Sol gel graphene/TiO2 nanoparticles for the photocatalytic-assisted sensing and abatement of NO2.

Graphical abstract Highlights • Novel chemically mixed sol gel TiO 2 and graphene composite catalyst. • Catalyst with dual NO 2 sensing and abatement capabilities. • Conductometric sensing of NO 2 in the range 70–1750 ppb. • Photocatalytic abatement of NO 2 under simulated sunlight radiation 280–780 nm. Abstract Human exposure to volatile organic compounds and NO 2 can lead to health problems, therefore strategies to mitigate against the risks are required. Abatement and sensing are approaches which could both neutralise and monitor these species thus providing a safer environment and warning occupants of harmful levels. This paper presents pure TiO 2 and TiO 2 /graphene hybrids synthesized through a sol-gel route. Electron optical, helium ion microscopy, X-ray diffraction and spectroscopic methods have been applied to elucidate the physical and chemical behaviour. NO 2 sensing properties of TiO 2 /graphene hybrids formed by the addition of graphene to the reaction vessel prior to initiating the sol gel reaction followed by annealing (GTiO 2 S), and an alternative manufacturing method involving the addition of graphene to TiO 2 nanoparticles which had already been annealed (GTiO 2 M) were compared and evaluated. A conductometric sensor based on TiO 2 /graphene prepared using material GTiO 2 S showed a higher response to NO 2 compared to sensors based on pure TiO 2 and TiO 2 /graphene prepared with material GTiO 2 M. Under UV irradiation generated by a low power LED, the sensor showed a remarkably enhanced response to 1750 ppb NO 2 , about double the response in the dark, and a limit of detection of about 50 ppb of NO 2 (Signal/Noise = 3). Photocatalytic tests to assess the degradation of NO x showed that TiO 2 /graphene hybrids using material GTiO 2 S were the most active amongst the whole series of TiO 2 -based materials. Our data highlights the unique characteristics of material GTiO 2 S TiO 2 /graphene and the suitability for multi-purpose applications in the field of environmental monitoring and remediation. The capability of the material for both sensing and abatement of NO x could be exploited to offer a safer environment through providing a warning of the presence of NO x whilst also reducing levels. [ABSTRACT FROM AUTHOR]