TY - JOUR

T1 - Glycine buffered synthesis of layered iron(II)-iron(III) hydroxides (green rusts)

AU - Yin, Weizhao

AU - Huang, Lizhi

AU - Pedersen, Emil Bjerglund

AU - Frandsen, Cathrine

AU - Hansen, Hans Chr. Bruun

PY - 2017

Y1 - 2017

N2 - Layered FeII-FeIII hydroxides (green rusts, GRs) are efficient reducing agents against oxidizing contaminants such as chromate, nitrate, selenite, and nitroaromatic compounds and chlorinated solvents. In this study, we adopted a buffered precipitation approach where glycine (GLY) was used in the synthesis of sulfate-interlayered GR (GRSO4) by aerial oxidation of FeII or co-precipitation by adding FeIII salt to an aqueous solution of FeII at constant pH. In both the oxidation and the co-precipitation methods pure crystalline GRSO4 was precipitated in the presence of 70mM GLY (pH 8.0), whereas in the absence of GLY, synthesis failed under similar conditions. Gycine functions as both a pH buffer and a ligand; FeII-GLY complexes serve as a source of base (FeII-GLY+H2O→FeII +H-GLY+OH-) during GR formation, supplying about 45% of the total base required for the synthesis. The GLY buffer decreases pH fluctuations during base addition and hence allows for fast GRSO4 precipitation, minimizing byproduct formation. The use of other pH buffers [4-(2-hydroxyethyl)piperazine-1-ethanesulfonic acid and 2-amino-2-(hydroxymethyl)-1,3-propanediol] was also tested but failed. Mössbauer spectroscopy, X-ray diffraction, Fourier transform infrared, transmission electron microscopy, and FeII measurements confirmed the purity, stoichiometry, and pyroaurite-type structure of the obtained GRSO4. The formula of GRSO4 was found to be FeII 4.08FeIII 1.98(OH)11.6(SO4)1.00, and the tabular GR crystals had a lateral size of 100-500nm and a thickness of about 40nm. Upscaling of the synthesis by either 25 times in volume or 20 times in FeII concentration resulted in pure GRSO4 products. Compared with the conventional unbuffered GRSO4 synthesis method, the present method can provide pure products with a controllable, fast, and low-cost process.

AB - Layered FeII-FeIII hydroxides (green rusts, GRs) are efficient reducing agents against oxidizing contaminants such as chromate, nitrate, selenite, and nitroaromatic compounds and chlorinated solvents. In this study, we adopted a buffered precipitation approach where glycine (GLY) was used in the synthesis of sulfate-interlayered GR (GRSO4) by aerial oxidation of FeII or co-precipitation by adding FeIII salt to an aqueous solution of FeII at constant pH. In both the oxidation and the co-precipitation methods pure crystalline GRSO4 was precipitated in the presence of 70mM GLY (pH 8.0), whereas in the absence of GLY, synthesis failed under similar conditions. Gycine functions as both a pH buffer and a ligand; FeII-GLY complexes serve as a source of base (FeII-GLY+H2O→FeII +H-GLY+OH-) during GR formation, supplying about 45% of the total base required for the synthesis. The GLY buffer decreases pH fluctuations during base addition and hence allows for fast GRSO4 precipitation, minimizing byproduct formation. The use of other pH buffers [4-(2-hydroxyethyl)piperazine-1-ethanesulfonic acid and 2-amino-2-(hydroxymethyl)-1,3-propanediol] was also tested but failed. Mössbauer spectroscopy, X-ray diffraction, Fourier transform infrared, transmission electron microscopy, and FeII measurements confirmed the purity, stoichiometry, and pyroaurite-type structure of the obtained GRSO4. The formula of GRSO4 was found to be FeII 4.08FeIII 1.98(OH)11.6(SO4)1.00, and the tabular GR crystals had a lateral size of 100-500nm and a thickness of about 40nm. Upscaling of the synthesis by either 25 times in volume or 20 times in FeII concentration resulted in pure GRSO4 products. Compared with the conventional unbuffered GRSO4 synthesis method, the present method can provide pure products with a controllable, fast, and low-cost process.

KW - Glycine ligand

KW - Green rust sulfate

KW - Homogenous precipitation

KW - Layered double hydroxides (LDHs)

U2 - 10.1016/j.jcis.2016.11.076

DO - 10.1016/j.jcis.2016.11.076

M3 - Journal article

C2 - 27894515

AN - SCOPUS:85007107011

VL - 497

SP - 429

EP - 438

JO - Journal of Colloid and Interface Science

JF - Journal of Colloid and Interface Science

SN - 0021-9797

ER -