Novel Z-scheme Co3O4/WO3 nanocomposite performance in adsorption and photocatalytic degradation of ethylparaben and methylene blue in water

Abstract

Effective removal of organic pollutants from water bodies using both adsorption and photocatalysis provides an effective solution for both ecological and environmental importance. Degradation of organics such as parabens using photocatalytic process with visible light irradiation is challenging. However, semiconductor photocatalysis based on solar radiation utilisation whose mechanism involves absorption of photons when irradiated by sunlight or illuminated light, is possible. WO3 has been exploited for its visible light utilisation whereas a novel Z–scheme photocatalyst formed when WO3 is doped with Co3O4 has shown enhanced photocatalysis and adsorption performance. Z-scheme WO3/Co3O4 semiconductor nanocomposite exhibits high photoactivity due to the suitable band gap matching between the two semiconductors as they share photoexcited electrons in the conduction band (CB) that can easily migrate to each other’s valence band (VB) to recombine with holes under solar light irradiation. In the present work, novel Co3O4/WO3 (ratio 3:7) nanocomposites were successfully synthesised via two-step route including the solvothermal process and subsequent wet impregnation method. The Co3O4/WO3 nanocomposites were applied for efficient removal of methylene blue and ethylparaben from water. Powder x-ray diffractometer (pXRD), scanning electron microscope (SEM), UV–vis diffuse reflectance spectroscopy (UV–vis DRS), x–ray photoelectron spectroscopy (XPS), and Brunauer–Emmett–Teller (BET) were used to characterise the prepared nanocomposites. The adsorption and photocatalytic activities of WO3 and Z-scheme Co3O4/WO3 nanocomposites (30 wt% of Co3O4) were evaluated by monitoring adsorption and photocatalytic activities of methylene blue and ethylparaben from water. The results confirmed that adsorption and photoactivity efficiencies of Co3O4/WO3 nanocomposites were higher than either WO3 or Co3O4 individually. The percentage removal efficiencies using Z-scheme Co3O4/WO3 in the degradation of methylene blue and ethylparaben were 100% and 88% respectively, after 15 min. The improvement of adsorption capability could be attributed to the increase of specific surface areas by addition of Co3O4 whereas photocatalytic performance may be attributed to lower recombination rates. Furthermore, the effects of water parameters and radical scavengers on the adsorption and degradation processes were also investigated. It was noted that were major active species in the removal of methylene blue and ethylparaben. A probable mechanism on the enhanced photocatalytic performance was proposed based on the band structure and radical trapping experiment. The novel Z-scheme Co3O4/WO3 nanocomposite developed in this study has great potential for degradation of organic pollutants in wastewater matrix. To the best of our knowledge, there is no literature that has reported the synthesis of Co3O4/WO3 nanocomposite for the application of removal of organic pollutants.