Polypyrrole: a reactive and functional conductive polymer for the selective electrochemical detection of heavy metals in water

Sall M.L., Fall B., Diédhiou I., Dièye E.H., Lo M., Diaw A.K., Gningue-Sall D., Raouafi N., Fall M.

Water pollution by heavy metals and nitrite ions is a public health concern around the world because they can degrade the quality of drinking water and cause serious diseases. Lead and cadmium are probably the most dangerous heavy metals. Indeed, lead contamination can affect fertility and pregnancy, cause infantile diseases and other mutagenic and carcinogenic effects. Exposure to cadmium can cause death in mammals, and nitrite ions are also very harmful. For all these reasons, it is necessary to find effective techniques to quantify the levels of these pollutants. Recently, there is great hope in the use of organic conducting polymers in the field of heavy metals detection. In this review, we presented studies of the toxicity of several heavy metals and nitrite ions and on their impact on the environment and human health. Also, the recent developments in the use of OCPs and their application in the detection of heavy metals and nitrite ions have been examined.

Xu G., Li X., Cheng C., Yang J., Liu Z., Shi Z., Zhu L., Lu Y., Low S.S., Liu Q.

Migration of heavy metals from food contact materials to contained foods and drinks will cause severe health problems. The in situ analysis of the heavy metal ions inside these containers is in high demand. In this study, a fully integrated battery-free and flexible electrochemical tag is presented for wireless in situ detections of heavy metal ions in various containers. The circuit part of the tag is integrated with square wave anodic stripping voltammetry (SWASV) technique and near field communication (NFC) module, enabling on-board electrochemical sensing, wireless data transmission, and power harvesting. The circuits showed high consistency with commercial electrochemical workstation in SWASV analysis. A screen-printed flexible electrode array is connected with the circuit board. The working electrodes were modified with gold and bismuth nanoparticles respectively, which showed high sensitivity, selectivity, linearity, and reproducibility in the detections of lead and cadmium. The tag achieved quantitative detections of heavy metal ions in various containers, including enamelled cup, ceramic teapot, and dark-red enameled pottery. With proper encapsulation, the miniaturized passive and flexible tag can be attached to the inside surface of various containers for a long time. The wireless detections of heavy metal ions can be achieved just with an NFC-enabled smartphone outside the container. The platform provides a simple and effective solution for in situ analysis of toxic and harmful substances, which can be widely used in the areas of food safety and water quality monitoring.

Sakhraoui H.E., Mazouz Z., Attia G., Fourati N., Zerrouki C., Maouche N., Othmane A., Yaakoubi N., Kalfat R., Madani A., Nessark B.

104 MHz surface acoustic wave sensors, functionalized with two polypyrrole (PPy) imprinted polymers, were designed for lead ion detection in liquid media. The main difference between the two ionic imprinted polymers (IIP) is related to the nature of the chelating agent: L-Cysteine (LCys) for the former and acrylic acid (AA) for the latter. Performances of the IIPs based sensors were compared in terms of sensitivity, limits of detection (LOD), dissociation constants and selectivity. The gravimetric results indicated that both designed sensors can detect picomolar concentrations of lead ions. These values are, in fact, significantly inferior to the World Health Organization (WHO) maximum accepted limit in drinking water, and among the lowest LODs ever reported in the literature. The relevant dissociation constants, calculated from the most appropriate fits of the calibration curves, were estimated at: Kd 1 = (1.1 ± 0.4) × 10 -10 M and Kd 2 = (1.1 ± 0.8) × 10 -5 M for L-Cys-IIP/Pb 2+ and Kd 1 = (1.1 ± 0.3) × 10 -13 M and Kd 2 = (5.9 ± 1.8) × 10 -10 M for AA-PPy-IIP/ Pb 2+ , thus confirming the strong binding between the designed IIPs and lead ions. Selectivity tests were investigated with mercury, cadmium, copper, zinc, and nickel divalent ions, which largely coexist with lead ions in soils, rivers, and wastewaters.

Verla E.N., Verla A.W., Enyoh C.E.

