2 research outputs found
Facile Synthesis of Titania Nanowires via a Hot Filament Method and Conductometric Measurement of Their Response to Hydrogen Sulfide Gas
Titania nanostructures are of increasing interest for
a variety of applications, including photovoltaics, water splitting,
and chemical sensing. Because of the photocatalytical properties of
TiO<sub>2</sub>, chemical processes that occur at its surface can
be exploited for highly efficient nanodevices. A facile and fast synthesis
route has been explored that is free of catalysts or templates. An
environmental scanning electron microscopy (ESEM) system was employed
to grow titania nanowires (NWs) in a water vapor atmosphere (∼1
mbar) and to monitor the growth in situ. In addition, the growth process
was also demonstrated using a simple vacuum chamber. In both processes,
a titanium filament was heated via the Joule effect and NWs were found
to grow on its surface, as a result of thermal oxidation processes.
A variety of nanostructures were observed across the filament, with
morphologies changing with the wire temperature from the center to
the end points. The longest NWs were obtained for temperatures between
∼730
°C and 810 °C. Typically, they have an approximate thickness
of ∼300 nm and lengths of up to a few micrometers. Cross sections
prepared by focused-ion-beam milling revealed the presence of a porous
layer beneath the NW clusters. This indicates that the growth of NWs
is driven by oxidation-induced stresses in the subsurface region of
the Ti filament and by enhanced diffusion along grain boundaries.
To demonstrate the potential of titania NWs grown via the hot filament
method, single NW devices were fabricated and used for conductometric
sensing of hydrogen sulfide (H<sub>2</sub>S) gas. The NW electric
resistance was found to decrease in the presence of H<sub>2</sub>S.
Its variation can be explained in terms of the surface depletion model
American Healthy Homes Survey: A National Study of Residential Pesticides Measured from Floor Wipes
The U.S. Department of Housing and Urban Development in collaboration with the United States Environmental Protection Agency conducted a survey measuring lead, allergens, and insecticides in a randomly selected nationally representative sample of residential homes. Multistage sampling with clustering was used to select the 1131 homes of which a subset of 500 randomly selected homes included the collection of hard surface floor wipes. Samples were collected by trained field technicians between June 2005 and March 2006 using isopropanol wetted wipes. Samples were analyzed for a suite of 24 compounds which included insecticides in the organochlorine, organophosphate, pyrethroid and phenylpyrazole classes, and the insecticide synergist piperonyl butoxide. The most commonly detected were permethrin (89%), chlorpyrifos (78%), chlordane (64%), piperonyl butoxide (52%), cypermethrin (46%), and fipronil (40%). Mean and geometric mean (GM) concentrations varied widely among compounds, but were highest for <i>trans</i>-permethrin (mean 2.22 ng/cm<sup>2</sup> and GM 0.14 ng/cm<sup>2</sup>) and cypermethrin (mean 2.9 ng/cm<sup>2</sup> and GM 0.03 ng/cm<sup>2</sup>). Results show that most floors in occupied homes in the U.S. have measurable levels of insecticides that may serve as sources of exposure to occupants