Influence of solution pH on the performance of photocatalytic membranes during dead-end filtration

• Performances of TiO2/Al2O3 membranes under different pH conditions were investigated.
• pH significantly influences water flux performances.
• Higher flux were obtained at point of zero charge of membranes.
• A dye solution was used to evaluate the efficiency of photocatalytic membranes.
• pH of the solution strongly influences initial degradation rate of Acid Orange 7.

The behavior of TiO2/Al2O3 composite membranes under different pH conditions was investigated. Filtration and photodegradation were coupled by using these TiO2/Al2O3 membranes in a photocatalytic membrane reactor under UV light. Membrane performances were first evaluated by measuring water flux and then by measuring permeate flux and degradation rate during filtration of a model molecule Acid Orange 7 (AO7). Experimental results clearly showed that water permeability of alumina and TiO2/Al2O3 composite membranes is influenced by pH conditions. Nonetheless, flux variation with pH is less pronounced for TiO2/Al2O3 composite membranes. In addition, UV light enables a stabilization of flux because of hydrophilic properties of TiO2. For both membranes, higher permeate flux were obtained at the isoelectric point. It appeared that surface of composite membrane is photoreactive and permits to mitigate membrane fouling with an efficiency which depends on pH of the solution. Initial degradation rate of AO7 also depends on pH as it influences not only the surface properties of TiO2 but also the dissociation of AO7 and the formation of hydroxyl radicals. Higher initial degradation rate was observed under acidic conditions (pH = 4).