Controlled synthesis of cadmium carbonate nanowires, nanoribbons, nanorings and sphere like architectures via hydrothermal method

Abstract

Crystalline nanowires, nanoribbons, nanorings and sphere like architectures of cadmium carbonate have been synthesized with the spontaneous self-assembly of nanocrystals in aqueous solution under hydrothermal condition. The powder X-ray diffraction (PXRD) patterns of these materials exhibit phase pure hexagonal structure. The perfect circular nanorings with radius 375–437 nm, as a new member of nanostructured cadmium carbonate family are being reported for the first time. The width of the cadmium carbonate nanowires/nanoribbons and nanorings, respectively are found to be in the range 11–30 and 26–50 nm as observed by transmission electron microscope (TEM). The effect of temperature and concentration of urea on the cadmium carbonate morphology is discussed. The plausible growth mechanism for the formation of nanorings is also proposed.

Introduction

In recent years, there has been great research interest in the synthesis of nanostructured CdXO₃ (X = C, Si, Ge, Sn, Pb) materials because of their wide range of technological applications [1]. For instance, cadmium carbonate has been used as core material for fabrication of hollow polyelectrolyte capsules, solid phase reactor for indirect determination of cyanide, and precursor for the preparation of technologically important CdO nanostructured material [2], [3], [4]. Concerning their unique structural features and new properties generated with ring cavities [5], [6], [7], [8], several attempts have been made for preparation of meso- or nanoscopic ringlike structures over the past few years [9], [10], [11], [12], [13], [14]. Because of increasing structural complexity and demanding precision control, nonlithographic synthesis of functional ringlike objects in strict circular, oval, or polygonal forms may represent a next challenge of nanofabrication. There have been several reports on the generation of ringlike structures. In particular, carbon nanotube rings [9], [10], [11], zinc oxide coils and hexagonal rings [12], [13], [14], CuO nanorings [15], CdS rings [16], titanium dioxide [17], SnO₂/SiO₂ [18], NbSe₃ [19], and CaCO₃ [20] rings have been prepared.

Nanostructured cadmium carbonate has been previously reported in several morphologies including particles [21], wires [22], belts [23], [24] and some complex nanostructures [25]. Recently, quasi monocrystals of cadmium carbonate polygonal rings such as tetragonal, pentagonal and hexagonal rings formed by aggregation of nanoparticles are also fabricated via solvothermal method [26]. To the best of our knowledge, crystalline cadmium carbonate circular nanorings have not been reported so far.

In the present study, urea, a low cost and environmentally benign chemical has been employed as carbonate source for the preparation of cadmium carbonate nanowires, nanoribbons and nanorings. Obviously, urea is widely used in fertilizers as a convenient source of nitrogen and also an important feedstock for the chemical industry. It is also used as a source of hydroxide ion and carbon dioxide for the production of nanostructural alkoxides, carbonates and oxides of metal [27], [28], [29]. The proposed simple hydrothermal method required neither expensive, environmentally unfriendly organic surfactants or solvents, nor special equipment.