Microwave Assisted Synthesis of Cu₂O Crystals with Morphological Evolution from Octapod to Octahedron

Experimental Section

CuCl2·2H2O (99%, Aldrich), polyethylene glycol (PEG, Mw 20,000, Aldrich), D-(+)-glucose (ACS reagent, Aldrich), and N,N,N',N'-tetramethyl ethylenediamine (TMEDA, 98%, TCI) were used as received, without any further purification. The experimental conditions for the preparation of Cu2O products with various morphologies are summarized in Table 1. For the typical preparation of Cu2O product (sample number 9 in Table 1), 10 mL of a 0.125 M D-(+)-glucose aqueous solution and 6.0 g PEG were added to 138.1 mL of a 0.0362 M CuCl2·2H2O aqueous solution, with stirring at room temperature for 30 min. Then, 1.86 mL TMEDA was added to the mixed solution. The reactants concentrations of CuCl2·2H2O, D-(+)-glucose, TMEDA, and PEG are 33.3 mM, 8.33 mM, 83.3 mM, and 2.00 mM, respectively. To investigate the morphology evolution of the Cu2O products, the different amounts of CuCl2·2H2O, D-(+)-glucose, TMEDA, and PEG were used, with keeping a constant relative amount of reactants. The total volume of the aqueous solution was fixed to 150 mL. A final mixed solution in an open beaker was placed into a commercial microwave oven (Magic MWO-230KD, 2.45 GHz, 800 W). We used the open reaction system for the safety free from unexpected explosion. The microwave was operated for just 2 min. The final temperature of the mixed solution was increased to approximately 80 ℃. After finishing the microwave irradiation, the reacted solution was placed in ice-water to quench the reaction quickly, for reducing the thermal heating effect on the Cu2O products. The powder forms of Cu2O products were obtained by using a centrifuge at 4000 rpm for 10 min. The Cu2O products were then washed several times with ethanol and water, and then dried at 60 ℃ for 12 h in a drying oven. The average yield for the preparation of Cu2O products is approximately 46%. The crystal structure of the Cu2O products was characterized by powder X-ray diffraction (XRD, PANalytical, X’pert-proMPD). The morphology of the Cu2O products was examined by using scanning electron microscopy (SEM, Hitachi S-4300).