Photocatalytic degradation using one-dimensional TiO2 and Ag-TiO2 nanobelts under UV-LED controlled periodic illumination

Semiconductor photocatalysis such as ultraviolet/TiO2 (UV/TiO2) can be used in environmental remediation. It is an advanced oxidation process that can degrade organic contaminants through redox reactions. Unmodified TiO2 can only generate electron-hole pairs in the UV range so it has limited efficiency. Highly efficient materials are required for this process to be implemented at a large scale. In this study, three methods were used to investigate and improve the efficiency of UV/TiO2 slurry systems: (i) synthesizing one-dimensional TiO2, (ii) formation of Schottky junctions, and (iii) application of UV-light emitting diode (UV-LED) under controlled periodic illumination (CPI). These methods were quantified by measuring the formation of 2-hydroxyterephthalic acid (HTPA) as a probe molecule. In order to improve the charge separation in TiO2, one-dimensional TiO2 nanobelts (TNB) were synthesized using a hydrothermal method and Ag nanoparticles were deposited on these nanobelts to form metal-semiconductor junctions. Ag-TNB was found to have HTPA formation rate greater than 1.33 and 2.59 times than that of P25 and TNB, respectively, under continuous illumination. UV-LED CPI was used to explore changes in photonic efficiencies by using duty cycles from 10% to 100%. At a duty cycle of 10%, normalized HTPA formation rate was 1.75, 1.40, and 0.70 times the HTPA formation rate at continuous illumination for commercial TiO2 (P25), TNB, and Ag-TNB nanomaterials, respectively. The pulse frequency was varied from 0.05 Hz to 25 Hz. Under high frequencies, the HTPA formation rate was greater for Ag-TNB and P25 samples compared to the lowest frequency (0.05 Hz). Ag-TNB was determined to be an effective photocatalyst using CPI by demonstrating photon-limiting behaviour when lowering the duty cycle.