Polyaniline (PANI) : an innovative sampling support for VOCs in air matrices : A comparison between PANI and carbon active performances by GC/MS approach

Volatile organic compounds (VOCs) find widely application in different fields ranging from laboratories to medicine as well as petroleum industry. As a consequence, recently analytical and environmental chemistry has paid attention to their determination in order to monitor environmental pollution and take care of human health. Among the diverse environmental matrices, soil gas and air are the most interested ones. Currently, official analytical methods are available for VOCs’ analysis. Most of these approaches (NIOSH, OSHA, etc.) are based on the use of CS2 as the solvent extraction and carbon active as the absorbent support. Although many drawbacks are related to the use of CS2 (high toxicity, air pollutant, analytical interferences, etc.), currently it is still employed in numerous sectors. Even though in some cases it can be easily replaced by other less toxic solvents (e.g. methanol), concerning VOCs’ extraction by carbon active-based support, it is still the most performant one. Even though carbon was the first material to be used as VOCs’ absorbent, other materials have been recently investigated. Among them, zeolites and polymers have shown interesting properties in this regard. In order to overcome these inconvenient and replace CS2 with methanol for VOCs’ extraction, in this work we present an innovative polymeric material (polyaniline) able to substitute carbon active as the support for sampling and subsequent analysis VOCs. Inspired by our experience in the field of environmentally friendly synthesis of polyaniline (PANI) [1] and its application in different sectors, [2, 3], here we report our recent results in the use of two different types of PANI as the support for VOCs’ sampling and analysis. Polyaniline (PANI) is a popular conductive polymer that has attracted much attention in separation sciences due to its versatile properties such as hydrophobicity, large p-conjugated structure, polar functional groups, and good thermal and chemical stability [4]. Here, polyaniline was prepared in form emeraldine salt (PANI/HCl, half-oxidized half-protonated form) as a powder by two different approaches (a traditional one, PANI1, and a green one, PANI2 [1]). PANI1 and PANI2 resulted characterized by different morphology, ranging from worm-like (PANI1) to stone-like (PANI2) and different electroconducting properties, three thousands higher for PANI1 than for PANI2, that represents an indirect measure of the conjugation and protonation level. In order to test these polymers as absorbent supports for VOCs, a few milligram of each material (main layer) was introduced in a sampling glass tube, followed by a security layer made of active carbon as a check breakthrough. The glass tubes were loaded by a mixture of VOCs (having a vapor pressure greater than 10-1 Torr at 25°C and 760 mm Hg [5]) in form of gas using a flow rate of 50 mL/min for 10 minutes. Then, the two layers were separated. The main layer (PANI) was treated for 30 min with 1 mL of methanol, whereas the security layer was extracted with 1 mL of CS2. The extracted fractions were analyzed by GC/MS and quantified by the internal standard method. The results demonstrated that PANI1 was able to quantitatively retain all analytes, as also confirmed by the security layer, displaying performances similar to those obtained with carbon active using CS2. On the contrary, PANI2 released in the security layer about the 20-30% of the total amount of VOCs. Although the different behaviour of the two polymeric materials can be related to many factors, our results suggest that the difference in morphology and conductivity are the most important ones. In fact, the different morphology of the materials strongly affects their porosity, making PANI1 highly porous whereas PANI2 more compact. As a consequence, the highly porous PANI1 is characterized by higher surface area guaranteeing good retaining properties. Moreover, its higher conductivity, related to an extended conjugation and a high protonation level, ensures the presence of a high number of protonated imine units responsible of electrostatic interactions useful for VOCs absorption. On the base of these preliminary results our efforts will be addressed in the preparation of highly porous PANI2 in order to realize an innovative green material active in this field. This will represents an important goal in the field of VOCs’ sampling and analysis allowing to eliminate CS2 and introduce as absorbent support a smart and performing green material. 1. C. Della Pina, E. Falletta, M. Rossi, Catalysis Today, 160, 11-27 (2011) 2. C. Della Pina, E. Zappa, G. Busca, E. Falletta, Sensors and Actuators B: Chemical, 201, 395-401 (2014) 3. R. Castagna, M. Tunesi, B. Saglio, C. Della Pina, A. Sironi, D. Albani, C. Bertarelli, E. Falletta, Journal of Applied Polymer Science, 133(35), 43885(1-10) (2016) 4. O. Bunkoed, T. Rueankaew, P. Nurerk, P. Kanatharana, Journal of Separation Science, 39(12), 2213-2438 (2016) 5. Compendium Method EPA TO 15 1999