Abstract
WO3 nanorods and GO (at 1 wt% loading) doped WO3 were synthesized using a template free deposition-hydrothermal route and thoroughly characterized by various techniques including XRD, FTIR, Raman, TEM-SAED, PL, UV-Vis, XPS, and N2 adsorption. The nano-materials performance was investigated toward photocatalytic degradation of methylene blue dye (20 ppm) under visible light illumination (160 W, λ> 420) and gas sensing ability for ammonia gas (10–100 ppm) at 200°C. HRTEM investigation of the 1%GO.WO3 composite revealed WO3 nanorods of a major d-spacing value of 0.16 nm indexed to the crystal plane (221). That relevant plane was absent in pure WO3 establishing the intercalation with GO. The MB degradation activity was considerably enhanced over the 1%GO.WO3 catalyst with a rate constant of 0.0154 min−1 exceeding that of WO3 by 15 times. The reaction mechanism was justified dependent on electrons, holes and •OH reactive species as determined via scavenger examination tests and characterization techniques. The drop in both band gap (2.49 eV) and PL intensity was the main reason responsible for enhancing the photo-degradation activity of the 1%GO.WO3 catalyst. The later catalyst initiated the two electron O2 reduction forming H2O2, that contributed in the photoactivity improvement via forming •OH moieties. The hexagonal structure of 1%GO.WO3 showed a better gas sensing performance for ammonia gas at 100 ppm (Ra-Rg/Rg = 17.6) exceeding that of pure WO3 nanorods (1.27). The superiority of the gas-sensing property of the 1%GO.WO3 catalyst was mainly ascribed to the high dispersity of GO onto WO3 surfaces by which different carbon species served as mediators to hinder the recombination rate of photo-generated electron-hole pairs and therefore facilitated the electron transition. The dominancy of the lattice plane (221) in 1%GO.WO3 formed between GO and WO3 improved the electron transport in the gas-sensing process.
Highlights
The nanoscience and nanotechnology have allowed the development of nanosized materials of unique electronic and optical properties quite different from those of their bulk states (Pang et al, 2010)
By applying Bragg’s law, the calculated interlayer spacing of graphene oxide (GO) is 0.83 nm, providing an expansion than graphite analog depicted at 0.34 nm
The pure WO3 sample is wellcrystallized in a single phase with exposing diffraction peaks at 2θ equal 24.68◦, 28.17◦, 36.52◦, 49.85◦, and 55.43◦, indexed to hexagonal WO3 (JCPDS 85-2459)
Summary
The nanoscience and nanotechnology have allowed the development of nanosized materials of unique electronic and optical properties quite different from those of their bulk states (Pang et al, 2010). Composite materials including metal oxide nanoparticles have drawn great attention due to their unique chemical and physical properties, which make them applicable for use in photocatalysis and gas sensing (Bittencourt et al, 2006; Guo et al, 2012; Chen et al, 2013). WO3-based nanomaterials with various morphologies have been widely investigated for chemical gas sensors (Chu et al, 2017; Kaur et al, 2018; Gao et al, 2019) such as for detecting NH3, H2, and ethanol (Tsai et al, 2017; Chen et al, 2018; Morsy et al, 2018, 2019) It has attracted a lot of interest in photocatalysis theme because of its strong adsorption, manipulated energy band gap and visible light absorption (Zhang et al, 2017). Graphene can facilitate the nucleation and growth of the nanocrystals and help achieving its stability and size beside it can orientate the oxide crystal growth (Zhang et al, 2015; Quan et al, 2017)
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