One pot green synthesis of MnCO3–rGO composite hybrid superstructure: application to lithium ion battery and biosensor

Abstract

Herein, hierarchical superstructures of MnCO₃ and MnCO₃–rGO hybrid nanocomposites with controlled morphologies, such as cube, spherical, dumbbell, and oval, were synthesized via an environmentally friendly hydrothermal treatment using green tea extract (GTE) as a reducing agent as well as a shape controlling agent. During the hydrothermal treatment, the GTE produces carbonate species in the presence of a strong oxidising agent, such as KMnO₄, and reduces graphene oxide to graphene. Different superstructures of MnCO₃ and MnCO₃–rGO were obtained by controlling the reaction time. A tentative growth mechanism for the generation of MnCO₃ superstructures is proposed based on the morphologies obtained at different intervals of time. Additionally, MnCO₃ and MnCO₃–rGO have been used as anode materials for Li-ion batteries. Galvanostatic charge–discharge study shows intercalation/de-intercalation of lithium, which is a characteristic of a battery material. Based on this, it can be concluded that the as-synthesized MnCO₃ and MnCO₃–rGO with controlled morphologies are important electrode materials for Li-ion batteries. At a current rate of 0.06C, the MnCO₃–rGO electrode produces a specific discharge capacity of 340 mA h g⁻¹ after 50 cycles of charge–discharge. MnCO₃–rGO is also examined for dopamine (DA) detection using amperometric techniques. Linear current responses were obtained for the DA concentration in the range between 0.2 and 300 μM with 0.999 as the correlation coefficient. The limit of detection (LOD) for DA is found to be 20 nM. The response is not hindered by the presence of other bioanalytes and is reproducible, and the prepared electrodes are stable over a month when stored in a vacuum dessicator.