Photothermal Desorption of Toluene from Carbonaceous Substrates Using Light Flash.

Evan L Floyd,Claudiu T Lungu,Jonghwa Oh,Jacob S Shedd,Toluwanimi M Oni,Karim Sapag

doi:10.3390/nano12040662

Abstract

Millions of workers are occupationally exposed to volatile organic compounds (VOCs) annually. Current exposure assessment techniques primarily utilize sorbent based preconcentrators to collect VOCs, with analysis performed using chemical or thermal desorption. Chemical desorption typically analyzes 1 µL out of a 1 mL (0.1%) extraction volume providing limited sensitivity. Thermal desorption typically analyzes 100% of the sample which provides maximal sensitivity, but does not allow repeat analysis of the sample and often has greater sensitivity than is needed. In this study we describe a novel photothermal desorption (PTD) technique to bridge the sensitivity gap between chemical desorption and thermal desorption. We used PTD to partially desorb toluene from three carbonaceous substrates; activated carbon powder (AC-p), single-walled carbon nanotube (SWNT) powder (SWNT-p) and SWNT felts (SWNT-f). Sorbents were loaded with 435 ug toluene vapour and irradiated at four light energies. Desorption ranged from <0.007% to 0.86% with a single flash depending on substrate and flash energy. PTD was significantly greater and more consistent in SWNT-f substrates compared to AC-p or SWNT-p at all irradiation energies. We attribute the better performance of SWNT-f to greater utilization of its unique nanomaterials properties: high thermal conductivity along the nanotube axis, and greater interconnection within the felt matrix compared to the powdered form.

Highlights

Every year millions of tons of volatile organic compounds (VOCs) are released into the environment by anthropogenic sources globally and domestically [1,2,3] with a portion of these emissions resulting in occupationally exposed workers
We explored the use of high intensity photo flash to thermally desorb toluene from three sorbents; activated carbon powder (AC-p), single-walled carbon nanotube powder (SWNT-p) and single-walled carbon nanotube felt (SWNT-f)
Using the modified model to predict the initial mass of each sorbent, we find that predictions of Mo are within 7.5%, 4.6% and 3.1% of the true initial mass (435 μg toluene) for AC-p, SWNT-p and SWNT felts (SWNT-f), respectively (Figure 9)

Summary

Introduction

Every year millions of tons of volatile organic compounds (VOCs) are released into the environment by anthropogenic sources globally and domestically [1,2,3] with a portion of these emissions resulting in occupationally exposed workers. An effective sorbent captures VOCs on its surface through physical adsorption (i.e., physisorption) using weak molecular interactions. In many cases the preferred sorbent for VOC sampling is high surface area, highly microporous activated carbon (AC). AC samplers have good analyte stability, are compact, inexpensive and can be used in active or passive sampling. Active sampling generally has better sensitivity than passive sampling because a greater volume of air can be sampled but requires a calibrated pump and Nanomaterials 2022, 12, 662.

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