Preparation Of Graphene-sulphide Quantum Dots Composites And Their Application Of Photoelectrochemical Sensing

Quantum dots (QDs)-based sensor for chemical and biological detection is presently a technologicalhot topic because of the following advantages: fast response, high sensitivityand small dark current; singleQDs are not stable and prone to aggregate due to large active surface area, which results in deteriorations ofphotoelectrochemical properties. To enhance the photocurrent generated by the semiconductor materials, itis essential to retard the recombination of electron-hole pairs in the semiconductors by introducing efficientelectron-transport matrices, such as noble metal, carbon nanotube and graphene. It is well known thatgraphene has been extensively considered as promising candidates for two-dimensional planar conjugationstructure, its large specific surface area and high electron mobility.Photoelectrochemical sensing has generally applied for the detection of biological or chemicalmolecules. In detection process, light is used to induce electron transfer betweenphotoelectrochemical-active species and electrode for generating the detectable photocurrent signal. PECtechnique presents higher sensitivity and selectivity.This paper research preparation of graphene-sulphide quantum dots composites and their applicationof photoelectrochemical sensing. The main contents of this thesis are as follows:(1) Preparation of graphene-CdS quantum dots composites and their photoelectrochemical sensingglucose: GR-CdS QDs were prepared through one-step hydrothermal method using Cd(CH3COO)22H2O,thiourea and poly (acrylic acid). The phase structure of the products were characterized by TEM, HRTEM,XRD, XPS, FTIR and UV-vis. TEM and HRTEM results proved that CdS QDs with average size of~6nmwere homogeneously dispersed on graphene sheets. The photoelectrochemical property ofgraphene-CdS/ITO electrode was researched and developed to detect glucose. The sensor exhibited goodselectivity and linear relationship from0.1-4mM with detection limit of7μM(2) Preparation of graphene-CdS composites and their photoelectrochemical sensing Cu2+utilizing PVPas surfactant, CdSO4and Na2S2O3were prepared graphene-CdS composites via a facile hydrothermalmethod. TEM results proved that CdS with average size of~30nm were homogeneously dispersed ongraphene sheets. The photoelectrochemical property of graphene-CdS/ITO electrode was researched and developed to detect Cu2+. The sensor exhibited good selectivity and linear relationship from10μM to80μM with detection limit of9.5nM(3) Preparation of graphene-ZnxCd1-xS quantum dots composites and photoelectrochemical sensingCu2+. We prepared graphene-ZnxCd1-xS (x=0~1) quantum dots via a one-step hydrothermal approach inaqueous solution. By varying of Zn/Cd molar ratios (x=0~1) in precursors could be gained a series ofGR-ZnxCd1-xS with different the band gaps (2.3~3.6eV). The controlled experiments proved thatgraphene-Zn0.8Cd0.2S/ITO electrode with2mg graphene dosage exhibited the highest photocurrent atapplied voltage of0.2V. Therefore, a photoelectrochemical sensor was developed to detect Cu2+usinggraphene-Zn0.8Cd0.2S/ITO electrode. The sensor exhibited good selectivity and linear relationship from1μM to120μM with detection limit of6.5nM(4) Preparation of graphene-ZnS quantum dots composites and their photoelectrochemical sensingHg2+: we prepared graphene-ZnS quantum dots via a one-step hydrothermal approach. TEM and HRTEMresults proved that ZnS QDs with average size of~6nm were homogeneously dispersed on graphene sheets,a photoelectrochemical sensor was developed to detect Hg2+using graphene-ZnS/ITO electrode. The sensorexhibited good selectivity and linear relationship from40μM to400μM with detection limit of1μM...