M. Espinosa-Jiménez

Investigation of alumina/( +)-catechin system properties. Part I: a study of the system by FTIR-UV -Vis spectroscopy

Abstract Catechin belongs to a group of flavonoids, which are present in many fruits and plants. Catechin is often employed in model investigations on antioxidant behavior of flavonoids. Recently also some anti-disease properties of flavonoids were reported. In this paper investigations were carried out on alumina/(+)-catechin solution system. FTIR spectra were taken for the catechin samples retaken from its aqueous solutions at pH 3, 5.5 (natural) and 10.5. In other series, the solutions were contacted with an alumina powder during 20 days. Also UV–Vis spectra were taken for similar solutions incubated for 1, 7, 20, 50 and 70 days with and without contact with alumina. It appeared that the alumina essentially accelerated the autooxidation processes occurring in the solutions. The results show that the processes have completed between day 20 and 50, because the UV–Vis spectra for day 50 and 70 overlapped. Moreover, it looks that this is a specific property of alumina, which behaves as a catalyst. Similar experiments with silica showed that during 50 days, this oxide affected the processes only slightly.

The uptake of a reactive dye by bleached cotton and its effect on the electrical properties of the interface: I. Electrokinetic properties

An experimental investigation on streaming potential, sorption, and electrical conductance of porous plugs of bleached cotton in aqueous solutions of a reactive dye, Remazol brilliant blue R (RBB-R), at varying temperatures is described. The absolute value of the (negative) zeta potential of cotton decreases appreciably when temperature is increased at concentrations of RBB-R in solution up to ca. 10-4 mole/liter, the reverse trend being observed at higher dye concentrations. Similar behavior was deduced for the surface charge density of the fiber. The uptake of dye by the fiber is favored by the increase in temperature, this fact being in accordance with the chemical nature for the bonds involved. However, physical contributions, mainly H-bonds, cannot be neglected at the lowest temperatures studied. The effective dyeing surface has been found to increase linearly with temperature. Surface conductanc, ks, predominates in the total electrical conductance of the system, k, at low concentrations of dye in solution, while it is the bulk component, kb, which predominates in the higher concentration range.

Interpretation of colloidal dyeing of polyester fabrics pretreated with ethyl xanthogenate in terms of zeta potential and surface free energy balance

Data are presented on the adsorption of the colloidal dye Disperse Blue 3 onto polyester fabric (Dacron 54, Stile 777), the fabric being pretreated with different amounts of the surfactant potassium ethyl xanthogenate (PEX). This study has been made by means of both the evolution of the zeta potential of the fiber/dye interface and the behaviour of the surface free energy components of the above systems. The kinetics of adsorption of the process of dyeing, using 10(-4) M of PEX in the pretreatment of the fabric, shows that increasing temperature of adsorption decrease the amount of colloidal dye adsorbed onto the fabric. This fact shows that the principal mechanism involved in this adsorption process is physical in nature. The adsorption isotherms of the colloidal dye onto polyester pretreated with different amounts of PEX, shows that the adsorption of the dye is favored with the increase in the concentration of the surfactant used in the pretreatment. This fact shows that the pretreatment with PEX is a very interesting aspect of interest in textile industry. The zeta potential of the system fabric/surfactant shows that this parameter is negative (about -25 mV) for the untreated fiber and decreases in absolute value for increasing concentration of the surfactant on the fiber, the value of the zeta potential of the system being -5 mV for 10(-2) M of PEX. This behavior can be explained for the chemical reaction nucleophilic attack between the carboxyl groups of polyester, ionized at pH 8, and the thiocarbonyl group of the xanthogenate ion. On the other hand, the zeta potential of the system polyester pretreated with PEX/Disperse Blue 3 at increasing concentrations of the surfactant and the dye shows that this parameter increases its negative value strongly with increasing concentration of the surfactant used in the treatment. This can be explained for the hydrogen bonds between the hydroxy groups of the dye and the S- ions of the thiocarbonyl group of the surfactant preadsorbed onto the fiber.

Investigation of alumina/(+)-catechin system properties. Part II: ζ-potential and surface free energy changes of alumina

Abstract The effects of (+)-catechin adsorption to the alumina surface were studied by ζ-potential and surface free energy determination. The presence of catechin causes essential changes in the alumina ζ-potential, which at the concentration slightly higher than 10 −5 M reverses from the positive into negative one. At constant concentration of catechin (10 −3 M), the effect on ζ-potential of alumina as a function of pH appears in a drastic shift of the isoelectric point, from pH 8.4 to 4.6, and the equilibrium is established practically within 2 h. This is probably due to relatively low p K a =4.6 for catechin 3′-OH group deprotonation. At high alkaline environment (pH≥10), even in the presence of catechin in the solution, the hydroxyl OH − ions play principal role in the surface charge formation for the alumina. At such pH catechin molecule is double negatively charged and hence its adsorption on highly negatively charged alumina surface is rather restricted. Nevertheless, various dimeric forms of catechin, which are formed at the alkaline pH, probably adsorb on the alumina surface. This appears in small increase in apolar surface free energy component at natural and alkaline pH. On the other hand, at acidic pH 3 small increase of the electron acceptor interaction is observed. This may result from increased number of hydroxyl groups on the alumina surface originating from the adsorbed molecules of catechin, which are mostly undissociated at this pH. The interactions of catechin with alumina surface seems to be also of some specific nature, because neither changes in the ultraviolet–visible (UV–vis) absorbance (Part I) nor in the ζ-potentials had occurred in the silica suspensions in which also catechin was present.

