Ethylenimine in the synthetic routes of a new silylating agent: chelating ability of nitrogen and sulfur donor atoms after anchoring onto the surface of silica gel

Two-Dimensional Indium Selenide for Sulphur Vapour Sensing Applications

Surface-to-volume ratio in two-dimensional (2D) materials highlights among their characteristics as an inherent and intrinsic advantage taking into account their strong sensitivity to surface effects. For this reason, we have proposed in this work micromechanically exfoliated 2D nanosheets of InSe as an optical vapour sensor. As a proof of concept, we used 2-mercaptoethanol as the chemical analyte in vapour phase to monitor the change of the InSe photoluminescence (PL) before and after exposure to the analyte. For short vapour exposure times (at low analyte concentration), we found a PL enhancement of InSe nanosheets attributed to the surface localization of Se defects. For long vapour exposure times (or higher concentrations) a PL reduction is observed, probably due to the diffusion of molecules within the nanosheet. These results confirm the capability of 2D InSe as a photoluminescent sensor of vapours, because of its sensitivity to surface passivation or volume diffusion of molecules.

Syntheses and catalytic activities of new metallodendritic catalysts

Metallodendritic catalysts showed high selectivity in the epoxidation of olefins even after being used for at least five cycles.

Synthesis of silica gel supported salicylaldehyde modified PAMAM dendrimers for the effective removal of Hg(II) from aqueous solution

A series of silica gel supported salicylaldehyde modified PAMAM dendrimers (SiO2-G0-SA ∼ SiO2-G2.0-SA) were synthesized and their structures were characterized by FTIR, XRD, SEM, TGA, and porous structure analysis. The feasibility of these adsorbents for the removal of Hg(II) from aqueous solution was first described and the adsorption mechanism was proposed. The adsorption was found to depend on solution pH, the generation number of salicylaldehyde modified PAMAM dendrimers, contact time, temperature, and initial concentration. Results showed that the optimal pH was about 6 and the adsorption capacity increased with the increasing of generation number. Density functional theory (DFT) method was used to investigate the coordination geometries and the chelating mechanism. Adsorption kinetics was found to follow the pseudo-second-order model with film diffusion process as rate controlling step. Adsorption isotherms revealed that adsorption capacities increased with the increasing of temperature. Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherm models were employed to analyze the equilibrium data. The adsorption can be well described by Langmuir isotherm model and took place by chemical mechanism. The thermodynamics properties indicated the adsorption processes were spontaneous and endothermic nature. The maximum adsorption capacity of SiO2-G0-SA, SiO2-G1.0-SA, and SiO2-G2.0-SA were 0.91, 1.52, and 1.81 mmol g(-1), respectively. The considerable higher adsorption capacity compared with other adsorbents indicates SiO2-G0-SA ∼ SiO2-G2.0-SA are favorable and useful for the uptake of Hg (II), and can be potentially used as promising adsorbents for the effective removal of Hg(II) from aqueous solution.

Synthesis, characterization and application of a novel mercapto- and amine-bifunctionalized silica for speciation/sorption of inorganic arsenic prior to inductively coupled plasma mass spectrometric determination

A bifunctional sorbent, (NH(2)+SH)silica, containing both amine and mercapto functionalities was prepared by modification of silica gel with 3-(triethoxysilyl)propylamine and (3-mercaptopropyl)trimethoxysilane. In addition to the bifunctional sorbent, silica gel was modified individually with the functional mercapto- and amino-silanes, and the mono-functional sorbents, namely (SH)silica and (NH(2))silica, were also mechanically mixed ((NH(2))silica+(SH)silica) for the sake of comparison of sorption performances. It has been demonstrated that (SH)silica shows quantitative sorption only to As(III) at two pH values, 1.0 and 9.0, while (NH(2))silica displays selectivity only towards As(V) at pH 3.0. On the other hand, the bifunctional (NH(2)+SH)silica possesses the efficient features of the two mono-functionalized sorbents; for example, it retains As(III) at a wider pH range, from 1.0 to at least 9.0 with the exception at pH 2.0, and it also shows quantitative sorption to As(V) at pH 3.0. This property gives the bifunctional (NH(2)+SH)silica a better flexibility in terms of sorption performance as a function of solution pH. The mechanically mixed (NH(2))silica+(SH)silica exhibits a similar but less efficient sorption behavior compared to the bifunctional sorbent. Desorption of both As(III) and As(V) species can be realized using 0.5M NaOH. The validity of the proposed method was checked through the analysis of a standard reference material and a good correlation was obtained between the certified (26.67 μg L(-1)) and determined (27.53±0.37 μg L(-1)) values. Spike recovery tests realized with ultrapure water (93.0±2.3%) and drinking water (86.9±1.2%) also confirmed the applicability of the method.

