Tetra-tert-butyl copper phthalocyanine-based QCM sensor for toluene detection in air at room temperature

• We report a ttb-CuPc based QCM sensor for detection of toluene vapor.
• ttb-CuPc is very sensitive to toluene as compared to CuPc and F16CuPc.
• Drifts in the sensor signal because of temperature variations have been corrected.
• Sensor exhibited high resolution in response with good signal to noise ratio.
• Sensor is partially selective toward volatile organic compounds.

The sensing properties of tetra-tert-butyl copper phthalocyanine (ttb-CuPc) toward toluene at room temperature are reported in this manuscript. Thin films of ttb-CuPc were obtained by thermal evaporation. The similarities between powdered and layered material have been confirmed by FTIR analysis. Taking into consideration the interactions involved between material and the target gas, Quartz Crystal Microbalance (QCM) was chosen as transducer. The key role of tertiary butyl groups grafted at the periphery of the phthalocyanine ring on toluene sensitivity has been firstly established. Despite reproducible frequency shifts for toluene exposures at the same concentration, sensor drifts were observed and attributed to temperature effects on quartz crystal. Such thermal influence on sensor responses has been minimized by short exposure times and temperature compensation on sensor signal. The strong affinity of ttb-CuPc to toluene as compared to other phthalocyanines, the repeatability of sensor responses, the reversibility of involved gas/material interactions, a resolution higher than 10 ppm and a threshold of detection lower than 35 ppm have been established from experiments. The partial selectivity has been also highlighted toward others gases like CO, NO2, H2S and xylene. At last, the relevance of metallo-phthalocyanine thin films as sensitive coatings on QCM devices to detect volatile organic compounds in real-time situation will be discussed.

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