Visible-light driven graphene oxide/titanium dioxide hydrogels for photocatalytic reduction of nitrite

Photocatalysis is particularly suitable for removing nitrite (NO₂⁻) under irradiation from liquid samples. A reusable photocatalyst gel with high conversion selectivity is currently not available. This study investigated graphene oxide (GO)/titanium dioxide (TiO₂)/polyethylene diacrylate (PEGDA) hydrogels (GTHs) as a reusable catalyst, which can degrade NO₂⁻ into nitrogen gas (N₂) under visible light. GO-modified TiO₂ can narrow the energy band gap of TiO₂ from 3.39 to 2.89 eV and achieve a NO₂⁻ removal efficiency of more than 98% in 6 h under light-emitting diode irradiation. Formic acid used as a hole scavenger achieved a N₂ selectivity of 75.6 ± 1.1%. The NO₂⁻ removal efficiency and N₂ selectivity of GTHs were not affected by high salinity water. GTHs can eliminate 94.0 ± 2.0% NO₂⁻ and achieve a N₂ selectivity of 64.9 ± 2.1%. After ten cycles, GTHs retained a removal efficiency of 80–90%. The results indicate that GTHs are a promising material for wastewater treatment.