**4. Nanoremediation**

Tague defines remediation as "all measures taken for treatment of damaged wells for restoring an optimal performance" [4]. Nowadays, the environment requires those actions for the protection of human health and all living systems on Earth. Environmental remediation consists of the eradication, removal, or transformation of contaminants from natural resources [43]. Although remediation is a complex task, nanoremediation has emerged as an optimal alternative for the removal of pollutants from different waters (groundwater, surface water, and residual water), soil, air, and sediments [43].

*Trace Metals in the Environment - New Approaches and Recent Advances*

**D Main methodology Ref.**

colorimetric reader

the quenching of QD

aqueous extract of *Vigna mungo* beans for

in water using ion

removal of metals and degradation of organic pollutants. The adsorbed metal enhanced the photocatalytic degradation of organic Xiao et al., Gan eta al., and Cao et al. [29–31]

Devaiah Chonamada

Choudhary et al. [35]

Chu et al. [36]

Dhandole et al. [37]

Zendehdel et al. [38]

Jin et al. [39]

et al. [34]

0D Smartphone-based

0D Detection through

system

emission

reduction

0D Detection of residuals

metals

2D in 2D Quantification and

pollutants

bacteria

metals and removal of

detection of Cd(II) and Pb(II) in real samples from lake and tap water

0D in 3D Quantification of

2D in 3D Electrochemical

0D Green approach using

**Ion Nanostructure and sizes**

Hg2+ Spherical silver

Spherical gold nanoparticles ~15 nm

Mn–doped ZnS quantum Dots ~5 nm

nanoparticles (10–30) nm

Core-shell nanoparticles. ZnS coated up conversion nanoparticles 60 nm in diameter and 20 nm in the shell

Rhodium/ antimony co-doped TiO2 nanorod and titanate nanotube ~20 nm

Functionalized Fe3O4/ NaP zeolite nanocomposite ~30 nm

SnS-decorated Bi2O3 nanosheets (3–4) nm

Cd2+ Hg2+ Cu2+

Hg2+ Pb2+ Cd2+

Ag+ Cu2+ Hg2+

Pb2+ Cd2+ Cu2+ Zn2+

Pb2+ Cd2+

Pb2+ Cd2+

**Table 1.**

of solvent, energy, time, and the release of odd substances to the environment. An extract of *Vigna mungo* beans was used as a reducing agent of nanoparticles to minimize the use of traditional chemical compounds and solvents; the detection

*New methodologies using nanostructures for sensing and quantification of heavy metals.*

In previous investigations, two processes were combined to enhance the implementation of nanostructures on heavy metal detection [36–38]. The main advantage of this approach is that after the detection and quantification steps, the removed metal agglomerates in a nanometric size scale that is useful for further remediation. After quantification and removal of any heavy metal, it is possible to

them for the detection of another kind of contaminants. The ZnS nanoparticle can

enhanced the photocatalytic degradation of organic pollutants. The degraded pollutants were orange (II) dye and bisphenol-A. Metals increased photodegradation

, Cu2+, and Hg2+ coated on ZnS and use

[36]. The metal adsorbed on TiO2 nanostructures

limit for Hg2+ ions was near 0.13 μM [35].

convert core-shell nanoparticles, such Ag+

remove up to 3.98 μmol of Ag<sup>+</sup>

**170**

Water is by far, one of the most contaminated resources in the planet; that is why the remediation and removal of contaminants are an urgent need together with easy and fast monitoring tools. The available treatments used for removal of heavy metals from water are classified as follows: chemical precipitation, membrane filtration, ion exchange, reverse osmosis, and adsorption [44]. The adsorption using nanomaterials has been of great interest since several nanostructured adsorbents have demonstrated a high performance [44–46]. Adsorption on nanostructured materials is complicated, but some authors have proposed possible mechanisms that depend mainly on the nature of the surface area. The fundamental mechanisms are based on physical adsorption (physisorption), chemical adsorption (chemisorption), electrostatic attraction, and sorption-precipitation [9, 47, 48]. **Figure 3** shows a schematic representation for the adsorption mechanisms of heavy metal on porous nanomaterials. Lu et al. reported that biochar, a 3D network, is a material rich in cations and surface interaction sites for lead adsorption. Electrostatic cation exchange or metal exchange reactions mechanisms may occur when calcium (Ca2+), magnesium (Mg2+), potassium (K+ ), and sodium (Na+ ) ions released from biochar in the adsorption of Pb ions, but the electrostatic interaction and surface complexation with pi-cationic and functional groups interaction, may also happen in the adsorption of Pb ions [48].
