The hydrolytic route to Co-porphyrin-doped SnO2 gas-sensing materials: Chemical study of Co-porphyrin versus Sn(IV) oxide interactions

SnO2 and SnO2 + Co-porphyrin solids were prepared from SnCl4 in propanol and hydrolyzed to sol. Thermal behavior of samples obtained at 110 °C was studied in the 20–600 °C interval by thermal analysis coupled with mass spectrometry for identification of released species. The original samples maintain residual Sn–OR, Sn–OH and Sn–Cl groups up to 350 °C. The sample doped with 1% Co-porphyrin differs for a significant presence of residual Sn–Cl species, accounting for SnCl4 release in the 300–340 °C range. solid state NMR analysis reveals disordered SnO2 species in the sample heated at 250 °C and non-uniform SnO6 units in the SnO2 + Co-porphyrin sample at 110 °C, due to persistence of Sn–OR and Sn–OH groups. This complexity is lost at 250 °C. X-ray diffraction analysis confirms all these data. The sensing efficiency of these materials versus alcohols is ascribed to the presence of an open, incomplete SnO2 structure, which is more pronounced in the Co-porphyrin-doped sample.