Application of carbon nano-powders for a gas micro-preconcentrator

Abstract

This paper presents a feasibility study on the development of a gas preconcentrator based on micro-reactor technology on silicon. The objectives are to select a gas adsorbent material, to produce a silicon micro-reactor with an integrated heater, and finally to introduce the most suitable adsorbent into the micro-channels of the device. Preliminary results related to the characterization of a carbon adsorbent for the development of a device for the preconcentration of benzene are reported. Carbon nano-powders have been tested as adsorbent material by the determination of the breakthrough time on a dedicated test bench consisting of gas sensors and a non-selective photoionization detector (micro-PID) analyzer. A fluidic deposition process allows filling up the silicon micro-channels with the carbon nano-powder. The interest in using porous silicon to enhance the binding of the carbon nano-particles in the micro-channels was also investigated. A silicon micromachined preconcentrator filled with 0.30 mg of commercial activated charcoal powder (Aldrich, 30-100 nm) was designed and built up. The total capacity of adsorption was determined by using the breakthrough time, which is of 2.2 min under a gas flow of 100 ppm of benzene at 1 l/h. Preliminary tests of preconcentration with 100 and 1.3 ppm benzene in dry air were performed.

A micro gas preconcentrator with improved performance for pollution monitoring and explosives detection

“…The different channels are designed with the necessity of having some pillars or walls within the channels in order to control the powders deposition by fluidic solutions [23,24] . The neutral microchannel is designed without structures in the internal chamber while the zigzag design with channel system at inlet/outlet, mostly used in this work, is made with "V" shaped structures in order to improve the flow distribution not only during the adsorbent deposition but also during experiments.…”

“…[24] These experiments on the fluidic deposition of the adsorbent have shown that the presence of pillars in the preconcentration chamber, particularly in the "zigzag" design, is a key factor to homogenize the distribution of the liquid flow through the entire device and to enhance the carbon deposition. It was observed that the use of porous silicon has increased the quantity of deposited carbon in the micro-channels.…”

“…This heating element is used to heat the device at temperatures up to 500°C with a very homogeneous distribution of the temperature considering the good thermal conductivity of the silicon, as it was reported in our previous works . 182 [23,24] To have a good regulation of temperature, the micro-preconcentrator is suspended in a metallic box (Figure 2). …”

A micro gas preconcentrator with improved performances for environmental monitoring

“…In order to have an autonomous component, for either the thermal treatments of the adsorbent materials and the desorption of the trapped gases, a platinum heater is integrated on the backside of the device by screen printing and the electrical connections are made with gold wires pasted on a platinum lacquer. This heating element is used to heat the device at temperatures up to 500 °C with a very homogeneous distribution of the temperature considering the good thermal conductivity of the silicon, as it was reported in our previous works [1,2].…”

“…In a previous study [1,2], a gas pre-concentrator based on porous silicon micro-channels filled with carbon nanopowders from a fluidic solution has been developed. The present work aims to improve the performances of this device, with new approaches in the design as well as in the choice of adsorbent materials and modes of operation.…”