Cu2O microsphere, microspherical composite of Cu2O/Cu nanocrystals and various Cu microcrystals: In situ hydrothermal conversion of Cu-aminodiphosphonate complexes

We describe here a complex precursor hydrothermal route to prepare uniform Cu2O microsphere, spherical composite of Cu2O/Cu nanocrystals with controlled size and composition and a wide range of novel copper microstructures using {[Cyclohexyl(phosphonomethyl)amino]methyl}phosphonic acid (dP) as both the complexing and reducing agent. It is noteworthy that changing the characteristic of initially formed Cu2 +-aminodiphosphonate complex precursor via manipulating synthetic parameters was crucial to the growth of the final product. Time order of growth process at pH = 9 has been revealed: (1) aggregation of Cu2O nanoparticles to form spherical microstructure, (2) recrystallization of Cu2O nanoparticles parallel to reductive transformation from Cu2O to Cu to produce spherical Cu2O/Cu microstructure consisting of larger nanoparticles and (3) increasing the nanoparticle size of Cu2O/Cu microstructure as the content of Cu phase increases. At pH = 14, only pure Cu microcrystals of different shapes were obtained. The effects of concentration and molar ratio of starting materials, reaction time and temperature on the growth process and morphology of copper microcrystals were investigated. Finally, a possible growth mechanism is proposed. The obtained samples have been characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and Fourier Transform infrared spectroscopy.