Transport Of Graphene Oxide Nanoparticles Research Articles

Effects of Temperature, Ionic Strength and Humic Acid on the Transport of Graphene Oxide Nanoparticles in Geosynthetic Clay Liner.

With the wide application of graphene oxide nanoparticles (GONPs), a great amount of GONP waste is discarded and concentrated in landfills. It has been proven that GONPs have strong toxicity and could gather toxic substances due to their high adsorption capacity. GONPs will seriously pollute the surrounding environment if they leak through the geosynthetic clay liner (GCL) in landfills. To investigate various factors (temperature, ionic strength (IS) and humic acid (HA)) on the transport and retention of GONPs in the GCL, a self-designed apparatus was created and column tests were carried out. The experimental results show that GONPs could be transported through the GCL. The mobility and sorption ratio of GONPs in GCL decreased with an increase in temperature and IS, and increased with an increase in HA. The temperature had little effect on the deposition ratio of GONPs in the GCL. The deposition ratio of GONPs in the GCL increased with IS, and decreased with an increase in HA. The transport of GONPs in GCL, glass beads and quartz sand was compared, and the results show that the retention ability of the GCL is much better than other porous materials. The experimental results could provide significant references for the pollution treatment in landfills.

Effects of phosphate on the transport of graphene oxide nanoparticles in saturated clean and iron oxide-coated sand columns

In this study, transport behaviors of graphene oxide (GO) in saturated uncoated (i.e., clean sand) and goethite-coated sand porous media were examined as a function of the phosphate. We found that phosphate enhanced the transport of GO over a wide range of solution chemistry (i.e., pH 5.0–9.0 and the presence of 10 mmol/L Na+ or 0.5 mmol/L Ca2+). The results were mainly ascribed to the increase of electrostatic repulsion between nanoparticles and porous media. Meanwhile, deposition site competition induced by the retained phosphate was another important mechanism leading to promote GO transport. Interestingly, when the phosphate concentration increased from 0.1 to 1.0 mmol/L, the transport-enhancement effect of phosphate in goethite-coated sand was to a much larger extent than that in clean sand. The observations were primarily related to the difference in the total mass of retained phosphate between the iron oxide-coated sand and clean sand columns, which resulted in different degrees of the electrostatic repulsion and competitive effect of phosphate. When the background solution contained 0.5 mmol/L Ca2+, phosphate could be bind to sand/ goethite-coated sand surface by cation bridging; and consequently, promoted competition between phosphate and nanoparticles for deposition sites, which was an important mechanism for the enhanced effect of phosphate. Moreover, the DLVO theory was applicable to describe GO transport behaviors in porous media in the absence or presence of phosphate. Taken together, these findings highlight the important status and role of phosphate on the transport and fate of colloidal graphene oxide in the subsurface environment.

Effects of pressure on graphene oxide nanoparticle deposition and transport in GCLs

The leakage of graphene oxide nanoparticles (GONPs) in landfills poses a great threat to the environment. A series of column tests were conducted to investigate the effects of hydrostatic pressure, input concentration and bentonite modification on the transport of GONPs in the geosynthetic clay liner (GCL). The experimental results show that pressure affected the mobility of GONPs at high input concentrations, while this effect was smaller at low input concentrations. The retention of GONPs in a GCL containing thermally modified bentonite (TMB) and sodium-modified bentonite (SMB) was greater than that in a GCL containing unmodified bentonite. The type of TMB, SMB and unmodified bentonite was granular bentonite. The sorption and deposition of GONPs in GCLs were also investigated. Pressure affected the deposition of GONPs by decreasing the permeability of the GCL and delaying the transport of GONPs but had little effect on the sorption of GONPs. The dependence of GONP retention on pressure was greater at high input concentrations than that at low input concentrations. The sorption of GONPs in TMB and SMB was much greater than that in unmodified bentonite because of the greater specific surface area and lower negative zeta potentials of TMB and SMB.

Transport of graphene oxide nanoparticles in saturated kaolinite- and goethite-coated sand columns: effects of low-molecular-weight organic acids.

