Juhl K M S, Bovet N, Hassenkam T, Dideriksen K, Pedersen C S, Jensen C M, Okhrimenko D V, Stipp S L S
Nano-Science Center, Department of Chemistry, University of Copenhagen , Copenhagen, Denmark.
Langmuir. 2014 Jul 29;30(29):8741-50. doi: 10.1021/la500791m. Epub 2014 Jul 15.
We investigated the adhesion of two functional groups to α-alumina as a model for the adsorption of organic molecules on clay minerals. Interactions between organic compounds and clay minerals play an important role in processes such as drinking water treatment, remediation of contaminated soil, oil recovery, and fabricating complicated nanomaterials, and there have been claims that organic compound-clay mineral interaction created the ordering that is necessary for the genesis of life. In many organisms, interaction between organic molecules and biominerals makes it possible to control the growth of bones, teeth, and shells. Adhesion of carboxylic acid, -COO(H), and pyridine, -C5H5N(H(+)), on the {0001} plane of α-alumina wafers has been investigated with atomic force microscopy (AFM) in chemical force mapping (CFM) mode. Both functional groups adhered to α-alumina in deionized water at pH < 5, and adhesion decreased as NaCl or CaCl2 concentration increased. X-ray photoelectron spectroscopy (XPS) showed that Na(+) and Ca(2+) adsorbed to the α-alumina surface at pH < 5, decreasing surface interaction with the carboxylic acid and pyridine groups. We interpret the results as evidence that the tips adhere to alumina through hydrogen bonding when only water is present. In solutions containing NaCl and CaCl2, cations are adsorbed but Cl(-) is not. When NaCl solutions are replaced by CaCl2, Ca(2+) replaces Na(+), but rinsing with ultrapure deionized water (pH 5.6) could not restore the original protonated surface. The results demonstrate that the alumina surface at pH 3 has a higher affinity for inorganic cations than for -COO(H) or -C5H5N(H(+)), in spite of the known positive surface charge of α-alumina {0001} wafers. These results demonstrate that solution salinity plays an important role in surface properties, controlling surface tension (i.e., contact angle) and adsorption affinity on α-alumina and, by analogy, on clay minerals.
我们研究了两个官能团与α-氧化铝的粘附情况，以此作为有机分子在粘土矿物上吸附的模型。有机化合物与粘土矿物之间的相互作用在诸如饮用水处理、污染土壤修复、石油开采以及制造复杂纳米材料等过程中起着重要作用，并且有人声称有机化合物 - 粘土矿物相互作用产生了生命起源所必需的有序性。在许多生物体中，有机分子与生物矿物之间的相互作用使得控制骨骼、牙齿和贝壳的生长成为可能。我们利用原子力显微镜（AFM）的化学力映射（CFM）模式研究了羧酸（-COO(H)）和吡啶（-C5H5N(H(+))）在α-氧化铝晶片{0001}面上的粘附情况。在pH < 5的去离子水中，这两个官能团都能粘附在α-氧化铝上，并且随着NaCl或CaCl2浓度的增加，粘附力下降。X射线光电子能谱（XPS）表明，在pH < 5时，Na(+)和Ca(2+)吸附在α-氧化铝表面，减少了与羧酸和吡啶基团的表面相互作用。我们将这些结果解释为仅存在水时探针通过氢键粘附在氧化铝上的证据。在含有NaCl和CaCl2的溶液中，阳离子被吸附，但Cl(-)不被吸附。当NaCl溶液被CaCl2取代时，Ca(2+)取代了Na(+)，但用超纯去离子水（pH 5.6）冲洗并不能恢复原来的质子化表面。结果表明，尽管已知α-氧化铝{0001}晶片表面带正电荷，但在pH 3时，氧化铝表面对无机阳离子的亲和力高于对 -COO(H)或 -C5H5N(H(+))的亲和力。这些结果表明，溶液盐度在表面性质中起着重要作用，控制着α-氧化铝以及类推到粘土矿物上的表面张力（即接触角）和吸附亲和力。
