[Sorption Mechanism and Site Energy Distribution of Acetaminophen on Straw-derived Biochar]

As one of the large dosages of pharmaceutical and personal care products (PPCPs), acetaminophen is widely present in the water environment and presents potential environmental risks. Therefore, it is necessary to study the removal mechanism of acetaminophen from the environment. Based on the high-value conversion demand of agricultural straw resources in China, straw-derived biochar prepared by pyrolysis has a good application prospect for the sorption and purification of acetaminophen in water. However, the sorption process and mechanism of straw-derived biochar for acetaminophen remain unclear. Four types of straw (rice, wheat, maize, and bean straw) were chosen as raw materials, and straw-derived biochars were prepared through the pyrolysis method at 400℃ and 500℃. The batch sorption experiments were used to study the sorption of acetaminophen to different sources and different pyrolysis temperature biochars. The effect of humic acid and pH on the sorption process was also studied. The results showed that:based on the Freundlich and site energy distribution models, the sorption of acetaminophen on biochar at 500℃ biochar was significantly higher than that at 400℃ biochar (the sorption coefficient K_F was 1.16-2.53 times higher), and 500℃ biochar had more high-energy sorption sites. For high-temperature pyrolysis biochar, the primary sorption mechanism was pore sorption and π-π effect; for low-temperature pyrolysis biochar, the primary sorption mechanism for removing acetaminophen was H-bonding. The presence of humic acid enhanced the sorption of acetaminophen, which was attributed to the strong interaction between the humic acid selected in the experiment and acetaminophen, thus promoting adsorption. The decrease in sorption capacity of biochar caused by the increasing pH was mainly attributed to the pore blockage resulting from the aggregation of acetaminophen molecules. The pore sorption and π-π interaction of acetaminophen on straw-derived biochar could be promoted by increasing pyrolysis temperature. These experiments on humic acid and pH show that straw-derived biochar is not affected by humic acid and has good sorption performance in a low pH environment.