Claudio Airoldi

Some studies of crosslinking chitosan-glutaraldehyde interaction in a homogeneous system.

Chitosan dissolved in acetic acid reacted with glutaraldehyde solution, ranging in concentration from 0.10 to 25.0 x 10(-2) mol dm3. The modified polymers were characterized by means of carbon, hydrogen and nitrogen elemental analysis, scanning electron microscopy, X-ray diffractometry, 13C nuclear magnetic resonance (NMR), infrared and Raman spectroscopies. The uptake of metallic cations in aqueous medium was checked through copper. The obtained data from 13C NMR, infrared and Raman spectroscopies evidenced the formation of an ethylenic double bond in the chitosan glutaraldehyde interaction. These data suggest that free pendant amine groups of chitosan polymer interact with the aldehydic group of the glutaraldehyde to form stable imine bonds, due to the resonance established with adjacent double ethylenic bonds. The crosslinking is formed by the nonuniform length of chains and by terminal unities. The crosslinking formation can involve two chitosan unities belonging, or not, to the same polymeric chain. The sequence of reactions was established for a chitosan:glutaraldehyde molar proportion of 1:20. The degree of crystallinity and particle size decreased as the amount of glutaraldehyde was increased in the polymer. Physical and chemical properties are not just affected for the chitosan glutaraldehyde reaction, but are also affected strongly by the dissolution of the natural chitosan.

Application of Brazilian pine-fruit shell as a biosorbent to removal of reactive red 194 textile dye from aqueous solution kinetics and equilibrium study.

The Brazilian pine-fruit shell (Araucaria angustifolia) is a food residue, that was used as biosorbent for the removal of non-hydrolyzed reactive red 194 (NRR) and hydrolyzed reactive red 194 (HRR) forms from aqueous solutions. Chemical treatment of Brazilian pine-fruit shell (PW), with chromium (Cr-PW), with acid (A-PW), and with acid followed by chromium (Cr-A-PW) were also tested as alternative biosorbents for the removal of NRR and HRR from aqueous effluents. It was observed that the treatment of the Brazilian pine-fruit shell with chromium (Cr-PW and Cr-A-PW) leaded to a remarkable increase in the specific surface area and average porous volume of these biosorbents when compared to unmodified Brazilian pine-fruit shell (PW). The effects of shaking time, biosorbent dosage and pH on biosorption capacity were studied. In acidic pH region (pH 2.0) the biosorption of NRR and HRR were favorable. The contact time required to obtain the equilibrium was 24h at 25 degrees C. The equilibrium data were fitted to Langmuir, Freundlich, Sips and Redlich-Peterson isotherm models. For NRR reactive dye the equilibrium data were best fitted to the Sips isotherm model using PW and A-PW as biosorbents, and Redlich-Peterson isotherm model using Cr-PW and Cr-A-PW as biosorbents. For HRR reactive dye the equilibrium data were best fitted to the Sips isotherm model using PW, A-PW and Cr-A-PW and the Redlich-Peterson isotherm model for Cr-PW as biosorbent.

Kinetics and thermodynamics of textile dye adsorption from aqueous solutions using babassu coconut mesocarp

Extracted babassu coconut (Orbignya speciosa) mesocarp (BCM) was applied as a biosorbent for aqueous Blue Remazol R160 (BR 160), Rubi S2G (R S2G), Red Remazol 5R (RR 5), Violet Remazol 5R (VR 5) and Indanthrene Olive Green (IOG) dye solutions. The natural sorbent was processed batchwise while varying several system parameters such as stirring time, pH and temperature. The interactions were assayed with respect to both pseudo-first-order and second-order reaction kinetics, with the latter the more suitable kinetic model. The maximum adsorption was obtained at pH 1.0 for all dyes due to available anionic groups attached to the structures, which can be justified by pH(pzc) 6.7 for the biosorbent BCM. The ability of babassu coconut mesocarp to adsorb dyes gave the order R S2G>VR 5>BR 160>IOG>RR 5, which data were best fit to Freundlich model, but did not well-adjusted for all dyes. The dye/biopolymer interactions at the solid/liquid interface are all spontaneous as given by free Gibbs energy, with exothermic enthalpic values of -26.1, -15.8, -17.8, -15.8 and -23.7 kJ mol(-1) for BR 160, R S2G, RR 5, IOG and VR 5, respectively. In spite of the negative entropic values contribution, the set of thermodynamic data is favorable for all dyes removal. However, the results pointed to the effectiveness of the mesocarp of babassu coconut as a biosorbent for removing textile dyes from aqueous solutions.

