Surface charge and surface chemical characteristics of magnetites substituted with nickel, cobalt and chromium

Mathur, B.S.; Venkataramani, B.

doi:10.1016/s0927-7757(97)00297-5

Cited by 5 publications

(2 citation statements)

References 36 publications

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“…Figure 2 shows that the pKa values for TEEN, TRISd, and TEAd are each well below those estimated for -:CCl3. Likewise, the pKa values for dissociation of the magnetite surface species FeOH2 and FeOH have been estimated at 5.6 (61) and 8.5 (62), respectively. Therefore, the -:CCl3 could readily extract a proton from any of the buffer molecules or surface sites and would be at a minimum an effective competitor for the protons in water.…”

Section: Resultsmentioning

confidence: 99%

Influence of Amine Buffers on Carbon Tetrachloride Reductive Dechlorination by the Iron Oxide Magnetite

Danielsen

Gland

Hayes

2004

Environ. Sci. Technol.

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The influence of amine buffers on carbon tetrachloride (CCl4) reductive dechlorination by the iron oxide magnetite (FeIIFeIII2O4) was examined in batch reactors. A baseline was provided by monitoring the reaction in a magnetite suspension containing NaCl as a background electrolyte at pH 8.9. The baseline reaction rate constant was measured at 7.1 x 10(-5)+/-6.3 x 10(-6) L m(-2) h(-1). Carbon monoxide (CO) was the dominant reaction product at 82% followed by chloroform (CHCl3) at 5.2%. In the presence of 0.01 M tris-(deuteroxymethyl)aminomethane (TRISd), the reaction rate constant nearly tripled to 2.1 x 10(-4)+/-6.5 x 10(-6) L m(-2) h(-1) but only increased the CHCl3 yield to 11% and did not cause any statistically significant changes to the CO yield. Reactions in the presence of triethylammonium (TEAd) (0.01 M) increased the rate constant by 17% to 8.6 x 10(-5)+/-8.1 x 10(-6) L m(-2) h(-1) but only increased the CHCl3 yield to 8.8% while leaving the CO yield unchanged. The same concentration of N,N,N',N'-tetraethylethylenediamine (TEEN) increased the reaction rate constant by 18% to 8.7 x 10(-5)+/-4.8 x 10(-6) L m(-2) h(-1) but enhanced the CHCl3 yield to 34% at the expense of the CO yield that dropped to 35%. Previous work has shown that CHCl3 can be generated either through hydrogen abstraction by a trichloromethyl radical (radical CCl3), or through proton abstraction by the trichlorocarbanion (-:CCl3). These two possible hydrogenolysis pathways were examined in the presence of deuterated buffers. Deuterium tracking experiments revealed that proton abstraction by the trichlorocarbanion was the dominant hydrogenolysis mechanism in the magnetite-buffered TRISd and TEAd systems. The only buffer that had minimal influence on both the reaction rate and product distribution was TEAd. These results indicate that buffers should be prescreened and demonstrated to have minimal impact on reaction rates and product distributions prior to use. Alternatively, it may be preferable, to utilize the buffer capacity of the solids to avoid organic buffer interactions entirely.

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Section: Resultsmentioning

confidence: 99%

Influence of Amine Buffers on Carbon Tetrachloride Reductive Dechlorination by the Iron Oxide Magnetite

Danielsen

Gland

Hayes

2004

Environ. Sci. Technol.

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“…Thus, working on synthesized solid particles with a composition similar to those found in coolant circuits, for example magnetite, is a widespread method [13,14]. A pure and well crystallized magnetite is also more suitable for the study of basic sorption and redox properties.…”

Section: Introductionmentioning

confidence: 99%