On-Site H2O2 Generation for Water Reuse Treatment Systems

Water reuse is a current issue in many western states where widespread drought, an issue exacerbated by climate change, constitutes water shortages. H₂O₂, a green oxidant commonly used in water treatment, is added to water in batch and used to generate ⸱OH under UVC photolysis to remove organic and inorganic contaminants in the water. However, purchasing, transportation, and storage of bulk H₂O₂ poses a significant cost for the water reuse treatment process. This research aims at generating on-site H₂O₂ for use in water reuse treatment facilities.

Photocatalysis is a promising approach for onsite H₂O₂ generation. As in many photocatalytic processes, separation of photoholes and electrons is key to efficient H₂O₂ generation. We deposited Au nanoparticles on TiO₂ (P25) nanoparticles to form a metal/semiconductor Schottky junction and improve charge separation. P25, a powder form of TiO₂ containing both anatase and rutile phases, creates a porous film of TiO₂, allowing maximal surface area for electron transfer. We deposited gold nanoparticles onto the TiO₂ via deposition precipitation (DP), which evenly deposits Au onto the porous surface. We designed and built a millifluidic reactor to test the Au-P25 samples under UVA light (365 nm). The use of Au nanoparticles in conjunction with the TiO₂ greatly increases the generation of H₂O₂ due to the electron generated by the excited gold and transferred to the TiO₂ surface.

We explored different methods for Au DP to determine optimal loading of Au nanoparticles onto the TiO₂ surface. We also calcinated the TiO₂ films at different temperatures; calcination temperatures above 600℃ began to form primarily rutile phase TiO₂, while temperatures below left primarily anatase phase. XRD supports these findings. Au-P25 samples calcinated at 650℃ show substantial on-site H₂O₂ generation (>40uM), this is valuable for water treatment using H₂O₂. When samples are tested in 5% EtOH, a common electron donor that decreases incidences of recombination, there is an increase of H₂O₂ generation in rutile phase samples. However, the EtOH decreased the H₂O₂ generation rate in anatase phase samples. The proposed mechanism of H₂O₂ generation is that dissolved oxygen in the water adsorbs to the TiO₂ surface and two-electron reduction generates H₂O₂. With this mechanism, we expect EtOH would increase H₂O₂ yield on both sample types (anatase and rutile phase TiO₂). This suggests the need for further research to examine the mechanism of H₂O₂ generation on anatase and rutile phase TiO₂.