Adsorption study of silica gel particle for improvement in design of adsorption beds used in solar driven cooling units

Simulations using Ansys Fluent 6.3.26 have been performed to look into the adsorption characteristics of a single silica gel particle exposed to saturated humid air streams at Re=108 & 216 and temperature of 300K. The adsorption of the particle has been modeled as a source term in the species and the energy equations using a Linear Driving Force (LDF) equation. The interdependence of the thermal and the water vapor concentration field has been analysed. This work is intended to aid in understanding the adsorption effects in silica gel beds and in their efficient design. (C) 2013 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).

An electroanalytical application of 2-aminothiazole-modified silica gel after adsorption and separation of Hg(II) from heavy metals in aqueous solution

2-Aminothiazole covalently attached to a silica gel surface was prepared in order to obtain an adsorbent for Hg(II) ions having the following characteristics: good sorption capacity, chemical stability under conditions of use, and, especially, high selectivity. The accumulation voltammetry of mercury(II) was investigated at a carbon paste electrode chemically modified with silica gel functionalized with 2-aminothiazole (SIAMT-CPE). The repetitive cyclic voltammogram of mercury(II) solution in the potential range -0.2 to + 0.6 V versus Ag/AgCl (0.02 mol L-1 KNO3; V = 20 mV s(-1)) show two peaks one at about 0.1 V and other at 0.205 V. The anodic wave peak at 0.205 V is well defined and does not change during the cycles and it was therefore further investigated for analytical purposes using differential pulse anodic stripping voltammetry in differents supporting electrolytes. The mercury response was evaluated with respect to pH, electrode composition, preconcentration time, mercury concentration, cleaning solution, possible interferences and other variables. The precision for six determinations (n = 6) of 0.02 and 0.20 mg L-1 Hg(II) was 4.1 and 3.5% (relative standard deviation), respectively. The detection limit was estimated as 0.10 mu g L-1 mercury(II) by means of 3:1 current-to-noise ratio in connection with the optimization of the various parameters involved and using the highest-possible analyser sensitivity. (c) 2006 Elsevier Ltd. All rights reserved.

Adsorption of CuX2 (X = Cl-, Br-, and ClO4-) on a silica gel surface chemically modified with thiazolidine-2-thione from acetone and ethanol solutions

The isotherms of adsorption of CuX2 (X = Cl-, Br, ClO4-,) by silica gel chemically modified with thiazolidine-2-thione were studied in acetone (ac) and ethanol (eth) solutions at 25 degrees C. The following equilibrium constants (in 1 mol(-1)) were determined: a) CuCl2, 1.9 x 10(3) (ac), 1.6 x 10(3) (eth); b) CuBr2, 1.7 x 10(3) (ac), 1.2 x 10(3) (eth); c) Cu(ClO4)(2), 1.1 x 10(3) (ac), 1.0 x 10(3) (eth). The electron spin resonance spectra of the surface complexes indicate a tetragonal distorted structure in the case of lower degrees of metal loading on the chemically modified surface. The d-d electronic transition spectra show that for the ClO4- complex, the peak of absorption did not change for any degree of metal loading, and for Cl- and Br complexes, the peak maxima shift to higher energy with lower metal loading.

4-amine-2-mercaptopyrimidine modified silica gel applied in Cd(II) and Pb(II) extraction from an aqueous medium

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Preconcentration and determination of Cu(II) in a fresh water sample using modified silica gel as a solid-phase extraction adsorbent

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Attachment of 2,2-bipyridine onto a silica gel for application as a sequestering agent for copper, cadmium and lead ions from an aqueous medium

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

DEVELOPMENT OF A CHEMICALLY MODIFIED ELECTRODE BASED ON CARBON PASTE AND FUNCTIONALIZED SILICA-GEL FOR PRECONCENTRATION AND VOLTAMMETRIC DETERMINATION OF MERCURY(II)

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 able 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 l-1 was constructed. The precision for six determinations of 0.122 and 0.312 mg l-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 l-1. A study for foreign ions was also made.

