Institut Pluridisciplinaire Hubert Curien, UMR 7178 CNRS/UdS, 23 rue du Loess, BP 28, 67037 Strasbourg Cedex 2, France.
J Colloid Interface Sci. 2010 Feb 15;342(2):437-44. doi: 10.1016/j.jcis.2009.10.057. Epub 2009 Oct 27.
We have investigated the effect of solution parameters on the adsorption of phosphate ions and on charges and structures, i.e., on the nature of species, at the alpha-Al(2)O(3) colloid/solution interface by using the batch method, zeta potential measurements, and in situ ATR-FTIR spectroscopy. The uptake of phosphate decreases with the extent of surface deprotonation (i.e., pH), imparts negative charges to the colloid surface, and induces IEP shifts showing chemical sorption. Use of complementary techniques provides evidence that phosphate is sorbed at low pH (3.3) by a combination of surface reactions of complexation and precipitation, whose relative contributions depend on phosphate loading. Surface complexation includes fast reactions of ligand exchange with single coordinated hydroxyls, and electrostatic attraction of H(2)PO(4)(-) ions at positively charged surface sites. This is supported by experiments at low coverage showing sharp and linear decrease of zeta potential (i.e., surface charge) with amount of phosphate sorbed. At high coverage, zeta potential values are low and independent of phosphate loading. Formation of surface precipitates of Al-phosphate is inferred from the assignment of the ATR-FTIR absorption band at 1137cm(-1), whose intensity increases with phosphate solution content and reaction time, to the P-O-stretching vibration mode for phosphate sorbed at high concentrations on alpha-Al(2)O(3). In situ ATR-FTIR spectroscopy reveals also structural reorganizations of surface hydroxyls with time, due to surface hydration and to surface precipitation continuing over extended periods along alumina dissolution.
我们通过批量法、动电电位测量和原位 ATR-FTIR 光谱研究了溶液参数对磷酸根离子吸附以及对电荷和结构（即物种的本质）的影响，即在α-Al(2)O(3)胶体/溶液界面上。磷酸根的摄取随表面脱质子化程度（即 pH 值）的增加而减少，使胶体表面带负电荷，并诱导 IEP 偏移，表明化学吸附。使用互补技术提供的证据表明，在低 pH 值（3.3）下，磷酸根通过络合和沉淀的表面反应的组合吸附，其相对贡献取决于磷酸根的负载量。表面络合包括配体与单配位羟基的快速交换反应，以及带正电荷的表面位点对 H(2)PO(4)(-)离子的静电吸引。这得到了在低覆盖率下的实验支持，表明在吸附的磷酸根量增加时，动电电位（即表面电荷）急剧且线性下降。在高覆盖率下，动电电位值较低且与磷酸根的负载量无关。推断出表面磷酸铝沉淀物的形成，是因为在 1137cm(-1)处的 ATR-FTIR 吸收带的分配，其强度随磷酸溶液含量和反应时间的增加而增加，该吸收带对应于在高浓度下吸附在α-Al(2)O(3)上的磷酸根的 P-O 伸缩振动模式。原位 ATR-FTIR 光谱还揭示了由于表面水合作用和氧化铝溶解过程中持续延长的表面沉淀，表面羟基随时间的结构重排。
