An innovative CS2-free approach to VOCs monitoring in air matrices : methanol as a valid substitute of carbon disulphide

TOPICS: 1) Sustainable remediation approaches , case studies 4) Innovative technologies in site remediation 10) Risk management and risk communication, stakeholder engagement Volatile organic compounds (VOCs) are organic species characterized by a vapor pressure greater than 10-1 Torr at 298 K and 1 atm [1]. Numerous sources are responsible of VOCs emission, such as industrial plants, vehicles and so on. Owing to their high toxicity, the presence of VOCs in air matrices negatively affects indoor and outdoor quality air. The consequences on human health range from sensory irritation to increase in allergies, etc. In the field of air matrices soil gas represents an emerging environmental compartment. Soil gas is defined as the atmosphere present in pore spaces of soil matrices. These pores can undergo contamination phenomena because of exposure to volatile pollutants. Therefore, one of the most recent aim of the analytical and environmental chemistry consists in VOCs monitoring and analysis in soil gas matrices. Among different approaches developed to VOCs abatement [2], the use of adsorbent materials results to be the most effective. Currently, numerous official analytical methods for VOCs analysis (NIOSH, OSHA, etc.) are based on the use of carbon disulfide (CS2) as the solvent extraction and activated carbon as the adsorbent support. Even though CS2 represents the recommended solvent extraction by the official methods, it exhibits high toxicity and shows drawbacks related to air pollutant and analytical interferences. As a consequence, the possibility to replace CS2 with a less toxic solvent could represent an interesting challenge. In the present work we report our recent achievements in the VOCs monitoring by an innovative approach based on the use of a less toxic solvent extraction (methanol) and a polymeric-based material (polyaniline) as the sorbent support. Although polyaniline has been deeply investigated as sensing materials for VOCs detention [3], to the best of our knowledge it has not been investigated for sampling or abatement/adsorption purposes. Polyaniline was synthesized by different approaches and spectroscopically characterized. Then, commercial glass tubes were filled with a proper amount of polyaniline. Each tube was properly loaded with a mixture of 20 VOCs as gases. Thereafter, the VOCs adsorbed on sorbent material were extracted with methanol. For all the polyanilines VOCs adsorption/desorption efficiency was evaluated, obtaining results similar to those presently achieved by official method employing commercial activated carbon and CS2. The best material was subjected to an easy regeneration process and reused maintaining a high adsorption/desorption efficiency up to five times. [1] Compendium Method EPA TO 15 1999; [2] S. Majumbar, D. Bhaumik, K. K. Sirkar, G. Simes, Environ. Prog., A pilot-scale demonstration of a membrane-based absorption- stripping process for removal and recovery of volatile organic compounds, 20, 2001, 27-35; [3] S. Pandey, Highly sensitive and selective chemiresistor gas/vapor sensors based on polyaniline nanocomposite: A comprehensive review, JSAMD, 1, 2016, 431-453.