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A miniaturized chemical sensor is here described for the analysis of environmental pollutants (VOC: volatile organic chemicals). It is used for remote detection of formaldehyde (FA) fumes in the atmosphere, and is based on the redox reaction between FA and silver nitrate. The sensor is worn as a bracelet and the data acquired are transferred via a Bluetooth channel to a smartphone. A dedicated software transforms the signal from a grey to a color scale. The signal response has been assessed over low (20 to 120 ppb) as well as higher (1-15 ppm range) levels. The sensor has been applied to monitor potential FA fumes of some artwork in the Summer Palace in Beijing and the modifications induced by FA treatment on a precious Stradivarius violin. The performance of this novel sensor is compared with a commercial apparatus widely adopted, namely the Honeywell MultiRAE Lite wireless portable multi-gas monitor (pumped model).

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RESUMEN

ABSTRACT: The mechanism for the formation of double-layer vertically aligned carbon nanotube arrays (VACNTs) through single-step CVD growth is investigated. The evolution of the structures and defect concentration of the VACNTs are tracked by scanning electron microscopy (SEM) and Raman spectroscopy. During the growth, the catalyst particles are stayed constantly on the substrate. The precipitation of the second CNT layer happens at around 30 min as proved by SEM. During the growth of the first layer, catalyst nanoparticles are deactivated with the accumulation of amorphous carbon coatings on their surfaces, which leads to the termination of the growth of the first layer CNTs. Then, the catalyst particles are reactivated by the hydrogen in the gas flow, leading to the precipitation of the second CNT layer. The growth of the second CNT layer lifts the amorphous carbon coatings on catalyst particles and substrates. The release of mechanical energy by CNTs provides big enough energy to lift up amorphous carbon flakes on catalyst particles and substrates which finally stay at the interfaces of the two layers simulated by finite element analysis. This study sheds light on the termination mechanism of CNTs during CVD process. GRAPHICAL ABSTRACT: The mechanism for the formation of double-layer vertically aligned carbon nanotube arrays (VACNTs) through single-step CVD growth was investigated. The growth of the second CNT layer lifts the amorphous carbon coatings on catalyst particles and substrates.