Yoshitaka Gushikem

Sorption and preconcentration of metal ions in ethanol solution with a silica gel surface chemically modified with benzimidazole

The adsorption isotherms of MCl(2) (M Mn, Ni, Cu, Zn and Cd) and FeCl(3) by silica gel chemically modified with benzimidazole molecules ( Si(CH(2))(3)NC(7)H(5)N) were studied in ethanol solution at 298 K. A column made of modified silica was used to adsorb and preconcentrate the above metal ions from ethanol solution. Elution was done with 0.1 M hydrochloric acid in an ethanol/water mixture having a mole fraction of water of 0.8. The material was applied in the preconcentration of metal ions from commercial ethanol normally used as engine fuel.

Sorption and preconcentration of some heavy metals by 2-mercaptobenzothiazole-clay

2-Mercaptobenzothiazole loaded on previously treated clay was prepared, characterized and used for sorption and preconcentration of Hg(II), Pb(II), Zn(II), Cd(II), Cu(II) and Mn(II) from an aqueous solution. The support used was a natural clay previously treated with sulphuric acid solution. Adsorption isotherms of metal ions from aqueous solutions as function of pH were studied at 298 K. Conditions for quantitative retention and elution were established for each metal by batch and column methods. The chemically treated clay was very selective to Hg(II) in solution in which Zn(II), Cd(II), Pb(II), Cu(II) and Mn(II) were also present.

Cyclic voltammetry studies of copper and nickel hexacyanoferrate immobilized on a silica gel surface coated with titanium(IV) oxide

Abstract The cyclic voltammetric behavior of copper and nickel hexacyanoferrate complexes immobilized on a silica gel surface coated with Ti(IV) oxide indicated good chemical stability for the copper complex film and that the nickel film undergoes a structural change with time. The potential of the redox reaction Ti+{M[FeIII(CN)6]}− + C + e− → Ti+{CM[FeII(CN)6]}− (M = Cu2+, Ni2+; C = K+, NH4+, Na+, Li+; Ti denotes Ti(IV) oxide substrate on a silica gel surface) is dependent on the degree of reticulation and the affinity of C to the transition metal hexacyanoferrate solid film. The cyclic voltammetry waves in Li+ and Na+ as the supporting electrolyte were broadened for Ti{Cu[FeII/III(CN)6]}, suggesting that the diffusion of these cations through the zeolitic cavity of the surface complex was hindered because of their larger hydrated ionic radii compared with those of K+ and NH4+. The Ti{Ni[FeII/III(CN)6]} cyclic voltammetry waves depend on the capacity of the electroactive species on the Ti(IV) oxide surface to interact with the cationic species of the supporting electrolyte.

Preconcentration of metal ions on silica gel modified with 3(1-imidazolyl)propyl groups

Abstract Silica gel functionalized with 3(1-imidazolyl)propyl groups and packed in a glass column is used to adsorb and preconcentrate metal ions from ethanol solution. Elution is done with 0.1 M hydrochloric acid in an ethanol/water mixture having a mole fraction of water of 0.85. The modified silica is applied to preconcentrate metal ions (Cu, Ni, Fe, Zn and Cd) from commercial ethanol, normally used as engine fuel. The method is suitable for quantifying these metals at low μg 1−1 levels.

SiO2/Nb2O5 sol–gel as a support for HRP immobilization in biosensor preparation for phenol detection

Abstract A SiO 2 /Nb 2 O 5 mixed oxide was prepared by a sol–gel processing method based on TEOS and NbCl 5 as precursors and HCl as catalysts. A material having a specific surface area of 703 m 2 g −1 , average pore diameter of 2.4 nm and 5 wt.% of Nb was obtained. An amperometric peroxidase-based biosensor for phenol was constructed by immobilizing the enzyme onto the SiO 2 /Nb 2 O 5 sol–gel matrix by adsorption and cross-linking with glutaraldehyde and mixing with graphite powder to make a modified carbon paste. The biosensor performance for phenol detection, investigated in a flow injection system, was based on mediated electron transfer of horseradish peroxidase (HRP), avoiding the direct electron transfer of HRP, which was blocked by the sol–gel matrix. With optimized conditions, a linear response range from 5 to 25 μmol dm −3 for phenol was obtained with a sensitivity of 3.2 nA dm 3 μmol −1 . The detection limit of the biosensor for phenol was 0.5 μmol dm −3 and the analytical frequency was 27 samples h −1 . The biosensor response was tested for various phenol substrates and the highest response was observed for 2-amino-4-chlorophenol. During 200 determinations, the biosensor kept the same response for phenol. The modified carbon paste retained its activity during 6 months of storage under refrigeration.

