Diffusion adsorption rates and the mass transfer mechanism controlled by intra-particle diffusion is studied for four graphene adsorbents with ethanol using THZ time-domain spectroscopy. Materials studied in this article, rGO, FG, GO, and GO-COOH, are characterized for pore size distribution. The adsorption evaluation steps through the entire process of volatilization, diffusion, and adsorption. THz-PSO, and the THz-DEM analysis are employed to determine whether diffusion serves as a rate-limiting factor in the adsorption process. The study concludes that hydrophobic interaction and hydrogen bonds were the determining factors affecting the adsorption rate.