The sorption of ionizable benzotriazole(BTA) to corncob biochars pyrolyzed at different temperature(i.e., 300oC, 500oC and 800oC) was investigated in this study. Biochars produced at higher temperature showed higher surface area, micropore volume and aromaticity. Consequently, the sorption of BTA changed from absorption to adsorption for biochars pyrolyzed at 300 oC and 800 oC, respectively. Solution p H affected speciation of BTA and surface charge properties of biochars. For BTA^0, H-bond, partition and micropore filling are dominant sorption mechanisms. For BTA-, it is suggested that negative charge-assisted H-bond plays an important role in sorption. Corncob biochar pyrolyzed at high temperature(e.g., 800 oC) showed the highest sorption affinity for BTA. Ca^(2+) in solution enhanced BTA^- and BTA^0 sorption through cation-bridge and surface complexation.
Soil-air partitioning is an important diffusive process that affects the environmental fate of organic compounds and human health. In this review, factors affecting the soil-air partitioning of polychlorinated biphenyls(PCBs) and total dichloro-diphenyl-trichloroethanes(p,p'- and o,p'- isomers of DDT, DDD, and DDE) are discussed. Hydrophobicity is an important factor that influences soil-air partition coefficients(KSA), and its effect can be explained through enthalpy of phase change for soil-air partitioning transfer(ΔHSA). For more hydrophobic compounds, a sharp increase in the KSA of PCBs and organochlorines can be seen in the early aging period. During the aging period, the temperature has a significant effect on the more hydrophobic organic compounds. The content and properties of soil organic matter influence the KSA of the target compounds. Generally, KSA decreases with increasing relative humidity in soils. The linear trend between KSA and temperature(T) changes at 0 °C. Freezing the air or soil in experiments would change the research results. On the basis of factors influencing soil-air partitioning, a multipleparameter(T, organic carbon fraction(fOC), and octanol-air partition coefficient(KOA)) model is put forward to predict the KSA values for PCBs and total DDTs.
Dissolved organic matter plays a critical role in affecting sorption properties of biochar for organic contaminants.In this study,dissolved humic acid(DHA)as a representative of dissolved organic matter and oak sawdust-derived biochar as a sorbent were prepared and characterized.Roles of DHA in sorption of benzotriazole(BTA),an emerging organic contaminant,to biochar in different electrolyte solutions were investigated.The results revealed the dual roles of DHA in BTA sorption to biochar.On the one hand,DHA can compete for sites and/or block pores available for BTA to inhibit the adsorption of BTA to biochar.On the other hand,the sorbed DHA on biochar can serve as additional partitioning phase to promote the partition of BTA.The finding was in accordance with the site energy distribution analysis of BTA sorption that the site energy of the highest occurring frequency in the DHA-BTA system was lower than that in the DHA-free system(3.41-10.4 versus 13.1-20.1 kJ mol^(−1)).The variation in apparent BTA sorption to biochar affected by DHA was thus a combination of changes in both its partition and adsorption properties.A modified Dual-mode model including the aqueous concentration of DHA was proposed to predict the effect of DHA on BTA sorption to biochar in different electrolyte solutions,which showed good prediction performance with most BTA sorption coefficient(K_(d),L g^(−1))deviations within 0.1 log unit.
