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Nanopore reactive adsorbents for the high-efficiency removal of waste speciesRelated Patent Categories: Liquid Purification Or Separation, Processes, Ion Exchange Or Selective Sorption, Including Diverse Separating Or Treating Of Liquid, Prior To Ion Exchange Or SorptionNanopore reactive adsorbents for the high-efficiency removal of waste species description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060207942, Nanopore reactive adsorbents for the high-efficiency removal of waste species. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS REFERENCE TO RELATED APPLICATIONS [0001] This application is related to Provisional Application No. 60/152,339, filed Sep. 7, 1999. FIELD OF THE INVENTION [0003] This invention relates to nanoporous reactive adsorbents and to the use thereof in removing impurities from liquids. More particularly, this invention relates to silica based nanoporous adsorbents having very high density of chemical surface modifying ligands further modified to include chemically reactive species and to the use thereof for purifying contaminated liquids. TECHNOLOGY BACKGROUND AND COMPARISON WITH EXISTING ART [0004] The most common method of removing waste species from a liquid stream is by adsorption. Such a method can be applied to water purification in a continuous operation with water flowing through a column or over a fixed bed of the solid adsorbent. Commercial ion-exchange resins and carbon black filters are examples of this approach. [0005] The common characteristics of an efficient adsorbent include a large surface area and connected (i.e. open) porous structure for fast diffusion. Recent developments in this technical field include the incorporation of molecular recognition functional species (i.e. metal-binding ligands) onto the surface of various inorganic or organic carrier materials to achieve the selective adsorption of a particular group of ions out of the background ions. Among all the carrier materials explored in this developmental field, the synthetic silica gel is the most widely studied. This is because the synthetic nanoparticle silica contains a large amount of active silanol groups on its surface, necessary for the incorporation of metal-binding ligands, and has an exceptionally high surface area as well as open porous structure, necessary for achieving a rapid high-capacity adsorption. [0006] Although much prior art has been developed based on the identical principle of incorporating metal-ion binding functional groups onto the surface of nanopore silica, the characteristics of the resulting silica-ligand composite products may differ significantly.sup.1, 2, 3, 4, 5, 6, 7 depending on the routes of processing. .sup.1 L. Mercier and T. Pinnavaia, Adv., Mater., 9, No. 6, pp 500-503 (1997) .sup.2 L. Mercier, C. Detellier, Environ. Sci. Technol, 29. p 1316 (1995) .sup.3 M. S. Iamamoto, Y Gushikem, J. Colloid Interface Sci. 129, p 162 (1989) .sup.4 E. I. S. Andreotti, Y Gushikem, J. Colloid Interface Sci. 142, p 97 (1991) .sup.5 W. C. Moreira, Y Gushikem, O. R. Nascimento, J. Colloid Interface Sci. 150, p 115 (1992) .sup.6 U.S. Pat. No. 5,814,226, September 1998, Lawrence L. Tavlarides, Nandu Deorkar .sup.7 U.S. Pat. No. 5,817,239 October 1998, Lawrence L. Tavlarides, Nandu Deorkar. [0007] Different processing techniques may start with silica gels similar in porosity and specific surface area (surface area per gram of silica) but could end up with products of distinctly different loading of the ligand groups. Or, two composites may contain a similar amount of loading of functional groups and yet differ considerably in adsorption efficiency. [0008] One of the present inventors has recently developed an advancement in technology of the surface modification of low-density silica gel (CSMG) which can produce high surface area silica with extremely high loading of functional groups that increases the adsorption efficiency and capacitance of the silica adsorbent to a significantly higher level; this technology is the subject matter of U.S. application Ser. No. 09/601,888, filed Aug. 9, 2000, based on Provisional Application Ser. No. 60/074,026, filed on Feb. 9, 1998 and International PCT Application PCT/US99/02181, filed Feb. 3, 1999, the disclosures of which are incorporated herein in their entirety by reference thereto. [0009] The present inventors recognized that a high-capacity adsorption may lead to a much higher concentrated environment of adsorbed specie on the surface of an adsorbent when compared with the specie concentration in the passing stream. Such increased specie