Bioadsorption of methyl violet from aqueous solution onto Pu-erh tea powder

Chinese unique Pu-erh tea powder (PTP), with leached active ingredients, was used here to adsorb methyl violet (MV), a cationic dye. The effects of several variables on the removal of methyl violet were studied at 25 °C, including pH value, contact time, quantity of the adsorbent, initial concentration, and particle size of the adsorbent. The results showed that the particle size of the adsorbent significantly affected the adsorption process, and the nano-sized PTP particles had the best adsorption efficiency. The equilibrium data was analyzed using Langmuir, Freundlich, and Tempkin isotherms models. The pseudo-second-order kinetics model best explained the MV adsorption by PTP of any particle size. The intra-particle diffusion model was also used to analyze the adsorption process, and it was found that smaller adsorbent particles had a bigger boundary layer effect.