有机酸在γ-Al_2O_3表面自发单层分散及苯甲酸-γ-Al_2O_3表面结构的研究

Spontaneous Monolayer Dispersion of Organic Acids on the Surface of γ-Al_2O_3 and Studies on Surface Structure of Benzoic-γ-Al_2O_3 System

有机酸如苯甲酸,水杨酸,邻-或对-苯二甲酸,酒石酸均可在γ-Al_2_3表面自发单层分散,分散的临界温度取决于有机酸分子中极性基团的数目和极性的强弱.XRD,Raman,FT-IR,UV-vis和TG对苯甲酸-γ-Al_2O_3体系的表征结果表明,苯甲酸在室温下即可在γ-Al_2O_3表面自发单层分散;分散后,苯甲酸分子间的氢键缔合结构垮塌;苯甲酸的羧基与γ-Al_2O_3表面羟基发生相互作用并缩水形成类似羧酸盐的结构;分子中的苯环与载体表面没有直接的相互作用.XRD相定量测得的分散阈值为1.1mmol苯甲酸/100m^2γ-Al_2O_3,与按苯环垂直表面计算所得的最大分散容量1.2mmol/100m^2相近.

Many organic acids, such as benzoic acid, salicylic acid, o - or p-?phthalic acid and tartaric acid, can disperse spontaneously onto the surface of γ - Al2O3 in a monolayer state. The critical dispersion temperature depends on the number and polarity of the polar groups in the molecule. The structure of benzoic acid - γ - Al2O3 system has been characterized by XRD, Raman, FT - IR, UV - vis and TG. The results show that benzoic acid can disperse onto the surface of γ - Al2O3 very readily, even at room temperature. After dispersion, the H- bond association structure among benzoic acid molecules collapses and the carboxyl groups react with the surface hydroxyl groups of γ - Al2O3 to form a salt - like structure on the surface. There is not any direct interaction between the benzene ring of benzoic acid molecule and the surface of γ - Al2O3. The dispersion threshold determined by XRD is 1.1 mmol benzoic acid /100m2 γ - Al2O3, which is very close to the utmost monolayer dispersion capacity 1. 2mmol/100m2 calculated according to a model that the benzene ring in benzoic acid molecule is perpendicular to the surface of γ-Al2O3.