Interaction of cadmium nitrate with the surface of functionalized organosilicas

Abstract

The adsorption of Cd II cations on the surface of amorphous macroporous silicas chemically modified by β cyclodextrin and its functional derivatives was studied. The adsorption of Cd II cations was shown to follow the equation of the Freundlich isotherm for the heterogeneous surface. Analysis of the adsorption kinetic curves showed that two parallel processes occurred on the surface of β cyclodextrin containing silicas. A substantial increase in the adsorption of Cd(NO 3 ) 2 is a result of the formation of uncharged supramolecular structures on the surface of silica adsorbents. The composition of these structures depends on the polarizability of function al substituents of β cyclodextrins.Chemical immobilization of macrocyclic organic com pounds on the surface of oxide materials is accompanied by the formation of host-guest inclusion complexes with ions and molecules. As a result, active sites are formed, which are capable of sorbing and in this way extracting and concentrating trace amounts of toxic substances. 1-3 Among oxide materials, highly dispersed amorphous sili cas are undoubtedly advantageous. These adsorbents are characterized by high chemical, hydrolytic, thermal, and radiation stability, and the structure and reactivity of their active sites on the surface are well studied. 4-6The purpose of the present work is to study the effect of the surface structure of β cyclodextrin containing silicas on the adsorption of Сd II cations from weakly acidic dilute solutions. ExperimentalChemical immobilization of β cyclodextrin (β CD) was car ried out on the surface of highly dispersed amorphous macro porous silica (Silochrome C 120) by multistep chemical modifi cation. The interaction of hydroxylated silica (adsorbent 1) with γ aminopropyltriethoxysilane gave aminopropylsilochrome (adsorbent 2). Organosilicas chemically modified with β CD were synthesized by reacting aminopropylsilochrome with mono(toluenesulfonyl) β CD (adsorbent 3), the bromo substi tuted derivative of heptakis(toluenesulfonyl) β CD with amino propylsilochrome (adsorbent 4), and the bromoacetyl groups of adsorbent 4 with thiosemicarbazide (adsorbent 5).The structural adsorption parameters, chemical composi tion, and structure of the surface layer of the silica adsorbents (Table 1) were determined from the low temperature nitrogen adsorption isotherms, elemental and chemical analyses, poten tiometric titration, and data of thermogravimetry, IR spectros copy, and 1 Н NMR spectroscopy.The adsorption of cations Cd II was studied at 22 °C under static conditions by the method of separate weighed samples from 2.5•10 -4 -4.0•10 -3 М aqueous solutions of Cd(NO 3 ) 2 with pH ~1 at different contact times with silicas and at different concentrations of the equilibrium solution. Suspensions con taining 0.025 g of the silica adsorbent and 20 cm 3 of a Cd(NO 3 ) 2 solution were maintained at constant temperature for 4 h in a JULABO SW22 aqueous thermostat with continuous shaking. The content of Cd II in the starting and equilibrium solutions was determined...

Theoretical Analysis of the Mackay Icosahedral Cluster Pd55(PiPr3)12(μ3‐CO)20: An Open‐Shell 20‐Electron Superatom

“…Group 10 clusters of a certain size also tend to aggregate in a compact fashion. [28][29][30][31][32] However, no general electron-counting rules developed for high nuclearity spherical clusters [4] seem to apply to these species in a comprehensive manner. On one side, they often do not obey the classical Wade-Mingos rules.…”

The kinetics of adsorption binding of Ba2+ ions by trimethylsilylated silica

“…The common kinetic models of adsorption processes are the absorption (diffusion) model and the Elovich kinematic model [13][14][15][16]. In the last two decades, researchers have used the Lagergren equation of the pseudo-first or pseudo-second order for an analytical description of the kinetics of adsorption processes [15][16][17][18][19].…”

“…In the last two decades, researchers have used the Lagergren equation of the pseudo-first or pseudo-second order for an analytical description of the kinetics of adsorption processes [15][16][17][18][19].…”