New application for TiO2 P25 photocatalyst: A case study of photoelectrochemical sensing of nitrite ions.

Developing photoelectrochemical (PEC) sensors based on photocatalytic materials has recently attracted great interest as an emerging technology for environmental monitoring. TiO2 P25 is a well-known highly active photocatalyst, cheap, and produced commercially on a large scale. In the current work, a practical and durable TiO2-based PEC sensor has been fabricated by immobilizing TiO2 P25 nanoparticles at disposable screen-printed carbon substrates using drop-casting method. The fabricated PEC sensor has been applied for the anodic-detection and determination of nitrite (NO2-) ions under UV(A) light (LED, 365 nm) using chronoamperometry (CA) and differential pulse voltammetry (DPV). Linear calibration curves were obtained between the photocurrent responses and the concentrations of NO2- ions in the ranges of 0.1-5.0 and 0.5-10 mg L-1 for CA and DPV, respectively. Surprisingly, the detection limits (sensitivities) of the fabricated sensor towards NO2- ions under light were enhanced by a factor of 4.75 (4.1) and 8.3 (37.4) for CA and DPV, respectively, in comparsion with those measured in the dark. It is found that the photo-excitation of TiO2 facilitates the photooxidation of NO2- ions via the photo-generated holes whereas the photogenerated electrons contribute to the enhanced photocurrent and consequently the enhanced detection limit and sensitivity. The fabricated TiO2-based PEC sensor exhibits a good stability, durability, and satisfying selectivity for NO2- ions determination. These results indicate that the TiO2-based PEC sensor fabricated by utilizing cheap and commercially available components has great potential for being transferred from lab-to-factory.