**3. Measurement methods using nanostructures**

All the elements from the periodic table are suitable to form nanostructures in all dimensions, individually or combined, increasing in this way the variety of properties, behavior, and functionality. As a result, new opportunities are now available with nanotechnology to enhance the efficiency of existing methods for detection, quantification, and remediation of pollutants. However, environmental remediation is still a challenge and some important facts should be considered, such as selectivity, efficiency, reusability, eco-friendly, and low cost. It is important to notice that nanomaterials are non-biodegradable and so they tend to accumulate in organisms, leading to serious health problems when ingested by humans [17]. Thus, using nanotechnology either as a remediation strategy or measurement method needs to consider the recuperation and reutilization of nanomaterials as mandatory steps.

Some authors have conducted relevant investigations to know the levels of heavy metals in water. Florence Lagarde and Jaffrezic-Renault proposed complementary methods for the monitoring and treatment of metal-contaminated water [18], which Agostino et al. resumed in two main sections: fast and conventional [19]. The first consists of the development of in-situ, low cost, non-specific early warning systems to operate online. The second one is focused on accurate detection and quantification using conventional methods that are expensive, more time consuming, and require manual operation.

Detection and quantification of heavy metals are crucial tasks in the characterization of different water types: surface water, groundwater, tap water, and wastewater. Nowadays, the monitoring of toxic effects becomes mandatory since water resources are being scarce, and the development of monitoring tools is essential for an easy, fast, and accurate detection of heavy metals in a few steps. Sensing is an integral part of both fast and conventional measurement methods for the quantification of heavy metals proposed in nowadays research [20]. Nanotechnology used in sensing improves not only the efficiency but also the selectivity and reduces the time needed in each step of the methodology of quantification of heavy metals in water. Sensing using nanotechnology can be implemented in-situ for a faster detection of heavy metals in water with a low-cost technique, followed by the quantification with a sensitive and accurate analytical method on-lab such as atomic absorption spectroscopy, X-ray fluorescence, electrochemical techniques, and among others that are described below.

Some of the 0D nanostructures used for the detection and quantification of heavy metals in water are the metal nanoparticles. These nanoparticles can be made of gold (Au), silver (Ag), titanium oxide (TiO2), iron oxide (Fe3O4), zinc sulfide (ZnS), or cadmium sulfide (CdS) due to the facility that these materials offer to modify their surface, and the easiness they offer to control their reproducibility and flexibility in an aqueous medium [21]. The heavy metals are detected by a spectroscopic, electrochemical, or optical technique. The methodologies adapted to these strategies using nanostructures have some advantages and disadvantages as can be expected [22]. The spectroscopic methods allow not only the detection but also

**169**

*Low Dimensional Nanostructures: Measurement and Remediation Technologies Applied to Trace…*

the quantification step, and they are usually very sensitive to multiple heavy metal ions. Some examples of spectroscopic techniques are ICP-MS (inductively coupled plasma mass spectrometry), AAS (atomic absorption spectroscopy), HR-SPS (highresolution surface plasmon resonance spectroscopy), and SERS (surface-enhanced Raman spectroscopy). SERS is useful for sensing applications since the surface plasmon resonance of metal nanoparticles can be identified with a detection limit of 10 ppt in a pH buffered solution, and of 70 ppt in a real sample when compared with AAS, whose detection limit is around 0.2 ppb [22]. ICP-MS quantifies a wide variety of elements in one-single analysis step with high accuracy, sensitivity, and selectivity. Low detection limits for metal ions can be achieved by using ICP-MS, normally in the ppt range [23, 24]. Such techniques are typically used for quantification but not for sensing. The main disadvantage of the spectroscopic methodologies is the high cost of the analytical instrumentation, the time-consuming procedures, and the use of sophisticated equipment that requires trained personnel [22, 25]. On the other hand, electrochemical methods are low cost, low time-consuming, and easy to handle. They can be conducted under any of the following techniques: potentiometric, amperometric, voltammetric, impedimetric, or electrochemiluminescence. They have a high sensitivity and low detection limits (from 0.25 ng/L to 0.12 μg/L) [26–28]. The main advantage of the electrochemical methods is the possibility of sensing or monitoring of pollutants with in-line systems coupled with water streams. However, the design and miniaturization of the electrodes needed to build portable sensors are one of their major challenges [22, 28]. The use of optical methods for the detection of heavy metals is also an economical and fast option. Optical procedures usually utilized for this purpose are absorption, reflection, or luminescence spectrometry. The main limitations could be that some non-optical

