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Novel Cyclodextrin Polymer Adsorbents for PFAS Removal
Published in David M. Kempisty, LeeAnn Racz, Forever Chemicals, 2021
Yuhan Ling, Gokhan Barin, Shan Li, Matthew J. Notter
Ionic strength is generally evaluated by the metrics of TDS and conductivity. While ionic strength varies considerably among different water matrices, no significant effects have been observed on the treatment capacity of cyclodextrin polymers for PFAS from the level of ionic strength in water. As noted in previous sections, PFAS adsorption on DEXSORB+ relies on the formation of host-guest complexes in the 0.78 nm interior cavity of β-cyclodextrin, and interactions with positive surface charges to further increase adsorption affinity and selectivity.
Filtrative Particle Removal
Published in Maik W. Jornitz, Filtration and Purification in the Biopharmaceutical Industry, 2019
It is evident from the foregoing that empowering the attractive VDW forces requires the shortening of the Debye length. This can be accomplished by the addition of ions in the form of salts. Contrarily, the low ionic content of dilute solutions results in extending the Debye lengths. This renders the weak attractive forces impotent against the strong long-range Coulombic forces of repulsion. The addition of ions to the solution makes possible the dominance of the attractive forces. The ionic strength of a solution is a measure of its salt or ion content. Upon the reduction of the Debye length as occasioned by the addition of ions, the short-range attractive VDW forces enable the appropriate surface sites on the organism to interact with those on the filter. Since there are as many opportunities for the VDW force orientations to exercise repulsions, as there are to encourage attractions, the domination by the attractive tendencies requires explanation. Actually, both the attractive and repulsive forces are reduced by the addition of ions, but the repulsive power is the one more affected. On balance the attractive forces emerge the stronger.
Sediment-bound Contaminant Transport Dynamics in and Around Vidy Bay
Published in Nathalie Chèvre, Andrew Barry, Florence Bonvin, Neil Graham, Jean-Luc Loizeau, Hans-Rudolf Pfeifer, Luca Rossi, Torsten Vennemann, Micropollutants in Large Lakes, 2018
Neil D. Graham, Jean-Luc Loizeau
Colloid stability is additionally influenced by the ionic strength of the suspension. Increased ionic strength compresses the electric double layer (EDL) surrounding the colloid, thereby decreasing the measured zeta potential (Ceronio and Haarhoff, 2005; Subramanian et al., 2010). This EDL compression reduces steric and electrostatic hindrance between colloids and leads to destabilization. Increased ionic strength also means an increased cation concentration. Cations that are available to adsorb to the colloid surface, partially neutralize the surface charge character and diminish the electric repulsion between colloids (Tipping and Higgins, 1982).
Interactions of microplastics with contaminants in freshwater systems: a review of characteristics, bioaccessibility, and environmental factors affecting sorption
Published in Journal of Environmental Science and Health, Part A, 2023
Farhad Avazzadeh Samani, Louise Meunier
Ionic strength is defined as the total concentration of ions in solution. The sorption affinity of metal ions onto MPs decreases with increased ionic strength. This sorption behavior has been described in various studies. Notably, the effect of ionic strength due to the presence of Pb2+ in solution was evaluation in a study of the sorption of Cd2+ onto PA, PS, PVC, ABS, and PET MPs in a synthetic earthworm gut and in a sediment system.[64] In all cases, the Cd2+ sorption was suppressed as ionic strength increased. This is corroborated by another study by the same group, where the sorption capacity of Cd2+ on CPE, PVC, and PE MPs decreased with increased ionic strength.[62] The authors reported different sorption behaviors for Cu2+ and Pb2+ compared to that of Cd2+ in response to ionic strength. Increasing ionic strength in solutions resulted in a slight sorption inhibition of Pb2+ on all MPs and decreased sorption of Cu2+ MPs, except for that on CBE, for which decreased by less than 40%.[62] Such inhibitions may be explained as follows: (i) the competition for active sorption sites on sorbate increases as the concentration of ions increases; (ii) the ionic activity decreases as the ionic strength increases in solution.[28,62]
Activated carbon, zeolite, and ceramics immobilized TiO2 photocatalysts for the enhanced sequential uptake of dyes and Cd2+ ions
Published in Journal of Dispersion Science and Technology, 2022
Najm Us Saqib, Rohana Adnan, Irfan Shah, Muhammad Arshad, Muhammad Inam
The removal of pollutants by heterogeneous photocatalysis is a pH-dependent process. Charges associated with both the catalyst surface and pollutants are reliant on the pH of the medium, which affects the adsorption and degradation of contaminants.[15] Meanwhile, in an aqueous solution, surface sites of metal oxides are protonated and deprotonated liable to the pH of the solution, which gives rise to a surface potential. As the ionic strength increases, the attractive forces between the surface sites become higher and the particles form aggregates.[26] Therefore, the selection of proper pH conditions can affect the adsorption of anionic and cationic pollutants on the surface of metal oxide NPs.
Selective removal of aluminum, nickel and chromium ions by polymeric resins and natural zeolite from anodic plating wastewater
Published in International Journal of Environmental Health Research, 2021
The uptake of heavy metals by ion exchange resins depends on many factors, such as charge density and diameter of hydrated cations, ionic strength of background solution, pH and temperature. The higher charge density (+4, +3 and +2) provides better uptake efficiency. On the other hand, the diameter of hydrated cation is also important that cations having the smallest diameters show the maximum uptake efficiency (Erdem et al. 2004; Demirbas et al. 2005; Abo-Farha et al. 2009). Although aluminum (0.05 nm) has the smallest ionic diameter with respect to nickel (0.070 nm) and chromium (0.064 nm), the diameter of hydrated aluminum with 0.475 nm is bigger than those of nickel (0.404 nm) and chromium (0.461 nm) (Nightingale 1959). To evaluate competitive effect of metals concentrations on the resin uptake, the removal performances of these metals should be analyzed under similar concentrations, i.e., the initial aluminum concentration of 10 mg Al/L, nickel concentration of 5.5 mg/L and chromium concentration of 8.1 mg/L. As seen from Figure 5(a2 and b2), while the highest removal was observed for nickel with 99% and 95%, aluminum removal efficiencies were 49% and 52% by Amberlite IR120 and 95% by Lewatit TP207, respectively. Chromium was removed by only 12% by both resins. Although aluminum has the highest charge density, its removal performance was much lower than nickel because of the diameter of hydrated aluminum, which is higher than that of nickel. The least preferred metal was chromium due to its lower charge density and bigger diameter. The effect of diameter of hydrated metal was reported by Abo-Farha et al. (2009) that Ce4+ ions (0.101 nm) with the smallest diameter have maximum adsorption, although Pb2+ ions with the biggest diameter (0.1200 nm) have minimum adsorption. Erdem et al. (2004) observed that the maximum adsorption was obtained for the Co2+ with least diameter among the same charge of metals (Co2+ >Cu2+>Zn2+>Mn2+) by zeolite. Kang et al. (2004) also reported similar results for Co2+, Ni2+ and Cr3+ removal on an Amberlite IRN-77 cation-exchange resin.