Nine public school playgrounds across Owerri metropolis were investigated for metal fractions for three years (2012, 2013 and 2014) in order to assess bioavailability, average daily dose (ADD) and risk assessment code (RAC) of five heavy metals. A six steps sequential extraction procedure was used to quantify metal fractions with A ANALYST 400 Perkin Elmer AAS. Data of metal concentration was subjected to models and results revealed interesting information that could aid in decision making concerning children playground safety. Significant (p > 0.05) amounts of Zn, Co and Cu were found in the bioavailable fractions in all playgrounds for both seasons. Mean Percent bioavailability in 2012 ranged from Co (9.4) to Zn (28.11) though maximum bioavailability was observed for Mn (55) and minimum for Cu (3). In 2013 bioavailability ranged from Zn (36) to Ni (40.2) while maximum bioavailability was observed for Cu (69) and minimum for Mn (20). In 2014 it ranged from Co (58.6) to Mn (61.1) with maximum bioavailability for Cu (80) and minimum for Cu (21). Bioavailability of these metals in dry and rainy seasons followed the order; Zn > Ni > Cu > Mn > Co. Categorizing bioavailability the order was Residual > Non-bioavailable > Bioavailable. Average daily dose (ADD) showed that exposure to metal-contaminated soil by ingestion were most prominent for Zn and Mn but high ADD values were recorded in 2014 with Zn (1583.7 mg/Kg/day) as the highest. In 2012, values of RAC showed that only Zn (50) at CSO was high whereas almost all playgrounds showed RAC above 50. There was a general increase in RAC from 2012 to 2014. Thus, these metals may be readily bioavailable to children and in the long run constitute health problems for children who use these playgrounds regularly.

Wang N., Zhao W., Shen Z., Sun S., Dai H., Ma H., Lin M.

An electrochemical sensor based on a NH2-MIL-53(Al)/polypyrrole (PPy) nanocomposite modified gold electrode for determination of ultra-trace Pb (II) and Cu (II) was developed. The PPy nanowires were synthesized through a chemical polymerization process, and the NH2-MIL-53(Al) was deposited on the PPy nanosubstrates by an in-situ electrochemical method. Field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) spectroscopy and attenuated total reflection infrared (ATR-IR) spectroscopy were used to study the structural features of the nanocomposite. The electrochemical behavior of the NH2-MIL-53(Al)/PPy nanocomposite toward Pb (II) and Cu (II) was investigated by differential pulse voltammetry (DPV) technique. Due to the synergistic effect of the PPy and NH2-MIL-53(Al), the nanocomposite modified electrode exhibited good sensing performance to Pb (II) and Cu (II) in the range of 1–400 μg L−1 with detection limit of 0.315 μg L−1 and 0.244 μg L−1, respectively. The limit of detection and the sensitivity of the NH2-MIL-53(Al)/PPy nanocomposite modified electrode were significantly enhanced than those of the individual modified electrodes. The effective electrochemical property of the nanomaterial for the Pb (II) and Cu (II) could provide a new direction for the heavy metal ions determination.

Lo M., Seydou M., Bensghaïer A., Pires R., Gningue-Sall D., Aaron J., Mekhalif Z., Delhalle J., Chehimi M.M.

Highly sensitive multicomponent materials designed for the recognition of hazardous compounds request control over interfacial chemistry. The latter is a key parameter in the construction of the sensing (macro) molecular architectures. In this work, multi-walled carbon nanotubes (CNTs) were deposited on diazonium-modified, flexible indium tin oxide (ITO) electrodes prior to the electropolymerization of pyrrole. This three-step process, including diazonium electroreduction, the deposition of CNTs and electropolymerization, provided adhesively-bonded, polypyrrole-wrapped CNT composite coatings on aminophenyl-modified flexible ITO sheets. The aminophenyl (AP) groups were attached to ITO by electroreduction of the in-situ generated aminobenzenediazonium compound in aqueous, acidic medium. For the first time, polypyrrole (PPy) was electrodeposited in the presence of both benzenesulfonic acid (dopant) and ethylene glycol-bis(2-aminoethylether)-tetraacetic acid (EGTA), which acts as a chelator. The flexible electrodes were characterized by XPS, Raman and scanning electron microscopy (SEM), which provided strong supporting evidence for the wrapping of CNTs by the electrodeposited PPy. Indeed, the CNT average diameter increased from 18 ± 2.6 nm to 27 ± 4.8, 35.6 ± 5.9 and 175 ± 20.1 after 1, 5 and 10 of electropolymerization of pyrrole, respectively. The PPy/CNT/NH2-ITO films generated by this strategy exhibit significantly improved stability and higher conductivity compared to a similar PPy coating without any embedded CNTs, as assessed by from electrochemical impedance spectroscopy measurements. The potentiometric response was linear in the 10−8–3 × 10−7 mol L−1 Pb(II) concentration range, and the detection limit was 2.9 × 10−9 mol L−1 at S/N = 3. The EGTA was found to drastically improve selectivity for Pb(II) over Cu(II). To account for this improvement, the density functional theory (DFT) was employed to calculate the EGTA–metal ion interaction energy, which was found to be −374.6 and −116.4 kJ/mol for Pb(II) and Cu(II), respectively, considering solvation effects. This work demonstrates the power of a subtle combination of diazonium coupling agent, CNTs, chelators and conductive polymers to design high-performance electrochemical sensors for environmental applications.

