CoPc/rGO and CuPc/rGO Nanocomposites: Comparative Characterization and Study of Their Gas Sensing Properties

Nanocomposites made of tetrahexyloxy-substituted Co or Cu phthalocyanines adsorbed onto reduced graphene oxide (rGO) have been prepared for detection of volatile organic compounds (VOCs). Such nanocomposites could be formed in organic solvents, thanks to the high solubility of the substituted phthalocyanines, establishing van der Waals and π-π stacking interactions with rGO. UV-visible, FT-IR, and XPS characterizations evidenced the energy transfer between rGO and the phthalocyanines; this adsorption ability is highly suitable to form nanocomposites exhibiting improved electronic properties. The gas sensing properties of various VOCs were explored by conductometric measurements conducted on interdigitated electrodes modified with the nanocomposites, highlighting the effect of the alkyloxy substituents and phthalocyanine's metal. All exhibited high affinity to ammonia gas compared with other VOCs. The CuPc/rGO nanocomposites showed higher sensitivity with a lower limit of detection (0.4 ppm) compared to CoPc/rGO (1 ppm), while phthalocyanines alone give lower sensitivity, where the limit of detection of CuPc(OHex)₄ is 5.7 ppm and CoPc(OHex)₄ shows a nonlinear fit. We explained this behavior by improved energy transfer between rGO and CuPc(OHex)₄, favoring the coordination of ammonia. Detection of ammonia gas in real samples has been achieved to further demonstrate the efficiency of these sensors.