One–step reductive synthesis of Ti3+ self–doped elongated anatase TiO2 nanowires combined with reduced graphene oxide for adsorbing and degrading waste engine oil

Abstract A sustainable photocatalyst of Ti 3+ self–doped elongated anatase nanowires combined with reduced graphene oxide (TiO 2 NWs@rGO) was prepared via a facile one–step reductive synthesis process using NaBH 4 as reductant for the first time. The obtained optimal TiO 2 NWs@rGO composite has a large surface area,182 m 2  g –1 , which demonstrates strong adsorption capacity due to the multilayered structure built by highly crystallized nanowires of TiO 2 and ultrathin rGO layers. When the photocatalyst was applied in removing waste engine oil (100 mL, 50 mg L –1 ), it exhibited outstanding performance with up to COD 98.6% removal extent (from 145 initial to 2 mg L -1 final COD) after 5 h, which is 34.1% higher than that of TiO 2 NWs (64.5% COD removal extent). Gas chromatography–mass spectrometry analyses of residual waste engine oil after photocatalysis shows significant reductions of C 6 –C 19 chemicals as well as total disappear of C 15 ,C 16 , C 17 , C 18 chemicals. The outstanding photocatalytic activity of TiO 2 NWs@rGO benefits from sensitive response to visible light, improved surface reactivity and high electron flux enabled by rGO and Ti 3+ in TiO 2 . In addition, this composite catalyst can be self–cleaned, and recycled for reuse, which suggests promising potential for waste engine oil treatment.