Comparison of synthesis of chelating resin silica-gel-supported diethylenetriamine and its removal properties for transition metal ions

Four kinds of silica-gel (SG)-supported diethylenetriamine (DETA) chelating resins SG-DETA-1, SG-DETA-2, SG-DETA-3, and SG-DETA-4 were prepared by functionalization of silica-gel via so-called "heterogeneous-direct-amination" (hetero-DA), "homogeneous-direct-amination" (homo-DA), "heterogeneous end-group protection" (hetero-EGP), and "homogeneous end-group protection" (homo-EGP) routes, respectively. These functionalized reactions on silica-gel were confirmed through elemental analysis, infrared spectroscopy, X-ray diffractometry, porous analysis, and thermogravimetry. Element analysis revealed that the direct-amination routes and homogeneous condition were more beneficial than the corresponding end-group protection routes and heterogeneous condition to the syntheses of chelating resins with high N content. Several metal ions, such as Ag(+), Cu(2+), Ni(2+), Hg(2+), Zn(2+) and Pb(2+), were chosen as representatives to investigate the relationship between adsorption capacities and N content of ligands onto the surface of silica-gel. The experiments results showed that all resins, SG-DETA-1, SG-DETA-2, SG-DETA-3 and SG-DETA-4, had a better adsorption for Hg(2+) and Cu(2+) than others. One conclusion should be drawn from the above compared experiments, that is, higher N content of silica-gel resins does not ensure a higher utilization ratio of N.

Aplicação de Al-PILC na adsorção de Cu2+, Ni2+e Co2+ utilizando modelos físico-químicos de adsorção

Amostra de esmectita pertencente a Serra de Maicuru (Estado do Pará, Norte do Brasil, região amazônica) foi pilarizada com Al13, A Argila pilarizada com alumínio (Al-PILC) foi caracterizada por DRX, MEV e EDS. Para a análise textural foram utilizadas isotermas de adsorção-desorção utilizando o nitrogênio. Este artigo é dirigido ao estudo da adsorção de metais pesados. A adsorção dos íons de Cu2+, Ni2+e Co2+ foi realizadas com a matriz Al-PILC em temperatura ambiente com soluções aquosas contendo os íons metálicos. Os modelos de adsorção adotados foram os de Langmuir, Freundlich e Temkin que foram aplicados aos valores obtidos experimentalmente com regressão linear. A equação de Langmuir foi o melhor modelo de linearização com r = 0,999. A equação de Freundlich apresentou limitações em altas concentrações, mas foram obtidos valores (Kf e n) bastante aceitáveis utilizando este modelo. Os parâmetros foram utilizados para calcular a quantidade de Nf em função de Cs.

Thioglycolic acid grafted onto silica gel and its properties in relation to extracting cations from ethanolic solution determined by calorimetric technique

Thioglycolic acid was immobilized onto silica gel surface using 3-aminopropyltrimethoxysilane as precursor silylating agent to yield silica. The amount of thioglycolic acid immobilized was 1.03 mmol per gram of silica. This new surface displayed a chelating moiety containing nitrogen, sulfur, and oxygen basic centers which are potentially capable of extracting cations from ethanolic solution, such as MCl3 ( M=Fe, Cr, and Mo). This process of extraction was carried out by the batch method when similar chemisorption isotherms were observed for all cations. The data were adjusted to a modified Langmuir equation. The sequence of the maximum retention capacity was Cr(III) > Mo(III) > Fe(III). The same adsorption was determined by calorimetric titration and the enthalpic values of -35.75 +/- 0.02, 32.90 +/- 0.15, and -84.08 +/- 0.12 kJmol(-1) for chromium, molybdenum, and iron, respectively, were obtained. From the calculated Gibbs free energy -23.4 +/- 0.2, -27.2 +/- 0.2, and -32.7 +/- 0.3 kJmol(-1), the variations in entropy obtained were 42 +/- 1, 201 +/- 1, 172 +/- 1 JK(-1)mol(-1) for the same sequence. All thermodynamic values are in agreement with the spontaneity of the proposed cation-basic center interactions for these chelating processes.

