Characterization of chromium oxide hydrate gel

New sol–gel synthetic route to transition and main-group metal oxide aerogels using inorganic salt precursors

“…The particles that make up the gel appear to be uniform and not a mixture of crystalline phases as has been reported by Saraswat et al for the synthesis of chromia gel by precipitation from aqueous solution with base. [5] Although straightforward, the base addition method is somewhat time consuming as the gel must be washed and the water exchanged for a solvent that is miscible with CO 2 (l).…”

“…Microscopy results from a report by Saraswat et al on a chromium oxide hydrate gel, prepared by precipitation with hydroxide, showed the presence of at least three different phases, two of which were crystalline. [5] The gel shown in Figure 2 appeared amorphous, as is did not diffract electrons under the electron microscope. Table 2 summarizes the surface areas, pore volumes, and average pore sizes for some chromia aerogels.…”

“…[2] For example, vibrant chromia (the generic term for hydrated chromic oxide of unknown hydration) gels have been prepared by such methods by several researchers. [3][4][5] Although the preparation of aerogels and xerogels of chromia has been previously accomplished, there are relatively few reports in the literature describing it. [6][7][8] The main synthetic route employed relies on high temperature (~300 °C) supercritical solvent processing.…”

Abiotic reduction of Cr(VI) by humic acids derived from peat and lignite: kinetics and removal mechanism

“…Cr K-edge XAS spectra were collected from selected humic acid samples recovered from the low concentration Cr(VI) batch experiments (the ‘Cr(VI)-humic acid batch experiments’ section) on beamlines I18 and B18 at the Diamond Light Source, UK. Reference spectra were also collected for standard laboratory chemicals and precipitated Cr-hydroxide (Saraswat and Vajpe 1984). X-ray absorption near edge (XANES) spectra were summed and normalised using Athena v0.9.24 (Ravel and Newville 2005), and background subtracted extended X-ray absorption fine structure (EXAFS) spectra were fitted to model coordination environments using Artemis v0.9.24 (see SI sections S1.2 and S1.3 for details).…”

Differential scanning calorimetry studies on aged iron(III)-chromium(III)-hydroxide coprecipitates

“…Therma/Ana/., 36~ 1990 water in chromium hydroxide is to be associated with the availability of a larger population of coordinatively unsaturated chromium ions [11] in the chromium hydroxide, which has a high surface area, and therefore greater affinity for water ligands. This may be better seen from a consideration of the bulk compositions of the hydroxides: CreO3.4.4H20 [14] and FezO3.2.2.H20 [15]. A mierostructural characterization of the coprecipitates using electron microscopy [2] indicated that:…”