Martín M. Dávila-Jiménez

Performance of mango seed adsorbents in the adsorption of anthraquinone and azo acid dyes in single and binary aqueous solutions.

In this study the husk of mango seed and two carbonaceous adsorbents prepared from it were used to study the adsorption behavior of eight acid dyes. The adsorbed amount in mmol m(-2) decayed asymptotically as the molecular volume and area increased. The interaction between the studied dyes and the mesoporous carbon was governed by the ionic species in solution and the acidic/basic groups on the surface. Less than 50% of the external surface of the microporous carbon became covered with the dyes molecules, though monolayer formation demonstrating specific interactions only with active sites on the surface and the adsorption magnitudes correlated with the shape parameter of the molecule within a particular dye group. The adsorption behavior in mixtures was determined by the molecular volume of the constituents; the greater the molecular volume difference, the greater the effect on the adsorbed amount. We also demonstrated that the raw husk of the mango seed can be used to remove up to 50% from model 50 mg l(-1) solutions of the studied acid dyes.

In situ and ex situ study of the enhanced modification with iron of clinoptilolite-rich zeolitic tuff for arsenic sorption from aqueous solutions

Adsorption methods have been developed for the removal of arsenic from solution motivated by the adverse health effects of this naturally occurring element. Iron exchanged natural zeolites are promising materials for this application. In this study we introduced iron species into a clinoptilolite-rich zeolitic tuff by the liquid exchange method using different organic and inorganic iron salts after pretreatment with NaCl and quantified the iron content in all trials by XRF spectroscopy. The materials were characterized by XRD, FTIR, FTIR-DR, UV-vis, cyclic voltammetry, ESR and Mössbauer spectroscopies before and after adsorption of arsenite and arsenate. The reached iron load in the sample T+Fe was %Fe(2)O(3)-2.462, n(Fe)/n(Al)=0.19, n(Si)/n(Fe)=30.9 using FeCl(3), whereby the iron leachability was 0.1-0.2%. The introduced iron corresponded to four coordinated species with tetrahedral geometry, primarily low spin ferric iron adsorbing almost 12 mug g(-1) arsenite (99% removal) from a 360 mug(As(III)) L(-1) and 6 mug g(-1) arsenate from a 230 mug(As(V)) L(-1). Adsorption of arsenite and arsenate reached practically a plateau at n(Fe)/n(Si)=0.1 in the series of exchanged tuffs. The oxidation of arsenite to arsenate in the solution in contact with iron modified tuff during adsorption was observed by speciation. The reduction of ferric iron to ferrous iron could be detected in the electrochemical system comprising an iron-clinoptilolite impregnated electrode and was not observed in the dried tuff after adsorption.

Electrochemical treatment of textile dyes and their analysis by high-performance liquid chromatography with diode array detection

Several textile dyes were individually exposed to electrochemical treatment. Chromaticity variation and the formation of degradation products were followed using a UV spectrophotometer and HPLC with diode array detection. Dyes studied belong to the azo (color index, C.I. 15,510), methine (C.I. 48,013), indigo (C.I. 73,040), natural (C.I. 75,760) and arylmethane (C.I. 42,000) classes. Aliquots of the solutions treated at constant potential were analyzed and compared with control dye solutions. The final electrolysis solutions obtained by using different electrode materials: Pt, Ti and diamond presented different chromatograms. It was found that the novel (in this application) diamond electrode is efficient in studying the degradation of various dyes. Possible fragmentation and molecule moiety rearrangement are proposed as a result of the electrochemical treatment.

Adsorption of metal cations from aqueous solution onto a natural and a model biocomposite

Batch adsorption studies have shown that a solid material (CACMM) extracted from a cactus was able to sorb Cu 2 , Cd 2 ,C r 3 , CrO4 ,F e 3 ,N i 2 ,P b 2 and Zn 2 from aqueous solutions in the concentration range 100/1000 mg l 1 . Fractions of CACMM with different particle diameter presented different sorption patterns upon the studied metal cations. Copper retention was much greater than that of other cations for all the fractions under identical experimental conditions with a maximum efficiency of 84% for 1000 mg l 1 Cu 2 solutions. Adsorption magnitude onto large particles of CACMM1 (450 (mm) decreased in the series Cu 2 � /Ni 2 � /Cr 3 � /Pb 2 � /Zn 2 � /Cd 2 � /Fe 3 that correlates with the stability constants of the respective oxalate complexes indicating that the interaction of the metal cations follows a surface adsorption/complexation mechanism. The composition of a model composite, which simulates the sorption capacity of the natural cactus powders upon copper, was found. # 2003 Elsevier Science B.V. All rights reserved.

Removal of metal ions from aqueous solution by adsorption on the natural adsorbent CACMM2

The adsorption of Cd2+, Cr3+, Cu2+, Fe3+, Ni2+, Pb2+ and Zn2+ from aqueous solution was used to study the sorption properties of the adsorbent CACMM2 extracted from a cactus. Quantitation of the cation concentrations was performed by HPLC with diode array detection using on-column complex formation with 8-hydroxyquinoline. Removal degree from 100 mg M(n+) l(-1) solutions followed the series: Cu>Cd>Fe>Ni>Cr>Zn. Henry and Freundlich constants were determined since adsorption did not reach saturation plateaux in the studied concentration interval. Sorption of chromium by CACMM2 was stronger than the sorption onto lignin, calcium oxalate and cellulose up to 1,000 mg Cr3+ l(-1). Copper and iron were desorbed to a greater extent, while lead adsorption was practically irreversible. CACMM2 was able to remove more than 83% of chromate in a freshly prepared and exhausted chromate commercial solution.