population density on the pore surface could significantly increase the reaction rate of the adsorbed specie with other reactants existing nearby. Moreover, the change in the electronic state of adsorbed specie during chemisorptions could also affect its reaction rate favorably. The adsorbent, therefore, could function as a heterogeneous catalyst for the chemical reaction of adsorbed species. If the adsorbed waste specie can be converted to a less harmful or even useful specie by such a reaction, the adsorbent then becomes a reactive adsorbent. The additional option of in-situ reaction to convert the adsorbed specie provided by a reactive adsorbent can significantly increase its treatment capacity because the converted waste species normally do not occupy the surface adsorption sites any longer. The present invention is based, in part, on the recognition and utilization of the foregoing considerations. SUMMARY OF THE INVENTION [0010] This invention has been accomplished by embedding reactive species into the structure of a nanopore adsorbent in order to convert waste or undesirable species in situ during filtration as well as to increase the treatment capacity of the adsorbent towards a specific waste specie and/or recoverable specie having intrinsic value. [0011] Thus, for example, the present invention, in one particular embodiment, provides for treating heavy metal ions in a waste stream. However, this invention may also be extended to other reactive adsorption applications by appropriate selection of the embedded reactive species. [0012] In another aspect of the invention, there is provided a regeneration scheme that utilize the reactive nature of the nanopore adsorbent by applying backwash effluent repetitively through the reactive adsorbent to first remove the adsorbed species and then react them with the reactant embedded within the adsorbent. Such a regeneration scheme does not require additional treatment of the backwash effluent and is hereby given the name of close-end regeneration. [0013] The above features of the present invention are accomplished according to one embodiment of the invention by a composite nanopore reactive adsorbent comprising [0014] a continuous phase comprised of adsorbent particles and interstitial pores therebetween, and [0015] a phase comprised of reactant particles contained in domains surrounded by the adsorbent particles and their interstitial pores, thereby forming an intimate admixture of adsorbent particles, reactant particles and interstitial pores, [0016] wherein the size of the reactant particles is at least several times larger than the size of adsorbent particles such that the interstitial pores predominantly reside with the adsorbent particles, and [0017] wherein the relative volume fraction of the interstitial pores in the continuous phase to that of the adsorbent particles is larger than the percolation threshold value so that the continuous phase contains connected open pores. [0018] Preferably, in the above nanopore reactive adsorbent, the adsorbent particles are formed from precipitated silica or the adsorbent particles comprise chemically surface modified amorphous silica gel. In a preferred embodiment of this aspect of the invention, the reactant particles are comprised of metal effective as an in-situ reducing reagent, such as, for example, magnesium, aluminum, iron, and/or zinc. However, the reactant particles may be comprised of a solid redox reagent effective to react with an adsorbed species, or in still another embodiment, the reactant particles are comprised of a catalyst, such as an enzyme, or other organic or inorganic catalyst, which is effective to react with an adsorbed species. [0019] According to another aspect, the present invention provides a method for producing the composite nanopore reactive adsorbent as described above, comprising: [0020] reacting an inorganic metal oxide nanoporous gel precursor characterized by a plurality of open channels within the gel structure and hydroxyl reactive groups on the surface thereof, with a coupling reagent reactive with said hydroxyl reactive groups, in an aqueous alcoholic medium under an inert atmosphere and at an elevated temperature within the range of from about 40.degree. C. to about 80.degree. C. to cause the coupling reactant to condense and react with said hydroxyl reactive groups to form a grafted metal oxide sol; [0021] (b) mixing and stirring the grafted silica sol with reactant particles; and Continue reading about Nanopore reactive adsorbents for the high-efficiency removal of waste species... 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