**Table 1** summarizes some examples of detection and quantification of heavy metals using nanostructures, reported in recent literature, where the spectroscopic,

For a fast and in situ detection, some authors propose an innovative and cheap methodology based on an online operation aided by a smartphone. The strategy uses the wavelength shifting of the resonant plasmon. It means that nanoparticles suffer a color change, from red to purple, when cadmium (Cd2+), mercury (Hg2+), or copper (Cu2+) ions are present on a solution [29–31]. The nanosensor uses a gold nanoparticle-based assay platform that records, processes signals within the range of 1 ng/mL–32 ng/mL of Hg2+, and proposes a concentration of 0.28 ng/mL as the limit of detection [29]. The *in situ* detection of Cd2+ with the nanogold-based detection system controlled by the smartphone is fast and reliable as it displays a linear range for the Cd2+ concentration, between 2 and 20 μg/L with a detection limit of 1.12 μg/L [30]. This range is below the permissible limit of Cd2+ ion in water and smaller than those based on non-portable and other nano-based technologies [32]. The main advantage for these types of systems is the portability, as well as the immobilization of metal ions to gold nanoparticles that allows the tuning of sensitivity. For example, the aptamer is a particular recognition of Cd2+ [33], with a low recognition of Pb2+, and acceptable detection even though the specimen contains

The quenching of quantum dot (QD) was studied for cadmium (Cd2+), mercury (Hg2+), and lead (Pb2+) to understand the colorimetric/visual sensors. The composite formed by Mn-doped ZnS QD and graphene oxide detects Pb2+ down to 0.4 ppb. Further, the interaction between the metal ion and the passivating ligands attached to the QD also contributes partway to the specific detection combined with the quenching of QD [34]. The green approach is also present on the fast detection, which is vital since the production of nanostructures requires to minimize the use

*DOI: http://dx.doi.org/10.5772/intechopen.93263*

indicators interfere with some metal ions [22].

other metal ions in high concentration [30].

electrochemical, and optical methodologies have been applied.

#### *Low Dimensional Nanostructures: Measurement and Remediation Technologies Applied to Trace… DOI: http://dx.doi.org/10.5772/intechopen.93263*

the quantification step, and they are usually very sensitive to multiple heavy metal ions. Some examples of spectroscopic techniques are ICP-MS (inductively coupled plasma mass spectrometry), AAS (atomic absorption spectroscopy), HR-SPS (highresolution surface plasmon resonance spectroscopy), and SERS (surface-enhanced Raman spectroscopy). SERS is useful for sensing applications since the surface plasmon resonance of metal nanoparticles can be identified with a detection limit of 10 ppt in a pH buffered solution, and of 70 ppt in a real sample when compared with AAS, whose detection limit is around 0.2 ppb [22]. ICP-MS quantifies a wide variety of elements in one-single analysis step with high accuracy, sensitivity, and selectivity. Low detection limits for metal ions can be achieved by using ICP-MS, normally in the ppt range [23, 24]. Such techniques are typically used for quantification but not for sensing. The main disadvantage of the spectroscopic methodologies is the high cost of the analytical instrumentation, the time-consuming procedures, and the use of sophisticated equipment that requires trained personnel [22, 25]. On the other hand, electrochemical methods are low cost, low time-consuming, and easy to handle. They can be conducted under any of the following techniques: potentiometric, amperometric, voltammetric, impedimetric, or electrochemiluminescence. They have a high sensitivity and low detection limits (from 0.25 ng/L to 0.12 μg/L) [26–28]. The main advantage of the electrochemical methods is the possibility of sensing or monitoring of pollutants with in-line systems coupled with water streams. However, the design and miniaturization of the electrodes needed to build portable sensors are one of their major challenges [22, 28]. The use of optical methods for the detection of heavy metals is also an economical and fast option. Optical procedures usually utilized for this purpose are absorption, reflection, or luminescence spectrometry. The main limitations could be that some non-optical indicators interfere with some metal ions [22].