Kinetics and equilibrium parameters of Hg(II) adsorption on silica–dithizone

Sílica-dithizone (Sil-dtz) was synthesized and used to adsorb Hg(II) in solution at pH 6.0. Increasing the temperature accelerates the mass transfer of Hg(II) to the silica surface. The kinetic data were evaluated using the traditional pseudo-first-order Lagergren equation and an alternative Avrami kinetic equation. From the latter equation, two regions presenting distinct kinetic parameters were found, at 25 and 35 degrees C, and the use of the parameter n was also related to the determination of distinct kinetic orders. Variations of the adsorption kinetic rate in relation to the time and the temperature were also calculated and are discussed. The adsorption isotherms data were well fitted to the Freundlich model. Interestingly, good adsorption data correlation of the Langmuir model and experimental values was observed only at 45 and 50 degrees C, suggesting, for this temperature range, the formation of complexes with the proportion Hg:dithizone 1:1 on the silica surface.

Chemisorption and Thermodynamic Data of the Interaction between a Chelate Free Acidic Center with Basic Groups Attached to Grafted Silicas

The molecule 2-aminoethanethiol was added to the grafted silylant agent [(3-chlorosilylpropyl)trimethoxysilane] (cpts) onto silica gel(triple bond SilCl), obtaining a surface (triple bond SilSNH(2)) and giving 0.70 mmol g(-1) of nitrogen; the surface of silica was modified with [(3-mercaptosilylpropyl)trimethoxysilane] (mpts) with surface (triple bond SilSH), giving 0.78 mmol g(-1) of sulphur. Both matrices, (triple bond SilSNH(2)) and (triple bond SilSH), adsorb copper and cobalt acetylacetonates from ethanolic solution. Adsorption, using a batchwise process, showed that copper chelate was the most adsorbed. The interactions between the basic centers attached to organic chains of these modified silicas with the cations in the chelates Me(acac)(2) [M=Cu and Co] were followed through calorimetric titrations. Exothermic enthalpic results were obtained for the triple bond SilSNH(2) matrix. The spontaneity of these systems was reflected in negative free Gibbs energy and positive from entropic values.

Two Independent Routes to Synthesize Identical Silicas by Grafting Ethylenimine or 2-Aminoethanethiol, Their Cation Adsorbing Abilities, and Thermodynamic Data

The same grafted silica gel surface was obtained through two distinct procedures: (i) by immobilization of the compound 2-aminoethanethiol on precursor 3-chloropropylsilylsilica gel in a heterogeneous method, and (ii) by reacting ethylenimine with 3-mercaptopropyltrimethoxysilane to give a new silylating agent, which was anchored on the silica gel in a homogenous method. The first anchored surface gave 0.70 mmol g(-1) of molecules covalently bonded per gram of silica. This value contrasts to that obtained with the homogeneous conditions, with 1.74 mmol of pendant groups per gram of silica. Both organofunctionalized surfaces have the ability to adsorb divalent cations from aqueous nitrate solution. The adsorption was performed using a batchwise process and the maximum adsorption capacity followed the sequence Cu>Ni>Co and Ni>Cu>Co for surfaces prepared by the homogeneous and heterogeneous methods, respectively. Through calorimetric titrations, the thermodynamic values of cation-basic center interactions were obtained. Exothermic enthalpy results were obtained for all interactive processes. The calculated free Gibbs energy is in agreement with the spontaneity of the reactions and the positive entropy values for all reactions are favorable for this system.

