Synthesis of metal and metal oxide nanoparticles, liquid–liquid extraction and application in supercapacitors

Abstract

Suspensions of Ag and MnO2 nanoparticles in n-butanol were prepared by synthesis in aqueous solutions and liquid–liquid extraction to the n-butanol phase. Lauryl gallate (LG) was used as a reducing agent for the fabrication of Ag nanoparticles from AgNO3 solutions. MnO2 nanoparticles were prepared by the reduction of KMnO4 with n-butanol. LG showed strong adsorption on Ag and MnO2 particles allowing for their liquid–liquid extraction. The adsorption mechanism involved complexation of metal atoms on the particle surface with phenolic OH group of LG. The synthesis and liquid–liquid extraction method offers benefits for nanotechnology, which were demonstrated by the fabrication of advanced supercapacitor electrodes and devices. LG allowed co-dispersion of multiwalled carbon nanotubes (MWCNT) and MnO2 in the n-butanol phase. In this strategy as-synthesized MnO2 nanoparticles were mixed directly with MWCNT. This avoided the difficulties associated with extracting particles from aqueous suspensions and subsequent particle agglomeration during the drying stage. The MnO2-MWCNT nanocomposite electrodes showed an exceptionally high capacitance of 8.0 F cm−2 at a scan rate of 2 mV s−1 and significant improvement in capacitance retention at high charge-discharge rates. Excellent capacitive performance was achieved at high active mass loading and a large ratio of active material to current collector mass. It was found that such capacitive behavior resulted from improved co-dispersion and mixing of MnO2 and MWCNT. The composite MnO2-MWCNT electrodes were used for the fabrication of asymmetric supercapacitor devices, which showed good electrochemical performance in a voltage window of 1.6 V. The proposed method can be used for other applications of nanoparticles of metals and oxides in nanotechnology.