Comparative studies on the adsorption of metal ions from aqueous solutions using various functionalized graphene oxide sheets as supported adsorbents

Preparation and Characterization of Graphene Oxide for Pb(II) and Zn(II) Ions Adsorption from Aqueous Solution: Experimental, Thermodynamic and Kinetic Study

“…The values of C were helpful to determine the boundary thickness: a larger C value corresponded to a greater boundary layer diffusion effect. Therefore, the kinetics were affected by some other adsorption processes in the system as shown by the value of β obtained in the Elovich model, that according to the correlation coefficient values, it could be concluded that the Elovich model described chemically the adsorption of Pb(II) and Zn(II) onto the GO adsorbent [ 125 , 126 , 127 , 128 , 129 , 130 , 131 ].…”

“…The possibility of intraparticle diffusion was explored using the Weber–Morris model [ 127 , 128 , 129 , 130 , 131 ]. The Weber–Morris model is expressed by Equation (12) [ 73 , 128 , 129 ]: in this expression K I is the intraparticle diffusion rate constant (mg g min 1/2 ) and is obtained from the slope of the corresponding graph. To prove the existence of intraparticle diffusion in the adsorption process, the amount of Pb(II) and Zn(II) adsorbed, q t , at any time t (mg/g), was represented as a function of the square root of time (t 1/2 ).…”

“…These values of the rate constants were less than 1, which showed that the velocity of the ions to the internal structure of graphene oxide was not favored. [ 86 , 125 , 126 , 127 , 128 , 129 , 130 , 131 ]. These results allowed us to conclude that the intraparticle diffusion kinetic model was not the determining step of the velocity for the ion adsorption processes having a C intercept that was > 0 <1.…”

“…The positive values obtained for ΔH o for the ion-GO system indicate that the nature of the studied process is endothermic. To explain this behavior (GO) they are favorable at high temperatures because all metal ions are dehydrated and their solubility in the aqueous solution increases with increasing temperature [ 128 , 129 , 130 , 131 ]. Furthermore, the positive ΔS o values reflect the affinity of the GO adsorbent towards metal ions in aqueous solutions and an increase in the disorder at the solid–solution interface during the adsorption process [ 63 , 90 , 91 , 92 , 93 , 94 , 95 , 96 , 97 , 98 ].…”

Graphene oxide quantum dots immobilized on mesoporous silica: preparation, characterization and electroanalytical application

“…This fact can be explained by the good adsorption properties of GO towards metal ions. 1,61 Covalent immobilization of GOQDs on the silica surface was performed via an earlier-established procedure for the covalent attachment of carboxyl-containing organic compounds on SiO 2 -NH 2 , by the acylation of immobilised aminosilane in anhydrous solvent (DMF) in the presence of DCC. 10,14 An excess of GOQDs was separated from the nal product by multiple decantations of the precipitate alternating with ultrasonic treatment of SiO 2 -GOQDs in DMF.…”