• Abstract and Figures
• Public Full-text

www.nature.com/scientificreports OPEN Nanoremediation of As and metals polluted soils by means of graphene oxide nanoparticles Diego Baragaño 1*, Rubén Forján1, Lorena Welte2 & José Luis R. Gallego1 The capacity of graphene oxide nanoparticles (nGOx) to reduce or increase As and metals availability in polluted soils was compared with that of zero valent iron nanoparticles (nZVI). The nanomaterials used in this study were characterized by X-ray techniques, CHNS-O analysis, dynamic light scattering, and microscopy procedures such as atomic force microscopy. To assess the capacity of these materials to immobilize pollutants, feld samples of two soils were treated with nZVI and nGOx at a range of doses (0.2%, 1% and 5%). Availability tests were then performed. nGOx efectively immobilized Cu, Pb and Cd, but mobilized As and P (even at low doses), in the latter case irrespective of the simultaneous presence of high concentrations of metals. In turn, nZVI promoted notable immobilization results for As and Pb, a poorer result for Cd, and an increased availability for Cu. Soil pH and EC have been slightly afected by nGOx. On the whole, nGOx emerges as a promising option for mobilization/immobilization strategies for soil nanoremediation when combined with other techniques such as phytoremediation. Industrial activities have released large amounts of metals (Cu, Cd, Pb, Zn, etc.) and metalloids (especially As) into the environment and caused serious damage to the ecosystem1. In addition, metals and metalloids can endanger human health, as many of them are toxic even at very low concentrations, and even carcinogenic (e.g. As) and mutagenic2. Unlike organic pollutants that can degrade into harmless small molecules, the abovemen- tioned inorganic pollutants are recalcitrant to many biochemical reactions and thus particularly difcult to remove from soils3. Regarding As, several studies have confrmed that between 52,000 and 112,000 tons of this metalloid are released into the environment every year1,4,5. Many diseases, such as lung cancer, skin cancer, bladder cancer, etc., can be caused by contact with As6,7. Given that As is highly toxic for humans, and also for plants and animals, it has been classifed as a priority hazardous pollutant. Unlike the aforementioned metals, As is an anionic contam- inant. In this regard, simultaneous remediation of soils afected by anionic and cationic contaminants is a chal- lenge8; i.e., As remediation is even more complex in contexts of concurrent pollution with metals. In fact, classical remediation approaches attempt, among other objectives, to raise the pH of soils contaminated with cationic metals and thus stabilize them. However, this approach causes As to be solubilized9. Overall, the various remedi- ation strategies available focus on the disjuncture between immobilization and mobilization of the pollutants10. Soil nanoremediation by means of Fe-nanoparticles (nZVI) simultaneously reduces the availability of As and metals in polluted soils, as shown in recent pilot-scale in situ trials11, and by means of hybrid soil-washing tech- niques12. nZVI have a Fe° core surrounded by an oxide/hydroxide shell, which grows thicker as iron oxidation progresses. In addition, nZVI present a large specifc surface area, thus ofering a high adsorption capacity and high reactivity13,14. Te greater reactivity ofen ascribed to nanoparticles is the result of a larger overall surface area, greater density of reactive sites on the particle surfaces, and/or higher intrinsic reactivity of the surface sites15. Metal-nZVI interactions can be summarized as the following: reduction, adsorption, oxidation/reoxida- tion, co-precipitation and precipitation16. Other nanocompounds such as Fe-oxides17,18 have also been tested as an alternative to nZVI, although most studies have focused on water remediation19,20. In this context, graphene oxide nanoparticles (nGOx) have also been used in the aquatic environment to remove metals and other toxic elements6,21. However, to the best of our knowledge, the capacity of nGOx for soil remediation purposes has not been tested to date. 1INDUROT and Environmental Technology, Biotechnology and Geochemistry Group, Campus de Mieres, Universidad de Oviedo, Mieres, Asturias, Spain. 