Feeding silkworm with sodium molybdate solution sprayed mulberry leaves for the preparation of carbonized silk with high capacity

Carbonized silk paves the way for the design and construction of wearable electronics. The composition of silk fibers can be modulated by feeding silkworms with specific diets, which can enhance the functionality of the carbonized silk. In our previous work, the silkworms were fed ammonium molybdate tetrahydrate solution sprayed mulberry leaves to obtain carbonized silk fibers (CSF) possessing a maximum specific capacitance of 298 F/g at 0.2 A/g. In this work, we fed the silkworms sodium molybdate solution sprayed mulberry leaves, for which silkworms present a high tolerance, in order to raise the quantity of the element Mo incorporated within the silk. Transmission electron microscopy - energy dispersive X-ray spectroscopy was utilized to observe and analyze grains, grown through the process of carbonization, inside the carbonized silk. It was confirmed that the composition of those grains are MoO2. Electrochemical measurements show these CSF based electrodes possess outstanding capacitance behavior with a specific capacitance of 524 F/g at 0.2 A/g. Additionally, the electrodes show excellent cyclability. The capacitance retention ratio can reach up to 96.84% after 5000 galvanostatic charge/discharge cycles at 0.2 A/g. Our strategy is straightforward and does not require any hazardous or organic solvents, therefore is an illustration of a green procedure for functionalized CSF synthesis. Furthermore, because the precursor fed to silkworm is water soluble and can be easily dispersed over the surface of mulberry leaves, the method described is suitable for bulk and large scale production of functionalized CSF.