Summary And Conclusions

A new class of hybrid nanoporous materials has been developed for removing toxic heavy metals, oxyanions, and radionuclides from aqueous waste streams. Tests showed that thiol-SAMMS designed for heavy metal adsorption showed significant loading (0.56 to 6.37 meq/g) and high selectivity (Kd: 4.6 x 101 to 3.5 x 108 ml/g) for contaminants such as Cu, Pb, Cd, Ag, and Hg.

Results of the arsenate and chromate adsorption tests indicated that Cu-EDA SAMMS very effectively adsorbed both these oxyanions with predicted adsorption maxima of ~2.1 meq/g, with distribution coefficient ranging from 1.7 x 102 to 1.0 x 106 ml/g. Adsorption experiments conducted using Ag- and Hg-capped thiol SAMMS sorbents very effectively adsorbed 125I from a groundwater matrix. Both forms of thiol-SAMMS exhibited very high distribution coefficients (Kd: 2.9 x 104 to 1.2 x 105 ml/g), indicating that radioiodine was sorbed with high specificity even in the presence of anions in the groundwater that were present in significantly higher concentrations than radioiodine.

Another sorbent, designed to adsorb radiocesium (Cu-EDA FeCN SAMMS) specifically, when tested exhibited loading as high as 1.33 meq/g and distribution coefficients ranging from

7.7 x 102 to 4.8 x 104 ml/g. Tests conducted using carbamoylphosphonate-functionalized nanoporous substrates (APH and PPH SAMMS) showed that these sorbents very effectively adsorbed Pu(IV) from solutions containing complexing ligands, such as EDTA, citrate, phosphate, sulfate, and nitrate. Distribution coefficients as high as 2 x 104 ml/g confirmed that the CMPO-based functionalities assembled on nanoporous substrates are very effective scavengers for actinide ions such as Pu.

Self-assembled monolayers of selected functionalities on nanoporous silica substrates can achieve very high sorbate loadings very rapidly with relatively high specificities. These novel classes of sorbent materials therefore will be very effective in removing a wide range of targeted contaminants from waste streams.

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