**4. Analytical role of square wave anodic stripping voltammetry (SWASV)**

Electrochemical techniques have the capability to maintain environmental interfacial processes at high rates and efficiencies by directionally and accurately controlling the electron transfer processes. An electrochemical technique where the analyte of interest is first electrodeposited onto the sensing electrode and removed

#### **Figure 3.**

*General scheme of electrochemical sensing and detection of inorganic pollutants (heavy metal ions) through SWASV.*

or 'stripped' with a sharp and intense peak by applying an oxidizing potential. During removal of pollutants, the peak current is measured as a function of time or function of the potential between the indicator (sensor) and reference electrodes. The redox probe is introduced as the inner reference to provide a built-in correction towards the signal transduction. The peak current ratio of analyte signal to probe signal is employed as the detected signal for analyte determination. The potential is varied as a square wave superimposed on a linear sweep. The potential separation between the stripping peaks can clear enough to distinguish the various heavy metal ions. The detection is expressed as sensing signals. The stripping peak currents are controlled by the amount of target metal ions adsorbed on the electrode surface. Striping peak current is directly proportionate to concentration of analyte. The SWASV is more prone over other voltammetry technique because of excellent sensitivity and unique ability to detect metals simultaneously. SWASV includes two independent procedures: deposition and stripping. First, in the deposition process (electrochemical reduction), metal ions can be reduced under a certain potential from the analyte solution to the working electrode. Inversely, when anodic potential is applied, the reduced metals are oxidized to their ions. Interference ions reduce the peak current for detected analyte during electrochemical analysis. Peak current varies with concentration of analyte and it increases linearly up to optimum concentration range which is also referred to as linear range concentration profile. Square-wave anodic stripping voltammetry is commonly used for metal detection due to its high sensitivity and low (nM–pM) detection limits. **Figure 3** indicates schematic sensing analysis and detected signal for pollutants [15].

#### **5. Adsorption sites and its electrochemical sensitivity**

The adsorption activity is related to the number of active functional groups on the surface of the carbon nanomaterials with highly oxidized surfaces showed a greater adsorption affinity for the stabilizers. Electro catalytic activity is related with hydrophobic or hydrophilic, positive or negative redox active groups of carbon nanomaterials**.** *Li et al.* reported MWCNTs are highly efficient to remove perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) from aqueous solution in light of their environmental persistence [36]. Bismuth modified CNT polystyrene Sulfonate (PSS) composite electrode for simultaneous detection of Pb(II) and Cd(II) by anodic stripping voltammetry. The designed composite electrode shows synergistic effect of bismuth and Polystyrene sulfonate. Since, polymeric dopant acts as cation-exchanger and CNT as an efficient signal transducer for sensitive and simultaneous detection of lead and cadmium. The detection limits were estimated to be 0.04 ppb for Pb(II) and 0.02 ppb for Cd(II) at 2 min accumulation. The presence

**79**

**Table 1.**

GQDs-Au NPs

Au NPs/CNF

CyS-MWCNT BifeO3-CNF Gly/RGO/PANi

CS-HS-MWCNTs CNPE-(CTS-ECH)

AuNPs-HOOC-MWCNT

G/PANi

PPy/CNFs NCQDs-GO

PAA-CoFe2O4/CNTs

CA/RGO

*Application of Carbon Nanomaterials Decorated Electrochemical Sensor for Analysis…*

**5.1 Influence of surface group (chromophores) and sensing sites**

The electro catalytic properties of Carbon nanodots material depend on the presence of functional groups on the surface electrode because the material is a great electron acceptor and donor electron with the presence of some functional groups such as hydroxyl groups. Calixarenes [39] have three-dimensional spherical basket, cup or bucket shapes. **Figure 4(a)** depicts structural integrity of Calixarenes [39]. The spherical core volume is utilized in ion selective electrodes and membranes. It can capture stationary phases. The macrocyclic ring structure

depends on macrocyclic ring size and ionic size of metal ion. Calixarenes can coordinate with the metal ions to increase the sensitivity of the electrochemical sensors. The metal ions, Fe(III), Cd(II), and Pb(II) gave a linear relationship with

**Designed sensor/GCE Pollutants Sensitivity LOD Technique Reference**

2.47 μA/Nm 3.69 μA/nM -

0.02 nM 0.05 nM 0.02 nM

0.1 μM 1 ppb

1 ppb 15 ppb 0.0015 μM 0.07 nM 0.02 nM 3 nM 10 nM 1.0 μg/L 0.1 μg/L 0.05 μg/L 7.45 μg/L 1.17 μg/L 0.17 μM 0.89 μM

15.20 μA/μM 41.3 μA/μM 36 μA/μM 212 μA/μM

45.53 μA/μM

CNHs/GO 4-NCB 54.47 μA/μM 10 nM SWASV [48]

*Different electrochemical sensor for detection of pollutants and analytical parameters.*




SWASV

[38]

[39] [32]

[40]

[41] [42] [33] [43] [44] [45] [46] [47] [21]

SWASV

SWASV

DPASV

DPV SWASV SWASV -

SWASV SWASV SWASV SWASV SWASV SWASV

of MWCNTs can greatly enhance the conductivity of the hybrid nanocomposites and also make the GO plane unfold, whereas, the GO components can give the hybrid an important property to capture metal ions in aqueous. The CNT/rGO as nanohybrid materials exhibit strongly adsorption the organic components through the π-π interactions, a high electrical transport, and conductivities [37]. *Ruecha et al.* developed of an electrochemical sensor for simultaneous detection of Zn(II), Cd(II), and Pb(II) using a graphene–polyaniline (G/PANI) nanocomposite electrode in a linear working range of 1–300 μg/L. The anodic peak potential −1.31, −0.98 and − 0.75 V were recorded with well separation. **Table 1** shows different capacity for different electrochemical sensor towards inorganic /organic pollutants. The carbon nanomaterials are integral part of sensing materials. The CNMs are very prone to stabilize the

*DOI: http://dx.doi.org/10.5772/intechopen.96538*

structural integrity and reproducibility.

is efficient ionophores for metal ions viz. Na+

their concentrations at 1.0–10 nM on the CA/RGO/GCE.

Hg(II) Cu(II) Fe(III),Cd(II) Pb(II) Cd(II),Pb(II) Cu(II) Pb(II), Hg(II) Cd(II) Pb(II) Cu(II) Catechol Cd(II) Pb(II) Hg(II) Cu(II) Zn(II) Cd(II),Pb(II) Pb(II) Cd(II) Pb(II) Hydroquinone Catechol

*Application of Carbon Nanomaterials Decorated Electrochemical Sensor for Analysis… DOI: http://dx.doi.org/10.5772/intechopen.96538*

of MWCNTs can greatly enhance the conductivity of the hybrid nanocomposites and also make the GO plane unfold, whereas, the GO components can give the hybrid an important property to capture metal ions in aqueous. The CNT/rGO as nanohybrid materials exhibit strongly adsorption the organic components through the π-π interactions, a high electrical transport, and conductivities [37]. *Ruecha et al.* developed of an electrochemical sensor for simultaneous detection of Zn(II), Cd(II), and Pb(II) using a graphene–polyaniline (G/PANI) nanocomposite electrode in a linear working range of 1–300 μg/L. The anodic peak potential −1.31, −0.98 and − 0.75 V were recorded with well separation. **Table 1** shows different capacity for different electrochemical sensor towards inorganic /organic pollutants. The carbon nanomaterials are integral part of sensing materials. The CNMs are very prone to stabilize the structural integrity and reproducibility.
