Abstract
In the last decade, selective photocatalytic processes have been developed for fabrication of value-added chemicals with promising activities and selectivities. However, to achieve highly selective photocatalytic oxidation is still presenting a formidable challenge because of the generation of non-selective •OH radicals. Also, photocatalysis could be associated with two major problems including: (i) low photocatalytic efficiency (i.e. activity and selectivity) and (ii) unsatisfactory visible-light responsive photocatalytic materials. To develop highly efficient visible-light photocatalytic materials, several photocatalysts modification strategies such as bandgap modification, selective growth of crystal facets and surface treatment have been explored. To achieve this feat, morphology-controlled CeO2 nanostructures (i.e. CeO2-NPs, CeO2-NRs and CeO2-NCs) and heterostructured CeO2 interfaces (i.e. CeO2- MO, MO = SnO2, ZnO, TiO2, Nb2O5, MoO3, CuO, Co3O4, NiO, MnO2 & Fe2O3) were successfully synthesized by solution processes and characterized by the XRD, BET, UV/Vis, PL, XPS, EPR, SEM and TEM analytical techniques. According to the data, CeO2-NRs photocatalyst gave the best pinene conversion amount of 33.6% and pinene oxide selectivity of 54.3% as the major product after 5 h reaction time. The CeO2-NRs photocatalyst was recycled 5 times without any significant loss of its photocatalytic activity. Furthermore, CeO2-NRs photocatalyst was versatile for the photooxidation of HMF under visible light irradiation to afford DFF selectivity of 40.3% as the major product and oxalic acid formation (23% selectivity) at 70% HMF conversion. The heterostructured CeO2-based interfaces showed an increase in the photocatalytic efficiency when compared to pure CeO2 NPs in the selective oxidation of Pinus wood-derived α-pinene to aroma oxygenated derivatives. Particularly, the Fe2O3-CeO2 and NiO-CeO2 photocatalysts afforded good pinene conversions of 71.3% and 53.1%, respectively. The corresponding pinene oxide selectivities of 57.3% and 58.2% for Fe2O3-CeO2 and NiO-CeO2 photocatalysts were obtained after 5 h reaction. Furthermore, the heterojunction MoO3-CeO2 nanocatalyst offered the best pinene oxide selectivity of 63.8% at 65.8% pinene conversion after 5 h visible light irradiation at 25 °C. Also, H2O2 and reaction temperature had a positive influence on the photoactivity but negatively affected the product selectivity. selectivity. Lastly, the heterojunction MoO3-CeO2 nanocatalyst exhibited potential for application for various types of biomass-derived chemicals, including HMF, furfural, vanillyl alcohol, isoeugenol and glycerol.
Ph.D. (Chemistry)