Studies On The Preparation, Characterization And Sensing Applications Of Liquid Phase-Exfoliated Graphene Modified Electrodes Toward Cd²⁺ And Pb²⁺

The problem of heavy metal pollution has been recognized as an issue of global concern. Cadmium and lead, typical examples of heavy metals, exist in the environment extensively, and attract much attention due to their high toxicity. It is well established that Cd²⁺ and Pb²⁺ have the greatest detrimental effects on kidney and nervous system.Therefore, it is worthwhile to develop a sensitive, rapid and operationally simple method for the determination of trace levels of Cd²⁺ and Pb²⁺. In this thesis, we developed a highly sensitive determination method for trace levels of Cd²⁺ and Pb²⁺ based on the enhancement of graphene produced by one-step liquid-phase exfoliation of graphite powder in NMP. The main contents includes the following two parts:1. Graphene nanosheets?GS? were easily prepared by one-pot ultrasonic exfoliation with the spectrum pure graphite in NMP, and used to modified glass carbon electrode?GS/GCE?. It was found that the anodic stripping peak currents of Cd²⁺ and Pb²⁺ increased greatly on the surface of GS/GCE. Compared with the bare GCE, GS/GCE showed higher accumulation ability for Cd²⁺ and Pb²⁺ and increased the anodic stripping peak currents of Cd²⁺ and Pb²⁺. More importantly, the response signals of Cd²⁺ and Pb²⁺ on GS/GCE further enhanced significantly in the presence of Bi3+, showing remarkable synergistic signal enhancement effects. As a result, a highly sensitive electrochemical sensor was successfully developed for Cd²⁺ and Pb²⁺ based on synergistic signal enhancement effects. The linear range was from 0.5 to 100 ?g L^-1 for Cd²⁺, and from 0.1 to 100 ?g L^-1 for Pb²⁺. Based on three signal-to-noise ratio, the values of detection limit were calculated to be 0.35 ?g L^-1and 0.045 ?g L^-1 for Cd²⁺ and Pb²⁺ after 3-min accumulation. Additionally, ICP-MS was also used to testify the accuracy of the proposed method. It was found that the obtained results were in good agreements, and the relative error was below 9%.2. Graphene were facilely prepared through one-step liquid-phase exfoliation of graphite powder in NMP with the sodium citrate as assistance agent?GS-cit?. Effects ofgraphite concentration and ultrasonic time on the GS-cit was characterized with transmission electron microscopy?TEM?, atomic force microscope?AFM?, dynamic light scattering particle size analyzer, raman spectra and anodic stripping voltammetry?ASV?.The results show that the introduction of the sodium citrate not only improved the efficiency of the graphene's preparation, but also significantly enhanced the signals of Cd²⁺and Pb²⁺. Based on the synergistic enhancement effects of GS-cit, a novel electrochemical sensor was developed for Cd²⁺ and Pb²⁺, the linear ranger was from 1 to 100 ?g L^-1 for Cd²⁺,and 0.5 to 100 ?g L^-1 for Pb²⁺, the limit of detection was 0.49 ?g·L^-1 for Cd²⁺ and 0.21?g·L^-1 for Pb²⁺. Additionally, ICP-MS was also used to testify the accuracy of the proposed method. It was found that the obtained results were in good agreements, and the relative error was below 7%.