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

Photocatalysis is particularly suitable for removing nitrite (NO 2 − ) 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 (TiO 2 )/polyethylene diacrylate (PEGDA) hydrogels (GTHs) as a reusable catalyst, which can degrade NO 2 − into nitrogen gas (N 2 ) under visible light. GO-modified TiO 2 can narrow the energy band gap of TiO 2 from 3.39 to 2.89 eV and achieve a NO 2 − removal efficiency of more than 98% in 6 h under light-emitting diode irradiation. Formic acid used as a hole scavenger achieved a N 2 selectivity of 75.6 ± 1.1%. The NO 2 − removal efficiency and N 2 selectivity of GTHs were not affected by high salinity water. GTHs can eliminate 94.0 ± 2.0% NO 2 − and achieve a N 2 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. • High conversion rate of NO 2 − to N 2 using GO/TiO 2 hydrogels. • Photocatalytic reduction of NO 2 − under visible-light (430–460 nm) irradiation. • Photocatalytic reaction dominant in high removal efficiency (94%) of NO 2 − . • Use of formic acid as a hole scavenger to improve N 2 selectivity from NO 2 − . • Retention of 80% of photocatalytic activity after ten reaction/regeneration cycles.