**1. Introduction**

Sustainable environment requires development of portable sensors for monitoring heavy and toxic metallic pollutants. Nanomaterials and nanostructures play a vital role as an adsorption sites into sensors [1] that leads to shift sensitivity, selectivity, multiplexed detecting ability towards high performance in terms of capability and portability [2]. Nanomaterials-based sensors exhibit an extremely high surface area, which can increase the number of binding sites [2] available for the adsorption of metal ions. Heavy metal pollution becomes a concern for global sustainability. Carbon nanomaterials [3] act as electrochemical sensors because they have higher sensitivities, lower limit detection, and faster electron transfer kinetics than traditional detection electrodes [4]. An electrochemical sensor is an analytical device in which a recognition element is integrated within or intimately associated with a physical transducer [5] (an electrode) that transfers the analytical signal to an electronic circuit for the purpose of detecting a target analyte. The development of active electro catalysts plays a key role in the design of efficient, reliable, stable, and innovative sensing devices. Electrochemical detection is highly favored by the characteristics of rapid detection, high sensitivity and selectivity, high adsorption capability and large surface area [6]. Functionalized CNTs are good electrochemical sensing materials and can impart strong electro catalytic activity [7] to electrochemical reaction for most environmental pollutants such as heavy metal ions, organic pollutants containing electro active group. Environmental pollution is considered as a worldwide public problem, including heavy metals, inorganic/ organic compounds, toxic gases, pesticides, antibiotics [8], bacteria, etc., which becomes a serious issues to human health and smooth environment [9]. The catechol (1, 2-dihydroxybenzene) is a phenolic compound which is extensively used in dye, petroleum refinery, plastic, antioxidant, cosmetics, medicines. The high toxicity and low degradability cause eczematous dermatitis, depression of the central nervous system (CNS) and a prolonged rise of blood pressure. With industrial development, many metal ions have discharged into natural environment. Unfortunately, metal ions, especial heavy metal ions, are easily caused soil and water polluted. Ordered mesoporous carbon have well-ordered and tunable porous structures and surface which have pore sizes in the range of 2–50 nm, Porosity offers high specific surface areas (more than 2000 m<sup>2</sup> g−1). However, the grafting of organic, inorganic or biomaterials into mesoporous carbon produces different functional groups and binding capacity which further improving their analytical performances. CNMs have received significant attention as candidate materials for detecting [10, 11] NOx, NH3, CO, SO2 etc. For example, sensing of nitrogen oxide (NOx), a major air pollutant emitted from power plants, which causes neurodegenerative diseases. The interfacial interaction can be enhanced by the surface-functionalization of nanotubes. The polar groups [12] on the nanotube surface increase the adsorption affinity of the electron-donor or acceptor pollutants and consequently offer better response. The detection of mercury ion at the Au-NPs interface is more sensitive and selective because they can form amalgam only with Hg compared to other metal ions. The electrochemical sensing performance had a relationship with the adsorption capacity, which excites the design of new sensing materials. The amino group on the surface of functionalized CMS [13] is bringing increased attractive force in adsorption of heavy metal ions. Though increasing the deposition time improves the sensitivity, it also lowers the detection limit because of the surface saturation at high metal ions concentrations. Carbon nanomaterials endowed with unique physiochemical properties were found to be most suitable for electrochemical detection of heavy metal due to their ease to modify, high sensitivity, good selectivity and high reproducibility. Unmodified CNTs are unable to chelate metal ions in aqueous solutions and cannot work as good electrode materials for the ASV analyses. The hydrophilic hybrid nanocomposites are able to adsorb heavy metal ions from aqueous solution due to the rich chelating groups. Carbon nano tubes (CNTs) exhibited effective adsorbent as well as sorbents for heavy metal ions. Therefore, it is reasonable to construct electrochemical sensors using the CNT or graphene-functionalized redox electrodes entity for detection of heavy metal because they are capable to detect simultaneously a majority of heavy metal ions with high resolution for defined and measured concentrations. The stripping techniques and particularly square wave and differential pulse anodic stripping voltammetry ensured alternative and extensive explored sensitive electrochemical

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activity towards pollutants.

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

or reduced graphene oxide (rGO) are used as an working electrode material; however, low sensitivity and potential interferences lowers their sensing capacity due to inherent irreversible agglomeration of graphene particle which excites researcher to develop green idea in the designing of native grapheme [15] based detecting electrodes as electrochemical sensor. Low sensitivity and poor selectivity related with the large over potential and the interference from the reduced substance, such as oxygen, H2O, encountered in the nitro aromatic compound (organic pollutants). Nitrophenols readily accumulate in organisms and are difficult to naturally degrade because of the high structural stability. The sensitivity can be improved by incorporating metal nano-particle over the surface of functional sites [16]. Owing to the high specific surface area, chemical stability, high p-conjugation and hydrophilic properties, GO can offer an excellent electrode platform for

