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

Research highlights: {yields} Synthesis details self-assembly of SnO{sub 2} in aqueous hexamethylenetetramine solution. {yields} Hydrogen bonds clustering around the hexamethylenetetramine interact with the non-polar SnO{sub 2} surfaces. {yields} Self-assembly was possible with aqueous tin (II) chloride solution and not with aqueous tin (IV) chloride solution. -- Abstract: The present report details the effects of synthesis time, concentrations of hexamethylenetetramine (HMTA) and precursor tin (II) chloride solutions on the self-assembly of SnO{sub 2} nanocrystals. High-resolution electron microscopy images revealed that the structures were made of randomly attached SnO{sub 2} nanocrystals with sizes in between {approx}2 and 5 nm. X-ray photoelectron spectroscopy (XPS) showed that the Sn3d region was characterized by the spin-orbit splitting of the Sn3d{sub 5/2} ground state at {approx}487.6 eV and by the Sn3d{sub 3/2} excited state at {approx}496.1 eV, which was attributed to the Sn{sup +4} oxidation state of the SnO{sub 2} 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 SnO{sub 2} nanocrystals in the presence of aqueous HMTA solution.