Low temperature hydrothermal synthesis mechanism and thermal stability of p-type CuMnO2 nanocrystals
Abstract
We first report an oxidation–reduction reaction mechanism for the hydrothermal synthesis of CuMnO2 nanocrystals at the low temperature of 80 °C. In detail, CuMnO2 nanocrystals with 50–100 nm size could be obtained based on a hydrothermal reaction from the starting materials of Cu(NO3)2, Mn(NO3)2/MnCl2/MnSO4 and NaOH at 80 °C for 24 h. During the hydrothermal reaction, Cu2+ was reduced to Cu+ and Mn2+ was oxidized to Mn3+, and finally CuMnO2 nanocrystals formed. The TGA analysis indicates the studied CuMnO2 was stable in a N2 atmosphere and the CuMnO2 remained unchanged at a high sintering temperature (500 °C). Moreover, the Mott–Schottky plot results demonstrate that CuMnO2 nanocrystals show p-type semiconductor behaviour. The flat band potential (Efb) position and carrier density of the CuMnO2 nanocrystals are 0.28 V vs. reversible hydrogen electrode (RHE) and 2.46 × 1018 cm−3, respectively. After the CuMnO2 nanocrystals were sintered at 300 °C in N2, the Efb position shows a negative shift to 0.23 V vs. RHE and the carrier density increased to 1.58 × 1019 cm−3. This quick and facile method opens a new route for the preparation of other delafossite oxides, which can be used in some optoelectronic devices such as photoelectrochemical cells and photovoltaic cells.