Maria R. M. C. Santos

Synthesis, characterization, chemisorption and thermodynamic data of urea immobilized on silica

Urea has been covalently immobilized onto silica gel by reaction of urea with a silanized agent attached to silica or by reaction of the previously synthesized molecule containing both urea and silanizing agent with the support, giving 0.55 and 0.92 mmol of urea per gram of silica, respectively. The physical surface area and infrared, proton and solid-state carbon NMR spectra are similar for both surfaces, which extract MCl2(M = Ni, Co, Zn, Cu, Cd, Hg) from acidic water, ethanol and acetone solutions at 298 K. The retention of cations in aqueous solution increases the pH, with Ni and Hg being the most strongly adsorbed. The chemisorption isotherms obtained in non-aqueous media are similar and fit the Langmuir equation. The sequence of maximum retention capacity is Zn < Cu < Hg < Ni < Co and Cu < Co < Zn for ethanol and acetone, respectively. The integral heats of adsorption of cations by the immobilized surface at 298.2 K were larger in ethanol. With the exception of Co (ΔH=+25.51 ± 0.08 kJ mol–1), the cation interactions are exothermic in acetone. The value for Cd (ΔH=–35.91 ± 0.04 kJ mol–1) contrasts with the results found in ethanol, which are endothermic and about one-third of the Cd value. Electronic spectra of the solid suspended in carbon tetrachloride, collected after batchwise adsorption, are in agreement with a tetrahedral geometry for Ni, Co and Cu.

Thermodynamic Data of 6-(4′-Aminobutylamino)-6-deoxycellulose Sorbent for Cation Removal from Aqueous Solutions

The natural biopolymer cellulose was first modified with thionyl chloride, followed by reaction with 1,4-diaminebutane to yield 6-(4′-aminobutylamino)-6-deoxycellulose. From 1.85% of nitrogen incorporated in the polysaccharide backbone, the amount of 0.66 ± 0.11 mmol of this molecule was anchored per gram of the chemically modified cellulose. The resulting chemically immobilized surface was characterized by elemental analysis, infrared spectroscopy, and nuclear magnetic resonance of the carbon nucleus in the solid state and thermogravimetry. The newly synthesized biopolymer gave maximum sorption capacities of 0.32 ± 0.03, 0.29 ± 0.01, 0.26 ± 0.03 and 0.25 ± 0.02 mmol g−1 for divalent copper, cobalt, nickel, and zinc cations, using the batch method, whose data were fitted to different sorption models. The thermal effects obtained from a calorimetric titration procedure gave favorable thermodynamic data for cation sorption from aqueous solutions at the solid/liquid interface, suggesting the use of this anchored biopolymer for cation removal from the environment.

Phosphated Cellulose as an Efficient Biomaterial for Aqueous Drug Ranitidine Removal

Crystalline cellulose chemically modified through a reaction with sodium trimetaphosphate (STMP) in an acidic or basic condition yielded Cel-P4 and Cel-P10. These phosphated solids were characterized by elemental analysis, X-ray diffraction (XRD), infrared (IR) spectroscopy, scanning electron microscopy (SEM), nuclear magnetic resonance (NMR) at the solid state for phosphorus nucleus and dispersive X-ray energy. The elemental results demonstrated that the phosphorylation reaction was more efficient in the basic medium, as supported by the amount of phosphorous content. The synthesized biomaterials decreased in crystallinity in comparison to the precursor cellulose, with an increase in roughness and present two distinct phosphorus environments in the formed structure. The phosphated cellulose in an alkaline condition was applied to sorb the drug ranitidine. This process was applied in varying pH, time, temperature and concentration. The best sorption kinetic model to fit the experimental data was the pseudo-second-order with a coefficient correlation of 0.8976, and the Langmuir isotherm model was the most adjusted to the variation in concentration. The efficient drug sorption has a low dependence on temperature, with maximum values of 85.0, 82.0 mg and 85.7 mg·g−1 for Cel-P10 at 298, 308 and 318 K, respectively. The best sorption occurred at pH = 6 with a saturation time of 210 min.

Thermochemical study of adducts of urea with zinc, cadmium and mercury: some correlations for urea derivatives

Abstract The adducts ZnX 2 ·2ur (X = Cl, Br, I), CdX 2 ·2ur (X = Br, I), CdX 2 · ur (X = Cl, Br, I) and HgX 2 ur (X = Cl, Br) have been characterized. The shifts of the stretching vibrations to low frequency ( v CO) and to high frequencies ( v CN and v NH) indicated that urea (ur) is oxygen-bonded to the metals. The standard molar enthalpies for the reaction MX 2 (c)+ n ur(c) = MX 2 · n ur(c) Δ r H m ⊖ were determined by solution-reaction calorimetry, given the following values: ZnCl 2 ·2ur(c), −59.72±0.30; ZnBr 2 · 2ur, −59.41±0.89; ZnI 2 · 2ur, −81.74 ±0.89; CdCl 2 · ur, −21.54±0.18; CdBr 2 · ur, −13.88±0.28; CdI 2 · ur, −30.75±0.36; CdBr 2 · 2ur, −24.40+0.21; CdI 2 · 2ur, −19.69±0.17; HgCl 2 · ur, −9.39±0.13 and HgBr 2 · ur, +1.00 ±0.78 kJ mol −1 . From these values, the standard molar enthalpies of formation (Δ f H m ⊖ ) and of decomposition (Δ D H m ⊖ ), and lattice enthalpy (Δ M H m ⊖ ) were calculated and the mean molar enthalpy of the metal-oxygen bond [t D (M-O)] was estimated. The thermochemical results indicate a decrease in stability of the adducts from zinc to mercury. The degree of hydrogen bonding affects differently the enthalpies of formation of adducts in solid state for urea and its derivatives.

Phonon confinement model to measure the average sizes of anatase nanoparticles synthesized by a solvothermal method using H2O2

Universidade Federal do Piaui Centro de Ciencias da Natureza Departamento de Quimica Departamento de Fisica LIMAV