| Cadmium(Cd) is one of the most toxic heavy metals on the priority pollutant list and is of great concern in the environment, because of its toxicity to animals and humans even at low concentrations. Molecular imprinting has become a powerful method for the preparation of robust materials that have the ability for high selective adsorption of target chemical species. Molecular imprinting is a process where functional and cross-linking monomers are co-polymerized in the presence of the target analyte (the imprint molecule), which acts as a molecular template. The functional monomers form a complex with the imprint molecule initially, and then their functional groups are held in position by the highly cross-linked polymeric structure. Subsequently, the removal of the imprint molecule reveals binding sites that are complementary in size and shape to the analyte. In that way, a molecular memory is introduced into the polymer, which is capable of rebinding the analyte with a very high specificity. In recent years, research on Cd(II)-imprinted polymers has become a hot spot.In chapter1, the definition, source, harm and characteristic of pollution of heavy metals were introduced. The origin, main features and principle of imprinted technology polymers, and were reviewed. The preparation and application of imprinted polymers were also reviewed. The research progress of Cd(II)-imprinted polymers were evaluated. The objective and innovation of this paper were presented.In chapter2, a simple procedure was developed to synthesize new Cd(II)-imprinted amino-functionalized silica gel sorbents, Cd(II)-imprinted thiocyanato-functionalized silica gel sorbents and Cd(II)-imprinted thiol-functionalized silica gel sorbents by combining a surface molecular imprinting technique with a hydrothermal assisted process with Cd(Ⅱ) as the template,[(aminoethylamino)ethylamino]propyl-trimethoxysilane (AAAPTS),3-thiocyanatopropyltriethoxysilane (TCPTS) and mercaptopropyltrimethoxysilane (MPS) as the functional monomer, and epichlorohydrin as the cross-linking agent. Sorbents was characterized by FTIR, SEM, TGA-DTA and nitrogen adsorption. These results indicated that TCPTS, AAAPTS and MPS had been successfully immobilized onto the surface of silica gel. The uneven, rough template imprint cavities were formed on the surface of silica gel by cross-linking action. The BET of functionalized imprinted silica gel sorbents was more than that of non-imprinted silica gel sorbents. In chapter3, the adsorption capacity, adsorption rate, selectivity, effect of pH, desorption and reuse properities of Cd(II)-imprinted amino-functionalized silica gel sorbents, Cd(II)-imprinted thiocyanato-functionalized silica gel sorbents and Cd(II)-imprinted thiol-functionalized silica gel sorbents were investigated by the static adsorption-desorption experiment method. Results showed that the maximum static adsorption capacity of functionalized imprinted silica gel sorbents prepared by hydrothermal heating method was much more than that of sorbents prepared by the conventional heating method. Sorbents offered a fast kinetics for the adsorption of Cd(II) for20min, had a substantial binding capacity in the range of pH4-8, and could be used repeatedly. The sorbents were found to adsorb selectively Cd2+in the presence of Co2+, Ni2+, Zn2+and Cu2+interferences in the same medium.In chapter4, equilibrium data of Cd(II)-imprinted amino-functionalized silica gel sorbents, Cd(II)-imprinted thiocyanato-functionalized silica gel sorbents and Cd(II)-imprinted thiol-functionalized silica gel sorbents fitted perfectly with Langmuir isotherm model compared to Freundlich isotherm model. The straight lines with extremely high correlation coefficients (r2>0.99) were obtained. There was a low difference of adsorption capacity of imprinted functionalized silica gel sorbents between the experiment and calculation values. Various thermodynamic parameters such asΔGo, ΔHo and ASo were evaluated. Negative values of ΔGo of Cd(II)-imprinted amino-functionalized silica gel sorbents, Cd(II)-imprinted thiocyanato-functionalized silica gel sorbents and Cd(II)-imprinted thiol-functionalized silica gel sorbents indicated that the adsorption process was spontaneous. The positive standard enthalpy change of imprinted functionalized silica gel sorbents suggested that the adsorption of Cd(II) by sorbents was endothermic, which was supported by the increasing adsorption of Cd(II) with increase in temperature. The positive values of ΔSo exhibited that the randomness increased with the adsorption of Cd(II) on imprinted functionalized silica gel sorbents. Kinetic studies of Cd(II)-imprinted amino-functionalized silica gel sorbents, Cd(II)-imprinted thiocyanato-functionalized silica gel sorbents and Cd(II)-imprinted thiol-functionalized silica gel sorbents indicated that the low correlation coefficients for pseudo-first-order kinetic model for sorbents were observed, indicating a poor pseudo-first-order fit to the experimental data. The adsorption imprinted functionalized silica gel sorbents for Cd(II) followed a pseudo-second-order model. The straight lines with extremely high correlation coefficients (r2>0.99) were obtained. There was a low difference of adsorption capacity of imprinted functionalized silica gel sorbents between the experiment and calculation values.In chapter5, we investigated the application of Cd(Ⅱ)-imprinted amino-functionalized silica gel sorbents, Cd(II)-imprinted thiocyanato-functionalized silica gel sorbents and Cd(II)-imprinted thiol-functionalized silica gel sorbents for the selective removal and recovery of Cd2+from wastewaters. The removal rate of Cd2+was about80%from mine wastewater.In chapter6, Cd(II)-imprinted amino-functionalized silica gel sorbents, Cd(II)-imprinted thiocyanato-functionalized silica gel sorbents and Cd(II)-imprinted thiol-functionalized silica gel sorbents could be employed as an effective adsorbent material for the selective removal of Cd(II) from aqueous solutions. |
PDF Full Text Request