助溶剂对有机酸在生物炭上的吸附的影响尚未得到很好的理解。为此,吸附(logKm,Lkg-1)的三种芳香酸(苯甲酸(BA,pKa=4.20),1-萘甲酸(1-NAPA,pKa=3.70),和9-蒽酸(9-ANTA,pKa=3.65)作为甲醇体积分数(fc=0.0、0.25和0.5)的函数进行评估,液体pH值(2.5和7.0),离子组成(CaCl2和KCl)和离子强度(0.005M,0.5M,和1MCaCl2)。使用巨大的芒草衍生的生物炭(ZPC为2.86)作为吸附剂。对于所有溶质,在pH2.5时测得的吸附系数(logKm)(即,pH
pKa)下影响变得明显。在fc=0.0(从0.005M增加到1M)时增加Ca2+浓度使该值增加0.32log单位Km。这些现象表明在液相中溶解的Ca2+的重要作用,很可能是由于芳族羧酸盐和生物炭表面之间形成了阳离子桥(即,[R-COO--Ca2+]-{Biochar-})。甲醇混合物的介电常数的降低可以加强该桥的形成。无论破产能力(σ)的程度如何,随着溶质芳香环数量的增加,Km按BA>1-NAPA>9-ANTA的顺序降低,其中fc=0.0。总之,生物炭的吸附潜力可以通过增加pH和fc而显著减弱,并且在不存在二价阳离子的情况下。
Influence of the cosolvent on the sorption of organic acids on biochar has not been well understood. For this purpose, the sorption (log Km, L kg-1) of three aromatic acids (benzoic acid (BA, pKa = 4.20), 1-naphthoic acid (1-NAPA, pKa = 3.70), and 9-anthroic acid (9-ANTA, pKa = 3.65) was evaluated as a function of methanol volume fraction (fc = 0.0, 0.25, and 0.5), liquid pH (2.5 and 7.0), ionic composition (CaCl2 and KCl) and ionic strength (0.005 M, 0.5 M, and 1 M CaCl2). A giant Miscanthus-derived biochar (ZPC of 2.86) was used as the sorbent. For all solutes, the sorption coefficients (log Km) measured at pH 2.5 (i.e., pH < pKa) tended to decrease with increasing fc, as expected from the
cosolvency model, while the result obtained at pH 7.0 was not fully explained by the same model. The log Km of 1-NAPA in the CaCl2 system was always greater than in the KCl system (p < 0.05) and the impact became pronounced at high pH (>pKa) with increasing fc. Increasing the Ca2+ concentration at fc = 0.0 (from 0.005 M to 1 M) enhanced the value by 0.32 log unit of Km. These phenomena indicate a significant role of dissolved Ca2+ in the liquid phase, most likely due to the formation of cation bridges between aromatic carboxylates and the biochar surface (i.e., [R-COO--Ca2+]-{Biochar-}). A decrease in the dielectric constant of the methanol mixture could fortify the formation of this bridge. Regardless of the degree of
cosolvency power (σ), as the number of aromatic rings of solutes increases, Km decreases in the order BA > 1-NAPA > 9-ANTA, where fc = 0.0. In conclusion, the sorption potential of biochar can be significantly weakened by increasing pH and fc, and in the absence of a divalent cation.