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

A sustainable photocatalyst of Ti3+ self-doped elongated anatase nanowires combined with reduced graphene oxide (TiO2 NWs@rGO) was prepared via a facile one-step reductive synthesis process using NaBH4 as reductant for the first time. The obtained optimal TiO2 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 TiO2 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 TiO2 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 TiO2 NWs@rGO benefits from sensitive response to visible light, improved surface reactivity and high electron flux enabled by rGO and Ti3+ in TiO2. In addition, this composite catalyst can be self-cleaned, and recycled for reuse, which suggests promising potential for waste engine oil treatment.