Garcia-Cabezon C., Garcia-Hernandez C., Rodriguez-Mendez M.L., Martin-Pedrosa F.

In this work, a method to improve the protection against corrosion of porous sintered stainless steel is presented. It is based on the electrodeposition of polypyrrole (PPy) layers doped with a large size counterion such as dodecylbenzenesulphonic acid (DBSA), a conducting polymer with high corrosion resistance and good biocompatibility. The efficacy of PPy coating depends on the adequate adhesion between the metal substrate and the coating layer. The protection against corrosion has been tested using 316 L stainless steel (SS) powder sintered at different conditions to evaluate the effect of the sintering atmosphere (nitrogen and vacuum) and cooling rates (furnace and water) on corrosion resistance, while wrought 316 L SS has been used as reference material. In addition, two electrochemical deposition techniques have been tested to select the most adequate. Open circuit potential evolution, anodic polarization measurements and electrochemical impedance spectra have been used to evaluate corrosion protection in phosphate buffer saline medium. It has been evidenced that a more homogeneous and stable coating was obtained in the case of porous stainless steel. The corrosion potential shifted to nobler values and the anodic polarization branch became more stable. Coated porous samples have a good passivation performance with a lower stable passive current density and a higher breakdown potential. The transfer electronic resistance and the impedance module increase more than one order of magnitude. Therefore, the porosity of sintered stainless steel is seen as an advantage for the improvement of the adherence of the PPy coatings. The best corrosion protection is found for samples sintered in nitrogen and water-cooled.

Cho J.H., Gao Y., Choi S.

Human access to safe water has become a major problem in many parts of the world as increasing human activities continue to spill contaminants into our water systems. To guarantee the protection of the public as well as the environment, a rapid and sensitive way to detect contaminants is required. In this work, a paper-based microbial fuel cell was developed to act as a portable, single-use, on-site water quality sensor. The sensor was fabricated by combining two layers of paper for a simple, low-cost, and disposable design. To facilitate the use of the sensor for on-site applications, the bacterial cells were pre-inoculated onto the device by air-drying. To eliminate any variations, the voltage generated by the microorganism before and after the air-drying process was measured and calculated as an inhibition ratio. Upon the addition of different formaldehyde concentrations (0%, 0.001%, 0.005%, and 0.02%), the inhibition ratios obtained were 5.9 ± 0.7%, 6.9 ± 0.7%, 8.2 ± 0.6%, and 10.6 ± 0.2%, respectively. The inhibition ratio showed a good linearity with the formaldehyde concentrations at R2 = 0.931. Our new sensor holds great promise in monitoring water quality as a portable, low-cost, and on-site sensor.

Hamouma O., Kaur N., Oukil D., Mahajan A., Chehimi M.M.

Low-cost, conductive Pap@CNT-NH2@PPy composites were prepared through sonochemical polymerization of pyrrole in the presence of oxidizing agent and tosylate co-dopant (TS) on cellulosic paper strips decorated with aminophenyl-modified multiwalled carbon nanotubes (CNT-NH2). The modified paper electrodes were examined by XPS, Raman, and SEM. The characterization of the electrochemical properties of the paper electrodes was conducted by cyclic voltammetry and electrochemical impedance spectroscopy. The Pap@CNT-NH2@PPy end materials served as chemiresistive NH3 sensors and exhibited an outstanding response of 525% to 0.1 ppm level of NH3 at RT with good stability for a long period of time. The LOD was found to be as low as 0.04 ppb. To sum up, this work demonstrates that combining aryl diazonium-modified carbon nanotubes and in situ sonochemical polymerization on paper surface permits to provide low cost, functional materials for gas sensors other paper electronic applications.