2Kleinscale S.L., Calle Montoro 4 9D, 28922, Alcorcón, Madrid, Spain. *email: [email protected] SCIENTIFIC REPORTS | (2020) 10:1896 | https://doi.org/10.1038/s41598-020-58852-4 1 www.nature.com/scientificreports/ www.nature.com/scientificreports Figure 1. Morphology of nGOx as observed in SEM images. Figure 2. AFM images of nGOx and topographic profles. Graphene oxide is a novel extremely oxidative form of graphene acquired by graphite chemical exfoliation22, and it is considered one of the most interesting materials to have emerged in recent years23. Te reactivity of nGOx is conferred by a large specifc surface area and the presence of a large amount of chemically bonded oxygen on the surface, including carbonyl and carboxyl groups at the layer ends and hydroxyl and epoxy groups on the base plane24–27. Tus, the functional groups containing oxygen atoms have lone electron pairs that can efciently bind a metal ion to form a metal complex via electrostatic interaction and coordination23,28. Also, the presence of these oxygen atoms allows hydrogen to bind to water molecules, thereby conferring nGOx solubility in water29. Tis property can promote reactivity with the pollutants in the solution phase of soils. Given the preceding considerations, the main objective of this study was to determine the efect of nGOx addition to soils in two distinct paradigmatic scenarios of As-polluted soils. To this end, nGOx was tested in a soil with high concentrations of As, Cd, Cu, Pb and Zn. Complementary experiments were also carried out soil from a brownfeld afected only by a high concentration of As. In addition, in both cases, we compared the efects of nGOx with those of nZVI, the most widely used type of nanoparticle in soil remediation. Results Characterization of synthesized graphene oxide nanoparticles. SEM revealed the characteristic fake shape of nGOx (Fig. 1). Te chemical analysis obtained by CHNS determination revealed the presence of 49.75% of C, 2.39% of H, 0.01% of N and 0.95% of S, and thus the oxygen content was estimated to be 46.9%. AFM analysis was used to determine fake thickness (Fig. 2). Several topographic profles were measured, and an average thickness of 1.5 nm was determined, which is consistent with the results of other studies30. Te XRD patterns of graphite and graphene oxide powders are shown in Fig. 3A. Te difraction peak of graphite at 26° corresponded to an interplanar spacing of (002) hexagonal layers of carbon atoms (d002 = 3.36A)31. However, this peak was absent in graphene oxide (GO), and another peak difraction appeared at the range 9.0–11.20°, corresponding to (001) plane of GO32. Te change in the XRD difraction peak from 26° to 10° indicates the transformation of graphite into graphene oxide33,34. SCIENTIFIC REPORTS | (2020) 10:1896 | https://doi.org/10.1038/s41598-020-58852-4 2 www.nature.com/scientificreports/ www.nature.com/scientificreports Figure 3. (A) XRD patterns of graphite and graphene oxide powders. (B) TGA analysis of nGOx. Te TGA plot consisted of three weight losses (Fig. 3B). First, a mass loss of approximately 11.9% occurred at 373 K, due to the elimination of absorbed water on the sample. Next, a loss of 30.5% was detected at 573 K, corresponding to the decarboxylation of graphene oxide. Finally, from 1073 K, successive decompositions of the material took place. Tese results are in agreement with Chung et al.25 and Sofa et al.35. Te specifc surface area determined through BET was 150 ± 2 m2.g−1 (n = 3). Similar results were obtained by other authors25. Te zeta potential of nZVI was −32.6 mV due to the polyacrylic acid (PAA) coating36. In contrast, nGOx are not covered, so the zeta potential value, −13 mV, corresponded to the functional groups of the material. Te pH value of nGOx was 2.5 in the three prepared suspensions, which indicates that is an acidic material. In contrast, nZVI presented a basic pH value of 11.5. Infuence of nZVI and nGOx on the available concentrations of Cu, As, Cd, Pb and Zn in the As-Metals polluted soil (AM). Te diferences between As and metals availability in the soil AM are shown in Fig. 4 (P < 0.05). Pb, Cd and Zn showed a similar behavior. Specifcally, Pb immobilization was remarkable and signif- icantly increased as the doses of nGOx and nZVI rose (Fig. 4A,D, P < 0.05). However, Cd availability was only slightly reduced at the highest nGOx dose, whereas Zn availability presented a signifcant reduction at only the highest doses of nGOx and nZVI (Fig. 4B,E, P < 0.05). In contrast, analysis of Cu and As availability revealed notable diferences between nGOx and nZVI yields (Fig. 4C,F, P < 0.05). For Cu, significant decreases were detected with increasing doses of nGOx (Fig. 4C). However, nZVI treatment did not afect Cu availability, except for a slight increase observed at the highest dose. Regarding As, opposite efects were observed, i.e., As availability was signifcantly increased as the dose of nGOx rose (Fig. 4C) while, on the other hand, it was clearly diminished afer nZVI addition, more notably as the dose increased (Fig. 4F). Infuence of nZVI and nGOx on the concentrations of available As in the As-polluted soil (A). As explained above, and unlike soil AM, soil A presented only As pollution. Tus, Fig. 5 shows only variation in As availability in the diferent treatments. Regarding nGOx, the available content of As was increased as the dose of the nanoparticles rose, this increase being particularly marked at the highest dose (64% increase in As SCIENTIFIC REPORTS | (2020) 10:1896 | https://doi.org/10.1038/s41598-020-58852-4 3 www.nature.com/scientificreports/ www.nature.com/scientificreports Figure 4.

Load more

  10

Copy Link