Stannous oxide is an important functional material which contributes to a wide range of applications in energy storage and optoelectronic devices. In the present study, the single crystalline self-assembled stannous oxide (SnO) 2D nano-square sheets have been synthesized with template-free hydrothermal growth method. The morphology, composition and structure were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) with selected area electron diffraction (SAED), energy dispersive X-ray (EDX), X-ray diffraction (XRD) and Raman spectroscopy, respectively. FESEM results have illustrated that the size of self-assembled 3D hierarchical polygon-shape structure of SnO is in the range of 8-12 mu m and the average size of the nano-square sheets is about 100 nm. X-ray diffraction (XRD) and selected area electron diffraction (SAED) patterns have revealed that the prepared SnO nano-square sheets exist in single-crystalline nature. Two Raman modes A(1g) = 211 cm(-1) and B-1g = 113 cm(-1) were observed by Raman spectroscopy, which is consistent with nano tetragonal phase SnO. Furthermore, the chemical valence of Sn and relative atomic composition of as-prepared SnO have been confirmed by X-ray photoelectron spectroscopy (XI'S). Ultraviolet-visible-near infrared spectrophotometry was used to study the transmittance behavior of SnO nano-structures and direct optical band gap of 3.16 eV was acquired by using Davis-Mott model. The first ever study on hydrogen absorption characteristics of SnO nano-square sheets performed at 373 K shows good absorption capacity of 1.194 wt.%. (c) 2012 Elsevier Ltd. All rights reserved.