Experimental Studies On Adsorption And Preconcentration Of Mercury In Water By Carbon Nanotubes

Mercury in the environment, especially in water can be bioaccumulated and biotransformed into different species. During the cycling of mercuy in the environment, the concentration and toxicity can be enhanced by thousands of times. The methylated into organic mercury compounds are with high genetic and neural toxicity. So, it is a serious issue to remove mercury at trace level in water. There are many methods for heavy metals removal. Among them, the adsorption method is the most popular and effective one. However, most of the commercial absorbents are not very suitable and effective for mercury removal because of the limited adsorption capacity, low specificity and non-recycling property. Therefore, it is very important and significant to develop new methods and materials which can remove mercury in water effectively with high capacity. It will be also more attractive if the materials can be recycled after using.A series of composite carbon nanomaterials were synthesized in our work. The materials were characterized by instruments such like VSM, SEM, TEM and XRD. The adsorption properties of the materials to mercury in water were investigated and evaluated. The mechanism of adsorption was also discussed. The main results of this thesis:(1) Carbon nanotubes (CNTs) modified by concentrated nitric acid had the maximum efficiency for adsorption. The modified carbon nanotubes was packed in a mini-column and used as a solid phase extraction column for the preconcentration of Hg2+. The variables affecting on the preconcentration were investigated and optimized.(2) Ag, Pd and Se were used to synthesize the composite carbon materials. The carbon nanotubes coated with Ag, Pd and Se particulate had much higher adsorption capacity for mercury compared with that without modification by Ag, Pd and Se.(3) The magnetic CNTs (CNTs@Fe3O4) was prepared by using chemical co-precipitation method. The composite material could be well separated from aqueous solution by a permanent magnetic field. The adsorption properties of the material for mercury in water were studied.(4) Then, the composte magnetic CNTs materials coated with Ag, Pd and Se were also synthesized. The adsorption capacity for mercury had been enhanced geatly by the modification of Ag, Pd and Se. The materials also had the properties of magnetic separation, and recycling.(5) From the results of SEM, EDS, TEM and XRD analysis, the possible mechanism of adsorption was discussed. Thermodynamics and kinetics of adsorption were also analyzed for the discussion of adsorption mechanism in this thesis.