The light enhanced gas selectivity of one-pot grown porphyrins coated ZnO nanorods

The interplay between photosensitivity and gas sensitivity has been observed in many organic and inorganic materials. For instance, the exposure to UV light can enable metal oxide semiconductors to detect gases at room temperature. In this paper, the effects of visible light and volatile compounds on porphyrin-coated ZnO nanorods have been studied by the Kelvin probe technique. The hybrid material was prepared according to a one-pot procedure adding porphyrins directly to the precursor solution of the ZnO nanostructure hydrothermal method growth. Changes of contact potential differences were measured with respect to amines and alcohols. Under illumination sensors responses are found larger than those measured in the dark. In both cases, the sensitivity is unexpectedly controlled by non selective dispersion interactions but the increase of sensitivity due to illumination is correlated with the electron donating characteristics of the absorbed species in a coordinative bond formation process. Since coordination is expected to be energetically dominant in the interaction between volatile compounds and porphyrins, the differential measurement, in dark and in light, provides a method to evidence the selective interactions.