The pillaring of Na-montmorillonite with cationic oligomers of hydroxyaluminum (COHA) in the presence of an aqueous solution of polyvinyl alcohol resulted in the formation of a clay having a large surface area and pore volume. The pore-size distribution determined from a N2 adsorption/desorption hysteresis was narrow and centered at about 25 Å. The peak width at half height in the distribution curve was < 5 Å. As a result of delamination, the layer structure of the prepared clay was found from X-ray powder diffraction measurements to be lost. Short-range ordering, however, still existed in this delaminated clay, because exchangeable cations in the montmorillonite completely exchanged with Al3+, a requisite step for pillaring.

The order of adding the starting materials (Na-montmorillonite, polyvinyl alcohol, and COHA) greatly affected the surface area and the pore volume of the delaminated clay. Two orders of addition (Namontmorillonite, then COHA, then polyvinyl alcohol; and COHA, then Na-montmorillonite, then polyvinyl alcohol) gave no measurable surface area and pore volume. Two other orders of addition (polyvinyl alcohol, then COHA, then Na-montmorillonite; and polyvinyl alcohol, then Na-montmorillonite, then COHA) gave surface areas of 107 and 160 m2/g and pore volumes of 0.13 and 0.29 cm3/g, respectively. The amounts of the COHA solution and polyvinyl alcohol added greatly influenced the surface area and pore volume of the delaminated clay. Both properties increased monotonically with increasing amount of added polyvinyl alcohol, and increased to a maximum and then decreased with increasing amount of added COHA solution. The maximum surface area of the prepared delaminated clay was 330 m2/g.

Pillared, regularly and randomly interstratified illite/smectite (I/S) was prepared by interacting aluminum chlorohydrate with I/S in aqueous dispersion. I/S samples from Kinnekulle, Sweden, ranging in composition from 30–60% smectite layers, were used as starting clays. The pillaring resulted in a separation of the smectite layers in the I/S of about 9 Å, as estimated by X-ray powder diffraction and by nitrogen adsorption studies. Only the smectite layers of the clay were modified by the pillaring procedure. The pillared products had surface areas of 200–260 m2/g and pore volumes of about 0.18 cm3/g. The uptake of Al by the clay and the micropore surface area of the pillared products were proportional to the fraction of smectite layers in the I/S. The thermal and hydrothermal stability of the pillared I/S was similar to that of pillared montmorillonite prepared using the same procedure.

Beidellite was synthesized hydrothermally from a noncrystalline gel at 320°C and 130 bar pressure. The beidellitic character of the product was verified by infrared spectroscopy on the NH4+-exchanged form. Intercalation was achieved with hydroxy-aluminum solutions having different OH/Al molar ratios. The solutions were investigated by several methods, including 27Al nuclear magnetic resonance. Essentially, two Al species were detected: monomelic Al and a polymerized form containing Al in four-fold coordination. This latter species was found to be selectively fixed in the interlamellar region, which resulted in a stable spacing of 18 Å at 110°C and 16.2 Å at 700°C. The pillared beidellites had specific surface areas of > 300 m2/g, mainly due to micropores. Both Brönsted and Lewis acid sites were evidenced by infrared spectroscopy using pyridine as a probe molecule.

Hectorite and saponite are exchanged with [Al13O4(OH)24(H2O)12]7+ and the amount of Al3+ adsorbed and Na+ released are followed as a function of the exchange conditions. On saponite the reaction is a pure ion exchange with 2–2.15 mmol Al3+/g adsorbed and release of 0.80 mmol Na+/g. On hectorite the ion exchange is accompanied by supplementary hydrolysis-polymerization of Al13. When excess Al is offered in the form of Al13, ion exchange is incomplete and is accompanied by precipitation and polymerization of Al13 on the surface of both hectorite and saponite. The typical spacing of 1.8 nm is developed after washing, when at least 1.3–1.4 mmol Al3+/g is adsorbed. Above a loading of 2.2–2.5 mmol/g the 1.8 nm spacing is obtained without washing. Only pillared saponite with a loading of at least 1.9 mmol Al3+/g is thermally stable up to 550°C.

Griffithite, a high Fe content saponite (Griffith Park, California) was pillared with Al polymeric solutions, using different Al/clay ratios. The cation exchange began when Al-polycation solutions were added, being completed during the dialysis of the samples. Pillared solids were obtained by calcination of intercalated precursors at 500 °C. The content of A12O3 increased from 7.35% in the natural griffithite to about 14% in the pillared samples, equivalent to the fixation of about 1.4 mmol Al per g of clay. The surface areas of the pillared griffithite were between 230–300 m2 g-1. The intercalation and pillaring of griffithite were easier than that of a less-crystalline nonferrous saponite.

