The detection of toxic gases has long been a priority in industrial manufacturing, environmental monitoring, medical diagnosis, and national defense. The importance of gas sensing is not only of high benefit to such industries but also to the daily lives of people. Graphene-based gas sensors have elicited a lot of interest recently, due to the excellent physical properties of graphene and its derivatives, such as graphene oxide (GO) and reduced graphene oxide (rGO). Graphene oxide and rGO have been shown to offer large surface areas that extend their active sites for adsorbing gas molecules, thereby improving the sensitivity of the sensor. There are several literature reports on the promising functionalization of GO and rGO surfaces with metal oxide, for enhanced performance with regard to selectivity and sensitivity in gas sensing. These synthetic and functionalization methods provide the ideal combination/s required for enhanced gas sensors. In this review, the functionalization of graphene, synthesis of heterostructured nanohybrids, and the assessment of their collaborative performance towards gas-sensing applications are discussed.
A simple, highly sensitive, accurate, and low-cost electrochemical sensor was developed for the determination of over-the-counter painkiller, paracetamol (PC). The enhanced sensing capabilities of the developed sensor were fabricated by the single-step modification of disposable pencil graphite electrodes (PGEs) with the simultaneous electrochemical reduction in graphene oxide and antimony (II) salts. For this purpose, an electrochemically reduced graphene oxide–antimony nanoparticle (ERGO-SbNP) nanocomposite material was prepared by trapping metallic nanoparticles between individual graphene sheets in the modification of PGEs. Structural characterization by FTIR and Raman spectroscopy was employed to confirm the presence of oxygen functional groups and defects in the conjugated carbon-based structure of GO. Morphological differences between the modified PGEs were confirmed by HRTEM and HRSEM for the presence of nanoparticles. The modified electrodes were further electrochemically characterized using CV and EIS. The electrooxidation of PC on an ERGO-SbNPs-PGE was achieved by adsorptive stripping differential pulse voltametric analysis in 0.1 mol·L−1 phosphate buffer solution at pH = 7.0. The optimum current response was used to record a detection limit of 0.057 µmol·L−1 for PC. The electrochemical sensor was further used in real sample analysis for a commercially available pharmaceutical tablet (500 mg PC), for which the percentage recovery was between 99.4% and 100.8%.
Electroanalysis of heavy metal ions in the presence of cupferron ligands has been extensively studied due to its ability to form stable metallic coordination complexes. Herein, electrochemically reduced graphene oxide (ERGO) sheets were for the first time employed in conjunction with low-cost, disposable pencil graphite rods and in-situ plated thin mercury films (HgF) for the simultaneous detection of Cd2+, Cu2+, Pb2+, and Zn2+ in the presence of cupferron as a chelating agent by square-wave adsorptive cathodic stripping voltammetry (SW-AdCSV). The technique is based on the catalytic reduction of adsorbed cupferron-metal ion complexes at the surface of the ERGO-HgF-PGE at 0.1 V for 60 s in 0.1 M acetate buffer solution (pH 4.6). Owing to the improved electronic and surface effects associated with ERGO inclusion, improved sensitivity was further achieved. Under optimized conditions, the ERGO-HgF-PGE showed a linear relationship from 20 to 200 µg.L-1 with detection limits below the US-EPA of 0.17 μg.L-1 , 0.02 μg.L-1 , 0.17 μg.L-1 and 0.14 μg.L-1 for Cd2+, Cu2+, Pb2+ and Zn2+, respectively at a deposition time of 60 s. The ERGO-HgF-PGE exhibited highly reproducible results with negligible intermetallic interferences and applied successfully to the determination of trace metals in tap water with satisfactory results.
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