Impact of Flow Velocity on Transport of Graphene Oxide Nanoparticles in Saturated Porous Media

Abstract

Saturated column experiments were conducted to systematically examine transport of graphene oxide nanoparticles (GONPs) in sand porous media at different solution ionic strengths (ISs) with different flow velocities. Results show that deposition of GONPs increase with decreasing IS. However, the Derjaguin-Landau-Verwey-Overbeek (DLVO) interaction energy calculations using a surface element integration technique show that the energy barrier increases with increasing IS for the sheet-shaped colloids interacting with a planar sand surface. In contrast, the presence of nanoscale protruding asperities (NPAs) can cause a decrease in the energy barrier with increasing IS, which facilitates the attachment in primary minima at higher IS. At a given IS, increasing flow velocity increases attachment efficiency on the rough sand surfaces. Torque analysis shows that the maximum hydrodynamic torques are smaller than the adhesive torques, even for GONPs located on the NPAs where the adhesions are the lowest. Consequently, the attachment efficiency cannot be reduced by increasing flow velocity. Additional column experiments confirm that deposited GONPs cannot be detached by increasing flow velocity. Conversely, increase of flow velocity may enhance approaching of GONPs in low-flow regions such as concave areas of sand surfaces and subsequent attachment. Although it has been recognized in the literature that the presence of NPAs can cause decrease of attachment efficiency with increasing flow velocity for spherical colloids under both unfavorable and favorable chemical conditions, our results highlight a different role of surface roughness in attachment and detachment of sheet-shaped colloids under unfavorable conditions.

Delineating the Relationship between Nanoparticle Attachment Efficiency and Fluid Flow Velocity

“…For systems with significant secondary energy minima (as observed for NPs with organic surface coatings), a flow velocity increase can reduce secondary minimum deposition and enhance NPs’ primary minimum deposition via increasing kinetic energy. We observe that such enhancement underpins an increasing attachment efficiency phenomenon previously observed in prior studies. ,− …”

“…Based on this work, the role of organic coating material(s) seems significant but is not specifically delineated. Without organic surface coatings (natural organic matter and/or artificial organic coating), increasing attachment efficiency trends have been also reported by others. ,,,,,, …”

“…Intuitively, attachment efficiency can be expected to be negligible (constant) or even decrease with increasing flow velocity as hydrodynamics can hinder attachment. ,,, Computationally, Bai and Tien proposed a predictive framework for attachment efficiency in terms of flow velocity. , In their model, the hydrodynamic torque (from lift and drag forces) releases the deposited particles, resulting in decreasing attachment efficiency. Supporting this, several previous studies yielded results that were consistent with Bai and Tien’s predictions of decreasing attachment efficiency with respect to the flow. − However, there have been a number of conflicting observations recently reported. ,− An empirical attachment efficiency model (correlating 80 data sets), developed by Phenrat et al, implies that the attachment efficiency increases as a function of the flow velocity, contrary to the model of Bai and Tien. , For the Phenrat empirical model, only NPs that were surface-encapsulated with organic coatings were considered. Based on this work, the role of organic coating material(s) seems significant but is not specifically delineated.…”

“…Without organic surface coatings (natural organic matter and/or artificial organic coating), increasing attachment efficiency trends have been also reported by others. 17,26,28,30,32,33,35 Other system parameters, including surface heterogeneity, residual polymers/surfactants, and aggregation dynamics, have also been proposed as potentially sensitive variables when discerning unexpected attachment efficiency behavior(s). 1,2,29,36,37 In particular, physical heterogeneity, including nano-and microscale roughness, can influence particle retention and release.…”

Transport of Microplastic Particles in Saturated Porous Media

“…This was due to the reason that decreasing solution IS increased the repulsive energy barrier and decreased the depth of the secondary minimum (see Figure 1 and Table 2). Therefore, both the deposition at the primary and secondary minima were reduced at low ISs [61,62]. Note that even if the attachment occurred at physical and chemical heterogeneities, such attachment was still influenced by the solution IS under unfavorable chemical conditions [52].…”