Green Graphene–Chitosan Sorbent Materials for Mercury Water Remediation

Abstract

The development of new graphene-based nanocomposites able to provide synergistic effects for the adsorption of toxic heavy metals in realistic conditions (environment) is of higher demand for future applications. This work explores the preparation of a green nanocomposite based on the self-assembly of graphene oxide (GO) with chitosan (CH) for the remediation of Hg(II) in different water matrices, including ultrapure and natural waters (tap water, river water, and seawater). Starting at a concentration of 50 μg L–1, the results showed that GO–CH nanocomposite has an excellent adsorption capacity of Hg (II) using very small doses (10 mg L–1) in ultrapure water with a removal percentage (% R) of 97 % R after only two hours of contact time. In the case of tap water, the % R was 81.4% after four hours of contact time. In the case of river and seawater, the GO–CH nanocomposite showed a limited performance due the high complexity of the water matrices, leading to a residual removal of Hg(II). The obtained removal of Hg(II) at equilibrium in river and seawater for GO–CH was 13% R and 7% R, respectively. Our studies conducted with different mimicked sea waters revealed that the removal of mercury is not affected by the presence of NO3– and Na+ (>90% R of Hg(II)); however, in the presence of Cl–, the mercury removal was virtually nonexistent (1% R of Hg(II)), most likely because of the formation of very stable chloro-complexes of Hg(II) with less affinity towards GO–CH.

The Era of Nanomaterials: A Safe Solution or a Risk for Marine Environmental Pollution?

“…An additional material employed for marine environmental remediation is the graphene oxide chitosan-based (GO-CH-based). It is a hydrogel with a 3D macrostructure developed taking advantage of the ability of GO to self-assembly in presence of the natural biopolymer such as chitosan [ 141 , 142 ]. Chitosan is a non-toxic and hydrophilic compound deriving from the alkaline deacetylation of chitin, which boosts the adsorption ability of the hydrogel.…”

“…Chitosan is a non-toxic and hydrophilic compound deriving from the alkaline deacetylation of chitin, which boosts the adsorption ability of the hydrogel. Nevertheless, GO-CH nanocomposites was not efficient in removing Hg from seawater [ 141 ]. On the other hand, chitosan-grafted carbon nanotubes (CTS-g-CNTs) are gaining more attention as a viable material to remedy contaminated seawater from radioactive Cs.…”

Chitosan and graphene oxide-based nanocomposites for water purification and medical applications: A review

“…"Chitosan nanocomposites," BioResources 16(4), 8525-8566. 8543 Bessa et al (2020) reported Hg (II) removal efficiency (97%) from ultra-pure water with a small mercury dose using CS-GO composite. Simultaneously, using the tap water, river, and seawater, removal efficiency was reduced to about 81%, 13%, and 7%, respectively.…”

Effective and simple removal of Hg from real waters by a robust bio-nanocomposite

“…The percentage of removal (R, %) in seawater was 81% after 6 h, which is relevant considering the competition for the surface's chemically active groups and the possible presence of stable mercury chloro-complexes. 12,13 Nevertheless, the GOPEI nanocomposite did not sustain its structure when immersed in water, and after several hours of vigorous magnetic stirring, it disintegrated into very small particulates. This requires the use of time-consuming centrifugation or filtration with a very fine filter to completely remove the GOPEI from the water matrix after treatment, which is not suitable for large-scale water remediation applications.…”