Refluxing chromium (III) acetate with a Na+-montmorillonite suspension gives rise to the intercalation of linear Cr(III) polyhydroxo-acetate oligomers. Thermally stable chromia pillared mont-morillonite materials are obtained upon calcination under ammonia up to 625°C, and basal expansions up to 6 Å are maintained. The porous materials retain high surface areas (366–464 m2 g−1), a micropore volume of 0.1 cm3 g−1 and narrow pore size distributions centered between 7.5 and 12 Å. The most thermally stable materials in air were those prepared under ammonia at 625°C, containing NH4+ as the exchangeable ion.

Hydrotalcites of high aluminum content have been synthesized from aluminate liquors of varying composition and activated magnesia obtained by calcination of hydroxide or hydroxycarbonate precursors. Lattice parameter measurements and chemical analyses of 21 synthetic hydrotalcites show that the aluminum substitution $$\left( {\rm{X = \frac{{Al}}{{Al + Mg}}}} \right)$$ for most of the products is about 0.35, which is at the maximum experimentally-observed limit of solid solubility. Pillared hydrotalcites were also prepared by molybdate, Chromate, and silicate anion replacement. A maximum distance of 10.4 Å between the brucite-like layers was observed for the Mo7O246− intercalated material.

Saponite, hectorite, and laponite have been pillared with cationic Al clusters, and special attention has been given to the solution chemistry or Al. Pillared saponite is obtained after exchange with refluxed Al solutions; while for hectorite, Al solutions treated with ammonium acetate give a pillared product with 1.8–1.9 nm spacing and thermal stability up to 873 K. In both types of solutions, the Keggin ion Al cluster is a minority species or totally absent. The typical 1.8–1.9 nm spacing is only obtained after washing. The quality of the pillared material can be judged from its thermal stability, its surface area, and the width of the d001 line before and after pillaring. The width should not exceed 0.3 nm before calcination and 0.5 nm after calcination. The latter criterion reflects the importance of the crystallinity of the parent clay for successful pillaring. Pillaring in concentrated conditions occurs by a combination of ion exchange and precipitation of Al and gives materials that exhibit poor thermal stability.

Two major species were identified in Fe-treated montmorillonite: monomeric or dimeric hydroxoaqua cations $\text{Fe}{(\text{OH})}_x^{(3-x)+}$${\rm{Fe}}({\rm{OH}})_x^{(3 - x) + }$ (form I), and polymeric structures with edge-shared Fe(O,OH)6 (form II). These species have different electron spectra (absorption maximum is 29,600 cm−1 in form I, and 26,000 and 28,000 cm−1 in form II), chemical and thermal stability, and electrochemical behavior. Form I behaves as a partly exchangeable cation in interaction with Cu2+ from Cu-trien solution and Ni2+ from Ni-EDTA, that can be used for selective quantitative analysis. On heating above the dehydration temperature (∼100–150°C) montmorillonite with Fe3+ in form I is converted to a mica-like structure and Fe3+ ions are fixed more strongly in the montmorillonite structure. Form II behaves similarly to hydrous ferric oxides, but its thermal crystallization to hematite is postponed to ∼500–600°C. The Fe3+ cations in the interlayer space are much less thermally stable than Al pillars in pillared interlayered clays (PILCs). Form I is more active in oxidative dehydrogenation of propane, while form II is the active species in sorption of As and the non-specific combustion of propane. To produce only form II by the treatment of montmorillonite with Fe3+, its load must be kept below ∼20 wt.%; otherwise the usual hydrous ferric oxides are formed.

A comparative study of the behavior of four types of smectite is reported: two with a low Fe content, SHCa-1 (hectorite from San Bernadino, California), SWy-1 (montmorillonite from Wyoming) and two nontronites NG-1 (from Hohen Hagen, Germany) and SWa-1 (Grant County, Washington). Cation exchange was performed with a freshly prepared 1 M Fe nitrate aqueous solution. Intercalation with the same solution partially neutralized with an anhydrous carbonate solution, giving a molar ratio of OH−/Fe = 2 was also studied. The modified clays were characterized by X-ray diffraction, N2 adsorption-desorption, Mossbauer spectroscopy, thermogravimetric analysis, atomic absorption spectroscopy, X-ray fluorescence and inductively coupled plasma analysis.

