This study integrated batch experiments and theoretical calculations to understand the equilibrium adsorption and kinetic interaction of CdSeS/ZnS alloyed quantum dots nanoparticles (QDNPs) in sand porous media under different ionic strengths (ISs; 0.001–0.2 M NaCl). Our experimental results showed that equilibrium was reached for QDNP concentration between solid phase and bulk solution due to reversible adsorption of the QDNPs on sand surfaces. Derjaguin-Landau-Verwey-Overbeek (DLVO) interaction energy calculations showed that the repulsive energy barriers were low and primary energy wells were shallow (i.e., comparable to the average kinetic energy of a colloid) at all tested solution ISs. Hence, the QDNPs could mobilize into and simultaneously escape from the primary wells by Brownian diffusion, resulting in the reversible adsorption. Additional batch experiments confirmed that a fraction of adsorbed QDNPs was released even without any perturbation of system conditions. The release was more evident at a lower IS because the primary energy wells spanned more narrowly at low ISs and thus the nanoparticles have a higher possibility to escape out. The batch kinetic experiments showed that the adsorption of QDNPs followed first- and second-order kinetic interactions at low and high ISs, respectively. These results indicate that the well-known colloid filtration theory that assumes irreversible first-order kinetics for colloid deposition is not suitable for describing the QDNP adsorption. The findings in our work can aid better description and prediction of fate and transport of QDNPs in subsurface environments.

这项研究结合了批处理实验和理论计算，以了解在不同离子强度（ISs； 0.001–0.2 M NaCl）下，CdSeS / ZnS合金量子点纳米颗粒（QDNPs）在砂多孔介质中的平衡吸附和动力学相互作用。我们的实验结果表明，由于QDNPs在沙子表面的可逆吸附，固相和本体溶液之间的QDNP浓度达到了平衡。Derjaguin-Landau-Verwey-Overbeek（DLVO）的相互作用能计算表明，在所有测试溶液ISs上，排斥能垒都很低，一次能源井很浅（即，与胶体的平均动能相当）。因此，QDNPs可以通过布朗扩散迁移到初级井中并同时逃逸，从而导致可逆吸附。额外的批处理实验证实即使在不干扰系统条件的情况下，也会释放出一部分吸附的QDNP。在较低的IS下释放更明显，因为在较低的IS下一次能阱跨度更窄，因此纳米粒子更有可能逸出。间歇动力学实验表明，在低和高IS下，QDNPs的吸附分别遵循一阶和二阶动力学相互作用。这些结果表明，假设胶体沉积具有不可逆的一阶动力学的众所周知的胶体过滤理论不适用于描述QDNP吸附。我们工作中的发现可以帮助更好地描述和预测地下环境中QDNP的命运和运输。