Yang Xiaofang, Roonasi Payman, Holmgren Allan
Division of Chemistry, Department of Chemical Engineering and Geosciences, Luleå University of Technology, Luleå, Sweden.
J Colloid Interface Sci. 2008 Dec 1;328(1):41-7. doi: 10.1016/j.jcis.2008.08.061. Epub 2008 Sep 6.
The sorption of sodium silicate by synthetic magnetite (Fe3O4) at different pH conditions (pH 7-11) and initial silicate concentrations (1 x 10(-3) and 10 x 10(-3) molL(-1)) was studied using in situ attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. The analysis of infrared spectra of sodium silicate in solution as well as adsorbed on magnetite nano-particles clearly showed the evolution of different silicate species depending on pH and silica concentration. The silicate concentration studied (10 x 10(-3) molL(-1)) contained polymeric or condensed silicate species at lower pH as well as monomers at high pH, as evident from infrared spectra. Condensation of monomers resulted in an increased intensity of absorptions in the high frequency part (>1050 cm(-1)) of the spectral region, which contains information about both silicate in solution and sorbed silicate viz. 1300 cm(-1)-850 cm(-1). In the pH range studied, infrared spectra of sorbed silicate and sorbed silicate during desorption both indicated the presence of different types of surface complexes at the magnetite surface. The sorption mechanism proposed is in accordance with a ligand exchange reaction where both monodentate and bidentate complexes could exist at low surface loading level, the relative proportion of the complexes being due to both pH and concentration in solution. Oligomerization occurred on the magnetite surface at higher surface loading.
利用原位衰减全反射傅里叶变换红外光谱（ATR-FTIR）研究了合成磁铁矿（Fe3O4）在不同pH条件（pH 7 - 11）和初始硅酸盐浓度（1×10⁻³和10×10⁻³ molL⁻¹）下对硅酸钠的吸附情况。对溶液中以及吸附在磁铁矿纳米颗粒上的硅酸钠的红外光谱分析清楚地表明，不同硅酸盐物种的演变取决于pH值和二氧化硅浓度。从红外光谱可以明显看出，所研究的硅酸盐浓度（10×10⁻³ molL⁻¹）在较低pH值下含有聚合或缩合的硅酸盐物种，在高pH值下含有单体。单体的缩合导致光谱区域高频部分（>1050 cm⁻¹）吸收强度增加，该区域包含溶液中硅酸盐和吸附硅酸盐的信息，即1300 cm⁻¹ - 850 cm⁻¹。在所研究的pH范围内，吸附硅酸盐和解吸过程中吸附硅酸盐的红外光谱均表明磁铁矿表面存在不同类型的表面络合物。提出的吸附机制符合配体交换反应，在低表面负载水平下可能同时存在单齿和双齿络合物，络合物的相对比例取决于pH值和溶液浓度。在较高表面负载下，磁铁矿表面发生了低聚反应。
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