**Table 1** summarizes some examples of detection and quantification of heavy metals using nanostructures, reported in recent literature, where the spectroscopic, electrochemical, and optical methodologies have been applied.

For a fast and in situ detection, some authors propose an innovative and cheap methodology based on an online operation aided by a smartphone. The strategy uses the wavelength shifting of the resonant plasmon. It means that nanoparticles suffer a color change, from red to purple, when cadmium (Cd2+), mercury (Hg2+), or copper (Cu2+) ions are present on a solution [29–31]. The nanosensor uses a gold nanoparticle-based assay platform that records, processes signals within the range of 1 ng/mL–32 ng/mL of Hg2+, and proposes a concentration of 0.28 ng/mL as the limit of detection [29]. The *in situ* detection of Cd2+ with the nanogold-based detection system controlled by the smartphone is fast and reliable as it displays a linear range for the Cd2+ concentration, between 2 and 20 μg/L with a detection limit of 1.12 μg/L [30]. This range is below the permissible limit of Cd2+ ion in water and smaller than those based on non-portable and other nano-based technologies [32]. The main advantage for these types of systems is the portability, as well as the immobilization of metal ions to gold nanoparticles that allows the tuning of sensitivity. For example, the aptamer is a particular recognition of Cd2+ [33], with a low recognition of Pb2+, and acceptable detection even though the specimen contains other metal ions in high concentration [30].

The quenching of quantum dot (QD) was studied for cadmium (Cd2+), mercury (Hg2+), and lead (Pb2+) to understand the colorimetric/visual sensors. The composite formed by Mn-doped ZnS QD and graphene oxide detects Pb2+ down to 0.4 ppb. Further, the interaction between the metal ion and the passivating ligands attached to the QD also contributes partway to the specific detection combined with the quenching of QD [34]. The green approach is also present on the fast detection, which is vital since the production of nanostructures requires to minimize the use

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

frameworks, aerogels, and composites.

ing, and require manual operation.

among others that are described below.

**3. Measurement methods using nanostructures**

recuperation and reutilization of nanomaterials as mandatory steps.

classification of some examples of nanostructures: 0D nanostructures are quantum dots, nanoparticles, fullerenes, clusters, metal nanoparticles, or graphene quantum dots, among others. One-dimensional structures are carbon nanotubes, single layer graphene nanoribbons, graphite nanoribbons, or nanobars. Two-dimensional nanostructures include nanofilms, graphene, graphene oxide, and two layered graphene. Three-dimensional nanomaterials include graphite, metallic-organic

All the elements from the periodic table are suitable to form nanostructures in all dimensions, individually or combined, increasing in this way the variety of properties, behavior, and functionality. As a result, new opportunities are now available with nanotechnology to enhance the efficiency of existing methods for detection, quantification, and remediation of pollutants. However, environmental remediation is still a challenge and some important facts should be considered, such as selectivity, efficiency, reusability, eco-friendly, and low cost. It is important to notice that nanomaterials are non-biodegradable and so they tend to accumulate in organisms, leading to serious health problems when ingested by humans [17]. Thus, using nanotechnology either as a remediation strategy or measurement method needs to consider the

Some authors have conducted relevant investigations to know the levels of heavy metals in water. Florence Lagarde and Jaffrezic-Renault proposed complementary methods for the monitoring and treatment of metal-contaminated water [18], which Agostino et al. resumed in two main sections: fast and conventional [19]. The first consists of the development of in-situ, low cost, non-specific early warning systems to operate online. The second one is focused on accurate detection and quantification using conventional methods that are expensive, more time consum-

