Effect of activated carbon microstructure and adsorption mechanism on the efficient removal of chlorophyll a and chlorophyll b from Andrographis paniculata extract

In order to reveal the effect of activated carbon (AC) properties on the adsorption of chlorophyll a (Chl a) and chlorophyll b (Chl b) in Andrographis paniculata extract, four commercial activated carbons were first tested and characterized. The results showed that activated carbon 1 (AC1) had the best surface area, pore structure and adsorption capacity. Therefore, adsorption isotherms, adsorption kinetics and adsorption mechanism were further carried out on AC1. The application of Langmuir model (R² > 0.978) and Freundlich model (R² > 0.977) indicated that the adsorption process of Chl a and Chl b on AC1 may be a complex adsorption process of single-layer and multilayer adsorption. The adsorption kinetics indicated that the pseudo-second-order kinetic model (R² > 0.999) was dominant and was mainly chemisorption. The intra-particle diffusion model (R² > 0.937) shows that the intra-particle diffusion is the rate-limiting step. The decrease of adsorption of AC1 to Chl a and Chl b due to the oxidation of acrylic acid proves the importance of π-π interaction.