Nanostructured Pt functionalized multiwalled carbon nanotubes (MWNTs) produced by catalytic chemical vapor deposition are good room-temperature hydrogen sensors. MWNTs have been synthesized by catalytic chemical vapor deposition of acetylene using a fixed-bed catalytic reactor over hydrides of Mm(0.2)Tb(0.8)CO2 obtained through hydrogen decrepitation technique. Purified and chemically treated MWNTs have been functionalized by Pt resulting in nanostructured dispersion of Pt on CNTs. Structural, morphological, and vibrational characterizations have been carried out using XRD, SEM, TEM, HRTEM, Raman spectroscopy, and FTIR spectroscopy, respectively. Dispersion of Pt on MWNTs was confirmed by elemental analysis using EDX. Systematic investigations of hydrogen sensing properties of Pt-MWNT ensembles have been carried out. The Pt-MWNTs thin films are stable after several cycles of adsorption and desorption. The change in electrical resistance due to hydrogen adsorption is reversible, with increases to saturation on exposure to hydrogen gas. The result demonstrates that the Pt-MWNTs are p-type semiconductor materials, and chemically treated MWNTs functionalized with Pt show the better hydrogen sensing response at room temperature.

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We have systematically investigated hydrogen sensing properties of pulsed laser deposited palladium thin films with reference to their crystallinity, surface morphology and film thickness. Thin films were deposited on clean quartz substrates at varying growth parameters. Structural and surface morphological characterizations have been carried out using X-ray diffraction, scanning electron microscopy and atomic force microscopy. Thin films with nanostructured surface morphology were achieved. Electrical resistance measurements, carried out in situ, by a two-probe technique in a chamber with a provision to introduce a known concentration of hydrogen gas and air, showed saturation on exposure to hydrogen gas. The change in electrical resistance due to hydrogen loading is found to be reversible. The sensor response time is typically 10–20 s. The Pd films are stable after several cycles of hydrogenation and dehydrogenation.

This study uses spatiotemporal patterns in ambient concentrations to infer the contribution of regional versus local sources. We collected 12 months of monitoring data for outdoor fine particulate matter (PM2.5) in rural southern India. Rural India includes more than one-tenth of the global population and annually accounts for around half a million air pollution deaths, yet little is known about the relative contribution of local sources to outdoor air pollution. We measured 1-min averaged outdoor PM2.5 concentrations during June 2015–May 2016 in three villages, which varied in population size, socioeconomic status, and type and usage of domestic fuel. The daily geometric-mean PM2.5 concentration was ∼30 μg m−3 (geometric standard deviation: ∼1.5). Concentrations exceeded the Indian National Ambient Air Quality standards (60 μg m−3) during 2–5% of observation days. Average concentrations were ∼25 μg m−3 higher during winter than during monsoon and ∼8 μg m−3 higher during morning hours than the diurnal average. A moving average subtraction method based on 1-min average PM2.5 concentrations indicated that local contributions (e.g., nearby biomass combustion, brick kilns) were greater in the most populated village, and that overall the majority of ambient PM2.5 in our study was regional, implying that local air pollution control strategies alone may have limited influence on local ambient concentrations. We compared the relatively new moving average subtraction method against a more established approach. Both methods broadly agree on the relative contribution of local sources across the three sites. The moving average subtraction method has broad applicability across locations.