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Bioflocculants Relevant for Water Treatment and Remediation
Published in Sheila Devasahayam, Kim Dowling, Manoj K. Mahapatra, Sustainability in the Mineral and Energy Sectors, 2016
K. A. Natarajan, K. Karthiga Devi
Bridging occurs when a flocculant forms threads or fibers that adsorb onto more than one particle, capturing and binding them together. The polymer molecule comes into contact with the colloidal particles, the reactive groups of the polymer attach to the surface of the particle thus leaving other portions of the molecule extending into the solution. The polymer/flocculant adsorbs onto the surface in loops (i.e., the segments extending into the solution) and tails (i.e., segments adsorbed on the surface). Thus, when another particle (with free adsorption site) comes into contact with these extended loops and tails, it attaches forming a particle–polymer–particle aggregate, thereby acting as a bridge. This attachment of segments leading to the formation of strong bonds is made more effective due to the short distances involved, which can overcome electrostatic repulsions between particles having the same net charge (Ganczarczyk, 1983). This mechanism is dependent on the molecular weight of the bioflocculant, the charge on the polymer and particle, ionic strength of the suspension and the nature of mixing (Salehizadeh and Shojaosadati, 2001; Ebeling et al., 2005). This mechanism is much prevalent in high molecular weight polyelectrolytes of large low density (Sharma et al., 2006). Hence, high molecular weight flocculants produce larger, loosely packed flocs and fragile flocs (Ebeling et al., 2005). For effective interparticle bridging, this mechanism functioning simultaneously with charge neutralization brings about efficient settling resulting in shear resistant flocs. A simplistic model illustrating the bioflocculation mechanism is given in Figure 16.2.
Physical Hazards
Published in John F. Rekus, Complete Confined Spaces Handbook, 2018
Still another engulfment hazard is produced by a condition known as “bridging.” Bridging is a condition that results when a layer of material extends across the cross-section of a bin, hopper or silo that has been emptied from below (Figure 5-14). While bridges often appear to be solid, they can give way without warning swallowing up workers who are standing on top of them. They can also break apart under their own weight and fall onto entrants working beneath them.
A pyrazolone-based dinuclear Cu(II) Schiff-base complex: DFT studies on the rate-determining steps of the tautomerism in the ligand and molecular docking modelling with COVID-19 main protease (6LU7)
Published in Journal of Coordination Chemistry, 2023
Liana Ghasemi, Mahdi Behzad, Azar Gharib, Ali Arab, Alireza Abbasi
The IR spectrum of the ligand (Figure S3) is related to the presence of the OH and imine functional groups. The sharp and intense band at 1622 cm−1 confirms the presence of C = N. Another signal above 3300 cm−1 is related to the ν(O–H) stretch [35,36]. The sharp band at 3427 cm−1 in the FTIR spectrum of the complex (Figure S4) was assigned to the N–H stretch of the coordinated NH2 group. The ʋ(C–O) stretch of the free Schiff-base ligand was at 1120 cm−1, shifted to lower wavenumbers (about 1020 cm−1) after complexation, suggesting coordination of this oxygen atom to the Cu2+ ions. In the complex, signals at 1591 and 1471 cm−1 are related to the νasym (CO2) and νsym (CO2) in acetate, respectively [37,38]. These data show that the acetate group is a bridging ligand.
Cu(II) complexes with coordinated pyrazine-dioxide: pyrazine-bridged chains
Published in Journal of Coordination Chemistry, 2022
Christopher P. Landee, Diane A. Dickie, Mark M. Turnbull, Jan L. Wikaira
With such a start, it is not surprising that pyrazine has become so common as a bridging ligand in coordination chemistry and especially in magnetochemistry. It is limited to mono- or bi-dentate coordination and provides good control of structure with its preference for linear motifs. As a result of these highly favorable properties, pyrazine and substituted pyrazine derivatives have been employed in formation of a wide variety of low-dimensional lattices, such as magnetic ladders [10] as well as both square [11] and rectangular [12] layered structures. Pyrazine mediates antiferromagnetic exchange in its bridging mode, with J/kB values typically in the −5 to −18 K range for copper(II) based systems [13], while the nickel complex Ni(pz)2(ClO4)2 exhibits a value of nearly 0 K [14]. The parameters controlling the exchange are still not well understood and further work is needed.
Novel heterometallic Zn(II)-L-Cu(II) complexes: studies of the nucleophilic substitution reactions, antimicrobial, redox and cytotoxic activity
Published in Journal of Coordination Chemistry, 2022
Asija Halilagić, Enisa Selimović, Jelena S. Katanić Stanković, Nikola Srećković, Katarina Virijević, Marko N. Živanović, Biljana Šmit, Tanja V. Soldatović
To a stirred aqueous solution of [ZnCl(terpy)(H2O)](ClO4) 0.06 g (0.16 mmol, 25 mL) an aqueous solution of the bridging ligand (pyrazine or 4,4′-bipyridyl) (0.16 mmol, 15 mL) was added dropwise at 30 °C. After 1 h the solution of [CuCl(terpy)(H2O)](ClO4) 0.06 g (0.16 mmol, 15 mL) was added dropwise. The pH was adjusted to 4.5 by 0.1 MHClO4, and the reaction mixture was left to stir overnight. The resulting colored solution was filtered and kept aside for slow evaporation at room temperature. The color of the complex powder was blue-green when the bridging ligand was pyrazine and green when 4,4′-bipyridyl was used. Purification of both complexes was done by reprecipitation in small amounts of methanol and removal of the solvent by rotary evaporation. The obtained powders were washed with small amounts of ether and then dried in vacuo. The schematic presentation of the synthesis is given in Scheme 1.