| Metal-organic frameworks (MOFs) are infinite crystalline networks resulting from the bonding of metal ions, which act as coordination centers, with polyfunctional organic molecules. As a result, they are stable nanoporous materials with high mechanical and thermal stability. Applications of MOFs for catalysis, gas storage, and separation are the focus of considerable research. In this paper, metal-organic framework was proposed for analytical purpose, and the main study includes three parts:Chapter2Metal-organic framework modified carbon paste electrode for lead sensorMetal-organic framework (MOF) is a relatively new group of interesting materials for specific electrochemical sensing because of its electrocatalytic activity and large surface area. Here, a Zn4O(BDC)3(MOF-5; BDC2-=1,4-benzenedicarboxylate) modifed carbon paste electrode for lead detection was developed. The electroanalytical procedure comprised two steps:chemical accumulation of the adsorbed metal ions at the modified electrode surface, followed by electrochemical detection of the pre-concentrated species using differential pulse voltammetry. It was found that the MOF-5was capable of adsorbing lead ions from aqueous solutions and could determine the ions prominently at optimum experimental conditions. Many important parameters to acquire the best electrochemical response were carried out, including the amount of MOF-5, different electrolyte solutions, pH, deposition potential, deposition time and interferences due to other ions. Finally, a calibration graph was obtained with a linear range from1.0×10-8to1.0×10-6mol L-1(R2=0.9981) and detection limit was found to be4.9×10-9mol L-1. The relative standard deviation for eleven replicate measurements was3.4%at1.0×10-7mol L-1of lead level. The proposed method was used for the determination of lead in the real water samples and standard reference materials.Chapter3Multi-walled carbon nanotubes and metal-organic framework nanocomposites as novel hybrid electrode materials for the determination of nano-molar levels of lead in a lab-on-valve formatMetal-organic frameworks have been the subject of intense research because of their unique physiochemical properties. The presented study investigates application of multi-wall carbon nanotubes and metal-organic frameworks (MWCNTs@Cu3(BTC)2) nanoparticles modified electrode for the determination of trace levels of lead. The nanocomposites were prepared by solvothermal synthesis and characterized by Fourier transform infrared spectra, X-ray diffraction spectrometry, and scanning electron microscopy. The experimental procedure was carried out by accumulating lead on the electrode surface and subsequently measured with differential pulse anodic stripping voltammetry in a lab-on-valve format. The main parameters affecting the analytical performance, including the amount of MWCNTs@Cu3(BTC)2suspension, supporting electrolyte and its pH, stripping mode, and flow rate have been investigated in detail. Under the optimum conditions, the oxidation peak current displayed a calibration response for lead over a concentration range from1.0×10-9to5.0×10-8mol L-with a excellent detection limit of7.9×10-10mol L-1. The relative standard deviation of7successive scans was3.10%for1.0×10-8mol L-1lead. The established method showed a great improvement in sensitivity and sample throughput for lead analysis.Chapter4Fabrication of metal-organic frameworks and graphite oxide hybrid composites for solid-phase extraction and preconcentration of luteolinA novel solid-phase extraction sorbent, metal-organic frameworks and graphite oxide hybrid composites, was prepared by solvothermal technique. The morphology and properties of the resultant material were examined by Fourier transform infrared spectroscopy, X-ray diffraction and field emission scanning electron microscopy. To evaluate the extraction performance of the resultant sorbent, luteolin was chosen as a model analyte. The extraction conditions were optimized. Based on these, a convenient and efficient solid-phase extraction procedure for the determination of luteolin was established and the subsequent quantification step was performed by square wave anodic stripping voltammetry. Under the optimal conditions, the oxidation current increased linearly with increasing the concentration of luteolin in the range of5.0×10-9to5.0×10-7mol L-1with a correlation coefficient of0.9983and a detection limit of7.9×10-10mol L-1. The relative standard deviation of7successive scans was4.20%for5.0×10-8mol L-luteolin. This work not only proposes a useful method for sample pretreatment, but also reveals the great potential of metal-organic frameworks based hybrid materials as an excellent sorbent in solid-phase extraction. |
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