Spontaneous monolayer dispersion of organic acids on the surface of γ-Al2O3 and studies on surface structure of benzoic-γ-Al2O3 system

Many organic acids, such as benzoic acid, salicylic acid, o - or p - phthalic acid and tartaric acid, can disperse spontaneously onto the surface of gamma - 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 - gamma - 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 gamma - 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 gamma - 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 gamma - Al2O3. The dispersion threshold determined by XRD is 1.1 mmol benzoic acid /100m(2) gamma - Al2O3, which is very close to the utmost monolayer dispersion capacity 1.2mmol/100m(2) calculated according to a model that the benzene ring in benzoic acid molecule is perpendicular to the surface of gamma - Al2O3.