The effect of tannic acid on the electrical properties of the interface and the non-linear streaming potential of cellulose in a cationic dye solution

An experimental investigation on streaming potentials of porous plugs of cellulose in both the linear and the non-linear range is described. The variation of electrokinetic coefficients with the concentration of a cationic dye in solution has been studied and the influence of mordant on the electrical properties of the interface of cellulose/cationic dye solution systems has been analysed. The second-order electrokinetic coefficients have been interpreted in terms of modifications of generalized coefficients produced by changes in thermodynamic forces.

Effect of a cationic dye on the surface free energy of Leacril fabric

Abstract Changes in Leacril fabric surface free energy components (Lifshitz-van der Waals γ S LW , electron donor γ s − , and electron acceptor γ s + ) due to absorption of the cationic dye Crystal Violet (CV) were determined by means of the thin-layer wicking technique. It was found that the treatment of Leacril with different amounts of CV produced practically no changes in the value of the γ S LW component. However, the above treatment reduces the γ S + component practically to zero. In contrast, the γ S − component increases from 60 mJ m −2 for untreated Leacril up to 79 mJ m −2 for Leacril treated with 10 −4 M CV, with a very sharp decrease of γ s − to 67 mJ m −2 for increasing concentrations of CV (up to 10 −2 M). The initial increase in γ S − with 10 −4 M CV could be due to the presence of three disubstituted aromatic amine groups in the molecule CV. These groups are strong electron donors and their presence increases the value of the γ S − component of the Leacril. The initial value of 60 mJ m −2 of the γ S − component for the untreated Leacril could be due to the presence of a large amount of both sulphonate and sulphate end-groups on untreated Leacril. These groups are also donors of electrons. For increasing concentrations of CV in the treatment of Leacril, the electrostatic interactions between the cation of the dye and both the sulphonate and sulphate end-groups of the Leacril produce a blockade of these groups on the fabric and a decrease of the γ S − component to a value of 67 mJ m −2 for a concentration of 10 −2 M CV. The amount of CV uptake by Leacril increases with the concentration of the cationic dye in solution and with the temperature of absorption. It is concluded that the absorption of CV on Leacril takes place by means of electrostatic attractions between the disubstituted aromatic amine groups of the cationic dye used and both the sulphonate and sulphate end-groups of Leacril. These groups could impart hydrophilicity to the surface of the Leacril and hence acid-base interactions between the molecules of the cationic dye and the surface of the fabric could explain the interactions between the CV and the Leacril. The value of 67 mJ m −2 obtained for γ S − after the treatment of Leacril with 10 −2 M CV could be due to the final presence of the three (electron donor) disubstituted aromatic amine groups per molecule of the cationic dye on the Leacril surface due to the absorption process of the dye on the Leacril fabric.

The uptake of a reactive dye by bleached cotton and its effect on the electrical properties of the interface: II. Kinetics and thermodynamics

Abstract Data on the kinetics and thermodynamics of absorption of Remazol brilliant blue R on bleached cotton at different temperatures are presented. It is established that the increase in temperature of the system increases the dye content of the fiber. The experimental time—sorption isotherms were found to be represented by the exponential kinetic equation Mt = Meq(1 - e−kt), where Mt and Meq refer to the amounts of reactive dye uptaken by the cellulosic fiber at time t and at equilibrium, respectively, and k refers to the rate constant. The empirical rate constant k has been found to decrease with temperature. Values of half-dyeing time at different temperatures are presented. The sorption equilibria of RBB-R by bleached cotton are described by a Freundlichs isotherm type equation. Changes of enthalpy and entropy related to the process of dyeing were calculated from the Clausius—Clapeyron equation. Isosteric heats of dyeing have been found to be positive and of the order of 20 to 105 kJ/mole. The global change of entropy is positive and of the order of 85 to 430 J/mole K. The best thermodynamic conditions for the uptake of dye by the fiber appear at the highest temperatures, as the standard free energy of dyeing takes then the more negative values. From the results obtained the conclusion can be derived that the absorption of RBB-R by bleached cotton in the investigated temperature interval takes place with establishment of strong chemical bonds although physical contributions cannot be neglected.