, mechanically and chemically stable composite nanofibers with high water absorption capacity. The similar nanofiber diameters (<300 nm) and HMO particle sizes (<100 nm) rendered PAN as a binder to have minimal hindrance to the HMOs. Exposure of HMOs on the fiber surface provided good accessibility to the Li+ source, as indicated by the minimal loss of Li+ adsorption capacity of HMOs in PAN as compared to the support-free powdered HMO. All tested adsorbents followed Langmuir-type Li+ adsorption (qm). Increased HMO loadings resulted in improved adsorption performance as more HMOs were exposed on fiber surface and became less affected by the binder; the highest qm = 10.3 mg/g obtained from 60 wt% HMO/PAN was only 4% lower than the support-free HMO. Adsorption loss after ten reuses was minor (<4%), which suggests the long-term stability of HMO/PAN. In seawater desalination retentate, HMO/PAN (60 wt%) preferentially adsorbed Li+ over other cations, achieving 99–5312 Li+ separation factors and high Li+ distribution coefficient (KD = 770). Li+ was concentrated up to 486 times while interfering cations were enriched only up to <7 times. Overall results demonstrate the potential use and recyclability of the developed HMO/PAN composite nanofiber for Li+ recovery from seawater or other prospective sources.

Adsorption of Th4+, U6+, Cd2+, and Ni2+ from aqueous solution by a novel modified polyacrylonitrile composite nanofiber adsorbent prepared by electrospinning

In this study, SiO2 nanoparticles were modified by 3-aminopropyltriethoxysilane (APTES) and then applied to prepare a novel polyacrylonitrile (PAN) composite nanofiber adsorbent by the electrospinning method. In addition, the adsorbent was characterized by SEM, BET, and FTIR analyses. Then the effects of pH, SiO2 and APTES content, adsorbent dosage, contact time and temperature were investigated. Moreover, adsorption experiments were carried out with initial concentrations in the range of 30–500mgL−1 and the adsorbent affinity for metal ions was in order of Th4+>U6+>Cd2+>Ni2+. Furthermore, it was observed that the optimum pH for adsorption was different for each metal. Some isotherm and kinetic models were applied to analyze the experimental data, among which the Langmuir and pseudo-second order models were better than the others. The regeneration study showed that the adsorbent could be used for industrial processes repeatedly without any significant reduction in its adsorption capacity. Based on the Langmuir model, the maximum adsorption capacity of Th4+, U6+, Cd2+, and Ni2+ at 45°C was 249.4, 193.1, 69.5 and 138.7mgg−1, respectively. Besides, the calculated thermodynamic parameters showed an endothermic as well as chemical nature through the adsorption process.

Efficient adsorption of gold ions from aqueous systems with thioamide-group chelating nanofiber membranes

We report on the efficient adsorption of gold ions from aqueous systems with thioamide-group chelating nanofiber membranes. The obtained membranes were prepared by a combination of chemical modification and electrospinning process. It was found that the maximum adsorption capacities of the chelating nanofibers toward Au(III) ions were 15.86mmol/g, 23.50mmol/g and 34.60mmol/g, when the temperature was 298, 323 and 348K, respectively. The nanofibers display a high adsorption efficiency for Au(III) ions. The Langmuir adsorption isotherm was applied to describe the adsorption processes. Kinetics of the Au(III) ions adsorption was found to follow pseudo-second-order rate equation. Furthermore, the as-prepared thioamide-group chelating nanofiber membranes, as well as Au(III) ions adsorbed nanofiber membranes, were carefully examined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). Based on the characterization results, a possible mechanism of Au(III) ions adsorption with the thioamide-group chelating nanofiber membranes was proposed. This study provides a promising nanofiber adsorbent with high and efficient adsorption property for heavy metal ions removal.

Preparation of lead-ion imprinted crosslinked electro-spun chitosan nanofiber mats and application in lead ions removal from aqueous solutions

Herein we report a novel and high efficient lead ion-imprinted adsorbent of chitosan nanofiber mats by electrospinning of chitosan solution with Pb(II) as template and glutaraldehyde as crosslinker. The structure of the resulting nanofiber mats was characterized by Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), X-ray Photoelectron Spectroscopy (XPS) and Thermal Gravimetric analysis (TGA). The equilibrium adsorption capacity for Pb(II) ions of such chitosan nanofiber adsorbents can arrive at 577mg/g, which is two or five times higher than that of the common chitosan-based adsorbents. The kinetic study demonstrates that the adsorption of Pb(II) ions follows a pseudo-second-order model. Besides, the comparative adsorptions of Pb(II), Cu(II), Cd(II), Ni(II) and Zn(II) ions were also studied, which show the equilibrium adsorption capacity in the order of Pb(II)>Cu(II)>Cd(II)>Ni(II)>Zn(II). The nanofiber adsorbents can be regenerated under EDTA and still has equilibrium adsorption capacity of 359mg/g for the second Pb(II) ion adsorption.

