Sorption site stabilization

U.S. EPA defines MNA as the reliance on natural processes, within the context of a carefully controlled and monitored site cleanup approach, to achieve site-specific remediation objectives within a time frame that is reasonable compared to that offered by other more active methods. The natural processes include biodegradation, dispersion, dilution, sorption, volatilization, stabilization, and transformation. These processes reduce site risk by transforming contaminants to less toxic forms, reducing contaminant concentrations, and reducing contaminant mobility and bioavailability. Other terms for natural attenuation in the literature include intrinsic remediation, intrinsic bio-remediation, passive bioremediation natural recovery, and natural assimilation. 30... 

Qads.(max) = 5.7 molecules by unit cell). Generally speaking, Qacis.(max) is closely related to the molecular size, as it is observed for the other molecular species. Secondly, as shown on Figure 5, sorption isotherm sub-step observation could be another signature of zeolite inner surface influence. Such isotherm sub-step reflects a phase transition existence between a fluid phase and a solid phase stabilized by the inner surface sorption sites. 

The sorption data of Cd2+ and Pb2+ by B. subtilis and E. coli were well described by a one-site complexation model (r2 > 0.9) with Cd2+ showing somewhat lower sorption affinities than Pb2+ (Kulczycki et al. 2002). A two-site sorption model yielded an improved fit but only for the E. coli data. The stability constants for the high- and low-affinity sorption sites differed by several orders of magnitude. The total metal sorption capacity of E. coli increased, and moved closer to the value of B. subtilis when the presence of low-affinity sorption sites was allowed. Ngwenya et al. (2003) used potentiometric titrations to assess the different types of sites present... 

Neptunium and plutonium sorption behaviors were remarkably similar, implying that they had similar sorption reactions and solution species. Both NaOH and NaA102 decreased neptunium and plutonium sorption. Several explanations can be offered to rationalize this behavior. First, NaOH and NaAlO, may have reacted with the sediment minerals to yield solids of lower sorptive capacity. Aluminate ion, as an anionic species, also may have competed with the similar neptunate and plutonate anions for sorption sites. Finally, sodium hydroxide may have stabilized the hydrolyzed Np02(0H) and Pu02(0H)2" species in solution, as was shown in the solubility tests, and prevented sorption. Explanation of the effect of NaOH and NaA102 on neptunium and plutonium sorption will require further investigation. 

The adsorption and desorption of metals onto the surface-exposed sorption sites of clay particles can approach equilibrium in seconds to minutes in well-mixed streamwaters. Similarly, the response of a pH electrode, which often stabilizes in a few seconds in stirred solutions, reflects the rapid rate of equilibration of aqueous protons with protons adsorbed on the hydrated surface of the glass electrode. 

The dispersity of Pd on the prepared catalysts is influenced by K2 - a constant which characterizes the interaction of a catalyst precursor and the support the dispersity of metal palladium increases vnth the increase of K2 [21]. Therefore, Pd dispersity on, e.g., a CFC-1 based catalyst is higher than that on a carbon bla PM-105 based one, though similar surface coverage and nearly equal total concentrations of sorption sites (i.e., Ai) are observed. Thus, supports such as CFC are capable of stabilizing the finely dispersed Pd phase. In fact, with the obtained data, the CFC can be thought as a specific and rather promising family of new adsorbents and catalyst supports. 

Root products may be classified into types on the basis of their (1) chemical properties, such as composition, solubility, stability (e.g., hydrolysis, oxidation), volatility, molecular weight etc. (2) site of origin and (3) e.stablished, not just perceived, functions. The chemical properties determine in turn their biological activity and how the compounds will behave in soils their persistence in soil is very much an outcome of their chemical behavior, particularly sorption and their biodegradability. 

Low temperature CO sorption experiments monitored with the IR spectroscopy were used to determine the nature of active (acid) sites present in the Fe-TON zeolites. It is well known that CO is a useful probe molecule for Lewis acid sites. Narrow and well resolved bands appear in the region 2135 - 2150 cm"1. The IR spectra of CO sorbed in amount sufficient to cover all Lewis sites in the Fe-TON of different Si/Fe ratios are presented in Figure 2A. The samples of a high iron content (Si/Fe=27, 36) showed a significantly lower thermal stability. The activation of the NFL form of these Fe-TON... 

The mere exposure of diphenyl-polyenes (DPP) to medium pore acidic ZSM-5 was found to induce spontaneous ionization with radical cation formation and subsequent charge transfer to stabilize electron-hole pair. Diffuse reflectance UV-visible absorption and EPR spectroscopies provide evidence of the sorption process and point out charge separation with ultra stable electron hole pair formation. The tight fit between DPP and zeolite pore size combined with efficient polarizing effect of proton and aluminium electron trapping sites appear to be the most important factors responsible for the stabilization of charge separated state that hinder efficiently the charge recombination. 

Functionalized polymers are of interest in a variety of applications including but not limited to fire retardants, selective sorption resins, chromatography media, controlled release devices and phase transfer catalysts. This research has been conducted in an effort to functionalize a polymer with a variety of different reactive sites for use in membrane applications. These membranes are to be used for the specific separation and removal of metal ions of interest. A porous support was used to obtain membranes of a specified thickness with the desired mechanical stability. The monomer employed in this study was vinylbenzyl chloride, and it was lightly crosslinked with divinylbenzene in a photopolymerization. Specific ligands incorporated into the membrane film include dimethyl phosphonate esters, isopropyl phosphonate esters, phosphonic acid, and triethyl ammonium chloride groups. Most of the functionalization reactions were conducted with the solid membrane and liquid reactants, however, the vinylbenzyl chloride monomer was transformed to vinylbenzyl triethyl ammonium chloride prior to polymerization in some cases. The reaction conditions and analysis tools for uniformly derivatizing the crosslinked vinylbenzyl chloride / divinyl benzene films are presented in detail. 

Analyte stability in treated stainless steel canisters is related to the polarity of the molecule and the number of water molecules in the matrix air. At a relative humidity of about 10%, sufficient water molecules are available to form a monolayer on the inner surface of a 6 1 spherical canister. Water molecules are thought to coat the active sites and minimize sorption of surface-active VOCs. However, if samples of air at high relative humidity are pressurized, water can condense in the container, and polar molecules can partition into the liquid water. As the air sample is withdrawn for analysis, the water will evaporate, liberating polar molecules dissolved in the water and increasing analyte concentrations in subsequent samplings of the container. 

An intriguing application of these Pd nanoparticles in basic research concerns the question of the solubility of H2 in such materials relative to bulk palladium [47]. Hydrogen concentration-pressure isotherms of surfactant-stabilized palladium clusters and polymer-embedded palladium clusters with diameters of 2, 3 and 5 nm were measured with the gas sorption method at room temperature. The results show that, compared to bulk palladium, the hydrogen solubility in the a-phase of the clusters is enhanced fivefold to tenfold, and the miscibility gap is narrowed. Both results can be explained by assuming that hydrogen occupies the subsurface sites of the palladium clusters. The Pd-H isotherms of all clusters show the existence of hysteresis, even though the formation of misfit dislocations is unfavorable in small clusters. Compared to surfactant-stabilized clusters, the polymer-embedded clusters show slow absorption and desorption kinetics. Moreover, evidence for a cubic-to-icosahedral transition of quasi-free Pd-H clusters by the hydrogen content was reported [47c]. 

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