Photocatalytic reduction of NO3− by immobilized Ag-modified TiO2 with tailored facets: Performance and mechanism

TiO 2 -based photocatalytic nitrate reduction is highly efficient for nitrate treatment. However, TiO 2 powders present challenges in recovery and reuse, necessitating immobilization to enhance recyclability. Additionally, existing research primarily focuses on the role of photogenerated electrons in nitrate removal, neglecting the impact of simultaneously generated free radicals on the reaction. To investigate the synergistic effects of electrons and free radicals in recyclable photocatalytic nitrate reduction, this study layered TiO 2 with specific crystal facets and a silver coating on a recyclable plane. Results indicate that hydroxyl radicals (·OH) can reoxidize ammonia nitrogen, inhibiting the interfacial reduction process and adversely affecting nitrate removal. Exposing the reductive (101) crystal facet and depositing silver nanoparticles helps promote electron migration to the nanoparticle surface for participation in the reduction process, while reducing free radical formation. This approach increases the nitrate degradation rate by 2.38 times compared to TiO 2 with the exposed (001) crystal facet. In contrast, the photocatalytic reduction efficiency of TiO 2 with exposed oxidative (001) crystal facet is reduced due to increased free radical formation influenced by surface positive charges. This study provides a cost-effective and reusable solution for nitrate removal in water, enhancing its potential in practical water treatment applications.