Infrared spectroscopic, X-ray powder diffraction, diffuse reflectance, and electron-spin resonance examination of homoionic bentonite from Sardinia treated with diazomethane indicates that poly-methylene was formed in the interlayer position. Polymerization can be attributed to the acidic properties of the residual water in the interlamellar space, depending on the nature of the exchanged ion. The presence of an interlayer polymer causes the clay to assume strong hydrophobic properties.

The adsorption of D-glucosamine (2-amino-2-deoxy-D-gIucose) in the protonated or neutral form on homoionic Cu2+-bentonite was investigated by infrared (IR) and electron spin resonance (ESR) spectroscopy and chemical analyses of solution. The results show that the interaction of the glucosamine hydrochloride with the clay complexed a small fraction of interlayer metal ions with neutral amino sugar molecules. In contrast, the adsorption of free glucosamine was much more favorable and resulted in interlayer copper(II) complexes, mainly those in which the ligand was coordinated through amino and deprotonated hydroxyl groups. Part of the amino sugar molecules, however, were transformed into glucosammonium, replacing copper as the saturating ion.

Analytical, spectroscopic, and X-ray powder diffraction techniques were used to investigate the adsorption of the herbicide sodium acifluorfen (acifluorfen = 5-[2-chloro-4-(trifluorornethyl)phenoxy]-2-nitrobenzoic acid) from aqueous solution onto Cu2+-, Al3+-, Fe3+-, and Ca2+-saturated montmorillonite. As indicated by infrared and electron spin resonance spectra, which are coincident with those of the corresponding solid metal complexes, and by the basal spacings, which are the same for all the samples, acifluorfen extracted the exchangeable ions from the clay interlayer and precipitated them on external surfaces. The process involved the replacement of sodium as the saturating ion and was due to the formation of insoluble complexes between the herbicide and polyvalent metal ions.

The adsorption of the pesticide Fluazifop, (RS)-2-[4-[[(5-trinuoromethyl)-2-pyridin-yl]oxy]phenoxy] propanoic acid, on homoionic Cu2+-, Fe3+-, and Al-bentonites was investigated by infrared and electron spin resonance spectroscopy. For comparison, the binary complexes of the acid containing the above ions were prepared and characterized. On the whole, the results show that the interaction of the acid with the clay may have involved both the protonation of the pyridine nitrogen atom, due to a proton transfer from the acid metal-bound water, and the formation of direct bonds between the carboxylate groups and the exchange cations. The extent of these interactions was dependent on the nature of the metal ions, the Cu ions being more effective in producing CHCl3-extractable neutral carboxylate complexes, while Al and Fe favored the formation of species bearing protonated nitrogen atoms and un-dissociated carboxyl groups.

The adsorption from chloroform solution of the herbicide diclofop, (RS)-2-(4-(2,4-dichlorophenoxy)phenoxy)propionic acid, and its methyl ester diclofop-methyl on Cu2+-, Al3+-, and Fe3+-exchanged bentonite samples was investigated. For comparison, the complexes formed by diclofop were synthesized and studied. Diclofop adsorbed on the clays and formed carboxylate bonds to the interlayer ions. Diclofop-methyl also adsorbed, but its interaction involved the formation of hydrogen bonds with water molecules in the interlayer. Traces of diclofop were observed in both the solution and the clays after adsorption of diclofop-methyl, indicating that some hydrolysis of the ester to the corresponding acid occurred. Thus, pesticides forming neutral complexes with interlayer cations in montmorillonite in soils may be extractable by solvents and therefore released into the environment.