The Adsorption of Pentachlorophenol from Aqueous Solutions onto Exchanged Al-MCM-41 Materials

The ability of a mesoporous molecular sieve to adsorb chlorinated phenols was studied experimentally. Thus, the adsorption isotherms of pentachlorophenol (PCP) from aqueous solutions were measured on (M)Al-MCM-41 (M = Na + , K + , Cu 2+ , Cr 3+ ) at intervals of 10 K between 303 K and 323 K. The experimental isotherms obtained were of the S-type in terms of the classification of Giles and co-workers. The best fit of the adsorption isotherm data was obtained using the Freundlich model. The adsorption affinity of PCP increased in the order (K)Al-MCM-41 < (Cr)Al-MCM-41 < (Na)Al-MCM-41 < (Cu)Al-MCM-41. At the same temperature, the adsorption of PCP on (Cu)Al-MCM-41 was more pronounced compared to its adsorption on alumina-pillared montmorillonite and mesoporous alumina aluminium phosphates. Analysis of the isosteric curves showed that (Cu)Al-MCM-41 and (Na)Al-MCM-41 presented a heterogeneous profile. In contrast, (K)Al-MCM-41 and (Cr)Al-MCM-41 did not exhibit energetic heterogeneity throughout the entire range of coverage

Removal of Congo red by thermally and chemically modified halloysite: equilibrium, FTIR spectroscopy, and mechanism studies

Unmodified halloysite and its heated and heat-processed/acid-leached forms were utilized for the adsorption of Congo red (CR) from aqueous medium. The samples were analyzed by ICP and nitrogen adsorption prior to the adsorption of the pollutant. We then studied the adsorption equilibrium of CR and the regenerating cycles of the most effective adsorbent. A special attention was paid to Fourier transform infrared analysis to elucidate the mechanism of CR adsorption onto halloysite materials. The thermochemical treatment results in the dehydroxylation of halloysite and an increase in SiO2 content. The modification increases specific surface area up to 503 against 63m(2)g(-1) for unmodified halloysite. The Redlich-Peterson isotherm yields the best fit of the Congo red adsorption. The best adsorbent was found to be the heat-treated/acid-leached sample. It interacts with Congo red molecules through an outer-sphere complexation mechanism by implying silanol species and amino and sulfoxide groups. Understanding the interactions between pollutants and halloysite materials is an essential approach to improving the use of these clays in sewage treatment

Development and characterization of a new dolomite-based catalyst: application to the photocatalytic degradation of pentachlorophenol

PMID = 3097594

Adsorptive properties of X zeolites modified by transition metal cation exchange

International audienceThe ionic exchange of the NaX zeolite by Ni(2+) and Cr(3+) cations was progressively driven and studied by adsorption of nitrogen and carbon dioxide. For each cation-exchanged X zeolite sample, the development of characteristics such as profile of isotherms, RI criterion, isosteric adsorption heat and microporous volume using both the Dubinin-Radushkevich (DR) equation and the t-plot, was followed through the nitrogen adsorption. Results show that the cationic exchange process, in the case of Cr(3+) introduced at middle degree, is accompanied by a textural damage for Cr(x)X, in contrast to Ni(2+)-exchanged X zeolites. This degradation occurs without significant presence of mesopores, because the RI criterion values were found to be much lower than 2.2. The CO(2) adsorption isotherms were measured at intervals of 30 K from 273 K and the equilibrium pressures ranged from 0.5 to 600 Torr. The experimental data were correlated by the Toth model. The associated three adjustable parameters were estimated by nonlinear least-squares analysis. The effect of temperature on the model parameters and the Henry's law slope, K (H) , represented by the product of Toth parameters, are discussed

Methodological approach to the chloramphenicol adsorption by acid-leached halloysites: Preparation, characterization, performance and mechanism

International audienc

Development and characterization of a new dolomite-based catalyst: application to the photocatalytic degradation of pentachlorophenol

