Synthesis Of Silica-gel Modified With Multidentate Ligands For Adsorption To Heavy Metal Ions

Heavy metal pollution of environment has become a serious problem. Therefore,an effective removal of heavy metal ions from environment is very crucial.Adsorption is generally preferred for the removal of heavy metal ions due to its highefficiency, remarkable simplicity and low cost. The amine groups have been found tobe one of the most efficient functional groups for heavy metal ion removal. Varioustypes of polyamines were anchored to silica gel to synthesis some chelatingadsorbents. However, the regularities obtained from different researchers about heavymetals adsorption on silica gel modified with aliphatic amines are not consistent.The chelating adsorbents possessing polyamines as sole functional group stillsuffered from disadvantages including the low adsorption selectivity and capacitytoward divalent metals. Consequently, those materials containing polyamines areusually as starting materials to prepare further chelating resins possessingmultidentate ligands which have better complexing abilities in comparison to theother polymer ligands. The dithiocarbamates, iminodiacetate, methyl acrylate andSchiff’s base derivatives of polyamines are the most common examples ofmultidentate ligands. There is no reported about the difference of adsorption ability toheavy metals between adsorbents containing the three kinds of multidentate ligandsabove. Adsorbents containing two kinds of multidentate ligands which weresynthesized via the primary and secondary amines of amine-functionalized silica gelare not reported yet.This article synthesized four kinds amined silica gel and studied their properties ofPb2+adsorption. Then, SG-DETA and SG-TEPA were chose as starting materials toanchored multidentate ligands. Finally, SG-TSD which showed high adsorptioncapacity and strong affnity to Hg2+was screened as chelating adsorbent for heavymetal removal from environment. The main contents and results of this article are asfollowed:(1) A series of polyamines, NH2(CH2CH2NH)n-1H(where n=2-5, i.e. EDA-,DETA-, TETA-and TEPA-), were attached to silica gel. The amined silica gels exhibited better adsorption capabilities for Pb2+than for Cu2+or Zn2+. Adsorptionkinetic data for Pb2+could be well fitted by the pseudo-second-order kinetic equationand the adsorption equilibrium processes could well fit the Langmuir. A clear unevennumber effect (by which the amount of adsorption is enhanced in the cases of DETAand TEPA) was observed in both adsorption kinetic constants and saturatedadsorption capacities for Pb2+.(2) Silica gel modified with DETA (SG-A) was chose as starting materials to graftmultidentate ligands. All these synthesized materials showed adsorption to Pb2+,Hg2+, Cu2+, Zn2+and Cd2+. The results showed that SG-AD and SG-ASD showed ahigher performance towards Pb2+and Hg2+, while the maximum adsorption capacitywas188.7mg/g on SG-AD. Adsorption kinetics suggested that the adsorptionprocesses of Pb2+and Hg2+on SG-AD and SG-ASD were followed a pseudo-second-order model. The Langmuir model was applied to fit the experimental equilibriumdata for SG-AD and SG-ASD. SG-ASD which contained two kinds of multidentateligands showed strong chelating affinity to Hg2+.(3) Multidentate ligands functionlized SG-T were synthesized according to themethod of SG-A modification. The synthesized materials showed the same adsorptionproperties to Pb2+, Hg2+, Cu2+, Zn2+and Cd2+compared with materials obtained fromSG-A. SG-TD showed the maximum adsorption capacity to Hg2+，20.5%higher thanSG-AD. SG-TSD showed the highest affinity constant to Hg2+.0.57g/L of SG-TSDhad litter effect on the growth and pigment synthesis of R. palustris CQV97andMarichromatium sp.283-1. SG-TSD can significantly relieve inhibition of Hg2+tothe growth and pigment synthesis of the two bacterias above.In conclusion, A clear uneven number effects was observed in both adsorptionkinetic constants and saturated adsorption capacities for Pb2+.0.57g/L of SG-TSDhad litter effect on the growth and pigment synthesis of R. palustris CQV97andMarichromatium sp.283-1. SG-TSD can significantly relieve inhibition of Hg2+tothe growth and pigment synthesis of the two bacterias above.