Al-pillared Bentonite Research Articles

Co-aluminosilicate based electrodes

The influence of aluminosilicate support on the catalyst efficiency was investigated. Three different aluminosilicate materials containing cobalt (II) ion as active specie for phenol or nitrite oxidation were obtained. The first sample was zeolite 13X impregnated with Co by impregnation/thermal degradation procedure using Co-acetylacetonate. Bentonite was pillared with Al 3+/Co 2+ mixture to obtain the second sample. For the third one Co was introduced into Al-pillared bentonite by ion-exchange using Co(NO 3) 2*6H 2O. Reactions of either phenol or nitrite oxidation were used as test reactions for the investigation of the influence of the type of aluminosilicate support on the catalytic activity of Co.

Catalytic oxidation of aromatic VOCs with Cr or Pd-impregnated Al-pillared bentonite: Byproduct formation and deactivation studies

The catalytic behavior of chromium and palladium-impregnated Al-pillared bentonite for the oxidation of aromatic VOCs, i.e. chlorobenzene or xylene, was investigated. The Cr-impregnated bentonite showed high activity for the total oxidation of cholorobenzene and xylene but the materials were completely deactivated during the reaction at 600 °C. Atomic absorption, XPS, XRD and TG analyses suggested three main causes for the deactivation, i.e. the loss of Cr due to the formation of volatile CrO2Cl2, a strong decrease on the surface area due to the collapse of the pillars and the formation of coke. For the Pd supported pillared bentonite, the impregnation procedure completely destroyed the Al-pillars but produced a very active and stable catalyst to oxidize aromatic contaminants. However, in the case of chlorobenzene almost 20% yield of the hazardous hexachlorobenzene was obtained likely by an oxychlorination process.

Effect of OH −/Al 3+ and Al 3+/clay ratios on the adsorption properties of Al-pillared bentonites

In this work, the adsorption properties of Al-pillared bentonites were investigated by using phenol and 2-chlorophenol as model pollutants. The Al-pillared bentonites were prepared by the conventional method of pillaring involving the mixing of a dilute clay suspension with a dilute pillaring solution. To study the effect of textural changes on the adsorption properties, the adsorbents were prepared by using different OH −/Al 3+ and Al 3+/clay ratios. It was determined that the adsorbed amounts of phenol decrease with increasing OH −/Al 3+ and Al 3+/clay ratios. Adsorption of 2-chlorophenol on the adsorbent adsorbing the highest amount of phenol was studied. It was found that the amounts adsorbed are nearly same for both of the adsorbates at low equilibrium concentrations and a slight difference is observed at concentrations exceeding 60 mg/L. The adsorbed amounts were compared with the amounts adsorbed by hexadecyltrimethylammonium bromide (HDTMA)–bentonite. It was obtained through the modification of bentonite with hexadecyltrimethylammonium bromide, in an amount equivalent to 100% of cation exchange capacity of the clay. It was observed that the adsorbed amounts of phenol are approximately three times higher in the case of Al-pillared bentonite having 1.44 and 1.8 OH −/Al 3+ and Al 3+/clay ratios, respectively. This behavior is attributed to the high surface area. Although the adsorbed amounts of 2-chlorophenol on the Al-pillared bentonite are same with that of phenol, they are lower than the amounts adsorbed on HDTMA–bentonite and it was concluded that the existence of pseudo-organic layer is of importance in the case of the adsorbates having low water solubility and the form of the sample 1 modified with HDTMA will be more efficient.

Effect of Fe and Ce on Al-pillared bentonite and their performance in catalytic oxidation reactions

Abstract A Colombian bentonite was modified by intercalation with polyhydroxocationic solutions of Al 3+ containing Fe 3+ and Ce 3+ . Addition of these solutions led to the formation of pillared clays with important catalytic properties in three environmental impact reactions: phenol oxidation in diluted aqueous medium, oxidation of CO and 2-propanol oxidation in gas phase. The catalytic tests revealed the activity of the introduced iron species and the promoter effect of the cerium on the catalytic activity of these species. X-ray diffraction and the transmission electron microscopy results indicated, respectively, the formation of oxide nanoparticles inside and outside of the interlayer spaces of the clay mineral structure. Mossbauer spectroscopy analysis revealed the presence of iron oxides with oxidation state +3 and hematite structure on the solids.