Korkut S., Göl S., Kilic M.S.

Borrill A.J., Reily N.E., Macpherson J.V.

We highlight the fundamentals and challenges involved with anodic stripping voltammetry (ASV) using solid electrodes providing a practical guide to anyone wishing to undertake analytical ASV.

Kuznetsova O.V., Bychkova Y.V., Timerbaev A.R.

Ogunfowokan A.O., Adekunle A.S., Oyebode B.A., Oyekunle J.A., Komolafe A.O., Omoniyi-Esan G.O.

This study determined the concentrations of some heavy metals (Cd, Pb, Mn, Cu and Zn) in urine samples of patients with kidney, liver and lung related diseases (age 15–70 years); and tissue samples (kidney, liver and lung) that were pathologically abnormal from corpses (age 21–50 years) during autopsies at the Obafemi Awolowo University Teaching Hospitals Complex, Ile-Ife, Nigeria. It also determined the effects of age distribution, gender and life styles on the urine samples of patients with the aforementioned diseases. A total of 35 urine samples of the patients were analyzed out of which 15 had kidney related diseases, 10 had liver related diseases and 10 had lung related diseases. Four urine samples were used as controls. The urine samples were collected before meal and the age, sex, occupation and personal habit of patients were considered when taking samples. The samples were digested using micro-wave assisted digestion method and analyzed with Atomic Absorption Spectrophotometer. The results showed that the concentrations of Cd (0.052–0.093 µg mL−1), Pb (0.150–0.376 µg mL−1), Mn (0.014–0.278 µg mL−1), Cu (0.738–2.475 µg mL−1) and Zn (0.476–0.975 µg mL−1) in urine samples (male and female) were higher than those of the control samples (Cd: 0.035 µg mL−1, Pb: 0.253 µg mL−1, Mn: 0.045 µg mL−1, Cu: 0.040 µg mL−1 and Zn: 0.716 µg mL−1) and also higher than the standard human urine levels of metals recommended by World Health Organisation. Also, Mn had the highest concentrations of all the metals determined in kidney, liver and lung tissues analysed. The study concluded that the high concentrations of heavy metals obtained confirmed the associated health complications noticed in the patients.

Essousi H., Barhoumi H., Bibani M., Ktari N., Wendler F., Al-Hamry A., Kanoun O.

This study reports a new chemical sensor based on ion-imprinted polymer matrix using copper nanoparticles-polyaniline nanocomposite (IIP-Cu-NPs/PANI). This sensor was prepared by electropolymerization using aniline as a functional monomer and nitrate as template onto the copper nanoparticles-modified glassy carbon (GC) electrode surface. Both ion-imprinted (IIP) and nonimprinted (NIP) electrochemical sensor surfaces were evaluated using UV-Visible spectrometry and scanning electron microscopy (SEM). The electrochemical analysis was made via cyclic voltammetry (CV), linear sweep voltammetry (LSV), and impedance spectroscopy (IS). Throughout this study various analytical parameters, such as scan rate, pH value, concentration of monomer and template, and electropolymerization cycles, were optimized. Under the optimum conditions, the peaks current of nitrate was linear to its concentration in the range of 1μM-0.1M with a detection limit of 31μM and 5μM by EIS and LSV. The developed imprinted nitrate sensor was successfully applied for nitrate determination in different real water samples with acceptable recovery rates.

Lo M., Diaw A.K., Gningue‐Sall D., Oturan M.A., Chehimi M.M., Aaron J.

