Influence of aqueous hexamethylenetetramine on the morphology of self-assembled SnO2 nanocrystals

The present report details the effects of synthesis time, concentrations of hexamethylenetetramine (HMTA) and precursor tin (II) chloride solutions on the self-assembly of SnO2 nanocrystals. High-resolution electron microscopy images revealed that the structures were made of randomly attached SnO2 nanocrystals with sizes in between ∼2 and 5 nm. X-ray photoelectron spectroscopy (XPS) showed that the Sn3d region was characterized by the spin-orbit splitting of the Sn3d5/2 ground state at ∼487.6 eV and by the Sn3d3/2 excited state at ∼496.1 eV, which was attributed to the Sn+4 oxidation state of the SnO2 samples. We also found that the self-assembly could be achieved only with aqueous tin (II) chloride solution, and not with aqueous stannic (IV) chloride solution. A plausible growth mechanism is proposed in order to analyze the distinctive self-assembly of SnO2 nanocrystals in the presence of aqueous HMTA solution.