Preparation of a novel electrospun polyvinyl alcohol/titanium oxide nanofiber adsorbent modified with mercapto groups for uranium(VI) and thorium(IV) removal from aqueous solution

A novel polyvinyl alcohol (PVA)/titanium oxide (TiO2) nanofiber adsorbent modified with mercapto groups was synthesized by electrospinning. The adsorbent was characterized by Scanning Electron Microscopy (SEM), Fourier Transform Infrared (FTIR) and Brunauer–Emmett–Teller (BET) analysis. The influence of several variables such as TiO2 and mercapto contents, adsorbent dose, pH, contact time, initial concentration of U(VI) and Th(IV) ions and temperature were studied in batch experiments. The results showed that the sorption capacities of both metal ions for the modified PVA/TiO2 nanofibers were remarkably greater than those of the unmodified nanofibers. The kinetic data were described with pseudo-first-order, pseudo-second-order and double-exponential models. Three isotherm models, namely Freundlich, Langmuir and Dubinin–Radushkevich were used for analysis of equilibrium data. The maximum sorption capacities of U(VI) and Th(IV) by Langmuir isotherm are estimated to be 196.1 and 238.1 (mg/g) at 45°C with pH of 4.5 and 5.0, respectively. Calculation of ΔG°, ΔH° and ΔS° showed that the nature of both metal ions sorption onto the nanofiber was endothermic and spontaneous and was favored at higher temperature. The sorption capacity did not change remarkably after five cycles of sorption–desorption. The selectivity order of uranium and thorium sorption onto the adsorbent was Th(IV)>U(VI). The inhibitory effect of competitive Th(IV) ion on the U(VI) sorption was greater than the inhibitory effect of competitive U(VI) ion on the Th(IV) sorption in the binary systems. Also the inhibitory effect was increased with increase of concentration of metal ions.

Nanofiber adsorbents for high productivity downstream processing

Electrospun polymeric nanofiber adsorbents offer an alternative ligand support surface for bioseparations. Their non-woven fiber structure with diameters in the sub-micron range creates a remarkably high surface area. To improve the purification productivity of biological molecules by chromatography, cellulose nanofiber adsorbents were fabricated and assembled into a cartridge and filter holder format with a volume of 0.15 mL, a bed height of 0.3 mm and diameter of 25 mm. The present study investigated the performance of diethylaminoethyl (DEAE) derivatized regenerated cellulose nanofiber adsorbents based on criteria including mass transfer and flow properties, binding capacity, and fouling effects. Our results show that nanofibers offer higher flow and mass transfer properties. The non-optimized DEAE-nanofiber adsorbents indicate a binding capacity of 10% that of packed bed systems with BSA as a single component system. However, they operate reproducibly at flowrates of a hundred times that of packed beds, resulting in a potential productivity increase of 10-fold. Lifetime studies showed that this novel adsorbent material operated reproducibly with complex feed material (centrifuged and 0.45 µm filtered yeast homogenate) and harsh cleaning-in-place conditions over multiple cycles. DEAE nanofibers showed superior operating performance in permeability and fouling over conventional adsorbents indicating their potential for bioseparation applications.

PAN-based carbon nanofiber absorbents prepared using electrospinning

This study takes polyacrylonitrile (PAN) as a raw material for PAN-based nanofiber nonwoven prepared using electrospinning. First we construct a thermal-stable process for the fabrication of oxidized nanofiber nonwovens as the precursor. A semi-open high-temperature erect furnace is then used with steam as the activator, through carbonization and activation processes to prepare carbon nanofiber absorbents continuously. The experiment varies the production rate and activator flow rate to prepare carbon nanofiber absorbents. Experimental results show that carbon nanofiber adsorbents are primarily made up of micropores and mesopores, averaging under 20 A. Given a production rate of 10–20 cm/min with a matching activator feed rate of 120 ml/min, the specific surface area can reach about 1000 m2/g, producing an adsorption ratio of carbon tetrachloride over 200 %.