In the cation exchange process, the goethite impurities grew with the Fe-rich clays but not with the Fe-poor clays. This exchange was also found to have no effect on the thermal stability and structure of the clay minerals with low Fe content, whereas it had a slight effect on the structure of the Fe-rich clays and on their thermal stability. The extent of the intercalation, however, appears to depend on the expandability of the clay layers to accommodate the Fe(III) polycations, and increases from the nontronites to montmorillonite and to hectorite. This intercalation treatment has only a slight effect on both the structure and the thermal stability of hectorite and montmorillonite. In contrast, the nontronites undergo a dramatic change in both their structure and thermal stability. The formation of Fe oxyhydroxide and oxide phases in both procedures becomes very important when the initial structural Fe content of the clay minerals is high, increasing from SHCa-1, SWy-1, SWa-1 to NG-1. The contribution of the structural Fe of the clays to the formation of the Fe oxyhydroxide is not negligible, because of partial leaching of Fe from the octahedral sheet of Fe-rich clays due to the low pH of the solutions.

Natural smectites bind aflatoxins from water effectively, but the complex chemical environment in the guts of mammals and other animals can limit binding of aflatoxins. Many efforts have been made to enhance the adsorption capacity and affinity of smectites for aflatoxins in the presence of biological compounds. The main objective of the present study was to modify smectite structures by pillaring and cation exchange to enhance aflatoxin B1 adsorption capacity and selectivity. Smectite was pillared with Al and Al-Fe polycations or saturated with Ca, Mg, Zn, or Li. Structural changes in smectites with or without heat treatment were determined using X-ray diffraction and Fourier-transform infrared spectroscopy. Equilibrium aflatoxin B1 adsorption to the smectites was measured in aqueous solution and in simulated gastric fluid. Pillaring with the polycations expanded smectites in the z-direction to 18.6 Å and the expansion was stable after heating at 500°C. Changes in the Al–OH–Al infrared bands in the stretching region supported the formation of pillared clays. Migration of Mg, Zn, and Li into the octahedral sites of the smectite was observed as Mg and Zn saturation yielded a d spacing of 15 Å at 200°C which collapsed to 9.6 Å at 400°C. The 14.6 Å peak of the Li-saturated smectite collapsed to 9.6 Å at 200°C while the 15 Å Ca-saturated smectite peak was stable up to 400°C. The unheated Al- and AlFe-pillared smectites adsorbed significantly more aflatoxin B1 from an aqueous suspension than did unpillared clay. In both water and simulated gastric fluid, heat treatment decreased aflatoxin B1 adsorption to pillared smectites, but heat treatment increased aflatoxin B1 adsorption to unpillared smectites. Without heat treatment, smectites saturated with divalent cations (Ca, Mg, Zn) adsorbed more aflatoxin B1 from an aqueous suspension than the smectite saturated with a monovalent cation (Li). Ca-saturated smectite showed the greatest aflatoxin B1 adsorption, 114 g kg–1, from aqueous suspension after 400°C heat treatment. The Zn-, Mg-, and Li-saturated smectites showed maximum aflatoxin adsorption of 107, 93, and 90 g kg–1, respectively, after 200°C heat treatment. From simulated gastric fluid with pepsin, the 200°C heated, Zn-saturated smectite had maximum aflatoxin B1 adsorption of 68 g kg–1. Pillared smectites effectively adsorbed aflatoxin B1 from aqueous suspension, but Ca- and Zn-saturated smectites after heat treatment might improve the selectivity of smectites for aflatoxin B1 over pepsin and enhance the efficacy of smectite as a feed additive.

Syntheses of Na-magadiite were performed under hydrothermal conditions in a water/alcohol medium. It is only possible to obtain a pure and well crystallized magadiite sample using a water/ethanol medium at a water/ethanol molar ratio of ∼0.12. As shown by thermal analysis and 1H liquid nuclear magnetic resonance spectroscopy, ethanol is not incorporated into the magadiite. Intercalation of dodecyl- and hexadecyltrimethylammonium cations in the interlayer space of Na-magadiite at different theoretical ion-exchange rates shows that the experimental ion-exchange rates are in good agreement with the theoretical ones. However, scanning electron micrographs of the sample having a theoretical ion exchange rate of 25–75% shows that the exchanges are not homogeneous (both thin and thick platelets are present). Attempts to obtain a Si-pillared compound starting from C16TMA-magadiite as the host material leads to a microporous compound having a BET surface area of 778 m2g-1.