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Use of Carbon Nanotubes as Sorbents for Heavy Metal Remediation from Wastewater
Published in Chaudhery Mustansar Hussain, Ajay Kumar Mishra, Nanocomposites for Pollution Control, 2018
Akil Ahmad, David Lokhat, Siti Hamidah Mohd Setapar, Asma Khatoon, Mohammad Shahadat, Mohd Rafatullah
Carbon nanotubes (CNTs) chemically modified with organic moieties and treated with concentrated nitric acid containing significantly different chemical donor functionalities (-N, -P, -O, -S) find increasing and promising interest for the sorption of trace and precious metal ions. Several functional group atoms are capable of chelating trace elements. The atoms most frequently used are nitrogen (e.g. N present in amines, azo groups, amides and nitriles), oxygen (e.g. O present in carboxylic, hydroxyl, phenolic, ether, carbonyl, phosphoryl groups) and sulphur (e.g. S present in thiols, thiocarbamates and thioethers) (Ahmad et al., 2015; Latorre et al., 2012). The nature of the functional group will give an idea of the selectivity of the ligand towards trace elements. For soft metals, the following order of donor atom affinity is observed: O < N < S. A reversed order is observed for hard cations. For a bidentate ligand, affinity for a soft metal increases with the overall softness of the donor atoms: (O, O) < (O, N) < (N, N) < (N, S). The order is reversed for hard metals. In general, the competition for a given ligand essentially involves Group I and Group II metals for O sites, and metals of Group II and Group III for N and S sites. The competition between metals of Group I and Group III is weak.
Introduction to Organometallics
Published in Samir H. Chikkali, Metal-Catalyzed Polymerization, 2017
Samir H. Chikkali, Sandeep Netalkar
As explained earlier, even though H2O has two lone pairs of electrons, it cannot function as a bidentate ligand. Hypothetically, if we consider that H2O donates both of its lone pair to single central metal ions, it would still be bound to the metal through a single atom and hence would be considered as a monodentate ligand. For a ligand to function as a bidentate system, two valence pairs of electrons on two separate atom sites are required. For example, ethylene diamine and oxalate dianion bind to the metal through two separate atoms and hence is considered as bidentate ligand (Figure 1.5). Bidentate ligands form one of the most important classes of ligands in metal-catalyzed polymerization. The significance of bidentate ligands is presented in Chapters 2, 3, 4, 6, and 7. Similarly, a ligand with three lone pairs of electrons would serve as tridentate ligand (Figure 1.5) and so on.
Aqueous Solvent Removal of Contaminants from Soils
Published in Donald L. Wise, Debra J. Trantolo, Edward J. Cichon, Hilary I. Inyang, Ulrich Stottmeister, Remediation Engineering of Contaminated Soils, 2000
James C. O'Shaughnessy, Frederic C. Blanc
Chelating agents are helpful in removing metals from soil particles. A chelating agent is an organic that contains an anionic portion termed a ligand, which forms a bond with a metal cation. This structure is termed a metal complex and allows more metal to enter into the washwater solution. A ligand that can form two bonds to a lone metal ion is called a bidentate ligand, while ligands that can form more than two bonds to a metal ion are called polydentate ligands. A polydentate ligand which can form six bonds to a metal ion is termed a hexadentate ligand. Ethylenediaminetetraacetate (EDTA) is a hexadentate ligand which has been used as a scavenger to remove heavy metals such as lead from the human body. EDTA is relatively safe and is used in consumer food products, soaps, and cleaners. The authors have used EDTA to remove metals from contaminated soils (10-12). Naturally occurring organic ligands form organometal complexes which impede metal removal in water and wastewater treatment. Similarly, once the chelating agent metal complex has been created in the soil washing operation, treating the resulting washwaters may become more difficult, requiring extensive pH alteration to break the complex.
Role of Phase Modifiers in Controlling the Third-phase Formation During the Solvent Extraction of Trivalent Actinides
Published in Solvent Extraction and Ion Exchange, 2019
K. Rama Swami, K. A. Venkatesan, M. P. Antony
Partitioning of trivalent actinides from HLLW and transmutation into short or stable products in accelerated-driven systems has been proposed for the long-term safe management of HLLW.[1–3] Since americium and curium exist in trivalent oxidation state, the separation of americium and curium from HLLW requires more basic bidentate or tridentate ligands as compared to the monodentate ligands employed in PUREX process.[4–6] Strongly polar ligands containing amidic and phosphoryl moieties have been developed and employed for the extraction of trivalent actinides from nitric acid medium representing HLLW. For instance, the bidentate ligands such as carbomoyl phosphine oxide and malonamide and the tridentate diglycolamides are popular.[5–9] To dissolve these strongly polar ligands in a nonpolar diluent such as n-dodecane, generally employed for nuclear reprocessing applications, the alkyl groups attached to these ligands are optimized to give significant solubility in the n-dodecane phase and poor solubility in the aqueous phase.[7–9] Since these ligands contain polar co-ordinating groups tethered with nonpolar long-chain alkyl groups, they are regarded as amphiphiles.[10,11]
Synthesis, characterization, crystal structure, in-vitro cytotoxicity, antibacterial, and antifungal activities of nickel(II) and cobalt(III) complexes with acylthioureas
Published in Journal of Coordination Chemistry, 2020
Mahira Khan, Naqeebullah Khan, Kinza Ghazal, Sara Shoaib, Irshad Ali, Muhammad Khawar Rauf, Amin Badshah, Muhammad Nawaz Tahir, Attiq-Ur Rehman
This work reports the synthesis of two acylthioureas, their metal complexes and evaluation of their bioactivities. The prepared compounds have been well characterized by utilizing various characterization tools such as elemental analyses, FT-IR, 1H and 13C NMR. The ligands are present in deprotonated forms in complexes which induce electronic delocalization in the frame –C(O)NC(S)–. X-ray structures reveal that 1 and 2 exhibit square planar and octahedral geometries, respectively. The ligands are coordinated through sulfur and oxygen donor sites in a bidentate way.