Visible light active TiO2 photocatalytic filtration membranes with improved permeability and low energy consumption

Abstract

Visible light active ultrafiltration (UF) membranes coated with modified nanostructured titania (m-TiO2) were for the first time developed using a sol–gel preparation technique combined with a dip-coating deposition procedure. It has been confirmed that the structural, morphological and physicochemical properties of the modified titania membranes strongly depend on the dip-coating and calcination rates. The modified membranes were incorporated in a water purification photocatalytic reactor in continuous flow filtration conditions and tested for the photocatalytic degradation of azo-dye model compounds (namely methyl orange – MO and methylene blue – MB) with very promising results. The photocatalytic experiments took place under ambient operating temperature and low pressure without any compromise on the efficiency of the membrane's permeate flux. Without irradiation, the permeability drops with increasing flow rates of the solution that is forced to penetrate through their pore structure. The photocatalytic efficiency depends on the effluent flow rate however, under both UV and visible light, the permeability was continuously increasing due to the photoinduced hydrophilicity effect. Compared to MO, the MB pollutant was degraded at much higher rate due to its better adsorption, independently of the type of the membrane. The permeability of the membranes increases with the volume treated due to the wettability of the m-TiO2 treated membrane, rendering the need for regeneration or anti-fouling procedures unnecessary and making the process more energy efficient. Due to the low temperature function and the photoinduced hydrophilic effect of the modified TiO2 photocatalytic UF membranes, the photocatalytic reactor can efficiently work without any extra device, fact that leads to low installation and operating costs and provides an energy efficient procedure of cleaning polluted aqueous solutions.