Liu Xiaoyu, Wu Wenhao, Lin Daohui, Yang Kun
Department of Environmental Science, Zhejiang University, Hangzhou, 310058, China.
Key Laboratory of Environmental Pollution and Ecological Health of Ministry of Education, Hangzhou, 310058, China.
Heliyon. 2024 Feb 2;10(3):e25729. doi: 10.1016/j.heliyon.2024.e25729. eCollection 2024 Feb 15.
Knowledge of organic compounds adsorption by adsorbents is essential for evaluating the environmental fates of organic compounds and removing them from the environment. Linear adsorption, as a supplement to the traditionally nonlinear adsorption, was previously proposed for the linear sorption of organic compounds on the mesoporous surface of carbon nanotubes (CNTs) in multi-solute system. However, CNTs are not the ideal adsorbent to verify the linear adsorption mechanism, because of their partition-like phase components such as mobile graphene layers that could be responsible for the linear sorption through linear partition mechanism instead, and thus the linear adsorption theory was argued. In this study, therefore, mesoporous activated carbon (MAC), widely accepted as the model free of partition phase components, was selected as an adsorbent to investigate the adsorption of typical organic compounds in the bi-solute system for verifying whether the linear adsorption phenomenon existed or not. The isotherm of nitrobenzene on MAC was changed from nonlinear to linear with 4-nitrophenol up to 1400 mg/L, and the linear isotherm slope decreased more as 4-nitrophenol concentration increased until 4000 mg/L. It agreed with the characteristics of adsorption (i.e., competition) but not partition (i.e., noncompetition), confirming the existence of linear adsorption. The isotherm linearity was attributed to the reduction of adsorption interactions by displacement and multilayer adsorption. Moreover, linear adsorption of apolar compounds on MAC could occur with apolar or polar competitors, while for polar compounds, linear adsorption could occur with only polar competitors. The observed linear sorption and the competition of organic compounds in the bi-solute system on MAC free of partition phase components verified that the linear adsorption existed, which gives a new insight into the adsorption theory for organic compounds. The results could provide better fundamental theory of adsorption for improving the accuracy of environmental risk assessment of organic pollution and enhancing the efficiency of organic pollution control in the environment.
了解吸附剂对有机化合物的吸附情况对于评估有机化合物的环境归宿以及从环境中去除它们至关重要。线性吸附作为对传统非线性吸附的补充,此前被提出用于多溶质体系中有机化合物在碳纳米管(CNT)介孔表面的线性吸附。然而,CNT并非验证线性吸附机制的理想吸附剂,因为其具有类似分配的相成分,如可移动的石墨烯层,这可能通过线性分配机制导致线性吸附,因此线性吸附理论受到质疑。因此,在本研究中,被广泛认为是无分配相成分模型的介孔活性炭(MAC)被选作吸附剂,以研究双溶质体系中典型有机化合物的吸附情况,从而验证线性吸附现象是否存在。当4-硝基苯酚浓度高达1400 mg/L时,硝基苯在MAC上的等温线从非线性变为线性,并且随着4-硝基苯酚浓度增加至4000 mg/L,线性等温线斜率下降得更多。这与吸附(即竞争)而非分配(即非竞争)的特征相符,证实了线性吸附的存在。等温线的线性归因于置换和多层吸附导致的吸附相互作用的降低。此外,非极性化合物在MAC上的线性吸附可与非极性或极性竞争剂发生,而对于极性化合物,线性吸附仅可与极性竞争剂发生。在无分配相成分的MAC上观察到的双溶质体系中有机化合物的线性吸附和竞争,验证了线性吸附的存在,这为有机化合物的吸附理论提供了新的见解。这些结果可为提高有机污染环境风险评估的准确性和增强环境中有机污染控制的效率提供更好的吸附基础理论。