Detection and quantification of heavy metals are crucial tasks in the characterization of different water types: surface water, groundwater, tap water, and wastewater. Nowadays, the monitoring of toxic effects becomes mandatory since water resources are being scarce, and the development of monitoring tools is essential for an easy, fast, and accurate detection of heavy metals in a few steps. Sensing is an integral part of both fast and conventional measurement methods for the quantification of heavy metals proposed in nowadays research [20]. Nanotechnology used in sensing improves not only the efficiency but also the selectivity and reduces the time needed in each step of the methodology of quantification of heavy metals in water. Sensing using nanotechnology can be implemented in-situ for a faster detection of heavy metals in water with a low-cost technique, followed by the quantification with a sensitive and accurate analytical method on-lab such as atomic absorption spectroscopy, X-ray fluorescence, electrochemical techniques, and

Some of the 0D nanostructures used for the detection and quantification of heavy metals in water are the metal nanoparticles. These nanoparticles can be made of gold (Au), silver (Ag), titanium oxide (TiO2), iron oxide (Fe3O4), zinc sulfide (ZnS), or cadmium sulfide (CdS) due to the facility that these materials offer to modify their surface, and the easiness they offer to control their reproducibility and flexibility in an aqueous medium [21]. The heavy metals are detected by a spectroscopic, electrochemical, or optical technique. The methodologies adapted to these strategies using nanostructures have some advantages and disadvantages as can be expected [22]. The spectroscopic methods allow not only the detection but also

**168**


#### **Table 1.**

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

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

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 convert core-shell nanoparticles, such Ag+ , Cu2+, and Hg2+ coated on ZnS and use them for the detection of another kind of contaminants. The ZnS nanoparticle can remove up to 3.98 μmol of Ag<sup>+</sup> [36]. The metal adsorbed on TiO2 nanostructures enhanced the photocatalytic degradation of organic pollutants. The degraded pollutants were orange (II) dye and bisphenol-A. Metals increased photodegradation

**171**

*Low Dimensional Nanostructures: Measurement and Remediation Technologies Applied to Trace…*

after 5 hours in a batch experiment (70% of dye and 80% of Bisphenol A) due to the photodeposition of metal ions on the TiO2 nanoparticle surface [37]. Functionalized Fe3O4/NaP zeolite nanocomposite removed metal, more than 95%, after removed bacteria (*Bacillus subtilis*) [38]. A different methodology was employed for *in situ* measurements by electrochemical detection using SnS-decorated Bi2O3 nanosheets. The composite exhibited high sensitivity and efficient detection for the removal of heavy metals with high toxicity, which limits of detection was 1.50 nM for Cd2+ and

Quantification of metallic ions is essential during the different steps of the water cycle that goes through various biological processes. The main quantification techniques are atomic absorption spectrometry, inductively coupled plasma mass spectrometry, anodic stripping voltammetry, X-ray fluorescence spectrometry, and microprobes. These techniques require sample pretreatment procedures, analyte pre-concentration steps, and expensive instrumentation [40]. Due to the presence of dangerous heavy metal ions in water, an instantaneous measurement and quantification are desirable. The use of nanotechnology, along with the investigation of novel approaches, will allow the quantification of heavy metals in an inexpensive, rapid, and simple way. For example, Stenberg, Massad-Ivanirb, and Ester Segal presented a nanostructured porous silicon (Si) biosensor for the detection and quantification of copper ion in real water samples. The monitoring is based on the Laccase relative activity. Lacasse is an enzyme, a multi-copper oxidase, immobilized within the oxidized nanostructured porous silicon. The Laccase-based biosensor exhibited a lower detection limit of 1.30 μM, smaller than other values [41].

