Adsorption of microcystin-LR by rice straw biochars with different pyrolysis temperatures

Abstract

Biochars derived from rice straw (RS biochars) at various pyrolysis temperatures (300 °C, 400 °C, 500 °C, 600 °C, and 700 °C) were studied to explore their adsorption ability of microcystin-LR (MC-LR) and to find out the associations between structural properties of different RS biochars and their adsorption capacity. The BET surface area determination was performed RS-700,biochar was found to contain the specific surface area of 360.9 m 2 g −1 , which was significantly larger than others. In addition, with the increase of pyrolysis temperatures, the larger and denser pore canals of RS biochars could be seen through the observation of surface morphologies and microstructures Moreover, the adsorption kinetic and equilibrium models were determined for different RS biochars. For all adsorbents, the adsorption kinetics were well fitted with the pseudo-second-order kinetic model ( R 2 :0.9455-0.9956) and the adsorption equilibrium were well described with Freundlich model ( R 2 >0.9). The removal of MC-LR was positively related to the pyrolysis temperatures of RS biochars. RS-700 biochar exhibited the maximal adsorption capacity of 10.96 μ g g −1 , which was more than 2 times as much as that of RS-300 biochar. And the adsorption amount of MC-LR increased substantially with the increasing initial concentration of MC-LR. Furthermore, the effect of pH value was also evaluated for the better understanding of adsorption mechanisms. • RS biochars pyrolyzed at different temperatures are used for the removal of MC-LR. • The higher the pyrolysis temperatures, the better the adsorption capacity. • RS biochars have better adsorption ability at lower pH .