Maria G. da Fonseca

Silica gel containing sulfur, nitrogen and oxygen as adsorbent centers on surface for removing copper from aqueous/ethanolic solutions

Silica gel was modified firstly with aminepropyltrimethoxisilane obtaining the matrix named as SILNH(2). The SILNH(2) silica reacted subsequently with thioglycolic acid Sil-Ntga. The elemental analysis showed the presence of 0.98mmolg(-1) of organic moieties immobilized on silica. Infrared and (13)C NMR spectroscopic data in conjunction with thermogravimetric measurements are in agreement with the suggested functionalization. The ion adsorption properties of the silica Sil-Ntga were studied using copper ions in aqueous/ethanolic solutions in concentrations ranging from 4.0x10(-3) to 5.0x10(-2)moldm(-3) at different temperatures. The new modified silica showed a good sorption ability for copper at lower temperatures and its reuse capacity was demonstrated.

Chitosan-montmorillonite biocomposite as an adsorbent for copper (II) cations from aqueous solutions

Chitosan-montmorillonite (KSF-CTS) beads were prepared by crosslinking with pentasodium tripolyphosphate (TPP). Montmorillonite (KSF-Na), CTS and KSF-CTS biocomposite were used to remove Cu(II) from aqueous solutions. These materials were characterized before and after copper adsorption by XRD, FTIR and thermogravimetry (TG). The data indicated that the adsorption process proceeds kinetically according to a pseudo-second-order model. The adsorption processes were adjusted to the Langmuir model for KSF-Na and CTS and to the Temkin model for KSF-CTS. The maximum adsorption capacity followed the order CTS>KSF-CTS>KSF-Na. Percentages desorption of copper ions from the KSF-CTS composite after three desorption cycles were 86%, 85% and 84%, respectively, using EDTA as regeneration agents.

Cation removal using cellulose chemically modified by a Schiff base procedure applying green principles

Pentane-2,4-dione (acetylacetone) molecules were covalently incorporated under several different conditions to ethylene-1,2-diamine (en)-modified cellulose, using polar solvents or without solvents. The quantitative amount of en incorporated was given from 0.37+/-0.01 to 3.03+/-0.01 mmol of nitrogen per gram of cellulose, depending on the synthetic routes and after Schiff base formation this percentage was reduced by 1.38-6.12%. The synthetic routes indicated that lower solvent volumes produced higher amounts of en incorporation. However, the highest degree of pendant groups on the polymeric cellulose structure was obtained from a solvent-free reaction route. This procedure was applied for synthesizing all Schiff bases, causing a decrease in the amount of nitrogen. The available basic centers on the best covalently bonded biopolymer were investigated for adsorption of divalent copper, cobalt, nickel, and zinc from aqueous solution, with a capacity order of Cu2+ > Co2+ > Ni2+ > Zn2+.

New amino-inorganic hybrids from talc silylation and copper adsorption properties

Abstract The aminated trialkoxysilanes were immobilized on natural talc mineral surface. The obtained inorganic-organic hybrids, designated as TCx (x = 1 to 3) are related to 3-aminopropyl-, N-propylethylenediamine- and N-propyltriethylenediaminetrimethoxysilane, respectively. The number of amino groups attached to the pendant organic chains were 4.38, 2.56 and 2.03 mmol g -1 for TCx (x =1 to 3), respectively. The obtained materials maintain the original structure of the precursor talc and some changes in basal spacing were observed. The infrared spectra showed bands associated with the organic moieties ν(NH) at 3363 and 3293 cm -1 , symmetric and assymmetric ν(C-H) at 2930 and 2867 cm -1 and the weak δ(Si-C) band at 1130 cm -1 . The decrease in intensity of the absorption, corresponding to ν(Mg-OH) vibration was detected, whose behavior is in agreement with XRD data, that indicated a functionalization only on surface. The adsorption properties for copper cation in aqueous solutions were also observed due to the presence of amino groups of the attached organic chains covalently bonded on surface.

SELF-ORGANIZED INORGANIC-ORGANIC HYBRIDS INDUCED BY SILYLATING AGENTS WITH PHYLLOSILICATE-LIKE STRUCTURE AND THE INFLUENCE OF THE ADSORPTION OF CATIONS

Two analogous inorganic-organic hybrids with a phyllosilicate-like structure SILMgl and SILMg2, containing 3-aminopropyl- and N-propylethylenediaminetrimethoxysilane were synthesized through a sol-gel process. These hybrids adsorbed divalent cations of cobalt, nickel, copper, and zinc from aqueous solution to give the effectiveness of adsorption capacities in the sequence Cu2+ > Zn2+ > Ni2+ > Co2+. SILMgl has a higher capacity of adsorption than SILMg2. Elemental analysis, X-ray diffractometry, thermal analysis, infrared and nuclear magnetic resonance spectroscopies, and energy dispersive system microscopy characterized all hybrids. The proposed adsorption mechanism involves dissolution of the precursor matrix, formation of a phyllosilicate around the adsorbed ion, and a complexation of the cation by the amino-pendant groups in the interlayer. These new phyllosilicates are more crystalline than the original hybrids. The adsorption of Co2+ increases the interlayer distance to maximum values of 1.81 and 2.24 Å for SILMg1 and SILMg2, respectively. Thermal analysis data showed a decrease of thermal stability with cation adsorption. Si-O-Si groups were detected by infrared spectroscopy in all hybrids and a band at 1384 cm1 was assigned to the nitrate counter anion, which indicates the participation of this ion in the sphere of coordination of the interlayer complexes. The photomicrographs obtained by scanning electron microscopy showed the organized distribution of the sheet structure for these synthesized phyllosilicates.