Quantification of the metal ion content, as well as the chemical speciation of the different chemical forms of a specific metal in water, becomes essential to estimate its toxicity and persistence in living organisms. The environmental health effects can be understood by the study of natural chemistry, quantification, and speciation of chemical species of metal ions. The chemical form of any metal depends strongly on the chemical conditions in which it is exposed, and the toxicity not only relays on its ionic form but also on the chemical species that formed. For example,

(Hg2+). Speciation analysis requires complex, expensive, and time-consuming preseparation analyses, which are incompatible with *in situ* measurements. Guerrini et al. [42] presented a Surface-Enhanced Raman Scattering (SERS) methodology

of an active platform of closely spaced spherical gold nanoparticles anchored on polystyrene microparticles. The ion receptor, mercaptopyridine (MPY), forms strong bonds between the gold atoms and the mercaptan group, and coordinates a

is determined by the changes in vibrational SERS of MPY, which could give insights on the qualitative and quantitative modifications correlated with Hg2+ or CH3Hg+

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),

) is the toxic specie of the inorganic mercury II

. In this work, the SERS consisted

. The coordination with nitrogen

.

*DOI: http://dx.doi.org/10.5772/intechopen.93263*

1.40 nM for Pb2+ [39].

the methylmercury ion (CH3Hg+

**4. Nanoremediation**

soil, air, and sediments [43].

for the chemical speciation of Hg2+ and CH3Hg+

nitrogen group with both species Hg2+ and CH3Hg+

#### *Low Dimensional Nanostructures: Measurement and Remediation Technologies Applied to Trace… DOI: http://dx.doi.org/10.5772/intechopen.93263*

after 5 hours in a batch experiment (70% of dye and 80% of Bisphenol A) due to the photodeposition of metal ions on the TiO2 nanoparticle surface [37]. Functionalized Fe3O4/NaP zeolite nanocomposite removed metal, more than 95%, after removed bacteria (*Bacillus subtilis*) [38]. A different methodology was employed for *in situ* measurements by electrochemical detection using SnS-decorated Bi2O3 nanosheets. The composite exhibited high sensitivity and efficient detection for the removal of heavy metals with high toxicity, which limits of detection was 1.50 nM for Cd2+ and 1.40 nM for Pb2+ [39].

Quantification of metallic ions is essential during the different steps of the water cycle that goes through various biological processes. The main quantification techniques are atomic absorption spectrometry, inductively coupled plasma mass spectrometry, anodic stripping voltammetry, X-ray fluorescence spectrometry, and microprobes. These techniques require sample pretreatment procedures, analyte pre-concentration steps, and expensive instrumentation [40]. Due to the presence of dangerous heavy metal ions in water, an instantaneous measurement and quantification are desirable. The use of nanotechnology, along with the investigation of novel approaches, will allow the quantification of heavy metals in an inexpensive, rapid, and simple way. For example, Stenberg, Massad-Ivanirb, and Ester Segal presented a nanostructured porous silicon (Si) biosensor for the detection and quantification of copper ion in real water samples. The monitoring is based on the Laccase relative activity. Lacasse is an enzyme, a multi-copper oxidase, immobilized within the oxidized nanostructured porous silicon. The Laccase-based biosensor exhibited a lower detection limit of 1.30 μM, smaller than other values [41].

Quantification of the metal ion content, as well as the chemical speciation of the different chemical forms of a specific metal in water, becomes essential to estimate its toxicity and persistence in living organisms. The environmental health effects can be understood by the study of natural chemistry, quantification, and speciation of chemical species of metal ions. The chemical form of any metal depends strongly on the chemical conditions in which it is exposed, and the toxicity not only relays on its ionic form but also on the chemical species that formed. For example, the methylmercury ion (CH3Hg+ ) is the toxic specie of the inorganic mercury II (Hg2+). Speciation analysis requires complex, expensive, and time-consuming preseparation analyses, which are incompatible with *in situ* measurements. Guerrini et al. [42] presented a Surface-Enhanced Raman Scattering (SERS) methodology for the chemical speciation of Hg2+ and CH3Hg+ . In this work, the SERS consisted of an active platform of closely spaced spherical gold nanoparticles anchored on polystyrene microparticles. The ion receptor, mercaptopyridine (MPY), forms strong bonds between the gold atoms and the mercaptan group, and coordinates a nitrogen group with both species Hg2+ and CH3Hg+ . The coordination with nitrogen is determined by the changes in vibrational SERS of MPY, which could give insights on the qualitative and quantitative modifications correlated with Hg2+ or CH3Hg+ .
