Electrochemical determination of methylmercury via modulating bandgap of sulfur doped graphitic carbon nitride

Abstract

Methylated mercury compounds are neurotoxins; they are ubiquitous in muddy sediments of water bodies under anaerobic conditions. A variety of coupled techniques such as capillary gas chromatography with inductively coupled plasma mass spectroscopy, or atomic fluorescence spectroscopy is used for detection of methylated mercury compounds. However, a sensitive analytical method for rapid screening of methylated mercury compounds is required. This work it was developed an electrochemical method for the detection of methylmercury in environmental samples using chemically modified Au electrodes via the bandgap modulation strategy. For the chemical modification, the sulfur-doped g-C3N4 was used as a starting material. The forbidden bandgap of the sulfur-doped g-C3N4 was regulated with urea and thiourea admixture fabricated by thermal polymerization at an optimal ratio (urea: thiourea = 3:1; hereafter UT-gCN (3:1). The UT-gCN (3:1) modified Au electrode was used for rapid detection of CH3Hg+ by differential pulse voltammetry (DPV) method operated at −0.80 V deposition potential, 800 s accumulation time in NaAc/HAc buffers (pH=5.0). The calibration curve of CH3Hg+ showed linearity within concentration range 0–25 ppb CH3Hg+ with 0.52 μA/ppb sensitivity and 0.175 ppb detection limit. The new electrochemical sensor is robust and interference-free to Cu2+, Cd2+, Pb2+, Bi3+, As3+. The efficiency of the UT-gCN(3:1) sensor can be replenished by protonation with HCl. Present results indicate the potential applications of UT-gCN (3:1) modified Au electrodes in the rapid detection of methylmercury in environmental samples.