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Adsorption on Silica and Active Carbon
Published in Rolando M.A. Roque-Malherbe, Adsorption and Diffusion in Nanoporous Materials, 2018
The common point linking the different forms of silica are the tetrahedral silicon–oxygen blocks [14], giving that one of the Pauling ionic radius-ratio rules asserts that since R(Si4+)/R(O2−) is between 0.225 and 0.414. Thenceforward, silicon is tetrahedrically joined to oxygen in silica. If the tetrahedral units are regularly arranged, in that case, periodic structures materializing the different crystalline polymorphs are developed [23]. In the case when tetrahedra are randomly packed, producing a nonperiodic structure that gives rise to various forms of amorphous silica, in which this random association of tetrahedra shapes the complexity of the nanoscale and mesoscale morphology of amorphous silica pore systems [24].
Impact of Factors on Remediation of Anions (Fluoride, Nitrate, Perchlorate, and Sulfate) Via Batch Adsorption Processes
Published in Deepak Gusain, Faizal Bux, Batch Adsorption Process of Metals and Anions for Remediation of Contaminated Water, 2021
Deepak Gusain, Shikha Dubey, Yogesh Chandra Sharma, Faizal Bux
The effect of anions on fluoride adsorption capacity is also investigated on the basis of ionic radii in addition to charge-to-ionic radius ratio (Chen, Zhang, He, et al. 2016). The ionic radius of bicarbonate (1.56 Å) was closer to the ionic radius of fluoride (1.33 Å), as compared to that of sulfate (2.30 Å). Hence, bicarbonate easily fits into the mineral arrangement of the adsorbent, i.e. apatite, which leads to a significant decline in adsorption of fluoride as compared to sulfate. Similarly, the chloride and nitrate have higher ionic radius (1.8 Å) and lesser effect on the adsorption of fluoride.
Adsorption (on Solids) and Absorption (in Fluids) of Gases (CCS Procedures) (Surface Chemistry Aspects)
Published in K. S. Birdi, Surface Chemistry of Carbon Capture, 2019
The equilibrium constant K for Na—MFI (4.88 ± 0.02 10−3 Torr−1) was found to be larger than for K—MFI (1.15 ± 0.02 10−3 Torr−1). This was found to be in agreement with the different polarizing characteristics of the cations (e.g., Na+ and K+). In fact, the local electric field generated by the unsaturated cations depends on the charge/ionic radius ratio, which is larger for Na+ than for K+ (ionic radius of Na+ = 0.97 Å and of K+ = 1.33 Å. As regards the charge/ionic radius ratio, the maximum coverage attained at pCO = 90 Torr was larger for Na—MFI (θ ≈ 0.3) than for K—MFI (θ ≈ 0.1). This shows that there is a correlation between adsorption and the size of the cation. For example: The analyses of the adsorption data for CO further showed that the magnitude of (standard free energy) ∆Gads° for CO adsorption at the two alkaline-metal sites was obtained from the Langmuir equilibrium constant K: ∆Gads° = −RT (ln K) In both cases the adsorption process in standard conditions was found to be endothermic: ∆Gads° = +13.4 kJ mol−1 for Na—MFI;and ∆Gads° +17.0 kJ mol−1 for K—MFI. Further studies also showed that after vacuum treatment the two Na+ · · · CO and K+ · · · CO adspecies were absent. This shows that CO was absent after the vacuum treatment of the solid.
Investigation of structural and dielectric properties of subsolidus bismuth iron niobate pyrochlores
Published in Journal of Asian Ceramic Societies, 2020
F.A. Jusoh, K.B. Tan, Z. Zainal, S.K. Chen, C.C. Khaw, O.J. Lee
Figure 2 displays a linear relationship between lattice constant and composition, x that obeyed the Vegard’s law. The calculated ionic radius ratio, rA/rB, for all these BFN pyrochlores is found to be in the range 1.724–1.727, which is still within the pyrochlore stability range [13]. In addition, the substitution of Nb5+ (0.64 Å) by a relatively larger Fe3+ (0.645 Å) at the B-site causes a slight expansion of the unit cell [16]. This is ascertained by a shift in (222) peak position towards lower angle with increasing x (inset of Figure 2). The refined lattice constants of Bi3.36Fe2.08+xNb2.56−xO14.56−x (−0.24 ≤ x ≤ 0.48) pyrochlores are found to be in the range 10.5071 (4)–10.5107 (7) Å. The variation is noticeably small, which could be due to the small difference between the ionic radii of these two cations, i.e. less than 0.005 Å. On the other hand, the elemental analyses of these BFN pyrochlores are determined by inductively coupled plasma optical emission spectroscopy (ICP-OES). BFN pyrochlores are confirmed to have correct chemical stoichiometries in which their experimental and calculated atomic values are in a good agreement, i.e. less than 5% error (Table 1).
First-principles prediction of high oxygen-ion conductivity in trilanthanide gallates Ln3GaO6
Published in Science and Technology of Advanced Materials, 2019
Joohwi Lee, Nobuko Ohba, Ryoji Asahi
To investigate the stability of these Ln3GaO6, we consider Pauling’s radius ratio rule [52]. This rule suggests that favorable CNs of cations in the crystal structure depend on the ionic radius ratio (rLn3+/rO2−) of cations (Ln in this study) and anions (O in this study, 1.4 Å [53]). According to this rule, the conditions of 0.41 ≤ rLn3+/rO2− < 0.59 and 0.59 ≤ rLn3+/rO2− < 0.73 correspond to favorable CNs of Ln of six and seven, respectively [54]. As shown in Figure 2(b), in general, rLn3+ decreases with increasing atomic number of Ln with values of 0.86 (Lu)–1.03 (La) Å. These values can be converted to rLn3+/rO2− of 0.61 (Lu)–0.74 (La). This suggests that as rLn3+ is larger (the atomic number of Ln is smaller), it prefers to form the CN of cation of seven rather than of six. The CNs of Ln of Ln3GaO6 and Ln2O3 are seven and six, respectively. Therefore, as rLn3+/rO2− value is larger (the atomic number of Ln is smaller), Ln3GaO6 is preferred to be formed rather than binary oxides, which can be confirmed by the energy differences between Ln3GaO6 and binary oxides as shown in Figure 6. Lu3GaO6 becomes less stable than the binary oxide because its rLn3+/rO2− (0.61) is decreased to near the limit of 0.59.
Application of resins with functional groups in the separation of metal ions/species – a review
Published in Mineral Processing and Extractive Metallurgy Review, 2018
Rene A. Silva, Kelly Hawboldt, Yahui Zhang
The preference of specific metal–ligand bonding and stability depends on physicochemical properties such as stability/solubility constant of the formed complex, ion charge of the ligand and metal ion, electronegativity, geometry, and ionic diameter (Martell and Hancock 2013). Besides stability/solubility constants, the rest of the above-mentioned properties influencing the metal–ligand bonding are summarized under the Pearson Hard and Soft Acids and Bases (HSAB) theory. Thus, the ligands of the functional groups in resins behave as bases (i.e., electron donors) and the metal ions as acids (i.e., electron acceptors) following the Lewis theory of acids and bases (see Table 1). Hard acids are ions with low electronegativity, non-polarizable, have high charge to ionic radius ratio, and are attracted to hard bases of high electronegativity. In contrast, soft acids are polarizable ions with low charge to ionic radius ratio and with relatively high electronegativity that matches the relatively low electronegativity of soft bases (Martell and Hancock 2013; Zaganiaris 2013).