The application of electron spin resonance spectroscopy to studies on copper(II) doped pillared clays

Pillared montmorillonites have been synthesized by treating Na-montmorillonite with Al₁₃ or Zr₄-polymer solutions, prepared either by stirred or refluxed methods. The interaction of exchangeable copper(II) with these materials was studied by means of electron spin resonance (ESR) spectroscopy. These studies show that in general both mobile and immobile Cu(II) are present. Also, ESR measurements indicate the presence of a distorted octahedral cupric species in the micropore regions that is chemisorbed to an Al₁₃ or Zr₄ pillar by displacement of some H₂O ligands. The nature of Cu(II) is dependent on the interlayer spacing, the dehydration state of the pillars and the method of preparation, especially of the Zr₄-polymer. At high temperature, copper structure changes from octahedral to square planar which strongly interacts with the dehydroxylated polymers. XPS helps to clarify the studied phenomena.