To develop conducting organic polymers (COPs) as luminescent sensors for determination of toxic heavy metals, a new benzene sulfonic acid-doped polypyrrole (PPy-BSA) thin film was electrochemically prepared by cyclic voltammetry (CV) on flexible indium tin oxide (ITO) electrode in aqueous solution. PPy-BSA film was characterized by FTIR spectrometry, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The optical properties of PPy-BSA were investigated by ultraviolet (UV)-visible absorption and fluorescence spectrometry in dimethylsulfoxide (DMSO) diluted solutions. PPy-BSA fluorescence spectra were strongly quenched upon increasing copper(II) ion (Cu2+ ) and lead(II) ion (Pb2+ ) concentrations in aqueous medium, and linear Stern-Volmer relationships were obtained, which indicated the existence of a main dynamic fluorescence quenching mechanism. BSA-PPy sensor showed a high sensitivity for detection of both metallic ions, Cu2+ and Pb2+ , with very low limit of detection values of 3.1 and 18.0 nM, respectively. The proposed quenching-fluorimetric sensor might be applied to the determination of traces of toxic heavy metallic ions in water samples.

Mukendi M.D., Salami O.S., Mketo N.

Molecularly imprinted electrochemical sensors (MI-ECSs) are a significant advancement in analytical techniques, especially for water quality monitoring (WQM). These sensors utilize molecular imprinting to create polymer matrices that exhibit high specificity and affinity for target analytes. MI-ECSs integrate molecularly imprinted polymers (MIPs) with electrochemical transducers (ECTs), enabling the selective recognition and quantification of contaminants. Their design features template-shaped cavities in the polymer that mimic the functional groups, shapes, and sizes of target analytes, resulting in enhanced binding interactions and improved sensor performance in complex water environments. The fabrication of MI-ECSs involves selecting suitable monomeric units (monomers) and crosslinkers, using a target analyte as a template, polymerizing, and then removing the template to expose the imprinted sites. Advanced methodologies, such as electropolymerization and surface imprinting, are used to enhance their sensitivity and reproducibility. MI-ECSs offer considerable benefits, including high selectivity, low detection limits, rapid response times, and the potential for miniaturization and portability. They effectively assess and detect contaminants, like (toxic) heavy metals (HMs), pesticides, pharmaceuticals, and pathogens, in water systems. Their ability for real-time monitoring makes them essential for ensuring water safety and adhering to regulations. This paper reviews the architecture, principles, and fabrication processes of MI-ECSs as innovative strategies in WQM and their application in detecting emerging contaminants and toxicants (ECs and Ts) across various matrices. These ECs and Ts include organic, inorganic, and biological contaminants, which are mainly anthropogenic in origin and have the potential to pollute water systems. Regarding this, ongoing advancements in MI-ECS technology are expected to further enhance the analytical capabilities and performances of MI-ECSs to broaden their applications in real-time WQM and environmental monitoring.

Bourkeb K.W., Abdessemed D., Alaoui-Sossé B., Chronopoulou L., Baaloudj O., Herlem G.

Bisphenol A (BPA) has been suspected of being ecotoxic for the last few years, even though it has been in use for almost 100 years. It has had time to accumulate at all ecosystem levels via numerous pathways. As BPA is an endocrine disruptor, exposure to it even at low concentrations presents significant health risks. Therefore, it is essential to promptly and accurately detect this hazardous chemical compound in various water sources. In this work, the selective detection of BPA in various aquatic matrices has been studied using the analytical method of square wave adsorptive stripping voltammetry (SWAdSV). This method involves the use of a pencil graphite electrode that was coated with molecularly imprinted electropolymerized polyaniline and was modified with single-walled carbon nanotubes (SWCNT) as a working electrode. The procedures were detailed and explained, with electrochemical indication exhibited during the imprinting and modification of the electrode. Furthermore, the electrode was characterized throughout the process. For the application of the obtained sensor, the imprinting enhanced the material’s affinity for BPA relative to other competing molecules and selectivity experiments revealed only minor interference from other molecules in the detection of BPA molecules. Under optimal conditions, the sensor could operate linearly over the concentration range from 5.0 to 438.0 µM, with a detection limit of 4.61 µM (S/N = 3.3). The prepared sensor has effectively detected traces of BPA molecules in various real aqueous matrices, demonstrating their practical use in environmental monitoring.

Shoeb M., Mashkoor F., Naved Khan M., Kim B., Jeong C.

