Microwave assisted activation of silkworm excrement for fast adsorption of methylene blue and high performance supercapacitor

The activated carbon (AC) with an exceptionally high surface area was made of silkworm excrement (SE) by microwave-assisted KOH activation (MAKA). It was investigated for the potential applications in methylene blue (MB) adsorption and a supercapacitor electrode. The effect of activation time on the AC properties and performance was studied. The physical and chemical properties of the as-prepared samples were analyzed by FE-SEM, TEM, N₂ adsorption, and Raman spectroscopy. Remarkably, the AC with the largest specific surface area (SA_s) of 2530.3 m²g^-1 was produced by partial carbonization of SE at 400 °C (SE400-5) and then activated for only 5 min. The large SA_s is attributed to the abundance of micro-pores, leading to the enhanced MB absorption performance, as equilibrium was reached within 10 min at 25 ppm of MB concentration. The maximum MB adsorption capacity for SE400-5 was 902.56 mg g^-1. The adsorption isotherms revealed that the Langmuir model best fits the empirical data (R² ≥ 0.9813), indicating monolayer adsorption. The kinetic model fitted well to the Pseudo-second-order (PSO) (R² ≥ 0.9691). CV, GCD, and EIS measurements also evaluated the electrochemical properties of all samples. The electrodes were made without the addition of conductive material. The SE400-5 also had the lowest total resistance and highest total effective capacitance, which resulted in its highest specific capacitance (C_s) of 322 F g^-1 at 0.5 A g^-1. The capacitive retention of SE400-5 remained as high as 98% even after 10,000 cycles at 10 A g^-1. These results demonstrate that SE is a viable source of AC for MB adsorption and a supercapacitor electrode.