E. Terrado

SWCNTs AS ELECTRON WITHDRAWERS IN NANOCRYSTALLINE ANATASE PHOTOCATALYSTS

Single-walled carbon nanotube (SWCNT)/anatase TiO2 composite materials were prepared by successive sol–gel and hydrothermal processes. The composites contained thin SWCNT bundles embedded in aggregates of ~ 12 nm anatase crystallites. A series of SWCNT/TiO2 photocatalysts was prepared with various SWCNT contents; a SWCNT content of ~ 8 wt.% was found to be optimal for methylene blue (MB) degradation under combined UV/visible radiation. The optimized SWCNT/TiO2 composite demonstrated substantially higher photocatalytic activity than pure nanocrystalline anatase (5.2 times) and Degussa P-25 TiO2 powder (2.7 times). The MB degradation and mineralization processes were separately evaluated and complete decomposition of MB was shown to take place. The presence of SWCNTs caused an increase in the visible light absorbance of TiO2; however, SWCNT/TiO2 composites did not show any photocatalytic activity when the UV part of the UV/visible light source was filtered. Therefore SWCNTs worked as acceptors for the TiO2 photoexcited electrons, but did not act as sensitizers for TiO2.

Carbon nanotube-based SAW sensors

Surface acoustic wave (SAW) gas sensors based on the use of carbon nanotube (CNT) networks as sensitive layers have been investigated for the detection of atmospheric gas pollutants: volatile organic compounds (VOCs), NO2, CO, and H2 . SAW sensor configuration consists of a delay line made on a piezoelectric substrate (ST -X cut quartz) and a sensitive layer (CNTs) deposited between the interdigital transducers (IDTs). CNT networks were fabricated by airbrushing single-walled-(SWCNTs) and double-walled- (DWCNTs) CNT dispersions onto quartz substrates. Among all the tested CNT materials and gases, only DWCNT -based SAW sensors were sensitive upon exposure to low concentration of octane and toluene, providing fast response and recovery times to these VOCs.

Novel gas sensors based on carbon nanotube networks

Novel resistive gas sensors based on single-walled carbon nanotube (SWNT) networks as the active sensing element nave been investigated for gas detection. SWNTs networks were fabricated by airbrushing on alumina substrates. As-produced- and Pd-decorated SWNT materials were used as sensitive layers for the detection of NO2 and H2, respectively. The studied sensors provided good response to NO2 and H2 as well as excellent selectivities to interfering gases.

NO2 detection with Single Walled Carbon Nanotube Networks

Single-walled carbon nanotube (SWNT) networks were tested as gas sensors for nitrogen dioxide detection. Sensor films were fabricated by airbrushing SWNT dispersions on alumina substrates. Sensors were characterized by resistance measurements from 25 to 200degC. The best response to NO2 was obtained at 200degC. The tested SWNT sensors were sensitive to low NO2 concentrations in nitrogen and air atmospheres. Moreover, these sensors provided no response to interfering gases such as H2, NH3, toluene and octane. The effect of thermal treatments on the sensor response was also investigated.

Multi-Walled Carbon Nanotube Networks As Gas Sensors for NO2 Detection

Multi-walled carbon nanotube (MWNT) networks were investigated as resistive gas sensors for nitrogen dioxide detection. Sensor films were fabricated by airbrushing MWNT dispersions on alumina substrates. Sensors were characterized by resistance measurements from 25 to 250degC in air atmosphere, in order to find the optimum detection temperature. The best response to NO2 was obtained at 25degC. The tested MWNT sensors were sensitive to low NO2 concentrations in air atmosphere. Moreover, these sensors provided no response to interfering gases such as H2, NH3, toluene and octane. Thermal treatments, based in repeated heating and cooling of the films, increased the sensor response to NO2.