Nanoporous copper and copper oxide with hollow microsphere structure prepared by polystyrene template-assisted synthesis

The use of porous metals with highly porous nano- or submicro-structured walls for energetic materials applications has been considered in recent years. The aim of this work is to construct a stable porous structure for synthetize of copper azide primary explosive. For this purpose, hollow copper and copper oxide microspheres were successfully prepared by electroless plating using polystyrene (PS) templates with diameter of 529 nm. SEM and XRD analysis were conducted to characterize the microstructure and composition of the products, and ICP was used to measure the variation of Cu2+ concentration during plating. Results show that the amount of copper deposit increased with increasing pH value. By adding enough NaOH solution during plating, copper ions could be all reduced while the microstructure of copper coatings destroyed. The addition of stabilizers had a negative effect on PS/Cu core-shell structures. Hollow copper microspheres with shell thickness of 100 nm were obtained by sintering PS/Cu core-shell microspheres in N2 while hollow copper oxide microspheres were obtained in air.

Methods
Methods

PS microspheres are synthesized by soap-free emulsion polymerization using a mixed solution of deionized water and methanol as a dispersant, potassium persulfate as an initiator, and styrene as a monomer. The specific steps are as follows: 40 mL deionized water, 7 mL methanol, 0.08 g KPS and 5mL styrene are added in round-bottom flask fitted with two necks, and N2 is introduced into the bottle to purge O2 out for about 10 min. The flask is closed with silicone-greased stoppers and clamps, and then reacts in a 75 °C water bath at 500 rpm for 12 h. PS microspheres are obtained by washing the polymerized product and then drying in an vacuum oven at 50 °C for 24 h. The preprocessing of PS microspheres is given in Reference 18.

The electroless plating copper bath is consisted of CuSO4·5H2O (0.1 mol×L-1), Na2EDTA (0.12 mol×L-1), pH buffer (NaOH) and 2, 2-bipyridine (0.01g·L-1), potassium ferrocyanide (0.01 g·L-1) and methanol (50.00 mL·L-1)). The preprocessed PS was immersed into a freshly prepared copper bath, and dipped reductant HCHO (15.00 mL·L-1) under ultrasonic to start reaction. Then, the PS/Cu composite was obtained by centrifugation and rinsed with deionized water for three times and dried in vacuum oven at 50 °C. Finally, nanoporous copper and copper oxide microspheres are obtained by sintering PS/Cu core-shell at 400 °C for 1 h in the N2 and in the air with the heating rate of 5 °C·min-1, respectively.

Characterization

Particle size and the particle size distribution of PS microspheres are performed by laser particle size analyzer (Mastersizer 2000, UK). The thermal performances of PS microspheres and PS/Cu composites are measured by thermogravimetric analyzer (TG/DTA6300, Japan) at a heating rate of 10 °C·min-1 from 25 °C to 600 °C. The IR spectra of PS microspheres are collected by infrared spectrometer (TENSOR 27, Germany). The Cu2+ concentration is measured by inductively coupled plasma optical emission spectrometer (ICP-OES, PE OPTIMA 7000DV, USA). The microstructure of samples is observed by scanning electron microscopy (SEM, S4800, Japan). X-ray diffraction (XRD) analysis is performed on a diffractometer (Rigaku, Japan) with Cu Kα radiation in the range from 5° to 80°.