Using titanium dioxide (TiO 2 ) and its modified forms for the photocatalytic reduction of CO 2 reduction and production of hydrogen is a promising route for providing solutions to the world energy demand in the foreseeable future. Here, we report the synthesis of a series of efficient stable TiO 2 nanoparticles modified with multiwalled carbon nanotubes (CNTs) via a simple combined sonothermal method, followed by a hydrothermal treatment. In comparison to bare TiO 2 , the synthesized CNT−TiO 2 photocatalysts showed improved photocatalytic activities for CO 2 reduction under UVA as well as under visible light and water (H 2 O) splitting under visible light at ambient temperature and pressure. The 2.0CNT−TiO 2 has performed the best for methanol, hydrogen, and formic acid production from the reduction of CO 2 with yield rates of 2360.0, 3246.1, and 68.5 μmol g −1 h −1 under UVA, respectively. Its potential was further tested under visible light for methanol production, 1520.0 μmol g −1 h −1 . Also, the highest rate of hydrogen yield from water splitting was 69.41 μmol g −1 h −1 with 2.0CNT−TiO 2 under visible light at pH 2. The primary photocatalytic reactions of CNT−TiO 2 composites and their intimate structure were studied computationally. It was demonstrated that the binding of CNT to TiO 2 nanoparticles is preferable at (101) surfaces than at (001) facets. Interaction of CNT with TiO 2 results in common orbitals within the TiO 2 band gap that enables visible light excitation of the CNT−TiO 2 composites can lead to charge transfer between TiO 2 and CNT, whereas UV light excitation can result in charge transfer in any direction from CNT to TiO 2 and from TiO 2 to CNT. The latter process is operative in the presence of a sacrificial electron donor triethanolamine.
Two new surfactants, F 5 OM and F 5 DM, were designed as partially fluorinated analogs of ndodecyl-β-D-maltoside (DDM). The micellization properties and the morphologies of the aggregates formed by the two surfactants in water and phosphate buffer were evaluated by NMR spectroscopy, surface tension measurement (SFT), isothermal titration calorimetry (ITC), dynamic light scattering (DLS), small-angle X-ray scattering (SAXS), and analytical ultracentrifugation (AUC). As expected, the critical micellar concentration (CMC) was found to decrease with chain length of the fluorinated tail from 2.1-2.5 mM for F 5 OM to 0.3-0.5 mM for F 5 DM, and micellization was mainly entropy-driven at 25°C. Close to their respective CMC, the micelle sizes were similar for both surfactants i.e. 7 and 13 nm for F 5 OM and F 5 DM, respectively and both increased with concentration forming 4 nm diameter rods with maximum dimensions of 50 and 70 nm, respectively, at a surfactant concentration of ~30 mM. The surfactants were found to readily solubilize lipid vesicles and extract membrane proteins (MPs) directly from Escherichia coli membranes. They were found more efficient than the commercial fluorinated detergent F 6 H 2 OM over a broad range of concentrations (1-10 mM) and even better than DDM at low concentrations (1-5 mM). When transferred into the two new surfactants, the thermal stability of the proteins bacteriorhodopsin (bR) and FhuA were higher than in the presence of their solubilization detergents and similar to that in DDM; furthermore, bR was stable over several months. The membrane enzymes SpNOX and BmrA were not as active as in DDM micelles but similarly active as in F 6 OM. Together, these findings indicate both extracting and stabilizing properties of the new maltose-based fluorinated surfactants, making them promising tools in MPs applications.
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