Hérica A. Magosso

Gold nanoparticles hosted in a water-soluble silsesquioxane polymer applied as a catalytic material onto an electrochemical sensor for detection of nitrophenol isomers

The water-soluble 3-n-propyl-4-picolinium silsesquioxane chloride (Si4Pic(+)Cl(-)) polymer was prepared, characterized and used as a stabilizing agent for the synthesis of gold nanoparticles (nAu). The ability of Si4Pic(+)Cl(-) to adsorb anionic metal complexes such as AuCl4(-) ions allowed well-dispersed nAu to be obtained with an average particle size of 4.5nm. The liquid suspension of nAu-Si4Pic(+)Cl(-) was deposited by the drop coating method onto a glassy carbon electrode (GCE) surface to build a sensor (nAu-Si4Pic(+)Cl(-)/GCE) which was used for the detection of o-nitrophenol (o-NP) and p-nitrophenol (p-NP). Under optimized experimental conditions the reduction peak current increased with increasing concentrations of both nitrophenol isomers in the range of 0.1-1.5μmolL(-1). The detection limits were 46nmolL(-1) and 55nmolL(-1) for o-NP and p-NP, respectively. These findings indicate that the nAu-Si4Pic(+)Cl(-) material is a very promising candidate to assemble electrochemical sensors for practical applications in the field of analytical chemistry.

Surface functionalization of SBA-15 and a nonordered mesoporous silica with a 1,4-diazabicyclo[2.2.2]octane derivative: Study of CuCl2 adsorption from ethanol solution

This work describes the preparation and characterization of postfunctionalized ordered (SBA-15) and nonordered (SMD) mesoporous silicas with n-propyl-1,4-diazoniabicycle[2.2.2]octane chloride (DbCl) moiety. The main interest is based on the fact that these materials are excellent adsorbents due to the ability of functional groups to retain copper chlorides on their surfaces as anionic complexes CuCl(2+n)(n-). The specific surface areas (S(BET)) and average pore diameters (d(pore)) for SBA-15 and SMD are SBA-15, S(BET)=944 m(2) g(-1), d(pore)=9.0 nm; SMD, S(BET)=710 m(2) g(-1), d(pore)=11 nm. On functionalization with DbCl, reductions in the specific surface areas of the resulting materials (SBA-15/DbCl and SMD/DbCl) are observed and the following functionalization degrees (ϕ) were determined: SBA-15/DbCl, S(BET)=247 m(2) g(-1), ϕ=0.95 mmol g(-1); SMD/DbCl, S(BET)=83 m(2) g(-1), ϕ=1.2 mmol g(-1). The adsorption equilibria of CuCl(2) in ethanol were characterized, and the heterogeneous stability constants, β(1) and β(2), corresponding to formation of CuCl(4)(2-) and CuCl(3)(-) anionic species adsorbed on the surface were found. Also, the effective sorption capacities (t(Q)) were determined: SBA-15/DbCl, log β(1)=4.46, log β(2)=7.10, t(Q)=0.80 mmol g(-1); SMD/DbCl, log β(1)=4.95, log β(2)=7.52, t(Q)=0.75 mmol g(-1). Regeneration of the adsorbents requires a very simple procedure consisting of their immersion in aqueous solution followed by immediate release to the solution phase of the Cu(OH(2))(n)(2+) species, followed by chloride anions as the counterions.

Electrochemical behavior of hydroquinone and catechol at a silsesquioxane-modified carbon paste electrode

A carbon paste electrode modified with 3-n-propyl-4-picolinium chloride silsesquioxane polymer was tested as a sensor for dihydroxybenzene isomers. The sensor showed excellent performance for simultaneous electroanalytical determination of hydroquinone and catechol. The calibration curves obtained were linear in the concentration range of 10.0 to 450.0 µmol L1 for hydroquinone (r = 0.998) and 10.0 to 300.0 µmol L-1 for catechol (r = 0.997). The visual limit of detection was 10.0 µmol L-1 for both isomers.

