Interactions between model organic compounds and metal oxides

Because of their mechanical, thermal, and chemical resistance, ceramic materials are suitable for challenging water treatments, where different metal oxides (MeO) have been tested as active layers. However, organic fouling is a major drawback impacting its performance. Organics adsorb onto the membrane surface and into their pores during long-term operation, resulting in irreversible fouling. This investigation focussed on the interfacial interactions between model organic acids and MeO to obtain a fundamental understanding of the adsorption phenomena. Batch adsorption experiments of a series of small molecular weight, oxygenated, aromatic organic acids were performed with Al2O3, TiO2, and ZrO2 particles, at pH 4.2 and 7.6. The adsorption of simple acids was described by the Langmuir model and exhibited a strong dependence on the relative abundance of carboxyl groups, aliphaticity/aromaticity, alkyl chain length, and presence of hydroxyl groups. The adsorption of model compounds was higher at low pH and decreased with increasing pH. The difference in Al2O3, TiO2, and ZrO2 surface characteristics, as evidenced by TEM, XRD, and BET, led to differences in the adsorption density. The results obtained with these well-defined organic structures will assist in better understanding the interfacial interactions between complex natural organic matter molecules and MeO of different characteristics.