In Situ Infrared Speciation of Adsorbed Carbonate on Aluminum and Iron Oxides
In Situ Infrared Speciation of Adsorbed Carbonate on Aluminum and Iron Oxides
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DOI：
10.1346/ccmn.1997.0450605
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发表时间：
1997-12
影响因子：
2.2
通讯作者：
C. Su;D. Suarez
中科院分区：
文献类型：
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作者：
C. Su;D. Suarez
溶解无机碳在土壤矿物表面的吸附机制还不清楚。传统的红外（IR）研究吸附物种的无机碳使用空气干燥的样品可能无法揭示真正的物种在固体/水界面悬浮液。本研究的目的是获得信息的界面碳酸盐形态之间的固体和水相。用电泳和原位衰减全反射傅里叶变换红外光谱（ATR-FTIR）研究了碳酸氢根和碳酸根离子与X射线无定形（am）Al和Fe氧化物、三水铝石（γ−Al（OH）3）和针铁矿（α-FeOOH）的相互作用。碳酸盐的存在降低了矿物的电子迁移率，降低了矿物的零电荷点（PZC），这意味着专属性吸附。由于与Al和Fe氧化物表面的相互作用，通过降低阴离子对称性来支持碳酸氢盐和碳酸盐的内球络合。当固体与NaHCO 3或Na 2CO 3溶液反应时，在pH 4.1-7.8的am-Al（OH）3/水溶液中仅鉴定出络合的单齿碳酸盐。Am-Al（OH）3与1.0 M Na 2CO 3反应24 h后，转化为结晶的碱式碳酸铝钠、片钠铝石[NaAl（CO 3）（OH）2]和三羟铝石（α-Al（OH）3）。三水铝石对碳酸根的吸附量远小于am-Al（OH）_3，因此碳酸根在三水铝石上的红外吸收较弱。单齿碳酸盐可能也是三水铝石上的络合物。有证据表明，在悬浮液中的am-Fe（OH）3的界面区域中存在表面络合的碳酸氢盐和碳酸盐物种，并且它们的相对分布依赖于溶液pH。只有单齿碳酸盐被发现在1.0 M NaHCO 3中的针铁矿的界面区域。用配体交换反应描述了碳酸氢根和碳酸根与铝、铁氧化物表面官能团的相互作用。
Surface adsorption mechanisms of dissolved inorganic carbon species on soil minerals are not well understood. Traditional infrared (IR) study of adsorbed species of inorganic carbon using air-dried samples may not reveal true species in the solid/water interface in suspension. The purpose of this study was to obtain information on interfacial carbonate speciation between solid and aqueous phases. The interaction of bicarbonate and carbonate ions with X-ray amorphous (am) Al and Fe oxides, gibbsite (γ−Al(OH)3) and goethite (α-FeOOH) was examined by electrophoresis and in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. The presence of carbonate lowered the electropho-retic mobility and decreased the point of zero charge (PZC) of all minerals, implying specific adsorption. Inner-sphere complexation of bicarbonate and carbonate was supported by a lowering in the anion symmetry due to the interaction with Al and Fe oxide surfaces. Only complexed monodentate carbonate was identified in am-Al(OH)3/aqueous solution at pH 4.1-7.8 when the solid was reacted with either NaHC03 or Na2CO3 solutions. Am-Al(OH)3 was transformed to a crystalline sodium aluminum hydroxy carbonate, dawsonite [NaAl(CO3)(OH)2], and bayerite (α-Al(OH)3) after reacting with 1.0 M Na2CO3 for 24 h. Gibbsite adsorbed much less carbonate than am-Al(OH)3 such that adsorbed carbonate on gibbsite gave weak IR absorption. It is probable that monodentate carbonate is also the complexed species on gibbsite. Evidence suggesting the presence of both surface complexed bicarbonate and carbonate species in the interfacial region of am-Fe(OH)3 in suspension and the dependence of their relative distribution on solution pH is shown. Only monodentate carbonate was found in the interfacial region of goethite in 1.0 M NaHCO3. A ligand exchange reaction was proposed to describe the interaction of bicarbonate and carbonate with the surface functional groups of Al and Fe oxides.