Rení Ventura da Silva Alfaya

Use of rice straw as biosorbent for removal of Cu(II), Zn(II), Cd(II) and Hg(II) ions in industrial effluents.

Adsorption experiments were carried out using waste rice straw of several kinds as a biosorbent to adsorb Cu(II), Zn(II), Cd(II) and Hg(II) ions from aqueous solutions at room temperature. To achieve the best adsorption conditions the influence of pH and contact time were investigated. The isotherms of adsorption were fitted to the Freundlich equation. Based on the experimental data and Freundlich model, the adsorption order was Cd(II)>Cu(II)>Zn(II)>Hg(II) on the rice straw. This quick adsorption process reached the equilibrium before 1.5h, with maximum adsorptions at pH 5.0. Thermodynamic aspects of the adsorption process were investigated. The biosorbent material was used in columns for the removal of ions Cu, Zn, Cd and Hg of real samples of industrial effluent and its efficiency was studied.

Adsorption of FeCl3, CuCl2 and ZnCl2 on silsesquioxane 3-n-propylpyridiniumchloride polymer film adsorbed on Al2O3 coated silica gel

Abstract Silsesquioxane 3- n -propylpyridiniumchloride polymer (abbreviated as SiPyCl), was used to coat SiO 2 /Al 2 O 3 substrate surface to form the chemically modified solid SiO 2 /Al 2 O 3 /SiPyCl having the specific surface area S BET = 233 m 2 g −1 . The resulting polymer film was strongly adhered to the surface by means of ≡Al–O–Si bonding (where ≡Al stands for Al 2 O 3 grafted on SiO 2 surface) and presented an ion exchange capacity of 1.04 mmol g −1 . The metal halides, M Cl z [M= Fe(III), Cu(II) and Zn(II)], were adsorbed by the modified solid from ethanol solutions as neutral species by forming the surface anionic complexes described by the equation: m SiO 2 /Al 2 O 3 /SiPyCl+MCl z ⇆(SiO 2 /Al 2 O 3 /SiPy + ) m [MCl z + m ] m − , where FeCl 4 − , ZnCl 4 2− have tetrahedral and CuCl 4 2- distorted tetrahedral symmetries. The equilibrium coefficients, K , determined for each complex species showed that SiO 2 /Al 2 O 3 /SiPyCl has a high affinity for the metal ions. The following values expressed as log K were found: Cu=3.0, Zn=3.5 and Fe=3.0. The material could efficiently preconcentrate these metal ions from an ethanol solutions and release them in aqueous solution.

Adsorption of metal halides from ethanol solutions by a 3-n-propylpyridiniumsilsesquioxane chloride-coated silica gel surface

3-n-propylpyridiniumsilsesquioxane chloride polymer, abbreviated as SiPy+Cl-, was used to coat a porous silica gel, SiO2, surface to form the chemically modified solid SiO2/SiPy+Cl-. The resulting polymer film was well adhered to the surface and presented an ion exchange capacity of 0.74 mmol g(-1). Metal halides, MClz [M=Fe(III), Cu(II), and Zn(II)], were adsorbed by the modified solid from ethanol solutions as neutral species by forming the surface anionic complexes described by the equation: mSiO2/SiPy+Cl-+ MClz <=> (SiO2/SiPy+)m[MCl(z+m)]m-, where the [MCl(z+m)]m- species adsorbed on the surface are FeCl4-, ZnCl4(2-), and CuCl4(2-). Accurate estimates of the specific sorption capacities and the heterogeneous stability constants of the immobilized metal complexes were determined with the aid of computational procedures.

Chemically modified natural cotton fiber: a low-cost biosorbent for the removal of the Cu(II), Zn(II), Cd(II), and Pb(II) from natural water

AbstractIn this work, the removal of Cu(II), Zn(II), Cd(II), and Pb(II) ions from aqueous solution by natural cotton fiber modified with citric acid (NCFCA) is reported, using both batch and continuous systems. Specifically, kinetics and adsorption isotherms have been determined considering the effect of contact time, pH, and heavy metals concentration. Adsorption isotherms show that the experimental maximum adsorption capacity of Cu(II), Zn(II), Cd(II), and Pb(II) were 6.12, 4.53, 8.22, and 21.62 mg g−1, respectively, at 25°C and pH 5. Furthermore, breakthrough curves were obtained for the adsorption of heavy metals using a fixed bed column packed with NCFCA at pH 5, flow rate = 2.5 mL min−1 and 1.0 × 10–4 mol L−1 of metals concentration. The Thomas model has been used for data fitting of adsorption competitions of continuous experiments and for determining the design parameters that are useful to characterize the performance of the packed bed column. The natural water real samples were treated with the ...

Ion selective electrode for potentiometric determination of saccharin using a thin film of silsesquioxane 3-n-propylpyridinium chloride polymer coated-graphite rod.