The effects of low-molecular-weight organic acids (LMWOAs) on the transport of graphene oxide nanoparticles in saturated kaolinite- and goethite-coated sand columns were studied. Acetic acid, glycolic acid, malonic acid, and tartaric acid were chosen in the experiments. LMWOAs enhanced the mobility of GO by electrostatic/steric repulsion. In addition, they competed with GO for limited deposition sites on grain surfaces. The effects of organic acids on the transport of GO strongly depended on organic acid species. In general, the transport enhancement effects followed the order of tartaric acid > malonic acid > glycolic acid > acetic acid; this difference may be related to the number and type of functional groups of organic acids. Different LMWOAs enhanced the transport of GO in goethite-coated sand to a larger extent than did in kaolinite-coated sand under the test conditions; this was likely related to the differences of physicochemical characteristics between goethite and kaolinite. Organic acids significantly inhibited the deposition of GO at 0.5 mM Ca2+; this was possible that Ca2+ enhanced adsorption of organic acids by complexing with the surface O-functionalities of both LMWOAs and sand grain. Consequently, more organic acid molecules competed with GO for deposition sites on grain surfaces. Additionally, a two-site transport model was used to fit the transport data. Our findings have important implications for the understanding of the deposition and fate of GO in soil especially in rhizosphere environments where various low-molecular-weight organic acids are active.

Effects of low-molecular weight organic acids on the transport of graphene oxide nanoparticles in saturated sand columns

The impact of low-molecular weight organic acids (LMWOAs) on the transport of graphene oxide (GO) nanoparticles in saturated quartz sand was investigated. The different LMWOAs such as acetic acid, glycolic acid, malonic acid, and tartaric acid were used in experiments. The effects of LMWOAs on the transport of GO were markedly dependent upon organic acid species. In general, the transport enhancement effects followed the order of tartaric acid > malonic acid > glycolic acid > acetic acid, the regular pattern might be related to amount and type of functional groups of LMWOAs. Additionally, the different enhanced ability of LMWOAs was determined by their molecular weight. In the presence of Na+, the main deposition mechanism was ascribed to steric hindrance and competition between LMWOA and GO for deposition sites on grain surfaces under acidic conditions (i.e., pH 4.0 and 5.0). Batch adsorption experiments indicated the extents of competitive adsorption between LMWOAs and GO on quartz sand. In addition, the DLVO theory was not applicable to describe the transport of GO in the presence of LMWOAs at pH 5.0. Nevertheless, electrostatic and steric repulsion, existing between GO and sand grains, were the most important deposition mechanisms under the neutral condition (i.e., pH 7.0). When Ca2+ was the main cation in the background solution, the transport enhancement effects followed quite similar order to those of Na+, mainly due to different complexing strength of organic acids.

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

Core Ideas We examined the influence of flow velocity on transport of graphene oxide nanoparticles (GONPs). Attachment efficiency (α) increased with increasing flow velocity for GONPs. Hydrodynamic shear cannot release the attached GONPs, even from nanoscale asperities. Increasing flow velocity increased attachment of GONPs at concave surfaces. 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.

Cotransport of Graphene Oxide Nanoparticles and Kaolinite Colloids in Porous Media

This study examines the influence of pH and ionic strength ( $$I_{\mathrm{S}}$$ ) on the cotransport of graphene oxide (GO) nanoparticles and kaolinite (KGa-1b) colloids. Several flowthrough experiments were conducted in water-saturated columns, packed with either glass beads or quartz sand, in order to determine the transport behavior of GO and KGa-1b independently, as well as the cotransport behavior of GO together with KGa-1b. Various water chemistry conditions ( $$\hbox {pH}=4, 7, 10$$ and $$I_{\mathrm{S}}=7, 12, 27\,\hbox {mM}$$ ) were considered. Collision efficiencies were calculated using the classical colloid filtration theory. Interaction energy profiles between GO nanoparticles or KGa-1b colloids and glass beads or quartz sand were constructed for the various experimental conditions, by using measured zeta potentials and applying the classical Derjaguin–Landau–Verwey–Overbeek theory. The cotransport experimental breakthrough data suggested that by lowering the pH, the retention of GO nanoparticles is enhanced, due to a possible increase in heteroaggregation between GO nanoparticles and KGa-1b colloids. Also, by increasing the $$I_{\mathrm{S}}$$ values, the retention of GO nanoparticles was slightly increased. The mass recovery of GO nanoparticles was reduced, and the transport of GO nanoparticles was retarded in the presence of KGa-1b colloids. Furthermore, the retention of GO nanoparticles was greater for columns packed with quartz sand than glass beads.

