Surface assisted growth of CuSO 4 micro-and nano-spheres

Under similar conditions, only microand nanospheres of CuSO4 were observed. Such phenomenon was not observed from solutions of other ethanol soluble salts, such as CuCl2, Cu(NO3)2, Cu(OAc)2, FeCl2, FeCl3, NiCl2, CoCl2, NiSO4 (Figure 5). However, we cannot rule out the possibility to grow amorphous spheres from these salt solutions by varying the solvent, substrates, temperature, concentration etc., which is under investigation in our lab now. The property of the nano/ microspheres due to their large surface is under investigation as well. Although it is not sure whether the growth of nanoand microspheres is a unique phenomenon of CuSO4 in ethanol, the discovery of the micro/nanospheres of a salt solution may lead to the development of salt based nano/microspheres and applications of these nano/ microspheres.

In conclusion, we have synthesized nano/microspheres of CuSO 4 by using a facile solvent evaporation method. These spheres may have applications in medical and industrial fields. It is a hypothesis that the formation of amorphous CuSO 4 nano/microspheres may be due to relatively faster evaporation of ethanol than other solvents such as water, which resulted in differential stress and distribution of porosity Amorphous micro-and nano-sphere of CuSO 4 were synthesized on silicon or glass surface by evaporating ethanol from a CuSO 4 solution in ethanol. Factors, such as substrate and concentration, on the synthesis of the nano/microspheres were studied. The phenomenon was not observed from solutions of other ethanol soluble salts, such as CuCl 2 , Cu(NO 3 ) 2 , Cu(OAc) 2 , FeCl 2 , FeCl 3 , NiCl 2 , CoCl 2 , NiSO 4 . Nanospheres and microspheres have been widely used in fields such as agriculture, medicine, manufacturing, environment, energy, and cosmetic industries. These micro-and nano-materials can be synthesized from a variety of methods including hydrothermal synthesis [1] attrition [2] pyrolysis [3] thermal plasma [4] inert-gas condensation [5] sol gel process [6] etc. The synthesized materials include metals, polymers, metal oxides, ceramics, and composites. However, few works demonstrated the formation of micro-or nanospheres from water-soluble salt [7] When salts are recrystallized in solvents, the salts typically precipitated out in the form of regular or irregular crystals, which is a common property of salts. In this short communication, we demonstrate the formation of amorphous microand nano-sphere of CuSO 4 on silicon or glass surface by evaporating ethanol from a CuSO 4 solution in ethanol.
In our approach, a substrate (glass, silicon, or gold coated silicon plate) was submerged in a 20-mL vial with a 0.5 mL CuSO 4 solution in ethanol in it. Ethanol was allowed to evaporate at ambient temperature. The precipitated CuSO 4 solid on the substrate adopted a spherical shape at nanometer or micrometer dimension (Figure 1), which is a typical character of amorphous particles because of their microstructural isotropy. The amorphous character is also evidenced by the appearance of pimple, raspberry-like surface, in contrary to anisotropic crystalline whiskers corresponding to crystals. Some of the incomplete particles are in the shape of puckered plate, or hemispheres with defect.
The micro-and nano-spheres were only observed when ethanol was used. When preparing in DMF and water, irregular cluster of particles was observed from DMF or aqueous solutions (Figure 2).
Surface property of substrates also affects the formation of spheres, as evidenced by the observation of spheres on silicon or glass surfaces, but not on gold surface (Figure 3), suggesting the surface property plays a critical role in the formation of spheres. It is likely that the OH groups on silicon (there is a naturally oxidized thin film of SiO 2 on silicon) or glass surfaces provided multiple nucleation sites for CuSO 4 to precipitate out of the solution, which assisted the formation of the spheres.
When the concentration of CuSO 4 is lower than 1×10 -4 M, the irregular particles are small and not complete in the sphere shape Surface assisted growth of CuSO 4 micro-and nanospheres