Preparation and Characterization of Perfluorosulfonic Acid Nanofiber Membranes for Pervaporation-Assisted Esterification

Multilayer membranes were prepared by the combination of perfluorosulfonic acid/SiO₂ nanofibers and a poly­(vinyl alcohol) (PVA) pervaporation layer and were used to enhance the esterification of acetic acid (HAc) and ethanol (EtOH). The esterification–pervaporation experiments were carried out in a continuous membrane contactor. The effects of the temperature, the ratio of HAc to EtOH, and the ratio of membrane area to reaction volume were investigated. The results demonstrated that the membranes had good catalytic activities even at low temperature because of the nanofibrous structure of the catalysis layer. The conversion of HAc at 60 °C after 10 h was 10–15% more than the equilibrium conversion and by improved about 45% with respect to the equilibrium conversion after 55 h. The yield of EtAc was higher than 90%, which demonstrates that the difunctional membrane could enhance the esterification process greatly through the in situ removal of water

Theophylline Molecular Imprinted Composite Membranes Prepared on a Ceramic Hollow Fiber Substrate

Theophylline (THO) molecular imprinted composite membranes (MIM) were successfully prepared by thermal-initiated free radical polymerization on the surface of α-Al₂O₃ ceramic microporous hollow fiber substrate membranes. Molecular imprinted polymerization layer was synthesized by taking theophylline as the template molecule, methacrylic acid (MAA) as the functional monomer, ethylene glycol dimethacrylate (EDMA) as the cross-linker, and 2,2′-azobisisobutyronitrile (AIBN) as the free-radical initiator. After polymerization and the elution of the imprinted molecule, the <i>R</i>_max (the maximum pore size) upon the membrane surface decreased from 2.8 to 1.9 μm. The imprinted layer upon the ceramic membranes was investigated by scanning electron microscopy (SEM), atomic force microscope (AFM) and Fourier transform infrared spectroscopy (FTIR). SEM micrographs showed a 1 μm thick composite membrane, and AFM showed different surface roughness. Moreover, the selectivity separation factor of theophylline (THO) to theobromine (TB) was determined as 2.63 in a mixed feed solution, thus suggesting that the imprinting process allowed for preferential permeance and affinity selectivity to THO

Bacterial Light-Harvesting Complexes Showing Giant Second-Order Nonlinear Optical Response as Revealed by Hyper-Rayleigh Light Scattering

The second-order nonlinear optical (NLO) properties of light-harvesting complexes (LHs) from the purple photosynthetic bacteria Thermochromatium (Tch.) tepidum were investigated for the first time by means of hyper-Rayleigh scattering (HRS). The carotenoid (Car) molecules bound to the isolated LH1 and LH2 proteins gave rise to second-harmonic scattering; however, they showed an opposite effect of the collective contribution from Car, that is, the first hyperpolarizability (β) reduced substantially from (10 510 ± 370) × 10^–30 esu for LH1 to (360 ± 120) × 10^–30 esu for LH2. Chromatophores of Tch. tepidum also showed a giant hyperpolarizability of (11 640 ± 630) × 10^–30 esu. On the basis of the structural information on bacterial LHs, it is found that the effective β of an LH is governed by the microenvironment and orientational correlation among the Car chromophores, which is concluded to be coherently enhanced for LH1. For LH2, however, additional destructive effects between different Car molecules may account for the small β value. This work demonstrates that LH1 and native membranes of purple bacteria can be potent NLO materials and that HRS is a promising spectroscopic means for investigating structural information of pigment–protein supramolecules

Interfacial Polymerization with Electrosprayed Microdroplets: Toward Controllable and Ultrathin Polyamide Membranes

Commercial polyamide membranes for seawater desalination and water purification have low water permeability because of their relatively thick rejection layers. We report a novel interfacial polymerization method for synthesizing ultrathin polyamide layers with a precisely controllable thickness. Monomer solutions of <i>m</i>-phenylenediamine and trimesoyl chloride were electrosprayed into fine microdroplets. The polymerization reaction between microdroplets of different monomers leads to a fine and controllable amount of deposition. We fabricated smooth polyamide layers from 4 nm to several tens of nanometers in thickness, with a growth rate of approximately 1 nm/min. Our study provides a new dimension for the rational design and preparation of ultrathin polyamide membranes with tunable separation properties

Nanofoaming of Polyamide Desalination Membranes To Tune Permeability and Selectivity

Recent studies have documented the existence of discrete voids in the thin polyamide selective layer of composite reverse osmosis membranes. Here we present compelling evidence that these nanovoids are formed by nanosized gas bubbles generated during the interfacial polymerization process. Different strategies were used to enhance or eliminate these nanobubbles in the thin polyamide film layer to tune its morphology and separation properties. Nanobubbles can endow the membrane with a foamed structure within the polyamide rejection layer that is approximately 100 nm in thickness. Simple nanofoaming methods, such as bicarbonate addition and ultrasound application, can result in a remarkable improvement in both membrane water permeability and salt rejection, thus overcoming the long-standing permeability–selectivity trade-off of desalination membranes