Band Gap Opening in the Cycloaddition Functionalization of Carbon Nanotubes.

Covalent functionalization represents a promising avenue to tailor the electronic properties of carbon nanotubes. Recent experimental work has shown that cycloaddition of fluorinated olefins represents an effective approach to reduce the off-currents of mixed nanotube mats for transistor applications. We have studied the electronic structure characteristics of the corresponding [2 + 2] cycloaddition using dispersion-corrected density functional calculations. The band gap opening in chemically functionalized tubes is associated with the sp2 to sp3 rehybridization. Our calculation reveals that the experimentally observed suppression of metallic conductivity can be attributed to a symmetry aligned cycloaddition scheme that effectively transforms metallic tubes to semiconducting ones.

Deposition kinetics of bacteriophage MS2 to natural organic matter: role of divalent cations.

The role of divalent cations (i.e. Ca(2+) and Mg(2+)) in the deposition kinetics of the bacteriophage MS2 onto flat bare silica surfaces and Suwannee River Natural Organic Matter (SRNOM)-coated silica surfaces was investigated using a Quartz Crystal Microbalance (QCM) coupled with a radial stagnation point flow (RSPF) system. Experimental results demonstrated that attachment efficiencies of MS2 onto the SRNOM surface were seven to seventeen times higher in the presence of Ca(2+) than in the presence of Mg(2+). A similar trend was observed for the adsorption of polyglutamic acid, which is one of the carboxylate-containing amino acid residues found on the surface of MS2 capsids present on SRNOM-coated surfaces. The difference in attachment rates in a solution containing either Ca(2+) or Mg(2+) can be explained by a stronger tendency of Ca(2+) compared to Mg(2+) to form cation bridges by binding to carboxylate groups of both the SRNOM and the MS2 capsids. Moreover, higher attachment efficiencies of MS2 onto the SRNOM-coated silica surfaces compared to those on bare silica surfaces in the presence of either Ca(2+) or Mg(2+) at concentrations higher than 0.3 mM emphasized the important role of SRNOM carboxylate groups. Experimental data also showed reduced attachment efficiency of MS2 to SRNOM-coated surfaces in solution containing 1 mg/L SRNOM.

Enhanced visible-light-induced photocatalytic disinfection of E. coli by carbon-sensitized nitrogen-doped titanium oxide.

Nitrogen-doped titanium oxide (TiON) nanoparticle photocatalysts were synthesized by a sol-gel process, for disinfection using E. coli as target bacteria. Our work shows thatthe calcination atmosphere has strong effects on the composition, structure, optical, and antimicrobial properties of TiON nanoparticles. Powders calcinated in a flow of N2 atmosphere (C-TiON) contain free carbon residue and demonstrate different structures and properties compared to the TiON powders calcinated in air. Disinfection experiments on Escherichia coli indicate that C-TiON composite photocatalyst has a much better photocatalytic activity than pure TiON photocatalyst under visible light illumination. The enhanced photocatalytic activity is related to stronger visible light absorption of the carbon-sensitized TiON.

Efficacy of oligodynamic metals in the control of bacteria growth in humidifier water tanks and mist droplets.

Antimicrobial capsules were evaluated for their effectiveness to control bacterial contamination of cool mist humidifiers. These capsules contain a mixture of silver and copper promoted alumina beads designed to release low concentrations of these oligodynamic metals into the reservoir water for bacteria control. The reservoir water and mist droplets from the humidifier units were tested for the presence of bacteria over a three-week period. A control unit (without capsule) showed significant bacterial contamination by day three, which increased throughout the three-week test period, in both the reservoir and mist droplets, whereas the antimicrobial capsules reduced contamination during the first week, and minimized the presence of bacteria, in both the reservoir water and mist droplets, to less than 2% of the control unit throughout the three-week test period. It was also observed that, after each inactive weekend, the initial discharge of bacteria via the mist droplets in the control unit was significantly higher than during daily use. However, initial bacterial discharge from the test unit following weekend inactivity never exceeded 0.5% of the control unit. In conclusion, these capsules containing oligodynamic metals are effective in controlling bacteria growth in humidifier water tanks and mist droplets.