Aggregation and sedimentation of shattered graphene oxide nanoparticles in dynamic environments: a solid-body rotational approach

Abstract

Nanoparticle (NP) aggregation is typically investigated in either quiescent or turbulent mixing conditions; neither is fully representative of dynamic natural environments. In groundwater, complex interacting influences of advective-diffusive transport, pore tortuosity, and the arrival of aggregates from up-gradient pores impacts the aggregation behaviour of NPs, whereas in surface waters, continuous mixing of fresh particle and aged aggregate populations amends aggregation rates. To mimic such conditions, a cylinder reactor containing shattered graphene oxide NP (<100 nm) suspension was set to rotate with a Reynolds number (Re) close to one and with zero shear. Two main aggregation phases were then observed. Up to 250-350 min, NP remained near the rotational axis longer than in static conditions, giving rise to higher aggregation rates interpreted as an enhanced perikinetic aggregation and differential sedimentation due to mixing with resuspending aggregates. In this phase, a population-balance model estimated an attachment efficiency >5 times in the rotating system than in the static system. Later (5-13 h) aggregates collided with extensively each other, broke, and reformed on the rotating cylinder wall giving rise to larger, denser aggregates (>1 cm). These results thus shed new light on the differences in aggregation behaviour between porous media and other natural environmental systems compared to quiescent batch experiments.As production and application of graphene-based nanomaterials increase and taking into consideration their potential for environmental clean-up, concerns about their transport and fate in the environment are growing. A better understanding under realistic environmental conditions is required, in about process of aggregation which plays a fundamental role in long-term fate of nanomaterials, to help developing predictive models for managing the release of these nanomaterials. To investigate the impact of environmental dynamics on the aggregation processes of shattered graphene oxide nanoparticles, this study uses a solid-body rotational approach to mimic dynamics of interacting populations of nanoaggregate with different sizes and structures. This sheds light on the greater aggregation rates observed in the aquatic environments such as groundwater and surface water systems compared to those observed in simplifying laboratory batch experiments.

Transport and Retention of Free-Living Amoeba Spores in Porous Media: Effects of Operational Parameters and Extracellular Polymeric Substances

“…Regardless of the IS of the solution, the size distribution of spore suspensions did not change and the recorded images that focused on the bulk suspension in the parallel plate chamber show that the feed spores were mostly isolated from each other, indicating that no homoaggregation occurred before or after the test, excluding the impact of homoaggregation in the suspension on deposition behavior. Such phenomena were analogous to the observations reported in a similar study that noticed that dynamic conditions within porous media might induce aggregation of nanoparticles even though the homoaggregation might not happen in the quiescent batch experiments or the bulk at the same solution chemistry . With the advancement of the deposition process, such induced aggregation at low ionic strength might happen along with ripening, thus leading to a falling pattern in the plateau of the breakthrough curves (Figure a). , These results suggest that interaction between the attached spores to the upcoming spores played a more significant role in retention on the collector surface under low-IS conditions, compared to high-IS conditions.…”

“…Such phenomena were analogous to the observations reported in a similar study that noticed that dynamic conditions within porous media might induce aggregation of nanoparticles even though the homoaggregation might not happen in the quiescent batch experiments or the bulk at the same solution chemistry. 57 With the advancement of the deposition process, such induced aggregation at low ionic strength might happen along with ripening, thus leading to a falling pattern in the plateau of the breakthrough curves (Figure 3a). 58,59 These results suggest that interaction between the attached spores to the upcoming spores played a more significant role in retention on the collector surface under low-IS conditions, compared to high-IS conditions.…”

Comparison of a new mass-concentration, chain-reaction model with the population-balance model for early- and late-stage aggregation of shattered graphene oxide nanoparticles

“…Therefore, the rates are updated in every time steps of the numerical solution. The variation of over time through a ave,t might help better constraining the dynamic cascading aspect of the aggregation if the model is applied in realistic environmental condition [15]. It should be noted that this model considers the Brownian motion through τ, such that increasing temperature and decreasing size can promote thereby the aggregation rate.…”

“…One of the critical phenomena that controls NP fate and transport as well as their reactions and functionality in environmental and engineering systems is aggregation [12][13][14][15][16][17][18][19][20][21]. Efficient integration of aggregation models with other NP fate, transport, and reaction models is crucial to enable the estimation of NP release into aquatic environments and designing NP application strategies [22][23][24].…”

“…Recent investigation of the NP aggregation within systems such as porous media and surface waters revealed the need for further development of aggregation models to take realistic environmental complexity arisen from local particle resuspension into account [15]. There are several complex interactions which require consideration in a reactive transport model along with aggregation including NP reaction with existent pollutants [33,34], interaction with background colloids and natural organic matter (hetero-aggregation), [16,[35][36][37], and with porous media [21,25], as well as NP dissolution, sulfidation, and sedimentation [38][39][40].…”