Sand column experiments were performed under saturated conditions to investigate impact of humic acid (HA) on attachment of nC₆₀ nanoparticles (NPs) in NaCl and CaCl₂ at ionic strengths (ISs) from 1 mM to 100 mM and subsequent detachment via reducing solution IS. The attachment increased with increasing IS due to reduced repulsive Derjaguin-Landau-Verwey-Overbeek (DLVO) interaction energy and accordingly increased retention in primary energy wells. More attachments occurred in CaCl₂ compared to NaCl because Ca²⁺ exhibited greater charge screen ability and served as a bridging agent between the NPs and sand surfaces. The presence of HA significantly reduced nC₆₀ NPs attachment on sand surfaces (especially on nanoscale physical heterogeneities) in 10 mM NaCl and 1 mM CaCl₂ because of enhanced electrostatic and steric repulsions. Interestingly, although the HA did not cause reduction of attachment in 100 mM NaCl and 10 mM CaCl₂ compared to the case in absence of HA, the HA caused weak attachment of nC₆₀ on sand surfaces and then much more significant detachment by decreasing IS. The HA did not alter both attachment and detachment in 100 mM CaCl₂, because the Ca²⁺ at the high concentration caused formation of very stable complex of HA and NPs, and strong interaction of the complex with the sand surfaces via cation bridge. Our study highlighted that the HA can not only enhance the transport of NPs by inhibiting attachment as revealed in the literature, but also by the continuous capture and release of the NPs from surfaces in subsurface environments.

在饱和条件下进行砂柱实验，研究腐殖酸（HA）对离子强度（ISs）从1 mM到100 mM的nC ₆₀纳米颗粒（NPs）在NaCl和CaCl ₂中的附着的影响，然后通过还原溶液IS分离。由于减少的Derjaguin-Landau-Verwey-Overbeek互斥能量（DLVO），从而增加了对IS的附着，附着力也随之增加，并因此增加了对主要能量井的保留。与NaCl相比，CaCl _2中发生的附着更多，因为Ca ²⁺表现出更大的电荷筛选能力，并充当NP和沙面之间的桥连剂。HA的存在可显着降低nC ₆₀由于增强的静电和空间排斥力，NPs附着在10 mM NaCl和1 mM CaCl _2中的沙子表面上（尤其是纳米级物理异质性）。有趣的是，尽管与没有HA的情况相比，HA在100 mM NaCl和10 mM CaCl _2中的附着力没有降低，但是HA导致nC ₆₀在砂表面的附着力弱，然后通过降低IS导致显着的脱离。HA不会同时改变100 mM CaCl _2中的附着和脱离，因为Ca ²⁺在高浓度下，HA和NPs形成非常稳定的配合物，并通过阳离子桥与沙土表面形成强相互作用。我们的研究强调，HA不仅可以通过抑制文献中揭示的附着来增强NP的运输，还可以通过从地下环境中连续捕获和释放NP来增强NP的运输。