Immobilization of ethylene sulfide in aminated cellulose for removal of the divalent cations

Cellulose (Cel) was first chemically modified with thionyl chloride to increase its reactivity. In the next step CelCl was reacted with ethylenediamine (CelEn) and subsequently reacted with ethylene sulfide to obtain a solid substance, CelEnEs. The modification reactions were confirmed by elemental analysis, TG, XRD, (13)C NMR and FTIR. The chemically modified biopolymer CelEnEs had an order of divalent metal sorption of Pb(2+)>Cd(2+)>Ni(2+)>Co(2+)>Cu(2+)>Zn(2+), and the maximum adsorption capacities were found to be 6.282±0.023, 5.783±0.015, 5.561±0.017, 4.694±0.013, 1.944±0.062 and 1.733±0.020 mmol g(-1), respectively. The equilibrium data were fitted to Langmuir, Freundlich and Temkin models, and in general, the experimental data best fit the Freundlich model. This newly synthesized biopolymer proved to be a chemically useful material for cations removal from aqueous solution.

New thiol adsorbent grafted on silica gel: synthesis, characterization and employment for heavy metal adsorptions.

Silica gel surface has been modified in two reaction steps: (i) the silylating agent 3-mercaptopropyltrimetoxysilane was firstly immobilized to give a surface Sil-SH and (ii) this precursor incorporated an ethylene sulfide molecule to obtain the surface denoted Sil-SSH. This material was characterized by elemental analysis, IR spectroscopy, thermogravimetry, solid state 13C and 29Si NMR, and surface area measurement. These materials were employed as adsorbents for divalent heavy cations from aqueous solutions at room temperature and the isotherms were adjusted to a modified Langmuir equation. The maxima number of moles adsorbed were 1.0, 1.5, 1.6, 2.2, 2.4 and 3.3 mmol g(-1) for Co, Cu, Ni, Cd, Pb, and Hg, respectively.

Action of silylating agents on a chrysotile surface and subsequent reactions with 2-pyridine and 2-thiophene carbaldehydes

Chrysotile fibres have been modified in two distinct steps: first, the fibers were aminated with silylating agents such as 3-aminopropyltrimethoxysilane or N-[3-(trimethoxysilyl)propyl]ethylenediamine to give the products denoted CRI1 and CRI2, respectively. In the second step, these matrices reacted readily with 2-pyridine and 2-thiophene carbaldehydes to form C=N bonds, characteristic of a Schiff base. All immobilized materials were characterized by elemental analysis, IR spectroscopy, thermogravimetry, solid state 29 Si NMR, surface area measurements and X-ray diffractometry. Nitrogen elemental analysis indicated the presence of 1.20 and 2.87 mmol g –1 of pendant groups on CRI1 and CRI2 surfaces, respectively. The experimental C/N ratios are 3.14, 2.90, 3.14 and 4.49 for modified materials CRI1L1, CRI1L2, CRI2L1 and CRI2L2, respectively. These results are in agreement with the yields of the successive reaction steps. The original chrysotile structure was maintained for the aminated modified surfaces. The surface area of prepared materials decreased with functionalization to values of <5.0 m 2 g –1 . All matrices obtained from reaction with aldehydes showed a C=N band at 1636 cm –1 , which is related to Schiff bond formation. Products derived from the reaction with pyridine carbaldehyde showed bands associated with aromatic and aliphatic C-H stretching bands at 3050 and 2930 cm –1 , respectively and pairs of bands at 1590, 1570 and 1470, 1436 cm –1 are attributed to aromatic ν(C=C). These results indicate that the silylating agents are covalently bonded to the chrysotile surface.

Isotherm data of Fe3+, Cr3+ and Co2+ adsorved on surface of silica-propylpiperazinedithiocarbamato

Abstract The silylant agent chloropropyltrimetoxysilane immobilized on silica gel reacts with piperazine, followed by another reaction with carbon disulfide in the presence of sodium hydroxide, to produce a new matrix sodium propylpiperazinedithiocarbamato silica. The basic centres of the resulting surface complexes are the Cr3+, Fe3+ and Co2+ cations from aqueous solution. The adsorbed isotherms for cations were adjusted to fit Giles models. The isotherm for Cr3+ could be classified as L2, while those for Fe3+ and Co2+ fitted the subgroup 2 of C class. The isotherm data show that the capacity of the final carbamate surface to chemisorb Fe3+ and Co2+ is only one third that observed for Cr3+.

Brazilian Palygorskite as Adsorbent for Metal Ions from Aqueous Solution—Kinetic and Equilibrium Studies

Natural palygorskite was used as an adsorbent for the removal of copper, cobalt and nickel from an aqueous solution. All assays were performed under controlled conditions to establish the adsorption capacity of the solid. Initially, the clay was characterized by chemical analysis, XRD, infrared spectroscopy and thermogravimetry. Adsorption experiments for the ions in aqueous solution were carried out by a batch method through which the reaction time, initial concentration of cations, temperature and pH of the aqueous solution were systematically varied. First-order, pseudo-second-order and intraparticle diffusion models were used to describe the kinetic data. The results show that the processes were fitted well by the pseudo-second-order model. Moreover, the equilibrium solid–cation systems followed the Langmuir isotherm model. The results indicate that raw palygorskite could be employed as a low-cost material for the removal of heavy metals from aqueous solution.