Population-driven socioeconomic urban expansion, industrialization, and intensified modern agricultural practices are interlinked to environmental challenges culminating in compromised water quality due to pollution by toxic, persistent, and bioaccumulative heavy metal ions, pesticides, nitroaromatics, and other emerging pollutants. Considering the detrimental impact of pollutants on human health and ecosystem, their detection in different media including water is paramount. Notably, electrochemical techniques are more appealing owing to their recognized advantages. This research summarizes and evaluates the most recent advances in the electrochemical sensing of environmental pollutants such as heavy metal ions, pesticides, nitroaromatics, and other distinct emerging contaminants. Besides, the review focuses on the application of electrochemical detection of the selected pollutants through analysis of representative reports in the five years from 2016 to 2020. Therefore, the review is intended to contribute insights and guidelines to contemporary progress in specific electrochemical application practices based on graphene derivatives, toward the aforenamed pollutants. Thus, it focused on sensing methods such as cyclic voltammetry, anodic stripping voltammetry, and electrochemical impedance spectroscopy employing different sensing elements incorporating graphene. Moreover, the review also highlighted graphene synthesis pathways, sensor design strategies, and functionalization. Furthermore, the review showed that there is congruence in the literature that functionalized graphene and its derivatives remain as viable modifiers in electrochemical sensing of pollutants. Nonetheless, the study also appraised the absence of literature reports on electrochemical detection of natural organic matter substances like humic acid and fulvic acid using a graphene-based sensor. In reckoning, current challenges related to graphene synthesis and applicability, envisaged opportunities, and future perspectives are outlined.

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Graphene oxide (GO) decorated with silver (Ag), copper (Cu) or platinum (Pt) nanoparticles that are anchored on dodecylbenzene sulfonic acid (DBSA)-doped polyaniline (PANI) were prepared by a simple one-step method and applied as novel materials for high performance supercapacitors. High-resolution transmission electron microscopy (HRTEM) and high-resolution scanning electron microscopy (HRSEM) analyses revealed that a metal-decorated polymer matrix is embedded within the GO sheet. This caused the M/DBSA–PANI (M = Ag, Cu or Pt) particles to adsorb on the surface of the GO sheets, appearing as aggregated dark regions in the HRSEM images. The Fourier transform infrared (FTIR) spectroscopy studies revealed that GO was successfully produced and decorated with Ag, Cu or Pt nanoparticles anchored on DBSA–PANI. This was confirmed by the appearance of the GO signature epoxy C–O vibration band at 1040 cm−1 (which decreased upon the introduction of metal nanoparticle) and the PANI characteristic N–H stretching vibration band at 3144 cm−1 present only in the GO/M/DBSA–PANI systems. The composites were tested for their suitability as supercapacitor materials; and specific capacitance values of 206.4, 192.8 and 227.2 F·g−1 were determined for GO/Ag/DBSA–PANI, GO/Cu/DBSA–PANI and GO/Pt/DBSA–PANI, respectively. The GO/Pt/DBSA–PANI electrode exhibited the best specific capacitance value of the three electrodes and also had twice the specific capacitance value reported for Graphene/MnO2//ACN (113.5 F·g−1). This makes GO/Pt/DBSA–PANI a very promising organic supercapacitor material.

Lithium manganese phosphate nanoparticles (LiMnPO 4 ; LMP) as well as the nickel-doped (LMNP) and graphenised derivatives (G-LMNP) were synthesized. Electrochemical characteristics of the materials were examined using cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge-discharge. Lithium ion capacitors (LIC) fabricated using LMP and composite materials as positive electrodes and activated carbon as the negative electrode, exhibited a specific capacitance of 60 F g À 1 at a current load of 0.1 A g À 1 for the AC//G-LMNP LIC. Capacitance retention of 83 % was obtained by the AC//G-LMNP LIC after 750 cycles, with a high specific power of 19 kW kg À 1 at 0.5 A g À 1 .

A Li2MnSiO4/Al2O3 nanocomposite (LMSA) was prepared as positive electrode material for aqueous supercapatteries by hydrothermal synthesis of Li2MnSiO4 nanoparticles (LMS) followed by wet chemical coating with Al2O3. Scanning electron microscopy (SEM) mapping of the spherical LMSA nanoparticles indicated a homogenous distribution of the constituent atoms. Small‐angle X‐ray scattering (SAXS) measurements revealed that a prominent population of the nanoparticles show a center‐to‐center spacing of 7 nm. This is resulting in a large surface area accessible for the migration of Li‐ions and efficient charge storage, leading to improved electrochemical performance as a supercapattery electrode. X‐ray diffraction (XRD) and solid‐state nuclear magnetic resonance spectroscopy (SS NMR) studies portrayed the orthorhombic (Pmn21) crystalline phase of the LMSA and LMS materials which provides a good migratory pathway for the Li‐ions. The nanocomposite showed a high rate performance as a positive electrode in an aqueous supercapattery assembled with activated carbon as the negative electrode. The hybrid cell delivered a maximum specific capacitance of 141.5 F g−1 and a maximum specific power of 4020.8 W kg−1 with good cyclic stability and capacitance retention of 93.6 % after 100 cycles. These results the promising potential of the Li2MnSiO4/Al2O3 nanocomposite as candidate for advanced supercapatteries.