New Factorial Designs to Evaluate Chemisorption of Divalent Metals on Aminated Silicas

Adsorption processes of Cu(II), Co(II), and Hg(II) on two aminated silica gel surfaces with immobilized ethylenediamine and diethylenediamine groups were studied by a new 2(3) full factorial design. Two metal quantity levels, temperatures of 25 and 50 degrees C, and silica amounts of 100 and 200 mg were employed. Our study indicates that higher factorial design levels increase adsorption for all metals evaluated, with the exception of the mass parameter. Adsorption is also significantly affected by important antagonistic and synergistic effects involving all factors. Both functionalized silica gel surfaces present higher interactions and good perspectives in preconcentration studies for mercury. The factorial design results are also discussed in terms of some solvation properties for each of the metals studied. Copyright 2001 Academic Press.

Silylating Agents Grafted onto Silica Derived from Leached Chrysotile

Silica from leached chrysotile fibers (SILO) was silanized with trialkoxyaminosilanes to yield inorganic-organic hybrids designated SILx (x=1-3). The greatest amounts of the immobilized agents were quantified as 2.14, 1.90, and 2.18 mmol g(-1) on SIL1, SIL2, and SIL3 for -(CH(2))(3)NH(2),-(CH(2))(3)NH(CH(2))(2)NH(2), and -(CH(2))(3)NH(CH(2))(2)NH(CH(2))(2)NH(2) groups attached to the inorganic support. The infrared spectra for all modified silicas showed the absence of the Si-OH deformation mode, originally found at 950 cm(-1), and the appearance of asymmetric and symmetric C-H stretching bands at 2950 and 2840 cm(-1). Other important bands associated with the organic moieties were assigned to nu(as)(NH) at 3478 and nu(sym)(NH) at 3418 cm(-1). The NMR spectrum of the solid precursor material suggested two different kinds of silicon atoms: silanol and siloxane groups, between -90 and 110 ppm; however, additional species of silicon that contain the organic moieties bonded to silicon at -58 and -66 ppm appeared after chemical modification. These modified silicas showed a high adsorption capacity for cobalt and copper cations in aqueous solution, in contrast to the original SILO matrix, confirming the unequivocal anchoring of silylating agents on the silica surface. Copyright 2001 Academic Press.

The Pesticide 3-(3,4-Dichlorophenyl)-1,1-dimethylurea (Diuron) Immobilized on Silica Gel Surface

A route for 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) immobilization on silica gel was established after reacting at the first stage the precursor silylant agent 3-trimethoxysilylpropylamine to the support. The pesticide was covalently bonded to available amine groups of the precursor, giving 1.03 mmol of amine per gram of silica. Infrared, (13)C, and (29)Si NMR spectra are in agreement with the proposed reaction between nitrogen of the amine group of the previously anchored silica to carbon on the para-position of the aromatic ring of the pesticide. The immobilization is clearly affected by the presence or absence of disprotonating agent, to give 12.50 and 68.40% reaction yield, respectively; these results were confirmed through elemental analysis. Copyright 2001 Academic Press.

Ethyleneimine Anchored on Thiol-Modified Silica Gel Surface-Adsorption of Divalent Cations and Calorimetric Data

Activated silica gel was previously modified by the silylant agent 3-mercaptopropyltrimethoxysilane. The organofunctionalized silica gel containing pendant groups ended with the -SH functions reacted with the three-member cyclic ethyleneimine molecules to yield the new ligand attaching sulfur and nitrogen basic centers available to complex cations. This final anchored surface adsorbs MX(2) (M=Co(2+), Ni(2+), Cu(2+), and X=Cl(-), NO(3)(-)) at 298+/-1 K. A considerable increase in adsorption capacity was observed for nitrate counteranions. This process of extraction was followed by the batch method and the order of the maximum capacities found was Ni(2+)>Cu(2+)>Co(2+) for both series of salts. The pendant immobilized groups-cation interaction processes showed exothermic enthalpies. Those values are more pronounced for chlorides, with the largest values obtained for cobalt. The calculated DeltaG values are in agreement with the spontaneity of the proposed reactions and the complexation is entropically favored. Copyright 2000 Academic Press.