Synthesis and characterization of layered double hydroxides (LDHs) with intercalated chromate ions

Journal Article · Tue Jun 05 04:00:00 EDT 2007 · Materials Research Bulletin

DOI:https://doi.org/10.1016/j.materresbull.2006.09.021· OSTI ID:21000647

Prasanna, Srinivasa V ^[1]; Kamath, P Vishnu ^[1]; Shivakumara, C ^[2]

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1. Department of Chemistry, Central College, Bangalore University, Bangalore, Karnataka 560001 (India)
2. Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560012 (India)

Chromate intercalated layered double hydroxides (LDHs) having the formula M{sup II} {sub 6}M'{sup III} {sub 2}(OH){sub 16}CrO{sub 4}.4H{sub 2}O (M{sup II} = Ca, Mg, Co, Ni, Zn with M'{sup III} = Al and M{sup II} = Mg, Co, Ni with M'{sup III} = Fe) have been prepared by coprecipitation. The products obtained are replete with stacking disorders. DIFFaX simulations show that the stacking disorders are of three kinds: (i) turbostratic disorder of an originally single layered hexagonal (1H) crystal (ii) random intergrowth of polytypes with hexagonal (2H) and rhombohedral (3R) symmetries and (iii) translation of randomly chosen layers by (2/3, 1/3, z) and (1/3, 2/3, z) leading to stacking faults having a local structure of rhombohedral symmetry. IR spectra show that the CrO{sub 4} {sup 2-} ion is incorporated either in the T {sub d} or in the C {sub 3v} symmetry. The interlayer spacing in the latter case is 7.3 A characteristic of a single atom thick interlayer showing that the CrO{sub 4} {sup 2-} ion is grafted to the metal hydroxide slab. On thermal treatment, the CrO{sub 4} {sup 2-} ion transforms into Cr(III) and is incorporated into the spinel oxide or phase separates as Cr{sub 2}O{sub 3}. In the LDH of Mg with Al, Cr(III) remains in the MgO lattice as a defect and promotes the reconstruction of the LDH on soaking in water. In different LDHs, 18-50% of the CrO{sub 4} {sup 2-} ion is replaceable with carbonate anions showing only partial mineralization of the water-soluble chromate. The extent of replaceable chromates depends upon the solubility of the corresponding LDH, which in turn is determined by the solubility of the MCrO{sub 4}. These studies have profound implications for the possible use of LDHs for chromate amelioration in green chemistry.

• OSTI ID: 21000647
• Journal Information: Materials Research Bulletin, Journal Name: Materials Research Bulletin Journal Issue: 6 Vol. 42; ISSN MRBUAC; ISSN 0025-5408
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ANIONS
CARBONATES
CHEMICAL PREPARATION
CHROMATES
CHROMIUM OXIDES
COPRECIPITATION
CRYSTALS
HEAT TREATMENTS
HYDROXIDES
INFRARED SPECTRA
MAGNESIUM OXIDES
METALS
MINERALIZATION
SLABS
SPINELS
STACKING FAULTS
SYMMETRY
X-RAY DIFFRACTION