from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). All the solutions were prepared with deionized water 2.2. Apparatus In this work,electrochemical measurements were performed using a model VersaSTAT 3 electrochemical workstation (Princeton Applied Research, USA). We used a three electrode system in 5.0 mmol/L K3Fe(CN)6] solution containing 0.2 mol/L KCl at room temperature (RT. 25 °C) to measure electrochemical response, which composed of platinum wire as auxiliary electrode, Ag/AgCl electrode as reference electrode and modified gold electrode as working electrode. Before use. the surface of the gold electrode was polished by 0.3 mm and 0.05 mm alumina slurry, respectively Then the gold electrode was washed and sonicated in deionized water for 5 min. After drying at RT, it was subjected to sweep cyclically in 0.05 mol/L K3[Fe(CN)6] solution between -0.20 V and +0.60 V to judge the quality of the pretreatment process. Scanning electron microscope (SEM) images were obtained using field emission SEM (ZEISS, Germany). The Fourier transform infrared spectroscopy (FTIR) was recorded using Spectrum One FTIR apparatus (Perkin Elmer, USA). 2.3. Synthesis of CS-SNP CS-SNP composites were prepared according to previous method (Prakash et al., 2012). First of all, we dissolved 50 mg Cs into 10 mL of 1.0% (W) acetic acid solution and then stirred the mixture for 2 h at RT until it was completely dispersed. The pH was adjusted to 5.0 using 1.0 mol L-1 NaOH solution under vigorous stirring. Second, 10 ml of 30 mmol L AgNO3 was added to the prepared CS solution under stirring (30 min) at RT. Then, 1 uL of hydrazine hydrate (35%, v/v) was added to the resulting mixture The mixture was kept under constant stirring at 60 °C for 3 h. The CS-SNP composites were obtained by centrifugation and washed couple of times with deionized water. At last, the purified sample was dispersed in 10 mL deionized water. Therefore, CS-SP composites were obtained. 2.4. Preparation of GR-MWCNTs b The synthesis of GR-MWCNTs composites consisted of the