José A.A. Sales

The incorporation of propane-1,3-diamine into silylant epoxide group through homogeneous and heterogeneous routes

The polar organic molecule propane-1,3-diamine reacted: (i) with a 3-glycidoxypropyltrimethoxysilane silylant agent, previously anchored on a silica surface in a heterogeneous route to yield the product SiHT or (ii) with the same agent before immobilizing it on the support, in a homogeneous method, to produce a SiHM surface. The epoxy group was opened yielding chelating pendant groups bonded to the inorganic surface. Both products were characterized through elemental analysis, infrared spectroscopy, surface area and thermogravimetry. The ligand concentrations were 0.80 (SiHT) and 1.53 mmol (SiHM), per gram of silica. The heterogeneous route is an easier procedure to produce immobilization. However the homogeneous route provided conditions to obtain a higher density of pendant groups on the surface, which are potentially useful for extracting cations from solutions in an effective way.

Factorial design for optimization of flow-injection preconcentration procedure for copper(II) determination in natural waters, using 2-aminomethylpyridine grafted silica gel as adsorbent and spectrophotometric detection

The 2-aminomethylpyridine anchored silica gel (AMPSG) was successfully used as a sorbent in a simple spectrophotometric flow system for Cu2+ preconcentration in natural water samples, using sodium diethyldithiocarbamate as chromogenic agent (460 nm). The system was optimized using a full factorial design 25 to determine better analytical conditions to determine copper in the natural water samples such as those from river, tap, stream, spring, well, waste, synthetic brackish water and a water reference material (NIST-1640). The better conditions used were: 180 s loading; 30 s elution; 30 s regeneration of the column; loading flow rate 6.6 mL min−1; buffer solution for the preconcentration and regeneration of the column-acetate buffer pH 5.75; elution flow rate 1.6 mL min−1; eluent composition 0.20 mol L−1 HNO3. Under these conditions, the preconcentration factor obtained was 77, and the detection limit achieved was 3.0 ng mL−1. The recovery of spiked water samples ranged from 95.2 to 104.7%.

The increased termal stability associated with humic acid anchored onto silica gel

Commercial humic acid (HA) was anchored onto silica gel (SiAPTS) previously modified with 3-aminopropyltrimethoxysilane (APTS). HA was anchored onto SiAPTS through two routes: adsorption and covalent chemical immobilization onto the surface. The adsorption occurred by adding SiAPTS to HA in an aqueous solution, producing SiHA1, while chemical immobilization was performed by reacting HA suspended in N,N-dimethylformamide with SiAPTS, to yield SiHA2. The infrared spectra confirm HA immobilization using both procedures and the termogravimetric results showed that the anchored compounds have significantly thermal stability increased. While natural HA presents a thermal stability up to 200°C, the anchored compound presents a thermal stability near to 750°C.

Thermodynamic data for divalent cations onto new modified glycidoxy silica surface at solid/liquid interface

Ethylenediamine molecule was chemically bonded on a silica gel surface previously anchored with 3-glycidoxypropyltrimethoxysilane. This new surface was employed to adsorb divalent cation from aqueous solutions at 298±1 K. The series of adsorption isotherms were adjusted to a modified Langmuir equation from data obtained by suspending the solid with MCl2 (M=Cu, Ni, Zn and Co) solutions, which gave the maximum number of moles adsorbed as 1.54, 0.56, 0.45 and 0.36 mmol g-1 for Cu, Ni, Co and Zn, respectively. Suspended aliquots of the chemically modified surface were calorimetrically titrated and the thermodynamic data showed the system is favored enthalpically and by free Gibbs energy.

Useful aminoalcohol molecules incorporated in an epoxide silylating agent for silica organofunctionalization and thermodynamics of copper removal

Ethanolamine (E) and diethanolamine (D) molecules were incorporated onto a precursor 3-glycidoxypropyltrimethoxysilane (G) agent, followed by organofunctionalization of the silica gel through homogeneous (A) and heterogeneous (B) routes, to yield SiEA, SiDA, SiEB and SiDB hybrids. These chemically organofunctionalized silicas were characterized by several techniques, including infrared spectroscopy (FTIR), solid-state nuclear magnetic resonance (13C and 29Si NMR using CP/MAS), thermogravimetry and elemental analysis. Based on the obtained nitrogen percentages, the amount of pendant organic groups attached to the inorganic matrices SiEB, SiEA, SiDB and SiDA were calculated as 0.22 ± 0.04, 1.05 ± 0.03, 0.29 ± 0.02 and 0.89 ± 0.01, respectively. The infrared spectra presented characteristic bands attributed either to the inorganic framework or to the immobilized chains. Solid-state 13C NMR results clearly demonstrated that the organic moieties are covalently bonded to the inorganic framework, while 29Si NMR revealed the silicon atoms with distinct environments, Q and T, in agreement with the covalent attachment of organic moieties. The basic centers attached on the pendant groups have the ability to sorb copper from aqueous solution. This process was adjusted to the Langmuir model, to obtain maximum sorption values of 0.28 ± 0.02, 0.40 ± 0.02, 0.29 ± 0.03, 0.76 ± 0.02 mmol g−1 for SiEB, SiEA, SiDB and SiDA hybrids, respectively, from the isotherms. Thermodynamic data obtained from calorimetric titrations reflected the spontaneity of the reactions, which are also enthalpically and entropically favorable for the proposed cation/basic center interactions for these chelating processes at the solid/liquid interface.