One-step approach for synthesis of nanosized Cu-doped zeolite A crystals using the Cu–EDTA-complex

• [Cu(EDTA)]2−-complex was used to synthesized Cu-doped zeolite A nanocrystals.
• FT-IR and Raman spectroscopies provide information on the coordination of Cu2+.
• ESR data shows that Cu2+ ion in a tetragonal-distorted octahedral crystal field.
• The d-spacing between the adjacent lattice planes was enlarged by the complex.
• In situ X-ray and neutron diffraction patterns show changes in the unit cell.

Copper-doped nanosized zeolite A crystals were synthesized by an in situ templating approach using [Cu(EDTA)]2−-complex. The structural properties of the copper containing zeolite crystals were characterized by a suite of different techniques including SEM–EDX, ESR, mid-IR and Far-IR, Raman, in situ XRD and non-ambient neutron powder diffraction. The SEM investigations on the morphology show spheroidal zeolite A crystals with average size ∼200 nm. The asymmetric ESR spectrum shows that the Cu2+ ion is in a tetragonal-distorted octahedral crystal field. FT-IR and Raman spectroscopies provide information on coordination environment of the copper ion. The band due to stretching vibration of C–N bond, where N is coordinated to the copper ion (C–N–Cu), was observed at 1109 cm−1 in the mid-infrared region. The Raman band due to the Cu–O bond is present at 630 cm−1 indicating the coordination of the Cu2+-cation to COO−-group of the EDTA-ion. The XRD data shows an enlarged d-spacing between the adjacent zeolite lattice planes due to the presence of the [Cu(EDTA)]2−-complex in comparison to template-free LTA zeolite structure. LeBail fitting approach on temperature-dependent in situ X-ray and neutron diffraction profiles have demonstrated the expansion of the zeolite cell during the thermal treatment followed by subsequent contraction with the decomposition of the organic template.

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