In-suit synthesis of graphene/gold nanoparticles modified glassy carbon electrode for detection of lead in water and soil

Abstract: Lead is a toxic heavy metal which is extremely harmful to the human body. Lead and its compounds can cause great harm to nerves, hematopoiesis, digestion and kidneys. In agricultural production, lead in water and soil can be deposited in crops, which is one of the main causes of lead pollution. Therefore, the detection of lead in water and soil is very important. Recently, it was reported that square wave anodic stripping voltammetry (SWASV) by using different nanomaterials modified working electrode had great test performance in heavy metal ions detection. Compared with the traditional mercury or bismuth film modified electrode, which can have secondary pollution to the environment, nanomaterials modified electrode has lower detection limit and broader detection range, and can be more stable than mercury or bismuth film modified electrodes. In this study, the graphene and HAuCl4 were used to fabricate graphene/gold nanoparticles modified glassy carbon electrode. First, 5 μL graphene-DMF(1 g/mL) solution and 153 μL HAuCl4 (48.65 mmol/L) were added into 842 μL ethanol solution (50%). 6 μL suspension of GR/HAuCl4 was casted on a glassy carbon electrode, and kept for drying at room temperature. GR-AuNPs/GCE was electrochemically reduced in the 0.5 mol/L NaCl by cyclic voltammetry method between ?1.3 V and +0.8 V at 50 mV/s scan rate for 11 potential cycles. The electrochemical characterization of the GR/AuNPs/GCE was studied by cyclic voltammetry (CV) method. The results showed that the GR-AuNPs/GCE had better surface conductivity compared with the bare GCE and the GR/GCE. The modified electrode was used to detect the standard samples of lead (II) in acetate buffer solution by square wave anodic stripping voltammetry with an amplitude of 0.025 V, pulse width of 0.2 s, pulse period of 0.4 s, and scan range between ?1.3 and +0.8 V. The deposition potential was ?1.2 V and the deposition time was 180 s. Before the next cycle, the electrode was cleaned for 60 s at 0.8 V with stirring. For a better detection result, some detection conditions were optimized including the concentration of HAuCl4 in the GR-HAuCl4 mixed liquid, potential cycles of cyclic voltammetry, pH value of the acetate buffer solution, deposition potential and deposition time. Under all optimization conditions, the dissolution peak of lead ion (II) is ?0.08 V in acetate buffer solution, and had a linear response to lead ion (II) in the concentration range from 1 to 90 μg/L (R2 = 0.985), with the detection limit concentration of 0.27 μg/L. GR-AuNPs/GCE was successfully used to analyze the concentration of lead ion (II) in water and soil with standard join law. Water and soil used for this experiment was obtained from Hangzhou Dianzi University, both divided into five groups. Both water samples and soil samples had five concentrations from 10 to 50 μg/L. The recovery ranges of lead ion (II) in water samples and soil samples were 93.75%-109.2% and 93.82%-109.92%, with all RSDs were below 7%, which showed that the GR-AuNPs/GCE has a good detection performance for the actual samples.