A useful organofunctionalized layered silicate for textile dye removal

The octosilicate Na-RUB-18 has the ability to exchange its original sodium with cetyltrimethylammonium cations. This procedure leads to interlayer space expansion, with the aim of obtaining inorganic-organic nanostructured hybrids by chemical modification reactions. The silylating agent 3-trimethoxysilylpropylurea was attached to the inorganic layer using heterogeneous methodology. The new organofunctionalized material was characterized by elemental analysis, X-ray diffraction, (13)C and (29)Si nuclear magnetic resonances in the solid state, infrared spectroscopy, thermogravimetry and scanning electron microscopy. The amount of silylating agent immobilized on surface was 2.03 mmol g(-1), with a basal distance of 2.43 nm. Nuclear magnetic resonance of (13)C and (29)Si nuclei evidenced covalent bond formation between organosilyl and silanol groups at the surface. The new synthesized nanostructured layered material was able to remove the textile dye Reactive Black 5 from aqueous solution, followed through a batchwise process. The effects of stirring time, adsorbent dosage and pH on the adsorption capacity demonstrated that 150 min is enough to reach equilibrium at 298+/-1 K at pH 3.0. Based on error function values the data were best fitted to fractional-order kinetic models and compared to pseudo-first-order, pseudo-second-order and chemisorption kinetic models. The equilibrium data were better fitted to the Sips isotherm models.

Interaction of cations with SH-modified silica gel: thermochemical study through calorimetric titration and direct extent of reaction determination

The reaction of silica gel with 3-(trimethoxysilyl)propane-1-thiol, MPTS, produced a thiol-modified silica gel, Sil–SH. This material removes silver, mercury, copper, zinc and nickel ions from aqueous solutions. Enthalpy changes that occur in the interactions between Sil–SH and these cations were obtained by a calorimetric titration technique, in which thermal effects and the quantities of cations that interact at each titration point were determined simultaneously. From this procedure, values of the maximum capacity of interaction (Ns), enthalpies of interaction at different coverages of the surface [Δint(i)Hm ] and integral enthalpy of interaction for a monolayer (ΔmonHm) have been established. It is shown that this method permits charting the basic sites created upon modification. From Δint(i)Hm values, the sequence of the interaction strength between the basic sites of the silica-attached MPTS and the cations is Hg2+>Ag+>Cu2+>Ni2+>Zn2+ , in agreement with the concept of hard and soft acids and bases. The influence of some parameters concerning the thermodynamics of solvation of the indicated transition metals has been also taken into account in the investigation of these interaction processes.

Organofunctionalized kenyaite for dye removal from aqueous solution.

Crystalline layered sodium kenyaite was exchanged to proton kenyaite when reacted with hydrochloric acid solution, providing a new surface with available silanol groups that are able to couple with N-3-trimethoxysilylpropylethylenediamine silylating agent, after prior expansion of the basal distance with the polar organic solvent dimethyl sulfoxide. The resulting organofunctionalized nanomaterial (2N-Ken) was characterized by elemental analysis, infrared spectroscopy, X-ray diffraction, carbon and silicon nuclear magnetic resonances in the solid state, surface analysis, porosity, thermogravimetry, and electron scanning microscopy. The quantity of silylating agent incorporated into the nanospace, calculated from the nitrogen elemental analysis, was determined as 0.48 mmol g(-1), after expanding of the acidic precursor basal distance from 1.62 to 1.99 nm. The presence of a covalent silicon-carbon bond of the organosilyl moiety on the inorganic layered structure was confirmed through nuclear magnetic resonance. This new nanomaterial has the ability to extract the Sumifix Brilliant Orange 3R textile dye from aqueous solution, using a batchwise process. The effects of stirring time, adsorbent dosage, and pH on the adsorption capacity demonstrated that 4 h is enough to reach equilibrium at 298+/-1 K under pH 4.0. Based on error function values (F(error)) the data were best fitted to fractional-order and chemisorption kinetic models when compared to pseudo-first-order and pseudo-second-order kinetic models. The equilibrium data were better fitted to the Sips isotherm model.

