Investigation of Surface Affinity and Desorption Kinetics of Mixture of Volatile Organic Compounds on CuO-Based Resistive Gas Sensors

Analysis and understanding of the mixture of volatile organic compound (VOC) sensing are crucial for the development of sensors in conditions closer to real-life applications, such as health care, air quality monitoring, industrial safety, etc. In this study, we investigated the response dynamics of CuO-nanomaterial-based resistive sensors to 25–75 ppm of individual, binary, ternary, and quaternary mixtures of five VOCs—acetone, acetonitrile, isopropanol, methanol, and toluene at 300 °C. The CuO exhibited responses equal to the sum of its steady-state responses to individual VOCs for all the possible combinations of binary and ternary mixtures with 25 ppm of the constituent gases. A systematic study based on the recovery cycle was conducted by retracting the VOCs sequentially from the proximity of CuO surface after recording response cycle. Interestingly, the recovery time constant τ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rec</sub> was found to follow the order—isopropanol (96.93 – 435.45) ≥ methanol (111.82 – 313.21) > toluene (9.9 – 220.49) > acetonitrile (85.96 – 332.32) > acetone (could not be found) in all binary, ternary, and quaternary mixtures of VOCs, irrespective of the sequence of retraction of the VOCs from the mixture. Also, it was found that VOCs with –OH groups have higher adsorption capacity on the sensing layer as compared to –NH<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>, – C = O, and aromatic VOCs.