Inhibited transport of graphene oxide nanoparticles in granular quartz sand coated with Bacillus subtilis and Pseudomonas putida biofilms

Increasing production and use of graphene oxide nanoparticles (GONPs) boost their wide dissemination in the subsurface environments where biofilms occur ubiquitously, representative of the physical and chemical heterogeneities. This study aimed at investigating the influence of Gram-positive Bacillus subtilis (BS) and Gram-negative Pseudomonas putida (PP) biofilms on the transport of GONPs under different ionic strengths (0.1, 0.5, and 1.0 mM CaCl2) at neutral pH 7.2 in water-saturated porous media. Particularly, the X-ray micro-computed tomography was used to quantitatively characterize the pore structures of sand columns in the presence and absence of biofilms. Our results indicated that the presence of biofilms reduced the porosity and narrowed down the pore sizes of packed columns. Transport experiments in biofilm-coated sand showed that biofilms, irrespective of bacterial species, significantly inhibited the mobility of GONPs compared to that in cleaned sand. This could be due to the Ca2+ complexation, increased surface roughness and charge heterogeneities of collectors, and particularly enhanced physical straining caused by biofilms. The two-site kinetic retention model-fitted value of maximum solid-phase concentration (Smax2) for GONPs was higher for biofilm-coated sand than for cleaned sand, demonstrating that biofilms act as favorable sites for GONPs retention. Our findings presented herein are important to deepen our current understanding on the nature of particle-collector interactions.

The rapid coagulation of graphene oxide on La-doped layered double hydroxides

Since graphene oxide (GO) has been found to be one of the toxic graphene-based nanomaterials, the environmental behavior of GO has been studied extensively in aqueous solution systems. In this work, the large ionic radius lanthanum (La) was doped onto the layered double hydroxides (LDHs), which was conducive to remove the negatively charged GO. The results showed that the coagulation of GO on La-doped LDHs was dependent on pH and the types of electrolytes. After calcined at 400°C for 4h, the maximum GO removal capacities could reach 565.8mg/g on Mg/Al/La-CLDHs and 558.6mg/g on Ca/Al/La-CLDHs at GO initial concentration of 120mg/L and LDHs content of 0.2g/L. The short equilibrium time and high removal capacity suggested the huge advantage of LDHs in practical applications. More importantly, the La-doped LDHs could still exhibit high removal capacities after five cycles, indicating that the La-doped LDHs hold good reusability and could be used for GO pollution cleanup from water. The coagulation of GO on La-doped LDHs was mainly dominated by electrostatic attraction and hydrogen bond. These findings were useful to understand the environmental fate and transport of GO nanoparticles in aqueous systems.

Biofilms and extracellular polymeric substances mediate the transport of graphene oxide nanoparticles in saturated porous media

Understanding the fate and transport of graphene oxide nanoparticles (GONPs) in the subsurface environments is of crucial importance since they may pose potential risks to the environment and human health. However, little is known about the significance of biofilm on mobility of GONPs in the subsurface. Here we investigated the transport of GONPs in saturated sand coated with Bacillus subtilis (Gram-positive) and Pseudomonas putida (Gram-negative) biofilms, and their secreted extracellular polymeric substances (EPS) under environmentally relevant ionic strengths (1–50mM NaCl) at pH 7.2. Our results showed that irrespective of bacteria type, greater retention of GONPs occurred in biofilm-coated sand compared to clean sand, likely attributed to the increased surface roughness and physical straining. However, EPS showed negligible influence on GONPs transport, which was inconsistent with the findings in the presence of biofilms, while they exhibited comparable ζ-potentials. The different retention phenotype of GONPs in the presence of EPS was induced by hydration effect and steric repulsion. A two-site kinetic retention model well-described the transport of GONPs in porous media covered with different surface coatings, which proves the applicability of mathematical model in predicting nanoparticles’ mobility in the subsurface environments, when considering the potential effects of biofilm and EPS.

Stability and Transport of Graphene Oxide Nanoparticles in Groundwater and Surface Water.

