Carbon nanotubes as high performance sorbents for environmental applications

Abstract

From an environmental perspective the volatile organic compounds (VOCs) and semi volatile organic compounds (SVOCs) are very important. They can disperse from their sources in any media, and even at trace concentrations they are a threat to the humans and the ecosystem. The measurement of these organics at trace level is a major challenge and there is a need for instruments for rapid, on-line monitoring of these pollutants. This study evaluated the environmental applications of carbon nanotubes (CNTs) through the integration these inside microtrap for on-line gas chromatography system for monitoring of representative environmentally relevant adsorbates, volatile and semi volatile organic compound. The motivation behind such development is to eliminate contamination and errors associated with sample collection, transport, storage, and laboratory and to provide an automatic and sensitive system for monitoring of VOCs and SVOCs. Carbon nanotubes (CNTs) possess several highly desirable sorbent characteristics, which makes them attractive for a variety of applications including as micro-scale preconcentration. The main advantage of CNTs is that they are non-porous, thus eliminating the mass transfer resistance related to diffusion into pore structures. Their high aspects ratio leads to large specific capacity, consequently they have the potential to be the next high performance sorbent. A microtrap is small metal capillary tubing containing a small amount of sorbent. The microtrap is designed for preconcentration the analyte from flowing containing stream as well as moduled for an injector for gas chromatography (GC), when uses for on-line system. Variety of CNTs inside microtraps either packed or self assembled format for the online detection of gas chromatography system were developed. A comparative study between packed CNTs and self- The results obtained from developed microtraps with variety of CNTs sorbents for on-line GC system of organics, have shown high-capacity adsorption and fast quantitative desorption, and the process exhibited good reproducibility and long time stability. The elimination of non tubular carbons (NTC) from the CNT surface is important, as they reduce the performance of these sorbents. This research has explained that CNTs either single (SWNT) or multi-walled (MWNT) with both formats (packed or self-assembled) can be used for analytical applications in environment, and these can work as efficiently as other analytical techniques. Consequently, this will open the doors to the application of high-capacity, CNTs-based sorbents as an alternative to other sorbent in environmental monitoring and analysis. To evaluate further in-depth knowledge of the microtrapping phenomenon, apart from pure CNTs, the strategy of surface modification was employed and that was achieved through the process of microwave acid chemistry . Incorporation of functional groups on CNT has altered their surface nature which allows greater number of interactions and consequently changes their selectivity towards organic molecules and both sorption and separation efficiency for polar analytes was increased dramatically. This work suggests the process of purification and functionalization can influence the sensitivity of CNTs towards their microtrapping characteristics. Both physisorption and chemisorption of organics on nanotubes were possible, however, physisorption was seem to be more dominant as reflects from the excellent desorption efficiency of CNTs. The key findings of this work show the realistic environmental applications of CNTs by integrating them with online GC system.