Hybrid membrane VIS-LED photoreactor for simultaneous pharmaceuticals degradation and photocatalysts separation

Abstract

In recent years, TiO 2-assisted photocatalysis has become a potentially cost-effective and environmentally-sustainable treatment technology for water reclamation and reuse. However, TiO could be photoexcited only under UV irradiation due to its large band gap which hampers its commercial-scale application. In addition, the key challenge for applying the TiO 2 suspension system is that the TiO 2 particles have to be separated from the product water. This study therefore focused on (1) developing visible-light responsive TiO 2-based photocatalysts for photocatalytic degradation (PCD) of pharmaceuticals under visible-light irradiation, and (2) developing hybrid membrane photoreactor (MPR) systems for photocatalyst recovery and reuse in the photoreactor. The first phase of this study was the synthesis of C-sensitized and N-doped TiO 2 (C/N-TiO 2) for PCD of sulfanilamide (SNM) under visible-light-emitting diode (vis-LED) irradiation. It was found that the C/N-TiO 2 calcined at 300 °C (T300) exhibited the highest photocatalytic activity for SNM degradation, due to the presence of optimal content of carbonaceous species (serve as photosensitizer) and the nitrogen doping (lead to the remarkable red shift of absorption edge). The PCD of SNM was more efficient in acidic conditions due to the carbon photosensitizing effect. Bicarbonate, phosphate and silica could inhibit the SNM mineralization to different degrees. T300 exhibited good photochemical stability and its absorption onset could be extended to ca. 600 nm. In order to harness visible light and solar light more efficiently, another novel C-N-S tridoped TiO 2 was synthesized for PCD of tetracycline (TC) under visible-light and simulated solar irradiations in the second phase of this study. It was suggested that the photocatalyst with thiourea : Ti molar ratio of 0.