Glyphosate is one of the most word widely used herbicides, which is a non-selective, broad-spectrum systemic herbicide used to control perennial and annual weeds, its action is based on the ability to inhibit the biosynthesis of aromatic amino acids necessary for the shikimic acid pathway in plant metabolism. Although it is considered as an agrochemical that can be used in pest control, there is evidence of harmful effects on the environment such as: an imbalance in the nutrients of the fertile soil, a drop in butterfly populations, harmful effects on pollinators, such as bees, on aquatic organisms (phytoplankton, annelids, fish, etc.) among others. In addition, it has been found to cause cytotoxicity and damage to human cells (Schweitzer and Noblet, 2018; Joseph et al., 2019; Dharwal et al., 2020; Xiao et al., 2021; Zhou et al., 2021). For this reason, the WHO announced that glyphosate is also a probable carcinogen to humans (Samuel et al., 2017; Pereira et al., 2021).

Taking into account the necessity of removing this contaminant from the water, technological alternatives have been used over time such as, adsorption, membrane filtration, biodegradation with microorganisms, chemical coagulation, clarification, chlorination, ozonation, and photolysis. All of the aforementioned have shown the possibility of purifying water contaminated with glyphosate, however, adsorption has been positioned as a method of interest due to its simple design of operation, using low-cost adsorbents, and presenting high efficiency. For this purpose, different adsorbent solids have been used: clays, metal-organic framework, biochar, activated carbons, and nanostructured materials, the latter being of great current interest, given their physical and chemical properties (Yang et al., 2017; Sen and Chattoraj, 2021).

The importance of the topic is very high, and for this reason, this review presents a summary and a discussion of the advances of recent research in the capture of glyphosate from water using nanostructured materials.

In recent years, nanoscience and nanotechnology have positioned themselves as two concepts of great relevance in the world. Nanotechnology has gained great strength in the scientific world, the ability to handle the matter on a nanometric scale has opened the possibility of obtaining nanomaterials in the form of metals, ceramics, polymeric materials, or composite materials, with increasingly specific properties, capable of supplying a large number of technological and industrial needs (Kumar et al., 2018; Saleh, 2020; Mazari et al., 2021; Xu et al., 2021). Within a large number of applications of nanomaterials, the removal of contaminants is an area in which they are currently being widely used, taking advantage of their properties and versatility. In this sense, different investigations have demonstrated their usefulness in the adsorption of glyphosate from water sources. The most commonly used nanomaterials for this purpose include, namely, nanoparticles of metal oxides, nanoparticles of metals Ag, Zn, Fe, carbon nanotubes, and nanocomposites among others.

Different investigations have been carried out on the methods of preparing nanomaterials that allow them to be obtained with the desired shape, size and, chemical composition. Said methods can be classified into two large groups: precipitation methods and immobilization methods. Within the first category are modified emulsion precipitation, hydrothermal processing/solvothermal processing, sol–gel approach, and aerosol methods. On the contrary, the immobilization methods stand out: the gel-citrate method, the Penchini method, and low temperature combustion synthesis (Kolahalam et al., 2019; Kalaivani, 2021). The preparation techniques, mentioned earlier, lead to obtaining different forms of nanomaterials, with variable sizes and properties. In addition, they allow to induce small modifications in the synthesis processes that lead to various types of morphologies, electrical and optical properties. After the synthesis of nanomaterials, with aim to establish their characteristics in terms of size, shape, crystalline structure, chemical composition, optical, magnetic, and mechanical properties, techniques such as scanning electron microscopy (SEM), microscopy transmission electron (TEM), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), electronic energy loss spectroscopy (EELS) (Kranz and Mizaikoff, 2019; Senthil Kumar et al., 2019; Merugu and Gothalwal, 2021). Thanks to the aforementioned techniques, the properties of nanomaterials can be known, which determine their behavior and performance in different applications worldwide.

In order to obtain nanomaterials that are highly specific for adsorbing glyphosate, it is important to understand the adsorption mechanism of this molecule, which is carried out through physical and chemical interactions between its functional groups (-COOH, -NH₂, and -PO(OH)₂) and the materials (Pereira et al., 2021). In addition, the surface modification viability increases adsorbate–adsorbent affinity based on the understanding of the interaction that occurs between the glyphosate molecule with the materials. In this sense, different studies have established the possible mechanisms that may occur in the process of adsorption of this herbicide, among them: intraparticular diffusion in the pores of the adsorbent, complexation, hydrogen bonding, electrostatic interactions, and Van der Waals interactions (Guo et al., 2018; Dissanayake Herath et al., 2019; Pereira et al., 2021) (Figure 1).

The intraparticle diffusion of glyphosate through the porosity of the materials is considered the initial mechanism by which this molecule interacts with the adsorbents. In this way, the existing porous network plays a fundamental role in the removal of the herbicide since it can facilitate or restrict its passage depending on the size of the porosity that the material has (Herath et al., 2016).

For its part, the physical adsorption of glyphosate is mainly attributed to different molecular interaction forces, including permanent dipole/induced dipole interactions and quadrupole interaction, Van der Waals dispersion forces, π+-π electron donor–acceptor interactions, and hydrogen bonds through H-donor–acceptor interactions (Herath et al., 2016; Li et al., 2018; Pereira et al., 2021). In addition, the chemical adsorption of this substance on the nanomaterials must be considered, which depends on the electrostatic attractions between the molecule and the surface of the adsorbent material, the charges acquired by these two components involved in the retention mechanism are related to the pH of the medium, as discussed in the previous section.

