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Nanostructured Sulfur-Doped Porous Reduced Graphene Oxide for the Ultrasensitive Electrochemical Detection and Efficient Removal of Hg(II)

Manna, Bhaskar, Raj, C. Retna
ACS sustainable chemistry & engineering 2018 v.6 no.5 pp. 6175-6182
absorption, adsorption, annealing, carbon, electrochemistry, electrodes, endothermy, graphene oxide, mercury, metal ions, porosity, prototypes, remediation, silica, sorption isotherms, spectral analysis, sulfur, surface area, temperature, thermodynamics, toxicity
The selective detection and efficient removal of toxic Hg(II) are very challenging for environmental remediation and industrial processing. Herein, we demonstrate the selective electrochemical detection of Hg(II) and its removal using porous three-dimensional sulfur-doped reduced graphene oxide (pS-rGO). The thermal annealing of graphene oxide in the presence of dibenzyl disulfide and silica template at a controlled temperature of 900 °C yields pS-rGO, and it has a large surface area of 449.43 m² g–¹ and 9.96% sulfur in the carbon network. The favorable interaction of Hg(II) with pS-rGO owing to the porous structure and presence of a large amount of thiophenic sulfur is exploited for the electrochemical detection and removal of Hg(II). The selective electrochemical detection of Hg(II) is demonstrated at the potential of 0.2 V without any interference from coexisting other metal ions. The sensing platform could detect as low as 0.1 ppb (0.5 nM; S/N = 14) with a sensitivity of 11.98 ± 0.26 μA ppb–¹ cm–². The platform is highly stable, and only a 9% decrease in the initial current was noticed after 7 days of use. Removal of Hg(II) from water is successfully demonstrated with pS-rGO. It has a high Hg(II) uptake capacity of 829.27 ± 7.19 mg g–¹, which is higher than the uptake capacity of undoped porous rGO and nonporous S-rGO. It can be repeatedly used at least four times without any compromise in the Hg(II) uptake capacity. The adsorption process follows the Langmuir isotherm, and the thermodynamic parameters (ΔG°, ΔH°, and ΔS°) obtained evidence that the adsorption is spontaneous and endothermic in nature. Practical utility is demonstrated by developing a prototype Hg(II) decontaminant column packed with pS-rGO, and the column could successfully remove 99.99% of Hg(II). The results obtained with a pS-rGO-based electrode and prototype decontaminant column are authenticated with atomic absorption spectroscopic measurements. The performance of undoped nonporous rGO toward detection and removal is inferior to that of pS-rGO. The remarkable performance of pS-rGO highlights the role of both porosity and S doping.