The development of new catalysts from abundant raw materials, generating attractive photocatalytic activity, constitutes a real challenge in the context of sustainable development concerns. In this setting, a dolomite was treated at 800 degrees C (D800) and then chemically modified by Ca(NO3)(2) (CaD800) using a simple procedure. The resulting materials were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy (EDS), solid state UV spectroscopy, and used as catalysts of pentachlorophenol (PCP) degradation in aqueous solutions under UV light irradiation. The treatment of dolomite at 800 degrees C enabled a full decarbonation of CaMg(CO3)(2), with formation of CaO, Ca(OH)(2), and MgO. Additional CaO was generated after chemical treatment as revealed by EDS analysis; the Ca/Mg ratio increased from 1.29 (D800) to 1.44 for CaD800. This CaO in aqueous medium hydrates by giving Ca(OH)(2). CaD800 was found to be the best photocatalyst with a PCP degradation rate of 95% after only 1 h of treatment, for a CaD800/D800 degradation rate constant ratio of 1.58. In this regard, we investigated the Fourier transform infrared spectra of CaD800, PCP, and CaD800 loaded with PCP after degradation. We thus evidenced the involvement of Ca(OH)(2) in the PCP degradation process. Catalytic activity was discussed through the contribution of OH radicals and electrodonation

Real time control via a high order sliding mode controller of a multi-cellular converter

In this paper, we present a multi-cellular converter connected to a DC motor (DCM). We show its importance in the practical implementation of a (super twisting) control algorithm derived using the second order sliding mode technique. The validity of the controller is shown experimentally using a laboratory set-up

Improved ciprofloxacin removal by a novel organohalloysite obtained by phenylphosphonic acid intercalation

International audienc

Acidity study of X zeolites modified by nickel and/or chromium cations in the case of binary and ternary exchanges

International audienceA series of Ni(x)-, Cr(x) and CrNi(x)-exchanged X zeolites (x being the ion-exchange degree) was prepared and characterised by nitrogen adsorption, XRD. DTA/TGA and pyridine adsorption-desorption followed by IR spectroscopy. The objective is mainly to estimate quantitatively the number, strength and nature of acid sites and their dependence on the type of cation and its exchange level. A comparison between the binary and ternary exchanges was also established. The crystallinity and micropore volume losses were more significant for Cr(x)X and CrNi(x)X. The concentration of Lewis acid sites decreases with increasing the exchange degree for Cr(x)X and Ni(x)X, while it increases up to 39% for CrNi(x)X. An increase of the concentration of Bronsted sites was obtained. The fact that both the Lewis and Bronsted acidities markedly decrease between 423 and 623 K, proves that the available acid sites are overall weak. The pyridine desorption from the protonic sites is easier with CrNi(39)X than with Cr(39)X and Ni(40)X at 623 K, indicating a decrease in the strength in the case of ternary exchange. (C) 2012 Elsevier Inc. All rights reserved

Synergetic effects of Cu-Zn bimetallic ions exchanged in NaX on acid sites of M(

X zeolites were prepared by ion-exchange with Cu2+ and/or Zn2+ cations, at different concentrations of the exchange solution, and characterized by thermal analysis and nitrogen adsorption. The acidity of the samples was investigated by pyridine adsorption–desorption followed by in situ Fourier transform infrared (FTIR) spectroscopy. Desorption was carried out at 150, 250 and 350 °C. The objective is to estimate the nature and concentration of acid sites. A comparison between the binary (Cu(x)X, Zn(x)X) and ternary (CuZn(x)X) exchanges was also established (x = level of exchange) through the Cu(43)X, Zn(48)X and CuZn(50)X samples. Lewis acidity decreases overall with desorption temperature and the level of exchange. As the latter increases, there is a conversion of some Lewis sites into those of Brønsted during thermal treatment. In return, the concentration of Brønsted sites increases with the degree of exchange. The Brønsted acidity of CuZn(50)X at 350 °C is more important than the sum of those of Cu(43)X and Zn(48)X with respectively values of 73, 32 and 15 μmol g−1. Besides, the concentration of Brønsted sites for CuZn(50)X increases with desorption temperature. These features indicate the presence of a synergetic effect amplifying the strength of these sites when Cu2+ and Zn2+ cations compete for the occupancy of sites distributed in zeolite cavities