Adsorption performance of Al-pillared bentonite clay for the removal of cobalt(II) from aqueous phase

In this research, the natural bentonite clay collected from Ashapura Clay Mines, Gujarat State, India, was utilized as a precursor to produce aluminium-pillared bentonite clay (Al-PILC) for the removal of cobalt(II) [Co(II)] ions from aqueous solutions. The original bentonite clay and Al-PILC were characterized with the help of chemical analyses, methylene blue (MB) adsorption isotherm, powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and infrared spectroscopy (IR), while the thermal stability of the samples were studied using thermogravimetry (TG). Surface charge density of the samples as a function of pH was investigated using potentiometric titrations. Adsorption experiments were conducted under various conditions, i.e., pH, contact time, initial concentration, ionic strength, adsorbent dose and temperature. The most effective pH range for the removal of Co(II) ions was found to be 6.0–8.0. The maximum adsorption of 99.8% and 87.0% took place at pH 6.0 from an initial concentration of 10.0 and 25.0 mg l −1, respectively. Kinetic studies showed that an equilibrium time of 24 h was needed for the adsorption of Co(II) ions on Al-PILC and the experimental data were correlated by either the external mass transfer diffusion model for the first stage of adsorption and the intraparticle mass transfer diffusion model for the second stage of adsorption. The intraparticle mass transfer diffusion model gave a better fit to the experimental data. The Arrhenius and Eyring equations were applied to the data to determine the kinetic and thermodynamic parameters for explaining the theoretical behaviour of the adsorption process. The equilibrium isotherm data were analyzed using the Langmuir, Freundlich and Scatchard isotherm equations and the adsorption process was reflected by Freundlich isotherm. The efficiency of the Al-PILC was assessed by comparing the results with those on a commercial ion exchanger, Ceralite IRC-50. The suitability of the Al-PILC for treating Co(II) solutions was tested using simulated nuclear power plant coolant samples. Acid regeneration was tried for several cycles with a view to recover the adsorbed Co(II) and also to restore the adsorbent to its original state.

Sorption of Organic Compounds by Al and Zr-Hydroxy-Intercalated and Pillared Bentonite

AbstractOwing to their large and chemically active surface, hydroxy-intercalated and pillared clays can be potent sorbents for organic compounds. The sorption behavior of Al and Zr-hydroxy-intercalated bentonite (HAl-, HZr-MX80), Al and Zr-pillared bentonite (Al-MX80, Zr-MX80), and a commercial Al-pillared bentonite (EXM 534) for 3-chloroaniline (3-CA), atrazine (AT), and 3-chlorophenol (3-CP) was investigated. The results were compared with the sorption behavior of the untreated Na-rich bentonite (MX80) and granulated activated carbon (GAC). Also the influence of the salinity of the sorbate and the age of the sorbents was studied.Al and Zr-hydroxy-intercalated and pillared bentonites sorbed higher amounts of 3-CA, AT, and 3-CP than the untreated bentonite. The quantities sorbed related to the electron-donating properties of the sorbate and the acidity of the sorbents. Sorbed quantities increased from the hydroxy-intercalated to the pillared species, and from the Al to the Zr forms. The organic bases, 3-CA and AT, were sorbed in higher quantities than the organic acid 3-CP. For AT, the sorbents exhibited a high affinity. Aging of the samples and a high ionic strength of the sorbate reduced the sorption of 3-CA, whereas the sorption of AT was not affected greatly. The sorption capacity of GAC for organic bases was generally higher than that of the hydroxy-intercalated and pillared bentonites.The data suggest that at initial concentrations at a ppm level, 3-CA and AT can be entirely removed from aqueous solutions by Al and Zr-hydroxy-intercalated and pillared bentonites. These materials, especially Zr-pillared bentonites, represent potent alternative sorbents for atrazine, chloroanilines, and probably a wide range of other organic bases.

Sorption of Heavy-Metal Cations by Al and Zr-Hydroxy-Intercalated and Pillared Bentonite

AbstractThe sorption of Cd, Cu, Pb, and Zn ions by Na-rich bentonite, Al and Zr-pillared Na-rich bentonite (Al-MX80, Zr-MX80), the uncalcined hydroxy-intercalated precursors (HAl, HZr-MX80), and commercial Al-pillared bentonite EXM 534 was investigated. Experiments were conducted in ultrapure water and artificial leachate with varying pH. The experiments were performed over periods to 30 wk. Sorption characteristics were described with one and two-site Langmuir isotherms. The non-exchangeable quantities of heavy metals were determined by fusion of the sorbents after ion exchange with ammonium acetate.The sorption of Cd, Cu, Pb, and Zn by bentonite was dominated by cation exchange. In artificial leachate, the sorption was reduced due to competition with alkali and alkaline-earth cations. The sorption of Cu, Zn, and Pb at pH 4.9 and Cd at pH 6.9 by Al and Zr-hydroxy-intercalated and pillared MX80 was governed also by cation exchange. In contrast, the sorbed quantities of Zn at pH 6.9 exceeded the cation exchange capacity (CEC) of HAl, HZr, Al, Zr-MX80, and EXM 534 and were partially non-exchangeable. The increase of the sorption of Zn with pH and its independence of the ionic strength of the solution at neutral pH suggest a complexation of Zn ions to surface hydroxyl groups of the intercalated Al and Zr-polyhydroxo cations and pillars. This complexation is the dominating sorption mechanism. Removal of dissolved Zn from solution with time is attributed to surface precipitation. Al-hydroxy and pillared bentonites are considered potential sorbents of Zn ions from neutral pH aqueous solutions, such as waste waters and leachates.