Adsorption of chromium(VI) by titanium(IV) oxide coated on a silica gel surface

Titanium(IV) oxide, coated on the surface of silica gel (surface area, 308 m2 g-1; amount of Ti(IV) per gram of modified silica gel, 1.8 x 10(-3) mol), was used to adsorb CrO4(2-) ions from acidic solutions. The exchange capacity increased at lower pH values and was affected to some extent by the acid used. The material was used to preconcentrate Cr(VI) from 0.5 ppm solutions of chromate very efficiently and virtually 100% recovery was achieved in every instance.

A NOVEL SYNTHETIC ROUTE FOR SUPPORTING RUTHENIUM COMPLEXES ON FUNCTIONALIZED SILICA-GEL

The immobilization of the ruthenium moiety Ru(NH3)4SO3 by reaction of trans-[Ru(NH3)4SO2(H2O)]2+ with silica gel functionalized with 3-(1-imidazolyl)propyl groups is reported. A 60% surface coverage was obtained in the proportion of the resulting material [=Si(CH2)3imN-Ru(NH3)4SO3]. The anchored Ru(II) complex was characterized and its reactivity investigated. Derivatives of CO, pyrazine, and isonicotinamide have been prepared and characterized by electronic and vibrational spectroscopies, as well as by chemical means. The [=Si(CH2)3imN-Ru(NH3)4SO4]Cl, obtained through oxidation of the corresponding ruthenium(II) sulfite species, has been characterized and the aquo and the oxalate derivative have been synthesized.

Characterization and catalytic activity of 2,6-dichlorophenyl substituted iron(III) porphyrin supported on silica gel and imidazole propyl gel

In this work we have made use of the study of the interaction between Fe(TDCPP)(+) and the axial ligands OH- and imidazole in order to help characterize the heterogenized catalysts Fe(TDCPP)SG and Fe(TDCPP)IPG through UV-VIS and EPR spectroscopies and thus, better understand their different catalytic activity in the oxidation of cyclohexane by PhIO. We have found out that in Fe(TDCPP)SG (containing 1.2 X 10(-6) mol Fe(TDCPP)(+)/g of support), the FeP bis-coordinates to silica gel through Fe-O coordination and it is high-spin (FeP)-P-III species. In Fe(TDCPP)IPG 1 (containing 1.1 X 10(-6) mol Fe(TDCPP)(+) and 2.2 X 10(-4) mol imidazole/g of support), the FeP is bis-ligated to imidazole propyl gel through Fe-imidazole coordination and using NO as a paramagnetic probe, we present evidence that Fe(TDCPP)(+) is present as a mixture of low-spin (FeP)-P-III and (FeP)-P-II species. This catalyst led to a relative low yield of cyclohexanol (25%) because the bis-coordination of the (FeP)-P-III to the support partially blocks the reaction between Fe(TDCPP)(+) and PhIO, thus leading to the formation of only a small amount of the active species Fe-IV(OP+, while the (FeP)-P-II species do not react with the oxygen donor. Increasing the amount of Fe(TDCPP)(+) and decreasing the amount of imidazole in the support led to the obtention of high-spin (FeP)-P-III EPR signals in the spectra of Fe(TDCPP)IPG 5 (containing 4.4 X 10(-6) mol Fe(TDCPP)(+) and 2.2 X 10(-5) mol imidazole/g of IPG), together with low-spin (FeP)-P-III species. This latter catalyst led to better cyclohexanol yields (67%) than Fe(TDCPP)IPG 1. Fe(TDCPP)IPG 5 was further used in a study of the optimization of its catalytic activity and in recycling experiments in the optimized conditions. Recycling oxidation reactions of Fe(TDCPP)IPG 5 led to a total turnover number of 201 and total cyclohexanol yield of 201%, which could not be attained with Fe(TDCPP)Cl in homogeneous solution (turnover = 96) due to the difficulty in recovering and reusing it.

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 FeCl3 by silica gel chemically modified with benzimidazole molecules (= SI(CH2)(3)-NC7H5N) 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.