A novel strategy for addressing industrial wastewater and energy storage issues has been introduced by constructing a symmetric supercapacitor device using the adsorption of antimony (Sb(III)) from wastewater, facilitated by RGO-Au-Ag2O/PIn NCs heralding a new era of efficiency and sustainability. The room temperature mediated synthesis of RGO-Au-Ag2O/PIn NCs demonstrates exceptional efficacy in Sb(III) removal. Moreover, we developed a sustainable approach by repurposing spent Sb(III) adsorbed RGO-Au-Ag2O/PIn NCs for energy storage, thereby reducing secondary pollution. The RGO-Au-Ag2O/PIn NCs presented the maximum removal efficiency of ∼ 90 % at 60 mg/L of initial Sb(III) concentration at pH 8 and 15 mg/25 mL. Experimental adsorption data of Sb(III) onto the RGO-Au-Ag2O/PIn NCs was well fitted with pseudo-second-order kinetic model and Langmuir adsorption isotherm model. Subsequently, the Sb-enriched waste adsorbent (RGO-Au-Ag2O/PIn@SbOx) was utilized to develop a symmetric supercapacitor device, which displayed an energy density of 40.66 Wh/kg alongside a power density of 1000 W/kg. Importantly, this device maintained 82 % capacitance retention even after 12,000 cycles. This research provides an effective method for repurposing exhausted adsorbents, potentially improving energy-efficient recycling of hazardous solid residues in an economical and environmentally friendly way.

Zine P.C., Narwade V.N., Patil S.S., Qureshi M.T., Tsai M., Hianik T., Shirsat M.D.

In this work, an amino-functionalized graphene oxide/polypyrrole (AMGO/PPy) composite-based novel sensing platform was established to monitor lead ions (Pb2+) at high sensitivity. AMGO was synthesized through a hydrothermal process and later formed a composite with PPy at varying concentrations. A physicochemical investigation of the synthesized materials was carried out using various characterization tools, while the electrochemical properties were examined by cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS) methods. The AMGO/PPy composite was deposited on a glassy carbon electrode (GCE), which was used for the real-time electrochemical detection of Pb2+. The AMGO/PPy sensor exhibited lower limits of detection (LOD) of 0.91 nM. In addition, the developed Pb2+ sensor exhibited excellent reproducibility, repeatability, selectivity, sensitivity, and long-term stability for 25 days. The AMGO/PPy composite emerges as a ground-breaking material for the electrochemical detection of Pb2+, holding significant potential for environmental monitoring and the protection of human health.

Jain N., Waidi Y.O.

Wang J., Ye J., Li G.

Li D., Yang F., Shi X., Tian G., Fu C., Liu Y., Guo Z.

Khatun M.N., Chanu M.A., Barman D., Ghosh P., Sarmah T., Adil L.R., Iyer P.K.

Sood Y., Singh K., Mudila H., Lokhande P.E., Singh L., Kumar D., Kumar A., Mubarak N.M., Dehghani M.H.

Recent advancements in polymer science and engineering underscore the importance of creating sophisticated soft materials characterized by well-defined structures and adaptable properties to meet the demands of emerging applications. The primary objective of polymeric composite technology is to enhance the functional utility of materials for high-end purposes. Both the inherent qualities of the materials and the intricacies of the synthesis process play pivotal roles in advancing their properties and expanding their potential applications. Polypyrrole (PPy)-based composites, owing to their distinctive properties, hold great appeal for a variety of applications. Despite the limitations of PPy in its pure form, these constraints can be effectively overcome through hybridization with other materials. This comprehensive review thoroughly explores the existing literature on PPy and PPy-based composites, providing in-depth insights into their synthesis, properties, and applications. Special attention is given to the advantages of intrinsically conducting polymers (ICPs) and PPy in comparison to other ICPs. The impact of doping anions, additives, and oxidants on the properties of PPy is also thoroughly examined. By delving into these aspects, this overview aims to inspire researchers to delve into the realm of PPy-based composites, encouraging them to explore new avenues for flexible technology applications.

Mahmoud R., Abdel-Hady E.E., Mohamed H.F., Ibrahim M., Abd El-Fatah G., Zaher A., Gadelhak Y.