The effects of groundwater and surface water constituents (i.e., natural organic matter [NOM] and the presence of a complex assortment of ions) on graphene oxide nanoparticles (GONPs) were investigated to provide additional insight into the factors contributing to fate and the mechanisms involved in their transport in soil, groundwater, and surface water environments. The stability and transport of GONPs was investigated using dynamic light scattering, electrokinetic characterization, and packed bed column experiments. Stability results showed that the hydrodynamic diameter of the GONPs at a similar ionic strength (2.1±1.1 mM) was 10 times greater in groundwater environments compared with surface water and NaCl and MgCl2 suspensions. Transport results confirmed that in groundwater, GONPs are less stable and are more likely to be removed during transport in porous media. In surface water and MgCl2 and NaCl suspensions, the relative recovery was 94%±3% indicating that GONPs will be very mobile in surface waters. Additional experiments were carried out in monovalent (KCl) and divalent (CaCl2) salts across an environmentally relevant concentration range (0.1-10 mg/L) of NOM using Suwannee River humic acid. Overall, the transport and stability of GONPs was increased in the presence of NOM. This study confirms that planar "carbonaceous-oxide" materials follow traditional theory for stability and transport, both due to their response to ionic strength, valence, and NOM presence and is the first to look at GONP transport across a wide range of representative conditions found in surface and groundwater environments.

Factors controlling transport of graphene oxide nanoparticles in saturated sand columns

The authors conducted column experiments and a modeling study to understand the effects of several environmental factors on the aggregation and transport of graphene oxide nanoparticles (GONPs) in saturated quartz sand. The GONPs were negatively charged and stable under the test conditions (0-50 mM NaCl; pH 4.8-9.0), and the Derjaguin-Landau-Verwey-Overbeek (DLVO) calculation indicated that deposition of GONPs was under unfavorable attachment conditions. The GONPs exhibited high mobility even at an ionic strength of 25 mM NaCl. The transport of GONPs was insensitive to the changes of pH (from 5.1 to 9.0), but the presence of 10 mg/L Suwannee River humic acid (SRHA) considerably enhanced transport at high ionic strength (35 mM NaCl), likely via enhanced steric repulsion and significantly inhibited stacking of GO flakes. Varying flow velocity also enhanced transport at high ionic strength. In general, GONPs exhibit greater mobility compared with other carbon nanoparticles because the aggregation and transport of GONPs are more resilient to changes in solution chemistry and hydrodynamic forces that favor aggregation and deposition of nanoparticles. A 2-site transport model incorporating both the blocking-affected attachment process and straining effects can effectively model the transport of GONPs. The high mobility of GONPs should be given full consideration in assessing their environmental risks.

Transport of graphene oxide nanoparticles in saturated sandy soil.

We examined the transport properties of graphene oxide nanoparticles (GONPs) in saturated sandy soil, under different solution chemistry conditions and flow velocities. GONPs exhibited high mobility in soil, even at 50 mM NaCl. While at relatively high ionic strength GONPs were less mobile in soil than in quartz sand, the differences were not significant. At a concentration of 0.5 mM, Ca(2+) significantly inhibited the transport of GONPs in soil, but only slightly inhibited the transport in quartz sand. This was because by complexing with the surface O-functionalities of both GONPs and soil components, Ca(2+) could enhance the aggregation of GONPs and bridge GONPs and soil grains. Increasing pH from 4 to 9 only slightly enhanced the transport of GONPs in soil, probably because the mobility of GONPs was already high at low pH. The presence of 10 mg L(-1) Suwannee River humic acid significantly enhanced the transport of GONPs in quartz sand at 35 mM, but only had a small effect for the transport in soil. This was possibly linked to the much smaller grain sizes and much more heterogeneous nature of the soil. Flow velocity had marked effects on the transport in soil, but essentially no effects on the transport in quartz sand. A two-site transport model incorporating both the blocking-affected attachment process and straining effects can effectively model the transport of GONPs. The high mobility of GONPs may have important implications for their environmental fate and effects.

Effects of Solution Chemistry on the Transport of Graphene Oxide in Saturated Porous Media

