Preparation and Properties of Nickel and Iron Oxides obtained by Calcination of Layered Double Hydroxides

Abstract

A constant pH precipitation method has been applied to obtain solids with Ni/Fe molar ratios of 2/1, 3/2, 1/1, 2/3, and 1/2. In all cases, a phase with the hydrotalcite-like structure is obtained, containing Ni II and Fe III in the brucite-like layers and carbonate in the interlayer, and, for samples with a Ni/Fe molar ratio lower than 2/1, amorphous hydrated iron oxides, undetected by X-ray diffraction, are also formed. The solids have been characterized by element chemical analysis, powder X-ray diffraction, differential thermal analysis, thermogravimetric and differential thermogravimetric analysis, FT-IR spectroscopy, temperature-programmed reduction and assessment of specific surface area by nitrogen adsorp-* Prof. V. Rives tion at Ϫ196°C. In all cases reduction leads to zero-valent state for the metals, reduced nickel particles probably favouring reduction of Fe III species; the specific surface area increases with the iron content, probably due to the amorphous nature of the hydrated iron oxides formed. Calcination at 1200°C in air leads to well crystallized solids, formed by NiFe 2 O 4 spinel and, additionally, rocksalttype NiO for Ni/Fe ratios larger than 1/2. In this way, solids with tailored compositions of these two phases can be prepared.

Fabrication of Ni‐Fe LDH/GF anode for enhanced Fe(III) regeneration in fuel cell‐assisted chelated‐iron dehydrosulfurization process

“…Figure presents the FT‐IR spectrum of the composite. The band located at around 3360 cm −1 is assigned to ν(OH) stretching vibration of hydroxyl groups and water molecules, whose bending vibration is responsible for the medium‐intensity band at 1630 cm −1 . The split bands at 1447 and 1370 cm −1 are ascribed to the anti‐symmetric stretching vibration of CO 3 2− species.…”

“…The band located at around 3360 cm −1 is assigned to (OH) stretching vibration of hydroxyl groups and water molecules, whose bending vibration is responsible for the medium-intensity band at 1630 cm −1 . 27,28 The split bands at 1447 and 1370 cm −1 are ascribed to the anti-symmetric stretching vibration of CO 3 2− species. The bands at low frequency region (below 1000cm −1 ) are attributed to hydroxometallic stretching and bending vibrations in brucite-type layer.…”

NiFe Layered‐Double‐Hydroxide‐Derived NiO‐NiFe2O4/Reduced Graphene Oxide Architectures for Enhanced Electrocatalysis of Alkaline Water Splitting

“…NiFe‐LDH/rGO was synthesized by the coprecipitation method from nickel and iron precursors salts (Ni 2+ /Fe 3+ molar ratio of 3:1) and graphene oxide (GO) homogeneous solutions. NiO‐NiFe 2 O 4 /rGO nanohybrids were then prepared by a facile one‐pot low‐temperature calcination route at 500 °C with NiFe‐LDH/rGO as the precursor; the calcination temperature is much lower than that of 1200 °C reported previously . Interestingly, a two‐step weight loss is observed below 400 °C in the thermogravimetric analysis (TGA) curve of NiFe‐LDH (Figure S1, Supporting Information).…”

“…NiO-NiFe 2 O 4 /rGO nanohybrids were then prepared by af acile onepot low-temperature calcination route at 500 8Cw ith NiFe-LDH/rGO as the precursor;t he calcination temperature is much lower than that of 1200 8Cr eported previously. [14] Interestingly, at wo-step weight loss is observed below 400 8Ci n the thermogravimetric analysis (TGA) curve of NiFe-LDH (…”

Controlling the Synthesis Conditions for Tuning the Properties of Hydrotalcite-Like Materials at the Nano Scale

“…89-0460], significant differences are observed for the relative intensities and width of the peaks. In any case, the spacing for the peaks are due to diffraction by the planes (003), close to 2θ = 10 • , (006), close to 2θ = 23 • , and (110); the first one of the doublet recorded just above 2θ = 60 • , and it has been used to calculate the lattice parameters of the samples, c and a, respectively, assuming a 3R polytype [40,41] according to the formulae c = (3/2) [d 003 + 2d 006 ] and a = 2d 110 [42]. The height of the repeating unit (i.e., one brucite-like layer and one interlayer space) corresponds to the d-value and is one third of the lattice parameter c, while parameter a corresponds to the average metal cation-metal cation distance (M − M) within a brucite-like layer.…”