Duck eggs are one of the most versatile cooking ingredients in which residue eggshells are discarded. Raw duck eggshells were calcined at temperatures between 300 to 900 °C, for 1, 3, and 5 h. Both the raw and calcined duck eggshells were characterized by FTIR, STA, XRD, XRF, TEM, BET, a particle size analyzer, and an impedance analyzer. The proper calcination conditions are: 900 °C and 1 h, yielding calcium oxide with a purity of 99.06 % w/w. The calcium carbonate of the rhombohedral form (CaCO₃) transforms completely into the calcium oxide or lime of the face centered cubic form (CaO) at 900 °C, as shown by XRD diffraction patterns. The transmission electron microscopy (TEM) images of the calcium oxide reveal a moderately good dispersion of nearly uniform particles. The calcium oxide has a white color, a spherical shape, high porosity, and narrow particles size distribution. The percentage of ceramic yield of the calcium oxide is 53.53, as measured by STA (TG-DTA-DTG). The calcium oxide has a N₂ adsorption-desorption isotherm indicating the meso-porosity range. The dielectric constant and the electrical conductivity of the calcined calcium oxide are 35 and 1:0×10⁻⁶(Ω·m)⁻¹, respectively, at the frequency of 500 Hz.

The electrical conductivity of 1879.49 ± 13.87 S cm⁻¹ was achieved for PEDOT:PSS, which is the highest value reported to date.

Graphene-based materials, namely commercial graphene (cm-G), commercial graphene oxide (cm-GO), reduced graphene oxide (rGO), and synthesized graphene oxide (OIHM-GO), and their composites with polyindole (PIn) were used as sensing materials for methanol vapor. The synthesized graphene oxide was prepared by the optimized improved Hummers' method. rGO was prepared from cm-GO by two different methods: thermally mild reduction at 120 °C to yield T-rGO and chemical reduction by ascorbic acid to yield C-rGO. Graphene-based material/polyindole composites were prepared by in situ polymerization. In this report, the sensing responses were evaluated from the responsive electrical currents at room temperature. cm-GO showed the highest methanol response because it possessed the highest number of oxygen species, which act as the active sites. The relative electrical conductivity response of the in situ cm-GO/dPIn composite to methanol was the highest amongst the composites. The in situ OIHM-GO/dPIn composite possessed the high relative conductivity response of 81.89 ± 2.12 at 11.36 ppm, a sensitivity of 7.37 ppm⁻¹ with R² of 0.9967 in the methanol concentration range of 1.14–11.36 ppm, a theoretical LOD of 0.015 ppm, and repeatability of at least 4 cycles with good selectivity. This work represents the first report of the preparation and testing of graphene-based materials/polyindole composites as methanol sensors.