Preliminary electrochemical study of phenothiazines and phenoxazines immobilized on zirconium phosphate

Abstract The electrochemical properties of one phenothazine (Methylene Blue) and one phenoxazine (Nile Blue) dye immobilized on zirconium phosphate were investigated by incorporation into a carbon paste electrode. The dyes presented a very stable redox property. The midpoint potentials ( E m ) were 150 and 50 mV vs. SCE for Methylene Blue and Nile Blue, respectively. The composition and pH of the supporting electrolyte did not affect the E m , in contrast to those observed for the dyes in solution phase or when adsorbed on carbon. These electrodes showed a good activity in a test made for electrocatalytic oxidation of NADH.

Adsorption of MX2 (M = Mn, Ni, Cu, Zn, and Cd; X = Cl, Br, and I) and FeCl3 by modified silica surface with imidazolylpropyl group

Abstract Silica gel surface modified with imidazolylpropyl group was used to adsorb MX 2 (M = Mn, Ni, Cu, Zn, and Cd; X = Cl, Br, and I) and FeCl 3 from ethanol and acetone solution. The adsorption capacity and the intensity of the adsorption were determined by using the Langmuir equation. The influences of the solvent, temperature, and degree of functionalization on the adsorption were also studied. The infrared spectra of the functionalized silica were recorded between 1700-1300 cm −1 . The bands of the imidazole skeletal vibrations are shifted to higher frequencies upon metal-to-base nitrogen interaction.

Development of a chemically modified electrode based on carbon paste and functionalized silica gel for preconcentration and voltammetric determination of mercury(II)

Abstract A mercury-sensitive chemically modified electrode (CME) based on modified silica gel-containing carbon paste was developed. The functional group attached to the silica gel surface was 3-(2-thiobenzimidazolyl)propyl, which is albe to complex mercury ions. This electrode was applied to the determination of mercury(II) ions in aqueous solution. The mercury was chemically preconcentrated on the CME prior to voltammetric determination by anodic stripping in the differential-pulse mode. A calibration graph covering the concentration range from 0.08 to 2 mg 1 −1 was constructed. The precision for six determination of 0.122 and 0.312 mg 1 −1 Hg(II) was 3.2 and 2.9% (relative standard deviation), respectively. The detection limit for a 5-min preconcentration period was 0.013 mg 1 −1 . A study for foreign ions was also made.

2-Mercaptobenzothiazole clay as matrix for sorption and preconcentration of some heavy metals from aqueous solution

2-Mercaptobenzothiazole loaded on previously polystyrene treated clay was prepared, characterized and used for sorption and preconcentration of Hg(II), Pb(II), Zn(II) and Cd(II) from an aqueous solution. The support used was a natural clay previously treated with sulphuric acid solution. Adsorption isotherms of metal ions from aqueous solutions as function of pH were studied at 298 K. Conditions for quantitative retention and elution were established for each metal by batch and column methods. The chemically treated clay was very selective to Hg(II) in solution in which Zn(II), Cd(II), Pb(II) and some transition metal ions were also present.

2-Mercaptoimidazole covalently bonded to a silica gel surface for the selective separation of mercury(II) from an aqueous solution

Abstract Silica gel with a specific surface area of 365 m2·g−1 and an average pore diameter of 60 A was chemically modified with 2-mercaptoimidazole. The degree of functionalization of the covalently attached molecule, (≡SiO)3(CH2)3—MI, where MI is the 2-mercaptoimidazole bound to the silica surface by a propyl group, was 0.58 mmol·g−1. In individual metal adsorption experiments from aqueous solutions by the batch procedure, the affinity order was HgII « CdII > CuII ∼ ZnII ∼ PbII > MnII at solution pHs between 4 and 7. Due to the high affinity by the sulfur atom, HgII is strongly bound to the functional groups. When solution containing a mixture of HgII, CdII, CuII, ZnII, PbII, and MnII ions was passed through a column packed with the adsorbent, HgII was the only one whose adsorption and elution was not affected by the presence of other ions.