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

Silica gel with a specific surface area of 365 m(2).g(-1) and an average pore diameter of 60 Angstrom was chemically modified with 2-mercaptoimidazole. The degree of functionalization of the covalently attached molecule, (drop SiO)(3)(CH2)(3) - MI, where MI is the 2-mercaptoimidazole bound to the silica surface by a propyl group, was 0.58 mmolg.(-1). In individual metal adsorption experiments from aqueous solutions by the batch procedure, the affinity order was Hg(II)much greater than Cd-II > Cu-II approximate to Zn-II approximate to Pb-II > Mn-II at solution pHs between 4 and 7. Due to the high affinity by the sulfur atom, Hg-II is strongly bound to the functional groups. When solution containing a mixture of Hg-II, Cd-II, Cu-II, Zn-II, Pb-II, and Mn-II ions was passed through a column packed with the adsorbent, Hg-II was the only one whose adsorption and elution was not affected by the presence of other ions.

Mullite whiskers grown from erbia-doped aluminum hydroxide-silica gel

Mullite whiskers and anisotropic grains that were derived from erbia-doped aluminum hydroxide-silica gel were studied. Firing 3.0-mol%-erbia-doped isostatically pressed pellets at 1600 degrees C for 1.0-8.0 h resulted in a high surface concentration of mullite whiskers. Their c-axes were aligned preferentially along the pellet surface; the maximum length was 50 mu m, and the maximum aspect ratio was 23. The pellet surface was fully covered by mullite whiskers, and small anisotropic grains with a low aspect ratio were observed in the bulk. The voids that were observed in the fracture surfaces were covered fully by mullite whiskers. The large number of voids resulted in an apparent density of 1.60 g/cm(3) in the sintered pellets. The molar ratio of alumina to silica in the whiskers was in the range of 1.30-1.45 tan average value of 1.31), regardless of whether the alumina/silica powder compositions were mixed in a 3:2 or 2:1 ratio.

PREPARATION AND CHARACTERIZATION OF TI(IV) OXIDE GRAFTED ONTO SILICA ON A SILICA-GEL SURFACE

Silica gel with a surface area of 500 m2g-1 and an average pore diameter of 60 angstrom was chemically modified with Ti(IV) oxide using the grafting method. The amount of metal oxide attached to the surface was 1.8.10(-3) mol g-1. The X-ray photoelectron spectra showed that the metal ion species on the surface are Ti(IV) in TiO2 and MTiO3 (M = Ca2+, Sr2+, Ba2+ and Pb2+), i.e. they have the binding energy of Ti2p3/2 = 458.7 eV. The dehydration of the solid at higher temperature increased the O(II)/Ti (O(II) = oxygen bound to titanium atom) ratio, presumably due to a reticulation of the hydrous Ti(IV) oxide on the silica surface at higher temperatures. Migration of Ti(IV) into the silica gel matrix was observed but the specific surface area was not significantly changed.

Small angle X-ray scattering and IR spectroscopy study of metal carbonyl complexes immobilized on a silica gel surface chemically modified with piperazine

The carbonyl complexes [WCl(CO)(3)(bipy) (HgCl)] (1), [Fe(CO)(4)(HgCl)(2)] (2) and W(CO)(6)] (3) were immobilized on a silica gel surface organofunctionalized with piperazine groups. The products obtained were studied by IR spectroscopy and small angle X-ray scattering (SAXS) techniques. The IR data show that the immobilization of heterobimetallic compounds 1 and 2, on the functionalized surface, occurred through the mercury atom, while for 3 the displacement of one CO group by the nitrogen of a piperazine molecule was observed. The data obtained from SAXS indicate that particles have a uniform size and reveal suitable modifications on the functionalized surface after immobilization of metal carbonyl complexes. The average intermolecular distance (l(ij)) for piperazine ligands on support is 8.7 Angstrom, for the metal carbonyl complex 1 it is 18.8 Angstrom, for complex 2 it is 16.2 Angstrom and for complex 3 it is 15.3 Angstrom. Copyright (C) 1996 Elsevier B.V. Ltd