NO2-sensing properties of octa(2-ethylhexyloxy) metallophthalocyanine LB films using quartz-crystal microbalance

Octa(2-ethylhexyloxy) metallophthalocyanines (MPcs) have been stacked in a multilayered form on a quartz-crystal microbalance (QCM) by using a Langmuir-Blodgett (LB) method. The NO2-sensing characteristics of these films are investigated in terms of the adsorption and desorption of NO2. The patterns of NO2 adsorption show different sensing properties depending on the kind of central metal atoms. The adsorption capacities to NO2 obtained from the saturation feature are 1.2 for H2Pc, 1.9 for CuPc, 0.7 for CoPe and 1.0 for PbPc. From the empirical adsorption kinetics study, the adsorption order and rate constant are also comparable, and CoPc had better sensing properties than the other three MPcs. However, the recovery of sensing output is hardly satisfactory even at high temperature (170 degrees C),and the absorbance spectra for repeated NO2 exposures can give some insights into the irreversible feature of MPcs to NO2.