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Macrocyclic Receptors for Precious Metal Ions
Published in Satish Kumar, Priya Ranjan Sahoo, Violet Rajeshwari Macwan, Jaspreet Kaur, Mukesh, Rachana Sahney, Macrocyclic Receptors for Environmental and Biosensing Applications, 2022
Satish Kumar, Priya Ranjan Sahoo, Violet Rajeshwari Macwan, Jaspreet Kaur, Mukesh, Rachana Sahney
In this regard, various research strategies and approaches to create tailor-made synthetic supramolecular assemblies for noble metal ions have been meticulously explored and reported in literature. A variety of macrocyclic receptors based on crown ethers, aza-crown ethers, thia-crown ethers, aza-thia-crown ethers, cyclam, cyclen, thiacalixarenes, pillarenes and their functionalized derivatives have been designed and exclusively investigated for a response towards precious metal ions. According to Pearson’s HSAB theory, ligands bearing S as donor atoms are classified as soft bases and tend to have an affinity towards soft acids, such as silver(I), gold(III) and platinum group of metals. For instance, the presence of sulphur atoms in place of the usual methylene bridges in thiacalixarenes remarkably modifies its properties than that of the parent calixarenes. Consequently, thiacalixarenes and their derivatives have been reported to exhibit modified solubility and better conformational flexibility as well as complexation ability towards soft metal ions (Fontàs et al. 2007). Likewise, the substitution of oxygen by sulphur atoms in the crown and aza-crown ethers can lead to greater soft metal ion discrimination. For example, mixed N, O, S- donor crown ethers have been efficiently used as selective extractants for soft metal ions (Xu et al. 2010).
Thermodynamic modeling of adsorption of dimethyl sulfide on raw and modified activated carbon by simplified local density model
Published in Petroleum Science and Technology, 2023
Hossein Jalilvand, Farzaneh Feyzi
This study is based on the experimental results of the authors’ previous research (Jalilvand, Feyzi, and Dehghani 2020). Walnut shell activated carbon (WSAC) and pistachio shell-activated carbon (PSAC) were obtained from Rafsanjan Pars Activated Carbon Company. DMS (99+%, extra pure) and n-hexane (95%, high purity) were purchased from Merck and Sigma Aldrich, respectively. They were used without further purification. Adsorption data of DMS from n-hexane (the model fuel), were obtained in the liquid phase on both kinds of activated carbon. Adsorption experiments revealed better performance of WSAC which was then selected as the adsorbent to be modified with various ions (Ag, Cu (I), Cu (II), and Fe (III)) using the wet impregnated method. Silver showed the highest adsorption capacity in comparison with other ions. This finding was interpreted with the hard-soft acid base (HSAB) theory. WSAC was then modified by various amounts of silver with 2, 4, 6, 8, and 10 mass percent, which were named as WSAC-Ag-2, 4, 6, 8, and 10, respectively. Several experiments were performed on each adsorbent and the adsorption isotherms were obtained (Jalilvand, Feyzi, and Dehghani 2020). These results, which are presented in Figure 2, showed that WSAC-Ag-6 was the best adsorbent. The overall performance of the adsorbents is: WSAC-Ag-6 > WSAC-Ag-4 > WSAC-Ag-2 > WSAC-Ag-8 > WSAC-Ag-10 > WSAC. Characterization of raw and modified adsorbents was performed. The surface parameters of adsorbents are tabulated in Table 1 (Jalilvand, Feyzi, and Dehghani 2020).
Ultrasonic and microwave effects on Prussian blue catalysed high-quality biodiesel production using Watermelon (Citrullus vulgaris) seed oil and alcohol extract (from fibrous flesh) as an exclusive green feedstock
Published in Biofuels, 2021
K. C. Rajanna, G. Krishnaiah, Srinivas Pasnoori, P. S. Santhoshi, Y. Rajeshwer Rao, K. S. K. Rao Patnaik
However, Prussian blue (PB) catalyzed mechanism differs from that of base catalyzed reactions. According to Pearson’s HSAB theory [59] “Hard acids (HA) prefer to bind to hard bases (HB) and soft acids (SA) prefer to bind to soft bases (SB)”. Prussian blue, with Fe (III) backbone is a hard acid with sufficient number of vacant orbitals. Therefore, it can easily form adducts with hard bases, such as triglycerides and hydroxy compounds. Triglyceride being a harder base than hydroxy compound prefers to interact with a hard acid PB to generate a transient electron deficient center at carbonyl carbon. The transient intermediate thus formed then probably reacts with hydroxy compound (for example ethanol) and affords biodiesel through transesterification path, followed by the regeneration of PB. The regenerated PB may further react with second and third ester moieties of triglyceride in subsequent steps. For simplicity reaction with first ester moiety is shown in the Scheme-3.
Kinetics, isotherms and thermodynamic modeling of Mn2+ and Zn2+ single and binary removal using mercapto functionalized silica aerogel
Published in Journal of Dispersion Science and Technology, 2019
Seyed Saeed Mirzaee, Esmaeil Salahi, Ali Khanlarkhani
Figure 10 shows binary adsorption of Zn2+ and Mn2+ ions. As it can be seen in Figure 10a, the presence of Mn2+ ions causes a slight decrease in Zn2+ ion adsorption (about %20). On the other hand, by increasing the Zn2+ ions, the adsorption of Mn2+ ions is greatly reduced (about %72) (Figur 10b). In simultaneous adsorption, competition between ions occurs due to finite adsorption sites at the same time. Hence, the affinity of the functional groups on the adsorbent surface to each of the ions plays a decisive role in the rate of adsorption. As previously stated (intra-particle diffusion section), the tendency of adsorbent to the Zn2+ ions is greater than Mn2+ ions. This phenomenon can be explained by hard and soft acids and bases (HSAB) theory. As classified by Pearson, Thiol group (HS), Zn2+ and Mn2+ could form soft bases, borderline acids and hard acids, respectively. So, based on HSAB theory, thiol group has higher affinity toward Zn2+ rather than Mn2+.[36,38]