| As a highly reactive porous material, silica gel is considered to be the best choice for asgood inorganic adsorbent supports because of its unique chemical stability, thermal stability,and high mechanical strength. Previous studies have shown that nitrogen-typed adsorbentshave excellent adsorption property for heavy metal ions. As promising nitrogen-typedfunctional groups, amidoxime group has high tendency to form strong complexes with a widerange of heavy metal ions due to its amphoteric group with both acidic and basic sites. So thechelating adsorptive materials carrying amidoxime groups are widely applied in theenrichment, recovery and removal of heavy metal ions. The high-performanceorganic/inorganic composites can be obtained by combination of silica gel and amidoximegroups.In this paper, we prepared silica gel suppored diethylenetriamine adsorbents based on theend group protection, combined with the traditional homogeneous and heterogeneous method,and using3-glyciddoxypropyltrimethoxysilane (GPTS) as coupling agent. The obtainedproducts were named of SG-HO-pD and SG-HE-pD. Then silica gel supported acrylonitrileintermediates SG-HO-pD-A and SG-HE-pD-AN were prepared through the reaction betweenamine groups on silica gels and acrylonitrile. After further modification by hydroxylaminehydrochloride, silica gel supported low generation amidoxime-terminated dendritic polymeradsorbents were prepared. All the products were characterized by porous structure analysis,FT-IR, SEM and elemental analysis. The results show that the homogeneous method is moreconducive than heterogeneous method in the synthesis of intermediates SG-HO-pD andSG-HE-pD, which lead to the higher nitrogen contents of SG-HO-pD-AO.The adsorptionproperties of two materials were investigated towards Hg(II), Ag(I), Zn(II), Cu(II), Pb(II),Ni(II) ions. The experiments show that the two materials have good adsorption performancefor Hg (II). The adsorption kinetics, isotherms, selectivity and regeneration performance weremainly studied towards Hg (II). The adsorption kinetic processes were governed by the flmdiffusion and followed the pesudo first-order wonderfully. Langmuir model can betterdescribe the process of mercury adsorption for two materials; the adsorption process for Hg(II) is governed by monolayer and chemical adsorption. Adsorption selectivity experimentsindicated that the two materials own good adsorption selectivity for Hg (II) in some binary-components solutions containing Hg (II). Finally, the two kinds of adsorbens possesswell desorption and regeneration capacities.The synthsis of nitrogen-typed silica gels based on end group protection methods canavoid effectively the crosslinked structures of organic reagents occurred in intramolecular andintermolecular reaction. The original porous and high-activity structure characteristics ofsilica gels can be saved. The contents of functional groups can also influence the adsorptionperformance in addition to the structure characteristics of materials. Other than the end groupprotection, the polyamines were used directly, using3-glyciddoxypropyltrimethoxysilane(GPTS) as coupling agent, two kinds of silica gel supported ethylenediamine anddiethylenetriamine SG-HO-dD-EDA and SG-HE-dD-DETA materials were preparedrespectively. Through the reaction between amine groups on silica gels and acrylonitrile,silica gel supported acrylonitrile intermediates SG-HO-dD-EDA-AN andSG-HO-dD-DETA-AN were prepared. After further modification by hydroxylaminehydrochloride, silica gel supported low generation amidoxime-terminated dendritic polymeradsorbents were prepared. All the products were characterized by porous structure analysis,FT-IR, SEM and elemental analysis. The adsorption properties of two materials wereinvestigated towards Hg (II), Ag (I), Zn (II), Cu (II), Pb (II) and Ni (II) ions. The experimentsshow that two materials have good adsorption performances for Hg (II) and Ag (I). Theadsorption kinetics, isotherms, selectivity and regeneration performance were mainly studiedtowards Hg (II) and Ag (I). The adsorption kinetic processes were governed by the flmdiffusion and followed the pesudo second-order for both Hg (II) and Ag (I). Langmuir modelcan better describe the process of Hg(II) and Ag(I) adsorption for two materials; theadsorption process for Hg(II) and Ag(I) is governed by monolayer and chemical adsorption.Adsorption selectivity experiments indicated that the two materials own good adsorptionselectivity for Hg (II) and Ag (I) in some binary-components solutions containing the two ions.Finally, the two kinds of adsorbens possess well desorption and regeneration capacities for Hg(II). |
