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The proteolytic enzyme α-chymotrypsin selectively cleaves the amorphous regions of silk fibroin protein (SFP) and allows the crystalline regions to self-assemble into silk microgels (SMGs) at physiological temperature. These microgels consist of lamellar crystals in the micrometer scale, in contrast to the nanometer-scaled crystals in native silkworm fibers. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and zeta potential results demonstrated that α-chymotrypsin utilized only the non-amorphous domains or segments of the heavy chain of SFP to form negatively charged SMGs. The SMGs were characterized in terms of size, charge, structure, morphology, crystallinity, swelling kinetics, water content and thermal properties. The results suggest that the present technique of preparing SMGs by α-chymotrypsin is simple and efficient, and that the prepared SMGs have useful features for studies related to biomaterial and pharmaceutical needs. This process is also an easy way to obtain the amorphous peptide chains for further study., (Copyright © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.)

In the last few years, the amount of industrial oily wastewater discharge and number of oil spill accidents have increased exponentially, spurring the development of highly efficient, cost-effective oil-water separation technologies. In this study, a dual pH- and ammonia-vapor-responsive polyimide (PI)-based nanofibrous membrane with high permeate flux and stability was developed for oil-water separations. The membrane was prepared by successively dip-coating electrospun PI in decanoic acid (DA)-TiO 2 and silica nanoparticles (SNPs). The novel SNP/DA-TiO 2 /PI membrane exhibits superhydrophobicity in air and superoleophilicity in neutral aqueous environments (e.g., at pH 6.5). However, the membrane becomes hydrophilic and superoleophobic in basic aqueous environments (e.g., at pH 12), resulting in only water permeation during oil-water separations. The oil-water separation potential of this innovative dual-responsive membrane was investigated using several model oil-water mixtures. The membrane has extremely high flux (6500±100 L m −2 h −1 ) and separation efficiency (>99%) and is reusable. In addition, thermal stability and abrasion resistance tests show that the membrane is highly stable under extreme conditions. This dual-responsive electrospun nanofibrous membrane has potential for use in industrial oil-polluted water and oil spill treatment and in systems that require selective oil-water permeation. Furthermore, changes in the surface wettability can also be induced by exposure to ammonia vapor, which might facilitate remote-controlled oil-water separations. [ABSTRACT FROM AUTHOR]

In modern society, traffic and transportation and the manufacturing industry and construction industries continuously release large amounts of dust and particles into the atmosphere, which can cause heavy air pollution, leading to health hazards. The haze disaster, a serious problem in developing countries such as China and India, has become one of the main issues of global environmental pollution in recent decades. Many air filtration technologies have been developed. Air filtration using electrospun fibers that intercept fine particles/volatile organic gases/bacterium is a relatively new, but highly promising, technique. Due to their interconnected nanoscale pore structures, highly specific surface areas, fine diameters, and porous structure as well as their ability to incorporate active chemistry on a nanoscale surface, electrospun fibers are becoming a promising versatile platform for air filtration. In this review, following a short introduction concerning the need for air filtration and filtration theory and mechanism, electrospun nanofibers membranes for air filtration have been highlighted, including the preparation (electrospinning process) and the parameters relevant to filtration efficacy. Additionally, various types (function) of the electrospun air filtration membranes have been classified in detail. Furthermore, their potential in the filtration of fine particles and chemical pollutants has been discussed. Finally, the challenges of their practical application and the future prospects have been summarized. Given that some advanced electrospun air filtration nanofibrous membranes exist for treating different contaminants from various types of polluted atmosphere, it is believed that they should make a significant contribution in protection against air pollution. [ABSTRACT FROM AUTHOR]

In recent years, efficient, cost effective oil-water separation technologies are highly desired due to frequent oil spill accidents. To design fibrous membranes for efficient oil-water separation, ‘flexible’ polyamide acid (PAA), being polyamide acid with ether linkages in the backbone, and ‘heavily’ fluorinated polybenzoxazine (F-PB) were synthesized. Cellulose acetate (CA) and PAA were co-axially electrospun; the PAA core was then imidizated at high temperature to obtain core/shell structured CA/polyimide (PI) electrospun fibrous membranes; subsequently the surface of the fibers was modified with F-PB, in the presence or in absence of silica nanoparticles (SNPs). The mechanical strength, surface wettability, chemical and thermal stability, and oil-water separation potential of thus obtained PI/CA fibrous membranes were evaluated. The membranes show a much higher critical tensile stress (130 MPa) and critical tensile strain (52%), when compared with CA fibrous membranes. Due to the use of the ‘heavily’ fluorinated polybenzoxazine, the membranes are superhydrophobic with a water contact angle of 162° and an oil contact angle which approaches 0°. Interestingly, the newly designed PI/CA/F-PB-1/SNP-4 membranes can effectively separate various oil-water mixtures, solely driven by gravity, with a high flux (3106.2 ± 100 L m −2 h −1 ) and a high separation efficiency (>99%) and thus possess great potential for oil–water separation. [ABSTRACT FROM AUTHOR]