Water-soluble copper phthalocyanine for optimization of gas-sensor characteristics of tin dioxide upon adsorption of ammonia

This paper presents the results of the investigation into the electrical conductivity of thin films based on tin dioxide (SnO$_2$) nanoparticles, a film consisting of copper phthalocyanine-3,4',4",4"'-tetrasulfonic acid tetrasodium salt (CuPc–4SO$_3$Na) molecules, and a composite film based on a mixture of equal parts by volume of the two materials upon adsorption of ammonia. The adsorption experiments have been carried out in a vacuum at room temperature with an increase in the ammonia pressure to 3 $\times$ 10$^3$ Pa from the residual gas base pressure of 5 $\times$ 10$^{-1}$ Pa. It has been found that, in the case of a single-component film based on SnO$_2$ nanoparticles, an increase in the electrical conductivity reaches 100% and is not completely reversible at room temperature after evacuation of the gas. For the single-component CuPc–4SO$_3$Na film and the composite CuPc–4SO$_3$Na/SnO$_2$ film, the electrical conductivities increase by a factor of 400 and 150, respectively. Upon evacuation of ammonia to the base pressure, the electrical conductivity decreases to the initial values for 1 s. The mechanism of the influence of adsorbed ammonia molecules on the electrical conductivity of the composite material under investigation has been discussed using the model of the formation of the composite sample, according to which the organic component is located in voids between the SnO$_2$ nanoparticles.