ABSTRACT A polymer coated graphite rod ion selective electrode for saccharin was constructed and evaluated for the determination of saccharin in artificial table top sweeteners. The polymer consists of a thin film of silsesquioxane 3-n-propylpyridinium chloride. The electrode response was based on the ion pair formed between saccharinate and the 3-n-propylpyridinium cation from the silsequioxane polymer. The electrode exhibits a Nernstian response for saccharin concentrations between 6.9×10-6 and 5.3×10-3 mol L-1 and a detection limit of 5.5×10-6 mol L-1. The electrode response for saccharin was fast (10-20 s) and the potential independent of pH in the range of 3 to 7. The selectivity coefficients K A, B pot for several anions usually present in commercial table top sweeteners were determined following the IUPAC recommendations. The potentiometric method with the ion selective electrode was validated by the HPLC reference method, through t8543226 determination of saccharin in commercial samples of table top sweeteners. The ion selective electrode is proved suitable for the routine quality control of table top sweeteners by potentiometry.

N-propylpyridinium chloride silsesquioxane polymer film on graphite: electrochemical study of a hexacyanoferrate (II) ion immobilized electrode for oxidation of ascorbic acid

A well polished graphite surface was coated with a thin film of N-propylpyridinium chloride silsesquioxane polymer. On to the strongly graphite-adhered polymer film the electroactive species [Fe(CN)6]4- was adsorbed by means of an ion exchange reaction. The resulting electrode (graph/SiPy+)4[Fe(CN)6 ]4- (graph = graphite and SiPy+ represents the N-propilpyridinium silsesquioxane polymer) was chemically very stable and was used to electrocatalytically oxidize ascorbic acid in solution (pH between 4.5-6.5) in 0.1 mol dm-3 KCl. The electrode was used to determine vitamin C in tablets and in processed orange juices. The results were in accord with those obtained by using the standard 2,6-dichlorophenolindophenol titration method.

Ammonium ion sensor based on SiO2/ZrO2/phosphate-NH4+ composite for quantification of ammonium ions in natural waters

Ion selective-electrode was constructed and evaluated for determination of ammonium ions in natural waters. The electrode consists of paste carbon with the composite SiO2/ZrO2/phosphate-NH4+ obtained through sol-gel process. The electrode exhibits a sub-Nernstian response for ammonium concentrations between 7.7´10-7 and 4.0´10-2 mol L-1 and a detection limit of 1.58´10-7 mol L-1 (8.5´10-3 ppm). The electrode response for ammonium was fast (1 minute). The selectivity coefficients KpotA,B for several ions usually present in natural waters were determined applying the matched potential method. The potentiometric method with the ion selective electrode was validated by the Berthelot method (standard method), through the determination of ammonium ions in natural waters. The ion selective-electrode proved suitable for routine quality control of natural waters by potentiometry.

Silsesquioxane 3-n-Propylpyridinium chloride: a new polymer for the potentiometric analysis of Cr(VI) in electroplating and leather industry wastes

A new polymer, silsesquioxane 3-n-propylpyridinium chloride (SiPy+Cl-), was used in the preparation of an electrode. The polymer coated graphite rod ion selective electrode for Cr(VI) was constructed and evaluated for the determination of Cr(VI) in samples of electroplating and leather industry wastes. This electrode exhibited a Nernstian response for Cr(VI) concentrations between 3.1´10-6 and 1.8´10-2 mol L-1 and a detection limit of 2.8´10-6 mol L-1 (0.15 ppm). The response of the electrode for Cr(VI) was fast (15 s) and the independent potential of pH in the range of 3.0 to 7.0. The selectivity coefficients for several anions showed that the electrode presents excellent performance. The sensor exhibits a shelf-life of 6 months with good reproducibility. Determination of Cr(VI) in electroplating and leather wastes using the sensor was successfully achieved.

Mexerica mandarin (Citrus nobilis) peel as a new biosorbent to remove Cu(II), Cd(II), and Pb(II) from industrial effluent

Abstract Adsorption experiments were carried out using waste Mexerica mandarin “Citrus nobilis” peel as a new biosorbent to adsorb Cu(II), Cd(II), and Pb(II) ions from aqueous solutions at room temperature. To achieve the best adsorption conditions, the influences of pH and contact time were investigated. The isotherms of adsorption were fitted to the Langmuir and Freundlich equations. Based on the experimental data the adsorption order was Pb(II)>Cd(II)>Cu(II) (in mg g−1) on the new biosorbent. This quick adsorption process reached the equilibrium before 20 min, with maximum adsorptions at pH 5.0. Kinetic studies were carried out using the pseudo-first-order and pseudo-second-order models. Thermodynamic aspects of the adsorption process were investigated. The new biosorbent was used in columns for the removal of Cu, Cd, and Pb ions of the samples of industrial effluent and its efficiency and regeneration potential were studied.