Application of temperature modified titanate nanotubes for removal of an azo dye from water in a hybrid photocatalysis-MD process

The presented studies have focused on application of modified titanate nanotubes (TNTs) for decomposition of Acid Red 18 in water. The TNTs were prepared via hydrothermal method. The post-treatment of TNTs was carried out by calcination of the as-received nanotubes at temperatures of 400–700 °C. The photocatalytic experiments revealed that the most active towards AR18 decomposition were TNTs calcinated at 600 °C (TNT600). However, the photocatalytic activity of the calcinated titanate nanotubes, regardless of the annealing temperature applied was found to be lower than that of P25. In the second step of the investigations, the TNT600 were applied for degradation of AR18 in a photocatalytic membrane reactor coupling photocatalysis with membrane distillation. The effect of photocatalyst loading on the effectiveness of degradation of AR18 was especially investigated. After 5 h of irradiation the amount of AR18 was lowered for ca. 67, 80 and 97% for TNT600 loadings of 0.1–0.5 g/dm3, respectively. The mineralization of the organics was significantly lower than the decolorization of the solution. The amount of TOC after 5 h of the experiment decreased for 20, 27 and 57%, for 0.1–0.5 g TNT600/dm3, respectively. Amongst products and by-products of AR18 photodegradation organic acids (formic, acetic and oxalic) and inorganic ions (nitrite, nitrate, ammonia and sulfate) were detected. The product of the hybrid process (distillate) was high quality water with conductivity in the range of 2.3–3 μS/cm.