Synthesis of Graphene Oxide Interspersed in Hexagonal WO3 Nanorods for High-Efficiency Visible-Light Driven Photocatalysis and NH3 Gas Sensing

Tarek M Salama; Mohamed Morsy; Rabab M Abou Shahba; Shimaa H Mohamed; Mohamed Mokhtar Mohamed

doi:10.3389/fchem.2019.00722

Synthesis of Graphene Oxide Interspersed in Hexagonal WO₃ Nanorods for High-Efficiency Visible-Light Driven Photocatalysis and NH₃ Gas Sensing

Front Chem. 2019 Nov 1:7:722. doi: 10.3389/fchem.2019.00722. eCollection 2019.

Authors

Tarek M Salama¹, Mohamed Morsy², Rabab M Abou Shahba³, Shimaa H Mohamed³, Mohamed Mokhtar Mohamed⁴

Affiliations

¹ Department of Chemistry, Faculty of Science, Al-Azhar University, Cairo, Egypt.
² Building Physics and Environment Institute, Housing and Building National Research Center (HBRC), Giza, Egypt.
³ Department of Chemistry, Faculty of Science (Girls Branch), Al-Azhar University, Cairo, Egypt.
⁴ Chemistry Department, Faculty of Science, Benha University, Benha, Egypt.

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 (R_a-R_g/R_g = 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.

Keywords: MB photocatalysis; gas sensing; graphene oxide; hexagonal WO3; hydrothermal method; visible light irradiation.