Polysaccharide-based hydrogels: preparation, characterization, and drug interaction behaviour.

Oxidized alginate (ADA) and oxidized alginate blended with chitosan (ADA-Chit) were prepared in the presence of borax and CaCl 2, and their interactions with an antifolate drug, pyrimethamine (PYR), have been investigated. Tablets with a mean diameter of 1.2 +/- 0.06 cm were produced and drug interactions were performed in dimethyl sulfoxide (DMSO) using isothermal titration calorimetry (ITC). From ITC responses, the enthalpy changes of interaction PYR/materials, Delta int H, have been determined and were found to be -11.73 +/- 0.517 kJ mol (-1) for ADA and -4.86 +/- 0.156 kJ mol (-1) for ADA-Chit. The PYR encapsulation of approximately 75% was achieved for both materials, as measured by UV spectrometer.

The incorporation of propane-1,3-diamine into silylant epoxide group through homogeneous and heterogeneous routes

The polar organic molecule propane-1,3-diamine reacted: (i) with a 3-glycidoxypropyltrimethoxysilane silylant agent, previously anchored on a silica surface in a heterogeneous route to yield the product SiHT or (ii) with the same agent before immobilizing it on the support, in a homogeneous method, to produce a SiHM surface. The epoxy group was opened yielding chelating pendant groups bonded to the inorganic surface. Both products were characterized through elemental analysis, infrared spectroscopy, surface area and thermogravimetry. The ligand concentrations were 0.80 (SiHT) and 1.53 mmol (SiHM), per gram of silica. The heterogeneous route is an easier procedure to produce immobilization. However the homogeneous route provided conditions to obtain a higher density of pendant groups on the surface, which are potentially useful for extracting cations from solutions in an effective way.

Removal of Cu(II), Fe(III), and Cr(III) from Aqueous Solution by Aniline Grafted Silica Gel

Abstract The aniline moiety was covalently grafted onto silica gel surface. The modified silica gel with aniline groups (SiAn) was used for removal of Cu(II), Fe(III), and Cr(III) ions from aqueous solution and industrial effluents using a batch adsorption procedure. The maximum adsorption of the transition metal ions took place at pH 4.5. The adsorption kinetics for all the adsorbates fitted better the pseudo second‐order kinetic model, obtaining the following adsorption rate constants (k2): 1.233 · 10−2, 1.902 · 10−2, and 8.320 · 10−3 g · mg−1 min−1 for Cr(III), Cu(II), and Fe(III), respectively. The adsorption of these transition metal ions were fitted to Langmuir, Freundlich, Sips, and Redlich‐Peterson isotherm models; however, the best isotherm model fitting which presented a lower difference of the q (amount adsorbed per gram of adsorbent) calculated by the model from the experimentally measured, was achieved by using the Sips model for all adsorbates chosen. The SiAn adsorbent was also employed for the removal of the transition metal ions Cr(III) (95%), Cu(II) (95%), and Fe(III) (94%) from industrial effluents, using the batch adsorption procedure.

Thermogravimetry as a Reliable tool to Estimate the Density of Silanols on a Silica Gel Surface

A method was developed to estimate the density of the silanol groups attached to silica gel surfaces from thermogravimetric data. Depending on the mechanism of condensation of silanol groups during heating, after removing physically adsorbed water, the results obtained ranged from 4.3 to 6.7 OH nm-2 for a series of silicas. The data are in good agreement with those obtained by other techniques. Thermogravimetry proved to be a reliable tool for this kind of study, with the great advantage of being a simple, quick and inexpensive method requiring only a few mg of the silica sample.