A transport study was performed in saturated porous media through a packed bed column to simulate fate of graphene oxide nanoparticles (GONPs) in the subsurface environment. Transport experiments, along with mass balances and column dissections, were conducted as a function of ionic strength (IS, 10(-3)-10(-1) M). Additionally, an extensive evaluation of the electrokinetic properties and hydrodynamic diameters of GONPs were determined as a function of IS and pH. The measured hydrodynamic diameter and the electrophoretic mobility (EPM) of GONPs indicated an insensitivity to pH, although IS did play a role. Results from a stability study indicated that the hydrodynamic diameter of GONPs was stable and unchanging at the lower range of IS (10(-3) and 10(-2) M) then became unstable when IS ≥ 10(-1.5) M KCl was achieved. Specifically, for IS ≥ 10(-1.5) M KCl, the hydrodynamic diameter became greater and showed a larger size range of particles than at the lower IS range (10(-3) and 10(-2) M). In addition, the EPM of GONPs became less negative over the IS range of 10(-3) and 10(-2) M KCl. Furthermore, GONPs were found to be increasingly mobile for IS ≤ 10(-2) M KCl. When GONPs were passed through the packed bed column at 10(-2) and 10(-1) M KCl, 5% and 100% of the GONPs were retained in the column, respectively. Finally, mass balances and column dissections revealed that in the first cm of the column 7% and 95% of the GONPs were deposited at 10(-2) and 10(-1) M KCl, respectively, confirming that the transport of GONPs is a function of IS. The fraction of GONPs eluted during the transport experiments provides insight into the contribution of aggregation and reversibly bound fraction of GONPs in saturated porous media.

Nanotechnology-Related Environment, Health, and Safety Research: Examining the National Strategy

Pick up a tube of sunscreen, a tennis racquet, an iPod, or any number of other consumer products, and there’s a good chance that it’s been “nano-enabled,” meaning it contains nanoscale particles designed to give it some beneficial feature. An estimated $147 billion worth of nano-enabled commercial and consumer products were sold in 2007, according to Lux Research, a market analysis firm in New York City. Citing the firm’s latest estimates, Lux analyst David Hwang predicts that figure could top $3.1 trillion by 2015, reinforcing a broad view that nanotechnology is fueling a new industrial revolution. Yet nanotechnology’s spread through the market has been met with mounting concerns over the potential human health effects of these miraculous materials. Because of their small size—100 nano-meters or less—nanomaterials have unique physical properties that can influence their uptake, distribution, and behavior in the body. Indeed, some nano-particles have been shown to penetrate into cells, where they can trigger inflammatory responses and oxidative stress. Canada and California recently took the unprecedented step of imposing mandated disclosure requirements on nanomaterial use and toxicity assessment. Issued 29 January 2009, Canada’s law targets domestic companies and institutions that manufacture or buy more than 1 kilogram of nanomaterial per year. According to the new regulations, these entities must now reveal how much nanomaterial they use, how they use it, and what they know about its toxicity. California’s law, issued 2 February 2009, limits its scope to carbon nanotubes, a class of nanomaterial used in electronics, optics, and biomedical applications. Under the new regulation, by February 2010 companies that manufacture, import, or export carbon nanotubes in California must disclose information about the toxicity and environmental impacts of their products. Meanwhile, experts in nanotoxicology and risk assessment have become increasingly polarized, represented on one side by the National Research Council (NRC) and on the other by the National Nanotechnology Initiative (NNI), a government-wide collaboration coordinated by the National Science and Technology Council in the Executive Office of the President. In February 2008, the Nanotechnology Environmental and Health Implications (NEHI) Working Group of the NNI released a document titled Strategy for Nanotechnology-Related Environmental, Health, and Safety Research. This document is meant to present the U.S. government’s agenda for studying nano-particle hazards, and describes 246 related projects that were ongoing in 2006, representing a combined investment for that year of $68 million. The document also purports to “address prioritized research areas . . . and to advance knowledge and support risk decision-making—both of which are essential for the responsible development of nanotechnology.” Clayton Teague directs the National Nano-technology Coordination Office, which was responsible for drafting the federal strategy. He says the strategy was developed in extensive consultation with regulatory agencies, research organizations, the business community, and nongovernmental organizations. “We believe the strategy represents needs and agreements about what the agencies plan to do,” he says. “Funding agencies are telling us that they’re using the document to formulate solicitations for future research in this area.” But on 25 February 2009, a panel assembled by the NRC issued its own report, describing what it calls serious shortcomings in the strategy document. According to the NRC panel, which was assembled at the request of the NNI, the strategy exposes weaknesses in the government’s understanding of potential nanotechnology risks today and does not adequately address how they will be assessed in the future. NRC panel member Mark Weisner, a professor of civil and environmental engineering at Duke University, claims that many of the research programs described in the NNI’s document don’t actually address environmental, health, and safety (EHS) concerns. “If you take this portfolio at face value, it overstates the true level of effort in federally financed [nano-technology-related] EHS research,” he says.