TiO2 Immobilized on Manihot Carbon: Optimal Preparation and Evaluation of Its Activity in the Decomposition of Indigo Carmine

Applications of carbon-TiO2 materials have attracted attention in nanotechnology due to their synergic effects. We report the immobilization of TiO2 on carbon prepared from residues of the plant Manihot, commercial TiO2 and glycerol. The objective was to obtain a moderate loading of the anatase phase by preserving the carbonaceous external surface and micropores of the composite. Two preparation methods were compared, including mixing dry precursors and immobilization using a glycerol slurry. The evaluation of the micropore blocking was performed using nitrogen adsorption isotherms. The results indicated that it was possible to use Manihot residues and glycerol to prepare an anatase-containing material with a basic surface and a significant SBET value. The activities of the prepared materials were tested in a decomposition assay of indigo carmine. The TiO2/carbon eliminated nearly 100% of the dye under UV irradiation using the optimal conditions found by a Taguchi L4 orthogonal array considering the specific surface, temperature and initial concentration. The reaction was monitored by UV-Vis spectrophotometry and LC-ESI-(Qq)-TOF-MS, enabling the identification of some intermediates. No isatin-5-sulfonic acid was detected after a 60 min photocatalytic reaction, and three sulfonated aromatic amines, including 4-amino-3-hydroxybenzenesulfonic acid, 2-(2-amino-5-sulfophenyl)-2-oxoacetic acid and 2-amino-5-sulfobenzoic acid, were present in the reaction mixture.

Influence of Ni doping on the structural, optical and textural properties of TiO 2 nanocrystals prepared via an ultrasound assisted sol-gel method

Nanometric TiO2 and nickel-doped TiO2 powders were obtained by thermal decomposition of non-alkoxide precursors prepared using an ultrasonic-assisted sol–gel method. Ti4+ and Ni2+ were obtained from titanium oxide sulfate hydrate and nickel sulfate hexahydrate, respectively. X-ray powder diffraction and Raman spectroscopy confirmed the formation of only the anatase phase in both oxides, and no titanates were observed. The Ni-doped material was determined to be a solid solution with a stoichiometry of Ti0.96Ni0.04O2−y. The incorporation of nickel lowers the band gap calculated from the UV–Vis diffuse reflectance spectroscopic data, and affects the specific surface area, density, and acid–base characteristics. Mesoporosity developed as a result of particle agglomeration and differed among samples, as determined based on the total pore volume.

Photoproducts of carminic acid formed by a composite from Manihot dulcis waste

Carbon-TiO2 composites were obtained from carbonised Manihot dulcis waste and TiO2 using glycerol as an additive and thermally treating the composites at 800 °C. Furthermore, carbon was obtained from manihot to study the adsorption, desorption and photocatalysis of carminic acid on these materials. Carminic acid, a natural dye extracted from cochineal insects, is a pollutant produced by the food industry and handicrafts. Its photocatalysis was observed under different atmospheres, and kinetic curves were measured by both UV-Vis and HPLC for comparison, yielding interesting differences. The composite was capable of decomposing approximately 50% of the carminic acid under various conditions. The reaction was monitored by UV-Vis spectroscopy and LC-ESI-(Qq)-TOF-MS-DAD, enabling the identification of some intermediate species. The deleterious compound anthracene-9,10-dione was detected both in N2 and air atmospheres.

Characterization and adsorption properties of powders prepared from cactus pulp

Two cactaceous powders, labelled CACMM1 and CACMM2, are shown to contain calcium oxalate and to consist of globular or cubosome particles. The samples were characterized by X-ray diffractometry, spectroscopic, thermic, nitrogen and water adsorption methods and compared with other organic compounds. The pore systems have been analysed from adsorption isotherms, t-plots and pore size distribution curves. The bioadsorbents CACMM1 and CACMM2 exhibited low specific surface area values and presented pores in the mesopore range. Composite adsorption isotherms for the binary mixtures benzene-hexane and benzene-cyclohexane on cactaceous powders have been established and revealed preferential adsorption of hexane and cyclohexane in the respective system. Also the adsorption behavior of dyes from aqueous solution was studied to complete the diversity of adsorbate molecules. Linear adsorption isotherms were obtained up to 6 mM dye equilibrium concentration.

Using Akaike Information Criterion to Select the Optimal Isotherm Equation for Adsorption from Solution

In this study, we measured the adsorption of Basic Blue 41 (BB41) dye on a maize cob adsorbent and on two model adsorbents (cellulose triacetate and cellulose acetate propionate). The experimental adsorption data were evaluated with the isotherm equations of Langmuir, Freundlich, Langmuir–Freundlich and Dubinin–Radushkevich, and constants were obtained exclusively by non-linear regression. In order to select the optimal isotherm equation, Akaike information criterion was used. The celluloses obeyed the Langmuir isotherm in the temperature range tested, whereas the corncob followed the Freundlich equation. This comparative study shows that limited amounts of the cationic dye were adsorbed on the model celluloses than on the cob. BB41 was neither adsorbed horizontally nor vertically onto the cob, whereas it competed with water molecules and despite saturation, did not exhaustively occupy the surface of the celluloses. The Gibbs free energy of adsorption was evaluated using the equilibrium constants obtained by several procedures and the results were found to be inconsistent.