Department of Plant and Environmental Sciences, Faculty of Life Sciences, University of Copenhagen, Thorvaldsensvej 40, DK-1871 Frederiksberg C, Denmark.
Department of Plant and Environmental Sciences, Faculty of Life Sciences, University of Copenhagen, Thorvaldsensvej 40, DK-1871 Frederiksberg C, Denmark; Department of Chemistry, Aarhus University, Langelandsgade 140, 8000 Aarhus C, Denmark.
J Colloid Interface Sci. 2017 Jul 1;497:429-438. doi: 10.1016/j.jcis.2016.11.076. Epub 2016 Nov 22.
Layered Fe-Fe 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 (GR) by aerial oxidation of Fe or co-precipitation by adding Fe salt to an aqueous solution of Fe at constant pH. In both the oxidation and the co-precipitation methods pure crystalline GR 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; Fe-GLY complexes serve as a source of base (Fe-GLY+HO→Fe+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 GR 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 Fe measurements confirmed the purity, stoichiometry, and pyroaurite-type structure of the obtained GR. The formula of GR was found to be FeFe(OH)(SO), 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 Fe concentration resulted in pure GR products. Compared with the conventional unbuffered GR synthesis method, the present method can provide pure products with a controllable, fast, and low-cost process.
层状 Fe-Fe 氢氧化物（绿锈，GR）是一种有效的还原剂，可以还原氧化污染物，如铬酸盐、硝酸盐、亚硒酸盐和硝基芳香族化合物以及氯化溶剂。在这项研究中，我们采用了缓冲沉淀方法，其中甘氨酸（GLY）用于通过空气氧化 Fe 或在恒定 pH 值下向 Fe 盐的水溶液中添加 Fe 盐来合成硫酸盐插层 GR（GR）。在氧化和共沉淀两种方法中，在存在 70mM GLY（pH 8.0）的情况下，都沉淀出纯结晶 GR，而在不存在 GLY 的情况下，在类似条件下合成失败。甘氨酸既是 pH 缓冲剂又是配体；Fe-GLY 配合物在 GR 形成过程中充当碱源（Fe-GLY+HO→Fe+H-GLY+OH），提供合成所需总碱的约 45%。GLY 缓冲剂减少了碱添加过程中的 pH 波动，从而允许快速沉淀 GR，最大限度地减少副产物的形成。还测试了其他 pH 缓冲剂[4-(2-羟乙基)哌嗪-1-乙磺酸和 2-氨基-2-(羟甲基)-1,3-丙二醇]，但均未成功。穆斯堡尔光谱、X 射线衍射、傅里叶变换红外、透射电子显微镜和 Fe 测量证实了获得的 GR 的纯度、化学计量比和焦绿石型结构。GR 的化学式被发现为 FeFe(OH)(SO)，并且板状 GR 晶体的横向尺寸为 100-500nm，厚度约为 40nm。通过体积放大 25 倍或 Fe 浓度放大 20 倍进行合成放大，得到了纯 GR 产物。与传统的无缓冲 GR 合成方法相比，本方法可以提供具有可控、快速和低成本工艺的纯产物。