Likewise, it is important to consider that the glyphosate molecule can behave as a Lewis base, thanks to the free electrons of the N and O atoms that compose it, and that they can establish coordinated covalent bonds with different metals, forming thermodynamically stable complexes, such as glyphosate-Ca²⁺, glyphosate-Zn²⁺, glyphosate-Ni⁺, glyphosate-Fe³⁺, and glyphosate-Mg²⁺. The stability of the complexes formed with glyphosate decreases in the order Fe³⁺> Al³⁺> Cu²⁺> Zn²⁺> Fe²⁺> Mn²⁺> Ca²⁺> Mg²⁺ (Jiang et al., 2018; Serra-Clusellas et al., 2019; Pereira et al., 2021).

Although, so far, the adsorption mechanisms mentioned earlier are the ones considered for the removal of glyphosate in different nanostructured materials.

In the past 4 years, studies on the removal of glyphosate from water have increased, due to its toxicity and environmental impact (Yaqoob et al., 2020). Different conventional and unconventional experimental techniques have been investigated, involving physicochemical, biological, and advanced oxidation processes, among others, which are used separately or in combination for the treatment of wastewater containing glyphosate.

According to the investigations, each of these alternatives has left advantages and disadvantages, however, has not been possible to establish the strategy with the greatest potential to remove this herbicide from contaminated water sources.

One of the techniques for the removal of glyphosate from wastewater is adsorption, which is a simple strategy, easy to implement, with high efficiency, low cost, high pollutant removal rate, and low risk of secondary contamination. Of a large number of existing adsorbents, it has been shown that nanomaterials have great advantages in the removal of this herbicide through adsorption processes, however, this alternative has serious disadvantages, such as the difficulty of regeneration of the materials once saturated, giving origin to a new waste that must be treated and the existence of competition with other substances present in wastewater (Espinoza-Montero et al., 2020; Feng et al., 2020; Yaqoob et al., 2020).

Despite the aforementioned disadvantages, the use of nanomaterials for glyphosate adsorption has managed to position itself as a viable and promising technology to be implemented at a practical level in the world. For example, Soares et al. (2021), synthesized magnetic nanoadsorbents made up of magnetite coated with hybrid trimethylchitosan (TMC) silica shells, which were used in the removal of glyphosate from wastewater from the Aveiro treatment plant in Portugal, achieving a 76.8% elimination of the herbicide, reaching the concentration established normatively in the water quality standards. In addition, the nanoadsorbents are regenerated by 80% after four adsorption–desorption cycles, which shows the viability of using this technology in the remediation of water contaminated with glyphosate. For his part, Park et al. (2020), synthesized magnetite nanoparticles that act as scavengers of the herbicide, they can be reactivated by thermal treatment, allowing their cyclical use, achieving a removal in real surface waters of forests and fields in Germany of up to 92.5%, with which a lower concentration value is reached to the maximum allowed for this substance. Likewise, Páez et al. (2019), demonstrated the feasibility of using ZnO nanoparticles for the removal of between 70 and 90% of glyphosate present in simulated aqueous systems.

Until now, it has not been possible to establish a single and effective method for the treatment of water contaminated with glyphosate. For this reason, the scientific community is currently conducting studies aimed at the combined use of experimental techniques. For example, the combination of adsorption with the degradation of glyphosate by microorganisms and the combination of adsorption with advanced oxidation processes (Espinoza-Montero et al., 2020; Feng et al., 2020). In both cases, the use of nanomaterials has been of great interest given the exceptional properties that these present structures.

The main intention of this article was to give a mini-review of current knowledge related to nanomaterials and their use in capturing glyphosate from water. It was evidenced that, although, a large number of studies developed the preparation, functionalization, and use of nanoparticles, metal organic framework nanoadsorbents, nanotubes, nanobiochar, nanocomposites, graphene among other nanomaterials, in the removal of glyphosate from water have different aspects and have to be still investigated.

In accordance with the above, it's important that research be carried out on: the possibility of improving the structural, and chemical properties of nanoadsorbents, incorporating changes in the synthesis processes, or post-synthesis modifications that allow increasing the glyphosate retention capacity in the structures. Likewise, the optimization in the design of nanomaterials that leads to high efficiency and easy regeneration use in several adsorption–desorption cycles, which would promote the sustainability of this technology to be able to be implemented on a large scale worldwide.

In addition, most of the research carried out around this topic in the past 4 years is limited to the study of glyphosate adsorption in model solutions prepared at the laboratory level, leaving still to be explored the behavior and efficiency of nanostructures in real wastewater and in water bodies such as rivers, lakes, streams, etc. In this sense, there is still much to investigate on this topic, in such a way that the technological developments achieved so far can be scaled up and the existing limitations overcome.

In this sense, the combination of technologies for the treatment of water contaminated with glyphosate tends to be an alternative with a high potential to be studied in the coming years, with a view to achieving high efficiency in the elimination of the herbicide from the water, without generating substances secondary toxicities, under low-cost operating conditions, easy handling and implementation. For this reason, it is important to highlight that nanotechnology must continue to be incorporated into existing water treatment technologies since it has been proving to be very useful in the processes of removal and degradation of pollutants and is positioned as a promising alternative.

All authors listed have made a substantial, direct, and intellectual contribution to the work and approved it for publication.

This work was supported by the Universidad de los Andes, the Universidad Nacional de Colombia, and the Universidad del Tolima. JM-P also appreciate the support provided by the vice-rectory of research of the Universidad de los Andes (Bogotá, Colombia) with the program FONDO - PUBLICA TUS NUEVOS CONOCIMIENTOS O EXPÓN TUS NUEVAS CREACIONES.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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