Experimental Study On Sorption Of Benzotriazole To Biochars

Biochar has significant influence on migration and transformation of organiccontaminants in soil. But the sorption mechanisms of benzotriazole (BTA) on thebiochar are not clearly at present. Therefore, different biochars were selected assorbents in this study. Through laboratory batch experiments, the sorption mechanismof the BTA were discussed. The main conclusions are as follow.1. With increase of pyrolytic temperature, content of carbon increased andcontents of oxygen and hydrogen decreased. This indicates that the pyrolytic processof corncob caused the increase of carbon content and the removal of polar functionalgroups. Meanwhile, with increase of pyrolytic temperature, the pores of biochartransformed from macropores to micropores. This resulted in the gradual increase ofspecific surface area (SA) and micropore volume of biochars.2. With increase of pyrolytic temperature, the sorption mechanisms of BTA tobiochars change gradually from partition and adsorption to adsorption. Due to thedifference in the structural characteristics of biochars (e.g., ash, surface area), thesorption mechanism of corncob biochar is different from that of straw biochar.3. The solution pH influences existing species of BTA (BTAH2+，HBTA，BTA-)and subsequently affects the sorption behavior of BTA to biochars. When pH value inthe range of9.5-10.5, Kdvalues are small. Because that the BTA-is major proportionand which makes the effect of electrostatic repulsion strong.4. At certain pH, monovalent Na+had an inhibitory effect on the sorption ofBTA. The probable reason is that the hydrated radius of Na+(0.276nm) is smallerthan the molecular radius of BTA (0.4122nm). Therefore, Na+competed stronglywith BTA for the sorption sites on biochars. Bivalent Ca2+enhanced the sorption ofBTA to biochars. Surface complexation, ion exchange and the cation-bridge are theimportant mechanisms to promote the sorption of BTA.