Heavy metals are considered one of the many challenges facing the wastewater treatment industry. One of the main technologies required to face such a challenge is the fast, cost-effective, selective, and sensitive detection of such heavy metals. Recently, functionalized nanomaterials have emerged as promising electrode materials for the reliable electrochemical sensing of heavy metals in wastewater effluents. This chapter will focus on reviewing the recent reports related to the electrochemical detection of heavy metals using cost-effective nonprecious metal-based nanomaterials. Such nanomaterials include metals, metal oxides, layered double hydroxides, and carbonaceous, polymeric, and metal-organic frameworks. Moreover, special focus is provided for studies related to the disposable and portable applications of electrochemical methods. Numerous types of nanomaterials can be identified as promising candidates for the electrochemical detection of heavy metals below the limit required by the World Health Organization.

Al Kausor M., Gupta S.S., Chakrabortty D.

Graphene and graphene oxide (GO) are used for adsorbing toxic heavy metal ions, but they have disadvantages like aggregation of graphene layers due to strong π–π interactions and difficulty in separation. Thus, adsorption efficiency of bare graphene and GO is quite low. Surface modification techniques have improved GO’s adsorption capacity. Various GO-based materials, including chemically modified functionalized GO, non-metal- and metal-based GO composites, metal oxide-based GO and GO-organic compound composites, have been designed for wastewater decontamination. In this review article, the chemistry of graphene-based composites reported by various group of workers since last ten years is reviewed. The synthesis processes, characterizations of prepared materials and application as scavengers or adsorbents were critically analysed. The limitations and the future directions are also highlighted.

Santos-Ceballos J.C., Salehnia F., Romero A., Vilanova X., Llobet E.

Shehzad H., Shuang M.T., Chen J., Liu Z., Sharif A., Farooqi Z.H., Ahmed E., Begum R., Zhou L., Ouyang J., Irfan A., Chaudhary A.R., Shaukat S., Hussain U.

In this study, hierarchical mesoporous and N/P-codoped templated biocarbon was prepared from Bambusa Vulgaris culms through pyrolysis under reducing conditions. The biocarbon was functionalized with 2D-MoS2 nanosheets via hydrothermal reaction and later different mol fractions of polypyrrole (PPy) were electrodeposited to boost the electrode conductivity. The resultant BBC/PPy composites were characterized comprehensively using XRD, FTIR, SEM-EDX and BET. BBC/PPy-3 deposited with PPy-3 ( using 0.3 M pyrrole) exhibited superior electro-sorption performance due its enhanced specific resistance, Csp (140.4 F/g) and high specific surface area, Asp (128.77 m2/g). The heteroatoms doping into biocarbon brought the essential chelating capability and hydrophilicity. BBC/PPy-3 showed remarkable sorption capacity of 402.5 mg/g at optimized value of pH (4.5-5.0). The electrochemical impedance spectroscopic (EIS) data revealed that BBC/PPy-3 presented relatively small charge transfer resistance Rct (1.78 Ω cm2), minute electrolytic resistance, Rs (0.97 Ω cm2) and large double layer constant phase element, qdl (0.0357 S sn/ cm2). The galvanostatic charge discharge (GCD) curves showed all composites as stable supercapacitors. BBC/PPy composites proved themselves as competitive and selective materials for the economic removal of U(VI) from effluents containing low concentration of U(VI).

Dehghani P., Karthikeyan V., Tajabadi A., Assi D.S., Catchpole A., Wadsworth J., Leung H.Y., Roy V.A.

Mahmoud R., Abdel-Hady E.E., Mohamed H.F., Ibrahim M., Abd El-Fatah G., Zaher A., Gadelhak Y.

Heavy metals are considered one of the many challenges facing the wastewater treatment industry. One of the main technologies required to face such a challenge is the fast, cost-effective, selective, and sensitive detection of such heavy metals. Recently, functionalized nanomaterials have emerged as promising electrode materials for the reliable electrochemical sensing of heavy metals in wastewater effluents. This chapter will focus on reviewing the recent reports related to the electrochemical detection of heavy metals using cost-effective nonprecious metal-based nanomaterials. Such nanomaterials include metals, metal oxides, layered double hydroxides, and carbonaceous, polymeric, and metal-organic frameworks. Moreover, special focus is provided for studies related to the disposable and portable applications of electrochemical methods. Numerous types of nanomaterials can be identified as promising candidates for the electrochemical detection of heavy metals below the limit required by the World Health Organization.