adsorbing other molecules. High surface to volume ratio with active sites, controlled distribution of pore size, exceptional sorption capacity and high sorption proficiency make CNTs suitable material for the development of electro-analytical systems dedicated for the detection of heavy metal ions. Hence, ionated CNTs play important role in the metal ion sensing due to their better ion exchange capacity. Oxidized CNTs have a great potential for cation uptake compared to non oxidized CNTs. In other words, non oxidized CNTs have tendency towards uptake of anions compared to oxidized CNTs. The presence of an extended π-conjugation in organic conducting polymer (OCPs) confers the required mobility to charges that are present on polymer backbone and makes them electrically conducting [17]. The sensing intensifier played a facilitating role between the GCE surface and the target metal ions by bringing analytes closer to transducer surface resulting in appearance of intense electrochemical signals. CNFs with high length-to-diameter ratio are capable of offering additional active sites for nanoparticle loading or deposition. The carbon nanotubes alone as well as in their oxidized and in their composite forms have tremendous ability to adsorb the heavy metal ions. Unmodified CNTs are unable to chelate metal ions in aqueous solutions and cannot work as good electrode materials. This is due to deficiency of functional group and sufficiency of hydrophobic environment. The effective combination of two carbon nanostructures can not only improve solubility and conductivity but also make up functional deficiencies [18]. Functionalization could significantly assist in the improvement of surface capacitance. Thus, the modified GCE exhibits good electro oxidative

**2. Nanomaterials extended electrochemical sensing platforms**

Electrochemical Carbon Nanotube Filter Oxidative Performance [19] as a Function of Surface adsorption. The presences of surface resident reactive groups, or edge-plane like sites that are situated at the ends of their structures, and at defect sites, are responsible for the excellent electro catalytic activity of carbon nanomaterials. Nanoparticles exhibited high surface to volume ratio with functional and

methods for heavy metal ions detection. The carbon bound Fluorine [14] exhibited both ionic as well as covalent interface and significantly enhanced the capacitive performance of fluorinated GO compared to pristine GO. Further, the fluorinated GO has high affinity for the simultaneous detection of heavy metal ions Cd2+, Pb2+, Cu2+ and Hg2+ using square wave anodic stripping voltammetry (SWASV) as electrochemical tool. Fluorinated-graphene has gained great attention because of unique properties such as its high temperature resistance and enhanced electro catalytic activity. Electron withdrawing nature is arising from the strong electronegativity of F and electron donating nature from the lone-pair electrons. Graphene

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

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

methods for heavy metal ions detection. The carbon bound Fluorine [14] exhibited both ionic as well as covalent interface and significantly enhanced the capacitive performance of fluorinated GO compared to pristine GO. Further, the fluorinated GO has high affinity for the simultaneous detection of heavy metal ions Cd2+, Pb2+, Cu2+ and Hg2+ using square wave anodic stripping voltammetry (SWASV) as electrochemical tool. Fluorinated-graphene has gained great attention because of unique properties such as its high temperature resistance and enhanced electro catalytic activity. Electron withdrawing nature is arising from the strong electronegativity of F and electron donating nature from the lone-pair electrons. Graphene or reduced graphene oxide (rGO) are used as an working electrode material; however, low sensitivity and potential interferences lowers their sensing capacity due to inherent irreversible agglomeration of graphene particle which excites researcher to develop green idea in the designing of native grapheme [15] based detecting electrodes as electrochemical sensor. Low sensitivity and poor selectivity related with the large over potential and the interference from the reduced substance, such as oxygen, H2O, encountered in the nitro aromatic compound (organic pollutants). Nitrophenols readily accumulate in organisms and are difficult to naturally degrade because of the high structural stability. The sensitivity can be improved by incorporating metal nano-particle over the surface of functional sites [16]. Owing to the high specific surface area, chemical stability, high p-conjugation and hydrophilic properties, GO can offer an excellent electrode platform for adsorbing other molecules. High surface to volume ratio with active sites, controlled distribution of pore size, exceptional sorption capacity and high sorption proficiency make CNTs suitable material for the development of electro-analytical systems dedicated for the detection of heavy metal ions. Hence, ionated CNTs play important role in the metal ion sensing due to their better ion exchange capacity. Oxidized CNTs have a great potential for cation uptake compared to non oxidized CNTs. In other words, non oxidized CNTs have tendency towards uptake of anions compared to oxidized CNTs. The presence of an extended π-conjugation in organic conducting polymer (OCPs) confers the required mobility to charges that are present on polymer backbone and makes them electrically conducting [17]. The sensing intensifier played a facilitating role between the GCE surface and the target metal ions by bringing analytes closer to transducer surface resulting in appearance of intense electrochemical signals. CNFs with high length-to-diameter ratio are capable of offering additional active sites for nanoparticle loading or deposition. The carbon nanotubes alone as well as in their oxidized and in their composite forms have tremendous ability to adsorb the heavy metal ions. Unmodified CNTs are unable to chelate metal ions in aqueous solutions and cannot work as good electrode materials. This is due to deficiency of functional group and sufficiency of hydrophobic environment. The effective combination of two carbon nanostructures can not only improve solubility and conductivity but also make up functional deficiencies [18]. Functionalization could significantly assist in the improvement of surface capacitance. Thus, the modified GCE exhibits good electro oxidative activity towards pollutants.