Al2O3 coated with 3-n-propyl-1-azonia-4-azabicyclo[2.2.2]octane silsesquioxane chloride and its use for immobilization of cobalt(II) tetrasulfonated phthalocyanine in oxalic acid electrooxidation

A water-soluble polymer prepared by sol-gel process, 3-n-propyl-1-azonia-4-azabicyclo[2.2.2]octane silsesquioxane chloride, was adsorbed on alumina surface. This polymer-coated alumina was able to effectively immobilize cobalt(II) tetrasulfonated phthalocyanine complexes as counter ions. Cobalt phthalocyanine immobilized in this way is well and tightly adsorbed on Al2O3/3-n-propyl-1-azonia-4-azabicyclo[2.2.2]octane silsesquioxane chloride surface. Furthermore, when incorporated to a carbon paste electrode showed a good electrocatalytic response toward the acid oxalic oxidation, making it a suitable electrode material. A linear relationship (r = 0.998) between the current responses obtained by chronoamperometric measurements and the oxalic acid concentration in the range of 7.4 × 10-5 - 9.1 × 10-4 mol L-1 was observed. A detection limit of 18 µmol L-1 was also determined.

Adsorption of Metal Ions on Novel 3-n-Propyl(Methylpyridinium) Silsesquioxane Chloride Polymers Surface. Study of Heterogeneous Equilibrium at the Solid-Solution Interface

Os polimeros Si3Py+Cl- (A) e Si4Py+Cl- (B), cloretos de 3-n-propil (3s-metilpiridinio) silsesquioxano e 3-n-propil(4-metilpiridinio)silsesquioxano respectivamente, foram preparados pelo metodo de sintese sol-gel. Os valores de capacidade de troca ionica (mmol g-1) foram iguais a 0,90 e 0,81 para (A) e (B), respectivamente. Considerando a reacao nSiPy+Cl-(s) + M2+(sln) + 2Cl-(sln) (SiPy+)nMCl2+nn- (s), as constantes de equilibrio calculadas para cada etapa foram: (A): CuII, logK(2)1= 4,14(0,03), logK(2)2= 2,91(0,04); ZnII, logK(2)1= 3,3(0,3), logK(2)2= 4,9(0,3); (B): CuII, logK(2)1= 3,82(0,03), logK(2)2= 3,00(0,04); ZnII, logK(2)1= 3,93(0,03), logK(2)2= 3,55(0,08), onde K(2)1 e K(2)2 correspondem as constantes de equilibrio de adsorcao das especies MCl42- e MCl3-, respectivamente. No caso da adsorcao de ZnII sobre Si3Py+Cl-, em que K(2)2 > K(2)1, uma cooperatividade positiva e observada, ou seja, a adsorcao da especie MCl42-facilita a adsorcao da especie MCl3-. Nos demais casos, K(2)1> K(2)2, o que indica que a adsorcao da especie MCl42- dificulta a adsorcao da especie MCl3- na superficie dos adsorventes, indicando uma cooperatividade negativa.

A hybrid material as a sorbent phase for the disposable pipette extraction technique enhances efficiency in the determination of phenolic endocrine-disrupting compounds

In this study, the hybrid material 3-n-propyl(3-methylpyridinium) silsesquioxane chloride (Si3Py+Cl-) was synthesized and investigated as a novel sorbent phase for the disposable pipette extraction (DPX) technique coupled to high-performance liquid chromatography-florescence detection. This sorbent phase was characterized by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). Aqueous samples containing the phenolic endocrine-disrupting compounds bisphenol A (BPA), 17α-ethynylestradiol (EE2), 4-tert-octylphenol (4-t-OP), 4-octylphenol (4-OP) and 4-nonylphenol (4-NP) were subjected to DPX procedures and a series of optimizations was performed to determine the ideal extraction conditions using this approach. The proposed sorbent phase exhibited higher extraction efficiency than DPX-RP (reversed phase tips containing styrene-divinylbenzene), commonly used for the determination of the phenolic endocrine- disrupting-compounds under study. Satisfactory analytical performance was achieved with linear ranges from 2 to 100μgL-1 for 4-t-OP and 1-100μgL-1 for the other analytes. Limits of detection of 0.60μgL-1 for 4-t-OP and 0.30μgL-1 for other analytes, RSDs ranging from 1 to 20% and relative recoveries of 83-116% were obtained. Based on these satisfactory results, this sorbent phase represents a valuable alternative for the extraction of compounds with polar moieties in their structure.