Imobilização de ureia, metilureia e 1,3-dimetilureia sobre silica gel-sintese, caracterização, quimissorção de cations divalentes e termoquimica

AUTOR(ES)
DATA DE PUBLICAÇÃO

1992

RESUMO

Urea (u), methylurea (mu) and 1,3-dimethylurea (dmu) were anchored on silica gel surface in homogeneous and heterogeneous media being the more efficient. The silanized and modified surfaces were characterized by elemental analysis, infrared spectroscopy, C and H NMR in solution and by C NMR for the solids. The nitrogen analyses indicate the presence of 0.46; 0.15 and 0.25 mmol of bonded u, mu and dmu for each gram of silica. Divalent ions adsorbed by the batch gram of silica. Divalent ions adsorbed by the batch methad were: Co(1.18±0.01; 0.79±0.01), Cu(2.34±0.01; 2.14±0.01); Ni(1.64±0.01; 1.92±0.01); Zn(2.42±0.01; 1.34±0.01); Cd(1.26±0.01; 1.06±0.01) and Hg(2.01±0.01; 1.61±0.01).10 molg in ethanol on sil-u and sil-dmu surfaces, respectively and Co(2.43±0.01; 1.16±0.01); Cu(2.63±0.01; 2.41±0.01); Zn(2.28±0.01; 1.42±0.01).10 molg in acetone, on the same surfaces, which demonstrates that Cu and Zn are the best adsorbed in both solvents, while the opposite occurs with Cd and Co. In acetona, the sil-mu surface showed the adsorption order: Co(1.70±0.01) >Cu(1.13±0.01) >Zn(0.78±0.01).10 molg. The adsorption follows the degree of functionalization sil-u >sil-dmu >sil-mu and is sensitive to the nature of the solvent, with acetone >ethanol. The calorimetric titrations of the surfaces in both solvents give isotherms which are consistent with the modified Langmuir equation. With the linearization of these isotherms, the enthalpy of adsorption cation/surface and the interfacial equilibrium constant were obtained. The values of the enthalpies show that these processes are more exotermic in acetone. For example, the values Cu(-28.38±0.04; and 8.91±0.03) kJmol were obtained for sil-u in acetone and ethanol, respectively. With Co on the same surface the enthalpies obtained were +25.51±0.08 and -7.12±0.01 kJmol in acetone and ethanol, respectively. Cu with sil-u and sil-dmu surfaces gave exotermic values, (-28.38±0.04; 0.46) and (-4.34±0.01; 0.25) (kJmol; mmol), respectively, which is related to the degree of functionalization, as observed with the adsorption of acetone. Photoacoustic and electronic spectroscopies for Cu, Ni and Co cations complexed on the surfaces manifest the preference of the cations for a tetrahedral site.

ASSUNTO(S)

termoquimica quimica inorganica

ACESSO AO ARTIGO

Documentos Relacionados