茶树叶与根表面的XPS表征

利用X射线光电子能谱(XPS)研究了茶树叶与根的表面化学组成与结构。结果表明，茶树表面主要由C, O, N和Al等四种元素组成，在茶树叶远轴面还有少量的P和F。通过查阅标准图谱数据库、参照木材表面XPS分析结果，对茶树表面测得的C1s结合能采用曲线拟合与分峰，得到三种形态：结合能为285 eV的是C1，来自C—C或C—H，代表角质、蜡质等脂类化合物；C2的结合能在286.35 eV（近轴面）和286.61 eV（远轴面），是能够与氧形成单键的C—O，主要源于表面的纤维素；C3的结合能为288.04 eV（近轴面）和288.09 eV（远轴面），为CO基团标志，综合N（1s）的结合能（399～401 eV）和O（1s）的分峰情况，为蛋白质的酰基标志。茶树根表面除含有与叶表面相同的C1(结合能285 eV)、C2（结合能286.49 eV）和C3（结合能288.78 eV）所代表的角质、蜡质、纤维素和蛋白质之外，还出现了结合能为283.32 eV的C5。由于其结合能低于C1，推测为茶树根表面的有机金属形态。茶树叶和根表面没有木材表面具有的羧基C4，说明根系分泌的有机酸游离存在于根表面。对茶树表面O（1s）图谱的拟合结果与C（1s）结果相吻合。计算不同C和O形态所占的比例得知，茶树叶面远轴面含氧基团多于近轴面，呈较高的氧化状态，因此远轴面化学性质较活泼；与叶相比，茶树根的角质和蜡质含量显著降低，含氧基团相对增多，因此化学性质较活泼，适于水分子和其他溶质分子通过。由于蛋白质含量为根表面＞远轴面＞近轴面，表明根表面的湿润度高于叶表面，而远轴面湿润度高于近轴面。存在于茶树表面Al的结合能均大于单质铝72.7 eV，在73.50 eV以上，为Al₂O₃形态，这将增大茶树表面的吸附作用。由于根表面Al₂O₃含量高于叶面，显示根具有更强的吸附能力。

XPS Analysis of Tea Plant Leaf and Root Surface

XPS was applied to analyze the surface chemical composition and structure of the tea plant leaf and root. It was detected that the surface is made up of mainly 4 elements：C, O, N and Al, with little P and F in abaxial leaf. Based on the botanic epidermis structure and the chemical composition, with the help of the standard spectrum data bank on line and the wood XPS study results, and through line Gaussian and Lorentizian the mixed, the binding energy of C（1s） of the leaf surface was classified as 3 types: the first was C1, with the electron binding energy of 285 eV, from C—C or C—H group, representing lipid compound like cutin and wax. C2 with the binding energy of 286.35 eV in the adaxial and 286.61 eV in the abaxial, came from the single bond of carbon and oxygen C—O, mainly standing for cellulose. C3 with the binding energy of approximately 288 eV (288.04 eV in adaxial and 288.09 eV in abaxial) was the sign of CO group, which is acyl in protein with the confirmation of N（1s）（399-401 eV）and O（1s） analyses. In the root surface, besides the same compounds of cutin and wax (C1, binding energy 285 eV), cellulose (C2, binding energy 286.49 eV) and protein （C3，binding energy 288.78 eV）as in the leaf, there appeared C5 type with the binding energy of 283.32 eV . Because it was lower than C1, it was estimated as carbon linking to metal. Both the leaf and the root surfaces didn’t have C4, a type of OCO, which is common in wood surface with the highest oxidated carbon of 289-289.5 eV binding energy, indicating that organic acid secreted by the root existed freely on the root surface, without any chemical association with the surface compounds. The results of the separated spectrum of O（1s） supported the above C（1s） results. By the ratio of each type of C, there were more oxygen groups in the abaxial than in the adaxial, implicating more active chemical properties on the abaxial. Compared with the leaf, cutin and wax was little in the root and oxygen groups were many, verifying more active chemical property on the root surface and more water and solute molecules passing. Again the protein content was in the order of root, abaxial and adaxial, indicating the same order of the wetness degree. Higher binding energy of Al than 73.50 eV showed oxidized aluminum in tea plant surface, which might enhance the absorption, and more oxidized aluminum in the root meants that it has more powerful absorbability.