Abstract Biochar, a cost-effective carbonaceous material, has shown great promise in many applications such as soil remediation and wastewater treatment. Citric acid in soil and water environments may affect interactions between biochar and organic contaminants (e.g., tetracycline). To evaluate the effect of citric acid on the adsorption of tetracycline onto biochars, this study investigated the adsorption behavior of tetracycline onto biochars of two different pyrolysis temperatures (300 and 450 °C, referred to as BC_300 and BC_450) in the present of citric acid, accompanying with the effects of solution pH and Cu2+. The results indicated that citric acid significantly inhibited the adsorption of tetracycline onto both biochars, that was mainly due to the multi-mechanisms including pore blocking effect, surface adsorption sites competition, and steric hindrance induced by citric acid. Moreover, citric acid more significantly suppressed the adsorption of tetracycline onto the two biochars at pH 9.0 than at pH 5.0 and 7.0. Because increasing pH could promote electrostatic repulsion between the negative tetracycline and the negatively charged surface of biochars. Cu2+ had greater enhancing effect on the sorption of tetracycline onto BC_300 than BC_450 via cation-bridging effect. Meanwhile, citric acid inhibited the adsorption of tetracycline onto BC_300 to a larger extent than the adsorption onto BC_450 in the presence of Cu2+. That is possibly due to BC_300 has more surface oxygen-containing functional groups than BC_450. Thus, the effect of coexisting citric acid needs to be taken into account when biochar is increasingly used as an amendment in soil and water systems.

中文翻译：

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柠檬酸对生物炭吸附四环素的抑制作用：溶液 pH 值和 Cu2+ 的影响

摘要 生物炭是一种具有成本效益的碳质材料，在土壤修复和废水处理等许多应用中显示出巨大的前景。土壤和水环境中的柠檬酸可能会影响生物炭和有机污染物（例如四环素）之间的相互作用。为评价柠檬酸对四环素吸附在生物炭上的影响，本研究考察了四环素在两种不同热解温度（300°C和450°C，简称BC_300和BC_450）的生物炭上在柠檬酸存在下的吸附行为。 , 伴随溶液 pH 值和 Cu2+ 的影响。结果表明，柠檬酸显着抑制了四环素在两种生物炭上的吸附，这主要是由于孔隙阻塞效应、表面吸附位点竞争、和柠檬酸引起的空间位阻。此外，柠檬酸在 pH 9.0 下比在 pH 5.0 和 7.0 下更能显着抑制四环素在两种生物炭上的吸附。因为增加 pH 值可以促进负四环素和生物炭带负电荷表面之间的静电排斥。Cu2+通过阳离子桥连作用对BC_300吸附四环素的作用大于BC_450。同时，在Cu2+存在下，柠檬酸对四环素在BC_300上的吸附抑制程度大于在BC_450上的吸附。这可能是由于 BC_300 比 BC_450 具有更多的表面含氧官能团。因此，当生物炭越来越多地用作土壤和水系统的改良剂时，需要考虑共存柠檬酸的影响。