Libao An

Highly efficient chromium(VI) adsorption with nanofibrous filter paper prepared through electrospinning chitosan/polymethylmethacrylate composite.

Chitosan/polymethylmethacrylate (PMMA) composite nanofibrous membrane was prepared by electrospinning technique with a single solvent system. Characterization with Fourier transformation infrared spectroscopy (FT-IR) indicated that there was weak interaction (such as hydrogen bonds) between PMMA and chitosan. Scanning electron microscopy (SEM) measurements illustrated that the average diameter of the composite nanofibers decreased as the chitosan content was increased, while the number of nano/micrometer sized beads increased in the membrane. The composite nanofibrous membrane with chitosan:PMMA ratio of 0.3:1.0 exhibited a maximum adsorption capacity (67.0 mg g(-1)) of Cr(VI) in static adsorption, which was nearly three times higher than that of chitosan powder (22.9 mg g(-1)). The adsorption capacity of Cr(VI) via filtration became even higher, where the maximum value was 92.5 mg g(-1) at pH 3.0. Notably, most of Cr(VI) has been removed after the first filtration at all pH values (2.0-6.0) investigated in this report. The adsorption capacity of the composite nanofibrous membrane decreased slightly (17.1%) after three filtration cycles even with the solution of pH 2.0, which shall be attributed to the enhanced mechanical strength and acid fastness of the composite membrane. X-ray photoelectron spectroscopy (XPS) analysis indicated that amino groups played an important role in the adsorption of Cr(VI).

Electrospun H4SiW12O40/cellulose acetate composite nanofibrous membrane for photocatalytic degradation of tetracycline and methyl orange with different mechanism

H4SiW12O40 (SiW12)/cellulose acetate (CA) composite nanofibrous membrane was prepared by electrospinning in which CA was employed as the support of SiW12. Characterization with Fourier transformation infrared spectroscopy (FT-IR), Energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) indicated that SiW12 has been successfully loaded into the CA membrane and its Keggin structure remained intact. The as-prepared composite membrane exhibited enhanced photocatalytic activity in the decomposition of tetracycline (TC) and methyl orange (MO) compared with pure SiW12 under ultraviolet irradiation. The optimal mass ratio of SiW12 to CA was 1:4, and the corresponding degradation efficiency for TC and MO was 63.8% and 94.6%, respectively. It is noteworthy that the degradation rate of MO increased more evidently than that of TC under the same conditions, which may be attributed to the different role that CA nanofibrous membrane played in the TC and MO photodegradation process. Besides providing more contact area between SiW12 and the pollutant in TC photodegradation, CA membrane played an additional role that donated electron to SiW12 in the MO degradation process, leading to a different photocatalytic mechanism with greatly enhanced degradation rate. Moreover, the composite membrane presented an excellent reusability, which was mainly ascribed to the water-insolubility of CA and the hydrogen bonds between CA and SiW12. This work will be useful for the design of biopolymer-based membrane photocatalysts applied to antibiotics and dyes wastewater treatment.

Electrospinning preparation of a H4SiW12O40/polycaprolactam composite nanofibrous membrane and its greatly enhanced photocatalytic activity and mechanism

H4SiW12O40/polycaprolactam (PA6) composite nanofibrous membranes with a minimum average diameter of ∼70 nm were prepared by an electrospinning technique. Characterization with Fourier transform infrared spectroscopy (FT-IR), energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) indicated that H4SiW12O40 has been successfully loaded into the PA6 membrane and its Keggin structure was intact. The as-prepared H4SiW12O40/PA6 membranes exhibited greatly enhanced photocatalytic efficiency (≥96.0%) and excellent reusability in the degradation of methyl orange (MO) under ultraviolet irradiation, which may be attributed to the synergistic effect of PA6 and H4SiW12O40. The photocatalytic process was likely to be driven by the reductive pathway with a much faster degradation rate due to the electron donation from PA6 to H4SiW12O40. The hydrogen bonds between H4SiW12O40 and PA6 could enhance the stability of H4SiW12O40 in the membrane, so that there was nearly no loss of photocatalytic activity of the catalyst after three cycles of reactions. In view of this, H4SiW12O40/PA6 composite nanofibrous membranes exhibit potential for practical applications to eliminate organic pollutants from wastewater.

Electrospun H4SiW12O40/chitosan/polycaprolactam sandwich nanofibrous membrane with excellent dual-function: adsorption and photocatalysis

For comprehensive treatment of wastewater, an electrospun H4SiW12O40 (SiW12)/chitosan (CS)/polycaprolactam (PA6) sandwich nanofibrous membrane (SNM) with dual-functions of adsorption and photocatalysis was prepared to remove Cr(VI) and methyl orange (MO) from aqueous solution. The three layers of the SNM had good compatibility and thus no visible stratification phenomenon was observed in the SNM. Taking advantage of the merits of high porosity, good hydrophilicity, robust mechanical strength and superior water tolerance, the obtained SNM presented an excellent comprehensive performance with high adsorption capacity toward Cr(VI) (78.5 mg g−1), high photodegradation efficiency toward MO (96.7%) and good reusability. Based on the images of the SNM after Cr(VI) adsorption, the SiW12/PA6 layer (upper and bottom layer) was not affected in the adsorption process, which was consistent with our initial design. XPS analysis was carried out to investigate the mechanism of adsorption and photocatalysis. In the adsorption process, Cr(VI) was initially adsorbed on the CS/PA6 layer (intermediate layer), followed by the reduction of Cr(VI) to Cr(III) by the –NH2 of CS. The photocatalytic process was driven by the reductive pathway with faster degradation rate due to the electron donation from PA6 to SiW12. Although Cr(III) at the layer boundary was involved in the photocatalytic process, the photocatalytic activity of the SiW12/PA6 layer was almost not influenced. This work may provide a new and effective strategy to construct multifunctional nanofibrous membranes for the comprehensive treatment of wastewater.

Liquid crystallinity of carbon nanotubes

In this review, we first briefly recapitulate the orientation characteristics of liquid crystalline carbon nanotubes (CNTs), emphasizing their inherent properties. Both the high Youngs modulus and the strong attractive interaction between them make the liquid crystallinity apt to show splay deformations (splay defects). It is these defects that often produce apparent low-order structures for long and deformed nanotubes. However, the application of doping, shearing, magnetic or electric fields will be efficient routes toward highly ordered CNT assemblies from such defects. Then, we describe the electrical behavior of CNTs in the electric field, which combines desirable features of the CNTS with those of classical liquid crystals (LCs). An electric field will generate an induced dipole moment on CNTs and align them in the field direction, minimizing the dipolar energy. Finally, we review the potential application of CNTs in the area of liquid crystal displays (LCD). In the LC cell unit, CNTs as dopants in LC layers can have compatible stability with LCs, with the orientation consistent and with surprising complementary advantages. And also CNT films as nanostructured electrodes can substitute ITO electrodes in the LC cell unit, exhibiting a strong electrical anisotropy due to their excellent axial conductivity. Furthermore, CNT films as an alignment layer have the potential to replace the traditional PI film, aligning LC molecules effectively along the direction of the nanotubes. Besides, CNTs acting as polarizers can absorb or transmit incident light when the electric vector propagates parallel or perpendicular to the nanotube axis. All of these applications demonstrate that CNTs in LC ordering will effectively improve the performance of materials and their related devices. Thus, we should improve the ordering of CNT assemblies as far as possible, which is critical to make full use of their exceptional axial properties and further to develop novel materials and applications successfully.